STRUCTURAL STEEL EDUCATIONAL COUNCIL

TECHNICAL INFORMATION & PRODUCT SERVICE

March 2001

Large Seismic SteelBeam-to-Column Connections

by

Egor P. Popov, ProfessorShakhzod M. Takhirov, Ph.D.

Pacific Earthquake Engineering Research Center (PEER)University of California, Berkeley

Professor Egor Paul Popov standing next to his last steel connection test specimen(February 2001).

Egor Paul Popov, Professor Emeritus of Civil and Environmental Engineering at theUniversity of California, Berkeley, passed away Thursday, April 19, 2001, after a briefillness.

Professor Popov began his engineering studies at the University of California, Berkeley,and continued with graduate work at the California Institute of Technology, theMassachusetts Institute of Technology, and Stanford University, where he obtained hisdoctorate degree in 1946. In his lengthy and illustrious career, he was called upon byNASA for his engineering expertise and played a key role in the structural analyses of theAlaskan Pipeline and the Oakland-San Francisco Bay Bridge. Popov joined theDepartment of Civil Engineering at UC Berkeley in 1946, and was active in teaching andresearch there for more than 50 years. His research interests covered a wide spectrum oftopics in earthquake engineering, including cyclic testing and modeling of structuralmembers; the development, research, and application of the eccentrically braced frame;research on the seismic resistance of steel connections and the development of improvedconnection details; and the development of friction devices to retrofit existing structures.He was appointed the first chairman of AISCD's Committee on Seismic Provisions forSteel Buildings and served in this position for several years. Elected to the NationalAcademy of Engineering in 1976, Professor Popov was honored in 1999 with theEarthquake Engineering Research Institute's highest honor, the George W. HousnerMedal.

Table of Contents

Abstract...........................................................................................ii1 Review of the Previous Research1.1 Introduction.....................................................................................11.2 Overview .........................................................................................11.3 Tension Tests on A490 1 ¼ Bolts............................................................11.4 Test Specimen Design and Detailing.......................................................22 Connection Design and Estimate Calculations2.1. Test specimens based on the proposed design...........................................22.2. Basic Parameters Used in the Connection Calculation................................22.2.1. Calculation of Plastic Hinge Location in the Beam.....................................32.2.2. Calculation of Probable Plastic Moment at the Hinges.................................32.2.3. Beam Shear Calculation....................................................................32.2.4. Calculation of the Moment at the Centerline of the Column..........................42.2.5. Check for Strong Column - Weak Beam Condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42.3. The Connection Details Calculations......................................................52.3.1. Calculation of the T-section Stem Thickness at the Weakest Section near theColumn Face. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52.3.2. Calculation of the T-section Flange Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.3.3. Calculation of Bolt Size Between the T-section and the Column Flanges (Duringthe Design 1 ¼ inch High-Strength Bolts were Chosen)......................................72.3.4. Calculation of Weld Size to Beam Flanges for Both Specimens (3/4 inch FilletWeld Was Used). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 Experimental Program3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83.2 Test Specimens, Test Setup and Instrumentation.......................................93.2.1 Test Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93.2.2 Instrumentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95.2.3 Data Acquisition......................................................................................93.2.4 Loading History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103.2.5 Data Processing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103.3 Test Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113.3.1 Specimen 1.....................................................................................113.3.2 Specimen 2.....................................................................................124 Experimental Results and Conclusions4.1 Experimental results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134.2 Conclusions: advantages and disadvantages of proposed connections............134.2.1 Advantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134.2.2 Disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144.2.3 Future Research Directions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

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ABSTRACT

Two large bolted steel moment-resisting connections were studied by experiments. Theseconnections were single-sided beam-column assemblies that are representative of exteriorbeam-column connections, and they were composed of W36xl50 Grade 50 beams andW14x283 Grade 50 columns. T-sections were cut from W40x264 sections of Grade 50steel. The T-section stems were welded to the beams and pre-stressed by bolts to thebeam flanges in the shop. Final beam-to-column assembly required no additionalwelding: the T-section flanges were bolted to the column and the column shear tab wasbolted to the beam web. The specimens had two symmetrically located T-sections withthe difference in web geometry: the Specimen 1 had rectangular shape of stems, whereasthe Specimen 2 had U-shaped stems. During the cyclic testing the beam deformation wasminimal due to active participation of the T-section flanges: a separation between T-section flanges and the column flanges were observed. This separation was occurred duebending plastic deformation in the T-section flanges. This phenomenon allowed energydissipation and prevented the beam flanges and beam web from severe buckling.

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1 Review of the Previous Research

1.1 Introduction

The generally accepted detail of attaching steel beams to columns in seismic applicationsconsists of shear tabs attached to the column and direct welding of beam flanges with orwithout cover plates to column flanges. Numerous tests on this type of a connection weresupported by NSF with many specimens donated by the fabricators. The testing of suchspecimens was organized by SAC Joint Venture.

The moment capacity of such connections depends on cyclic endurance of flange weldsin both tension and compression. Under these conditions numerous tension weld failureswere observed both in the laboratory and the field. SAC has proposed six connections toavoid future weld failures. We propose another connection that avoids weld failures andit is field bolted and shop welded.

