火灾后混凝土楼盖剩余承载力试验及理论研究

Experimental and Theoretical Research on the Post-fire Mechanical Performance of the Concrete Beam-slab Specimens

为了研究混凝土楼盖火灾后承载性能和破坏模式,对3块灾后楼盖和2块常温楼盖开展力学性能试验,获得了混凝土楼盖裂缝、破坏模式、变形、混凝土和钢筋应变等发展规律。基于塑性铰线理论,考虑梁刚度和变形对楼盖极限承载力的影响,建立了灾后楼盖剩余承载力和破坏模式计算方法,并与试验结果进行对比。结果表明:不同承载机制致使灾后和常温楼盖破坏模式略有不同,灾后楼盖表现为板先破坏模式,常温楼盖表现为梁先破坏模式;受火楼盖中板格易发生灾后爆裂,致使其保护层脱落、有效厚度减少,以及钢筋与混凝土间黏结性能降低,进而倾向于发生弯曲破坏和冲切破坏;相比配筋方式,配筋率对楼盖极限承载力有更为重要的影响,随着板格配筋率提高,极限承载力增加,但发生脆性破坏的可能性增加,特别是采用双层双向配筋方式的板格;传统简支板和固支板屈服线理论,倾向于低估或高估楼盖承载力。本文方法考虑边梁刚度和竖向变形的影响,其所得楼盖极限承载力计算结果较为合理,可用于确定结构中楼盖火灾后破坏模式和制定合理的灾后加固及修复措施。

To investigate the post-fire residual capacity and failure mode of the concrete beam-slab specimens,the mechanical tests of three fire-damaged specimens and two reference specimens were conducted.The cracks,failure modes,deflections,and concrete and steel strains were ob-served during each test.Based on the conventional yield line method,the stiffness and deflection of the beam were considered to establish the the-oretical method,and the residual ultimate load and failure modes of the specimens can be analyzed,and the predicted results were compared to the experimental results.Results showed that different mechanisms of the reference and fire-damaged specimens led to different failure modes,in-cluding the first-panel failure and the first beam failure.In addition,due to the post-fire spalling,the concrete cover of the fire-damaged panel fell off,and its effective thickness and bond strength degraded.Thus,apart from the flexural failure,the punching failure mode of the fire-damaged specimen also occurred.Compared to the reinforcement layout,the reinforcement ratio had a considerable effect on the ultimate loads of the beam-slab specimens,increasing the reinforcement ratio of the panel led to its higher carrying capacity and the brittle failure easily appeared.The con-ventional simply supported and fixed yield line method tended to underestimate or overestimate the ultimate loads of the specimens.For the present method,the effect of the edge beam’s stiffness and the vertical deflection was considered,and thus it could reasonably predict the ultimate loads,the failure mode and the reinforcement or repair method of the fire-damaged beam-slab specimens.