Seismic respon of extended end plate joints to concrete-filled steel tubular
columns
Jingfeng Wang a ,b ,⇑,Lin Zhang a ,B.F.Spencer Jr.c
a
School of Civil Engineering,Hefei University of Technology,Anhui Province 230009,China b
Anhui Civil Engineering Structures and Materials Laboratory,Anhui Province 230009,China c
Department of Civil and Environmental Engineering,University of Illinois at Urbana-Champaign,IL 61801,USA
a r t i c l e i n f o Article history:
Received 2March 2012Revid 18December 2012Accepted 3January 2013
Available online 9February 2013Keywords:
Concrete filled steel tubular (CFST)Extended end plate connection Blind bolts
Seismic behaviour Cyclic loading Ductility
Energy dissipation Anchorage action
a b s t r a c t
This paper investigates the ismic behaviour of extended end plate connections to circular or square concrete-filled steel tubular (CFST)columns using blind bolts.Both the end plate type and the
column ction type are considered.Results of an experimental study involving four bolted moment-resisting connections subjected to cyclic loading are prented.The failure modes,hysteretic performance,strength and stiffness degradation,rigidity classification,and energy dissipation of the blind bolted extended end plate connections to CFST columns were estimated in detail to investigate the ismic behaviour.The anchorage action of reinforcing rebar welded to the bolt with concrete-filled steel tubes was also explored.The experimental results indicated the blind bolted extended end plate connections with circular or square CFST columns exhibited large hysteretic loops,good ductility,and excellent energy dissipation capacity.Failure modes for test specimens under cyclic loading were similar to tho under monotonic loading,and their rotation capacities satisfied the ductility design requirements for earthquake-resistance in most ismic regions.The experimental studies enable improvement in the practical design of blind bolted moment connections.
Crown Copyright Ó2013Published by Elvier Ltd.All rights rerved.
1.Introduction
The u of concrete-filled steel tubular (CFST)columns is effi-cient and economical for both column and bracing members in modern structures,due to their excellent static and earthquake-resistant pro
perties such as high strength and stiffness,good ductility,and large energy dissipation capacity.In the past two decades,some studies have been reported on the static and ismic performance of welded connections or other connections to CFST columns,such as Schneider and Alostaz [1],Elremaily and Azizin-amini [2],Kang et al.[3],Beutel et al.[4],Cheng and Chung [5],Ricles et al.[6],Wang et al.[7]and Han and Li [8].
Following the 1994Northridge and the 1995Kobe earthquakes,considerable attention was paid to mi-rigid connections in terms of their energy dissipation capability and ductility.However,a practical difficulty aris for engineers eking to employ on-site bolting in beam-to-column connections to have the high degree of fixity necessary for moment-resisting frames.The recent devel-opment of blind fasteners allows for bolt installation on only one side of the connection without the need for access within hollow steel ction (HSS)column [9,10].The commercially available blind bolts included the Lindapter Hollo-bolt,the Ajax ONESIDE bolt,the Huck blind bolt,and the Flowdrill connector.Each type of blind fas-teners differs in the bolt components,resistance mechanism and method of installation.Wang et al.[11]summarized some existing tests of blind bolted joints to HSS or CFST columns.
To overcome the inconvenience of extensive welding and the required high tolerance,there has been
a growing rearch interest in the blind bolted connections.Some studies have been conducted on the static behaviour of HSS or CFST column connections with various blind fasteners,such as Korol et al.[12],France et al.[13–15],Loh et al.[16],Yao et al.[17],Wang et al.[18],and Lee et al.[19–21].Korol et al.[12]summarized that the behaviour of the bolted moment connection involving W-shape beam and rect-angular hollow ction column using high-strength blind bolts is similar to that using ordinary A325bolts,in terms of moment capacity,stiffness and ductility;the blind bolts have a promising potential in structural connections to CFST or HSS columns.
