Engineering Structures 132 (2017) 808–821

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Engineering Structures

journal homepage: www.elsevier .com/locate /engstruct

Behavior of two new moment resisting precast beam to columnconnections subjected to lateral loading

http://dx.doi.org/10.1016/j.engstruct.2016.11.0600141-0296/� 2016 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: s_bahrami@cv.iut.ac.ir (S. Bahrami), madhkhan@cc.iut.ac.ir

(M. Madhkhan), fateme.shirmohammadi85@gmail.com (F. Shirmohammadi).

Saeed Bahrami a, Morteza Madhkhan a, Fatemeh Shirmohammadi b,⇑, Nima Nazemi c

aDepartment of Civil Engineering, Isfahan University of Technology, Isfahan, IranbWalter P Moore and Associates Inc., Kansas City, MO, USAcDepartment of Civil Engineering, University of Memphis, Memphis, TN, USA

a r t i c l e i n f o

Article history:Received 10 April 2016Revised 24 November 2016Accepted 26 November 2016Available online 10 December 2016

Keywords:Finite elementsPrecast concreteEnergy dissipationLateral stiffnessDuctilityLateral resistance

a b s t r a c t

In this study, two new moment resisting connections of beams to precast concrete columns under lateralload were analyzed via application of nonlinear finite element analysis software ABAQUS 6.10. The pre-cast connections considered were the beam-column connections in which precast beams is connected tocontinuous precast column with corbel using (i) inverted E (bolted connection) and (ii) box section(welded connection). Connection responses associated with lateral resistance, lateral stiffness, ductility,and energy dissipation were compared to a reference monolithic connection. Achieved lateral resistance,lateral stiffness and ductility of the proposed connections was approximately 98%, 80% and 80% of theequivalent monolithic connection, respectively. The effect of axial load on column and compressivestrength of concrete on behavior of the connections were studied. The analytical results show that theperformance of two proposed precast connections were close to the performance of corresponding mono-lithic connection.

� 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Advantages of precast concretes have increased worldwideusage of precast concrete structures. Beam to column connectionsin frame systems affect significantly the constructability, stability,strength and flexibility of structure. Furthermore, connections playan important role in the dissipation of energy and redistribution ofloads as the structure is loaded. Also, the creation of totally rigidconnections of beams to columns in precast structures is very dif-ficult and time-consuming, there by negating advantages gainedusing precast features Studies have shown that if a semi rigid con-nection stiffness is more than 80% of an equivalent monolithic con-nection stiffness, seismic behavior of the system will notsignificant change [1]. Therefore, properly designed connectionscould develop expected mechanical features and demonstrate alow-cost fast-construction system for multi-storey buildings.

In 1987, the research anddevelopment departmentof the PrecastConcrete Institution (PCI) conducted a laboratory investigation of 16samples of precast connections (eight simple and eight momentresisting connections). The aim of the project was to obtain connec-tions behavior such as resistance, ductility, energy dissipation,

sustainability and economical performance [2]. In 1989, Dolan andPessiki created laboratory models with scales of one-half and con-ducted an analytical study of connection in order to demonstratethat a computer model can be an appropriate and acceptablemethod for analysis of precast concrete connectionbehavior [3]. Bulland Park created laboratory specimens in order to evaluate seismicbehavior of one type precastmoment resisting beam to column con-nection in New Zealand [4]. This connection was made by placing aU-shapedprecast concretebeamat the joint, and the connectionwascompleted using in situ concrete and slabs. The connection has beenused tomake frame structures with small height. They adopted for-mulations for connection design also. French et al. had looked intothe issue of moving the connections away from the column face[5]. In their research, the connections were relocated to the beamspan at a distance away from the column faces. The models com-prised a precast reinforced concrete column and a precast partiallyprestressed beam. With such a frame configuration, the beam-column joint core, in which the reinforcement details are compli-cated, can be prefabricated precisely under factory conditions. Thereinforcement continuity will further enhance the integrity of thejoint and prevent premature failure. Most importantly, the coincid-ing condition between the inherent plastic hinge locations and theconnection regions can be avoided. Also researchers such asRestrepo et al. and Khoo et al. proposed beam to beam connections[6,7]. The primary variable in the tests was the connection detail

