Numerical Approach for proposing the live load distribution factor on bridge decks based on AASHTO 2010 code for the crawler loadingIntroduction According to Encyclopedia of Britannica, Bridge is astructure that spans horizontally between supports, whose function is to carry vertical loads[endnoteRef:1]. The earliest bridges, apart from nature made bridges, have been made by humans from the simple wooden or stone slab over a span. This process has been developed up to the ancient romans which started to design bridges which can withstand in more severe conditions, in compare to the earlier ones. Later on, the bridge development has been carried out within the different countries, functioning both as military and as commercial bridges, made out of timber, stone, and etc. In 19th century the possibility of larger bridge constructions has been provided, with the introduction of the truss system of the wrought iron, but with the lack of the tensile strength for supporting the loads. So with the arrival of steel, much larger bridges have been constructed, many using the idea of Gustave Eiffel. In 1927 , first welded road bridge in the world has been built, and up to now, many developments and establishments has been presented in the bridge design, by introducing newer materials, technologies and design innovations. [1: Bridge (engineering) -- Britannica Online Encyclopaedia, 2012-Bridge (engineering) -- Britannica Online Encyclopaedia [ONLINE] Available at: http://www.britannica.com/EBchecked/topic/79272/bridge [Accessed 28 October 2012]]

So in order to ensure a consistence approach and a good practice for the design and construction of bridge structures, since 20th Century, various codes and standards have been issued[endnoteRef:2]. AASHTO (American Association of State Highway and Transportation Officials), DIN 1072 (Germany Road and foot bridges), BS 5400 Bridges (British code for bridges), AS 5100 - bridges (Australian code for bridges), CAN/CSA-S6-00 (R2005) (Canadian Highway Bridge Design Code), are among the todays famous bridge standards. [2: STRUCTURE mag - Structural Engineering Magazine, Tradeshow: Structural Engineering Codes and Standards in the United States, 2012- STRUCTURE mag - Structural Engineering Magazine, Tradeshow: Structural Engineering Codes and Standards in the United States [ONLINE] Available at:http://www.structuremag.org/article.aspx?articleID=363 [Accessed 28 October 2012]]

Among these codes, AASHTO has a well-established probability based design methodology and load factors, which makes bridges resistance against almost all of the applied static and dynamics loads, mainly imposed by the vehicles (graph 1)[APPENDIX 1, AASHTO Load And Load Designation]. But it has no specific guidelines to design the highway bridges for the imposed loads by Crawlers or similar heavyweight tracked wheeler vehicles such as army tanks.

Graph 1- AASHTOs Load ProvisionsCrawlers are vehicles fixed on an undercarriage with a set of tracked wheels which also called crawlers, which their main function is to deliver the necessary stability and mobility at the site. Their usage is to perform lifting or load carrying on site with little setup operation, however they are extremely heavy vehicles, and usually need to disassemble and moved by trucks, from one project to another , which is an extremely expensive operation.Moreover, the rapid growth of technology, and the necessity of building strong bridges with longer service life, brings this question that weather bridges designed by AASHTO can cope with the futures demands or not? Amphibious Tracked Transport Vehicle, weighing four tons, and having massive tracks, which is designed for managing disaster both in water and land, may perhaps provide a better illustration of the problem (Figure 1).

Figure 1- Amphibious Tracked Transport Vehicle[endnoteRef:3] [3: Amphibious Tracked Transport Vehicle | Pedal Dozer Project, 2012-Amphibious Tracked Transport Vehicle | Pedal Dozer Project [ONLINE] Available at:http://pedal-dozer.com/amphibious-tracked-transport-vehicle/ [Accessed 29 October 2012]]

Besides, the importance of the clear bridge design method for tracked or wheeler vehicles, made some of the countries to provide specific guideline in their national codes for this purpose; Iranian Bridge design standard[endnoteRef:4], which has been taken from the DIN (German Code), is a good example. [4: ]

