121_aug_97

STRUCTURAL STEEL EDUCATIONAL COUNCIL

TECHNICAL INFORMATION & PRODUCT SERVICE

AUGUST 1997

Dynamic Tension Tests of

Simulated Moment Resisting

Frame Weld Joints

byE.J. Kaufmann

ATLSS Engineering Research CenterLehigh University

TABLE OF CONTENTS

I°

II.

III.

INTRODUCTION

TEST SPECIMENS

MECHANICAL PROPERTIES

Page

1

2

4

IV. TEST PROCEDURE

V. TEST RESULTS 7

VI. SUMMARY 8

VII. REFERENCES 9

APPENDIX A - Test Results

APPENDIX B - Weld Cost Comparisons

Index of Steel Tips PublicationsThe following is a list of available Steel Tips. Copies will be sent upon request. Some are invery limited quantity.

· Seismic Design of Special Concentrically Braced Frames· Seismic Design of Bolted Steel Moment Resisting Frames· Structural Details to Increase Ductility of Connections· Slotted Bolted Connection Energy Dissipaters· Use of Steel in the Seismic Retrofit of Historic Oakland City Hall· Heavy Structural Shapes in Tension· Economical Use of Cambered Steel Beams· Value Engineering & Steel Economy· What Design Engineers Can Do to Reduce Fabrication Costs· Charts for Strong Column Weak Girder Design of Steel Frames· Seismic Strengthening with Steel Slotted Bolt Connections· Seismic Design of Steel Column-Tree Moment-Resisting Frames· Dynamic Tension Tests of Simulated Resisting Frame Weld Joints

I. INTRODUCTION

Under the SAC Phase I program a pilot project was conducted to develop and evaluate arelatively simple and inexpensive test specimen for studying moment frame weld jointperformance (Ref. 1). A specimen was designed to simulate the behavior of a single beamflange-to-column flange weld joint which could be tested in a large capacity universal testmachine in tension under dynamic loading rates similar to earthquake loadings. The testspecimen concept is illustrated in Figure 1.

The results of the pilot test program showed that weld joints fabricated using electrodes withhigher notch toughness than the E70T-4 electrode in common use prior to the Northridgeearthquake, such as E7018, E70TG-K2, and E71T-8, performed satisfactorily in the test. Thiswas also in conjunction with improved detailing including removal of weld backing and weldtabs and adherence to D I.I welding code procedural requirements. The results indicated thatbrittle fractures initiating in the weld metal, as occurred in ETOT-4 welded connections, could beavoided when weld metal with a minimum CVN impact toughness requirement of 20 ft-lbs @-20F was used. Although only axial tension loads were applied in the test the results closelyparalleled the performance of similarly fabricated weld joints in full-size connection tests (Ref.2) and appeared to provide a viable means of assessing weld metal toughness requirements formoment frame applications.

To expand the test database to include other currently available flux-cored electrodes theStructural Steel Educational Council of the California Field Ironworkers Administration Trustsponsored additional testing, reported herein, to evaluate the performance of weld joints weldedwith other electrode types as well as duplicate tests performed in the pilot study. Eight testspecimens were fabricated by a commercial fabricator in California using three currently availableflux-cored electrodes (E70T-6, E70T-7, and E71T-8) and one shielded metal arc electrode(E7018). The fabricated specimens were then shipped to the ATLSS Engineering ResearchCenter at Lehigh University for testing.

Figure 1 Simulated Beam-Column Tension Specimen

II. TEST SPECIMENS

A sketch of the simulated beam flange-to-column flange weld joint test specimen is shownin Figure 2. The column element consists of an 8 in. length of a W14x176 wide flange shape(A572 Gr. 50) with one flange removed. A l"x 6" plate (A36) is groove welded to the columnflange face to simulate the beam flange-to-column flange connection. A slotted pull plate iswelded to the column web to permit the the assemblage to be gripped in a universal test machineand loaded in tension at static or dynamic loading rates. A simulated coped beam web plate istack welded to the beam plate to introduce welding restrictions similar to welding the bottomflange of a moment connection. The web plate was removed after welding to facilitateinstallation of test instrumentation.

Duplicate specimens were prepared using each of four electrode types. Table 1 gives a summary ofthe welding procedure parameters. In all eight specimens the weld tabs and backing were removedafter welding and a reinforcing fillet weld was applied to the weld root. All simulated beam flangeto column joints were fabricated to a 3/8" root and a 30° included angle.

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(one flange removed)

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IH. MECHANICAL PROPERTIES

The mechanical properties of the beam flange plate and column shape were determined aftertesting. Unyielded material located at the end of the grip length of the beam plate was used tofabricate standard 0.505 in. dia. tensile specimens. Standard 0.505 in. dia. specimens were alsofabricated from the W14 x 176 column flange at the ASTM A673 test location. Table 2 givesa summary of the base material properties. The stress-strain behavior of the two materials isshown in Figure 3.