1.2 Overview

An attempt at the above approach on several end-plate connections was made by K.C.Tsai and E.P. Popov at University of California, Berkeley (1988 and 1990). An exampleof this kind of a connection is shown in Fig. 1-1. It is of interest to note that directwelding of a beam to a column stub shown Specimen 9 in Fig. 1-1 results in goodbehavior, but the erection is not generally practical. Specimen 10 in Fig. 1-1 with no ribsover the beam flanges did not give satisfactory results. Specimen 10R with ribs over thebeam flanges at the column stub behaved very well under cyclic loading as can be seen inFig. 1-2. Note the required large thickness of the end plate (a connection based on thedesign of Specimens 10 and 10R may require shims during assembling).

The above approach recently was also pursued by T.M. Murray and his associates in2000 at Virginia Polytechnic Institute (VPI) with good results. They achieved a numberof successful tests with W36xl50 beams. It appears that for larger or heavier beams theuse of ribs over beam flanges at columns would be required.

An extensive excellent study of bolted connections has been done at Georgia Institute ofTechnology by R. Leon and his associates in 2000. The work is very comprehensive, butis limited to small and medium size members.

The newly developed and tested connection at University of California, Berkeley issomewhat related to the end plate connection but is more versatile as it is more readilyadaptable to a larger range of heavier beams. The new connection depends on the use ofA490 1 ¼ bolts in tension in oversize round holes (as in the column flange and in the T-section flange as well) and shop fillet welds.

1.3 Tension Tests on A490 1 ¼ Bolts

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In order to conduct ductility study on the A490 1 ¼ bolts two tests were performed. Forthe first test, a special device was built to test simultaneously the shank of the bolt and thethreaded part of the bolt below the nut. The actual failure occurred in the threaded region.The remarkable ductility of A490 bolt was clearly demonstrated and the load versuselongation diagram is presented on Fig. 1-3. Another experiment on a specimen ofconstant diameter machined from A490 bolt also showed excellent ductility. Figure 1-4shows stress versus strain diagram for this test.

1.4 Test Specimen Design and Detailing

One of newly developed connections using A490 1 ¼ bolts is shown in Fig. 1-5. Thedetails for the two specimens are shown in Fig. 1-6 and 1-7. In both cases the attachmentof a beams to a column is made using structural tees cut from W shapes (T-sections). Alarge choice of such sections is available. By rotating the beam all fillet welds can bedone in the shop in a down-hand position. Generous rounded fillets occur in all casesbetween a beam flange and the stem of the T-sections. Shop experience in fabricatingthese two specimens was very encouraging.

2 Connection Design and Estimate Calculations

2.1. Test specimens based on the proposed design.

The beams were fabricated from a W36xl50 section of A572-Gr.50 steel, the columnswere fabricated from a W14x283 section of A572-Gr.50 steel. The T-sections were madefrom W40x264 section of A572-Gr.50 steel. The geometrical properties of the beamsections used in the specimens are presented in Tables 2-1 though 2-3. They representwidely available data for standard rolled I-beams with W- shapes (see, for instance, AISC1995a).

The global dimensions and geometry of the specimens are shown in Fig. 1-5. Figures 1-6and 1-7 show the design details for the Specimen 1 and the Specimen 2. The materialproperties of the connections from mill certificate data are presented in Table 2-4. Thespecimens had two symmetrically located T-sections with the difference in the geometryof the stems: the Specimen 1 had rectangular shape of the stems, whereas the Specimen 2had U-shaped stems. The T-section stems were welded to the beams in the shop, and laterthe T-section flanges were bolted to the columns.

2.2. Basic Parameters Used in the Connection Calculation.

Nonlinear deformation of a building frame is typically accommodated through thedevelopment of inelastic flexural or shear stains within discrete regions of the structure.At large deformations these regions can develop into plastic hinges, which canaccommodate significant concentrated rotations without significant changes of the load,as shown in Fig. 2-1. This behavior is accompanied by significant energy dissipation,particularly by members involved in plastic deformation. The formation of plastic hingesin the beams is extremely desirable.

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2.2.1. Calculation of Plastic Hinge Location in the Beam.

The probable location for the formation of the plastic hinges is a basic parameter for theconnection calculations. Figure 2-2 shows the suggested location of the plastic hinge. Thelocation depends on the type of connection and our design is close to a cover-plate type,therefore the plastic hinge can be developed at the following distance from the face of thecolumn (FEMA 267a):

Lh= dsts+ db/4,

Where:db is a depth of the beam, the value of the beam depth db is presented in the Table 2-1;dsts is a total depth of the T-section. This parameter is 28.75 inches for the Specimen 1and 20 inches for the Specimen 2, as it is shown in Table 2-3.

Therefore the plastic hinge is located at the following distance from the face of thecolumn:

Lh= 37.7 inches, for the Specimen 1 andLh= 29.0 inches, for the Specimen 2.

2.2.2. Calculation of Probable Plastic Moment at the Hinges.

The probable value of the plastic moment, Mpr, at the location of the plastic hinge shouldbe calculated from the equation, proposed in FEMA-267b:

Mpr=1.1ZbFyb.Where:

Fyb is the actual yield stress of the beam material, as identified from mill test reports inthe Table 2-4,Zb is the plastic modulus of the beam section determined from the Table 2-1.Therefore for the proposed design and for chosen material properties Zb = 581 inch3, andFyb = 56.6 ksi, the probable value of the plastic moment is as following:

Mpr= 36173 kip*inch.