Figure 2- Crawler CraneFurthermore, the major role of crawlers in installation and maintenance of the bridges, makes it is not always easy and economical to carry them by trucks rather than letting the crawler to be transported by their own tracked wheels, especially when it requires dissembling massive crawlers for their transportation purposes. All of the mentioned demands make it substantial to design some of the bridges in a way that they can withstand crawlers (or any similar tracked vehicles) imposed load. Background As the result of the joint effort of the Highway Bridge engineers and Railroad designers, basis of the bridge design codification together with its provisions relevant to the live-load has been accomplished. The outcome was presented as a Final Report on Specifications for Design and Construction of Steel Highway Bridge Superstructure at the spring meeting of ASCE on April 9, 1924, and is published in the 1924 transactions of the American Society of Civil Engineers[endnoteRef:5]. [5: Seaman, H. R. Final Report on Specifications for Design and Construction of Steel Highway Superstructures. In Transaction, ACSE, Reston, Va., 1924]

Year AASHTO's Development

1931First printed version of AASHO StandardSpecifications for Highway Bridges and IncidentalStructures

1970AASHO becomes AASHTO

Early 1970AASHTO adopts LFD

Late 1970sOMTC starts work on limit-states basedOHBDC

1986AASHTO explores need to change

1990 AASHTO Load and Resistance Factor Bridge Design Specifications (LRFD Code)

1996 foundation data reinserted

1990sMore commentary added

2002 Upgraded to ASBI LFRD Segmental GuideSpecs.

major update in 2002MCF shear in concrete simplified and clarified severaltimes

2004Major change in steel girder design inanticipation of

2005seamless integration of curved steel bridgesending three decade quest

2005P/C loses updated

2006complete replacement of Section 10 Foundation Design

2006more concrete shear options

2007Streamline MCF for concrete shear design

1,000 year EQ maps and collateral changes

Seismic Guide Spec - displacement based

Pile construction update

2008Coastal bridge Guide Spec

2010AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS , Fifth Edition,

AASHTOSs Development[endnoteRef:6] [6: Wassef, W.G., 2010. THE DEVELOPMENT OF AASHTO LRFD BRIDGE DESIGN SPECIFICATION AS N EXAMPLE OF PROBABILISTIC-BASED SPECIFICATIONS. Journal of Bridge , (December), pp.759767. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)BE.1943-5592.0000214 [Accessed October 31, 2012].]

AASHTO 1996, is using S/D formula for limit state design of bridge, where S is the girder spacing, and D refers to the type of the bridge Structure. In line with these developments, an ultimate strength or limit states design, called as Load Factor Design (LFD), was emerged in the 1960s. Subsequently, after several publications of the AASHTO, in the 1990s, AASHTO Load and Resistance Factor Bridge Design Specifications (LRFD Code) as an ultimate replacement for the AASHTO Standard Specifications for Highway Bridges, was presented. This newly introduced code has restructured bridge design practice in a more straightforward manner, by providing more accurate procedure for the distribution of the vehicles weight to its individual girders. LRFD code covers various limit states, comprising Service Limit State, Fatigue and Fracture Limit State, Strength Limit State (or Constructability), and Extreme Event limit State.As the AASHTO developed over time, several papers and articles have been written, especially after the introduction of LRFD method. These papers with their brief description can be seen in the following table (Table 2). NOTitleDateCountryAim of Paper

1Verification of AASHTO LRFD Specifications Live Load Distribution Formulas for HPS Bridges[endnoteRef:7] [7: Lin, M., 2004-Verification of AASHTO-LRFD Specifications Live Load Distribution Factor Formulas for HPS Bridges. Available at: http://etd.ohiolink.edu/view.cgi?ucin1108697828 [Accessed October 31, 2012].]

2004ChinaComparing true load distribution factor from the real tests on bridges and comparing them with the AASHTO LRFD Formulas.

2Simplified Shear Provisions of the AASHTO LRFD Bridge Design Specifications[endnoteRef:8] [8: Kuchma, D., Hawkins, N. & Kim, S., 2008. Simplified shear provisions of the AASHTO LRFD Bridge Design Specifications. PCI journal, pp.5373. Available at: http://cat.inist.fr/?aModele=afficheN&cpsidt=20326115 [Accessed October 31, 2012].]

2008USASimplified Shear Design of Structural Concrete Members.

3NCHRP, Simplified Live Load Distribution Factor Equations[endnoteRef:9] [9: NATIONAL et al., 2007. NCHRP, Simplified Live Load Distribution Factor Equations]

2007USATo determine a simpler and more accurate method to estimate live load effect on bridges.

