PERFORMANCE OF WELD-RETROFIT BEAM-TO-COLUMN SHEAR TAB CONNECTIONS

Transcription

1 PERFORMANCE OF WELD-RETROFIT BEAM-TO-COLUMN SHEAR TAB CONNECTIONS Colin A. Rogers; Mtthew Mrosi; Jcob Hertz Deprtment of Civil Engineering & Applied Mechnics, McGill University, Cnd Dimitrios Lignos School of Architecture, Civil & Environmentl Engineering, École Polytechnique Fédérle de Lusnne, Switzerlnd Robert Trembly; Mrco D Aronco Deprtment of Civil, Geologicl & Mining Engineering, École Polytechnique, Cnd robert.trembly@polymtl.c; mrco.dronco@polymtl.c ABSTRACT Single plte sher tb connections re simple mens to connect bems to their supporting members. The tb is fillet-welded to the supporting column in the fbriction shop, nd then field bolted to the bem web on the construction site. Situtions my rise on site in which the bolt holes do not lign. Insted of reming holes or refbricting the connection, cost efficient lterntive is to use weldretrofit connection between the bem web nd the sher tb. The AISC recommends tht this retrofit pproch not be tken due to concerns with the rottionl ductility of the connection; however, no test-bsed performnce evlution ws vilble for the weld-retrofit connection. The intent of the pper is to summrize the lbortory phse of reserch project in which vrious weld-retrofit schemes of sher tb connections were evluted. The connection performnce is compred with nominlly identicl bolted sher tb connections. 1. INTRODUCTION Single plte steel sher tb connections re commonly used to connect bems to their supporting column members. The tb is fillet-welded to the column in the fbriction shop; the bem web is then field bolted to the sher tb on the construction site. It is possible tht during the steel erection process the bolt holes in the bem web nd sher tb do not lign (Figure 1) due to detiling or fbriction errors, s well s construction miss-lignment. Insted of reming holes or refbricting the connection, cost efficient nd expeditious lterntive is to use weld-retrofit connection between the bem web nd the sher tb. The Americn Institute of Steel Construction (AISC) does not recommend tht this retrofit pproch be pplied due to concerns with the rottionl ductility of the connection; however, no test-bsed evidence ws vilble tht demonstrted the response to loding of this weld-retrofit connection. Hence, reserch project ws initited in which vrious weld-retrofit schemes of sher tb connections were evluted by mens of full-scle lbortory

2 testing. The connection performnce in terms of overll behviour, sher resistnce nd rottion cpcity is compred with nominlly identicl bolted sher tb connections. The scope of the study comprised 13 bem-to-column connection specimens of vrious size W-shpe members, originl bolt configurtions, nd weld-retrofits (Figure 2). This ws complemented by 7 mtching tests of the originl bolted sher tbs (Figure 2). Two of the weld-retrofit specimens consisted of replcement tbs hving only two bolt holes to id in erection; the remining, contined the full llotment of bolt holes. All bems nd columns were of ASTM A992 Grde 50 mteril, while the tbs were of ASTM A572 Grde 50 steel. The weld retrofit ws done in the lbortory fter the column nd bem hd been instlled in the test frme; certified welder with extensive experience in the steel fbriction industry completed the fillet welds of vrious ptterns. Shielded metl rc welding (SMAW) with E49 (E70) stick electrodes ws used, s would commonly be done on construction site. In contrst, E71T flux core electrodes were used for ll shop fbricted tb-to-column flnge welds with n dditionl CO2 shielding gs. This pper describes the design of the retrofit fillet welds nd the testing progrm, s well s the observed nd mesured performnce. Note tht this reserch ddresses the expected demnds on sher tb connection under the regulr grvity loding scenrio; it did not tke into ccount the higher rottionl demnds on sher tb connections resulting from progressive collpse, i.e. loss of column, nor the demnds tht might occur during mximum considered seismic event for pin connected structure. Figure 1: Misligned bolted sher tb connection requiring retrofit (courtesy of DPHV) Figure 2: Typicl bolted sher tb connection with mtching weld-retrofit detil