2.2.3. Beam Shear Calculation.

The shear in the beam, at the location of the plastic hinge should be determined. Thelength of the arm at plastic hinge location is calculated from total beam length, Lb, minusthe distance of the hinge location, Lh. Therefore the shear at the plastic hinge Vp can bedetermined from the formula:

Vp=Mpr/(Lb-Lh).

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Therefore the values of the shear at the location of the plastic hinge are

Vp= 375.7 kips, for the Specimen 1, andVp= 344.4 kips, for the Specimen 2.

2.2.4. Calculation of the Moment at the Centerline of the Column.

The moment at centerline of the column can be calculated as following, as it shown onFig. 2-3:

Mc = Mpr+ Vp (Lh + dc/2).

This expression is modified by using previous expression for the shear and the formulafor the moment calculation has the following form:

Mc = Vp (Lb + dc/2).

In our particular case the values of the moment at the centerline of the column are

Mc = 53485 kip*inch, for the Specimen 1, andMc = 49030 kip*inch, for the Specimen 2.

2.2.5. Check for Strong Column - Weak Beam Condition.

Buildings with the plastic hinges in the beams dissipate more energy than buildings withplastic hinges in the columns. Therefore, the connection in the building has to develop theplastic hinge in the beam rather than in the column. To determine if the desired strongcolumn - weak beam condition exists, the connection assembly should be checked for thefollowing condition (FEMA 267b):

Where:Zc - is the plastic modulus of the column section above and below the connection,Fyc - is the maximum specified yield stress for the column above and below,fa - is the axial stress in the column above and below,

- is the sum of the column moments at the top and the bottom of the panel zone,respectively, resulting from the development of the probable beam plastic moments, Mpr.

In our case the column moment at the top of the panel zone, Mct, and the moment at thebottom of panel zone, Mcb , are the same:

Mcb= Mct= (MC/2)(LC /2 - dc/2)/( Lc /2) .

For the proposed connection the last formula produces the following values for bothspecimens:

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Σ ΣZ F f Mc yc a c( ) / . .− > 1 0

ΣMc

Mcb= Mct= 23351 kip*inch for the Specimen 1 andMcb= Mct= 21406 kip*inch for the Specimen 2.

The axial stress in the column is calculated from the shear load acting in the columndivided by the effective area of the column cross section:

fab = f ab = Vp/Ac.

In case of the proposed connection the axial stress is calculated as following:

fab = fab = 4.51 ksi for the Specimen 1 andfab = fab = 4.13 ksi for the Specimen 2.

Therefore the main criteria for the strong column - weak beam condition will be satisfiedfor both specimens, because of the following results:

2.3. The Connection Details Calculations.

2.3.1. Calculation of the T-section Stem Thickness at the Weakest Section near theColumn Face.

The weakest cross section near the column face is located at the K-line of the T-section.This section is at a distance, which includes the flange thickness of the T-section, tsts andradius of the fillet in the K-line. This value is equal to 3 inches. The location of thesection is presented on Fig. 2-4. The moment at this location is calculated as following:

Mws = Vp(Lb – 3).

The numeric values for the moment in case of the proposed connection are calculated asfollowing:

Mws = 49214 kip*inch for the Specimen 1 andMws = 45114 kip*inch for the Specimen 2.

The chosen cross section consists of the cross sections of T-section stems and the crosssection of the shear plate, as it is shown in Fig. 2-5. The out of scale picture of the chosencross section with the dimensions used during the calculation is presented on Fig.2-5.The connection design allows a plastic deformation in this cross section. Therefore thetotal moment in this cross section will consists of two moments. The fist moment, M1 , iscalculated with the plastic modulus of the shear plate, Z1, and has the followingexpression:

M1 =Fysp* Z1 ,

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Σ ΣZ F f Mc yc a c( ) / . .− = >1 10 1 0

Σ ΣZ F f Mc yc a c( ) / . .− = >1 21 1 0

for the Specimen 1 andfor the Specimen 2.

where Z1 =(0.75*(24) 2) /4.

The corresponding numerical value (for Fysp = 56.6 ksi) is calculated as following and itis the same for both specimens:

M1 =6113 kip*inch.

The second moment, M2, is calculated with the plastic modulus of stems sections, Z2:

M2=Fyts*Z2,where Z2=2*18.4*16*0.96.

Therefore the numerical value of this moment (with Fyts = 64 ksi) can be calculated as

M2 =36176 kip*inch.

The total moment at this cross section calculated with the assumption of plasticdeformation of the section is:

Mdesigned =42289 kip*inch.

The difference between the designed moment, Mdesigned, and the expected one at thisweak section, Mws, is within 14 percent. This difference is acceptable, because the weakcross section has extremely small length (less then 3 percent of the beam depth) and it isfollowed by a very strong cross section. The strong cross section has very high value ofthe elastic section modulus and allows only elastic deformation up to the following valueof the moment:

Mstong =58415 kip*inch.

