Seismic Performance of RPC Hollow Rectangular Bridge Columns

Transcription

1 Seismi Perormane o RPC Hollow Retangular Bridge Columns G.Y. Zhao 1, G.P. Yan 2 and W.X. Hao 3,4 1 Leturer, Shool o Civil Engineering, Beijing Jiaotong University, Beijing. China 2 Proessor, Shool o Civil Engineering, Beijing Jiaotong University, Beijing. China 3 Ph.D Candidate, Shool o Civil Engineering, Beijing Jiaotong University, Beijing. China 4 Leturer, College o Urban and Rural Constrution, Agriultural University o Hebei, Baoding. China gyzhao@bjtu.edu.n ABSTRACT : Two hollow retangular bridge olumns with Reative powder onrete (RPC) were tested under a ylially reversed horizontal load. Based on the test results, the seismi behavior o suh olumns was presented. An analytial model was developed to predit the ore-displaement relationship o speimens. The test results were also ompared to the proposed analytial model. It was ound that the dutility ators o the speimens are over 4.0, and the proposed analytial model an predit the ore-displaement relationship o suh olumns with aeptable auray. KEYWORDS: Seismi perormane, Reative Powder Conrete, dutility, olumns, bridges 1. INTRODUCTION Reative powder onrete (RPC) is a new generation ementitious omposite material with ultra-high perormane (Rihard and Cheyrez 1995). It s haraterized by extremely superior physial properties, partiularly its ultra-high strength and good dutility. Enhaned properties o RPC are obtained though grain size optimization, inorporation o miro-silia and post-set heat-treating. Compressive strength o RPC an range rom 200MPa to 800MPa. By introduing ine steel ibers, RPC an ahieve remarkable lexural strength up to 50MPa. The material exhibits high dutility, more than 250 times greater than that o onventional onrete (Cheyrezy et al. 1998). It s easible to apply RPC to the onstrution o bridge olumns or better seismi perormane. RPC olumns may beome lighter due to ultra-high strength o RPC and seismi inertia loads may be redued. Dutility o RPC olumns an be improved beause o high lexural strength and rature energy absorption apaity o RPC. Consequently, the amount o lateral reinorement or oninement in olumns an be redued greatly. In this paper seismi perormane o RPC hollow retangular bridge olumns were investigated. Two speimens were tested under a ylially reversed horizontal load. An analytial model was also developed to predit the ore-displaement relationship o olumns. The Analytial model was veriied by experimental results. 2. EXPERIMENTAL PROGRAM Two retangular hollow olumns were made rom RPC with modiied mix design. Compressive strength o RPC is 140MPa and tensile strength is 20MPa. This type o mix an eiiently make osts lower and onstrution easier. The olumns were tested under a ylially reversed horizontal load. The tests belong to preliminary investigation o seismi perormane o RPC olumns, so axial ore was not applied in the tests or simpliity.

2 2.1. Speimens Dimensions o the speimens are shown in Figure 1. The ross setion o both speimens is 400 mm. The wall thikness o both speimens is 60 mm. The distane between the lateral loading point and the the top o the oundation is 1.4m. COL1 and COL2 are dediated to name the two speimens. Table 2.1 inludes details o the test speimens. Eah speimen ontains 16φ16 longitudinal rebars providing a reinorement ratio o 3.94% o the gross setional area o the olumn. Yielding strength o the longitudinal steel was 370 MPa. The volumetri ratio o transverse reinorement to RPC ore, measured out-to-out o perimeter ties, are 0.73% and 1.46% respetively, and spaing o the hoops are 100mm and 50 mm respetively. Lateral Load Φ16 LVDT LVDT LVDT 6mm@100(Speimen COL1) 6mm@50(Speimen COL2) Speimen Length L (m) (MPa) Figure 1 Detail o speimens Table 2.1 Properties o speimens Longitudinal reinorement d s (mm) y (MP) ρ l (%) Transverse reinorement d st (mm) s (mm) yh (MP) ρ s (%) COL COL Materials Modiied mix o RPC with 140MPa ompressive strength and 20MPa tensile strength was used. Although both the ompressive strength and tensile strength o RPC or speimens are less than that developed by Rihard and Cheyrez (1995), osts and onstrution diiulty may be redued greatly. That s important or the appliation o RPC to engineering pratie Test Setup and Loading Sequene The lateral load was applied with a 1000 kn MTS atuator. The applied lateral ore and the tip displaement were measured and reorded by the MTS sotware system. Three linear variable displaement transduers (LVDTs) are plaed to monitor the slippage and rotation o the oundation. The speimens were tested under displaement ontrol ollowing a predetermined displaement history. The displaement routines or the speimens onsist o several yles up to ailure (Figure 2). The displaement yles were repeated ive times to measure the strength degradation.