Compared with static studies,rearch on the ismic behav-iour of blind bolted connections to CFST columns has been limited.Mourad et al.[22]reported two cyclic load tests on blind bolted extended end plate connections to square HSS columns and inves-tigated the effect of joint flexibility on the frame respon under dynamic loading.Gardner and Goldsworthy [23]and Goldsworthy and Gardner [24]conducted a ries of cyclic tension tests on blind bolted T-stub connections to the circular CFST columns to
0141-0296/$-e front matter Crown Copyright Ó2013Published by Elvier Ltd.All rights rerved.dx.doi/10.struct.2013.01.001
⇑Corresponding author at:School of Civil Engineering,Hefei University of
Technology,Anhui Province 230009,China.Tel./fax:+865512901434.
E-mail address: (J.Wang).
investigate the u of extensions to blind bolts and stiffness of a T-type element.Elghazouli et al.[25]studied the cyclic behaviour of angle connections to square tubular columns by means of Lindap-ter Hollo-bolts.Yao et al.[26]completed a joint test to investigate double built-up tees connections to square CFST columns with Ajax oneside bolts under cyclic loading.Wang et al.[11]studied the hysteretic behaviour offlush end plate joints to circular or square CFST columns using Hollo-bolts.Mirza and Uy[27]investigated the experimental behaviour of compositeflush end plate connec-tions to square CFST columns with Ajax fasteners under low-prob-ability,high-conquence loading.Prently,little attention has been paid to investigating ismic performance of blind bolted ex-tended end plate connections to CFST columns.France et al.[13–15]studied extended end plate connections to square HSS or CFST columns usingflowdrill connectors under monotonic loading. Wang et al.[28]conducted a ries of static test on extended end plate connections to circular or square CFST columns with blind bolts,and also investigate the u of extensions to blind bolts.
This paper investigates the ismic behaviour of blind bolted extended end plate connections to circ
ular or square CFST col-umns.The parameters in the study include the end plate type and the column ction type.The failure modes,hysteretic perfor-mance,stiffness and strength degradation,ductility,and energy dissipation capacity of the typed connections are analyd and evaluated in detail.The anchorage action of reinforcing rebar welded to the bolt with concrete-filled steel tubes was also ex-plored.The experimental studies enable improvement to the prac-tical design of blind bolted moment connections.2.Experimental program
2.1.Specimen descriptions
Four extended end plate joints between concrete-filled steel tubular columns and steel beams with blind bolts were tested. The test specimens were subjected to a cyclic loading to simulate ismic loading conditions.In addition,a constant axial load was applied to each specimen to reprent the reaction from upper sto-ries.Fig.1illustrates the details of the extended end plate connec-tion specimens.The columns for specimen DEC1and DEC2are concretefilled circular steel tubes with a cross-ction of200Â10mm;the columns for specimen DES1and DES2are concrete filled square steel tubes with a cross-ction of200Â200Â10mm.The beams were commercial H-shape steel ctions with a cross-ction of HN300Â150Â6Â10mm for all test speci-mens.The test joints were fabricated and erected by laboratory personnel.The bare steel joint asmbly was constructedfirst. T
he steel beams and columns were asmbled by means of ex-tended end plate connections with blind bolts.All bolts for the con-nections werefinally tightened to a torque of442N m,and the initial pretension torque of the bolt was221N m according to specification GB50017[29].The circular or square steel tubular columns werefilled with lf-consolidating concrete(SCC)mix after the erection of the steel framework.