2.3.2. Calculation of the T-section Flange Size.

In order to find the thickness of the T-section's flange the flange was modeled as a fixed-end beam shown in Fig. 2-6. The concentrated load acts at the midpoint of the beam andrepresents the stem's puling force. The maximum force developed in the stem can becalculated as following:

P = Fyts Astem,

where the cross section area of the stem is Astem=16*0.96=15.36 inch2. Therefore thevalue of the load is as following:

P = 983 kips.

The statically indeterminate beam presented in Fig. 2-6, can be solved for the reactionforces and moments and they have the following expressions (AISC 1995a, page 4-195):

Ra= Rb =P/2,

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Ma= Mb=PL/8.

Therefore the reaction moment applied at the bolt location has the following maximumvalue:

Ma= Mb=584 kip*inch

The connection design assumes that the plastic deformations can be developed near thebolt location. Therefore the required plastic modulus of the flange cross section is asfollowing:

Z required = Ma /Fyts ,or Zrequired = 9.1 inch3.

The chosen flange of the T-section has to have the plastic modulus not lower then therequired one, and it's value for the chosen flange thickness is:

Zdesigned = 16*(1.73) 2/4 =11.97 inch3.

The elastic section modulus for the rectangular cross section of the flange is 1.5 timesless then the plastic one and is equal to

Sdesigned = 7.98 inch3.

Therefore the design allows the flange yielding but without developing a plastic hingenear the bolt location.

2.3.3. Calculation of Bolt Size Between the T-section and the Column Flanges (Duringthe Design 1 ¼ inch High-Strength Bolts were Chosen).

As it was discussed before the model for the T-section flanges is shown in Fig. 2-6.According this model the total axial force acting in each row (of 4 bolts) is:

Ra=Rb=P/2=492kips.

The corresponding axial force acting in one bolt is:

Rbolt=123 kips.

For the chosen 1 ¼ inch high-strength bolts the design tensile strength is (AISC 1995b)

Rbolt(LFRD)=104 kips.

The conducted tests on the high-strength bolts (see section 1.3 of this report) show veryhigh ductility of the used bolts, the bolt specimen started to yield at 132 kips with theultimate tensile load of 150 kips (see results presented on Fig. 1-3). These results explain

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the chose of the 1 ¼ inch high-strength bolts for the column and the T-sectionconnection.

2.3.4. Calculation of Weld Size to Beam Flanges for Both Specimens (3/4 inch FilletWeld Was Used).

The total length of the weld is different for the specimens, the length per the beam flangeis designed as following (including weld in U-shaped part for Specimen 2):

lweld - 2*23.5=47.0 inch for the Specimen 1 and.lweld = 2*14.75+2*9.25=48.0 inch for the Specimen 2.

The maximum force in the beam flange will be equal to the product of the flange crosssection area, Abflange, and the specified yield stress for the beam, Fyb :

Fmax = Abflange Fyb.

For the numerical parameters of the proposed connection, the value of this force is equalto

Fmax = 638 kips for both specimens.

The load per inch of the fillet weld is calculated as following:

Fper\inch =13.3 kips/inch for the Specimen 1 andFper\inch =13.6 kips/inch for the Specimen 2.

The required leg length is calculated the widely used expression

lleg = Fper\inch/(0.707*1.7*21 ksi).

The required leg length for the designed specimens is determined as following:

lleg =0.54 inch for the Specimen 1 andlleg =0.53 inch for the Specimen 2.

Based on the results of these calculations the 3/4 inch weld was used during themanufacturing the specimens.

3 Experimental Program3.1 Introduction

This section summarizes the results of cyclic testing of two full scale beam-columnbolted connection specimens. The specimens were designed by Prof. E.P. Popov andwere fabricated by Stoltz Metals, Inc. The tests were carried out in the Structural

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Research Laboratory of the Pacific Earthquake Engineering Research Center, Universityof California at Berkeley.

3.2 Test Specimens, Test Setup and Instrumentation

3.2.1 Test Setup

The specimens were tested in the Structural Research Laboratory of PEER, UC Berkeley.The test setup was designed to accommodate specimens with columns in verticalposition, as shown in Fig. 3-1. The specimens were attached to horizontal and verticalframes. The horizontal steel frame was pre-stressed to the strong floor. The columns inthe test specimens were attached to the horizontal frame and the vertical reaction frameusing short segments of W 14x311 to achieve near pinned boundary conditions.

The load was applied to the cantilever beam end by a 400-kip hydraulic actuator, througha clevis bolted to the beam end plate. The testing setup had displacement capacity of±7.75 inches and load capacity of ±350-kip. No axial load was applied to the column.The test was conducted using the beam end displacement control. The beam end was at adistance of 134 in from the column face. To prevent out of plane movement of the beam,a vertical bracing system was provided near the beam end. The photograph in Fig. 3-2shows a view of a test in progress.

3.2.2 Instrumentation

Many sensors were used to monitor the response of the specimens during the test in orderto understand the specimen behavior. Figure 3-3 shows the location of displacementmeasuring instruments on the specimens. The imposed displacement at the end of thebeam was measured by LVDT (Linear Variable Differential Transformer). Thisdisplacement is denoted by , a load cell in-line with the actuator measured axial force P.The DCDT (which is a LVDT with built-in solid state oscillator and phase-sensitivedemodulator) displacement transducers were used to provide the remaining displacementmeasurements. The deformation of the beam panel zone was calculated from readings at

and DCDT locations. Global deflection shape of the column was measured bydisplacement transducers. The amplitude of gap opening between the T-section

flanges and the column flanges was measured by two displacement transducers and

Strain gages and rosettes were glued at critical locations to investigate local response.Figures 3-4 shows these locations on the Specimen 1, the strain measuringinstrumentation for the Specimen 2 was the same, excluding some minor changes in gagelocations. Thirty-eight channels of data were used during testing.