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 809

between the beam and beam. For frames adopting mid-span beam-to-beam connections, Park noted that the precast components ofthis system can be very heavy and difficult to transport due to theirrelatively large dimensions. This transportation difficulty wouldthen hinder the choice of precasting the cruciform members forframes with long beams. Parastesh and Khaloo conducted experi-ments on one type precast concrete connections with a scale of 0.4under different bar ratio and stirrup distances in the beam. The pri-mary objective of their research was to develop moment resistantconnection of precast beam to precast column for zones with highseismicity. In these experiments, cruciform specimens were madeof continuous columns and beams that were separated. A gap wascreated in the columns to provide enough bearing area for sittingthe beams and transferring the construction loads before in-situconcrete becomes structural. The cross-section of the beams wasU-shaped at near connection, while the rest of cross-section wasrectangular. Forces resulting from flexure occurred due to overlap-ping of protruding bars from columns and beams buried within situ concrete [8,9]. The test results showed that the connectioncan be successfully designed and constructed to emulate cast-in-place construction. But, on site, the placement of the beams on col-umn need for using formwork and temporary vertical supports forthe beams. Shariatmadar and Zamani studied three interior precastconcrete connections and one monolithic reference connection(MO). In two proposed precast connections (PC1, PC2), columnwas discontinuous at connections. After placing the beams at theaxe of the column gap and entering the add-bars in beam and col-umn free gap, 100 mm top of precast beams, and free spaces of col-umn and beam were filled simultaneously with cast-in-placeconcrete. In the third connection (PC3), the column was continuousand the seated of the beamwas created by welding available pend-ing plates in the beams and column [10]. Fabrication of PC3 speci-men was easier from the other precast connection. Discontinuityof columns at each story level slowdown construction timeof build-ings of systems PC1 and PC2. Elliott et al. tested four semi rigid con-nections. Supports for beams are provided by means of steel corbelor solid section on each side of the columns which also transferredshear forces. The top bars passed from the columns and providedconnection continuity. This can lead to a low-cost fast-construction system formulti-storey buildings, wheremultiple sto-ries can be constructed at once. [11,12]. Connections were madeusing proprietary pinned jointed billet, cleat and welded plate con-nectors, to form cruciform assemblages subjected to sway and grav-ity load. They were not purposefully intended as moment resistingframe. In some cases 200 mm deep slab and high tensile reinforce-ment completed the connections. They reportedmoment resistanceand flexural stiffness gained from each of the connections. Alsoequationswere presented to calculate effective length factor for col-umn in semi rigid sway frame and percentage of rigidity of connec-tions. The Elliot et al. connections achieved 10–48%, and 8–40% ofstrength and stiffness of the corresponding monolithic connection,respectively. SAFECAST project, with the aim of validating multi-story precast concrete experimental models, performed 3 pseudodynamic seismic tests on full scale three story structural models.Hollow core section beams connected to column capitals servingas beams provided equivalent mechanical properties to that of T orI shape, offering economic advantage by increasing floor area. Con-nections are embedded inside the structural elements using steelconnectors and bolts. Finally, any remaining gaps are filled withgrout to finalize the process of forming the connection. Emulativebeam to column joints were reported to be satisfactory in terms ofstiffness and inter-story drift; yet, the structural responses differfrom a equivalent rigid joint and the connection behavior is catego-rized as semi-rigid [13,14]. Choi et al. performed experimental teston 4 precast beam to column assemblies and amonolithic assembly,in order to achieve structural continuity, high shear deformation

demand, strength, stiffness and drift requirements alongwith intro-ducing ease of erection and reliability [15]. Connectionswere simplyformed by connecting steel elements, embedded inside the struc-tural members that connect the beam and column using bolts; andfinally, fiber reinforced concrete in the joints slightly increase thetensile strength and shear toughness. Assemblies are laterallyloaded with reversing load pattern increasing the drift up to 5%. Interms of strength, connection were able to maintain over 75% ofthe strength at 3.5%. In connections where the plastic hinge wasdesigned to be away from the beam-column interface (Outsidetype), higher stiffness reduction was observed, while the connec-tions in which the plastic hinge location was near the column face(inside type) resembled more with the monolithic counterpart.The outside type, compared to other specimen, dissipated moreenergy and responded more ductile.

The presented manuscript provides the preliminary numericalstudy for proposing two new beam-to-column connections in pre-cast structures. The results of the presented study have been usedto construct 0.6-scale experimental specimens that are explainedin detail in Refs. [23] and [24]. As discussed in Ref. [24], the exper-imental results are in a good agreement with numerical resultspresented here. The proposed connections are designed not onlyto satisfy the required mechanical properties, but also minimizeconstruction time and labor work by providing simple constructionmethods. During the construction period, semi precast beams wereplaced on corbels, partly embedded inside the continuous columns.This will remove the need for shoring and temporary bracing tohold he precast unit in place and during the erection of the precastcomponents. Furthermore, the hidden corbel addresses the archi-tectural drawback of ordinary concrete corbels. These goals werealso among the objectives of SAFECAST project. The proposed con-nections in this study shows better performance in comparison toElliot connections, while not scarifying the ease of construction.

