NCHRP Report 485 – Bridge Software—Validation …onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_485aEp1-44.pdf · Live Load Actions (HL-93) 8. Factored Load Actions 9. Non-Composite

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APPENDIX E

SUBDOMAINS FOR PROCESS 12-50 AND REPORT IDS

E-4 SUBDOMAIN 1—Distribution of Dead Load to GirdersIntroduction, E-4Suite Description, E-4Analysis Engines, E-4Associated Process IDs, E-4Associated Report IDs, E-4Loadings Considered, E-4Definition of the Test Suite, E-4Assumptions, E-4Results, E-5Postprocessing, E-5Comparative Analysis, E-5

E-5 SUBDOMAIN 2—Live Load Distribution Factors—Simple SpanIntroduction, E-5Suite Description, E-5Analysis Engines, E-5Associated Process IDs, E-5Associated Report IDs, E-5Definition of the Test Suite, E-5Assumptions, E-6Data Flow, E-6Results, E-6Additional Considerations, E-6Postprocessing, E-6Comparative Analysis, E-6Report IDs, E-6

E-7 SUBDOMAIN 4—Prestressed Concrete Cross Sections Introduction, E-7Suite Description, E-7Analysis Engines, E-7Associated Process IDs, E-7Associated Report IDs, E-7Loadings Considered, E-7Definition of the Test Suite, E-7Special Considerations, E-7Assumptions, E-8Results, E-8Discussion, E-8Preprocessing and Postprocessing Examples and Issues, E-8Comparative Analysis, E-8

E-8 SUBDOMAIN 5—Steel Cross SectionIntroduction, E-8Suite Description, E-9Analysis Engines, E-9Associated Process IDs, E-9Associated Report IDs, E-9Loadings Considered, E-9Definition of the Test Suite, E-9Special Considerations, E-9Assumptions, E-9Results, E-9Discussion, E-10

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Preprocessing and Postprocessing Examples and Issues, E-10Comparative Analysis, E-10

E-10 SUBDOMAIN 6—Dead Load Actions (Superstructure)Introduction, E-10Suite Description, E-10Analysis Engines, E-10Associated Process IDs, E-10Associated Report IDs, E-10Loadings Considered, E-10Definition of the Test Suite, E-10Assumptions, E-11Results, E-11Postprocessing, E-11Comparative Analysis, E-11

E-11 SUBDOMAIN 7—AASHTO HL-93 Live Load Actions (Superstructure)Introduction, E-11Suite Description, E-11Analysis Engines, E-11Associated Process IDs, E-11Associated Report IDs, E-11Loadings Considered, E-12Definition of the Test Suite, E-12Assumptions, E-12Results, E-12Postprocessing, E-13Comparative Analysis, E-13Mathematical Model, E-13

E-13 SUBDOMAIN 8—Factored Load ActionsIntroduction, E-13Suite Description, E-13Analysis Engines, E-13Associated Process IDs, E-13Associated Report IDs, E-13Loadings Considered, E-13Definition of the Test Suite, E-14Assumptions, E-14Results, E-14Postprocessing, E-14Comparative Analysis, E-14

E-14 SUBDOMAINS 9, 10, 12, 13—Simple-Span Rolled-Beam and Plate GirderIntroduction, E-14Suite Description, E-15Analysis Engines, E-15Associated Process IDs, E-15Associated Report IDs, E-15Loadings Considered, E-15Definition of the Test Suite, E-15Special Considerations, E-16Assumptions, E-16Results, E-16Discussion, E-17Preprocessing and Postprocessing Examples and Issues, E-17Comparative Analysis, E-17

E-17 SUBDOMAINS 15 through 20—Simple-Span Prestressed GirderIntroduction, E-17Suite Description, E-18Analysis Engines, E-18Associated Process IDs, E-18

Associated Report IDs, E-18Loadings Considered, E-18Definition of the Test Suite, E-18Special Considerations, E-19Assumptions, E-19Results, E-19Discussion, E-20Preprocessing and Postprocessing Examples and Issues, E-20Comparative Analysis, E-20

E-20 SUBDOMAINS 9, 10, 12, 13, 15 through 20—Multi-Span Precast Prestressed and SteelSuperstructures

Introduction, E-20Suite Description, E-20Analysis Engines, E-21Associated Process IDs, E-21Associated Report IDs, E-21Definition of the Test Suite, E-21Multi-Span Precast Prestressed Concrete Superstructures, E-21Multi-Span Steel Girder Superstructures, E-22

E-24 SUBDOMAIN 30—PiersIntroduction, E-24Suite Description, E-24Analysis Engines, E-24Associated Process IDs, E-24Associated Report IDs, E-24Loadings Considered, E-24Definition of the Test Suite, E-25Results Format Database Structure, E-25Results, E-25Work Remaining on Piers Subdomain, E-26

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This appendix contains a comprehensive list of the Process12-50 report IDs and a synopsis of each subdomain for whichProcess 12-50 has been implemented. The Report ID list con-tains a detailed description of every Report ID currentlyavailable for Process 12-50. Each subdomain contains adescription of the test suite used for that subdomain alongwith a discussion of the subdomain results. The following isa summary of the subdomains presented in this appendix:

1. Dead Load to Girders2. Live Load Distribution Factors—Simple Span4. Prestressed Concrete Cross Sections5. Steel Cross Section6. Dead Load Actions (Superstructure)7. Live Load Actions (HL-93)8. Factored Load Actions9. Non-Composite Rolled Steel Sections

10. Non-Composite Steel Plate Girders12. Composite Rolled Steel Sections13. Composite Steel Plate Girders15. Non-Composite Prestressed I-Sections16. Non-Composite Prestressed Spread Box Sections17. Non-Composite Prestressed Adjacent Box Sections18. Composite Prestressed I-Sections19. Composite Prestressed Spread Box Sections20. Composite Prestressed Adjacent Box Sections30. Piers

The following subdomains were not implemented due toscope limitations determined by time and funding:

3. Live Load Distribution Factors—Continuous Span 11. Non-Composite Built-Up Steel Sections 14. Composite Built-Up Steel Sections

21-29. Not yet assigned

[READERS NOTE: Tables and figures follow the text inthis appendix.]

Table E-1 provides a list of the divisions in the Report IDsdefined for Process 12-50. A full list of the Report IDs is pro-vided in Table E-2. All Report IDs have not been imple-mented for all processes.

SUBDOMAIN 1—DISTRIBUTION OF DEADLOAD TO GIRDERS

Introduction

One of the most basic, yet important, calculations involvedin the analysis of a bridge system is the distribution of deadloads to the girders in the bridge system. This load includesthe weight of the girders, weight of the deck, weight of thewearing surface, and weight of any curbs, barriers, utilities,light fixtures, and so forth.

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Suite Description

This suite is designed to facilitate comparisons of aprocess to distribute dead loads to the girders in the cross sec-tion. The loads are listed in the Loadings Considered sub-section of this section. The weights of the various dead loadcomponents in the form of weight/length acting on the girderare reported. Both interior and exterior girders are examined.

Analysis Engines

Two independently developed computational processes(CPs) were used to generate the results presented in this testsuite. The first process is BRASS-GIRDER (LRFD) (here-after referred to as BRASS). Version 1.0, Release 03, of thesoftware was used and is based on the 1997 interim of theAASHTO LRFD Bridge Design Specifications (hereafter,LRFD Specifications). The second CP is a spreadsheet devel-oped specifically to test the distribution of dead loads.

Associated Process IDs

Process IDs 1 and 6 were the only IDs used for this sub-domain.

Associated Report IDs

Report IDs 10000–11999 are the primary focus of thissubdomain.

Loadings Considered

This subdomain examines the distribution of girder weight,deck weight, wearing surface weight, and the application ofany user-defined dead loads.

Definition of the Test Suite

The calculation of the weight of the girder is tested in thissubdomain. A basic I-section is entered as the girder, andportions of the cross section are varied in order to test thecomputation of the girder weight. The weight of the deck andwearing surface distributed to each girder are tested by vary-ing the spacing of the girders and the length of the overhang.The proper reading and implementation of user-defined loads(in N/mm) is tested by entering different values for the deadloads and ensuring that these are the same loads reported bythe program output. A sample of the input parameters for thissubdomain is presented in Table E-3.

Assumptions

Mathematical Model

The pertinent assumptions used for the generation of theactions are

• Girders are prismatic.• Loads are distributed using tributary area method.• Supports are pinned.

Results

The results for all Report IDs that both processes computeagree closely. Some examples of this agreement are shownin Figures E-1, E-2, and E-3. The complete results for thissubdomain are available on the accompanying CD-ROMs.

Postprocessing

See Appendix A for a description of methods that can beused to develop graphs similar to those used in this appendix.Appendix A also contains recommendations for postpro-cessing and data management for those who do not wish touse the tools provided on the accompanying CD-ROMs.

Comparative Analysis

The methods recommended for the numerical comparisonof results are outlined in Appendix H of the research team’sfinal report.

SUBDOMAIN 2–LIVE LOAD DISTRIBUTIONFACTORS—SIMPLE SPAN

Introduction

The generation of live load distribution factors is criticalfor any LRFD-based analysis where distribution factors arenot known. Cross sections with 3 to 12 girders with spacingvarying from 900 mm to 4900 mm are presented. This sec-tion contains descriptions of the analytical engines used todetermine the results, the different cases considered, and thekey assumptions used by all processes involved.

Suite Description

This test suite subdomain tests the ability of a process tocorrectly calculate the live load distribution factors for a sin-gle-span bridge cross section. Four different types of crosssections, as defined by Table 4.6.2.2.1-1 of the LRFD Speci-fications, are examined. The cross section types are as fol-lows:

1. Type A, cast-in-place concrete slab on steel beams;2. Type B, cast-in-place concrete slab on closed precast

concrete boxes;3. Type F, cast-in-place concrete slab on precast, voided

concrete boxes with shear keys; and

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4. Type K, cast-in-place concrete slab on precast concreteI- or bulb-tee sections.

Other deck types listed that fall under the definitions fortypes A, B, F, and K are beyond the scope of this project. Thetest suite reports moment and shear distribution factors forinterior and exterior girders.

Analysis Engines

Three independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and isbased on the 1997 interim of the LRFD Specifications. Thesecond CP is PennDOT’s PSLRFD program (hereafterreferred to as PSLRFD), which analyzes and designs pre-stressed concrete girder lines. PennDOT’s STLRFD (here-after referred to as STLRFD) is the third CP. This programanalyzes and designs steel girder lines. PSLRFD and STLRFD combine to analyze the same problems that BRASSanalyzes. A spreadsheet developed to test the BRASS distri-bution factor calculations was also used. This spreadsheet hasbeen modified to meet the requirements of this test suite.


Process IDs 1, 2, 3, and 6 were the only IDs used for thissubdomain.




The test suite was designed to test the live load distributionfactor generation for the cross section types listed in the suitedescription provided in this section. For each cross section,the spacing between the girders has been assumed to be con-stant. The width of the cantilever to the left is assumed to beone-half of the current girder spacing. The length of the bridgespan is varied from the shortest value in the range of applica-bility (defined in Tables 4.6.2.2.2b-1 through 4.6.2.2.3b-1 inthe LRFD Specifications) to the longest range of applicabil-ity, with one intermediate value. The girder spacing was alsovaried between the shortest and longest values in the rangeof applicability. For cross section types A and K, two inter-mediate values are used, while only one intermediate spanvalue was used for cross section types B and F. Table E-4

lists the parameters varied, as well as the start, stop, and incre-ment values for each parameter.