3 Figure 2 Lateral displaement sequene 3. TEST RESULTS 3.1. General Observations In both speimens, the irst rak ourred in the diretion perpendiular to the olumn axis in the plasti hinge region. As lateral ore inreased, lexural raking spread. Aterwards, the longitudinal rebars yielded in tension. During the last yle, bukling o the longitudinal bars was observed ater yielding o the perimeter ties (Figure 3), whih was an indiation o the ommenement o ailure. The ailure mode or both speimens was dominated by lexural eets Hystereti Loops (a) (b) Figure 3 Speimens at the end o testing. (a) COL1; (b) COL2. Lateral ore displaement hystereti loops or both olumns are shown in Figure 4. The response or the speimen COL2, with 50% higher amounts o transverse reinorement than the speimen COL2, shows a more stable response. This is a result o the high transverse reinorement, whih enabled transverse steel to eetively onine the ore onrete, thus reduing the drasti degradation o lateral strength. The maximum lateral ore are 152.8kN and 40.1kN or COL1 and COL2 respetively.

4 3.3. Dutility Fator and Energy Dissipation (a) (b) Figure 4 Hystereti loops o speimens. (a) COL1; (b) COL2. Dutility ator and energy dissipation apaity are important indies to quantiy the response o olumns in seismi design. Both types o indiators are omputed in this paper to ompare seismi perormane o olumns. From the response o RPC olumns, it s obvious to deine an elasti branh and yielding point. The ailure o RPC olumns is onventionally deined where the remaining apaity o the olumn has dropped to 85% o the maximum load. It an be seen rom Table 3.1 that the dutility ators or both speimens are 4.0 and 4.8 respetively. Speimen number Yielding displaement (mm) Yielding ore (kn) Table 3.1 Experimental results Ultimate displaement (mm) Maximum ore (kn) Dutility ator Energy dissipation (kn.mm) COL COL Eet o Amount o Transverse Reinorement. Figure 5 Lateral ore-displaement relationships

5 The volumetri ratio o oninement steel in COL2 is two times that in COL1. Figure 5 illustrates that speimen COL2 an sustain larger inelasti yli displaement than speimen COL1. The results presented in Table 3.1 indiate that speimen COL2 has a displaement dutility level 1.2 times that o speimen COL1. The dissipated energy o speimen COL2 is 40% higher than that or speimen COL1. It should be noted that yielding ore and maximum ore o speimen COL2 is a little lower than that o speimen COL1. Test results show that the volumetri ratio o oninement steel an improve dutility level o RPC olumns, but the eet on the strength improvement o olumns is not obvious 4. ANALYTICAL RESULTS 4.1. Constitutive Models o Materials The response o a struture under load depends to a large extent on the stress strain relation o the onstituent materials and the magnitude o stress. In this researh the stress strain relation o RPC in ompression is o primary interest. Figure 6 Stress-strain relationship o RPC Figure 7 Stress-strain relationship o steel Stress-strain relationship o RPC Beause researh on the ailure mehanisms o RPC under biaxial and triaxial loads is under way, a stress-strain relationship proposed rom uniaxial ompression tests is used to desribe behaviour o both unonined and onined RPC. In this model, as shown in Figure 6, the monotoni onrete stress strain relation in ompression is desribed by two regions: ε 2 ε = 2 εo εo ε ε (4.1), o ε ε o = εu εo, εo < ε εu (4.2) Where, is the ompressive strength o RPC ylinder; ε o is the RPC strain at maximum stress and equals to 0.003; ε u is the strain where the stress drops to 30% o peak stress and equals to