3 1.1 Bckground Informtion on the North Americn Sher Tb Design Method The design procedures for conventionl nd extended bolted bem-to-column sher tb connections in North Americ re best documented in the 14 th Edition of the AISC Steel Construction Mnul (2010) nd best described for extended configurtions by Muir nd Hewitt (2009). Extensive testing of bolted sher tb connections by vriety of reserchers dtes bck to the work of Lipson (1968); detiled review of the relevnt literture is found in the thesis of Creech (2005). Numericl evlutions of sher tb performnce hve lso been crried out by vrious reserchers (Shermn & Ghorbnpoor 2002). Connections re designed for block sher rupture, bolt bering, bolt sher, sher yielding of the plte nd sher rupture of the plte. For extended sher tb connections, the eccentricity of the bolt group is considered in determining the demnd on the fsteners. The mximum llowble thickness of the plte is clculted to ensure ductility in the connection. The flexurl yielding strength of the plte must lso be checked, in ddition to plte buckling. 2. WELD-RETROFIT SHEAR TAB TEST PROGRAM 2.1 Overview The weld-retrofit sher tb test progrm involved 7 bolted connections nd 13 weld-retrofit connections (Tble 1, Figure 3). Ech of the originl bolted sher tb connections ws initilly designed by Mrosi (2011), Mrosi et l. (2011), Hertz (2013) nd Hertz et l. (2015) following the method documented in the 14 th Edition of the AISC Steel Construction Mnul (2010), nd then tested under grvity loding ccounting for sher nd rottionl demnds. The clculted fctored resistnce of these connections ws tken s the strting point for the design of the weld detil for the retrofitted connections. For exmple, the resistnce of the full C weld for configurtion 1 ws designed to hve the sme fctored resistnce s the corresponding bolted connection. Tble 1: Summry of weld-retrofit sher tb test specimens Config. Bem Column Sher Tb Thickness (mm) Originl Bolted Connection Bolt,b Bolt Weld c Config. Size Size (mm) (mm) Weld Retrofit Weld d Config. Weld d Size (mm) 1 W310x60 W360x x Full C W310x60 W360x x Prtil C W310x60 W360x x Full C W310x60 W360x x Prtil C W610x140 W360x x Prtil C W610x140 W360x x L W610x140 W360x x Prtil C W610x140 W360x x L W920x223 W360x x Prtil C W920x223 W360x x Prtil C W310x74 W360x x Prtil C W610x140 W360x196 8 Temp. e Prtil C 6 13 W610x140 W360x Temp. e Prtil C 11 Configurtion & bolt size for the originl bolted connection; threds excluded. Bolt holes 1/16 (2mm) lrger. b #verticl rows x #bolts per row. c Weld from sher tb to column flnge (weld both sides of plte). d Retrofit weld shpe from bem web to sher tb. e Holes were provided only for two temporry instlltion bolts. f The distnce for ll configurtions (Figure 3) ws 76 mm, except #11 (152mm).

4 Config. 1 Config. 2 Config. 3 Config. 4 Config. 5 Config. 6 Config. 7 Config. 8 Config. 11 Config. 9 Config. 10 Config. 12 Config. 13 Figure 3: Detil drwings of weld-retrofit sher tb connections 2.2 Weld-Retrofit Design nd Fbriction Methodology The design checks were crried out using the conventionl nd extended sher tb design procedures, where pplicble, of the AISC Steel Construction Mnul (2010) to determine predicted resistnces for the single nd double row sher tb specimens (Mrosi 2011, Hertz 2013). The AISC conventionl design pproch, for exmple, does not pply to connections when multiple rows of bolts re present. Becuse the design ws done prior to mterils testing, overstrength vlues of 1.1Fy nd 1.1Fu were initilly

5 ssumed s the probble yielding nd ultimte strengths of the sher tbs when checking to ensure tht the sher tbs would fil prior to inelstic deformtions tking plce in the test bems. ASTM A325 snug tight bolts were used for design. Prcticing structurl engineers were consulted concerning the design of the retrofit-weld connections to determine wht types of retrofits my be used on construction sites. The weld group shpes included Full C, Prtil C nd n L (Figure 3). The logic behind using the Full C shpe weld ws to utilize the mximum spce vilble for the weld. The Prtil C shpe weld ws used becuse pst tests hd demonstrted tht most of the deformtion in the sher tb occurred over the distnce, nd hence it ws decided to void plcing weld in this loction to llow similr deformtions to occur. The L shped weld ws chosen to fcilitte the on-site welding procedure, where it ws nticipted to be difficult to weld in the confined spce between the top of the sher tb nd the underside of the upper flnge of the bem. Once the weld group shpes hd been identified, the predicted fctored resistnce of the respective bolt group ws set equl to the predicted fctored resistnce of the weld group, to determine the size of the fillet weld. This procedure ws enbled for ll specimens by using the instntneous centre of rottion (ICR) method s it is provided in the Cndin Institute of Steel Construction (CISC) Hndbook (2010), which is bsed on the Cndin Stndrds Assocition (CSA) S16 Design Stndrd (2009). The eccentricities used in clculting these weld group resistnces were tken s the distnce from the fce of the column to the centroid of the respective weld group. Typicl weld-retrofit specimens nd the in-lb fbriction of retrofit weld re depicted in Figure 4. Figure 4: Photogrphs of representtive weld-retrofit sher tb connections prior to testing (Test Configurtions 3 & 5) 2.3 Lbortory Testing Procedures Ech connection ws tested using cntilever pproch, whereby the bem ws supported t one end by the sher tb connection to column. Two hydrulic ctutors were operted in displcement control to pply sher force t the test connection nd to simulte rottion by lowering the end of the test bem. Figure 5 shows n overview of the test bem nd column, s well s the lterl brcing frmes nd bem end ctutor support frme. Figure 6 contins photogrphs of typicl specimen in plce. The ctutor in the foreground provided the end rection nd lowered the bem end s the test