4PCI Bridge Design Manual[endnoteRef:10] [10: PCI, 2012. PCI Bridge Design Manual. Systematic biology, 61(6), p.i1. Available at: http://www.ncbi.nlm.nih.gov/pubmed/23095404.]

--USA--

5Live Load Distribution Factors in Prestressed Concrete Girder Bridges[endnoteRef:11] [11: Barr, P., Eberhard, M. & Stanton, J., 2001. Live-load distribution factors in prestressed concrete girder bridges. Journal of Bridge Engineering, (October), pp.298306. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)1084-0702(2001)6%3A5(298) [Accessed October 31, 2012].]

2001USAEvaluation of flexural live-load distribution factors for a series of three span prestressed concrete girder bridges

6A refined Method for live load distribution prediction of bridges and comparative studies [endnoteRef:12] [12: Chen, Y., 2001. A refined Method for live load distribution prediction of bridges and comparative studies.]

2001USAPredicting the vehicle Load On the bridge Girder

7Construction Loads Produced During Heavy Lifting, Rigging and Handling Operations[endnoteRef:13] [13: Dennis S. Fedock, B.& W., 2001. Construction Loads Produced During Heavy Lifting, Rigging and Handling Operations. Journal of Bridge Engineering, pp.17. Available at: http://lib.dr.iastate.edu/etd/11158/ [Accessed October 28, 2012].]

2001USADetailed description of the construction loads to be considered in the analysis and design of handling systems for heavy component erection.

8Live Load Distribution Factors for a Three Span Continuous Precast Girder Bridge[endnoteRef:14] [14: BridgeSight, S.-, 2008. Live Load Distribution Factors for a Three Span Continuous Precast Girder Bridge.]

1998USAIllustrating the latest technique of computing LDF for the approximate procedure for calculating live load distribution factors.

9Live load distribution factors for glued-laminated timber bridges[endnoteRef:15] [15: May, J., 2008. Live load distribution factors for glued-laminated timber bridges. Available at: http://lib.dr.iastate.edu/etd/11158/ [Accessed October 31, 2012].]

2008USAStudy sponsored by the Forest Products Laboratory, with the objectiveof determining how truckloads are distributed to the structural members of glued-laminated timber bridges.

10Live Load Distribution Factors for Grid Reinforced Concrete Decks[endnoteRef:16] [16: LBFoster, 1998. Live Load Distribution Factors for Grid Reinforced Concrete Decks.]

1998USAA better understanding of grid reinforced concrete bridge deck behavior and its interaction with supporting members,

11Live Load Distribution Factors for Girder Bridges[endnoteRef:17] [17: Nesvold, S., 2002. LIVE-LOAD DISTRIBUTION FACTORS FOR GIRDER BRIDGES. Available at: http://mail.ce.udel.edu/cibre/reu/02reports/Nesvold.doc [Accessed October 31, 2012].]

2002USADetermining a new simplified formula that eliminates the iterations, creating an easier to use, yet accurate equation.

12Precast Balanced Cantilever Bridge Design Using AASHTO LRFD Bridge Design Specifications[endnoteRef:18] [18: Institute, A.S.B., Precast Balanced Cantilever Bridge Design Using AASHTO LRFD Bridge Design Specifications.]

2004USAProviding design Example for Segmental & Precast Cantilever Bridge, using AASHTO LRFD

13Optimized Design and Testing of a Prototype Military Bridge System for Rapid In-Theater Construction[endnoteRef:19] [19: Hanus, J. et al., 2006. Optimized Design and Testing of a Prototype Military Bridge System for Rapid In-Theater Construction. Available at: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA481580 [Accessed October 31, 2012].]

2005USADesigning a bridge with reduction in deployment requirements because of the use of in-theater materials.

14Design and analysis of bridge foundation with different codes[endnoteRef:20] [20: Aziz, H. & Ma, J., 2011. Design and analysis of bridge foundation with different codes. Journal of Civil Engineering and Construction , 2(May), pp.101118. Available at: http://www.academicjournals.org/jcect/PDF/Pdf2011/May/Aziz and Ma.pdf [Accessed October 31, 2012].]

2011ChinaDiscussed the design and analysis of bridge foundation subjected to load of train with four codes, namely AASHTO, BS, The Chinese National Standard and Chinese code.

