新型框架结构平移托换节点受力特性与设计方法研究

As a means of preservation, the technology of building moving offers a good approach to make good use of the old buildings and save the public resources and energies. And the demands of moving traditional buildings increase enormously in recent years following the rapid urbanization in China. During the moving of the frame structure, the superstructure should be cut off from the foundations and then supported by a series of underpinning joints. An inspection of the joints suggests that they are under rather complex stress conditions, and the old-to-new concrete interfaces requires carefully design and analysis to ensure the safety of the building moving. Two types of new underpinning joints are proposed in the present projects. One is improved by the implanted steel bars in the interface and the other is enhanced by the pre-stresses. Systematic experiments are carried out to investigate the behaviors of the newly proposed joints with considerations of beam height, shear-to-span ratio, longitude reinforcement, stirrups, interface bars or pre-stresses. A series of refined finite element models are also developed to investigate the new underpinning joints considering the damage of concrete and the debonding between the interfaces. Based on the results of experiments and numerical simulations, two analytical models are proposed in the present project, which are corresponding the two major failure modes of the underpinning joints. One is the strut-and-tie model related to the overall shear or compressive failure of the joint; the other is the modified shear-friction model, which represents the debonding failure of the joint. The proposed research lays a solid foundation for the design and analysis of the underpinning joints and improves the safety and reliability for the moving of frame structures.

框架结构平移工程中，主要采用四面包裹式托换节点进行柱的托换，托换节点处于弯、剪、扭复合受力状态，新旧混凝土界面是其受力的薄弱部位。为了改善界面的受力性能，提出两种新型托换节点，一种为在拟托换柱四周植入界面锚筋，另一种为在托换节点四周施加预应力。考虑托换梁高度、托换梁剪跨比、纵筋配筋、箍筋配筋以及界面锚筋或预应力等因素，对这两种新型托换节点进行试验研究，揭示其受力特性和破坏机制，并与普通托换节点进行对比研究。对托换节点建立精细化有限元模型，研究其应力变化及界面滑移。在试验研究基础上，结合有限元分析，考虑托换节点界面不破坏，建立托换梁的拉-压杆模型，得到托换梁的承载力计算公式；针对新旧混凝土界面，根据试验回归得到托换节点界面剪切摩擦系数，建立托换节点界面修正的剪切摩擦模型，得到界面的承载力计算公式。在试验研究基础上，根据不同的破坏机制选用不同的模型及参数，建立托换节点的承载力计算方法。

框架结构平移工程中，四面包裹式托换节点是做常用的托换形式。由于四面包裹式托换节点的空间受力特性，托换节点处于弯、剪、扭复合受力状态，而且还存在新旧混凝土界面的空间受力问题，使得托换节点的受力特性及破坏形式受众多因素影响，设计公式还不完善。本项目对四面包裹式托换节点进行了研究，同时提出了两种新型托换节点：预应力托换节点及界面锚筋托换节点，并对其进行了试验及理论研究。.首先对四面包裹式托换节点进行了试验研究，在试验中考虑剪跨比、纵筋配筋、配箍率、混凝土强度及梁柱结合面锚筋等因素，研究四面包裹式托换节点受力性能及破坏模式，并分析各影响因素对托换节点承载力及破坏形态的影响。研究发现，托换节点的破坏可以分为托换梁的受弯破坏和弯剪破坏，破坏模式主要受剪跨比影响，纵筋配筋参数也对其影响较大。同时梁柱的新旧混凝土界面在受力过程也易发生滑移失效。采用混凝土塑性损伤模拟混凝土的开裂破坏，并采用粘结单元模拟新旧混凝土界面性能，对托换节点进行了精细化数值模拟分析，得到了托换节点的受力全过程、裂缝分布情况及荷载位移曲线，与试验结果吻合较好。.托换节点试验中发现，托换梁在支座与加载点之间形成明显的斜裂缝，从而在支座与加载点之间形成斜压杆，下部钢筋受拉形成拉杆，符合拉-压杆的传力机制。建立了托换梁的修正拉-压杆模型，并推导得到了托换梁受剪承载力计算式。.针对托换节点的新旧混凝土界面在受力过程中也容易遭受破坏，因此提出了两种新型托换节点：预应力托换节点及界面锚筋托换节点。.通过研究不同预应力大小及预应力施加方向，对预应力托换节点进行了试验研究。研究发现，托换节点承载力与预应力随预加应力的增大而增大，基本呈线性相关；通过施加一定的预应力值，可以保证界面不发生滑移冲切破坏。托换节点双向施加预应力比单方向施加预应力受力更合理，且承载力提高20%。在试验研究基础上，推导得到预应力托换节点界面承载力公式。对界面锚筋托换节点的试验研究发现，托换节点通过布置界面锚筋，能够改变托换节点的破坏模式，控制梁柱界面在托换梁受剪破坏前不发生滑移破坏，同时提高了节点的延性。根据试验结果及界面受力性能的研究，提出了修正剪切摩擦模型，并进行界面承载力设计。在托换节点设计时，可以根据托换梁的受剪承载力及界面承载力确定界面锚筋的配置量，确保托换节点在托换梁受剪破坏前不发生梁柱界面的滑移破坏，实现托换节点的优化设计。