6 ws crried out; the blocking under the bem end ws removed prior to testing. Given the nticipted cpcity of Configurtion 10 in Figure 3, this ctutor ws replced with hydrulic jcks (Mrosi 2011). Lterl brcing frmes were erected long the length of the bem to prevent the occurrence of lterl torsionl buckling. A trget rottion of the bem (reltive to the fce of the column) ws chosen to be equl to 0.02 rd for the W310 sections nd rd for the W610 & W920 sections, to be reched t probble ultimte sher resistnce of the sher tb determined using resistnce fctor of 1.0, nd mteril properties of 1.1Fy nd 1.1Fu in the clcultions. The lower rottion trget ws pplied to the deeper bems becuse it ws nticipted tht smller midspn deflections would occur in rel single-spn loding scenrio due to ech bem s higher moment of inerti. A full description of the test setup nd loding protocols is vilble in the works of Mrosi (2011), Hertz (2014) nd D Aronco (2014). Figure 5: Schemtic drwing of bem-to-column sher tb connection test setup Figure 6: Photogrphs of bem-to-column sher tb connection test setup

7 2.4 Discussion of Test Results Photogrphs of representtive connection Configurtions 1 nd 7 re provided in Figure 7. The post-test deformtions for both the bolted nd weld-retrofit connections re shown. Note the similrity in terms of loction of inelstic dmge / yielding to the sher tb, which ws most extensive over the distnce. In the cse of Configurtion 1 ( Full C weld) the horizontl welds between the end of the bem web nd the centreline of the verticl bolt row frctured, effectively trnsforming this weld group into Prtil C shpe. The remining portion of the retrofit weld ws unffected. Configurtion 7 comprised Prtil C weld shpe, which ws not dmged during loding; inelstic deformtions were limited to the sher plte. Similr behviour cn lso be seen for the other Prtil C weld shpe specimens in Figure 8, including Configurtion 11, which possessed long distnce. Figure 7: Photogrphs of post-test deformtions for representtive bolted nd welded connections (Test Configurtions 1 & 7) Figure 8: Photogrphs of post-test deformtions for welded connections Prtil C weld (Test Configurtions 2,4,9 & 11) Pre nd post-test photogrphs of the two L shpe weld-retrofit specimens re provided in Figure 9. The response ws similr to tht observed for the Prtil C connections. Note however, the greter extent of inelstic dmge in Configurtion 8 compred with Configurtion 7 (Figure 7), whereby the plte yielding extended

8 pst the distnce. The retrofit welds for these specimens were not dmged. The welder involved in fbricting these two specimens, in ddition to those hving horizontl weld long the top of the sher tb, commented tht this top weld presented no difficulties during the in-lb fbriction. Figure 9: Photogrphs of post-test deformtions for welded connections L shpe weld (Test Configurtions 6 & 8) Figure 10: Photogrphs of post-test deformtions for welded connections Prtil C weld on replcement sher tb plte (Test Configurtions 12 & 13) The finl two weld-retrofit configurtions, for which the originl sher tb ws removed nd replced with plte tht only contined two bolt holes to id in instlltion, re depicted pre nd post-testing in Figure 10. Although the retrofit welds remined lrgely undmged for these specimens, the overll inelstic ction of the sher tb ws less compred with the other specimens tht contined the originl bolt holes. Nonetheless, these specimens were ble to rech the trget rottion demnd, s did ll other specimens, without ny sudden filure. Given tht the filure section of the sher tb ws greter in re thn the connections with the originl bolt holes, the ultimte resistnce exceeded tht of other similrly sized weld-retrofit test specimens.