Assumptions

Some of the key assumptions made for this test suite areas follows:

• The spacing of the girders is considered to be constant.• The girders are prismatic.• The cross section is the same along the entire length of

the bridge.

Data Flow

See Appendix A for a detailed description of how data aregenerated for this test suite subdomain. The input files forthis subdomain were generated using the loop method. Appen-dix A also describes various methods of postprocessing anddata management.

Results

This subsection contains a description of the data con-tained in the Results files generated by the two processes, aswell as some discussion of important trends seen in theseresults. All of the results may be found on the accompanyingCD-ROMs in either ASCII (XML) or database form. Notethat PennDOT PSLRFD and STLRFD programs do notreport any intermediate values for the live load distributionfactors. The values from the equations, the Lever Rule val-ues, and the rigid method values are not reported separately,only the controlling distribution factor is reported.

One of the most noticeable differences between the resultsof the different processes is how each process handles com-putations that fall outside the range of applicability as definedin the tables of the LRFD Specifications, Article 4.6.2.2.2.For situations where the bridge cross section falls outside thespecified range of applicability, BRASS uses the Lever Rulevalue for the results. PSLRFD and STLRFD issue a warningto the user and compute the distribution factor using theequations in the tables in Article 4.6.2.2.2 of the LRFDSpecifications. The spreadsheet will either use the LeverRule or the equations, depending on the cross section. Fig-ure E-4 shows an example of this situation. For this example,de (the distance from the outside web to the face of the curb)is 1990 mm, which is greater than the maximum specified bythe range of applicability in the LRFD Specifications(1700 mm).

Another difference is seen in the manner in which themoment and shear distribution factors are reported for the non-controlling cases (Report IDs 12000–12003 and 12030–12033)

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by BRASS and the spreadsheet. For these cases, BRASScomputes the distribution factor according to the formulaslisted in the appropriate table in the LRFD Specifications andnext checks to see if the rigid method should apply for thatparticular case. If so, it replaces the formula value with therigid method value if the rigid method value is larger. Thespreadsheet, however, assigns the formula value to the ReportID. It does not make the rigid method check until it is deter-mining the controlling distribution factor value (Report IDs12384–12388) for that particular girder. Therefore, in caseswhere the rigid method controls the distribution factor,BRASS reports the rigid method result twice, but the spread-sheet only reports it once. In Figure E-5, the spreadsheet isreporting the Lever Rule value, while BRASS is reportingthe maximum of the Lever Rule value and the rigid methodvalue. In Figure E-6, both processes are reporting the maxi-mum of all applicable methods and numbers of lanes loaded.Note that when the controlling factor is determined, bothprocesses agree for all cases.

Additional Considerations

This section lists some of the considerations that areunique to this test suite subdomain. One area of concern forthe calculation of distribution factors for cross sections oftypes A and K is the computation of the value of Kg. In thedevelopment of this test suite, the computation of Kg provedto be the most difficult part of the calculations to verify. Notethat the Input Parameters form in the results database con-tains all the information necessary to compute the value ofKg for each problem, as well as the value of Kg.

Postprocessing

Please see Appendix A for a description of methods thatcan be used to develop graphs similar to those used in thissection. Appendix A also contains recommendations for post-processing and data management for those who do not wishto use the tools provided on the accompanying CD-ROMS.


The methods recommend for the numerical comparison ofthe results are outlined in Appendix H of the research team’sfinal report.

Report IDs

Please see Table E-2 for a complete list of the Report IDsused in this subdomain.

SUBDOMAIN 4—PRESTRESSED CONCRETECROSS SECTIONS

Introduction

Computations for section properties are typically straight-forward for ordinary cross sections. Nonetheless, these com-putations are the basis for many other calculations requiredin bridge design and rating. Among other things, these sec-tion properties affect stiffness, stresses, section capacity, anddistribution factors. Therefore, errors in section propertiescan have a trickle-down effect on many downstream compu-tations. Many engineers start looking at program output bychecking the section properties to avoid simple input-relatederrors. This subdomain is useful in evaluating and comparingprogram output for the same reason. For example, if stressesor section resistances are in good agreement, it is likely thatthe section properties have been computed properly by theprocesses being compared. If they are not in good agreement,the section property subdomain is a good place to start thetroubleshooting process.

Suite Description

This prestressed concrete cross section test suite is con-structed to test the computations for cross-sectional proper-ties for prestressed I- and box-beam cross sections similar tothose shown in Figure E-7. The I-beam is modeled after anAASHTO I-beam but the section dimensions can be input tosimulate a bulb-tee. This was done successfully in some com-parisons involving Alaska DOT’s bulb-tee program. Furtherdetails can be found in Appendix D.

This test suite is intended to verify computations for elas-tic section properties but not for section resistance. Sectioncapacity issues are addressed in the girderline subdomains.

Analysis Engines

Two independently developed computational processes(CPs) were used to generate the results presented in this testsuite. The first process is BRASS. Version 1.0, Release 03, ofthe software was used and is based on the 1997 interim of theLRFD Specifications. The second process is PennDOT’sPSLRFD, another fully capable bridge analysis and designtool. It is based on the Pennsylvania Bridge Design Specifi-cation, but has a toggle to change to the AASHTO LRFDSpecifications.





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Loadings Considered

This subdomain was constructed such that all propertiesare independent of load, and therefore, only related to thegeometry of the cross section. Load-dependent propertiessuch as the yield moment are included in the prestressed con-crete girderline subdomains.


The set of input parameters required for the prestressedconcrete cross section subdomain is a subset of those requiredfor the prestressed concrete girderline subdomains. Manyparameters affecting the capacity of the prestressed beamalso affect the section properties and vice versa. Therefore,the input vector used in the girderline subdomain can also beused to generate cross section output data. This “linkage” ofthe prestressed concrete girderline and cross section testsuites has several benefits, including the following:

• The spreadsheet tools used to generate input and the data-base used to manipulate and view results can serve boththe girderline and the cross section subdomains, thusfewer spreadsheets and databases need to be maintained.

• Additions to either subdomain’s input vector potentiallymake the other subdomain more complete.

• As stated earlier, many of the output parameters in thegirderline subdomain are closely tied to cross sectionproperties. It is beneficial to have easy access to crosssection output when tracking down differences in resultsobtained in the girderline subdomains.

Although outside the scope of this work, both positive andnegative section properties are included for completeness inthe Report IDs for this subdomain.

Special Considerations

Both programs tested allow the “lumping” of all the pre-stressing steel at the center of gravity of strands. However,some portions of the prestressed girder subdomain can onlybe tested with a known prestressing steel strand pattern. Forexample, in a debonded strand analysis, where certain strandsare intentionally debonded to reduce tensile stresses in theconcrete near the end of the beam, the strand pattern must beknown. Having to define a strand pattern manually for eachgirder with a known strand pattern can be quite cumbersome.Therefore, some spreadsheet macros were written to auto-mate the generation of the strand pattern given a list of pos-sible strand locations in the beam cross section and a desiredcenter of gravity of the strand group. For harped-strand design,a special version of this macro generates a possible strand pat-tern given the midspan strand pattern and a desired center ofgravity at the end of the beam. The strand pattern macros tendto slow down the macro that writes the input to external ASCII

files; nevertheless, the use of such macros is much more effi-cient than manual definition of strand patterns.

Assumptions

Some of the primary assumptions associated with the def-inition of this suite are as follows:

• For composite girders, typical composite constructionstaging is assumed. As a result, section properties arecomputed for the beam-only, long- and short-term com-posite sections.

• For a prestressed concrete girder, the long- and short-term sections are often one and the same. However,some programs, such as PennDOT’s PSLRFD, allowthe prestressing steel to be transformed for the short-term loading section only. Therefore, Report IDs wereassigned to both the short- and long-term composite sec-tion properties to allow this flexibility.

Results

The procedures described in Appendix A for generatingthe data and postprocessing the results can be used to graph-ically review and compare the output of interest for a largenumber of bridge configurations in a short amount of time.Since all who review this document will not be able to workwith the electronic version of this subdomain, selected resultsare presented and discussed.

For the most part, the two processes that currently are partof this subdomain compared well for this subdomain. Somedifferences in the results were observed (especially in theshort-term composite section properties). The reason for thesedifferences was determined and the problem was corrected(see figures E-8 through E-10).

Figure E-10 shows significant differences in the short-term composite moment of inertia for a beam containingharped strands. Part of this difference is due to the fact thatPSLRFD transforms the prestressing steel when computingthis property and BRASS does not. However, this does notaccount for the lack of symmetry in the PSLRFD results. Areview of the standard program output does not show thissame lack of symmetry. Therefore, this appears to be a prob-lem in writing the database readable output file rather than anerror that affects program results.

This assessment can be verified by looking at stresses alongthe length of the beam for a case that includes live load. Fig-ure E-11 shows such a comparison for Service III tensilestresses at the bottom of the beam. The stresses are in goodagreement and the results are symmetric, as expected. There-fore, the problem appears to be limited to the database output.

Later confirmed, the database output was incorrectly report-ing the short-term composite moment of inertia. Figure E-12

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shows the corrected results. The figure still exhibits a differ-ence of about 4% due to the transformation of the prestress-ing steel.

Discussion

Selected comparisons of program output are presented.These plots are only a few of the tens of thousands of plotsthat could be selected for this subdomain. Herein, severalReport IDs were selected for a single Bridge ID. The pre-stressed concrete cross section subdomains currently containapproximately 360 girders and 34 different Report IDs. As aresult, the hardcopy version of this document cannot com-pletely cover all of the possible comparisons. This subdomainis available in electronic form so that the reader can investi-gate the possibilities in a self-directed fashion.

The spreadsheet and database tools developed allow theuser to generate and filter the enormous amount of data asso-ciated with this subdomain. The result is a set of tools thatgenerates comparison plots with ease. Without a high degreeof automation, the data generated would be unmanageable.

Preprocessing and Postprocessing Examplesand Issues

See Appendix A for a description of methods that can beused to develop graphs similar to those used in this docu-ment. Appendix A also contains recommendations for post-processing and data management for those who do not wishto use the tools provided in the accompanying CD-ROMs.


The methods for the numerical comparison of the results areoutlined in Appendix H of the research team’s final report.

SUBDOMAIN 5—STEEL CROSS SECTION

Introduction

Computations for section properties are typically straight-forward for ordinary cross sections. Nonetheless, these com-putations are the basis for many other calculations requiredin bridge design and rating. Among other things, these sec-tion properties affect stiffness, stresses, section capacity, anddistribution factors. Therefore, errors in section propertiescan have a trickle-down effect on many downstream compu-tations. Many engineers start looking at program output bydoing a quick check on the section properties to avoid sim-ple input-related errors. This subdomain is useful for evalu-ation and comparison of program output for the same reason.For example, if stresses or section resistances are in goodagreement, it is likely that the section properties have been

computed properly by the processes being compared. If theyare not in good agreement, the section properties’ subdomainis a good place to start troubleshooting.

Suite Description

The steel cross section test suites are constructed to test thecomputations for cross-sectional properties for steel rolledbeam and plate girder cross sections similar to those shownin Figure E-13. The scope of this subdomain is limited com-posite and non-composite steel rolled and plate girder crosssections. All cross sections are I-girders. This test suite isintended to verify computations for both elastic and plasticsection properties but not for section resistance. Section capac-ity issues are addressed in the girderline subdomains.

Analysis Engines

Two independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and is basedon the 1997 Interim of the LRFD Specifications. The secondCP is PennDOT’s STLRFD, another fully capable bridgeanalysis and design tool. It is based on the PennsylvaniaBridge Design Specification, but has a toggle to change to theLRFD Specifications.