15LRFD Bridge Design Specifications[endnoteRef:21] [21: AASHTO, L., 1998. LRFD bridge design specifications. Washington, DC: American Association of State , 41(Revision 1), pp.Section 13, Articles 13.8.2 & 13.8.3. Available at: http://scholar.google.com/scholar?hl=en&btnG=Search&q=intitle:LRFD+Bridge+Design+Specifications#1 [Accessed October 31, 2012].]

2012USA2012 AASHTO Revision

16Introduction to LRFD, Loads and Loads Distribution[endnoteRef:22] [22: Administration, F.H. & Chicago, I., Introduction to LRFD, Loads and Loads Distribution. , 0, pp.126.]

--Comprehensive Explanations

17CSiBridge Bridge Superstructure Design[endnoteRef:23] [23: CSI, 2010. CSiBridge Bridge Superstructure Design.]

2010USABridge Software Guide

18Bridge Crossings LFD vs. LRFD[endnoteRef:24] [24: Michael A. Grubb, P.E., 1997. Bridge Crossings LFD vs. LRFD. , (5).]

1997USAComparative Explanations

19TRB &AASHTO[endnoteRef:25] [25: Transportation, N.J.D. of, TRB &AASHTO.]

--USAProvide an overview of the mission, roles, and responsibilities AASHTO and TRB as they relate to the bridge community

20Special Issue on AASHTO-LRFD Bridge Design and Guide Specifications: Recent, Ongoing, and Future Refinements[endnoteRef:26] [26: Tobias, D.H., 2011. Special Issue on AASHTO-LRFD Bridge Design and Guide Specifications: Recent, Ongoing, and Future Refinements. Journal of Bridge Engineering, 16(6), pp.683683. Available at: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29BE.1943-5592.0000297 [Accessed October 28, 2012].]

2011USAProviding highlights of some of AASHTO's revisions over a broad range of bridge engineering topics.

21Evaluation of FRP Posttensioned Slab Bridge Strips Using AASHTO-LRFD Bridge Design Specifications[endnoteRef:27] [27: Nol, M. & Soudki, K., 2011. Evaluation of FRP Posttensioned Slab Bridge Strips Using AASHTO-LRFD Bridge Design Specifications. Journal of Bridge Engineering, (December), pp.839846. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)BE.1943-5592.0000226 [Accessed October 31, 2012].]

2011CanadaComparing the flexural performance of five FRP slabs and one steel-reinforced control slab to the design provisions of the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications.

22Determination of AASHTO Bridge Design Parameters through Field Evaluation of the Rt. 601 Bridge: A Bridge Utilizing Strong well 36 in. Fiber-Reinforced Polymer Double Web Beams as the Main Load Carrying Members[endnoteRef:28] [28: Restrepo, E., 2002. AASHTO Bridge Design Parameters through Field Evaluation of the Rt. 601 Bridge: A Bridge Utilizing Strongwell 36 in. Fiber-Reinforced Polymer Double Web Beams. Available at: http://scholar.lib.vt.edu/theses/available/etd-12162002-113130/ [Accessed October 31, 2012].]

2002USAdetails the field evaluation of the Rt. 601 Bridge in order to determine the following AASHTO bridge design parameters: wheel load distribution factor , dynamic load allowance IM, and maximum deflection & etc.

23AASHTO Connected Vehicle Infrastructure Deployment Analysis[endnoteRef:29] [29: Hill, C. & Garrett, J., 2011. AASHTO Connected Vehicle Infrastructure Deployment Analysis. Available at: http://trid.trb.org/view.aspx?id=1131369 [Accessed October 31, 2012].]

2011USADescribing a deployment scenario for Connected Vehicle infrastructure by state and local transportation agencies, together with a series of strategies and actions to be performed by AASHTO to support application development and deployment.

24UPDATE OF THE AASHTO GUIDE FOR SNOW AND ICE CONTROL[endnoteRef:30] [30: Dawood, H., ElGawady, M. & Hewes, J., 2011. UPDATE OF THE AASHTO GUIDE FOR SNOW AND ICE CONTROL. Journal of Bridge Engineering, (October), pp.735746. Available at: http://ascelibrary.org/doi/full/10.1061/(ASCE)BE.1943-5592.0000252 [Accessed October 31, 2012].]

