Experimental Research On Seismic Performance Of RC Beam-column Joints Under Freeze-thaw Environment

During the past forty years, many tests focused on concrete beam-column joints have been performed to investigate their working principle and failure mechanism, which lead to a mature understanding. However, the research fields are mostly limited to intact joints without much considering of the concrete durability. The freeze-thaw damage, one of the three major factors of concrete failure, has been put more attention since 1940 s because of its significance. But any breakthrough about the concrete freeze-thaw destruction mechanism has been made after hydrostatic pressure theory and permeability pressure theory. As opposed to this, Scholars and professionals in many countries realized that concrete as a kind of engineering materials,the performance degradation caused by freeze-thaw damage boils down to mechanical performance degradation. So overwhelming researches on mechanical property decrease have made some progress.Unfortunately, achievements in the study of interdisciplinary of concrete freeze-thaw durability and seismic performance are of severe shortage. Moreover, the decrease of structure and members mechanical property after freeze-thaw cannot be fully predicted based on the results of material mechanical property. Thus it is necessary to study on the seismic property of structure members under the condition of freeze-thaw environment. The following work is mainly completed through tests and theoretical analysis in this paper:(1) Based on the existing material freeze-thaw damage model of concrete and concrete freeze-thaw test datas and combined with experimental study in this paper and theoretical derivation, applicable freeze-thaw damage model of concrete members is established with loss ratio of relative modulus as the damage index;(2) Six frames of concrete beam-column joints designed to investigate the quantitative freeze-thaw influence on bearing capacity, ductility and energy dissipation capacity. And through the variation of beam longitudinal reinforcement bond-slip performance after freeze-thaw damage, study the impact of the freeze-thaw on the node failure mechanism, and explore the cause of joint mechanical property variation;(3) The restoring force model of joints after freeze-thaw damage is established. Tt is been embed in the RC frame structure and used in the finite element program. At last, take the frigid region Beijing for example, a 5 stories RC frame structure is designed and modeled with open-source program Open Sees.to establish the vulnerability curves of 0 year and 30 years are respectively in order to provide guidance to the establishment of cold region multiple-age vulnerability curve.