Table 3 gives AWS required and typical mechanical properties for the filler metals used.Mechanical properties of E70T-4 filler metal is also included for comparison. E70T-6, E71T-8and E7018 filler metals have a required Charpy V-notch (CVN) impact toughness requirementof 20 ft-lbs @ -20F. E70T-4 filler metal does not have a notch toughness requirement andtypically provides 5-15 ft~lbs @ +70F. E70T-7 filler metal, like E70T-4, also has no AWSminimum toughness requirement. Procedure qualification tests using E70T-7 weld metal hasindicated a notch toughness intermediate to E70T-4 and the higher toughness filler metals. Thesetests provided an average toughness of 8 ft-lbs @ OF. CVN test data for the various filler metalsis shown in Figure 4.

TABLE 2 MECHANICAL PROPERTIES

Y.S. T.S. Elong.(2") R.A.(ksi) (ksi) (%) (%)

W14 x 176 (Column) 56.6m 75.2m 38.6¢) 77.1¢)ASTM A572 Gr. 50

Beam Flange Plate 42.9 73.5 28.4 59.3ASTM A36

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Figure 3 Material Stress-Strain Behavior.

4

TABLE 3WELD METAL PROPERTIES

AWS Required Typical

Y.S. U . T . S . Elong. CVN Y.S. U.T.S. Elong. CVNksi ksi % fi-lbs ksi ksi % fi-lbs

E70T-4 60 min. 72 min. '22 min. .m 60-70 80-95 15-25 5-15@ +70F

E70TG-K2 58 min. 70-90 22 min. -(• 70-75 85-90 2 5 - 3 0 20-40@-20F

E71T-8 60 min. 72 min. 22 min. 20 min. 65-75 70-90 2 5 - 3 0 20-70@-20F @-20F

E70T-6 60 min. 72 min. 22 min. 20 min. 65-75 70-90 2 5 - 3 0 25-75@-20F @-20F

E70T-7 60 min. 72 min. 22 min. -¢) 60-65 80-90 22-26 5-10@ OF

E7018 58 min. 70 min. 22 min. 20 min. 65-75 75-85 2 5 - 3 0 90-120@-20F @-20F

1. No Requirement2. No Requirement, will meet 20 ft-lbs @-20F3. From manufacturer or laboratory tests

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TEMPERATURE, °F

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Figure 4 CVN test data for various filler metals.

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IV. TEST PROCEDURE

Specimens were tested in a PC-controlled 600 kip capacity universal test machine modified topermit dynamic load rates to be applied to the test specimen. With modification, a maximumcrosshead displacement rate of 0.15 inches/sec could be achieved. Dynamic tests were conductedin displacement control at the maximum crosshead displacement rate. In addition to recordingcrosshead displacements, a 2 in. displacement range linear variable differential transformer(LVDT) was also installed to measure weld joint displacements over the ungripped length of thebeam flange (approx. 8 inches) relative to the column flange face. Figure 5 shows aninstrumented test specimen installed in the test machine. Load, crosshead displacement, andLVDT displacement data were recorded with a PC data acquisition system.

Test specimens were loaded to failure in a single tension load cycle applied in two ramp ratesegments. Initially specimens were loaded at a crosshead displacement rate of 0.05 inches/secto a load of 60 kips (-10 ksi in beam flange plate) to seat the grips after which the displacementrate was increased to 0.15 inches/sec to failure. A typical LVDT displacement-time plot for adynamic test is shown in Figure 6. Over the 8 in. gauge length the displacement rate in thevicinity of the weld joint corresponds to a strain rate of -0.02 sec't. This strain rate correspondedto about 1 sec. loading through the elastic range. In comparison, strain rates for static loadingare typically of the order of 0.001-0.0001 sec't. After testing the specimens were examinedvisually for evidence of cracking or to determine the fracture origin, mode of fracture, and crackpath.

Figure 5 Test specimen installed in 600 kip test machine.

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Figure 6 Typical LVDT displacement vs. time plot.

V. TEST RESULTS

A summary of the results of the eight tests is given in Appendix B. With the exception of thespecimens welded with E70T-7 filler metal, all other test specimens behaved similarly. Duplicatespecimens welded with E7018, E71T-8, and E70T-6 filler metals failed by ductile tensile failureof the beam flange plate. No visual evidence of weld joint cracking was detected in any of thesetest specimens. Absence of whitewash flaking on the weld metal surface and column flange facearea also indicated that little or no inelastic deformations developed in these areas.