3.2.3 Data Acquisition

The test control and the data acquisition system were run by a PC Windows-based controland acquisition program called Automated Testing System (ATS) developed by SHRPEquipment Corporation of Walnut Creek, California. This Program is capable of signal

9

δ7

δ6

δ3δ2δ1

δ

d8δ

-

.

generation, four-channel servo-actuator command, and sixteen-channel data acquisition.For the tests the ATS system was used to monitor and control the displacement and force-feedback signals.

Other data were monitored and recorded using an AutoNet data acquisition system with acapacity of 64 channels. Pacific Signal Conditioners were used to amplify the transducersand the strain gages signals and to remove frequencies above 100 Hz from the analogsignal.

3.2.4 Loading History

The testing program was based on the ATC-24 document "Guidelines for Cyclic SeismicTesting of Steel Structures". The specimens were tested under displacement control,following a loading history consisting of stepwise increasing deformation cycles. Atcertain stage of plastic deformation of the specimens a few cycles with small amplitudewere imposed. Each loading step was defined by the peak beam end displacement and bythe number of cycle. Table 3-1 presents the testing program for the Specimen 1 and theSpecimen 2.

3.2.5 Data Processing

The specimen behavior was characterized by the following parameters: applied load,beam end displacement, total plastic rotation of the connection, panel zone sheardeformation, column deformation, deformation in the T-section flange, and beamdeflection. A test specimen layout, the corresponding measurements, and the chosenpositive direction of applied load, and measured displacements are shown on Fig. 3-3.

Total displacement of the beam end is caused by rigid body motion of theconnection, the deformations of the beam itself, column, panel zone, and deformation inthe T-section flange. The rigid body motion was possible due small flexibility in thevertical reaction frame. This part of the displacement was not too large, but it could notbe neglected. Therefore the beam end relative displacement was calculated from thetotal one by subtracting of the rigid body displacement. As a result of the column andpanel zone deformations, the panel zone rotates trough an angle and changes its initialconfiguration. Four displacement measurements ( and ) were used to computethe connection rotation due column deflection and panel shear deformation . Thetotal beam rotation can be separated into four components: rotation due deformation ofthe beam itself , rotation caused by rigid connection rotation , the contribution fromthe panel zone , and the rotation due gap opening in the T-sections . These valueswere determined as follows:• Total beam end displacement:• Relative beam end displacement: The remainder of the

calculation was done using this value of the displacement; where H is a distance frompin to pin along the column, and L is the distance from the beam end to the center lineof the column

• Total rotation:

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δtotal

δ1 δ2 δ4 δ5

δtotal

δ

, , ,

δ δ δ δ = - -total L H( ) / .6 3

θ δ= / L

γ

γ

θT

θb

θ

θc

θc

θc

• Connection rotation due column deflection: Where d is a distancebetween continuity plates

• Panel zone shear deformation: . Where a and b are thedimensions of the rectangular panel zone area (distance between targets in horizontaland vertical directions)

• Rotation due gap opening (and deformation) between T-section flange and columnflange:

• Total plastic rotation: Where M=PL0 (L0 is a distance from center-lineof the actuator to the face of the column) is the moment at the face of the column and

is the elastic stiffness determined from M versus curve. The unloading path ofone of the elastic cycles below the reverse point was used to estimate this stiffness, toavoid the influence of initial imperfections, clearances, hysteresis, etc.

A set of programs for the MATLAB 5.3 environment was created to process data and toplot results in accordance with the procedure described above.

3.3 Test Results

3.3.1 Specimen 1

Testing of the first specimen was conducted on July 30, 2000. The specimen sustained allloading steps up to and including the 5.69" beam tip displacement cycles withoutsignificant damage. Testing was stopped because the maximum load for the test setupwas reached. Photo of the specimen's close up side view after the test is presented on Fig.3-5. During the last set of the load reversals a slight buckling in the beam web andflanges was observed. The residual buckling in the beam flange and web is shown on Fig.3-6 and Fig. 3-7. During the test energy was dissipated by cyclic yielding of the flangesof the T-sections, the gap between the T-section and column flanges was opening andclosing periodically. The residual gap in the upper T-section is shown on Fig. 3-8.

Table 3-1 presents the loading protocol for the both specimens. The first row in the tablepresents total beam end displacement (in other words: beam end total verticaldeflection). The loading history for Specimen 1 is plotted in Fig. 3-9.

The plot of applied force versus beam tip displacement response is presented onFig. 3-10. The values of the displacement were obtained directly from the LVDT reading.The relative displacement ( ) was calculated from previous displacement by subtractingthe specimen's displacement as rigid body. Because of some small flexibility in thevertical reaction frame occurred this displacement could not be neglected. The plot ofapplied force versus relative beam tip displacement is presented on Fig. 3-11.

