【作者】 侯晓萌；

【导师】 郑文忠；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2009， 博士

【摘要】 火灾能造成建筑结构的严重破坏,甚至导致建筑结构的坍塌,预应力混凝土结构近年来发展较快,应用越来越多。结构抗火设计应同时满足预应力混凝土结构火灾下与火灾后的安全,目前欧洲抗火设计规范(EC2-1-2)虽对预应力混凝土结构抗火设计方法有所述及,但仍是初步的,尚需开展火灾下与火灾后预应力混凝土梁板力学性能的研究。论文主要开展了五个方面的研究工作。(1)预应力钢筋、非预应力钢筋高温后的力学性能是开展火灾后预应力结构损伤评估与修复的重要依据。针对目前高温后预应力钢筋、非预应力钢筋力学性能研究中未考虑高温下应力历程对高温后力学性能的影响这一问题,为考察高温后预应力钢筋及非预应力钢筋力学性能,砸碎38个火灾后预应力混凝土梁板试件的混凝土,取出预应力钢筋及非预应力钢筋,制作成481个预应力钢筋试件和489个非预应力钢筋试件,并对这些试件进行高温后的力学性能试验。基于试验结果,探索了高温后预应力钢筋和非预应力钢筋的相关强度、弹性模量、断后伸长率等的变化规律;分别给出了高温后预应力钢筋及非预应力钢筋的应力—应变曲线方程。试验结果表明,在经历相同的温度作用后,承受初始应力的预应力钢筋较未施加初始应力的预应力钢筋的强度低,初始应力水平(常温下初始应力与常温下钢筋极限强度的比值)为0.6较无初始应力时,预应力钢筋条件屈服强度降低约7.0%;而高温后非预应力钢筋强度受初始应力的影响不大。(2)我国《混凝土结构设计规范》(GB50010-2002)还没有对预应力混凝土结构抗火设计作出具体规定。为研究预应力混凝土梁板的抗火性能,合作完成38个预应力混凝土简支梁板、连续梁板抗火性能试验,探索了混凝土保护层厚度、荷载水平、综合配筋指标等关键因素影响对预应力混凝土梁板抗火性能的影响,提出了火灾下混凝土梁板的无粘结筋应力、跨中变形计算公式,考察了火灾下连续梁板支座反力的变化。(3)混凝土、预应力钢筋和非预应力钢筋的本构关系和预应力混凝土梁板的力学性能随温度—荷载途径而的不同而不同,从混凝土、普通钢筋和预应力筋的热—力耦合本构关系出发,用t时刻的混凝土应力计算t+1时刻混凝土的瞬态热应变、高温徐变,实现了混凝土热—力耦合本构关系的解耦,钢筋、预应力筋的处理方法与此相同,可获得火灾下预应力混凝土梁任意截面的弯矩—曲率全过程曲线,基于支座变形协调方程,可利用割线刚度法对支座反力进行迭代求解,通过对截面曲率积分可求得连续梁各截面的变形,进而实现了考虑热—力耦合影响的火灾下预应力混凝土梁板非线性全过程有限元分析。(4)结构抗火设计需要同时满足结构火灾下与火灾后的安全。完成了19个火灾后预应力混凝土、钢筋混凝土简支梁板、16个火灾后预应力混凝土连续梁板的力学性能试验,获得了试件变形与裂缝发展、连续梁板支座反力变化、无粘结筋应力变化、正截面承载力变化等试验现象和测试数据,研究结果表明:相同条件下,火灾后有粘结预应力混凝土板承载力降低幅度较无粘结预应力混凝土板大。基于上述火灾后预应力混凝土梁板力学性能试验结果,提出了火灾后无粘结筋剩余应力、极限应力、裂缝宽度计算公式和变形分析方法。(5)为满足预应力混凝土梁板抗火设计与火灾后损伤评估的需要,分总则、抗火设计方法和构造措施、混凝土爆裂验算与防爆裂构造措施、火灾后预应力混凝土梁板承载力、变形计算与修复建议等方面提出了预应力混凝土梁板抗火设计建议和火灾后损伤评估与修复建议。更多还原