2. Proposed two precast connections and reference monolithicconnection

Design and performance of completely rigid connections in pre-cast concrete structures is difficult and time-consuming. For someconnections, the need for framing or large volumes of in-situ con-crete undermines the inherent beneficial features of prefabrica-tions. Therefore, the industry of precast concrete structures seeksconnections with easy quick installation that provide requiredmechanical features.

Two moment-resisting precast connections are proposed andtheir performance is assessed in the presented study. The mono-lithic reference specimen (MC) was designed for comparison thebehavior of cast-in-place connection with precast connections.

Fig. 1 illustrates details of the interiormoment-resisting connec-tions for precast concrete frames before cast-in-place concreting. Inboth proposed connection systems, the prefabricated concrete col-umns are cast continuously in elevation with steel corbel embed-ded in the connection core to connect beam elements. Fourvertical bars are welded to the corbel in the connection zone ofthe precast columns to provide adequate shear strength and stabil-ity during the installation and prevent the slip of corbel during lat-eral loading. The steel corbel provide enough bearing area for sittingthe precast concrete beams and transferring the construction loadsbefore in-situ concrete becomes structural. Consequently, in theproposed systems, there is no need for using formwork and tempo-rary vertical supports for beam and slab elements. This can lead to alow-cost fast-construction system for multi-storey buildings,where multiple stories can be constructed at once.

In both connections, the precast beam is placed on the steelcorbel, and steel bars below the beam were connected to the steel

Fig. 1. Schematic interior precast connection.

810 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

corbel using bolts or welding and provide continuity. Two top con-tinuous bars of beams passed through the holes in the columns anddevelop negative moment. Cast-in-place concreting provides con-nection continuity. More details on of the two proposed connec-tions are provided in the following sections.

2.1. First precast connection (Specimen PC-1)

In the first proposed precast connection (PC-1), the precast con-crete beam was placed on the embedded steel corbel in the contin-

(a)Precast column

(c)Beam to column connection before

(d) precast beam to continuou

Fig. 2. Connection schema of first pre

uous column, and bottom threaded bars of the beam weretightened between the grooves of the corbel by two nuts and steelgaskets with thicknesses of 10 mm. The empty space of the con-nection area was filled with expandable grout. After grouting,two top bars were passed through two holes in the column. Thoseholes were also grouted, and the connection was completed by slabconcreting. The schematic of this connection is illustrated in. Thedetails of the first beam-to-column connection is shown in Figs. 2and 3.

(b)Precast beam

and after installation using two bolts

s column after installation

cast connection (specimen PC-1).

Fig. 3. Beam to column connection details of specimen PC-1.

Fig. 4. Beam to column connection details of specimen PC-2.

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 811

812 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

2.2. Second precast connection (Specimen PC-2)

In the second proposed connection (PC-2), a steel box section ofsize 120 � 120 � 10 mm embedded in the column was used as acorbel to connect the beam and joint core. Bars below the beamtransferred their force to columns through welding to a channelcross-section and then through channel-shaped welding to corbel.The connection details and schematic of the specimen PC-2 areshown in Figs. 4 and 5, respectively. A steel box section of size150 � 150 � 12 mm embedded in the column projects a distanceof 150 mm from the column face, was used as a corbel to connectthe beam and joint core. An inverted channel section with 12 mmthickness, 100 mm depth and length of 300 mm that 180 mmlength of it embedded into beam end, anchored into beam by weld-ing of Bottom longitudinal rebars on each flange. Length of afore-mentioned rebars and welding length were 2350 mm and130 mm, respectively. On site, the precast beams were seated onthe box section in each side of the column. After adjustment ofbeams on corbel, the channel flanges of the beams were weldedto the webs of corbel at both site. In fact positive moment musthave been transferred between beam and column by weldingrebars to plates and steel plates together. Then top rebars of beamswith length of 4900 mm were passed through the pending stirrupof the beams and two holes in the column. Those holes weregrouted and free spaces on top of the beams and between precastelements were filled with cast-in-place concrete. All the reinforce-ment and tensile strength and the concrete compressive strengthin PC-2 were equal to those of PC-1. This connection ensured thecontinuity of the beams bottom reinforcement without any lapsplicing of reinforcement.

After welding the channel to the box, the empty space was filledwith expandable high-strength grout, completing the connection.Similar to the previous connection, two bars with diameters of25 mm were passed from the columns, then the holes were filledwith grout, and connection was completed by slab concreting.

(a) Precast column (

(c) Welding of inverted chann

Fig. 5. Schematic of second precas

2.3. Monolithic reference connection (Specimen MC)

For comparing the result a cast-in-place a monolithic referenceconnection (specimenMC) was designed and modeled according toACI 318-2008. The beam section was 400 mm by 500 mm, the col-umn section was 400 mm by 400 mm, longitudinal top bar andbottom bar of beams and columns exactly were similar to speci-mens PC-1 and PC-2. The specimens were designed according tothe strong column - weak beam design concept so that the inelasticdamage of the column did not occur. The beam span was 5.0 m andthe height of the column was 3.0 m.