Report IDs 1 and 3 were the only IDs used for this sub-domain.



Loadings Considered

This subdomain was constructed such that all properties areindependent of load, and therefore, only related to the geom-etry of the cross section. Load-dependent properties such asthe yield moment are included in the steel girder subdomains.


The set of input parameters required for the steel crosssection subdomain is a subset of those required for the steelgirderline subdomains. Many parameters affecting the capac-

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ity of the steel girder also affect the section properties andvice versa. Therefore, the input vector used in the girderlinesubdomain can also be used to generate cross section outputdata. This “linkage” of the steel girderline and cross sectiontest suites has several benefits, including the following:

• Spreadsheet tools used to generate input and the databaseused to manipulate and view results can serve both thegirderline and the cross section subdomains, thus fewerspreadsheets and databases need to be maintained.

• Additions to either subdomain’s input vector potentiallymake the other subdomain more complete.

• As stated earlier, many of the output parameters in thegirderline subdomain are closely tied to cross sectionproperties. It is beneficial to have easy access to crosssection output when tracking down differences in resultsobtained in the girderline subdomains.

Although outside the scope of this work, both positive andnegative section properties are included for completeness inthe Report IDs for this subdomain.


Both programs tested allow the user to specify user-defined,rolled-beam properties. However each does so in a differentmanner. PennDOT’s STLRFD program facilitates this flexi-bility with a standard command. BRASS handles all sectiondata through a section library file. As a result, some additionalVBA coding was done to write the necessary rolled-beam sec-tion data as part of the macro that generates the input files.

Assumptions


• For composite girders, typical composite constructionstaging is assumed. As a result, section properties arecomputed for the steel-only, long- and short-term com-posite sections.

• Only rolled sections can have cover plates. These coverplates can be on the top flange, bottom flange, or bothtop and bottom. However, BRASS does not have thecapability to analyze a composite girder with a top coverplate. Such a condition is quite rare, so this limitation isconsidered to be minor.

• Reinforcing steel in the slab is assumed to be lumped ata single location vertically.

Results

The procedures described in Appendix A for generatingthe data and postprocessing the results can be used to graph-

ically review and compare the output of interest for a largenumber of bridge configurations in a short amount of time.Since all who review this document will not be able to workwith the electronic version of this subdomain, selected resultsare presented and discussed.

The two CPs currently part of this subdomain comparedwell for this subdomain. Figures E-14 through E-18 illustratethis agreement among BRASS and STLRFD.

Discussion

Selected comparisons of program output are presented.These plots are only a few of the tens of thousands of plotsthat could be selected for this subdomain. Herein, severalReport IDs were selected for a single Bridge ID. The steelcross section subdomains currently contain approximately145 girders and over 34 different Report IDs. As a result, theprinted version of this document cannot adequately cover allof the possible comparisons. This subdomain is available inelectronic form so that the reader can investigate the possi-bilities in a self-directed fashion.

The spreadsheet and database tools developed allow theuser to generate and filter the enormous amount of data asso-ciated with this subdomain. The result is a set of tools thatgenerates comparison plots with ease. Without a high degreeof automation, the data generated would be unmanageable.





SUBDOMAIN 6—DEAD LOAD ACTIONS(SUPERSTRUCTURE)

Introduction

The generation of dead load actions is critical for any bridgegirderline analysis. This test suite is limited to single-span,simply supported girderlines. This section contains a descrip-tion of the suite, a description of the analytical engines used todetermine the results, the loading considered, a definition ofthe test suite, the assumptions, and an outline of the input and

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output formats that should aid automated comparisons andplotting.

Suite Description

This suite is designed to examine the ability of a process tocompute the dead load actions from a variety of sources for agiven span. The loadings are described in detail in the Load-ings Considered subsection. The moments, shears, and deflec-tions are reported at various locations along the span(s),depending on the process used to generate the results.

Analysis Engines

Two independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and is basedon the 1997 interim of the LRFD Specifications. The secondCP is PennDOT STLRFD, another fully capable bridgeanalysis and design tool. It is based on the PennsylvaniaBridge Design Specification, but has a toggle to change to theLRFD Specifications.





Loadings Considered

Various types of dead loads are considered in this sub-domain. First, the self-weight of the girder is considered.First-stage (non-composite) component dead loads are con-sidered, including deck weight. The total of all first-stagecomponent dead loads are reported as well. Second-stage(composite) wearing surface and component dead loads alsoare considered.


The test suite was designed to test the dead load actiongeneration for single-span girderlines of various lengths. Thespans were selected to start near the minimum of the designrange and terminate near the practical limit for most rolled-steel shapes. As the length of the span is increased, the sizeof the rolled-steel girder is increased. Only rolled-steel gird-ers were considered for this test suite subdomain. Multiple

girder types and multiple span girderlines will be included infuture versions of this subdomain. The magnitudes of thecomponent dead loads for Stages 1 and 2, as well as Stage 2future wearing surface dead load, were also varied. Finally,the slab thickness, the concrete density, and the wearing sur-face weight were varied. A partial list of the input parame-ters is presented in Table E-5.

The remainder of the input parameters can be viewed inthe Results Database for this subdomain on the accompany-ing CD-ROMs.

Assumptions

Mathematical Model

The pertinent assumptions used for the generation of theactions are as follows:

• Girders are prismatic.• Supports are pinned.

Results

This section contains a description of the data contained inthe Results files generated by the three processes, as well assome discussion of important trends seen in these results. Allof the results may be found in the ASCII files included in theaccompanying CD-ROMs.

For most cases, the results for this subdomain agree almostexactly. The only problem seems to occur in the way thatSTLRFD reports the combined DC loads for Stage 1. A sam-ple plot is shown in Figure E-19. It appears that STLRFDreports the same result for two separate points in some cases.The cause of this error has yet to be determined, but by exam-ining the output file and the close agreement of most of thepoints in the chart, apparently the cause of the error is in theProcess 12-50 Report ID output.

For all other cases, the CPs show good agreement. FigureE-20 shows some examples of cases with no discrepancies.

Postprocessing

See Appendix A for a description of methods that can beused to develop graphs similar to those used in this section.This appendix also contains recommendations for postpro-cessing and data management for those who do not wish touse the tools provided in the accompanying CD-ROMs.



E-11

SUBDOMAIN 7—AASHTO HL-93 LIVE LOADACTIONS (SUPERSTRUCTURE)

Introduction

The generation of critical HL-93 live load actions is criti-cal for any LRFD-based analysis. Bridges with one to fivespans ranging in length from 6 to 96 m and with span ratiosranging from 1:1 to 1:5 are presented. This section contains adescription of the suite, a description of the analytical enginesused to determine the results, the loadings considered, a def-inition of the test suite, the assumptions, and an outline of theinput and output formats that should aid automated compar-isons and plotting.

Suite Description

This suite is designed to examine the ability of a processto compute the critical HL-93 live load actions for a givenspan(s). The loading is described in detail in the LRFD Speci-fications, Section 3.6. Included in the resulting actionsreported is a 33% dynamic load allowance for the designtruck and tandem loads. The live load distribution factors forall cases are 1.0. Load modifiers of 1.0 are used for all cal-culations. The maximum and minimum moments and shearsare reported at various locations along the span(s), depend-ing on the process used to generate the results.

Analysis Engines

Three independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and isbased on the 1997 interim of the LRFD Specifications. Thesecond CP is PennDOT PSLRFD, another fully capable bridgeanalysis and design tool. It is based on the PennsylvaniaBridge Design Specification, but has a toggle to change to theLRFD Specifications. The third CP is BTBeam; a softwarepackage designed to analyze a girderline and report deadload, live load, and combined actions.


Process IDs 1, 2, and 5 were the only IDs used for this sub-domain.



Loadings Considered

All three software packages consider the design truckwith rear axle spacing varied from 4.3 to 9 m as outlined inArticle 3.6.1.2.2 of the LRFD Specifications. They alsoconsider the design tandem and lane load as defined inArticles 3.6.1.2.3 and 3.6.1.2.4. A dynamic load allowanceof 0.33 is applied to all truck and tandem loads. BRASS,BTBeam, and PSLRFD all consider dual truck loadings(Article 3.6.1.3.1), and PSLRFD and BRASS consider thedual tandem loading recommended in C3.6.1.3.1 for nega-tive moments and reactions at interior supports. BTBeamdoes not consider the dual tandem loading, and BRASS hasan option to not consider the dual pair loading. Results arepresented for all problems with and without the tandempair, since the loading is not required by the LRFD Speci-fications.


The test suite was designed to test the live load genera-tion for girderlines from one to five spans, with varyingspan ratios. The spans were selected to start near the min-imum of the design range and terminate near the practicallimit for most standard prestressed shapes. The span lim-its, increments, and relationships are presented in TablesE-6 and E-7. First, the number of spans is varied from oneto five. For the single-span case, the span is increasedincrementally from the minimum to the maximum. Next,the two-span condition is considered. The length of thesecond span is increased incrementally from the minimumto the maximum while the length of the first span remainsconstant. After the second span has reached the maximum,the first span is increased incrementally once and then thesecond span is increased incrementally for the new valueof the first span length. This is repeated for the three-, four-, and five-span conditions, so that all possible combina-tions for the one-, two-, three-, four-, and five-span condi-tions are examined. This method is followed twice togenerate cases with relatively short and relatively longspans. A list of some of the cases generated is presented inTable E-8.

Some of the test problems have obviously unusual spanratios, such as a 32-m first span, 6-m second span, and 6-mthird span. The suite was designed to test such extreme casesas well as more typical conditions (32 m, 32 m, 32 m). Aproblem that surfaces in a case with an unusual span ratiocould indicate a problem that is more difficult to detect fortypical span ratios.

PennDOT’s PSLRFD does not consider spans longer than53.4 m; therefore, all problems with spans greater than 53.4m have results from BRASS and BTBeam only.

E-12

Assumptions

Mathematical Model


• Girders are prismatic.• Multiple-span girders are continuous.• Supports are pinned.• Analysis is for HL-93 live load.• Live load distribution factors are unity.• Load modifiers are unity.• Dynamic load allowances are 0.33 for axle vehicles.

Numerical Modeling

Some elements of the numerical models used in the suiteprocesses are outlined as follows:

• BRASS determines the critical truck/tandem positionby moving the loads across the bridge in steps of 1/100thof the smallest span length. The maximum actions andthe truck position that produces them are then stored.

• BTBeam determines the critical truck/tandem positionby first moving the loads across the bridge in large steps.It determines the controlling position and then steps theloads through the critical position using smaller steps.This process is repeated until convergence of the criti-cal action is achieved.

• PSLRFD determines the critical truck/tandem positionby first determining the peaks of the influence function.It then positions every axle and the centroid of the loadon the peak and stores the critical action.

These three processes are listed in Table E-3. The ProcessIDs used in the files are included on the accompanying CD-ROMs.

Results

This section contains a description of the data containedin the results files generated by the three CPs, as well assome discussion of important trends seen in these results.All of the results are contained in the ASCII files in theaccompanying CD-ROMs. The most noticeable differencein the results from the three CPs is the maximum negativemoments near the interior supports. PSLRFD and BRASSreport negative moments as much as 25% higher than thosereported by BTBeam. The reason for this discrepancy is thatBTBeam does not consider the dual tandem loading dis-cussed in Article C3.6.1.3.1 of the Commentary on the

LRFD Specifications. For all other actions, the three pro-grams match. An example of this discrepancy is shown inFigure E-21. Figure E-21 shows the negative moment plot-ted versus location as measured from the left end of the firstspan. The girderline shown has four spans (6 m, 19 m, 6 m,and 19 m) for a total length of 50 m. The supports are at loca-tions of 6 m, 25 m, 31 m, and 50 m. Near the support at the31-m point, the controlling moment for BTBeam is signifi-cantly lower than the moment reported by BRASS andPSLRFD.

