火灾后钢筋混凝土剪力墙抗震加固研究

Reinforce concrete (RC) shear walls have been widely used to resist the lateral force mainly induced by the earthquake, especially in high-rise structures. It is noted that the seismic performance of shear walls is deteriorated by elevated temperatures, which affects the safety of the overall structure. Usually, repair of heat-damaged RC shear walls would be the only solution to regain structural capacity. In this research, both analytical and experimental methods are employed to investigate the seismic behavior of the repaired RC shear walls. Firstly, RC shear walls under an axial compressive load are exposed to fire on one side. Secondly, the residual bearing capacity of fire-damaged shear walls is evaluated, and the specified repair technique is choosed for strengthening the specimens. These RC shear walls repaired after fire are tested under the combined action of constant axial load and lateral load reversals. The effects of different factors, such as fire duration and the axial load ratio, on the performance of repaired shear-walls in terms of their stiffness, ductility, energy dissipation and the ultimate strength are studied based on the test data. And the strengthening mechanism, as well as the effect of repair technique is studied. Finally, a finite element model based on the bond-slip relationship between reinforcement and concrete under cyclic loading after elevated temperatures is developed to predict the seismic behavior of heat-damaged RC shear walls.The validity of the numerical model is verified by comparing the test data with calculated results. The work provides experimental data and an analytical model for the future development of appropriate guidelines for the evaluation and rehabilitation of RC shear walls after fire.

钢筋混凝土剪力墙是高层建筑结构中的主要抗侧力构件，当遭受火灾作用后，其抗震性能会明显降低，影响结构的安全使用。为了使受火后受损的剪力墙构件能够恢复正常使用，需要对其进行适当修复加固。本课题采用理论和试验相结合的手段,针对火灾后加固钢筋混凝土剪力墙的抗震性能进行研究。首先，对钢筋混凝土剪力墙进行持荷状态下的受火试验；然后对受火后的剪力墙试件进行损伤评估，对其进行加固，并对加固后的试件进行低周反复荷载试验，研究不同受火时间、轴压比等因素对加固剪力墙承载能力、刚度、变形及耗能能力的影响规律，分析加固机理和加固效果；最后，建立高温后反复荷载作用下的钢筋与混凝土粘结-滑移本构关系，并利用此本构关系建立有限元模型，对火灾后加固剪力墙构件的荷载-位移关系进行模拟，通过与试验数据的对比，验证计算模型的有效性。通过本课题的研究，期望为火灾后钢筋混凝土结构修复加固提供可靠的计算模型和试验数据。

火灾作用导致钢筋混凝土剪力墙抗震性能明显降低，针对受损剪力墙构件采用适当修复加固措施，可以恢复正常使用。为了探究火灾后加固钢筋混凝土剪力墙抗震性能，课题组主要进行了以下研究工作：1）钢筋混凝土剪力墙明火受火试验；2）FRP加固火灾后钢筋混凝土剪力墙低周反复荷载试验，分析了加固方式、加固材料等参数对其抗震性能的影响规律；3）高温后钢筋与混凝土反复荷载作用下粘结滑移性能试验，分析了高温后钢筋与混凝土粘结性能变化规律。得到了以下主要结论：1）加固方式对CFRP加固火灾后剪力墙试件破坏形态影响较大：未施加机械锚固的加固试件，最终由于纤维布大面积剥离而破坏；而施加机械锚固的加固剪力墙试件，最终由于纤维布断裂、混凝土被压碎而导致破坏，表明施加机械锚固提高了纤维布的利用率。2）FRP加固受火后钢筋混凝土剪力墙试件的承载能力可以达到甚至超过受火前的水平。但是，与CFRP相比，BFRP加固受火后剪力墙承载能力提高幅度较小：利用CFRP并采用机械锚固加固的剪力墙构件极限荷载比加固前提高了26.8%，且比未受火构件增加了13.7%；利用BFRP采用同样加固方式的剪力墙构件极限荷载比加固前提高了17.9%，且比未受火构件增加了5.8%。3）与未加固试件相比，采用FRP加固火灾后剪力墙试件滞回环饱满，环数增多，承载能力和延性明显增加，且施加机械锚固方式后，滞回环饱满程度明显优于未施加机械锚固试件。与BFRP相比，CFRP加固剪力墙极限荷载更大，滞回环更饱满，滞回圈数更多，耗能更大。4）无论是单调荷载还是反复荷载作用下，由于箍筋的约束作用，高温后钢筋混凝土粘结试件表面未产生新裂缝，均发生了粘结-滑移破坏。5）高温作用降低了钢筋与混凝土之间的粘结强度，700℃高温作用后，钢筋与混凝土极限粘结强度下降了65%左右。在试验研究基础上，通过分析给出了高温后粘结强度的计算公式。