Based on the values of the relative beam tip displacement the total beam rotation iscalculated. The imposed moment versus beam total rotation is presented on Fig. 3-12.Figure 3-13 shows the applied moment versus the beam plastic rotation. The deformationof the column panel zone is presented on Fig. 3-14.

11

θ δ δc d= -( ) / .5 4

γ δ δ a b ab= - +( ) / ( )5 42 2 2

θ δ δT d= - /( ) .8 7

θ θ θpl M K= - / .

Kθ θ pl

δ total

δ total

δ

During the test the visible opening between the T-section flanges and the column flangeswas observed. The amplitude of the opening between flanges was measured in thefollowing way, the installed DCDT shows the relative displacement between targetslocated at the center plane of the column and the T-section flanges (see details in Fig.3-3). Therefore during mutual compression of two flanges this displacement is negative,whereas the tension in T-sections web increases this distance and it becomes positive.This relative displacement between the flanges is called as "gap opening" in the report.Figure 3-15a and 3-15b shows these values during the test. The gap opening between T-section flange and column flange for the upper T-section is presented on Fig. 3-15a. Thesame value for the lower T-section is presented on Fig. 3-15b. The beam rotation duethese openings in the T-sections is presented on Fig.3-16.

The imposed force versus beam rotation due panel zone rotation is presented on Fig. 3-17. The relative beam rotation calculated by subtracting rotation of the panel zone,rotation due gap opening in T-sections and the panel zone deformation is presented onFig.3-18.

3.3.2 Specimen 2

Testing of the second specimen was conducted on July 20, 2000. The specimen sustainedall loading steps up to the 5.69" beam tip displacement cycles and failed at the first rampof the last cycle. The fracture was caused by crack in the web of the lower T-section. Thecrack line started at the end of the weld and went through the hole for 1 inch bolt. Testingwas stopped after the finishing this cycle. Photo of the specimen's side view after thetesting is presented on Fig. 3-19.

During the test some energy was dissipated by cyclic yielding of the T-sections, the gapbetween the T-section and the column flanges was open and closed periodically. Theresidual gap in the top T-section is shown on Fig. 3-20.

At the end of the test a slight buckle in the beam web and flanges was observed. Theresidual buckling in the beam flanges is shown on Fig. 3-21 and Fig. 3-22.

The crack in the stem of the bottom T-section is shown on Fig. 3-23 and 3-24. Fig. 3-23presents the view of the location of this crack on the stem of the T-section. The locationwas close to the K-line of the T-section and it was parallel to it. The crack started fromthe end of the fillet weld, continues through the nearest hole for the 1 in bolt and ends atthe next bolt hole. The close view of the crack is presented on Fig. 3-24. The arrows tracethe crack line.

The loading protocol for the Specimen 2 is presented in Table 3-1. The loading history isplotted in Fig. 3-25.

The layout of the displacement measuring instrumentation was identical for bothspecimens given in Fig. 3-3. The displacement at the beam tip was measured by LVDT,whereas the remainder of displacement measurement was done using DCDT.

12

The plot of applied force versus beam tip total displacement is presented on Fig. 3-26.The values of the displacements were obtained directly from the LVDT reading. Therelative displacement was calculated from previous displacement by subtracting thespecimen's displacement as a rigid body. The flexibility of the reacting frame was takeninto account. The plot of applied force versus relative beam tip displacement is presentedon Fig. 3-27.

Based on the values of the relative beam tip displacement the total beam rotation iscalculated. The imposed moment versus the beam total rotation is presented on Fig. 3-28.Figure 3-29 shows the applied moment versus the beam plastic rotation. The deformationof the column panel zone is presented on Fig. 3-30.

During the test the visible opening between the T-section and column flanges wasobserved. The values of the gap opening were measured by DCDT. Figure 3-3la and 3-31b shows these values during the test. The gap opening between the T-section flangeand column flange for the top T-section is presented on Fig. 3-3la. The same data for thebottom T-section is presented on Fig. 2-31b. The beam rotation due these openings in theT-sections is presented on Fig. 3-32.

The imposed force versus beam rotation due panel zone rotation is presented on Fig. 3-33. The relative beam rotation calculated by subtracting rotation of the panel zone,rotation due gap opening in the T-sections and the panel zone deformation is presented onFig.3-34.

4 Experimental Results and Conclusions4.1 Experimental results

A brief summary of experimental results and key parameters characterizing theperformance of tested specimens is presented in Table 4-1. The beam end displacementcorresponds to the relative beam end displacement .

4.2 Conclusions: advantages and disadvantages of proposed connections

4.2.1 Advantages

The design and performance of the proposed beam-to-column connections shows thefollowing advantages:- all welding work can be done in a welding shop, in convenient welding positions

final assembling with bolts is relatively easy procedure and does not require arigorous quality assurance inspection (in order to achieve the required clamping forcebetween the column and the T-section flanges the widely available torque multiplierfrom WRIGHTTOOL: Model 9S393A was used; the device does not produce anynoise and has an accuracy of ±5%)

13

δ

-

after test disassembling of Specimen 2 shows that repairing and replacing beam withnew T-section is neither difficult nor expensivethe beam deformation is minimal due to active participation of the T-sections flangesand the column flanges during cyclic inputwith shims properly installed, the connection develops less residual straineliminating large quantities of field weld greatly helps the connecting work to keepup with the steel erection.