3. Loading and boundary conditions

The two proposed PC-1 and PC-2 connections and monolithicconnection MC were loaded in lateral form and constant axial forceon the column. The lateral force was applied to the system step bystep to specimens fail in positive direction or negative direction.The column was supported by pined connection at its base and freeon top. Roller supported was modeled to end of beams. Variousaxial loads was applied to the columns at each specimens. Theboundary conditions of specimens are shown in Fig. 6.

4. Numerical modeling

4.1. Material properties

To model the behavior of the two proposed moment-resistingconnections a finite element model was developed using ABAQUSsoftware. The beams have 400 � 500 mm rectangular cross-section and 2.5 m length. The columns have square cross-sectionwith dimensions of 400 mm. The longitudinal reinforcement ofthe beam and column was deformed bars of Grade 420, whilethe beam stirrups and column transverse ties were applied with

b) Precast beam-to-column connection

el section to corbel

t connection (specimen PC-2).

Fig. 6. Boundary condition and loading of specimens.

Fig. 7. Proposed stress-strain model for reinforcing steel by Mander et al. [20,21].

Fig. 9. Elliot et al. welded connection [12].

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 813

Grade 300 bars. The compressive strength of concrete and groutused for all specimens was 25 and 45 MPa respectively. Steelplates, U sections, and box sections used in the constructions wereof st 37 with f y ¼ 240 MPa and f u ¼ 360 MPa in which f y and f u are

Fig. 8. Modelling of bottom bar connection to the corb

yield and ultimate strengths respectively. The weld material is ofE60 electrode having as strengths f y ¼ 350 MPa andf u ¼ 430 MPa. Modulus of elasticity and Poisson’s ratio are consid-ered as 200 GPa and 0.3 for steel and 24 GPa and 0.2 for concrete,respectively.

Concrete material is modeled with ABAQUS predefined concretedamage plasticity. In this approach, damage parameter is definedas a function of strain, providing a multiplier that reduces the mod-ulus of elasticity as more stress, and consequently strain, is intro-duced. Damage parameter is separately defined for tension andcompression. For the elastic portion of the concrete deformations,

modulus of elasticity is considered to be 4700ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffif 0cðMPaÞ

qsuggested

by ACI-318-2011 [16]. The constitutive relationships, i.e. the stress

le using coupling nodal forces at PC-1 specimen.

Fig. 10. Mesh of connection TW1-C.

Fig. 11. Cracking distribution in numerical model compared to the experimental specimen connection TW1-C.

yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120

Late

ral L

oad

(kN

)

Displacement (mm)

MCPC-1PC-2

Fig. 13. Lateral load-displacement and energy dissipation c

0

25

50

75

100

0 0.0025 0.005 0.0075 0.01

Con

nect

or M

omen

t (kN

.m)

Relative Rotation (rad)

AnalyticalTW1-C__BM2

Fig. 12. Moment-relative rotation curve of Elliot et al. connection TW1-C [11].

814 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

strain relationship, in the nonlinear part is defined by modifiedHognestad quadratic curve. This constitutive stress-strain modelconsiders two major mechanisms of rupture in concrete materials:(a) tensile cracking and (b) compressive fracture. The compressivebehavior has a parabolic function up to the maximum compressivestress. After ultimate compressive point, the post cracking behav-ior is taken into account by specifying a post linear stress-strainrelation up to the maximum strain. The tensile behavior is linearinitially followed by a strain softening after the ultimate tensilepoint.

Modeling the cracks in the concrete material due to its rapiddevelopment is more difficult its observation in controlled envi-ronment is nearly impossible. Thus, a few assumptions are made;

up to f r ¼ 0:7ffiffiffiffif 0c

q, which is the modulus of rupture, concrete

noitapissidygrenE)b(

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Dis

sipa

ted

Ener

gy (k

N.m

)

Displacement (mm)

MCPC-1PC-2

urves of specimens under compressive load of 0:2f 0cAg .

noitapissidygrenE)b(yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120

Lat

eral

Loa

d (

kN)

Displacement (mm)

MCPC-1PC-2

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120

Dis

sipa

ted

Ene

rgy

(kN

.m)

Displacement (mm)

MCPC-1PC-2

Fig. 14. Lateral load-displacement and energy dissipation response of specimens under compressive load of 0:5f 0cAg .

noitapissidygrenE)b(yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

Late

ral L

oad

(kN

)

Displacement (mm)

MCPC-1PC-2

0

2

4

6

8

10

0 20 40 60 80 100 120

Dis

sipa

ted

Ener

gy (k

N.m

)

Displacement (mm)

MCPC-1PC-2

Fig. 15. Lateral load and energy dissipation versus displacement of specimens under tensile load of 0:5f yAs .

