【作者】 徐锋；

【导师】 吴智敏；

【作者基本信息】 大连理工大学 ， 结构工程， 2012， 博士

【摘要】 钢筋混凝土作为一种复合材料,能成功地应用于结构首先取决于钢筋与混凝土具有良好的粘结。钢筋与混凝土之间的粘结性能是影响钢筋混凝土结构承载力和使用性能的一个重要因素,也是钢筋混凝土结构进行理论和数值计算的必要参数。实际混凝土结构中,钢筋的粘结作用常常受到周围混凝土侧向约束,该约束作用将对粘结性能产生重要的影响。本论文主要通过中心拉拔试件研究了光圆钢筋与变形钢筋在单向和双向侧压应力下的粘结性能,考察了拉拔试件的不同破坏模式,分析了各粘结参数与复杂侧向压应力场之间的关系,构建了光圆钢筋和变形钢筋与混凝土之间的粘结本构关系。论文主要研究内容和结论如下：(1)对复杂侧向压应力作用下光圆钢筋的试验研究表明,有无侧压下光圆钢筋的粘结机理是不同的,其粘结-滑移曲线形状也不同。试验结果表明,其极限和残余粘结强度都随着侧向应力的增加而增大,但是残余强度与极限强度的比值基本保持不变。随着侧向应力的施加,极限粘结强度对应的滑移量先大幅下降,然在再随着侧向应力而增大。本文回归分析了各粘结参数与平均侧向压应力的关系,并基于粘结曲线的形状构建了光圆钢筋的粘结本构关系。结果表明,该本构关系与试验结果吻合良好。(2)对侧向压应力下钢筋与混凝土界面的应力状态进行了理论分析,通过取钢筋单元建立了应力平衡方程,推导了光圆钢筋的拉拔力和粘结强度的解析解,并将解析结果与试验结果进行了对比,并进行了参数分析。(3)侧向压应力作用下变形钢筋的试验研究表明,粘结试件的破坏模式与侧向压应力的大小有关,随着侧向压应力的不断增大,破坏模式从劈裂破坏转变为劈裂-拔出破坏直至拔出破坏。其粘结强度的变化也与破坏模式有关,总体上随着侧向压应力的增加而增加。通过试验数据分析并结合破坏模式,回归了粘结强度及其对应的滑移、残余强度及其对应的滑移与侧向应力的关系。(4)基于粘聚力的虚拟裂缝模型,对变形钢筋粘结试件的劈裂破坏进行了理论分析,假定虚拟裂缝面线性分布,同时假定内层混凝土开裂区满足等效弹性周向变形。该模型与静水压力劈裂试件和拉拔试件的结果吻合良好。最后,基于裂缝扩展准则研究了粘结试件的劈裂破坏全过程,并分析了其裂缝扩展阻力曲线(KR-曲线)。(5)为变形钢筋的粘结本构关系选择了合理的数学模型,并结合粘结参数的回归统计,合理地预测了复杂应力状态下其粘结-滑移全曲线,通过试验验证了粘结滑移关系与侧向应力场的路径无关,得出变化侧向应力场下的粘结-滑移曲线是无数定侧压应力场下粘结-滑移全曲线的叠加。更多还原

【Abstract】 The satisfactory use of reinforced concrete as a composite material in structures depends mainly on the fine bond action between reinforcing bars and concrete. The bond of reinforcing bars in concrete is a key factor affecting both the bearing capacity and the usability of reinforcing concrete structures, and is a requisite parameter for theoretical and numerical analysis of reinforced concrete structures. In real concrete structures, the bond action of reinforcing bars is usually influenced by the lateral confinement from surrounding concrete, and this confinement will exert significant influences on the bond performance. The main objective of this thesis is to study the bond performance of plain round and deformed reinforcing bars on pull-out specimens subjected to uniaxial and biaxial lateral pressures. The different failure modes of the bond specimens are examined and the bond parameters are analyzed with respected to the complex lateral pressure. Then, the bond constitutive relationships for plain round and deformed reinforcing bars are proposed. The main research contents and findings are summarized as follows:(1) The experimental study on plain round bars subjected to complex lateral pressure indicates that its bond mechanism is different before and after the lateral pressure is applied, and the corresponding bond stress-slip curves are also differs. The experimental results show that both the ultimate and the residual bond strength are increased by the increase in lateral pressure, but the residual to ultimate bond strength ratio basically remains constant. The slip at the ultimate bond strength firstly drops with the appearance of lateral pressure and then increases with the increase in lateral pressure. A regression analysis is conducted for the bond parameters with respected to the mean lateral pressure in this thesis. Then, a bond constitutive relation is proposed for plain round bars based on the characteristics of tested bond stress-slip curves, and the results show an agreement between the proposed and the experimental bond stress-slip curves.(2) The stress state at the interface between plain round bars and concrete subjected to complex stress state is analyzed theoretically. By equating the equilibrium of the stresses on a bar element, the analytic solutions for pull-out capacity and the bond strength of plain round bars are derived. The analytical predictions are then compared with the test results, and a parameter analysis is done. (3) The experimental study on deformed bars subjected to complex lateral pressure indicates that the failure mode of bond specimens depends on both the direction and the magnitude of complex lateral pressure. With the increase in complex lateral pressure, the failure mode changes from splitting failure, to splitting-pullout failure and to pullout failure. The variation of bond strength is related to the failure modes and generally increases with the increase in lateral pressure. Through analyzing the test data and combining the failure mode, the ultimate bond strength and the corresponding slip, and the residual strength and the corresponding slip are fitted with respected to the complex lateral pressures.(4) On the basis of the fictitious crack model considering the cohesive stress, a theoretical analysis is conducted for the splitting failure of bond specimens with deformed bars. In this analysis, the crack profile is assumed linear along the fictitious crack and the cracked zone of inner concrete follows an equivalent elastic circumferential deformation. The analytical predictions show a good agreement with the experimental results of both hydraulic pressure tests and bond tests. Subsequently, the whole process of splitting failure of bond specimens is numerically simulated based on the crack propagation criteria and then, the crack extension resistance curve is studied.(5) A suitable mathematical model is adopted for the bond constitutive relationship of deformed bars. With the regression of bond parameters, the present model reproduces the reasonable complete bond stress-slip curves under complex lateral pressure. The bond stress-slip curves are experimentally verified to be path-independent of the lateral complex pressure. As a result, the bond constitutive relations under variable complex lateral pressure can be considered as a superposition of numerous bond constitutive curves under constant complex lateral pressure.更多还原