Seismic rehabilitation of concrete frame beam-column joints.

摘要

Many reinforced concrete frame structures were designed and constructed before the development of seismic codes or according to earlier versions of seismic codes. Thus, these structures were designed only for gravity loads or for much lower lateral loads than the loads specified by the current seismic codes. Non-ductile reinforcement details in the form of insufficient shear reinforcement in the joint zone or inadequate anchorage length of beam bars are some of the main characteristics of these structures. Post-earthquake investigations confirmed the vulnerability of these structures to severe earthquakes. Poorly designed joints, especially the exterior ones, have been identified as critical structural elements that could fail prematurely. Many failure cases were recorded as a result of joint shear failure or anchorage failure of beam bars.; The objectives of this study were to investigate the seismic behaviour of existing concrete frames under simulated seismic loads as well as to develop effective rehabilitation schemes for strengthening concrete frames with non-ductile reinforcement details. The experimental part of this study was conducted to investigate the effect of non-ductile reinforcement details on the behaviour of the joint. Several rehabilitation schemes were proposed to mitigate the hazards caused by such poorly detailed concrete joints. These strengthening schemes included using of externally bonded fibre reinforced polymer (FRP) sheets and steel elements. Twelve exterior full-scale beam-column joints were tested under quasi-static cyclic loading. The specimens were divided into three groups, the first group has no transverse reinforcement in the joint zone, the second group has inadequate embedment length of beam bars and the last group has both no ties in the joint and inadequate anchorage length of beam bars. The joint shear resistance was improved using FRP jacket, whereas the inadequate anchorage conditions of beam bars were improved using FRP sheets or steel elements. The analytical part of this study was conducted to study the effect of FRP wraps on the compression behaviour of axially-loaded concrete elements and to develop analytical models to predict the shear response of concrete joints without transverse reinforcement, with transverse reinforcement or with FRP sheets. The proposed models were introduced into a non-linear dynamic analysis program and then used to simulate existing and rehabilitated beam-column subassemblies.; From the test results, several rehabilitation systems to improve the performance of non-ductile concrete joints were proposed and successfully evaluated. FRP jacket proved to be effective in upgrading the joint shear resistance. FRP sheets and steel elements were effective in upgrading the anchorage conditions of beam bars. The proposed shear and materials models, which were introduced into a macro model to represent beam-column joints, were capable of representing the cyclic behaviour of existing and rehabilitated beam-column subassemblies. These models would help the design engineers to assess existing structures and propose practical rehabilitation schemes for these structures.