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. STEEL BE~-TO-COLUMN MOMENT CONNECTIONS

Fritz Engineering Laboratory Report No. 333.

by Joseph S. Huang Wai F. Chen

Beam-to-Column Connections

LEHIGH U IVERSITY

Beam-to-Column Connections

STEEL BEAM-TO-COLUMN

MOMENT CONNECTIONS

by Joseph S. Huan'g Wai F. Chen

This work has been carried out as part of an investigation sponsored jointly by the American Iron and Steel Institute and the Welding Research Council

Department of Civil Engineering

Fritz Engineering Laboratory Lehigh University Bethlehem, Pennsylvania

February 1973

Fritz Engineering Laboratory Report No. 333.

STEEL BEAM-TO-COLUMN MOMENT CONNECTIONS

By Joseph S. Huang 1 , A.M. ASeE and Wai F. Chen^2 , M. AseE

1. I N T ROD U C T ION

One of the determining factors of economy in structural steel design is the moment-resisting beam-to-column connections. The selection of connec- tions is often based upon simplicity, duplication and ease of erection. The designer should avoid complicated and costly fabrication. ,Welded connections providing full continuity are commonly used in plastically designed structures. In recent years, A325 and A490 high-strength bolts have become the most com- monly used fasteners in field construction. Connections, which require a com" bination of welding and bolting, are also used in plastically designed struc-

tures. They are consid~red to be very economical.

1.1 PREVIOUS RESEARCH

Previous investigations on mome~t-resisting be~-to-column connec- tions conducted at Cambr~dge University, Cornell University, and Lehigh Univer- sity were summarized and discussed in Ref. 4. The types of connections studied

are: fully welded connections, welded top plate and angle seat connections,

bolted top plate and angle seat connections, end plate connections, and T- stub connections. In addition, the behavior of welded corner connections,' bolted lap splices in beams, and end plate type beam splices was discussed. The connecting media for these specimens were welding, riveting, and bolting. Only A325 hig~-strength bolts were used. The most important result of these tests ,is that for all properly designed and detailed welded and bolted moment connec- tions, the plastic moment of the adjoining member was reached and the connec- tions were able to develop large plastic 'rotation capacity. There were no pre- mature failures except those which could have been predicted and prevented. Recently, a series of eight tests of full-size steel beam-to-column

lResearch Asst., Fritz Engrg. Lab., Lehigh Univ., Bethlehem, Pa.

2Assoc. Prof. of Civil Engrg., Fritz Engrg. Lab., Lehigh U~iv., Bethlehem,

Fa.

connections was carried out at the University of California (8). The connec- tions were subjected to cyclic loading simulating earthquake effects on a building frame. Among those connections tested were two fully welded connec- tions, five flange-welded web-bolted connections, and one flange-welded con- nection. A325 bolts were ~sed in fastening the web shear plates. Beam sec- tions used were W18x50 and W24x76; column sections were W12x106. The connec~

tion specimens were made of ASTM A36 steel. All connections had horizontal

stiffeners which were connected to the columns by groove welds. Results of this series of tests show that the hysteresis loops in all cases were stable in shape under repeated loading cycles. The failure of connections was due to either local buckling of beam flanges or weld fracture, and occurred only after many cycles of loading beyond yield.

1. 2 STATm1ENT OF THE PROBLEM Currently, a test program consisting of twelve full-size beam-to- column connections is underway at Lehigh University under the guidance of the Welding Research Council' (6). The types of connections being studied are: (1) flange-welded web-bolted connections; (2) stiffened seated beam connections; (3) only flange-welded connections; and (4) bolted moment plate connections. .These connection specimens were made of ASTM A572 Gr. 55 steel, fastened with A325 and A490 bolts utilizing higher allowable shear stresse~, namely 30 ksi

for A325 and 40 ksi for A490, for bolts in bearing-type connections.

1.3 OBJECTIVE OF RESEARCH

· The o~jective of this study is to investigate the performance of those co~nections that are subjected to symmetrical loading conditions. Primary at- tention is focused upon the strength, deformation capacity and over-alI stiffness ~in the elastic range. The results of these tests will be utilized to formulate design procedures for safe, efficient, and economical beam-to-column connections.

moment-resisting capacity. The ratios of one flange area to web area, A~/Aw' for W14x74, W24x61, and W27x94 sections are 1.39, 0.44, and 0.60, respectively. The behavior of these sections should be representative of a wide range of wide-flange sections. It was desired to use column sections which did not need horizontal stiffeners. In each case the columns selected were the least column size based upon the AISC tension or compression flange criterion • .. .... + t· ~ ..,. ... ... M • •• column juncture the plastic moment and the factored shear capacity of single shear bolts in beam web would be reached concurrently. Beam span then was simply the ratio of' moment to shear values. All test specimens were fabricated from wide-flange shapes made of ASTM A572 Gr. 55 steel. A detailed report of material properties is given in

Ref. 10.