The extended end plate was fastened to the circular or square steel tube by HSBB blind bolts with extensions into the concrete core,as shown in Fig.2.Details of the HSBB blind bolt and its
Nomenclature
B width of square steel tube
b fb beamflange width
CFST concrete-filled steel tube
C k connection stiffness coefficient
C m connection moment coefficient
C h connection rotation coefficient
D exterior diameter of circular steel tube
E Young’s modulus of steel
EI bflexural rigidity for the beam
E c Young’s modulus of concrete超觉静思法
E e dissipated energy ability
f cu cube compressive strength of concrete
f u ultimate strength of steel
f y yield strength of steel
H column length
h b beam ction height
K j rigidity degradation coefficient
K ie initial stiffness of connection,defined as the scantflex-ural stiffness corresponding to20%M u in moment–rota-
tion curves
K rvice-level stiffness of connection,defined as scant flexural stiffness corresponding to60%M u in moment–
rotation curves
L beam length
L0distance from the load application point to the column wall常见函数求导公式
M connection moment
M y yield moment defined by the test joint
M e design moment capacity defined by EC3specification, M e=0.67M u
M m maximum moment of the test joint
M f moment of the test joint at failure state,M f=0.85M u
M bp design plastic moment resistance of the beam
n axial load level,n=N/N u N0axial load applied to the column
N u axial compressive capacity of the column
P test load on the beam end
P max maximum load on the beam end in the test
t fb beamflange thickness
t wb beam web thickness
t p end plate thickness
梦见捉黄鳝W dissipated energy in each cycle
W total total dissipated energy
h r connection rotation
h b beam rotation
h c column rotation
h r,y connection rotation corresponding to the yield moment
of the connection
h r,e connection rotation corresponding to the design mo-
ment capacity of the connection
h r,m connection rotation corresponding to the ultimate mo-
ment of the connection
h r,f connection rotation corresponding to the moment of the
connection at failure state
h r connection rotation
h y elastic yielding angular displacement
h u elastic–plastic angular displacement
[h e]elastic layer angular displacement
[h p]elastic–plastic layer angular displacement
l displacement ductility coefficient
l h angular displacement ductility coefficient
n e equivalent damping coefficient
D/D y number of cycles
D displacement of the beam end
几何题初一数学
占有善良的情人
D y displacement of the beam end corresponding to P y
k i strength degradation coefficient at the same loads
k j strength degradation coefficient at the total loads
J.Wang et al./Engineering Structures49(2013)876–892877
simple installation procedure are given in Wang et al.[28].The extension to the bolt was20mm diameter50mm length high strength reinforcing rebar of grade335N/mm2,as en in Fig.3. The reinforcing rebar was welded to the head of the bolt to form a complete unit.The experimental rearch by Gardner and Golds-worthy[23]and Wang et al.[28]has shown that provision for extension of the blind bolts into the CFST column improved the strength and initial stiffness of the connections.The high strength blind bolt ud in the tests is Grade10.hat exterior diameter of the bolts is20mm and the ultimate strength of the bolts is1000N/mm2).The ratio of the yielding strength to the ulti-mate strength of the bolt is0.9.
A summary of the test specimens is reprented in Table1.The rearch parameters in the study are the column ction type and the end plate thickness.The level of axial load(n)in the specimens is defi
ned as follow:n¼N=N uð1Þwhere N is the axial load applied to the CFST column,and N u is the axial compressive capacity of the CFST column calculated by using specification DB34/T1262[30]and using the recorded steel and concrete mechanical properties.The experimental tup is shown in Fig.4.
2.2.Material properties
Three tensile coupons cut from the steel tubes and sheets(ud in beams and end plates)were tested to determine the yield stress (f y),the ultimate stress(f u),Young’s modulus(E),and elongation at fracture(d).The results of the material tests of the steel coupons ud in the specimens are listed in Table2.The nominal yield stress and ultimate stress of the Grade10.9M20blind bolts were determined as900N/mm2and1000N/mm2,respectively.
878J.Wang et al./Engineering Structures49(2013)876–892
(a) Circular HSS (b) Square HSS
Blind bolts
Inner steel wall
Blind bolts
三方合同Inner steel wall
J.Wang et al./Engineering Structures 49(2013)876–892879
2.3.Cyclic loading apparatus
The general arrangement of the test tup is shown in Fig.5.The axial loading was applied by a hydraulic jack reacting against a steel frame onto an upper support at the top of the CFST column. To restrict the plane beam-to-column joint from lateral movement, the upper end of the CFST column was supported by a horizontal restraining beam,which was connected to the reaction wall.The lower end of the CFST column rested on a reinforced concrete foun-dation that was post-tensioned to the strongfloor and the reaction wall.