6 4.1.2 Stress-strain relationship o longitudinal rebars Longitudinal rebar is modeled as a linear elasti, linear strain hardening material with yielding stress σ y as shown in Figure Flexibility-based Fiber Beam-olumn Element Many beam-olumn element models to analyze R/C strutures under monotoni and yli loads have been proposed to date. Reent studies (Tauer et al. 1991; Spaone et al. 1996a; Spaone et al. 1996b; Neuenhoer and Filippou 1997; Neuenhoer and Filippou 1998) have shown lexibility-based iber beam-olumn element model is the most promising one. Flexibility-based iber beam-element model is based on ore interpolation untions within elements. The advantage o this model stems rom the realization that the ore interpolation untions satisy the element equilibrium in a strit sense irrespetive o the state o the element. Element states are deided by the integration o setion responses omputed using iber models. Flexibility-based iber beam-olumn element has been inluded in a Matlab toolbox named as NonlinSim or nonlinear stati and dynami analysis o strutures developed by Zhao (2006). Analytial investigations o RPC speimens were arried out using NonlinSim. Constitutive laws proposed or RPC and longitudinal reinorement aorementioned were used Comparison o Test Data with Analytial Result Figure 8 shows a omparison o the ore-displaement relationships or both tests and analytial models. It an be seen rom Figure 8 that the analytial models an predit the test results with reasonable auray. (a) (b) Figure 8 Experimental and analytial ore displaement diagrams. (a) COL; (b) COL2. 5. CONCLUSIONS Based on the studies presented in this paper the ollowing onlusions an be made. (1) The tested RPC hollow bridge olumns have aeptable seismi perormane beause dutility ators or both olumns are over 4.0. (2) Test results show that the volumetri ratio o transverse reinorement an improve dutility level o RPC olumns, but the eet on the strength improvement o olumns is not obvious. (3) The analytial model proposed predits the ore-displaement relationship o RPC hollow bridge olumns with aeptable auray.

7 6. ACKNOWLEDGEMENTS The researh has been unded by the National Natural Siene Foundation o China (NSFC) through Grant No Constrution and testing o the speimens were onduted by the third author as one part o his Ph.D researh work. REFERENCES Rihard, P., Cheyrez, M. (1995). Composition o reative powder onretes. Cement and Conrete Researh 25:7, Cheyrezy, M., Behloul,M., Dowd, W.M., Dauria, C.E.(1998). Reative Powder Conrete (RPC) appliation or seismi design. Amerian Conrete Institute Convention. Tauer, F.F., Spaone, E. and Filippou, F.C. (1991). A iber beam-olumn element or seismi response o reinored onrete strutures. EERC Report No. 91/17, Earthquake Engineering Researh Center, University o Caliornia, Berkeley. Spaone, E., Ciampi, V.and Filippou F.C. (1996a). Mixed ormulation o nonlinear beam inite element. Computer & Strutures 58:1, Spaone, E., Filippou, F.C. and Tauer, F.F. (1996b). Fibre beam-olumn model or nonlinear analysis o R/C rames: ormulation. Earthquake Engineering & Strutural Dynamis 25, Neuenhoer, A. and Filippou F.C. (1997). Evaluation o nonlinear rame inite-element models. Journal o Strutural Engineering 123:7, Neuenhoer, A. and Fillippou, F. (1998). Geometrially nonlinear lexibility-based rame inite element. Journal o Strutural Engineering 124:6, Zhao, G.Y. (2006). Nonlinear analysis and perormane-based seismi design o reinored onrete bridges. Ph.D thesis, Beijing Jiaotong University.