2.1.2 Fasteners and Holes

ASTM A325 and A490 bolts were used to assemble the joints. In bearing-type connection~, the allow~ble shear stresses used in design for A

and A490 bolts were 30 ksi and 40 ksi, respectively. The use of higher allow-

able shear stresses reflects the logical design criterion which would result if an adequate factor of safety were applied ~gainst the shear strength of the fasteners. This design criterion is based upon the results of a study of A7 and A440 steel lap and butt joints fastened with A325 bolts, and A440 steel joints connecte~ with A490 bolts (5). Tests have been subsequently carried out to. substantiate the suggested design criterion, especially the use of A490 bolts in A440 and A514 steel joints (12,7). Since both oversize holes and slotted holes are desirable to facilitate erection adjustments, and slotted holes may better facilitate the assumed distri- bution of shear and moment at the connections., experimental justification is required for beam-to-column connections assembled with high-strengt~ bolts with enlarged

., ... ~

and with slotted holes. Previous research has indicated that oversize holes, sized according to bolt diameter, do not adversely affect the slip behavior of friction-type joints or cause undesirable bolt-tension loss~s (2). It was also observed that slotted holes did not affect the strength of bearing-type joints. In the test program, 1-1/4 in. round holes ~ere used in top and bottom moment plates fastened with ~ in. diameter A490 bolts and designed as a

friction-type connection (Test C8 in Fig. 9). The use of 1/4 in. oversize holes

is the maximum size permitted in the current Specification (9). Slotted holes -II • ..... ~.... ... II- I .. ,.. .. "10.. I"~ ... ...... • ..~ ... .. __ 41... III were used in one-sided shear plate's fastened with ei'ther A490-X bolts (C3 in.

Fig. 4) or A325-X bolts (C8 and C9). The remaining joints had round holes 1/

in. larger than the nominal diameter of the bolt. Both A325 and A490 bolts were installed by the turn-of-nut method. Washers were not used for A325 bolts. In bearing-type connections, A bolts had a hardened washer under the element (nut or bolt head) turned in tightening. In the friction-type connection^ J (C8), a hardened washer was in- serted under both the head and nut. Nut rotation from snug tight condition was

1/2 turn as required by the Specification (9). All bolts were calibrated and

installed in the Fritz Laboratory. 2.1.3 Welds The connection specimens were welded according to the AWS Building Code (3). The welding process used for groove welds was the innershield pro- cedure; the electrodes were E70TG (flux cored arc welding with no auxiliary gas shielding). The type of filler metal for beam flange groove welds in the flat position and for moment plate groove welds in the horizontal position was NR- 311; NR-202 was used for beam web groove welds in the vertical-up position. The electrodes for fillet welds were E7028. In determining the size of fillet weld, the allowable shear stress on the effective throat was 21 ksi. Nondestructive testing methods were employed to inspect the welds before testing of the specimens. Groove welds were inspected by ultrasonic

.~';;--,

Council on Riveted and Bolted Structural Joints at its annual meeting on May 12, 1971). Figure 5 shows the joint detail of Test C4. Moment capacity was provided through direct groove welding of the beam flanges to the column ~la~ge~. Vertical s~ear was resisted by a t~o-p~ate w~14~~ ~tiffener pea~

which was designed according to Table VIII of the AISC Manual. The strength

of this connection should be greater than that of Test C5 shown in Fig. 6. In the case of Test C5, the beam was connected to the column by ,'. (^) groove..^ -.,.welds^ .-.^ only.^ It had........ neither't^ ....^ :,.t^ "^ P~l!I t"an^ 11II erection..:^ ^ ...~^ ..^ seat ~..nor^ '^ ...an^ ~..^ -^ ..... erectionII clip.