【Abstract】 Fire can severely destruct building structures and even cause it collapse. In recent years, prestressed concrete (PC) structures grow rapidly, which are used more and more widely. Structural fire design should ensure that the structure is safe during fire and after fire. Although fire design method of PC structure has been preliminarily mentioned in Eurocode 2-1-2: structural fire design (EC2-1-2), the mechaincal performance of PC beam and slab during/after fire need to be researched further. 5 parts of research work are accomplished in this dissertation.(1) The mechanical property of prestressing steel wire and non-prestressed steel bar after fire is the key factor in damage evaluation and repair after fire for prestressed structures. At present, the stress in the prestressing steel wire and non-prestressed steel bar at elevated temperature is not considered in their mechanical property after fire. In order to investigate the mechanical properties of prestressing steel wire and non-prestressed steel bar after fire, 38 prestressed concrete slabs and beams after fire are smashed and the prestressed steel wire and non-prestressed steel bar are taken out. A tensile test of 481 prestressing steel wires and 489 non-prestressing steel bars after fire is completed. Based on the experiment data, the relative strength, elastic modulus, and specific elongation of prestressing steel wire and non-prestressed steel bar after fire are obtained respectively. The strain-stress relationship of prestressing steel wire and non-prestressed steel bar after fire is obtained respectively. The experiment results show that: the strength of prestressing steel wire with initial stress after fire is lower than that without initial stress. For the prestressing steel wire with the ratio of initial stress to ultimate strength is 0.6 at normal temperature, the 0.2% yield strength of prestressing steel wire after fire is 7.0% lower than that without initial stress. But the strength of non-prestressed steel bar with and without initial stress after fire does not vary obviously.(2) Specific fire design method for PC structure has not been contained in Code for design of concrete structure (GB50010-2002) in China. 38 PC simple and continuous beams and slabs are test on the fire resistance. The influences of key factors such as concrete cover, load level and global reinforcement index to the fire resistance performance of PC beams and slabs are explored. The calculation formulas of the stress in the unbonded tendons and the deflection at mid-span of PC beam and slabs at elevated temperature are proposed, and the variation of support reaction at elevated temperature is obtained.(3) The constitutive model of concrete, prestressing steel wire and non-prestressed steel bar and the mechanical performance of PC beam and slab differ with different temperature-load paths. Based on the constitutive model of concrete, prestressing steel wire and non-prestressed steel bar considering the influence of thermal-mechanical coupling, and transient strain, compressive creep in concrete at time t+1 can be calculated through stress in concrete at time t, and then the coupled constitutive model of concrete can be decoupled, and prestressing steel wire and non-prestressed steel bar are disposed by the same way. Therefore, the whole progress of moment-curve analysis of PC beam and slab subjected to fire is completed. Based on the deflection compatibility equation at the support, the support reaction can be calculated by secant stiffness matrix iteration method, and the deflection of continuous beam and slab can be obtained by curve integral of cross section. Then the nonlinear finite element analysis of loading process for prestressed concrete continuous beam and slab at elevated temperature can be completed.(4) Structural fire design should ensure that the structure is safe during fire and after fire. 19 PC simple and 16 PC continuous beams and slabs are tested on mechanical performance after fire. Crack distribution and growth, deflection development, support reactions, stress in unboned prestressing steel wires, flexural carrying capacity as well as failure characteristics are obtained. The experiment results show that: the carrying capacity of bonded PC slab decreases grteater than that of the unbonded PC slab after fire under the same condition. Based on the experiment data, calculation formula of residual stress, ultimate stress in prestressing steel wire and crack width is put forward, and deflection analysis method of PC beams and slabs after fire is proposed.(5) In order to meet the requirement of fire design and repair method after fire for PC beam and slab, proposition on fire design and repair method after fire for PC beam and slab is proposed, which comprises general, effects of actions, characteristic values of resistance and fire design principles, thermal properties of material, mechanical properties of matireial during/after fire, calculation for temperature field, verification methods for crack, defletion and carrying capacity, concrete cover thickness for fire resistance of PC beams and slabs, detailing rules, check method on spalling of concrete of prestressed slabs and beams at elevated temperature and detailing rules to avoid concrete spalling etc.更多还原