2011USA__

25Live-Load Distribution Factors for Prestressed Concrete, Spread Box-Girder Bridge[endnoteRef:31] [31: Hughs, E. & Idriss, R., 2006. Live-Load Distribution Factors for Prestressed Concrete, Spread Box-Girder Bridge. Journal of Bridge Engineering, (October), pp.573581. Available at: http://ascelibrary.org/doi/pdf/10.1061/(ASCE)1084-0702(2006)11%3A5(573) [Accessed October 31, 2012].]

2006USAPresenting an evaluation of shear and moment live-load distribution factors for a new, prestressed concrete, spread box-girder bridge. Comparing the results with calculation to AASHTO.

26Evolution of Vehicular Live Load Models During the Interstate Design Era and Beyond[endnoteRef:32] [32: Kulicki, J. & Mertz, D., 2006. Evolution of vehicular live load models during the interstate design era and beyond. Transportation Research Circular E-C10, (3), pp.126. Available at: http://onlinepubs.trb.org/onlinepubs/circulars/ec104.pdf#page=7 [Accessed October 31, 2012].]

2006USAReviewing the evolution of live load design models for bridges and associated designspecification provisions before, during and after the Interstate era, taken as the last 80 years.

27Proposed Revisions to AASHTO-LRFD Bridge Design Specifications for Orthotropic Steel Deck Bridges[endnoteRef:33] [33: Kozy, B. & Connor, R., 2010. Proposed Revisions to AASHTO-LRFD Bridge Design Specifications for Orthotropic Steel Deck Bridges. Journal of Bridge , (December), pp.759767. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)BE.1943-5592.0000214 [Accessed October 31, 2012].]

2010USASummarizing proposed changes to the fifth edition of the AASHTO LRFD Bridge Design Specifications related to orthotropic deck bridges

28Live Load for Bridges Lateral Load Distribution and Deck Design Recommendations for the Sandwich Plate System (SPS) in Bridge Applications[endnoteRef:34] [34: Harris, D.K., 2007. Live Load for Bridges Lateral Load Distribution and Deck Design Recommendations for the Sandwich Plate System (SPS) in Bridge Applications. .]

2007USAInvestigating some ofthe key design issues considered to be limiting factors in implementation of SPS.

29Method to Compute Live-Load Distribution in Bridge Girders[endnoteRef:35] [35: Li, J. & Chen, G., 2010. Method to Compute Live-Load Distribution in Bridge Girders. Practice Periodical on Structural Design and , (November), pp.191198. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)SC.1943-5576.0000091 [Accessed October 31, 2012].]

2010USAIntroducing a new framework (elastic springs) to compute live-load distribution for bridge girders.

30Quantification of intermediate diaphragm effects on load distributions of Prestressed concrete girder bridges[endnoteRef:36] [36: Cai, C., Chandolu, A. & Araujo, M., 2009. Quantification of intermediate diaphragm effects on load distributions of premtremmed concrete girder bridges. PCI journal, pp.4863. Available at: http://cat.inist.fr/?aModele=afficheN&cpsidt=21348894 [Accessed October 31, 2012].]

2009USAAims to quantify the intermediate diaphragm influence on load distributions and presents an approach to develop correction factors for load distributions.

31Evaluation of load distribution factor by series solution for orthotropic bridge decks[endnoteRef:37] [37: Zou, B. et al., 2010. Evaluation of load distribution factor by series solution for orthotropic bridge decks. Journal of Aerospace , (1988), pp.240248. Available at: http://ascelibrary.org/doi/pdf/10.1061/(ASCE)AS.1943-5525.0000007 [Accessed October 31, 2012].]

2010USAConsidering important parameters that represent the response characteristics of the structure that are often omitted or limited in the AASHTO Specifications Providing explicit formulas using series solutions for LDF of orthotropic bridge decks, applicable to various materials but intended for fiber-reinforced polymer (FRP) decks.

32Behavior of Segmental Precast Post-Tensioned Bridge Piers Under Lateral Loads[endnoteRef:38] [38: Dawood, H., ElGawady, M. & Hewes, J., 2011. Behavior of Segmental Precast Post-Tensioned Bridge Piers Under Lateral Loads. Journal of Bridge Engineering, (October), pp.735746. Available at: http://ascelibrary.org/doi/full/10.1061/(ASCE)BE.1943-5592.0000252 [Accessed October 31, 2012].]

