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Engineering Structures

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Seismic performance of self-centering precast segmental bridge columnsunder different lateral loading directionsJunfeng Jiaa, Kaidi Zhanga, Suiwen Wub,⁎, Yang Guoc, Xiuli Dua, Xu Wangda Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, ChinabDepartment of Civil and Environmental Engineering, University of Nevada, Reno, USAc The Beijing Urban Construction Road & Bridge Group Co., Ltd., Beijing, Chinad School of Civil Engineering, Chongqing Jiaotong University, Chongqing, China

A R T I C L E I N F O

Keywords:Self-centering precast segmental bridge columnAccelerated bridge constructionCyclic testDifferent lateral loading directionsSeismic performance

A B S T R A C T

Self-centering precast segmental bridge columns (SC-PSBCs) have been intensively investigated in the pastdecade as one of prefabricated bridge components to expedite construction and improve seismic resilience.However, the application of SC-PSBCs is limited to the low seismicity areas due to insufficient knowledge abouttheir seismic performance. In particular, the behavior of SC-PSBCs is not clear under multi-directional seismicexcitations. In order to investigate the effect of lateral loading directions on the seismic performance of SC-PSBCs, five 1/10-scale identical SC-PSBC specimens with rectangular hollow sections were designed and testedunder lateral cyclic loading and a constant vertical load. Each specimen was loaded at a specific angle withrespect to the weak axis of the column section. The loading angles included 0, 30, 45, 60, and 90 degrees. Theseismic performance of the specimens was evaluated and discussed using the test results. It was found that theSC-PSBC specimens were of good ductility, and the favorable self-centering capacity was obtained under or-thogonal loading directions. Only considering the orthogonal loading direction in the design of SC-PSBCs is non-conservative since it may underestimate the local damage and residual displacement. The extent of prestress lossin each strand was very sensitive to the relative distance to the neutral axis depending on the loading directions.The equivalent viscous damping ratios of SC-PSBCs were in the range from 0.151 to 0.198 at a drift ratio of 4.0%.

1. Introduction

Accelerated bridge construction (ABC) has many advantages overthe conventional bridge construction methods, such as improved siteconstructability and work-zone safety, enhanced material quality andproduct durability, reduced onsite construction time and traffic im-pacts, and minimized environmental impacts [1,2]. Precast segmentalbridge columns (PSBCs) are frequently investigated and used in en-gineering practice as a vital component of precast bridge componentsand structures. However, their applications are still limited to lowseismicity areas due to insufficient knowledge of their seismic perfor-mance. In recent years, seismic resilience of infrastructures becomes apromising trend for earthquake resistance all over the world [3,4].According to related literatures, seismic resilience of bridge structuresis defined as the ability of bridge structures to reduce the chances of asevere earthquake, to absorb a shock if it occurs and to recover quicklyafterwards [5,6]. In order to combine the concept of seismic resiliencewith the ABC technology, the self-centering precast segmental bridgecolumns (SC-PSBCs) are frequently designed, where PSBCs are used

along with unbonded post-tensioning (PT) tendons. Extensive researchworks have been carried out on the constructability and seismic beha-vior of the SC-PSBCs [7–11]. Previous studies showed that the hys-teretic loops of the SC-PSBCs are of flag-shape, which will produce asmaller residual displacement but result in lower energy dissipation(ED) capacity after a severe earthquake when compared with the con-ventional monolithic columns.

The ED capacity is of importance for the SC-PSBCs. The most pop-ular countermeasure to improve the ED capacity of the SC-PSBCs is toadopt metallic yielding components or devices between adjacent seg-ments of the columns. The main ED components include mild steel bars[12–15], high-strength steel bars [16–18], shape memory alloy (SMA)bars [9,19,20], and exterior yielding devices [21]. Meanwhile, highperformance materials are usually adopted at the base of the columns toalleviate the local damage. These materials include steel or FRP tubes/jackets [22–24], fiber-reinforced concrete, engineering cementitiousconcrete (ECC) [25,26], and ultra-high performance concrete (UHPC)[15,27]. Other researchers chose to incorporate the elastomeric bearingpads into the base segment of the SC-PSBCs, which had been shown

https://doi.org/10.1016/j.engstruct.2020.111037Received 17 February 2020; Received in revised form 30 May 2020; Accepted 29 June 2020

⁎ Corresponding author.