Fig. 16. Cracking distribution in specimen PC-1 under compressive axial force of 0:2f 0cAg at drift 1%.

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 815

816 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

responds with the same manner as in compression; howeverYoung’s modulus in tension and compression, due to presence ofmicrocracks is slightly different, but it is neglected for the sake ofsimplicity. Beyond the strain corresponding to fr, stress is assumedto be linearly decreasing with strain, up to approximately 10–12times the rupture strain.

The monotonic behavior of longitudinal steel was modeledusing Mander et al. model [20]. The model of Mander et al.(1984) was developed as a result of many tension and compressioncoupon tests. This model, which takes into account elastic behav-ior, yield plateau, and strain hardening of steel material, has threemain regions, as shown in Fig. 7. The first region is a linear functionwith slope equal to steel’s modulus of elasticity; the region ends atthe yield point with stress equal to yield stress of steel. The secondregion simulates yield plateau, and the third region is an ascendingcurve up to the maximum strength of steel, simulating the strain

Fig. 17. Cracking distribution in specimen PC-2 und

Fig. 18. Cracking distribution in specimen PC-1 und

hardening region of steel behavior. The post-ultimate stress regionis not considered in the Mander et al. model [21].

4.2. Finite element modeling

It is possible to more thoroughly evaluate the stresses anddeformations in a structure using the FE analysis than can be doneexperimentally. The nonlinear analysis results in a better its load-ing to fracture. In the present study, the specimens were analyzedusing the ABAQUS software. Three-dimensional (3D) elementswere applied to simulate the concrete and steel plates, while rein-forcing bars were modeled as truss elements. ABAQUS 6.10 pro-vides 6 types of three-dimensional (3D) stress/displacementelements for modeling concrete, including the 4-node linear tetra-hedron, the 6-node linear triangular prism, the 8-node linear brick,the 10-node quadratic tetrahedron, the 15-node quadratic triangle

er compressive axial force of 0:2f 0cAg at drift 1%.

er compressive axial force of 0:5f 0cAg at drift 1%.

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 817

and the 20-node quadratic brick. To cover the concrete behavioralproperties and minimizing problematic convergence of 3D models,the 8-node linear brick element, titled C3D8R was chosen for 3Dmodeling. The suffix ‘‘R” at the title of the element indicates thereduction of integration points to decrease the required run time.This element has three degree of freedom at each node.

In ABAQUS, rebar can be specified as smeared layers in mem-brane, shell, or surface elements or they can be included in contin-uum elements by embedding rebar surface or membrane elementsinto continuum element. Here, steel bars were modeled by trusselements and interaction between bars and concrete were speci-fied using embedded capability in the software. This displacementcapability interpolates the node related to the bar, with the noderelated to the concrete element. This feature can simulate theinteraction of rebar and concrete to an acceptable limitation [17].In connection PC1, tensile force from the bottom bars are trans-ferred to the corbel via a nuts and a circular annulus plate. In themodel, the far end node of the bar is coupled to the face of an annu-

Fig. 19. Cracking distribution in specimen PC-2 unde

Fig. 20. Cracking distribution in specimen PC-1 u

lus object, so that the sum of the forces on the annulus plate isequal to the force of the bar. The plate is in contact with the innerface of the corbel to transmit the forces. Fig. 8, schematically,shows the coupling of the nodes on the plate face and the bar.Adhesion between concrete surfaces with steel sheets and surfacesbetween precast and in situ concretes was disregarded as insignif-icant. Only tangential behavior between surfaces was taken intoaccount. The average effective coefficient of static friction variedbetween concrete surfaces was 0.57 for dry interface to 0.7 forwet interface [18,19]. Proposed friction between the steel and con-crete surfaces was 0.7.

Welds connections in steel parts of the connection are modeled3 dimensionally in order to observe the stresses in the welds. Thisgives us the advantage of observing the stress in welds and adjust-ing the sizes and locations in order to minimize the stress concen-tration. Concrete to concrete or steel interfaces are considered tointeract only tangentially, since the normal contact strength isreasonably small. The concrete element was the linear 8-node

r compressive axial force of 0:5f 0cAg at drift 1%.

nder tensile axial force of 0:5f yAs at drift 1%.

0

5000

10000

15000

20000

Lat

eral

stif

fnes

s (k

N/m

) MC PC-1 PC-2

818 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

element with dimensions of 15 mm. Elements related to lineartwo-point rebar with dimensions measuring less than half of theconcrete element were also considered. Numerical integrationused in the software was the Gauss method, and the method ofnonlinear system solution of the software was the Newton Raph-son method. A maximum limit of 50 iterations was used for theconvergence and the tolerance was taken as 0.002. From the anal-yses it was observed that the convergence generally occurred inless than 7 iterations. Initial investigations on some specimensshowed the effect of geometric nonlinearity did not much varythe results since extremely large displacements did not occur.Hence, the geometric nonlinearity was neglected in the analysis.