2011USAPresenting a detailed three-dimensional finite-element (FE) model that was developed using the ABAQUS platform.

33AASHTO-LRFD Live Load Distribution Specifications[endnoteRef:39] [39: Zokaie, T., 2000. AASHTO-LRFD LIVE LOAD DISTRIBUTION SPECIFICATIONS. Journal of Bridge Engineering, 5(2), pp.131138. Available at: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%2910840702%282000%295%3A2%28131%29.]

2000USAPresenting the background on the development of the formulas and compare their accuracy with the S/D method.

34Live Load Distribution in Girder Bridges Subject to Oversized Trucks[endnoteRef:40] [40: Tabsh, S. & Tabatabai, M., 2001. Live load distribution in girder bridges subject to oversized trucks. Journal of Bridge Engineering, (February), pp.916. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)1084-0702(2001)6:1(9) [Accessed October 31, 2012].]

2001UAELIVE LOAD DISTRIBUTION IN GIRDER BRIDGES SUBJECT TO OVERSIZED TRUCKS

35Performance of AASHTO Girder Bridges Under Blast Loading[endnoteRef:41] [41: Islam, A.A. & Yazdani, N., 2008. Performance of AASHTO girder bridges under blast loading. Engineering Structures. Available at: http://www.sciencedirect.com/science/article/pii/S0141029607004907 [Accessed October 31, 2012].]

2008USAThe purpose of this research is to assess the performance of (AASHTO) girder bridgeunder blast loading.

36The Development of AASHTO LRFD Bridge Design Specification as an Example of Probabilistic-Based Specifications[endnoteRef:42] [42: Wassef, W.G., 2010. THE DEVELOPMENT OF AASHTO LRFD BRIDGE DESIGN SPECIFICATION AS N EXAMPLE OF PROBABILISTIC-BASED SPECIFICATIONS. Journal of Bridge , (December), pp.759767. Available at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)BE.1943-5592.0000214 [Accessed October 31, 2012].]

2011USAOverview of History and development on AASHTO

Table 1 - Papers written about AASHTOs LRFDAs it can be detected from the above table, large number of these papers focused on the reliability of LRFD and comparison of LRFD with the experimental data. Also, some of these papers provided the simplified formulae, which has been derived from LRFD formula, with less numbers of iteration.Furthermore, the obtained results from the relevant studies related to LRFD code has been presented as a brief summary in the following table (Table3).NO.Title DateResults

1Verification of AASHTO-LRFD Specifications Live Load Distribution Formulas for HPS Bridges2004Comparing the DF obtained from the tests and AASHTO Formula, shows AASHTO formulae is both applicable and conservative for High Performance Steel Bridges (HSP).

2Simplified Shear Provisions of the AASHTO LRFD Bridge Design Specifications2008The simplified provisions provided which are similar in concept to AASHTOs Standard specifications for Highway Bridges, contain a new expression for the web-shear cracking capacity, and use a variable-angle truss model to evaluate the contribution of shear reinforcement.

3NCHRP, Simplified Live Load Distribution Factor Equations2007The project objectives have been met by providing a simple, reasonably accurate method for the computation of live load distribution factors.

4PCI Bridge Design Manual___Bridge Design procedure

5Live Load Distribution Factors in Prestressed Concrete Girder Bridges2001If the distribution factors from the finite-element model of the bridge had been used to design the girders, instead of the conservative factors from the LRFD Specifications, the required release strength could have been reduced from 51 MPa (7,400 psi) to 44.1 MPa (6,400 psi). Alternatively, the bridge could have been designed for a 39% higher live load.

6A refined Method for live load distribution prediction of bridges and comparative studies

2001Comparing the refined method (FEM) with AASHTO Eq., shows that the refined method provides more information as well as more economical solution for the I girder

7Construction Loads Produced During Heavy Lifting, Rigging and Handling Operations2001The character and magnitude of loads produced during heavy lifting, rigging, and handling operations may be significantly different from the service loads for which a particular installation has been designed. These differences mandate the necessity for an evaluation of their effects

8Live Load Distribution Factors for a Three Span Continuous Precast Girder Bridge1998Design examples.

9Live load distribution factors for glued-laminated timber bridges2008Simplified live load distribution equations were developed following methods established for other bridge types where needed to improve the accuracy of determining how truckloads are distributed to structural members of glued-laminated timber bridges.