One hydraulic actuator of500kN capacity applied the load to the beam end was controlled in order to simulate ismic loading. In the formal loading pha,the vertical actuator applied the axial load to the column.Triangular waves are ud for displacement control,as shown in Fig.6.The loading history of the specimens
was generally bad on the ATC-24[31]guidelines for cyclic test-ing of structural steel components.The loading history included elastic cycles and inelastic cycles.The elastic cycles were con-ducted under displacement control at displacement levels of 0.25D y,0.5D y and0.7D y,where D y is the estimated vertical yield-ing displacement corresponding to the vertical yielding load P y(P y is approximately equal to0.7P uc,where P uc is the estimated ulti-mate vertical loading capacity).Two cycles were impod at each of the vertical displacement levels of0.25D y,0.5D y and0.7D y. The inelastic cycles were then taken to vertical displacement levels of D y,1.5D y,2D y,3D y,5D y,7D y and8D y.Three cycles were im-pod at each displacement level of D y,1.5D y and2D y;two cycles were impod at each additional inelastic displacement level de-scribed above.The magnitude of the displacement increas grad-ually until the testing specimens are damaged or have larger deformations.
The beam end displacement was automatically recorded by the hydraulic actuator acting on the bea
m end.In addition,Six Linear Variable Displacement Transducers(LVDTs)were mounted to measure the connection rotation,shear displacement and side-sway of the specimens.The layout of the LVDTs is illustrated in Fig.7.
Strain gauges were ud to monitor the strain respon in the beam,the end plate,and the steel tube.A total of47strain gauges were employed on each specimen.All readings were recorded using a PC-bad date acquisition system.The layout of the strain gauges is shown in Fig.8.
3.Test results and hysteretic behaviour
3.1.Failure modes
Detailed obrvations were made during the tests,including failure modes and load–displacement hysteretic curves.In the ca of the blind bolted extended end plate connections to CFST col-umns,the failure occurred in the following modes:(1)deformation of the end plate;(2)bucking deformation of the beam compressive flange;(3)bucking deformation of the beam web;(4)outward deformation of the columnflange;(5)welding crack between the beam compressiveflange and the thin end plate for square CFST column joints;(6)anchorages fracture of the tensile bolts with extensions in the square columns;and(7)crushing of the concrete core due to the larger connection rotation.
In this rearch,the majority of the failure modes of the joints under cyclic loading were similar to tho under monotonic load-ing[28].The failure of the test specimens were related with the end plate thickness and the column ction type.Examination of the joints after testing revealed that specimen DEC1and DEC2 were nominally identical,except that the end plate thickness was 12mm and18mm respectively.However,the end plate deforma-tion of specimen DEC1was more significant than that of specimen DEC2.Due to the thinner end plate(t p=12mm),the end plate strains in specimen DEC1were beyond the material yielding strain 1633le and the end plate deformation appeared in the beam ten-sileflange.For specimen DEC2,the steel beam was the weakest component compared with other he end plate,
Table2
Material properties of steel.
Specimen number Steel wall thickness(mm)Yield stress(N/mm2)Ultimate stress(N/mm2)Young’s modulus(N/mm2)Elongation at fracture(%)
Steel beamflange10349.3492.0 1.87Â10516.5
Steel beam web6312.5508.3 2.16Â10517.4
Circular steel tube10331.8484.5 1.94Â10518.2
Square steel tube10328.1490.6 2.01Â10521.7
Endplate-112323.3436.7 1.98Â10531.0
Endplate-218274.4414.4 1.93Â10524.8
880J.Wang et al./Engineering Structures49(2013)876–892
the CFST column and the bolts).Under cyclic loading,the buckling deformation of the beam compressiveflange appeared.The maxi-mum deformation of the end plate for specimen DEC1was 14mm,while specimen DEC2had no obvious deformation of the end plate,as illustrated in Figs.9and10.