The purpose was to determine the actual capacity of the beam flange groove welds. ' Figure 7 shows bolted top and bottom moment plate connection Test C6. The plastic moment was carried by flange plates which were fastened with 1 in. d~ameter A490-X bolts. The design procedure follows the example given on page 4-92 of the AISC Manual. The bracket stiffeners were designed with

the aid of Table VIII.

Test C7 is shown in Fig. 8. The vertical shear is resisted by a ·

one-sided shear plate connected to the beam web by three 1 in. diameter A490-X

bolts. Tests Cl, C6, and C7 were designed for the same amount of moment and

shear, and, therefore, their behavior should be comparable. Test CS"in Fig. 9 'was designed as a friction-type connection having

oversize holes in moment plates. The use of 1-1/4 in. round holes for 1 in.

diameter A.490-F bolts is permitted by the Specification (9). There is no re- duction in slip resistance of the jo int. The one-sided shear plates had

slotted holes and were designed as bearing-type connections. A continuous

bar was also attached on the side of the shear plate as shown in Fig. 9. Test C9 (Fig. 10) is similar to Test C8. For the purpose of com- parisan, the moment plates of Test C9 were designed as bearing-type connections having round holes 1/16 in. in excess of the nominal bolt'diameter.

For the purpose of rating the performance of those previously de- scribed connections, three fully-welded connections are included in this test

program. Test CIO is shown in Fig. 2; Tests CII and el2 are shown in Figs.

11 and 12, respectively. ~.3. TEST SETUP. (^) I ..... '.' ,. The test setup is shown in Fig. 13. The axial load in the column was applied by a 5,000,000 pound-capacity hydraulic universal testing machine. The y. .... III'~. .. "...../.. I ... "',.,fcrosshead ~t ~ '0lil.^ of^ the^ testing^ machine^ is^ shown.'. '*;, The beams''/It'· + ,"^ were • ~ 41 ".-. ..^ "1"1supported ... "....... .....' ...^ J by""..^ two... • .. •

pedestals resting on the floor. Rollers were used to simulate simply support~d

end conditions. Because the combination of the short span of the beam and the size of' shapes resulted in a compact setup, no lateral bracing was needed to provide stability.

3. T EST RES^ U L T S

Eight tests have been completed to date. The experimental results and reference values are given in Table 2. The strength of connections is indicated by the maximum load to predicted plastic limit load ratio Pm Ip (^) p • The deformation capacity is measured by the ratio of total deflection to the

predicted deflection at plastic limit load bm /~ p which is defined as the

ductility factor~. T·ab1e 3 (on page 17) summarizes the descriptions of failure of connections. The load-deflection curves of connections consisting of W27x94 berun

and W14x176 column are indicated in Fig. 14. Both C2 and C3 showed adequate

stiffness under working load. Slip occurred 'above the working load and the

A490 bolts eventually went into bearing· against the sides of the holes. In

addition, A490 bolts were able to deform to permit distribution of forces at maximum load. The ductility factors of C2 and C3 are 9.7 and 15.4, respec- tively; the deformation capacities of, C2 and C3'are adequate for design. The minimum required ductility factor has been recommended to be 4. The joint of C2 at plastic limit load is shown in Fig. 15. The failure of C2 was due to the

the column flange (Fig. 27). Connection ClO after testing is shown in Fig. 28. The compression horizontal stiffeners behaved satisfactorily; they buckled after the attainment of the predicted plastic limit load. The failure of CIG was also due to a fracture occurring at the fillet weld of the tension stiffener (Fj..g •. 29) _. (^) : ..- ..... "".,.. •• It ...

. The load-deflection curve of CII is shown in Fig. 30. This con- nection was designed for a shear capacity' at factored load of 52.5% Vp which

• 'II- - .." simulates.. ;'" .~ .. • • "III the^ loading^ ,,,^ condition..^ l.^ •^ ~:..^ •^ t^ '\IIin^ It^ a^4 t^ real.....^ •^ ...^ ".-."1^^ building. ...^ '&.IiI'lt..^ .,..^ if...^ •^ The maximum•^ til.^ )1"^ tI'^ ......load^ 't^ ...^ is"^ jII".4.^25 per cent greater than the predicted plastic li~it load. This substantial in-' crease in load-carrying capacity is attributed to the forming of plastic hinges at the joints (Fig. 31), and therefore, strain hardening sets in quickly in

localized zones. The testing of ell was terminated when fracture occurred at

the heat-affected zone of the groove weld at the tension flange (Fig. 32).