10Live Load Distribution Factors for Grid Reinforced Concrete Decks1998Result allows for the use more realistic design rules regarding live load distribution factors.

11Live Load Distribution Factors for Girder Bridges2002The new simplified equation was developed considering only composite and non-composite steel rolled beam bridges.

12Precast Balanced Cantilever Bridge Design Using AASHTO LRFD Bridge Design Specifications2004Providing draft design Example for bridge designers.

13Optimized Design and Testing of a Prototype Military Bridge System for Rapid In-Theater Construction2005The results showed a potential 50% weight savings compared to the US Army Rapidly Emplaced Bridge.

14Design and analysis of bridge foundation with different codes2011The results showed the Chinese codes are costly that the number of reinforcement bars in the pile cap and piles is more than those with AASHTO code and BS code with the same dimensions.

15LRFD Bridge Design Specifications2012AASHTO 2012 Revision

16Introduction to LRFD, Loads and Loads Distribution__Comprehensive Explanations

17CSiBridge Bridge Superstructure Design2010Bridge Software Guide

18Bridge Crossings LFD vs. LRFD1997Comparative Explanations

19TRB & AASHTO__Provide an overview of the mission, roles, andresponsibilities AASHTO and TRB as they relate to the bridge community

20Special Issue on AASHTO-LRFD Bridge Design and Guide Specifications: Recent, Ongoing, and Future Refinements2011Providing highlights of some of AASHTOs revisions over a broad range of bridge engineering topics.

21Evaluation of FRP Posttensioned Slab Bridge Strips Using AASHTO-LRFD Bridge Design Specifications2011Slabs containing prestressed CFRP tendons displayed much lower deflections for the given service load than those which did not.

22Determination of AASHTO Bridge Design Parameters through Field Evaluation of the Rt. 601 Bridge: A Bridge Utilizing Strong well 36 in. Fiber-Reinforced Polymer Double Web Beams as the Main Load Carrying Members2002Determination of the Bridge Design Parameters, according to AASHTO.

23AASHTO Connected Vehicle Infrastructure Deployment Analysis2011Development of a plan for a national footprint of DSRC RSEs under the direction of the AASHTO Connected Vehicle Working Group.

24Update of the AASHTO Guide for Snow and ICE control2011Updating of the AASHTO Guide for Snow and ICE control.

25Live-Load Distribution Factors for Prestressed Concrete, Spread Box-Girder Bridge2006The LRFD specifications predictions of girder distribution factors were accurate or conservative when compared to the finite element model for all girder distribution factors.

26Evolution of Vehicular Live Load Models During the Interstate Design Era and Beyond2006In post Interstate design era AASHTO LRFD. With these new design provisions, design is based on a more realistic evaluation of structural response and behavior than was available at the beginning of the Interstate era.

27Proposed Revisions to AASHTO-LRFD Bridge Design Specifications for Orthotropic Steel Deck Bridges2010Designs made according to these new provisions can be expected to perform very well and meet the design service life as per AASHTO-LRFD.

28Live Load for Bridges Lateral Load Distribution and Deck Design Recommendations for the Sandwich Plate System (SPS) in Bridge Applications2007Developing a lateral Load Distribution and Deck Design Recommendations for the Sandwich Plate System (SPS) in Bridge Applications

29Method to Compute Live-Load Distribution in Bridge Girders2010The Introduced framework can be used to compute live-load distribution without limits to parameters such as girder space, span length, and truck-wheel space.

30Quantification of intermediate diaphragm effects on load distributions of Prestressed concrete girder bridges2009Providing a useful tool for practicing engineers who may choose to account for intermediate diaphragm effects in the rating of existing bridges or design of new bridges.

31Evaluation of load distribution factor by series solution for orthotropic bridge decks2010The results correlate well with the FE results. It is also illustrated that the series solution can be applied to predict LDF for FRP deck-on-steel girder bridges, by favorable comparisons among the analytical, FE, and testing results for a one-third-scale bridge model.

32Behavior of Segmental Precast Post-Tensioned Bridge Piers Under Lateral Loads2011The FE models confirmed the experimental observations and showed that the SPPT pier system is able to withstand large lateral drift angels with minimal damage. Sensitivity analyses using the FE model showed that the model is sensitive to the softening behavior of the concrete material constitutive law

33AASHTO-LRFD Live Load Distribution Specifications2000A grillage or finite-element analysis is recommended for cases in which the simple formula method is not applicable.