Engineering Structures 221 (2020) 111037

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efficient in alleviating the local damage through shake table andpseudo-static experiments, and theoretical analysis [23,26].

It is noted that most of the previous studies focused on the seismicperformance of the SC-PSBCs under the unidirectional loading alongone of the principal axes of the column section. In fact, the bridgecolumns and structural systems are subjected to lateral loadings inbiaxial directions during an earthquake event due to the nature ofearthquakes. Therefore, it is essential to evaluate the effect of multi-directional loading on seismic performance of the bridge columns todevelop more reliable design procedure. Considerable progress hasbeen made on the effect of biaxial loading on the seismic performanceof monolithic columns over the last three decades [28–34]. They con-cluded that the biaxial loading tended to reduce the lateral strength,stiffness and ultimate ductility, and the reduction quantity was morepronounced in rectangular columns. In addition, the influence of thebiaxial loading path on the strength degradation was more significant inthe quadrangular path. Various loading paths were proposed and ap-plied laterally to investigate the effect of the biaxial loading. For ex-ample, Goto et al. tested four steel columns, in which three columnswere subjected to the biaxial cyclic loading with a circular loading pathand the other one was subjected to the uniaxial cyclic loading as a re-ference [35]. They found that the biaxial loading expedited the localbuckling and reduced the strength and ductility of these columns. Ucaket al. developed detailed numerical models to investigate the effect ofloading path on the behavior of the thin wall steel columns [32]. It wasfound that the bi-directional loading with different load paths willsignificantly decrease the ductility and energy dissipation capacity.Rodrigues et al. performed a series of tests on columns under biaxialloadings with different loading paths. The test results showed that theseismic performance of rectangular RC columns under biaxial loadingswere highly dependent on the loading paths [33,36,37]. Khaled et al.[38] performed bidirectional cyclic testing on reinforced-concrete rec-tangular bridge columns. The bidirectional cyclic displacement testprotocols with a “butterfly-shape” path were developed based on theresults of nonlinear time-history analysis of the bridge prototypes underspecific earthquakes. Although the bidirectional loading mode canrealize the actual displacement traces of bridges under earthquakes, ithas to be performed by complicated apparatus with a low-efficientloading process.

In recent years, some scholars proposed the unidirectional obliquelateral loading instead of the complicated bidirectional loading process[39,40]. The purpose of this measure was to improve the loading effi-cient and impose the effect of bidirectional loading to the maximumextent. Pham and Li [39] investigated experimentally and numericallyseismic behavior of reinforced columns under different lateral loadingdirections. It was found that the direction of seismic loads had a sig-nificant effect on the drift capacities and failure modes of both rec-tangular and square columns. Germano et al. [40] tested sixteen full-scale cantilever columns under lateral displacement loadings to verifythe effectiveness of steel fiber reinforced concrete on seismic perfor-mance of RC columns. In their study, the load was applied with respectto one of the principal axes of the column section at 0° and 45°, asuniaxial and biaxial loading, respectively. They found that the biaxialload was a more severe load condition than the uniaxial one, which hadlower ultimate displacement capacity, smaller ductility and less energydissipation.