0.2Agf'c 0.5Agf'c 0.5Asfy

Axial Load

Fig. 22. Lateral stiffness of specimens under various axial loads.

100

125

150

175

0.2Agf'c 0.5Agf'c 0.5Asfy

Max

imum

Lat

eral

Loa

d (k

N)

Axial Load

MC PC-1 PC-2

Fig. 23. Lateral resistance Capacity of beams under various axial load levels.

5. Verification of modeling

For verification of the developed finite element model, theElliott et al.’s welded plate connection (Fig. 9) was analyzed[11,12]. In a proposed Elliott et al. connection, the narrow mildsteel plate by 25 mm thick, 500 mm long and 100 mm deep wasanchored in the beam by welding two bent bars on each side ofthe plate. A solid section 100 � 100 mm cast into column projectsa distance of 90 mm from the beam bottom. The level of the billettop was at 190 mm from the bottom of the beam. After a doublesided fillet site weld was made to the narrow plate, 80 mm longand 20 mm thickness, a structural grade cast in situ infill concrete,completed the joint at the end of the beam (TW1-C). The centroidof the weld was therefore at 200 mm from the beam bottom. Theconnection contains two precast-insitu interfaces as indicated inFig. 9. Vertical load using hand pumped hydraulic jacks on precastbeam end were applied incrementally. Beam to column rotationswere measured using four linear displacement transducers asknown distances from the column face. The slope of vertical loadvs displacement graph measured at 90–300 mm from the columnface. For verification, a total of 4700 C3D8R elements and 2300T3D3 elements each with a size of about 30 and 15 mm, respec-tively, were used in the FE model (Fig. 10). Cracking distributionin analytical model and the Elliott et al.’s specimen’s cracking pat-tern are shown in Fig. 11. As it can be seen in Fig. 11, Shear crack,compressive cracks and gap opening at the top of beam to columnface under vertical load at experimental observation wereobserved at analytical model. The monotonic force-displacementcurve was obtained after applying the monotonic loading

Fig. 21. Cracking distribution in specimen PC-2 u

sequence. Fig. 12 shows the numerical and experimental connectormoment vs relative rotation graph of Elliot et al. connection TW1-C. In comparison with the resulted from the testing program, theanalytical model offers a good result. The two curves almost over-lap over the elastic region and nearby the maximum displacement.The face column moment that correspond to the maximum driftdiffer by only 1.69 kN m. Moreover, the analytical model sharesalmost the same initial stiffness as the testing specimen, the differ-

nder tensile axial force of 0:5f yAs at drift 1%.

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 819

ences being lower than 3.5%. In general, however, the comparisonof the numerical results with the experimental data shows that thenumerical model could capture quite accurately the overall behav-ior of the beam-to-column connection and the distribution of theforces along the connection bars.

6. Modeling results

The lateral force was applied to the column top step by stepuntil the specimen fails. The ultimate lateral displacement of thecolumn is defined to be corresponding to bar fracture or bar slip-

Table 1Numerical results from FE model.

Specimen Axial load Pmax (kN) dy (mm) du (m

MC �0:2f 0cAg 145 14 104PC-1 144 16 89PC-2 145 14.5 92

MC 163 14.5 103PC-1 �0:5f 0cAg 161 16 87

PC-2 158 14.5 90

MC 118 17.5 101PC-1 0:5f yAs 120 18.5 86PC-2 118 18.5 86

yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120

Late

ral L

oad

(kN

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

Fig. 24. (a) Lateral load and energy dissipation versus disp

yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100

Late

ral L

oad

(kN

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

Fig. 25. (a) Lateral load and energy dissipation versus displ

page or compressive concrete strain reaching ultimate strain ofconcrete.

Figs. 13 and 14 show load-displacement curves and energy dis-sipation of the connections under compressive axial load of 0:2f 0cAg

and 0:5f 0cAg , respectively. According to this figures, the ultimatedisplacement of monolithic concrete is greater than the ultimatedisplacement of precast connections. Energy dissipation of the sys-tem is equal to the area under the load-displacement graph.Results indicated that lateral strength and energy dissipation ofthe specimens improved when the axial load of the columnincreased. As shown in Fig. 15 changing compression load of

m)) l S PmaxPMC

lmaxlMC

SSMC

7.4 15,480 1 1 15.6 12,627 0.99 0.75 0.816.3 13,625 1 0.85 0.88

7.1 17,543 1 1 15.4 14,042 0.99 0.75 0.80

6.2 14,130 1 0.97 0.81

5.8 9600 1 1 14.6 9087 1.02 0.80 0.954.6 9407 1 0.80 0.98

noitapissidygrenE)b(

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120

Dis

sipa

ted

Ener

gy (k

N.m

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

lacement of specimen MC under axial load of 0:2f 0cAg .