34Live Load Distribution in Girder Bridges Subject to Oversized Trucks2001The results of the analysis showed that the use of the proposed modification factors with the specification-based GDFs can help increase the allowable loads on slab-on-girder bridges.

Table 2- Obtained Results from the Researched ArticlesCarefully observing the papers related to the AASHTO 2010s LRFD Code, as well as their results, there is no indication of a suggestion for the specific guideline related to crawlers (or to any similar heavy tracked wheeled vehicles) live load distribution factor on bridge deck. MethodologiesThe methodologies that have been used in relation to LRFD design method are mostly Numerical or Experimental; also, some of these papers are only discussing AASHTO provisions through applying further researches.Grouping above papers methodologies, it can be observed that both of the Numerical and Experimental approaches have been widely used toward the Evaluation of the AASHTOs LRFD Code, (graph 2).

Graph 2- Research Methodologies used in relation to AASHTOs ProvisionsAmong the papers using either numerical methods or methods used to verify the experimental data, the distribution of the calculation methods used in the 55% of the selected articles, has represented in the following graph (graph 3).

Graph 3- Calculation Methods used in the numerical approachesAs it can be observed in graph 3, 60% of the calculations have been performed using FEA, along with AASHTO LRFD formulae, and the rest 40% have only performed the analysis using AASHTO LRFD. Furthermore, considering the various studies that have been conducted on the distribution of wheel loads on the bridge deck, according to sanders (1984), the majority of analytical approaches can be classified into four numerical methods:1) Orthotropic plate theory 2) Harmony analysis and grillage analogies3) Folder-plate methods4) Finite element and finite strip methods[endnoteRef:43] [43: Lin, M., 2004. Verification of AASHTO-LRFD Specifications Live Load Distribution Factor Formulas for HPS Bridges. Available at:http://etd.ohiolink.edu/view.cgi?ucin1108697828 [Accessed October 31, 2012].]

The most commonly used advanced method within the mentioned methods, is finite element Analysis, (FEA). FEA divides the structure into a series of discrete elements, each possessing the same property as the actual structure, while performing analytical computer programs such as CSI SAP, or Autodesk Robot Structural Analysis Professional in order to predict stress and strain in the structure.

When evaluating the papers, it is found that in most of the experiments and calculations, the structural system of the evaluated bridge, was mostly a steel or concrete deck on the girder, which is presented in the graph 4.

Graph 4- diversity of the Bridges Structural System

Slab on multi girder, Slab on the double web beam, and sandwich plate system are among the other, less common types of the bridges structural system. Similarly, the evaluation of the materials used for girders in the researched papers indicates that mostly composite, pre-stressed or reinforced concrete girders have been used. In addition, high performance and composite steels is considered as a popular material for graders structural body (Graph 5).

Graph 5- materials used as graders structural body

Targets/aimSo in response to the vital need of having a live load distribution factor for crawlers loading in AASHTO, this reports objective is to produce a Finite Element model of the crawler loads on the bridge deck, and subsequently compare the derived results from the analysis with the LRFD Code, in order to modify the LRFD factor in relation to Crawlers Live load distribution on the bridge deck. Also the scope of this report, due to the time constraints, only considers steel girder bridges, and covering information only contains data on box-girders. This report does not cover any other type of bridge other than concrete slab on steel box girders.

Appendix 1AASHTO Load and Load DesignationSTRENGTH I: without wind.STRENGTH II: owner design / permit vehicles without wind.STRENGTH III: wind exceeding 55 mph.STRENGTH IV: very high dead-to-live load ratios.STRENGTH V: vehicular use with 55 mph wind.SERVICE I: normal operational use of the bridge with a 55 mph wind and nominal loads.Also control cracking of reinforced concrete structures.SERVICE II: control yielding of steel structures and slip of connectionsSERVICE III: control cracking of prestressed concrete superstructures.SERVICE IV: control cracking of prestressed concrete substructures.FATIGUE: repetitive vehicular live load and dynamic responses under a single truck.[endnoteRef:44] [44: American Association of State Highway and Transportation Officials, 2010. AASHTO LRFD Bridge Design Specifications.]

References