Postprocessing

See Appendix A for a description of methods that can beused to develop graphs similar to those used in this section.Appendix A also contains recommendations for postprocess-ing and data management for those who do not wish to usethe tools provided in the accompanying CD-ROMs.



Mathematical Model

The mathematical model for these bridge analysesshould be deterministic and, theoretically, no differencesshould exist. The influence lines for the beam should be thesame and the positioning of the various live loads for criti-cal load effects should, again theoretically, be identical.The implementation of the mathematics in the numericalmodel creates differences among comparative results. Theinfluence lines could be slightly different and the live loadpositioning algorithm will likely be different among CPs.These differences should not be significant and should beexplainable.

SUBDOMAIN 8—FACTORED LOAD ACTIONS

Introduction

The combination of computed and input dead and live loadactions is critical for any bridge analysis. This test suite islimited to single-span, simply supported girderlines. This sec-tion contains a description of the suite, a description of theanalytical engines used to determine the results, the loadingsconsidered, a definition of the test suite, the assumptions, andan outline of the input and output formats that should aidautomated comparisons and plotting.

E-13

Suite Description

This suite is designed to examine the ability of a process tocombine computed dead and live load actions from a varietyof sources for a given span. The loadings are described indetail in the Loadings Considered subsection. The moments,shears, and deflections are reported at various locations alongthe span, depending on the process used to generate the results.

Analysis Engines

Two independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and isbased on the 1997 interim of the LRFD Specifications. Thesecond CP is PennDOT STLRFD, another fully capablebridge analysis and design tool. It is based on the Pennsylva-nia Bridge Design Specification, but has a toggle to changeto the LRFD Specifications.





Loadings Considered

Various types of dead loads are considered in this subdo-main. First, the self weight of the girder is considered. First-stage (non-composite) component dead loads are consid-ered, including deck weight. The total of all first-stagecomponent dead loads are reported as well. Second-stage(composite) wearing surface and component dead loads arealso considered.

The live loads considered are from the HL-93 live loadingdefined in the LRFD Specifications. Both software packagesconsider the design truck with rear axle spacing varied from4.3 to 9 m as outlined in Article 3.6.1.2.2 of the LRFD Speci-fications. They also consider the design tandem and lane loadas defined in Articles 3.6.1.2.3 and 3.6.1.2.4. A dynamic loadallowance of 0.33 is applied to all truck and tandem loads.BRASS and STLRFD both consider dual truck loadings(Article 3.6.1.3.1), including the dual tandem loading rec-ommended in C3.6.1.3.1 for negative moments and reactionsat interior supports.


The test suite was designed to test the combination ofgenerated dead load and live load actions for single-spangirderlines of various lengths. All of the load combinationswith factors defined in the LRFD Specifications weretested. No combinations with user-defined factors wereinvestigated.

The spans were selected to start near the minimum of thedesign range and terminate near the practical limit for mostrolled-steel shapes. As the length of the span is increased, thesize of the rolled-steel girder is increased. Only rolled-steelgirders were considered for this test suite subdomain. Multi-ple girder types and multiple-span girderlines are recom-mended for future versions of this subdomain. The magni-tudes of the component dead loads for Stages 1 and 2 andStage 2 future wearing surface dead load were also varied.Finally, the slab thickness, concrete density, and wearing sur-face weight were varied. All live load distribution factorshave been assumed to be 1.0. A partial list of the input pa-rameters is presented in Table E-9.

The remainder of the input parameters can be viewed in theResults Database provided on the accompanying CD-ROMs.

Assumptions

Mathematical Model


• Girders are prismatic.• Multiple-span girders are continuous.• Supports are pinned.• Analysis is for HL-93 live load.• Influence lines (functions) are included within the CP.• Live load distribution factors are unity.• Load modifiers are unity.• Dynamic load allowances are 0.33 for axle vehicles.• Load factors are as defined in Article 3.4.1 of the LRFD

Specifications.

Numerical Modeling

Some elements of the numerical models used in the suiteCPs are outlined as follows:

• BRASS determines the critical truck/tandem position bymoving the loads across the bridge in steps of 1/100th ofthe smallest span length. The maximum actions and thetruck position that produces them are then stored.

• STLRFD determines the critical truck/tandem positionby first determining the peaks of the influence function.It then positions every axle and the centroid of the loadon the peak and stores the critical action.

E-14

Results

This section contains a description of the data containedin the results files generated by the three processes, as wellas some discussion of important trends seen in these results.All of the results are in the ASCII files on the accompany-ing CD-ROMs.

For most cases for which both processes report results, theresults agree well. Figure E-22 shows two examples of reportsthat show close agreement between the processes.

The processes differ for the reporting of minimum actions,however. BRASS uses the minimum dead load factors andcomputes the lowest possible results, while STLRFD usesthe maximum dead load factors. Both processes use the min-imum live load actions. Figure E-23 provides an example ofthis difference.

The complete results for this subdomain are available in bothdatabase and ASCII format on the accompanying CD-ROMs.

Postprocessing

Please see Appendix A for a description of methods thatcan be used to develop graphs similar to those used in thissection. Appendix A also contains recommendations for post-processing and data management for those who do not wishto use the tools provided in the accompanying CD-ROMs.


The methods recommended for the numerical comparisonof the results are outlined in Appendix H of the research team’sfinal report.

SUBDOMAINS 9, 10, 12, 13—SIMPLE-SPANROLLED-BEAM AND PLATE GIRDER

Introduction

The simple-span, rolled-beam and plate girder test suitecovers two types of simple-span girders: rolled-steel sectionsand plate girder sections. Both composite and non-compositegirders are covered in this test suite. Built-up steel sections(composed of plates and angles) are beyond the scope of thissuite. Parameters within the subdomains are varied so as tomaximize the coverage. For example, plate and effective slabwidth and thickness are varied to ensure that both compactand non-compact sections are included in the suite.

Some of the primary parameters varied in this suite are asfollows:

• Composite and non-composite girder material,• Girder type (rolled beam or plate girder),• Span length,• Girder spacing,

• Girder geometry (e.g., rolled beam designation and flangesizes),

• Interior/exterior girder,• Slab/haunch geometry,• Hybrid/homogeneous sections,• Constant and varying cross sections, • With and without cover plates (rolled beams only),• Fatigue (detail category and location), and• Stiffeners (transverse and bearing).

All test problems are girderlines. Subdomains 1 and 2 arededicated to the testing of dead and live load distribution thatreduces a girder system problem down to the girderline.

Suite Description

This test suite is composed of the following four sub-domains:

• Subdomain 9—Simple-Span Non-Composite SteelRolled I-Girders,

• Subdomain 10—Simple-Span Non-Composite SteelPlate I-Girders,

• Subdomain 12—Simple-Span Composite Steel RolledI-Girders, and

• Subdomain 13—Simple-Span Composite Steel Plate I-Girders.

Due to the commonality among input and output withinthese test suites, subdomains are grouped for the purposesof generating input/output, postprocessing results, and doc-umentation.

Analysis Engines

Two independently developed CPs were used to generatethe results presented in this test suite. The first CP is BRASS.Version 1.0, Release 03, of the software was used and isbased on the 1997 interim of the LRFD Specifications. Thesecond CP is PennDOT’s STLRFD, another fully capablebridge analysis and design tool. It is based on the Pennsyl-vania Bridge Design Specification, but has a toggle tochange to the LRFD Specifications.





E-15

Loadings Considered

Because subdomains have been constructed specificallyfor dead and live loads, variations in load-related parametersare limited in the girderline subdomain. The HL-93 vehiclewas used for all girders in the input vector and the live loaddistribution factor is a constant value. The dead loads varyappropriately for the girder spacing specified and are alsoaffected by the interior/exterior girder indicator. Additionaluniformly distributed loads are included for non-compositeand composite sections (if applicable).


Nearly 100 different parameters are required to define asimple-span steel plate girder or rolled-beam girderline. Vary-ing each of these parameters independently in the test suitewould generate an enormous amount of data that would beunmanageable. However, some of these parameters can bekept constant due to the fact that other subdomains test vari-ations in such parameters. An example of a set of parametersthat can be assumed to be constant is the girder live load dis-tribution factors. An entire subdomain is dedicated to liveload distribution so it was deemed unnecessary to vary dis-tribution factors within this subdomain. Even with reductionsin the list of possible variational parameters, the remainingparameters must be selectively varied to limit the number ofcases generated. This is a departure from the approach usedin the Live Load Actions test suite in which parameters wereassigned a minimum, maximum, and incremental value and allpossible combinations of the parameters were given. The def-inition of a test suite by using a vector of input data containingselectively varied parameters is termed a “vector approach.”

Rather than using a series of loops to vary all of the inputparameters, an input vector is utilized. Each record, or bridge,in the input vector corresponds to an input file that is generatedfor each engine being tested. The data for the input vectorreside in an Excel spreadsheet that facilitates variations in theinput parameters. For example, one can start with a base bridge(i.e., girderline) definition and vary one or more input param-eters using simple cell formulae while other (non-varying)cells are simply copied from the base bridge. A macro hasbeen written that writes all of the bridges in the input vectorout to a set of input files for each engine.

The input vector approach is not as “brute force” anapproach as the looping method of input definition. There-fore, the variation in parameters can be more carefullyselected to exercise the desired portions of the specifications.Because a spreadsheet is being used to contain the input vec-tor, supplementary calculations can be performed within thespreadsheet to aid in the variation of input parameters. Forexample, calculations for simple things like compactnesschecks can be performed within the subdomain spreadsheetso that one can dictate whether a compact or non-compactgirder is being defined without ever running the program. For

more complex criteria, the definition of the input vector datamay be an iterative process requiring that the program outputbe reviewed to ensure that the desired effect is beingachieved through the variation of input.

The LRFD Specification covers many possible girder con-figurations in Section 6. Sections can be either composite ornon-composite, compact or non-compact, homogeneous orhybrid, stiffened or unstiffened web. This results in manypossible permutations and each of these factors has animpact on the flexural and/or shear capacity of the section.Because the input parameters are being manipulated with aspreadsheet, additional supplemental calculations have beenincluded to aid in selecting the input to cover all desiredcases.


Both CPs tested allow the user to specify user-definedrolled-beam properties. However, each does so in a differentmanner. PennDOT’s STLRFD program facilitates this flexi-bility with a standard command. BRASS handles all sectiondata through a section library file. As a result, some addi-tional VBA coding was done to write the necessary rolled-beam section data as part of the macro that generates theinput files.

Assumptions


• Girder web depth is constant.• Live load is HL-93.• Number of lanes is four.• Dynamic load allowance (DLA) is constant (1.15 for

fatigue, 1.33 otherwise).• General load factors (η factors) are taken as ηI = 1.05,

ηD = 0.95, ηR = 0.95).• Live load distribution factor is taken as 0.85 lanes/

girder.• Concrete is normal density.• Plate girders may be stiffened or unstiffened; if the plate

girder is stiffened, the stiffener spacing is constant.• Plate girders can have varying flange and web plates.

For the simple-span plate girder, the plates are assumedto be arranged in a symmetrical fashion. For the half-span, the flange and web plates can have one transitionand these transitions need not be the same longitudinaldistance as shown in Figure E-24. The STLRFD andBRASS input is based on a sectional layout. Each platetransition requires that a new section be defined. Oneplate transition and section layout is also shown in Fig-ure E-24.