The two specimens welded with ETOT-7 filler metal showed mixed performance. Test SpecimenNo. 5 failed brittlely in the beam flange plate after significant yielding occurred in the plate.Examination of the fracture indicated that localized ductile tearing developed at the weld toe ofthe beam flange plate prior to initiation of brittle fracture (see Test No. 5 photographs inAppendix B). The tearing appeared to follow the weld fusion line although it was not clearwhether the tear propagated in weld metal or in the heat-affected-zone (HAZ). The duplicate testspecimen (Test No. 6) failed by ductile tearing of the beam flange plate, however, evidence ofsub-critical tearing at the same weld toe location and also in the adjacent base material was alsoobserved (see Test No. 6 photographs in Appendix B).

The cause of the weld toe tearing is not entirely clear, however, examination of the fracture incross-section in Test No. 5 also revealed significant weld toe undercut and a steep transition ofthe top reinforcement weld bead which was not observed in the other test specimens. Theundercut in Test No. 5 was measured to be 0.08" in depth which just exceeds the 1/16" maximumpermitted by Di.1. No undercut was measured in Test No. 6 although a similar steep transitionof the weld reinforcement also existed. The weld toe undercut observed in Test Specimen No.

7

5 may have influenced tearing initiation at the weld toe. It is also noteworthy that the E70T-7specimens were welded with a higher heat input than any of the other specimens (88 Kj/in vs.28-56 Kj/in) which may have resulted in a softer HAZ than in the other specimens. Ductiletearing at the weld toe at beam flange tips has also been observed in cyclically loaded full-scaleconnection tests after extensive plastic deformation of the beam flange has occurred (Ref. 2).

The test results support the current SAC recommendation for weld metal used in critical jointshaving a minimum CVN impact toughness of 20 ft-lbs @ OF (Ref. 3). All test specimens weldedwith filler metals which exceeded this requirement (ie. 20 ft-lbs @ -20F) performed well underintermediate strain rate loading. Although the ETOT-7 specimens did not satisfy the 20 ft-lb @OF recommendation (Avg. 8 ft-lbs @ OF) and also exhibited brittle behavior in one test, there wasno clear indication that weld metal fracture was causal to the failure. Additional test data on thefracture toughness and weld joint performance of this weld metal would be helpful in definingminimum weld metal toughness requirements.

VI. SUMMARY

1. Eight simulated beam flange-to-column flange weld joint test specimens werefabricated using three currently available flux-cored electrodes (E70T-6, E70T-7, E71T-8)and one shielded metal arc electrode (E7018). Duplicate specimens welded with fillermetals having a minimum CVN impact toughness requirement of 20 ft-lbs @ -20F (E70T-6, E71T-8, and E7018) performed satisfactorily under dynamic loading conditions.Duplicate specimens fabricated using an E70T-7 electrode with lower notch toughness (8ft-lbs @ OF) also performed satisfactorily although premature brittle fracture developedin one test presumably due to excessive weld toe undercut. The test results provideadditional confu'mation that brittle fracture in moment frame weld joints can besuppressed through adequate levels of weld metal toughness in conjunction with improvedweld joint detailing (ie. removing weld tabs and weld backing).

2. The test results support the current SAC recommendation for weld metal used incritical joints having a minimum CVN impact toughness of 20 ft-lbs @ OF.

8

REFERENCES

1. Kaufmann, E.J., Fisher, J.W., "A Study of the Effects of Material and Welding Factors onMoment Frame Weld Joint Performance Using a Small-Scale Tension Specimen", SACTechnical Report 95-08, 1995.

2. Xue, Ming, Kaufmann, E.J., Lu, Lc-Wu, Fisher, J.W., "Fracture and Ductility of MomentConnections Under Dynamic Loading", Proceedings ASCE Structures Congress, Portland,Oregon, 1997.

3. Interim Guidelines: Evaluation, Repair, Modification and Design of Welded Steel MomentFrame Structures, FEMA 267, 1995.

9

APPENDIX A - Test Results

l0

Test No.: !Test Date: 8/27/96Weld Electrode: E7018

Test Description: Specimen weldedwith 1/8"¢ E7018. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UTacceptable.

Test Result: No weld joint cracking.Specimen failed by ductile tensilefailure of the beam flange plate.

500

450

400

350

·• 300

"'•'250

G• 2000..J 15o

100

50

Test #1

F I i i,"" N

" ' I

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Crosshead Displacement (in)

11

Test No.: 2Test Date: 8/28/96Weld Electrode: E7018

Test Description: Duplicate ofTest gl. Specimen weldedwith 1/8"q• E7018. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UT ....acceptable.


T e s t # 2

50O

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100

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C r o s s h e a d Displacement (in.)

12

Test No.: 3Test Date: 8/29/96Weld Electrode: E71T-8

Test Description: Specimen weldedwith 0.072"¢ E71T-8. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UTacceptable.


Test #3

50O

450

4OO

• ' 350

300

v 2 5 0"0

2000

-..1 150

lO0

50

0

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Crosshead Displacement (in.)