To date, critical review reveals that most of the previous in-vestigations focused on the seismic performance of the SC-PSBCs underuniaxial loadings along the principal axes of the column section. Verylimited numerical and experimental studies were performed underbiaxial loadings. Marriott et al. [41] tested a post-tensioned precastbridge pier with external replaceable mild-steel dissipaters and amonolithic pier under biaxial loading, and the response caused bybiaxial loading was compared with that due to uniaxial testing ofidentical bridge piers to study the influence of biaxial loading. Theresults showed that the overall structural performance of two bridge

piers under biaxial loading is significantly reduced when comparedwith unxiaxial loading. Mashal et al. [42] experimentally investigatedthe seismic performance of four half-scale precast segmental bridgepiers under uniaxial and biaxial quasi-stastic cyclic loading. It wasshown that specimens perform in a similar manner that would be ex-pected from a monolithic connection. Ichikawa et al. [43] tested thebridge columns of UHPC segments at the plastic hinge region under anorbital bilateral cyclic loading to investigate the torsion of the columns.It was found that the bilateral loading could cause significant torsionbehavior of the bridge columns. Li et al. [44] numerically investigatedthe seismic performance of the precast concrete-filled circular steel tubesegmental columns under biaxial lateral cyclic loadings. They con-cluded that the biaxial cyclic loading paths could significantly influencethe strength, ductility and energy dissipation of the columns. In addi-tion, it was found that the biaxial cyclic loading could impose sig-nificantly larger residual displacement to the segmental columns thanthe uniaxial cyclic loading. Li et al. [45] carried out shake table tests ona precast segmental concrete column under bidirectional excitations. Inaddition, a cast-in-place monolithic column was tested as a reference.The results showed that significant twisting was observed in the seg-mental column under the bidirectional motions.

In this study, five 1/10-scale identical SC-PSBC specimens weredesigned and tested under different lateral cyclic loading directions toconsider the effect of biaxial seismic excitations. Each specimen wasloaded at a specific angle to the weak axis of the cross section. Theangles were 0, 30, 45, 60, and 90 degrees. The seismic behavior of theSC-PSBC specimens under different lateral loading directions wasevaluated and compared in detail in terms of the damage patterns,hysteretic curves, strength degradation, P-Δ effect, residual displace-ment, energy dissipation capacity, post-tensioned prestressing force andjoint opening.

2. Design concept of the SC-PSBCs

In 1993, the concept of the self-centering precast system was firstproposed in the PRESSS project for the precast beam-column concreteconnections [46,47]. Hewes and Priestley [20] introduced self-cen-tering concept to the unbonded post-tensioned precast concrete seg-mental bridge columns. Ou et al. [12] applied precast hybrid system tosegmental precast concrete columns with hollow cross sections, wheremany precast joints were present. The precast hybrid system is acombination of unbonded post-tensioning tendons and energy dissipa-tion bars across the joints between precast segments. The self-centeringmoment at each critical joint section from the posttensioning force andgravity load is designed to be higher than the moment from the energydissipation bars or devices. As a result, a “flag-shape” hysteretic beha-vior with appropriate hysteretic capacity and small residual displace-ment can be obtained, as depicted in Fig. 1(c). The “flag-shape” beha-vior mainly comes from two aspects. The first is the elastic nonlinearbehavior of the SC-PSBC with unbonded posttensioning tendons, asshown in Fig. 1(a). The second is the elastic-plastic relationship fromthe yielding of energy dissipation bars or additional damping devices,as shown in Fig. 1(b).

Based on the abovementioned design concept, the configuration ofthe SC-PSBCs with rectangular hollow section in this study is presentedin Fig. 2. The SC-PSBC consists of several prefabricated segments. Theprestressing tendons are passed through the embedded PVC ductswithin these segments and then post-tensioned to provide the restoringforces. Energy dissipation rebars are passed through the embedded steelcorrugated ducts. Epoxy resin is spread evenly at the joint surface ofthese segments to maintain the integrity of the column and flatness ofthe segment ends. The longitudinal ED rebars are unbonded with con-crete within a certain length at the bottom two joints. The purpose ofthe unbonded measure is to avoid stress concentration in this locationand premature fracture of rebars resulting from the joint opening.Under strong earthquake excitations, the ED rebars are responsible for

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dissipating energy by elastic-plastic yielding caused by opening andclosing of bottom joints. After the severe events, the PSBC will be drivento its original location with an acceptable residual displacement by therestoring forces provided by the prestress tendons and the vertical ex-ternal loads.