9 Normlized Connection Sher (V mesured / V ultimte ) Test 3 - Single Row of 3 Holes - Full "C" Retrofit Test 4 - Single Row of 3 Holes - Prtil "C" Retrofit Test 1 - Single Row of 3 Bolts Connection Sher (kn) Test 9 - Single Row of 6 Holes - Prtil "C" Retrofit Test 11 - Single Row of 6 Holes - "L" Retrofit Test 7 - Single Row of 6 Bolts Bem End Rottion Reltive to Column Fce (rds) Bem End Rottion Reltive to Column Fce (rds) Connection Sher (kn) Connection Sher (kn) The drop off in lod seen in Test 10 ws result of loding protocol The ctutor ws stopped Test 6 - Two Rows of 3 Holes - Prtil "C" Retrofit Test 5 - Two Rows of 3 Holes - Full "C" Retrofit Test 2 - Two Rows of 3 Bolts Test 12 - Two Rows of 6 Holes - "L" Retrofit Test 10 - Two Rows of 6 Holes - Prtil "C" Retrofit Test 8 - Two Rows of 6 Bolts Bem End Rottion Reltive to Column Fce (rds) Bem End Rottion Reltive to Column Fce (rds) Figure 11: Grphs of connection sher versus rottion for representtive bolted nd weld-retrofit sher tb connection tests Representtive grphs showing the reltionship between the mesured connection sher resistnce nd the rottion between the bem end nd column fce re provided in Figure 11. Ech grph includes the results for the originl bolted connection, s well s the two mtching weld-retrofit connections. Note: Tests 1, 3 & 4 re Configurtions 1 & 2; Tests 7, 9 & 11 re Configurtions 5 & 6; Tests 2, 5 & 6 re Configurtions 3 & 4; Tests 8, 10 & 12 re Configurtions 7 & 8. In ll cses, the weld-retrofit specimens were ble to rech the sme rottion cpcity s their mtching bolted sher tb connection. Furthermore, the ultimte resistnce levels ttined by the weld-retrofit connections re similr to their bolted sher tb connection counterprts. Moreover, the connections ll reched the force level ssocited with the AISC predictions. 3. CONCLUSIONS The lbortory results demonstrted tht these weld-retrofit connections cn rech resistnce nd rottion levels consistent with equivlent bolted sher tb con-

10 nections. There is no dvntge to using the Full C shpe weld group; in contrst, the uthors recommend the use of the Prtil C shpe weld since it does not restrict the deformtion of the sher tb over the distnce. The L shpe weld does provide for dequte performnce; however, given tht the welder for this study did not find the instlltion of the top horizontl section of retrofit weld to be difficult, one is not obliged to specify this shpe. Given tht the scenrio presented herein is retrofit solution to lck-of-fit on the construction site, using the originl sher tb with ll of its bolt holes is dvised. The wekened section is dvntgeous in terms of mintining the ductility of the sher tb connection. Using replcement sher tbs without bolt holes does rise the connection resistnce. ACKNOWLEDGEMENTS The uthors would like to thnk the ADF Group Inc. nd DPHV Structurl Consultnts for their technicl nd finncil support, s well s the Nturl Sciences nd Engineering Reserch Council of Cnd. REFERENCES AISC, Steel construction mnul, 13th Edition. Americn Institute of Steel Construction. Chicgo, AISC, Steel construction mnul, 14th Edition. Americn Institute of Steel Construction. Chicgo, CISC, Hndbook of Steel Constrution, 10 th Edition. Cndin Institute of Steel Construction. Mrkhm, CSA, Design of Steel Structures S16. Cndin Stndrds Assoction. Mississug, Creech DD, Behvior of single plte sher connections with rigid nd flexible supports. M.Sc. Thesis, North Crolin Stte Univ. Rleigh, D Aronco M, Behviour of double nd triple verticl rows of bolts sher tb connections nd weld retrofits. MASc Thesis, Dept. of Civil, Geologicl & Mining Eng., Ecole Polytechnique. Montrel, Mrosi M, Behviour of single nd double row bolted sher tb connections nd weld retrofits. MEng Thesis, Dept. of Civil Eng., McGill Univ. Montrel, Mrosi M, D Aronco M, Trembly R, Rogers CA, Multi-row bolted bem to column sher tb connections. 6 th Europen Conference on Steel nd Composite Structures, Budpest. 2011, Hertz J, Testing of extended sher tb connections subjected to sher. MEng Thesis, Dept. of Civil Eng., McGill Univ. Montrel, Hertz J, Lignos D, Rogers CA, Full-scle experimentl testing of extended bem-to-column nd bem-to-girder sher tb connections subjected to sher. STESSA th Interntionl Conference on the Behviour of Steel Structures in Seismic Ares, Shnghi. 2015, Pper No Lipson SL, Single-ngle nd single-plte bem frming connections. Proceedings of Cndin Structurl Engineering Conference. Toronto, , Muir LS, Hewitt CM, Design of unstiffened extended single-plte sher connections. AISC Engineering Journl 2009, 46 (2), Shermn DR, Ghorbnpoor A, Design of extended sher tbs. Americn Institute of Steel Construction Finl Report, Univ. of Wisconson. Milwukee, 2002.