13


Test Description: Duplicate ofTest #3. Specimen weldedwith 0.072"• E71T-8. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UTacceptable.


Test #4

500

450

400

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50

0

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5


14


Test Description: Specimen weldedwith 7/64"¢ E70T-7. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UTacceptable.

Test Result: Specimen failed bybrittle fracture of the beam flangeplate. Fracture initiated at the edgeof the beam flange plate from a localizedductile tear at the weld toe fromundercut. Fracture occurred at a load nerothe ultimate tensile strength of the beamplate. 0.93" LVDT displacement atfracture. No weld metal or column flangefracture detected.

Test #5

500

450

400

'•' 35O

-300

250%3(13 200o

...J 15o

100

50

f

J/ '

0 0.5 1 1.5 2 2.5 3 3.5 4

LVDT Displacement (in)

15


Top) Beam flange plate fracture surface Bottom) Enlarged view ofweld toe ductile tear

16


Top) Re-assembled cross-section of the fracture Bottom) Enlarged viewof the weld toe crack initiation location. Note the weld toe undercut.

17


Test Description: Duplicate ofTest #5. Specimen weldedwith 7/64"q• E70T-7. Weld tabs andbacking removed. Weld root re-inforcing fillet added. UTacceptable.

Test Result: Specimen failed byductile tensile failure of thebeam flange plate. Sub-criticaltears developed at the edge ofthe beam flange plate at the weldtoe (same location as Test #5)and in the base material adjacentto the weld toe. No weld metal orcolumn flange cracking detected.

Test #6

5OO

450

400

'G'350•L

-• 300

'• ' 250-O03 2O00

.._1 150

100

50

0

0.5 1 1.5 2 2.5 3 3.5

Crosshead Displacement (in.)4 4.5

18


Top) Sub-critical tearing of the beam plate at the weld toe andin adjacent base material. Bottom) Enlarged view of tears.

19


Test Description: Specimen weldedwith 3/32"¢ E70T-6. Weld tabs andbacking removed. Weld root re-inforcing fillet added.


Test #7

5OO

45O

4O0

'•' 350Q..• 300

•" 250'rJCd 200O--.I 150

100

50

0

] I - - L _ _

, / / •[

/ , II0 0.5 1 1.5 2 2.5 3 3.5 4 4.5


20


Test Description: Duplicate ofTest #7. Specimen weldedwith 3/32"4 E70T-6. Weld tabs andbacking removed. Weld root re-inforcing fdlet added.


Test #8

5OO

450

400

•'350

·• 300

250'0(13 200O

150

100

50

0.5 1 1.5 2 2.5 3 3.5

Crosshead Displacement (in.)4 4.5

21

APPENDIX B - Weld Cost Comparisons

22

COST COMPARISON

In order to provide the reader with a more complete picture, the Structural Steel Education Council(SSEC) has complied a cost comparison of the electrodes utilized in the Lehigh University tests. E 70T-4electrode which was used in earlier studies was requested by SAC. The 70T-4 electrode in the 0.120diameter was included because most estimating programs utilized that electrode as a basis for calculatingcomplete penetration costs in the fiat or horizontal position.

The cost comparison factors were determined by reviewing the cost data supplied by 3 of the erectormembers from the council and reviewed by the remaining members. They took the following factors intoconsideration when calculating those costs:

1. Cost of the Electrode

2. Labor to install the weld

3. Cost of equipment required to weld

It should be noted that the inefficiency costs of using additional welders in order to maintain a reason-able schedule was not included in the cost data, nor were the additional training costs associated with theuse off those electrodes not normally used for this application.

Cost Comparison Lehigh University Test Specimens

Manufacturer Process Manufacturer AWS AWS Notch Diameter Cost FactorDesignation Specifications Classifications Tough

Lincoln F C A W NR232 5.20 E71T8 Yes 0.072 3.1Lincoln F C A W NR305 5.20 E7OT6 Yes 3/32 2.0Lincoln F C A W NR311 ni 5.29 E70TG-K2 Yes 7/64 2.4Lincoln SMAW LH70 5.1 E7018 Yes 5/32 7.3Lincoln FCAW NS3M 5.20 E7OT4 No 0.120 1.0Lincoln F C A W NR311 5.20 E7OT7 No 7/64 1.4

COST FACTOR ASSUMPTION:1. Mid- 1997 California Labor and Electrode prices.2. Costs are based on field deposition of weld metal utilizing the AWS D1.1 parameters for volts,

amps; electrodes stick out and travel speed shown on the attached procedure qualificationrecords for each of the electrodes shown.

3. Cost of inspection not included.4. Based on welding under normal field conditions in the flat position.

23

STRUCTURAL STEEL EDUCATIONAL COUNCIL470 Fernwood DriveMoraga, CA 94556

(51 O) 631-9570

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121_aug_97