noitapissidygrenE)b(

0

2

4

6

8

10

12

0 20 40 60 80 100

Dis

sipa

ted

Ener

gy (k

N.m

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

acement of specimen PC-1 under axial load of 0:2f 0cAg .

noitapissidygrenE)b(yticapacdaollaretaL)a(

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100

Late

ral L

oad

(kN

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Dis

sipa

ted

Ener

gy (k

N.m

)

Displacement (mm)

fc=25 MPafc=30 MPafc=35 MPa

Fig. 26. (a) Lateral load and energy dissipation versus displacement of specimen PC-2 under axial load of 0:2f 0cAg .

820 S. Bahrami et al. / Engineering Structures 132 (2017) 808–821

0:2f 0cAg to tensile load of 0:5Asf y significantly decreased the lateralresistance, energy dissipation and ultimate deformation capacityby 22%, 32% and 7%, respectively.

The first flexural cracks were observed in the beam at 0.25%drift ratio in all the specimens and flexural yielding occurred ataround 1.0% drift level. The cracking distribution in specimensPC-1 and PC-2 under lateral load and compressive axial force of0:2f 0cAg , 0:5f

0cAg and tensile axial force of 0:5Asf y on column are

plotted in Figs. 16–21, respectively.Figs. 16 and 17 show the crack development in PC-1 and PC-2

specimens, respectively under compression load of. 0:2f 0cAg .Although, the strength of the specimen PC-1 reached its yield load,flexural cracks did not significantly propagate in the beam. Thisresult indicates that the yielding of the longitudinal rebars in thebeam concentrate to the beam-corbel joint. In PC-2, more flexuralcracks at bottom of beam at vicinity of beam-corbel joint can bedeveloped.

Crack distribution in PC-1 and PC-2 specimens under compres-sion load of. 0:5f 0cAg (Figs. 18 and 19) are very similar to the corre-sponding specimen under axial load of 0:2f 0cAg . Increasingcompressive axial load decreases the tensile stress of the beam-column connection. The longitudinal reinforcement of the columnyields before beam’s reinforcement. The deformation capacity andflexural strength of the connection is decreased, consequently.

Initial lateral stiffness (S) of the connection is equal to the initialslope of load-displacement curve. The changes in elastic stiffnessand maximum lateral resistance of connections are shown inFigs. 22 and 23, respectively. As it can be seen in Fig. 22, the initialstiffness of the monolithic concrete is greater than the precast con-nections. Increasing the compression axial load, the initial stiffnessdecreases and increasing the tensile axial force results in decreasein initial stiffness.

The displacement ductility factor (l) is the ratio of the ultimatedeformation (Du) to the initial yield deformation (Dy). It is not easyto determine yield points for the specimens directly from the lat-eral load-displacement curves. For each specimen, the load-displacement curve was used to define the yield and maximumdisplacements according to Park’s criteria [22] for equivalentelastoplastic energy absorption. Maximum lateral strength (Pmax),yield and ultimate displacement, initial stiffness and displacementductility factor of the precast connections to the monolithic refer-ence connection under various axial load levels on column arecompared in Table 1. Results show the new proposed specimenscan gain at least 99%, 80% and 75% of the Maximum lateralstrength, initial stiffness and displacement ductility factor of themonolithic reference specimen, respectively.

The effect of concrete compressive strength on the seismicbehavior of the connections were investigated. In Figs. 24–26load-displacement curve of specimens MC, PC-1 and PC-2 are plot-ted under various concrete compressive strength when the columnin under 0:2f 0cAg compression axial load. As these figures, increas-ing the compressive strength of concrete from 25 MPa to 35 MPa(40% increase), lateral strength, ultimate displacement and energydissipation capacity of the specimens increase only 2%, 3% and 4%respectively. However, the initial stiffness did not changed.

7. Conclusion

The present study investigated the performance of two pro-posed precast connections of precast beam to column connections.The proposed connections were analyzed under lateral load andvarious levels of axial force using nonlinear finite element modeldeveloped using ABAQUS. The following conclusions were drawnfrom this study:

� According to axial load of columns, the proposed connectionsshowed lateral resistance between 120 and 167 kN, about 98%of lateral resistance of the reference monolithic connection ineach level of axial load.

� Stiffness ratio of the precast connections to monolithic connec-tions ranged between 0.8 and 0.9 depending on the axial loadlevel of the column.

� The difference of lateral stiffness and resistance of the proposedconnections compared to an reference monolithic connectioncould be attributed to the difference of force transfer mecha-nism and position of the connection source (corbel presence,manner of force transfer of bars, grouted connection source,etc.).