E-16

Results

The procedures described in Appendix A for generatingthe data and postprocessing the results can be used to graph-ically review and compare the output of interest for a largenumber of bridge configurations in a short amount of time.Given that all who review this document will not be able towork with the electronic version of this subdomain, selectedresults are presented and discussed herein.

Flexural Stress

Figures E-25 and E-26 show the flexural stresses in the topand bottom flanges for the Strength I limit state. Althoughthe two programs are in general agreement, some differ-ences exist. At midspan, the difference between the stressesis approximately 5.5%, which indicates possible differencesin the section properties and/or the applied moment. A reviewof the section properties plots showed good agreementbetween the two programs. However, the factored Strength Imoment shows differences similar in magnitude to thestresses (see Figure E-27).

The flexural stresses for the Service II limit state are shownin Figure E-28. The two programs show good agreement forthis parameter.

Because the section properties and the unfactored stressesshow good agreement, but the factored stresses and momentsdo not agree, the difference appears to be in the load factor-ing. For this subdomain, the product of the load factors toaccount for ductility, redundancy, and operational impor-tance (eta factors) is approximately 0.95. However, the Penn-DOT programs limit this product to a value between 1.0 and1.16. If the product of the input factors is less than unity, it ischanged to a value of 1.0. Therefore, to achieve similar fac-tored results at the strength limit states, the eta factors wouldhave to be revised.

Flexural Capacity (Strength Limit State)

Figure E-29 shows the factored flexural capacity, Mr, forthe Strength I limit state. The difference between the BRASSand STLRFD results is negligible.

Shear Capacity (Strength Limit State)

Figure E-30 shows good agreement between BRASS andSTLRFD for the shear capacity at the Strength I limit state.The graph shown is for Bridge ID = 1, which corresponds toa rolled beam. The shear capacity computation for an unstiff-ened web is rather straightforward as compared to a stiffenedweb where moment–shear interaction may control. For this

reason, it is more likely that differences would be observedfor a stiffened web of a plate girder, particularly in regions ofhigh flexural stress.

Fatigue (Detail Category)

Figure E-31 shows the factored fatigue stress range for aparticular location along the beam. The results provided bythe two CPs differ significantly. The STLRFD results areapproximately 20% higher than the BRASS results. The dif-ference in the factored fatigue stress range was first thoughtto be due to the Pennsylvania traffic factor (PTF), whichSTLRFD applies to the LRFD fatigue load in addition to theload factor for fatigue. The default value for the PTF is 1.20,so this seemed a likely candidate for the discrepancy. TheSTLRFD input was reviewed to determine whether or not thedefault value was overridden and it was determined that avalue of 1.0 had been specified. A quick review of the STLRFDoutput seemed to indicate that the fatigue stress was beingcomputed properly.

The BRASS output was reviewed and it was found that ascale factor of 0.833 was being applied to the fatigue load.This scale factor is addressed in the BRASS documenta-tion. By default, BRASS applies this factor to account forthe single-lane multiple presence factor of 1.2 that is assumedto be included in the single-lane distribution factors speci-fied in the BRASS input file. The LRFD Specificationsindicate that the multiple presence factor is not to beincluded for the fatigue loading so BRASS accounts for thiswith a live load scale factor. In the steel subdomains, all dis-tribution factors (including those for fatigue) were taken asa constant value. STLRFD allows distribution factors forfatigue to be input directly but BRASS modifies the single-lane distribution factors for the fatigue loading. If the inputvalues for the fatigue distribution factors were modified for multiple presence, good agreement would be seen in theresulting fatigue stress ranges. Alternatively, BRASS’sTRUCKCODE command could be used to override thefatigue truck scale factor.

The comparison of the factored fatigue stress range is agood example of an acceptable, explainable difference. Thegraphical results allow the subdomain user to determine thatthere is a significant difference in the results. By selecting atabular display of the results, the exact magnitude of the dif-ference can be quantified easily. From this point, the programoutput can be viewed to further investigate such discrepan-cies. Subtle differences in assumptions made by programsare easy to miss, even with a good understanding of the pro-grams involved. The subdomain database makes such differ-ences easy to track down.

On the resistance side of the equation, the fatigue resultscompared well. Figure E-32 shows one such comparison for

E-17

a Category C detail at midspan. The detail was assumed to belocated 1 in. above the extreme fiber of the bottom flange.

Discussion

Selected comparisons of CP output have been presented inthis section. These plots are only a few of the tens of thou-sands of plots that could be selected for this subdomain. Inthis document several Report IDs were selected for a singleBridge ID. The steel girder subdomains currently containapproximately 130 girders and over 80 different Report IDs.As a result, the printed version of this document cannot ade-quately cover all of the possible comparisons. This subdo-main is being distributed in electronic form so the reader caninvestigate the possibilities in a self-directed fashion.

The spreadsheet and database tools developed allow theuser to generate and filter the enormous amount of data asso-ciated with this subdomain. The sample set of tools providedon the accompanying CD-ROMs can be used to generatecomparison plots with ease and provide an example of howthe Process 12-50 data may be analyzed. Without a highdegree of automation, the data generated would be unman-ageable.





SUBDOMAINS 15 through 20—SIMPLE-SPANPRESTRESSED GIRDER

Introduction

The simple-span prestressed girder test suite encompassesmany different configurations of simple-span prestressed,pretensioned girders. Many parameters are required to fullydefine a prestressed girder. The choice of parameters to varyand how to do so is discussed in this section. Some of the pri-mary parameters varied are as follows:

• Composite and non-composite girder material,• Girder type (i.e., I-girder, spread box, or adjacent box),• Span length,• Girder spacing,• Size of girder,• Interior/exterior girder,• Strand configuration (straight/bonded, straight/debonded,

and harped),• Known strand patterns or strands lumped at a specified

center of gravity,• Type of strands (low-lax or stress-relieved strands), and• Concrete strength.

All test problems are girderlines. Another subdomain isdedicated to the testing of dead and live load distribution thatreduces a girder system problem down to the girderline.

Suite Description

This test suite is composed of simple-span results for thefollowing six subdomains:

• Subdomain 15—Non-Composite I-Girders,• Subdomain 16—Non-Composite Spread Box Girders,• Subdomain 17—Non-Composite Adjacent Box Girders,• Subdomain 18—Composite I-Girders,• Subdomain 19—Composite Spread Box Girders, and• Subdomain 20—Composite Adjacent Box Girders.

Due to the commonality among input and output withinthese test suites, these subdomains have been grouped for thepurposes of generating input/output, postprocessing results,and documentation.

Analysis Engines

Two independently developed CPs were used to gener-ate the results presented in this test suite. The first CP isBRASS. Version 1.0, Release 03, of the software was usedand is based on the 1997 Interim of the LRFD Specifications.The second CP is PennDOT’s PSLRFD, another fully capa-ble bridge analysis and design tool. It is based on the Penn-sylvania Bridge Design Specification, but has a toggle tochange to the LRFD Specifications.




Report IDs 50000–59999 are the primary focus of thesesubdomains.

E-18

Loadings Considered

Because subdomains have been constructed specificallyfor dead and live loads, variations in load-related parametersare limited in the girderline subdomain. The HL-93 vehiclewas used for all girders in the input vector and the live loaddistribution factor is a constant value. The dead loads varyappropriately for the girder spacing specified and are alsoaffected by the interior/exterior girder indicator. Additionaluniformly distributed loads are included for non-compositeand composite sections (if applicable). The weight of dia-phragms also is included as a load to the girders.


Nearly 100 different parameters are required to define asimple-span prestressed concrete girderline. Varying eachof these parameters independently in the test suite wouldgenerate an enormous amount of data that would be unman-ageable. However, some of these parameters can be keptconstant due to the fact that other subdomains test varia-tions in such parameters. An example of a set of parametersthat can be assumed to be constant is the girder live loaddistribution factors. Subdomain 2 is dedicated to live loaddistribution so it was deemed unnecessary to vary distribu-tion factors within this subdomain. Even with reductions inthe list of possible variational parameters, the remainingparameters must be selectively varied to limit the numberof cases generated. This is a departure from the approachused in the Live Load Actions test suite in which parame-ters were assigned a minimum, maximum, and incremen-tal value and all possible combinations of the parameterswere given. The definition of a test suite by using a vectorof input data containing selectively varied parameters istermed a “vector approach.”

Rather than using a series of loops to vary all of the inputparameters, an input vector is utilized. Each record, orbridge, in the input vector corresponds to an input file that isgenerated for each engine being tested. The data for theinput vector reside in an Excel spreadsheet that facilitatesvariations in the input parameters. For example, one canstart with a base bridge (i.e., girderline) definition and varyone or more input parameters using simple cell formulaewhile other (non-varying) cells are simply copied from thebase bridge. A macro has been written that writes all of thebridges in the input vector out to a set of input files for eachengine.

The input vector approach is not as “brute force” anapproach as the looping method of input definition. There-fore, the variation in parameters can be more carefullyselected to exercise the desired portions of the specifications.Because a spreadsheet is being used to contain the input vec-tor, supplementary calculations can be performed within thespreadsheet to aid in the variation of input parameters. For

example, calculations for simple things like compactnesschecks can be done right in the subdomain spreadsheet sothat one can dictate whether a compact or non-compactgirder is being defined without ever running the program. Formore complex criteria, the definition of the input vector datamay be an iterative process requiring that the program outputbe reviewed to ensure that the desired effect is beingachieved through the variation of input.

To ensure that a wide variety of girder cross sections areincluded in the test suite, the PennDOT database of cross sec-tions was included as part of the suite. This set of cross sec-tions, probably larger than that used by any other State,includes 84 different I-girders (including AASHTO and Penn-DOT types), spread box girders, and adjacent boxes (28 ofeach type).


Both programs tested allow the “lumping” of all the pre-stressing steel at the center of gravity of strands. However,some portions of the prestressed girder subdomain can onlybe tested with a known prestressing steel strand pattern. Forexample, in a debonded strand analysis, where certainstrands are intentionally debonded to reduce tensile stressesin the concrete near the end of the beam, the strand patternmust be known. Having to define a strand pattern manuallyfor each girder with a known strand pattern can be quitecumbersome. Therefore, some spreadsheet macros werewritten to automate the generation of the strand patterngiven a list of possible strand locations in the beam crosssection and a desired center of gravity of the strand group.For harped-strand design, a special version of this macrogenerates a possible strand pattern given the midspan strandpattern and a desired center of gravity at the end of the beam.The strand pattern macros tend to slow down the macro thatwrites the input to external ASCII files. Nevertheless, theuse of such macros is much more efficient than manual def-inition of strand patterns.

Assumptions

Some of the primary assumptions associated with the def-inition of this suite are

• Live load is HL-93.• Number of lanes is four.• DLA is constant (1.15 for fatigue, 1.33 otherwise).• General load factors (η factors) are taken as ηI = 1.05, ηD

= 0.95, ηR = 0.95).• Live load distribution factor is taken as 0.95 lanes.• Concrete is normal density.• The number of unique shear stirrup ranges (per half-

span) is limited to three.

E-19

Results

The procedure described above for generating the data andpostprocessing the results can be used to graphically reviewand compare the output of interest for a large number of bridgeconfigurations in a short amount of time. Given that not allwho review this document will be able to work with the elec-tronic version of this subdomain, selected results are pre-sented and discussed in this section.

Losses

Prestressing losses are an important computation becausethey affect all stress and shear capacity calculations. A break-down of all of the loss components was not available from bothprograms. Figure E-33 shows the variation in total losses ascomputed by both analysis programs. PSLRFD shows a con-stant loss along the length of the member but BRASS com-putes losses that can vary along the length. However, beyondthe points located at the centerline of bearing, the resultsshow good agreement.