4. CON C L U S ION S

On the basis of the results of these completed tests, the following conclusions, which are valuable to the fabricated structural steel industry~ have been reached.

1. Flange-welded web-bolted connections have fulfilled design requirements, showing sufficient stiffness in the elastic range under working load, attaining pla~tic limit load, and exhibiting a very large amount of de- formation capacity near maximum load. This type of connection may be used in rigid frame construction (AISC Type 1).
2. A490 high-strength bolts performed satisfactorily. It is appropriate to design the one-sided web shear plate as a bearing-type joint using an allowable shear stress of 40 ksi.
3. The fillet welds connecting the shear plate to the column flange may be sized for vertical shear only; the moment due to the eccentricity of the applied load may be neglected.

4. Slotted holes may be used in one-sided shear ~lates that are designed as

bearing-type joints. ~. Fillet welds may be used in lieu of groove welds in connecting horizon- tal stiffeners to column flanges.

6. Welds approved by ultrasonic inspection were satisfactory. A careful weld .i,nspec.tion ... dur:ing• ,f.ab~ic~t~·o,n.~ •• wast 'f ..n~c.essary to ens~r.~ tije: ad~q~at~... pe;"~or- mance of connections. 5. A C K NOW LED G MEN T S · ".' ..'. Xhe projec.t· i-s' be.ing carried au·t .at.· the ~ Fritz;· .Engineer·ing:.:Labora- tory (L. S. Beedle, Director) as part of the research program of the Struc- tural C?nnections Division. (J. W. Fisher, Director),. The stud·y is sponsored jointly by the American Iron and Steel Institute and the Welding Research Council. Research work is carried out under the technical advice of the WRC Task Group, of which Mr. J. A. Gilligan is Chairman. The authors are especially grateful to Messrs. J. A. Gilligan, o.

W. Blodgett, ·C. F. Diefenderfer, W. E. Edwards and C. L. Kreidler for their

valuable suggestions and assistance in the fabrication of the specimens.

Thanks are also due Messrs. J. E. Regec, K; R. Harpel and the technicians of

Operations Division for their help in testing, and to Mr. R. Sopko for the

photography. The manuscript was reviewed by Dr. G. C. Driscoll, Jr. and

typed by Miss S. Matlock. The drawings were prepared by Mr. J. Gera. Their help is appreciated.

,,," 'III .,. ~ • .., .. 4" ., 'f ," .... .II 11:.

TABLE 2 TEST RESULTS

.Test (^) .' Experi-ment'al... .', ..^ Reference ... • 11 • t (^). , (^) : P' m p. (^) p' .' (^). '!:i' P 6 P P P ~ - P --ill...P P^ m^ ......!!!~ m m p ps pr (^) p p ps pr p (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)^ (11)

Cl 357.5 1.50^322 286 271 0.361^ 1.11^ 1.25^ 1.32^ 4.

... "..... ..^ .,^ ...^.^.^ ~^ ~^ ..^ •^ t^ 'II^ oiII^ ~^ ...^ ..^ " '

C2 826 2.67 748 590 522 .0.276^ 1.10^ 1.40^ 1.58^ 9.

C3 818 4.26' 748 590 522 0.276 1.09 1.39 1.57 15.

C4 660 0.57^748 590 522 0.276^ 0.88^ 1.12^ 1.26^ 2.

C5 380 1.72^748 370 522 --- 0.51^ 1.03^ 0.13^ --

CIO 364.5 1.57 322 286 271 0.361 1.13 1.27 1.34 4.

Cll 392.5 2.05 315 266 199 0.341 1.25^ 1.47^ 1.97^ 6. el2 838 3.63 74,8^590 522 0.276 1.12^ 1.42^ 1.61^ 13.

a. All loads (P) listed are column loads in kips; all deflections (~).are in inches.

-13.-,

~ ; • • ..l

A

Sym. --++--

Typ. Elevation

(FWI4y=^ 55ksdx..^74

v 2 u X 5¥4 11 )( 9¥ZIl^ '.

Shear Plate (Fy :: 55 ksi) (^3) in ~ I (^111) Viet! <P (^) A490-Round HolesX Bolts

l<t A A

Sym

\ 2 Bolts^ _3/^41 tpin^ A 13/^3016 "^7 HolesErection Elevation 3/Bocking^8 "^ x^ tllx 12 Strip^11 (A36) (Typ. )

.. ' (^) '·r~611X3Y2·~ Stiffener ft8'le (Fu•. - y=50ksil Sym.