3. Specimen design and fabrication

3.1. Geometric design

According to the General Specifications for Design of HighwayBridges and Culverts (JTG/D60-2015) [48], the Specifications for De-sign of Highway Reinforced Concrete and Prestressed Concrete Bridgesand Culverts (JTG/3362-2018) [49], the Guidelines for Seismic Designof Highway Bridges (JTG/T B02-01-2008) [50], a 30 m tall bridgecolumn with rectangular hollow-section was designed as the prototype,which is a typical pier used in the highway of China. In order to in-vestigate the influence of different lateral loading directions on theseismic performance of SC-PSBCs, five identical 1/10-scale bridgecolumn specimens were designed and constructed based on the proto-type column. The elevation view of the specimen, cross section of theloading block, the segments and the footing are shown in Fig. 3(a) to(d), respectively. Each of the specimens was loaded at a specific

intersection angle to the weak axis of the cross section. These angleswere 0°, 30°, 45°, 60°, and 90°. In order to obtain these loading direc-tions, the location of the loading block was remained unchanged for theconvenience of connecting with the horizontal actuator, while thefooting and bridge column segments were gradually rotated counter-clockwise, as will be seen in Fig. 5. These specimens were titled asspecimens C-0, C-30, C-45, C-60, and C-90. It is noted that the specimenC-0 means the loading direction along the weak axis of the column (i.e.loading about the strong bending axis), while the specimen C-90 re-presents loading along the strong axis (i.e. loading about the weakbending axis).

Each specimen consisted of six 500-mm long precast segments ofhollow section, which were named as segments S1 to S6 from thebottom to the top. The external dimensions of the cross section were550 mm × 320 mm and the wall thickness was 90 mm (see Fig. 3(c)).The total height of these six segments was 3000 mm (see Fig. 3(a)).According to the recommendations of AASHTO LRFD Bridge DesignSpecifications [51], the slenderness ratio of the segment was computedas 4.11 (see the clause 5.6.4.7.1), which was less than 35 to preventwall buckling. Eight 40-mm diameter steel corrugated ducts were em-bedded into each segment for the ED rebars. As depicted in Fig. 3(c),four 32-mm diameter PVC ducts were embedded inside each segmentfor the prestressing tendons, one at the center of each side. The thick-ness of cover concrete was 14 mm. The dimensions of the loading block,which was connected with the horizontal actuator at the intermediateheight, were 600 mm × 600 mm × 300 mm (see Fig. 3(b)). As aconsequence, the loading height of the specimens was 3150 mm. Theshear span to depth ratio was then calculated as 5.73 for the specimenC-0 and 9.84 for the specimen C-90. The bottom of the column wasconnected to a footing with dimensions of1,400 mm × 1,000 mm × 500 mm (see Fig. 3(d)), which was in turnfixed to the rigid lab floor through slip-critical threaded rods.

3.2. Reinforcement design

It is seen in Fig. 3(c) that each segment of the bridge columns hadtwenty four 8-mm diameter reinforcement bars which were not con-tinuous across the segment joints. This type of longitudinal bars is usedfor cracking control in that specific segment. Meanwhile they can re-duce the stress level of the concrete when prestressing tendons aretensioned. In addition, the transverse reinforcement bars were made of6-mm diameter rebars. The spacing was 50 mm in the segment 1 and90 mm in other segments. In order to calculate the longitudinal steelratio and volumetric of transverse steel rebars, the gross area of thecross section Ag was used which subtracted the areas of PVC tubes forthe prestressing tendons. Ag was equal to 0.121 m2. Table 1 summarizesthe ratio of the longitudinal and transverse reinforcements in the seg-ments and ED rebars throughout the whole height of the columns.

Under the lateral cyclic loading, the deformation of the SC-PSBCswill be concentrated on the bottom joints by joint opening. In order toalleviate stress concentration at the joints and to avoid premature

Fig. 1. “Flag-shape” hysteretic behavior of SC-PSBCs.

Fig. 2. Schematic configuration of the SC-PSBCs.