A similar effect of the end plate thickness occurred in specimens DES1and DES2,but the end plate deformation in the circular CFST column connections was obviously less than that of the square CFST column connections.For specimen DES1with the12mm thick end plate,the end plate was the
weakest component,becom-ing fully plastic during testing.The welding between the beam compressiveflange and the end plate cracked and tore.The strains of18mm thick end plate in specimen DES2exceeded the yield strain of1422le;however,the bending deformation of the end plate was less than that of specimen DES1.The maximum defor-mation of the end plate for specimen DES1and DES2was respec-tively28mm and16mm,as shown in Figs.11and12.
The steel tube was ctioned by using acetylene cutting torch to determine the specific failure modes of the blind bolts inside the column.The cracks and failure of the expod concrete infill was obrved and recorded.The concrete infill in the steel tube was re-moved to obrve the deformation of the bolts.Fig.13illustrates the internal failure mode of specimen DEC1after ctioning.The obrved results show that except for the concrete near the bolts in tension which was cracked,no obvious deformation appeared in the panel zone of the column and there was also no signs of bending and shear deformations of the bolts in the tests.
All specimens have performed in an acceptable manner and the tests were stopped due to large deformations,although the joints still remained intact.No unexpected failures occurred and all the bolt connectors performed satisfactorily.The test results showed the extended end plate connections to circular or square CFST col-umns with blind bolts exhibited high strength and stiffness and excellent
ductility for application in a moment-resisting frame.
3.2.Moment–rotation hysteretic curves
The behaviour of the beam-to-column connections is critically important to the composite frame respon,and is highly depen-dent on the moment–rotation(M–h r)relationship.For each load increment,the connection rotation(h r)is determined by the differ-ence between the measured beam end rotation(h b)and the col-umn rotation(h c).The recorded hysteretic curves of moment versus rotation of the connections for all specimens are shown in Fig.14.Fig.14indicated that there is an initial elastic respon for all specimens and the moment–rotation relationship can be considered roughly to be linear.Then,the stiffness gradually de-graded and the connection entered into the inelastic stage.With the increa in the beam end displacement,slight pinching effects were obrved in the hysteretic loop for the square CFST column specimen,which reflect the bolt slippage and the end plate defor-mation.After reaching the peak value in the moment–rotation hys-teretic curves,the tests of specimen DEC1and DEC2were stopped due to modest lateral instability of the beam.
With larger beam displacement,degradation in the connection stiffness was obrved,as illustrated in
Fig.14.The main reason for the stiffness degradation was yielding of the column wall and deformations of the end plate and the bolts.Measuring the forces in the blind bolts during the test is difficult becau of the chal-lenges in calibrating the blind bolts after installation.Examination of the high strength bolt after the test indicated no obvious failure signs except looning of the bolts or weldment fracture between the reinforcing rebar and the bolt.The connection stiffness degra-dation was possibly due to both a loss of bolt pretension force with the loading cycles and the permanent deformation of the column wall or the end plate.
The test results demonstrated that the large hysteretic loops for this type of connection are related with the end plate thickness and the column ction type.An incread end plate thickness en-hanced the hysteretic performance.Moreover,the energy dissi-pated cycle for the circular CFST column connection is greater than that for square CFST column connection,in same of the end plate thickness.
The test results showed that the moment versus rotation hys-teretic curves for the extended end plate connections to circular or square CFST columns were robust.At the same loading cycle dis-placement,the hysteretic curves have no obvious strength and stiffness degradation of the connection.Hence,this joint type has excellent ismic performance,so it can be ud in moment-resi
st-ing composite frames.
4.Analysis of test results and discussion
4.1.Moment–rotation envelope curves
According to the moment–rotation hysteretic curve in Fig.14, each maximum load point in a loading cycle was ud to construct the moment–rotation envelope curve for the connection,as illus-trated in Fig.15.
眉头长痘痘The test results showed the effects of the end plate thickness and the column ction type on the moment–rotation envelope
J.Wang et al./Engineering Structures49(2013)876–892881宋朝历史