4.2.2 Disadvantages

The chosen design and the failure of Specimen 2 show the following disadvantages andsuggested improvements:

steel along the K-line of the T-section must be carefully selected1 inch bolts (as used in Specimen 2 to pre-stress the T-section web to beam flange)requires a greater distance between the bolt and the end of the fillet weld.Alternatively, it appears that the bolts can be omitted altogether

- steel material of 1 ¼ " bolts has to be high quality as used in the tested connections- connection based on the proposed design require shims for field assembly- beams with welded top and bottom T-sections require more shipping space during

transportation.

4.2.3 Future Research Directions

Based on the conducted tests and followed data analysis the following future research onthis type of connections is planned:- conduct 3D finite element analysis (FEA) of the connection to explore the possibility

of exchanging the existing 1 inch bolts to clamps and to investigate the decision toremove some or all of them

- conduct 3D FEA of the connection to evaluate the critical parameters at the column-tee joint, including the T-section size, bolt diameter, the clamping load variation andthe prying action

- fabricate and test new specimens with an improved design based on the theoreticalresearch and results of the previous tests.

14

-

-

--

--

References:

1. Tsai, K.C. and Popov, E.P. 1990. Cyclic behavior of end-plate moment connections.ASCE J. of Struct. Engineering, Vol.116, No.11.

2. Tsai, K.C. and Popov, E.P. 1988. Steel Beam-Column Joints in Moment ResistingFrames. Report No. UCB/EERC 88/19, Earthquake Engineering Research Center,University of California at Berkeley.

3. Murray, T.M. et al. 2000. Cyclic testing of bolted moment end plate connections.Struct. And Materials Lab., Virginia Polytechnic Institute and State University.

4. Leon, Roberto et al. 2000. Tests on bolted connections. School of Civil andEnvironmental Engineering, Report No. SEMM 00-02, Georgia Institute ofTechnology.

5. FEMA-267. 1995a. Interim guidelines: evaluation, repair, modification and design ofwelded steel moment frames. FEMA Report No. 267. Washington, D.C.: FederalEmergency Management Agency.

6. FEMA-267. 1995b. Interim guidelines: advisory No. 1. supplement to FEMA 267.FEMA Report No. 267. Washington, B.C.: Federal Emergency Management Agency.

7. AISC. 1995a. Manual of steel construction. Load & resistance factor design. Vol.1,Structural members, Specifications & codes, Second edition. Chicago: AmericanInstitute of Steel Construction, Inc.

8. AISC. 1995b. Manual of Steel Construction. Load & Resistance Factor Design.Vol.2, Connections, Second edition. Chicago: American Institute of SteelConstruction, Inc.

15

Table 2-1. Dimensions of the W36xl50 beam.

Flange width,bfb

[inch]

12

Flangethickness, tfb

[inch]

0.94

Webthickness,

twb

[inch]0.625

Depth, db[inch]

35.85

Sectionmodulus,

zb[inch3]

581

Area, Ab[inch2]

44.2

Moment ofinertia, I b[inch4]

9040

Length, Lb[inch]

134

Table 2-2. Dimensions of the W14x283 column.

Flange width,bf

[inch]

16.125

Flangethickness, tfc

[inch]

2.06

Webthickness,

tf[inch]1.29

Depth, dc[inch]

16.74

Sectionmodulus,

Zc[inch3]

542

Area, Ac[inch2]

83.3

Moment ofinertia, Ic[inch4]

3840

Length, Lc[inch]

136

Table 2-3. Dimensions of the T-sections cut fromW40x264.

Flange width,fts [inch]

12

Flange thickness,

[inch]1.73

Stem thickness,tsts

[inch]0.96

Total depth for Specimen 1(Specimen 2), dsts

[inch]28.75 (20)

Length, Lts[inch]

16

Table 2-4. Material Properties.

No

123

Part of Connection

BeamColumn

T-section

Yield Stress, Fy[ksi]56.65264

Ultimate Stress[ksi]74.46679

Section Size

W36xl50W14x283

WT40x264

Grade

Gr50Gr50Gr50

Table 3-1. Testing program for the both specimens.

Total beam enddisplacement[inch]No of cycles

0.36

6

0.53

6

0.71

6

1.07

6

1.42

4

2.14

2

0.53

2

2.85

2

4.27

3

5.69

6** Only 2 cycles at this level were performed for Specimen 2.

16

tfts

Table 4-1. Short summary of test results

Key parametersYield load [kips]Beam end displacement at the yield point [inch]Elastic stiffness of the connection [kips/inch]Maximum beam end displacementBeam end displacement at failure [inch]Maximum imposed load [kips]Maximum imposed moment at the column face [kips*inch]Maximum connection rotation [ % ]Maximum plastic connection rotation [ % ]Maximum rotation due gap opening [ % ]Maximum relative beam rotation itself [ % ]

Specimen 12301.21805.2

N/A345

486454

2.51.00.6

Specimen 22301.21785.23.5327

431644

3.30.71.5*

This value is high because it includes the beam rotation after the bottom beam flange failure

17

Figure 1-1. Design details of end-plate connections for Specimens 10 and 10R, and thatof direct welding to column, Specimen 9 (K.C. Tsai, E.P. Popov 1988, 1990).

