| Fiber reinforced polymer(FRP)has been gradually widely used in modern construction for bridges and buildings because of its high corrosion resistance,high strength-to-weight ratio.The concrete-filled FRP tubular column(CFFTC)and the FRP-concrete-steel double-skin tubular column(DSTC),as two possible columns to be used in new structures,have received extensive attention from scholars in the past 20 years.However,majority of the research are limited on the circular CFFTC as well as circular DSTC,in order to understand the seismic performance of the rectangular CFFTC(RCFFTC)and rectangular DSTC(RDSTC),it is necessary to experimentally investigate the axial compressive behavior of the two above column under cyclic compression.To achieve this objective,this paper set up a series of experiments to study the axial cyclic compressive behavior of the RCFFTCs and RDSTCs.Furthermore,based on the test results and previous researches on RCFFTCs and RDSTCs,the design-oriented stress-strain models for the concrete inside the two types of columns are proposed,respectively.The specific research contents of this paper are as follows:(1)25 RCFFTCs were tested under either monotonic or cyclic compression and their axial compressive behavior were also studied.The key parameters in this study were the crosssectional aspect ratio,FRP thickness and the test loading mode.Then,the influence of key parameters on the axial compressive behavior of the specimens is discussed.The main conclusions are as follows: the load carrying capacity and ultimate strain of the specimens increased with the decrease of the cross-sectional aspect ratio as well as the increase of the FRP thickness;different loading modes have little effect on the ultimate state of the specimens.(2)On the basis of the experimental investigation and the summary of previous research,a new design-oriented cyclic stress-strain model for concrete-filled FRP tubes is proposed in this paper.The envelope curve adopted the monotone axial stress-strain model proposed by Wu and Wei.The unloading path in this paper is modified locally based on the model proposed by Yu et al.As for the reloading path,the form of the equations is also consistent with Yu et al.with the calculation formulas of several key parameters of the equation are revised,which are more consistent with the database results collected by the author.(3)25 DSTCs were tested under either monotonic or cyclic compression and their axial compressive behavior were also studied.The key parameters in this study were the crosssectional aspect ratio,FRP thickness and the test loading mode.Then,the influence of key parameters on the axial compressive behavior of the specimens is discussed.The main conclusions are as follows: the load carrying capacity and ultimate strain of the specimens increased with the decrease of the cross-sectional aspect ratio as well as the increase of the FRP thickness;different loading modes have little effect on the ultimate state of the specimens.(4)Based on the experimental study and other research results,this paper verifies the applicability of the constitutive model proposed in this paper,which is suitable for the concrete inside RCFFTCs under cyclic axial compression,to the confined concrete of RDSTCs.Test results showed that the constitutive model proposed in this paper can well predict the stressstrain curve of the confined concrete of RDSTCs under cyclic axial compression. |