� Ductility and energy dissipation of the proposed connectionswere measured at approximately70–80 percent of an equiva-lent monolithic connection. The final strain standard for theend of the analysis was considered to be 0.0038.

� Lateral stiffness, ductility, and energy dissipation of the connec-tions increased with increased compressive load of the column;however, sensitivity of the precast connections was less thanthe monolithic connections.

� Connections weakened when tensile load was applied. There-fore, the decreasing effect of tensile load should be consideredwhen designing structures and their connections.

� Increasing the compressive strength of concrete results inhigher ultimate displacement, lateral resistance and energy dis-sipation of connections.

S. Bahrami et al. / Engineering Structures 132 (2017) 808–821 821

� Regardless of the limitations of software ABAQUS, it can simu-late the mechanical behavior of concrete materials. Althoughmodeling many parameters in the software is not possible,study results offered an appropriate and acceptable estimationof the proposed connections behavior.

References

[1] Sucuoglu H. Effect of connection rigidity on seismic response of precastconcrete frames. PCI J 1995;40(1):94–103.

[2] Dolan CW, Stanton JF, Anderson RG. Moment resistant connections and simpleconnections. PCI J 1987;32(2):62–74.

[3] Dolan CW, Pessiki SP. Model testing of precast concrete connections. PCI J1989;34(2):84–103.

[4] Bull DK, Park R. Seismic resistance of frames incorporating precast prestressedconcrete beam shells. PCI J 1986;31(4):54–93.

[5] French CW, Amu O, Tarzikhan C. Connections between precast elements-failure outside connection region. J Struct Eng 1989;115(2):316–40.

[6] Restrepo JI, Park R, Buchanan AH. Tests on connections of earthquake resistingprecast reinforced concrete perimeter frames of buildings. PCI J 1995;40(4):44–61.

[7] Khoo JH, Li B, Yip WK. Tests on precast concrete frames with connectionsconstructed away from column faces. ACI Struct J 2006;103(3):18–27.

[8] Khaloo AR, Parastesh H. Cyclic loading response of simple moment-resistingprecast concrete beam-column connection. ACI Struct J 2003;100(4).

[9] Parastesh H, Hajirasouliha I, Ramezani R. A new ductile moment-resistingconnection for precast concrete frames in seismic regions: an experimentalinvestigation. Eng Struct 2014;70:144–57.

[10] Shariatmadar H. An investigation of seismic response of precast concrete beamto column connections: experimental study. Asian J Civ Eng-Build Housing2014;15(6):849–67.

[11] Elliot K, Davies G, Ferreira M, Gorgun H, Mahdi AA. Can precast Concretestructures be designed as semi-rigid frames? Part 1-The ExperimentalEvidence. Struct Eng 2003;81(16):14–27.

[12] Görgün H. Semi-rigid behavior of connections in precast concrete structures.Doctoral dissertation. University of Nottingham, Department of CivilEngineering; 1997.

[13] Negro P. Pseudodynamic tests on a full-scale 3-storey precast concretebuilding: global response. Eng Struct 2013;57:594–608.

[14] Dionysios A. Pseudodynamic tests on a full-scale 3-storey precast concretebuilding: behavior of the mechanical connections and floor diaphragms. EngStruct 2013;57:609–27.

[15] Choi H. Development and testing of precast concrete beam-to-columnconnections. Eng Struct 2013;56:1820–35.

[16] ACI Committee. Building code requirements for reinforced concrete andcommentary, ACI 318–11/ACI 318R-11. Detroit: American Concrete Institute;2011.

[17] ABAQUS (2010)/Theory Manual 6.10.[18] Rabbat BG, Russell HG. Friction coefficient of steel on concrete or grout. J Struct

Eng 1985;111(3):505–15.[19] Lee YH, Joo YT, Lee T, Ha DH. Mechanical properties of constitutive parameters

in steel–concrete interface. Eng Struct 2011;33(4):1277–90.[20] Mander JB, Priestley MJN, Park R. Seismic design of bridge piers, University of

Canterbury, New Zealand. Res Rep 1984;84(2).[21] Shirmohammadi F. Effect of load pattern and history on performance of

reinforced concrete columns. Doctoral dissertation. Kansas State University;2015.

[22] Park R. Evaluation of ductility of structures and structural assemblages fromlaboratory testing. Bull New Zealand Nat Soc Earthq Eng 1989;22(3):155–66.

[23] Bahrami S, Madhkhan M. Behavior under cyclic loading of a new momentresisting beam to continuous column connection for precast structures. PCI J2016 [submitted for publication].

[24] Bahrami S, Madhkhan M. Experimental performance of a new precast beam tocolumn connection using hidden corbel. Asian J Civ Eng 2016 [submitted forpublication].

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