Load

(ki

ps)

Beam Rotation (%)

Figure 1-2. Cantilever beam load versus beam rotation for Specimen 10R (K.C. Tsai, E.P.Popov 1988, 1990).

18

Figure 1-4. Stress versus strain for coupon test of A490 1 ¼ bolt material.

19

Figure 1-3. Load versus elongation for A490 1 ¼ bolt.

Figu

re 1

-5. G

loba

l dim

ensi

ons

and

geom

etry

of t

he te

sted

spe

cim

ens.

20

Figu

re 1

-6. D

esig

n de

tails

of S

peci

men

1.

21

Figu

re 1

-7. D

esig

n de

tails

of S

peci

men

2.

22

Figure 2-1. Desired plastic frame behavior with plastic hinges developed in beams.

Figure 2-2. Probable plastic hinge location.

23

Figure 2-3. Calculation of the moment at the centerline of the column.

Figure 2-4. The weakest cross-section of the beam near the column face.

24

Figure 2-5. Dimensions of the weakest cross section near the column face.

Figure 2-6. View of the column and T-section connection with the correspondingmechanical model.

25

Figure 3-2. View of a test in progress.

26

Figure 3-1. Test setup for both specimens.

Figure 3-3. Reference dimensions and measurements for the test specimens.

Figure 3-4. Strain gages and rosettes location for Specimen 1.

27

Figure 3-6. Residual beam flange buckling (after the test).

28

Figure 3-5. Specimen 1 after the test (side view).

Figure 3-7. Residual beam web buckling (after the test).

Figure 3-8. Residual gap opening in the upper T-section (after the test).

29

Figure 3-9. Loading history for Specimen 1.

Figure 3-10. Imposed load versus total beam end displacement for Specimen 1.

30

Tip

Dis

plac

emen

t [in

ch]

Time [sec]

Actu

ator

forc

e [k

ips]

Beam end total displacement [inch]

Actu

ator

forc

e [k

ips]

Beam end displacement [inch]

Figure 3-11. Imposed load versus beam end displacement for Specimen 1.

Mom

ent

[kip

s*in

ch]

Beam Rotation [%]

Figure 3-12. Moment versus beam total rotation for Specimen 1.

31

Mom

ent [

kips

*inch

]

Beam Plastic Rotation [%]

Figure 3-13. Moment versus beam plastic rotation for Specimen 1.

Actu

ator

forc

e [k

ips]

Panel zone shear deformation [%]

Figure 3-14. Imposed load versus deformation in panel zone for Specimen 1.

32

Actu

ator

forc

e [k

ips]

Relative displacement between flanges[inch]

Figure 2-15a. Relative displacement between column and top T-section flanges forSpecimen 1.

Actu

ator

forc

e [k

ips]

Relative displacement between flanges[inch]

Figure 3-15b. Relative displacement between column and bottom T-section flanges forSpecimen 1.

33

Actu

ator

forc

e [k

ips]

Rotation [%]

Figure 3-16. Imposed load versus beam rotation due gap opening in T-sections(Specimen 1).

Actu

ator

forc

e [k

ips]

Rotation [%]

Figure 3-17. Imposed load versus panel zone rotation for Specimen 1.

34

Actu

ator

forc

e [k

ips]

Relative beam rotation [%]

Figure 3-18. Imposed load versus relative beam rotation for Specimen 1.

35

Figure 3-19. Specimen 2 after the test (side view).

Figure 3-20. Specimen 2: Residual gap opening in top T-section.

36

Figure 3-21. Specimen 2: top beam flange buckling.

Figure 3-22. Specimen 2: bottom beam flange buckling.

37

Figure 3-23. Specimen 2: crack line location.

Figure 3-24. Specimen 2: close view of the crack line.

38

Figure 3-25. Loading history for Specimen 2.

Tip Displacement [inch]

Figure 3-26. Imposed load versus total beam end displacement (Specimen 2).

39

Forc

e [k

ips]

Tip

Disp

lace

men

t [in

ch]

Time [sec]

Forc

e [k

ips]

Tip Displacement [inch]

Figure 3-27. Imposed load versus beam end displacement (Specimen 2).

Beam Rotation [%]

Figure 3-28. Moment versus beam total rotation (Specimen 2).

Mom

ent

[kip

s*in

ch]

40

Mom

ent

[kip

s*in

ch]

Beam Plastic Rotation [%]

Figure 3-29. Moment versus beam plastic rotation (Specimen 2).

Forc

e [k

ips]

Panel Zone Shear Deformation [%]

Figure 3-30. Imposed load versus column panel zone deformation (Specimen 2).

41

Forc

e [k

ips]

Gap Opening [inch]

Figure 3-3la. Relative displacement between column and top T-section flanges(Specimen 2).

Forc

e [k

ips]

Gap Opening [inch]

Figure 3-31b. Relative displacement between column and bottom T-section flanges(Specimen 2).

42

Forc

e [k

ips]

Rotation [%]

Figure 3-32. Imposed load versus beam rotation due gap opening in T-sections(Specimen 2).

Forc

e [k

ips]

Rotation [%]

Figure 3-33. Imposed load versus panel zone rotation for Specimen 2.

43

Forc

e [k

ips]

Rotation [%]

Figure 3-34. Imposed load versus relative beam rotation for Specimen 2.

44

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