3/e'~x Backing I"x Strip12~1 (^) (A36)"':,' ': .• " Sym. IJi Clearance '--13/1~' St iHener X3~2' X 8 re. 'le" (Fy :: 50 ksj) (Typ )

-:. ..

Fig. 1 Test Cl

Section A-A (^) Scale: o^ ,^ 5 I 10 in_^ Scale.,^1 Fig. 2 Test CIO^0 1 5^10 In.

,~'- R':~4"--'., J~4"----'-""- J"----' _

( F^ WI41t176y :: 55 kSI)

&/l~' Plate X 2 Y2"XWllh 2I 1\1 Y;'- 1 6' +-II-..lE--~+----1~- • --------- Round(A36) Holes

3 Y2" //~~.lo--<TYP 30°

(F^ WI41t176y :55ksil 13 /", 13 /4^ u

ElevatIOn^ '.^ -^ 3/ Backing^8 "^ X^ l"^ II^12 Stnp^01 (A36) (Typ) E^ levotton

- 3/," Backing II I" x 12"Strip (A36) (Typ)

Pion View Scole- Fig. 3. Test C2^ o -5^10 in

Slot Detoll ~tl~6'^ ~ R'.^11 ~^ "X----J I~"-~ ~I,._ IJ' Fig. (^4) Test C~

Scole:l o 5 10 In

o 5

Seole:

·........."1.: Moment .lK)~. xPlate 12 1 /2^11

Pion View (Fy =50kSI)

Sym

Slot Detail

1 III,," 3 :0)3"'=9^ UIa~Shlms 01 1 I d/ 2 !/16' x 2"x 2o~i'. (FyEW24.61^ 55ksd^ !d,23'1" ,Plote Round withHoles 13/ 1 &, (^) I 4 .)/.')( 5 1 /,,",; 26 j;~' ·i~I (A36) (^) J 3(0)Sheor 3 11 ~:9" lFy '55k>l) (^) i ·~ I~,," 3/."xl^1 BackJn9x 13 Strip (A36) (Typ) ••~ III- tt. .,..Elevation ':T"~ A325.X 8<llt.^ I^ ..^ ~ ~~)~t~~~les

Scote: I I o 5

l3'/~' Moment X II Y,,- XPlate 24 Y2" (Fy =50ksi)

Test C

3Y~ "'--- -~ 3/,"X BOCklnQ I " (^) X 13"Strip (A36) Elevotion ( Typ ) Sym.

Sial Detoll 1'I'e" R;IU~]13"^ I!L"-^ ~,r----t ~. I ~ _.1J ", I

Fig. 9

Elevation

(FW24x61y ;: 55 kSI) ~ ?Y8~XBacking III x 12 Strip (^11) (A36) (Typ. )

W27 x 94 ir';:===~=========(F=y===5=5=kS=il==1^1 ----L Elevation

(FWI4y :: 55 x^176 ksi)

2. Bolts 3 / 4 ' (^) tP in (^) A30713/16 (^11) HolesErection

9 <I...--^ 3/ 811 X 4 It X 20 h II d;.: 2 Erection FL (A36)

.................... 3;8Bocking^11 X In x 8"Strip {A36} ( Typ.)

Sym. z:::;;~::zzif)~4;::rc=:~4^ 1"r-f5!;~ ~::s0:c:::s,'!~:=:SS:~::::S:S;==::S:S~:::::;:S;;::::S::S::;:::::S::S::::S:S:::i'- ~~1J6-"-?""""2-----«3 Tack Welds to Column Section A-A Section A~A^ ~...............---..^3 Tack Welds to^ Column

Fig. 11'

Scale: Test CII o^5 10m Fig. 12

Scole;

Test el2^ o^ '~^ lOin.

TABLE 3 DESCRIPT"ION ,OF FAILURE

C

C

Cl

C

Description of Failure Crack at the fillet weld of the tension stiffener. Tearing of column web along web-to~flange juncture. Fracture occurring at th~heat-affected zone of the tension flange,groove weld. Buckling of beam web and fracture of beam web initiated at the cope hole. C5 Fracture of beam web initiated at the cope hole.

Test

CIO Crack at the fillet' weld of the tension stiffener. ell Crack at the heat-affected zone of the tension flange groove weld. C12 Fracture at tension flange groove weld; excessive coluffiIt web .. deformation in the compression region.

Fig. "13 Test Setup