Experimental Study On Seismic Performance Of RC Frame Beam Under Freeze-thaw Cycles

RC frame structure, because of owning the advantage of simple rolling force, easy form, has been widely used in engineering structure across our nation as a kind of commonly used structure form. Freeze-thaw cycle, as one of the three major factors affecting concrete failure, is of great significance in the region of concrete durability.Hydraulic, marine, bridge and other concrete structures are commonly broken in the form of flaking, cracking loose inside by freeze-thaw cycles. Therefore, the study of RC frame structures deterioration of the mechanical properties in the freeze-thaw environment is of real significance. The research on seismic performance deterioration can provide advantageously means in earthquake engineering. In the paper, we focus on RC frame beams and do the research on the factors of concrete strength and freeze-thaw cycle times on RC frame beam specimen deterioration of the mechanical properties through experimental research and theoretical analysis. Based on threefold skeleton curves with negative stiffness segment, hysteretic model of RC frame beams is established. The main research contents and theoretical results are showed below:(1) We design several RC frame beams and do quasi-static tests, which had received N=0, N=100, N=200, N=300 times freeze-thaw cycles based on material’s properties of frost-resistant concrete structure to take the factors of concrete strength and freeze-thaw times into consideration in seismic performance deterioration. After the quasi-static test and on the basis of data processing, we obtain the hysteretic curve,skeleton curve, stiffness degradation, strength degradation and energy dissipation capacity degradation of the RC frame beams considering the factors of concrete strength and freeze-thaw cycling.(2) Based on threefold skeleton curves with negative stiffness segment, hystereticmodel of RC frame beams is established. According to regression analysis for the experimental data, the formula of skeleton curve characteristic point of corroded RC frame beams is obtained. Based on hysteretic energy cyclic degradation index, restoring force model established in this paper took into account pinching effect, strength degradation, unloading stiffness degradation, hardening stiffness degradation and reloaded stiffness accelerated degradation. The comparison between hysteretic curve calculated and experimental hysteretic curve demonstrates that: the restoring force model can describe the hysteretic characteristics of the RC frame beam fairly in freezethaw conditions.(3) Based on Open Sees, we investigate the influence on RC frame structures seismic performance deterioration of freeze-thaw cycling factor. We design a 5 stories RC frame structure,which is in Dalian district, Liaoning region,as an example of frigid region, and model it with open-source program Open Sees. Two kinds of RC frames(0year,50 years) has been selected to suffer 22 seismic waves whose amplitude would be regulated 7 times by Open Sees to obtain IDA(Increased Dynamic Analysis). And intercalation displacement angle is used as a performance criteria on RC frame to do analysis of the seismic vulnerability and establish the vulnerability curves in cold regions. The results verify that with the increasing of age, the probability of RC frame structure beyond a limit state would increase in the same seismic intensity and thus provide guidance of structure design in cold regions...