Final Stresses at Top of Girder

Figure E-34 shows a plot of final stresses (with all loadsand after all prestressing losses) at the top of a composite pre-stressed I-girder, factored for the Service I limit state. Theplot shows good agreement among stresses along the lengthof the girder. However, the stress calculated at the center ofbearing at the ends of the girder differs to a small degree.Note that PSLRFD outputs points at twentieth points, the endof transfer length, and the harp point (if applicable) locationbut BRASS provides data at tenth and harp points. The dif-ference in stresses at the end of the beam is attributed to dif-ferent assumptions regarding prestressing transfer length.The transfer length is an input item for the BRASS programand has been specified as 60-strand diameters per the LRFDSpecifications. PSLRFD assumes that the strands become fullytransferred 300 mm from the centerline of bearing. If thePSLRFD assumed transfer distance was specified in theBRASS input files, the stresses at the end match closely.

Final Stresses at Bottom of Girder

Figure E-35 shows a plot of final stresses at the bottomof a composite prestressed I-girder, factored for the ServiceIII limit state. The plot also shows good agreement betweenstresses along the length of the girder. The differences thatare apparent at the end can be attributed to the transfer lengthas discussed above. It is likely that small differences alongthe length of the girder are attributable to subtle differencesin the method used for calculating losses. BRASS calculates

varying losses along the length of the girder as well as foreach row of strands (vertically) but PSLRFD computes lossesonly once at the midspan of the girder.

Initial Stresses

Initial stresses (considering girder self weight and initiallosses only) at the top and bottom of the girder are shown inFigures E-36 and E-37, respectively. Again, good agreementis seen at the points output by both programs except at theends of the beam. This difference at the end would be negli-gible if both programs used the same transfer length.

Flexural Capacity

Figure E-38 shows the flexural resistance at the strengthlimit state for Bridge ID 1 as computed by both programs. Inthis figure, significant differences are seen along the entirelength of the girder. After investigation, it was determinedthat BRASS was including the effects of some mild steelintended to be effective only for negative flexure. With thismild steel excluded, the resulting comparison is as shown inFigure E-39.

Shear Capacity

Figures E-40 through E-44 show some of the key graphicalcomparisons for the shear capacity of a prestressed girder.Note that the BRASS results contain multiple result points foreach location. Because the shear capacity is a function of theinteraction between the applied moment and shear, BRASScomputes the shear capacity for the various components ofthe LRFD HL-93 vehicle (truck plus lane and tandem pluslane). Furthermore, the values are reported for both the min-imum and maximum shear for a total of four points per loca-tion. Nonetheless, the boundaries of the BRASS envelope ofresults can be compared to the PSLRFD results that are basedon the envelope of the HL-93 force effects. For example, thelower bound of the BRASS results for the factored shearresistance, Vr, compare favorably with the PSLRFD resultsover most of the span. In making this comparison, it is likelythat the differences are due to the differing correspondingmoment that was used to compute the shear capacity. Such acomparison would be useful to an agency trying to make apolicy decision regarding the use of concurrent or envelopeforce effects.

Discussion

Selected comparisons of program output are presented.These plots are only a few of the tens of thousands of plots thatcould be selected for this subdomain. In this document severalReport IDs were selected for a single Bridge ID. The pre-stressed girder subdomains currently contain approximately

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360 girders and over 70 different Report IDs. As a result, theprinted version of this document cannot adequately cover allof the possible comparisons. This subdomain is being distrib-uted in electronic form so that the reader can investigate thepossibilities in a self-directed fashion.

The spreadsheet and database tools developed allow theuser to generate and filter the enormous amount of data asso-ciated with this subdomain. The sample set of tools providedon the accompanying CD-ROMs generate comparison plotswith ease and provide an example of how the Process 12-50data may be analyzed. Without a high degree of automation,the data generated would be unmanageable.





SUBDOMAINS 9, 10, 12, 13, 15 THROUGH 20MULTI-SPAN PRECAST PRESTRESSED AND STEEL SUPERSTRUCTURES

Introduction

Using the methodology developed in Phase 1, the valida-tion process has been expanded to include pertinent items forcontinuous steel rolled beams or plate girders and prestressedconcrete I-beams and box beams. The continuous prestressedbeams are assumed to be simple-span beams made continu-ous for live loads and composite dead loads. Both the steeland concrete multi-span input generators were developed tohandle up to five continuous spans.

Suite Description

This test suite is composed of multi-span results for thefollowing six subdomains:

• Subdomain 9—Non-Composite Rolled Steel Sections• Subdomain 10—Non-Composite Steel Plate Girders• Subdomain 12—Composite Rolled Steel Sections• Subdomain 13—Composite Steel Plate Girders• Subdomain 15—Non-composite I-Girders• Subdomain 16—Non-composite Spread Box Girders• Subdomain 17—Non-composite Adjacent Box Girders• Subdomain 18—Composite I-Girders

• Subdomain 19—Composite Spread Box Girders• Subdomain 20—Composite Adjacent Box Girders

Analysis Engines

Currently, the input generators can create input files for the LRFD-based BRASS and PennDOT’s PSLRFD and STLRFD programs. The BRASS program was developedindependently of the two PennDOT programs and thus provides a valid basis for comparisons.


Process IDs 9, 12, and 13 were the only IDs used for thissubdomain.


Report IDs 40000–49999 (steel) and 50000–59999 (pre-stressed) are the primary focus of these subdomains.


The list of superstructure Report IDs has been expandedas appropriate for multiple spans. Originally, separate ReportIDs for the positive and negative sense of force effects andload-dependent effects were considered. This was revised touse an Auxiliary ID to indicate the load sense. This approachhas several benefits. First, the list of Report IDs becomessimpler because there is less duplication of items that areidentical except for the sense of the loading. Second, thisapproach will allow for the inclusion of more results becausethe developer may not always know the sense of the loadingfor a particular item at the time the results (specifically, theProcess 12-50 results) are being output.

Although it is desirable to have the sense informationincluded in the Process 12-50 output, the developer will havethe option of producing output for a particular Report ID withthe Auxiliary ID for load sense set to a value that representsan unknown sense. Without this approach we take the risk ofcreating a subdomain specification that contains a large num-ber of important result items that could be somewhat difficultfor the developer to produce. Because the strength of Process12-50 is increased with each additional participating devel-oper, the investigators did not think that this was a good riskto take.

For the Report IDs that are load-sense dependent (i.e.,dependent on the force effects being positive or negative),the Auxiliary ID allows a more direct comparison of resultswhen the load sense information is included. In the event thata particular developer cannot readily produce the load senseinformation for a given Report ID, the basic location/resultinformation may still be produced for comparisons with the

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data produced by other programs. While this is not ideal, theavailability of partially complete data for comparison is farbetter than no data at all.

The multi-span test suites are high-level test suites, mean-ing that they are a superset of a combination of lower leveltest suites. As such, these test suites require a very detailedset of input parameters. As a result, comparisons can be madebetween higher-level results (such as member capacities) aswell as “lower-level” results (such as section properties ordead and live load actions). This complete and comprehen-sive approach does not exclude the need for the test suitesthat exclusively test these lower-order results because somesimplifying assumptions have been made in this test suite(such as a constant live load distribution factor). Other sim-plifying assumptions are outlined for each of the subdomainslater in this section.

Multi-Span Precast Prestressed ConcreteSuperstructures

Introduction

This subdomain is comprised of multiple-span prestressedconcrete girder superstructures containing up to five spans ofequal or varying length. The girder types included in this sub-domain are I-girders, adjacent box beams, and spread boxbeams. Each span for a particular bridge girder must have thesame type of beam but the section size from span to span canbe varied. The strand configuration may be straight, harped,or debonded. Many of the other pertinent input parameterscan be varied, as was the case in the Phase I (simple-span) ofthis work.

Assumptions


• Live load is HL-93.• Roadway width (curb-to-curb) is 10.4 m or 13.4 m.• DLA is constant (1.15 for fatigue, 1.33 otherwise).• General load factors (η factors) are taken as ηI = 1.05,

ηD = 1.0, ηR = 1.0.• Live load distribution factor is taken as 0.95 lanes/girder.• Concrete is normal density.

Results

One of the primary design controls on a prestressed con-crete bridge girder is the service load stress level in thebeam at various locations along the beam at each criticalstage of loading. As such, service load stresses are a goodstarting point for comparing results between two differentprograms.

Because the stress computations are performed in the lat-ter stages of the CP, many computations leading up to thestress calculation must be correct to achieve a valid result.The stress calculations depend on section properties, deadloads, live loads, strand configuration, and prestressinglosses. Therefore, if good agreement is seen in the stressresults across a wide range of test cases, this is a good indi-cation that the input generation and a large part of the pro-grams being compared are working properly. Differences instress results signal a need for further investigation of someof the supporting results.

The figures discussed in this section contain results for athree-span prestressed concrete I-girder with harped strands.This bridge is only one of 112 I-girder bridges currently inthe test suite. Similar results can be compared for the 66spread box girders and the 114 adjacent box girders that arecontained in the multi-span concrete test suite.

Stresses, Section Properties, and Force Effects

Figures E-45 through E-47 contain comparison-of-serviceload stresses at various points along the three-span girder.Although good agreement is seen in the initial and final ser-vice load stresses at the top of the girder, Figure E-47 showssome significant differences in the final service load stress atthe bottom of the beam in the center span. Figures E-48through E-63 that follow show good agreement in the resultsfor section properties, prestressing strand stresses, and deadloads. The live load and factored moments are slightly dif-ferent. The cause for these differences was not fully resolved.

Section Capacity

Report IDs related to the flexural Strength Limit State,specifically the cracking moment and the factored flexuralresistance are shown in Figures E-64 and E-65, respectively.Good results can be observed in comparing these values forthe positive flexural cases. However, these comparisons weremade using a preliminary version of PSLRFD that did not yetinclude the corresponding negative flexural results for theseReport IDs.

Figure E-66 shows a comparison between BRASS andPSLRFD for the factored shear resistance. The LRFD-basedshear resistance computations are highly load-dependent,which results in numerous data points at each location forwhich output is produced. The shear computations are car-ried out for multiple combinations of shear and moment. Asa result, it is difficult to extract a meaningful comparison ofthe data, as can be seen in this figure. Cases like these demon-strate the usefulness of the Auxiliary IDs that can be used tofilter the data to a greater degree. At this time, however, thisadditional data is not being output by either of the programsbeing compared for this Report ID.

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Multi-Span Steel Girder Superstructures

Introduction

This subdomain comprises multiple-span steel girder super-structures containing up to five spans of equal or varyinglength. The test suit for this subdomain is primarily comprisedof composite steel plate I-girders, although continuous rolledbeam and non-composite beams are also included. The pri-mary basis for the test suite data is the 1979 United StatesSteel (USS) publication Composite Steel Plate Girder BridgeSuperstructures: Load Factor Design. Although the prelim-inary designs in this publication are based on load factordesign (LFD), they are considered a good basis for prelimi-nary design for both LFD and LRFD. As a result, much ofthe data in the test suite is centered around realistically-sizedgirders. For completeness, some atypical sections have beenadded to the test suite.

Typical Bridge Cross Section

Figure E-67 shows a typical bridge cross section for thepreliminary design data appearing in the USS LFD-baseddesigns. Both fully stiffened and partially stiffened girdershaving roadway widths of 34 ft and 44 ft are included in thetest suite. The span length and configurations vary widelyand although the USS manual uses 5-ft increments in thespan length, a 10-ft increment in the span length was chosenfor the test suite in order to keep the number of bridges downto a reasonable size.