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fracture of the ED rebars, the ED rebars were unbonded with a height200 mm at the joints 1 and 2 in this study by wrapping 2-mm thick tape.The length of unbonded ED rebars is referred to the reference andconfirmed by the nonlinear pretest analysis [14]. Detailed procedures

to compute the unbonded ED rebars are as follows. First, a value of theunbonded length was assumed. Second, the opening history of thecritical joint of the specimens under cyclic loading up to 5% drfit ratiowas computed using pushover analysis. Third, the strain history of the

Fig. 3. Configuration of the specimens and section details (unit: mm).

Table 1Details of the test specimens.

Specimen θ (°) L (%) T (%)S1/S2-S6

ED (%) λ ALI Vnj (kN) Vexp (kN)

C-0 0 1.74 2.60/1.44 0.75 5.73 0.13 710 86C-30 30 1.74 2.60/1.44 0.75 4.95 0.13 710 80C-45 45 1.74 2.60/1.44 0.75 5.12 0.13 710 70C-60 60 1.74 2.60/1.44 0.75 5.71 0.13 710 55C-90 90 1.74 2.60/1.44 0.75 9.84 0.13 710 40

Note: θ represents the angle between loading direction and weak axis of the column section (unit: degree); Land T represent longitudinal and transverse re-inforcement ratio in column segments, respectively; ED represents reinforcement ratio of ED rebars; λ represents the shear span to depth ratio. ALI represents axialload index; Vns and Vnj represent shear resistance of the segments and the joints, respectively.

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critical ED bar at the critical joint was calculated. Fourth, the fatiguelife or number of cycles to failure of the rebar corresponding to eachcycle of the strain history was computed and the damage index of therebar was calculated by linear damage rule. These procedures wererepeated until the damage index was close to the target value. At last,the unbonded length of unbonded ED rebars was determined. The de-sign objective is to ensure non-fracture of the ED rebars at 5% drift ratioof the specimens. In each specimen, eight 12-mm diameter steel re-inforcement bars were used as the ED rebars, which resulted in a re-inforcement ratio of 0.75%. The energy dissipation capacity and re-sidual displacement of PSBCs are heavily dependent on the cross-sectional area of ED rebars. The effect of ED rebars is characterized by acontribution rate ED, which is defined by Eq. (1) [14]:

=V V

Vexp exp

expED

0

(1)

whereVexp andVexp0 are the expected maximum lateral strength with andwithout consideration of the ED rebars, respectively. These two para-meters can be estimated by pushover analysis [12]. The ED was re-commended to be less than 35% by Ou et al. [14]. A preliminary pretestpushover analysis was conducted on these bridge columns and the EDwas determined to be 33%.

In each specimen, four steel prestressing strands were anchored atthe bottom of the foundation and passed through the column segments.Then, the strands were posttensioned by an oil jack to an initial pres-tress force and anchored at the top of the loading block. Each strandwas 15.2 mm in diameter, which was made of seven-wire bundles. Thestrands were unbonded from the concrete by the built-in PVC ducts inthe precast segments to avoid excessive strain concentration during aseismic event. As a result, the loss of posttensioning forces, which isinduced by the yielding of the steel strands, is delayed and avoided[14].

Axial load index (ALI), defined as the ratio of applied axial load tocompressive strength of the column, is computed by Eq. (2) [2].

= + = +ALI ALI ALI N Nf AG PG P

c g0' (2)

where NG and NP are the gravity load and post-tensioning force, re-spectively, and fc0

' is the 28-day nominal compressive strength of un-confined concrete, Ag is cross-section area of the specimen. In general,the gravity load ratio ALIG for most bridge columns is in the range from0.05 to 0.15 [52,53]. According to the clause 6.1.3 in the Guidelines forSeismic Design of Highway Bridges [50], the ALIG of the bridge columnshould be less than 0.3 for regular bridge structures. According to theresearch results from Bu et al. [54], the total ALI for the PSBC should beless than 0.3 to avoid P-delta failure. Based on the abovementionedspecifications and recommendations, the ALI for the gravity and post-tensioning forces of the designed specimens were both taken to be0.065 (i.e. 237 kN). Therefore, the total ALI was 0.13 for the test PSBCspecimens. To achieve the target np, each prestressing strand wasposttensioned to the prestress force of 59.25 kN. Note that the targetALIG (0.065 or 237 kN for axial load) was applied by a jack on the top ofthe column.

