高预应力度预应力混凝土框架抗震性能研究

发布时间：2018-11-12 08:07

【摘要】：我国预应力技术自上世纪80年代中期进入快速发展阶段后,在材料、工艺、设计理论与技术标准等方面,均有了长足的进步,总体已达到国际先进水平。然而,工程界对预应力结构在地震区的应用普遍比较谨慎,使用中有比较严格的限制,并要求采取多种措施。为保证预应力混凝土结构的抗震性能,国外规范大都采用单一指标控制设计截面,即规定配筋指数,该方法类似我国规范中限制框架梁端截面相对受压区高度的方法,国外的历次震害表明,预应力结构受损的占比较小,且多是由支撑结构倒塌、节点破坏等原因造成。我国现行规范在限制相对受压区高度的基础上,另设置了预应力度限值要求,且该指标限值较严,客观上常导致普通钢筋配筋量增加,节点区钢筋密集,施工及质量控制难度增加,且经济性降低,同时因梁超强易造成实际设计不是“强柱弱梁”。针对预应力度限值过严的问题,本文在总结以往相关研究成果的基础上,着重研究预应力度对预应力混凝土框架结构抗震性能的影响,主要研究内容及研究成果如下:首先,通过理论推导和分析,建立了截面延性系数的表达式,分析了影响截面延性的主要因素,包括混凝土强度、混凝土极限压应变、钢筋屈服强度、相对受压区高度及预应力度等,并证明了预应力度对截面延性影响较小,为放松预应力度的限值提供了理论依据;其次,为了验证放松预应力度限值的可行性,设计了两榀缩尺比例为1:3,预应力度分别为0.85、0.95的预应力混凝土框架,并进行了拟静力试验,观察其破坏形态,分析其延性、耗能等关键的抗震性能指标。试验研究结果表明:(1)高预应力度预应力混凝土框架仍具有较好的抗震性能,其破坏形态与中等预应力度预应力混凝土框架相似,仍表现为延性破坏,其滞回曲线呈“弓形”,且比较饱满;(2)尽管两个试件的预应力度均超过现行规范规定的上限值0.8,但均显示出良好的变形能力和耗能能力,延性系数均大于6.0,能量耗散系数均接近2.0;随着预应力度的增大,框架的变形能力及耗能能力均有所降低,但降低幅度不大。最后,根据理论分析及试验研究的成果,对高预应力度预应力混凝土框架设计进行了探讨:除应遵循基本的抗震设计原则外,应优先控制相对受压区高度指标,并采取必要的塑性铰区构造措施,最后是控制预应力度。综上,本文结合理论和试验研究,明确了预应力度指标并不是预应力混凝土结构抗震设计的关键性指标,且高预应力度框架结构仍具有良好的延性和抗震性能。结合本文研究提出的设计建议是:可将《混凝土结构设计规范》GB50010、《预应力混凝土结构抗震设计规程》JGJ140中有关预应力混凝土框架结构预应力度限值的规定适当放松,对二级、三级抗震等级,可将预应力度上限值放松至0.85,甚至取消该限值。
[Abstract]:Since the rapid development of prestressing technology in China in the middle of 1980s, great progress has been made in material, technology, design theory and technical standard, which has reached the international advanced level. However, the application of prestressed structures in seismic areas is generally cautious in engineering circles, and there are strict restrictions in their use, and various measures are required. In order to ensure the seismic behavior of prestressed concrete structures, the single index is used to control the design section in foreign codes, that is, the reinforcement index is prescribed. This method is similar to the method of limiting the height of the frame beam end section relative to the compression zone in the code of our country. The previous earthquakes abroad show that the damage of prestressed structures is relatively small, and most of them are caused by collapse of braced structures and damage of joints. On the basis of limiting the height of the relative compression zone, the current code of our country has also set up the limit value of prestress degree, and the limit value of this index is relatively strict, which often leads to the increase of reinforcement quantity of ordinary steel bar and the dense reinforcement in joint area. The difficulty of construction and quality control is increased, and the economy is reduced. At the same time, the actual design is not "strong column and weak beam" because of the super strength of beam. Aiming at the problem that the limit of prestress degree is too strict, based on the previous research results, this paper focuses on the influence of prestress degree on seismic behavior of prestressed concrete frame structure. The main research contents and results are as follows: first of all, Through theoretical derivation and analysis, the expression of section ductility coefficient is established, and the main factors affecting section ductility are analyzed, including concrete strength, concrete ultimate compressive strain, steel bar yield strength, relative compressive zone height and prestress degree, etc. It is proved that the degree of prestress has little effect on the ductility of the section, which provides a theoretical basis for the limit value of the degree of relaxation of prestress. Secondly, in order to verify the feasibility of loosening the limit of prestressing force, two prestressed concrete frames with a scale ratio of 1: 3 and a degree of prestress of 0.85U 0.95 are designed, and quasi-static tests are carried out to observe the failure patterns. Its ductility, energy dissipation and other key seismic performance indicators are analyzed. The experimental results show that: (1) the high prestressed concrete frame still has good seismic performance, and its failure pattern is similar to that of the middle prestressed concrete frame, and it still shows ductile failure. The hysteretic curve is arcuate and full. (2) although the prestress degree of the two specimens exceeds the upper limit value of current code, it shows good deformation capacity and energy dissipation capacity, the ductility coefficient is more than 6.0, and the energy dissipation coefficient is close to 2.0; With the increase of prestress degree, the deformability and energy dissipation capacity of the frame are decreased, but the extent of the reduction is not significant. Finally, according to the results of theoretical analysis and experimental research, the design of prestressed concrete frame with high prestressing degree is discussed. Besides the basic seismic design principle, the height index of relative compression zone should be controlled first. The necessary structural measures of plastic hinge area are taken, and finally, the degree of prestress is controlled. On the basis of theoretical and experimental research, it is clear that the index of prestressing force is not the key index of seismic design of prestressed concrete structure, and the high prestressing degree frame structure still has good ductility and seismic performance. Combined with the design suggestion of this paper, it is suggested that the limit of prestressed degree of prestressed concrete frame structure in GB50010, (Code for Design of concrete structures) < Code for Seismic Design of Prestressed concrete structures > JGJ140 can be relaxed appropriately, and the second grade can be relaxed. The upper limit of prestress can be relaxed to 0.85 or even cancelled.
【学位授予单位】：中国建筑科学研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU378.4;TU352.11

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