Data Format

The plate girder data is summarized in the USS manual inthe format illustrated in Figure E-68. This information wasentered into the input generation spreadsheets and the neces-sary code was written to translate this information into inputfiles for BRASS and STLRFD.

Although the plate girder data lends itself to a hierarchicalstorage method, a decision was made to store the data in a flatfile format (XML and CSV text files) for simplicity and toremain consistent with the method for storing other subdo-main input data. Much work has been done under variousbridge research projects to develop relational data structuresfor storing bridge data such as this so the Process 12-50research team decided against repeating this effort. The flatfile format of the input data requires that a limit be set on thenumber of section changes and transverse stiffener locations.The limit on the number of section changes and transversestiffener locations has been set to 50 and 120, respectively.There is no limit on the number of section transitions in anygiven span, only on the total number of transitions. However,some computational engines may have more or less severelimits than the limitations as defined in this subdomain. Cur-

rently, the maximum number of section changes and stiffenerlocations in the LFD data is 30 and 102, respectively, leavingsome room for expansion of the subdomain. As a result,although the input data for this subdomain may not be storedin the most efficient manner, it is straightforward and easilymanipulated into more structured formats. A portion of theXML version of the input data is shown in Figure E-69. AnXML style sheet (XSL) can be applied to the XML input todisplay it in a more readable format. The final XML inputformat for Process 12-50 data is presented in Appendix CCof the research team’s final report.

Assumptions


• Girder web depth is constant.• Live load is HL-93.• Roadway width (curb-to-curb) is 10.4 m or 13.4 m.• DLA is constant (1.15 for fatigue, 1.33 otherwise).• General load factors (η factors) are taken as ηI = 1.05, ηD

= 1.0, ηR = 1.0.• Live load distribution factor is taken as 0.85 lanes/girder.• Concrete is normal density.• Plate girders may be stiffened or unstiffened with vari-

able stiffener spacing, rolled beams are unstiffened.

Preliminary Results

Representative comparisons of section properties for a two-span plate girder structure are shown in Figures E-70 throughE-76. A review of Figures E-70 through E-72 for the steel-onlysection properties shows good agreement between BRASSand STLRFD.

Although Figure E-73 also shows good agreement betweenthe results for the composite moment of inertia for the short-term (live load) section, the section modulus to the top of thebeam shown in Figure E-74 does not compare as well.

The magnitude of the discrepancies observed in the com-posite section moduli may be somewhat misleading. Dif-ferences up to about 20% are observed in this parameter.However for the same girder, the neutral axis locationresults seem to be comparing very well. The difference inthe section moduli is because the neutral axis is locatedvery close to the top flange for positive flexure. As a result,a few millimeters difference in the distance from the elas-tic neutral axis to the extreme fiber in the top flange of thebeam can result in a large difference in the section moduli.In such a case, the section modulus for the top flange isquite high when compared to that of the bottom flange, sothe design of this particular section in positive flexure willoverwhelmingly be controlled by the state of stress in thebottom flange.

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Such comparisons underscore the need for careful inter-pretation and engineering judgment when reviewing results.The Process 12-50 database provides the means for quickidentification of such differences whether the comparisonsare done graphically or numerically. Once such differencesare identified, judgment is required to determine probablesources of such differences and whether those differences areof consequence.

Figure E-76 shows that the negative moment section mod-ulus results are in exact agreement between STLRFD andBRASS. Therefore, it appears that the differences in the com-posite moment section properties are related to assumptionsmade about the slab itself. As stated above, however, the dif-ferences that were noted in the composite moment sectionmodulus to the top of the beam are inconsequential becausethe composite section modulus to the bottom of the beamcontrols for this section and the BRASS/STLRFD results arealmost identical for that parameter.

The plastic section properties as reported by BRASS andSTLRFD were also in very close agreement (results notshown here).

Actions

Figures E-77 through E-81 show good agreement for theactions where both BRASS and STLRFD produce Process12-50 results. However, STLRFD appears to be producingsome additional data points as can be seen in Figure E-79. Atthis time, STLRFD is not producing Process 12-50 output forunfactored live load actions. This output would allow for fur-ther comparison of the actions and help to identify reasonsfor differences in the factored actions.

Figures E-82 and E-83 show that in the negative momentregions, differences can be observed in the factored moments.In the first phase of the NCHRP 12-50 project, some differ-ences in the negative live load moments were reported incomparisons between PSLRFD and BRASS. These differ-ences were attributed to the additional dual-tandem (tandemtrain) loading applied by PSLRFD. BRASS does allow thedual-tandem loading to be specified manually and this wasdone in the continuous girder test suite. Therefore, the dif-ferences seen in Figures E-82 and E-83 should not be due tothe live load effect but, more likely, are due to the manner inwhich the loads are factored.

BRASS uses a more rigorous method for determining thecritical factored force effects by applying both the minimumand maximum LRFD dead load factors to establish a sort of“dead load envelope.” The resulting dead load is combinedwith the minimum and maximum factored live load effect toachieve the total factored moments and shears. In contrast,STLRFD and PSLRFD simply use the maximum dead loadfactors to achieve the factored force effects. Note that thisdifference in the application of the load factors results in a7% difference in the factored negative moment at the pier inthis two-span bridge.

Stresses

Figures E-84 through E-87 show comparisons betweenstresses in the compression and tension flanges at the strengthand service limit states. At this time, the results do not com-pare very well and require further investigation. In part, thesedifferences appear to be due to a difference in the sign con-vention in the negative moment regions. In addition, the dif-ference in the methods for factoring loads as previously dis-cussed has a corresponding influence on the factored stresses.

Capacity

Figures E-88 and E-89 show representative comparisonsbetween the factored flexural and shear resistances at thestrength limit state, respectively. In the positive momentregions, the flexural resistances compare well. However in thenegative moment regions, the BRASS and STLRFD results arenot in very good agreement. Furthermore, STLRFD is not pro-ducing negative flexural resistance output properly at this timeand is also producing numerous zero-valued results.

As was the case with the shear results for the multiple-spanprestressed girder subdomains, the load-dependent shearcapacity is difficult to compare without further filtering basedon the Auxiliary ID, although it can be seen that some of thecapacities shown in Figure E-89 appear to be matching upquite well. However, without the ability to separate the capac-ity output into groups having common load cases, it is diffi-cult to compare the results directly. Currently, BRASS isindicating an unknown load sense and STLRFD is not pro-ducing load sense information for this Report ID.

Discussion

Using methods developed in Phase I of this project, thetest suites for steel and concrete superstructures have beenextended to include multiple-span units. Although the num-ber and complexity of the results is greater than that for sim-ple spans, Process 12-50 proved to be effective in quicklyidentifying differences in results. These differences can thenbe investigated and evaluated to determine if they are explain-able and intentional. Through the course of this investigation,several errors have been identified and corrected. Additionalwork can be done to include more results in the Process 12-50format to aid in determining the source of differences thatwere observed.

SUBDOMAIN 30—PIERS

Introduction

This section outlines the work done on developing a testsuite for bridge piers. The test suite is currently limited in

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scope to simple-geometry hammerhead and frame concretepiers. This section contains a description of the suite, a descrip-tion of the analysis engines used to determine the results, theloadings considered, a definition of the test suite problems,and an outline of the input and output formats that should aidautomated comparisons and plotting. Note that because of alimitation in BRASS-PIER (LRFD) (hereafter referred to asBRASS), all results are presented in U.S. customary units.

Suite Description

This suite is designed to examine the ability of a processto compute the loads, actions, and resistances necessary toperform a review of a concrete bridge pier. The loading isdescribed in detail in Chapter 3 of the LRFD Specifications.Simplifications and assumptions made on the loading are out-lined. Due to funding and time limitations, the suite is cur-rently limited to 11 hammerhead pier problems and oneframe pier problem.

Analysis Engines

Two independently developed CPs are used in this test suite.The first CP is BRASS-PIER (LRFD). The alpha test versionof this program was used. The second CP is PennDOT’sPAPIER (hereafter referred to as PAPIER), version 1.0. Bothprograms are based on the LRFD Specifications.


Process IDs 10 and 11 were the only IDs used for thissubdomain.



Loadings Considered

Both CPs consider the following loads: truck and lane liveloads, superstructure component and wearing surface deadloads, pier self-weight, wind, wind on live load, wind uplift,braking, centrifugal force, seismic, stream flow, ice, buoyancy,temperature, and shrinkage. Currently, only user-input super-structure component and wearing surface dead loads, pier self-weight loads, stream flow forces, ice forces, and user-inputlive load girder reactions have been implemented into the testproblems and validated between the CPs. These loadings areoutlined in the LRFD Specifications, Section Three. Theseloadings were implemented first because they are the sim-plest, and reconciling differences between the two programshas facilitated error checking for the input generation spread-

sheet. Now that the programs are reporting comparable resultsfor these loads, we feel confident that the programs are ana-lyzing the same pier definitions (i.e., both input files are rep-resenting the same structure).


The test suite has been defined to test the analysis of asimple-geometry hammerhead pier, and includes the calcula-tion of loads, actions, and resistances in the pier cap, columns,and footings. The problems are generated by varying the piercap, column, and footing dimensions, as well as the loadingparameters. For example, the ice force on a pier is a functionof several parameters, including stream flow direction rela-tive to the pier, the inclination of the column, the shape of thecolumn, etc. By varying these parameters, the calculation ofice forces can be tested. A partial list of the input parametersis presented in Table E-10.

Results Format Database Structure

The piers subdomain uses the same Results table format asthe rest of the subdomains. The structure of this table is out-lined in Table E-11 and Figure E-90. In order to track loadsas they are combined and transferred from the cap to thecolumns and finally to the footings, the Auxiliary ID has beenused to link to an additional Results table that provides adeeper hierarchy. Figure E-91 shows the structure of thedatabase, including the Auxiliary table, as implemented withinthe Piers Subdomain and BRASS.

Because the database structure has been changed, theResults viewer in the database was also updated to reflectthese changes. Figure E-92 shows the modified viewer. Thebasic difference from the previous viewers is that instead ofselecting from a long list of Report IDs, the user selects aReport ID that represents a general portion of the pier (31999for the cap, for example), and then refines the query usingother drop down choices. Included in the viewer are controlsfor selecting the limit state, sense, action, and load type. Fig-ure E-93 shows the Results viewer with the load type controlactive. Because several controls need to be set to define thequery, the graph is not updated until the user clicks on theReplot Graph button.

Results

Hammerhead Pier Results

Several test problems have been created using a generationspreadsheet similar to those used in other subdomains. Cur-rently, BRASS is the only program that produces results in theProcess 12-50 format automatically, so the PAPIER results arepasted into the database manually for viewing. This method is

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used to display selected results from PAPIER along withBRASS results. In order to determine which results to dis-play, they must first be compared in the text output files pro-duced by each program.

Figure E-94 shows the moment in the cantilevers of ahammerhead pier due to the pier self-weight. The plot showsthe moment in kip-ft versus the distance from the left edge ofthe pier cap. The region between 7.5 ft and 17.5 ft representsthe column, so no actions are shown in that portion of theplot. Similarly, Figures E-95 and E-96 show the moments inthe cantilevers due to the superstructure component and wear-ing surface dead loads, respectively. These loads were appliedby defining the locations of the girders resting on the pier capand then specifying the reactions due to the two types of loads.Note that the superstructure loads applied are not symmetric,so the flexural actions are different for each cantilever. Fig-ure E-97 shows the shear in the cantilevers due to self-weight.Note that the shear sign conventions for the two programsbeing compared are opposite. The shear magnitudes matchclosely.