The nominal shear resistance Vnj across the segment joints wascalculated by Eq. (3) according to AASHTO Section 5.11.4.4 [51] and islisted in Table 1. Note that no shear key was provided at the interface of

the adjacent segments. Only a small amount of epoxy was used in theinterface to seal the corrugated steel ducts and segment joints. In thisstudy, the contribution of epoxy to the shear resistance was not con-sidered.

= + +V A f P P[ 0.75( )]nj ED EDy G P0 (3)

where AED = total area of the ED bars; fEDy0 = specified yield strengthof the ED bars (392 MPa); PG = specified gravity load; and PP = speci-fied posttensioning force. The maximum expected shear demand, Vexp,for each column specimen can be predicted using pretest pushoveranalysis with the specified material properties and design parameters(see Tables 1 and 2). The real shear demand of each specimen is listedin Table 1. It is seen that the shear demand is much smaller than theshear resistance across the segment joints.

3.3. Materials properties

The material properties used in this experiment were tested basedon specific standards and procedures. The results are summarized inTable 2. In this table, the term “rebar cages in segments” refers to thelongitudinal and transverse mild steel reinforcement bars inside thecolumn segments which are discontinuous across the segment joints.The reinforcement bars were tested based on Metallic Materials-TensileTesting-Part 1: Method of Test at Room Temperature (GB/T 228.1-2010) [55]. It is noted that the concrete of these specimens was fromthe same batch and it was tested based on the Standard for Test Methodof Mechanical Properties on Ordinary Concrete (GB/T50081-2002)[56]. The average concrete strength at 28-day and the test day were25.2 MPa and 29.9 MPa, respectively. According to the China TechnicalCode for Application of Cementitious Grout (GB/T 50448-2015) [57],the grout to fill the duct of the prestress tendons was tested and thecompressive strength was 68.0 MPa. The prestress strands employed inthese specimens satisfy the requirements of the Steel Strand for Pre-stressed Concrete (GB/T 5224-2014) [58]. The tensile strength of theprestressing wire was 1860 MPa. The properties of all material prop-erties are summarized in Table 2.

3.4. Construction procedure

All of the specimens were constructed in the same way whichconsisted of 3 stages, as seen in Fig. 4. First, build the steel reinforce-ment cages for footing, column segments, and loading blocks, install theformworks of all precast components and embed the PVC ducts andsteel corrugated ducts, as seen in Fig. 4(a). Second, pour concrete for allcomponents using the same batch of concrete, and prepare concretecylinders for compressive strength tests and cure these cylinders in thesame environment as the specimens (see Fig. 4(b)). In the third stage,assemble all of the prefabricated components in the lab, as seen inFig. 4(c). To be specific, first, level the footing using a laser level.Second, wrap the energy dissipation rebars using 2-mm thick foam andtape for length of 200 mm below the intersections of S1-footing and S2-S1. Prior segments installation, the prestressing tendons and ED rebarswere passed through PVC ducts and corrugated ducts of the footingrespectively. The location of ED rebars was fixed temporarily at thebottom of the footing, and the bottom of the corrugated ducts wassealed and glued by thin plates. Then lift and stack up the segments 1 to

Table 2Measured material properties.

Concrete Grout Rebar cages in segments ED bars Steel strandsfco

' (MPa) fG' (MPa) fy(φ8/φ6) (MPa) fu(φ8/φ6) (MPa) fy (MPa) fu (MPa) fy (MPa) fu (MPa)

29.9 68.0 294/364 434/503 392 538 1678 1850

Note: fco' = specified compressive strength of the concrete; fG

' = specified compressive strength of the grout; fy = yield strength; fu = ultimate strength.

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