The next set of plots refers to a non-symmetrical hammer-head pier with double girder bearings (one each for back- andahead–on-line). Figures E-98 through E-100 show the deadload moments in the pier cantilevers due to various loadings.Once again, note that the gap in the diagram represents thewidth of the column, where no moment is displayed. Thesethree figures show excellent agreement between the two CPs.

The next three figures (Figures E-101 through E-103) showthe beam shear for the same load cases. Again, the shear signconventions are different, but the magnitudes match. There isone discrepancy in the shear values from the superstructureloading. For the point at 31 ft from the left edge of the piercap, BRASS reports a shear of −74.00 kips, and PAPIERreports a shear of 66.81 kips. The values at the other pointson the left cantilever match closely. This discrepancy is causedby precision differences in the placement of the load on theleft cantilever. In BRASS, the fifth girder falls at 30.9986 ftfrom the left end of the cantilever, while the cantilever lengthis 30.9988 ft. In PAPIER, the fifth girder falls at exactly30.9988 ft from the left end of the cantilever, the same as theleft cantilever length. PAPIER does not include this girder inthe shear calculation for the point at the right end of the leftcantilever. The reaction from the fifth girder is 7 kips, so ifthe fifth girder reaction is removed from the BRASS number,the values differ by 0.19 kips. Note that the moments com-pare closely because the lever arm that BRASS uses for thefifth girder reaction is practically zero.

Figures E-104 and E-105 show the moment and shearrespectively, in the cap due to user-input live load reactionsfor a double bearing pier (two sets of girder reactions). Notethat the live load actions differ by 20% between the two pro-grams. This is due to different methods of applying the mul-tiple presence factor. BRASS assumes that the user has takenthe multiple presence factor into account when entering the

live load girder reactions, while PAPIER assumes that thegirder reactions do not include the multiple presence factors.

The results reported by PAPIER for the live load actionsdo not include the multiple presence factor used for thecombined loading. In order to get the Strength I limit stateresults to agree, the BRASS girder reactions were multi-plied by the one-lane-loaded factor of 1.2 (PAPIER alwaysuses a factor of 1.2 for user-input live load girder reactions).Note that the live load actions differ by the factor of 1.2, butthe Strength I actions agree almost exactly. Figure E-106shows the Strength I moment in the pier cap.

A possible extension of the current work is comparisons oflive loads generated by the programs by entering the bridgedeck geometry and defining the truck and lane load reactions.Both programs then position lanes and trucks to produce themaximum actions in the cap, columns, and footings.

The results of the stream force computations by PAPIERand BRASS are presented in Figure E-107. Note that by multi-plying the force time by the lever arm in the BRASS calcu-lations, the same moment as reported by PAPIER is acquired(5 ft ∗ 16.799 kips = 83.99 ft-kips).

The results of the ice force computations by PAPIER andBRASS are shown in Figure E-108. Again, by multiplyingthe forces reported by BRASS by the moment arm, you willacquire the same moments as reported by PAPIER.

Comparisons have also been started for wind, braking, andcentrifugal forces. We have not yet been able to resolve dif-ferences in the results for these load cases. This difference islikely due to input errors, but due to funding restrictions thedifference was not resolved.

Frame Pier Results

The results for the one frame pier problem run to date arepresented. The loadings have been limited to self-weight deadload and a single, concentrated, user-input bearing load. Thepier used for the initial comparison is a frame pier with two30-ft columns (from the top of the footing to the top of thepier cap). The columns are spaced 28 ft apart, with a 5-ft can-tilever on each side of the bent. Figure E-109 shows the gen-eral geometry.

The applied external loading consists of a 10-kip concen-trated bearing force at the center of the main span. The shearand moment in the pier cap due to the structure self-weightare shown in Figures E-110 and E-111, respectively.

Without modifying the input, the programs only report themid-point results of the main span in common. By compar-

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ing these values, it is apparent that about a 3.5% differenceexists in the moments reported at this point. After thoroughlyreviewing the geometry, cross section dimensions, materialproperties, boundary conditions, and loads, the structureappears to be the same in both models. Based on an investi-gation of the BRASS code and the PAPIER documentationinto how the two programs model structures, the reasons forthese differences appear to be the modeling of the cap/column connections and the cap itself. PAPIER uses rigid linksat the column tops. In addition, PAPIER models the spans ofthe cap with multiple elements placed at the cap mid-depthlocation. BRASS uses a single element to connect column tops.The modeling assumptions are shown in Figure E-112.

A discrepancy of similar magnitude is noted in the shearsand moments due to a 10-kip concentrated load at the centerof the span, as shown in Figures E-113 and E-114.

It should be noted that the axial loads reported to the topof the columns due to the structure self-weight match almostexactly, with BRASS reporting 58.496 kips and PAPIERreporting 58.497 kips. The moments transferred to the col-umns, however, differ by about 3.5% as well. This differencecan also be attributed to the differences in the stiffness modelused by the two CPs.

Work Remaining on Piers Subdomain

A list of work beyond the scope of this project that remainsto bring the pier test suite up to the level of the superstructuretest suites follows:

• Program-generated live loads,• Resistance computations for the cap, columns, and foot-

ings,• Automation of a second process (PAPIER or another),• Expansion of hammerhead and frame pier problem suites,

and• Fine-tuning of the Results viewer based on deep hier-

archy.

The work performed to date on the piers test suite indi-cates that close agreement can be reached between separatepier programs. Close agreement is shown in the cap and col-umn actions for both solid shaft and frame piers for simpleload cases. This subdomain also demonstrates the use of adeeper hierarchy in the database. The deeper hierarchy allowsload tracking, as well as separation of results by sense,which produces clear Results graphs.

E-27

Figure E-1. Process agreement—girder self weight.

Figure E-2. Process agreement—slab weight: exterior girder.

Figure E-3. Process agreement—total Stage 2 DW: interior girder.

E-28

Figure E-5. Report differences—steel I-section: 1(a): single-lane loaded: moment: DF.

Figure E-4. Range of applicability differences—controlling moment factor: Girder 1: DF.

Figure E-6. Report agreement—controlling moment factor: Girder 1: DF.

E-29

Figure E-8. Moment of inertia of basic beam (Bridge ID = 7).

Figure E-9. Long-term section modulus (Bridge ID = 7).

Figure E-7. Prestressed I- and box-sections.

E-30

Figure E-12. Short-term moment of inertia, after correction (Bridge ID = 7).

Figure E-10. Short-term moment of inertia (Bridge ID = 7).

Figure E-11. Service III stresses at bottom flange (Bridge ID = 7).

E-31

beff

teffth

RolledI-Shape

bh

beff

teffth

PlateGirder

bh

Figure E-13. Steel I-sections.

Figure E-14. Moment of inertia of steel section (Bridge ID = 70).

Figure E-15. First moment of transformed section (Bridge ID = 70).

E-32

Figure E-18. Moment of inertia of compression flange about Y-axis, Iyc (Bridge ID = 70).

Figure E-16. Long-term composite section modulus (Bridge ID = 70).

Figure E-17. Plastic moment capacity (Bridge ID = 70).

E-33

Figure E-19. Inconsistent results—dead load moment.

Figure E-20. Program agreement—dead load moment.

-1800

-1600

-1400

-1200

-1000

-800

-600

-400

-200

0

0 10 20 30 40 50 60

Location (m

Mo

men

t (k

N*m

)

)

BTBeam

BRASS

PennDOT

Figure E-21. Example of negative moment.

E-34

Figure E-22. Program agreement—moment: factored: maximum: Strength I.

Figure E-23. Program differences—bending moment.

E-35

Plate Girder Layout

top flange 1 top flange 2 top flange 1

web 1 web 2 web 1

bot. flange 1 bot. flange 2 bot. flange 1

C

A

B

Span Length

B

C

A

Section Layout

top flange 1 top flange 2 top flange 1

web 1 web 2 web 1

bot. flange 1 bot. flange 2 bot. flange 1

C

A

B

Span Length

B

C

A

1 2 3 4 5 6 7

Figure E-24. Plate girder section transitions.

Figure E-25. Flexural stress in compression flange, Strength I (Bridge ID = 1).

E-36

Figure E-27. Maximum factored moment, Strength I (Bridge ID = 1).

Figure E-28. Service stressed in the tension flange (Bridge ID = 1).

Figure E-26. Flexural stress in tension flange, Strength I (Bridge ID = 1).

E-37

Figure E-29. Flexural capacity at the Strength I limit state (Bridge ID = 1).

Figure E-30. Shear capacity at the Strength I limit state (Bridge ID = 1).

Figure E-31. Factored fatigue stress range (Bridge ID = 1).

E-38

0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

To

tal L

oss

, Dfp

T (

MP

a {N

/mm

^2})

PSLRFD GirderLRFD

Figure E-33. Total losses (Bridge ID = 1).

-35

-30

-25

-20

-15

-10

-5

0

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

Fin

al c

on

cret

e st

ress

, ft

f (M

Pa

{N/m

m^

2})

PSLRFD GirderLRFD

Figure E-34. Final Service I stresses (Bridge ID = 1).

Figure E-32. Fatigue resistance (Bridge ID = 1).

E-39

-20

-15

-10

-5

0

5

10

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

Fin

al c

on

cret

e st

ress

, fb

f (M

Pa

{N/m

m^

2})

PSLRFD GirderLRFD

Figure E-35. Final Service III stresses (Bridge ID = 1).

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

Init

ial

con

cret

e st

ress

, ft

i (M

Pa

{N/m

m^

2})

PSLRFD GirderLR

Figure E-36. Initial stresses at top of girder (Bridge ID = 1).

-30

-25

-20

-15

-10

-5

0

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

Init

ial

con

cret

e st

ress

, fb

i (M

Pa

{N/m

m^

2})

PSLRFD GirderLRFD

Figure E-37. Initial stresses at bottom of girder (Bridge ID = 1).

E-40

0.00E+00

5.00E+08

1.00E+091.50E+09

2.00E+09

2.50E+09

3.00E+09

3.50E+094.00E+09

4.50E+09

5.00E+09

0 2000 4000 6000 8000 10000 12000 14000 16000

Distance (mm)

Fac

tore

d f

lexu

ral

resi

stan

ce,

Mr

(N-m

m)

PSLRFD GirderLRFD

Figure E-38. Flexural resistance at the strength limit state (Bridge ID = 1).

Figure E-39. Flexural resistance at the strength limit state (revised, Bridge ID = 1).

Figure E-40. Factored shear resistance at the strength limit state (Bridge ID = 1).

E-41

Figure E-41. Nominal shear resistance provided by concrete (Bridge ID = 1).

Figure E-42. Nominal shear resistance provided by steel.

Figure E-43. Shear design parameter, beta (Bridge ID = 1).

E-42

Figure E-44. Shear design parameter, theta (Bridge ID = 1).

Figure E-45. Initial service stresses—top of girder.

Figure E-46. Final service stresses—top of girder, factored for Service I (maximum compressivestress).

E-43

Figure E-47. Final service stresses—bottom of girder, factored for Service III (maximumtensile stress).

Figure E-48. Section properties: beam area.

Figure E-49. Section properties: beam moment of inertia.

Figure E-50. Section properties: composite moment of inertia for live loads.

Figure E-51. Section properties: longitudinal stiffness.

Figure E-52. Girder dead load moment.

E-44

Documents

NCHRP Report 485 – Bridge Software—Validation …onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rpt_485aEp1-44.pdf · Live Load Actions (HL-93) 8. Factored Load Actions 9. Non-Composite