Punching shear behavior of eccentrically loaded footings

在过去的研究中，许多研究人员都对中心荷载基础的冲剪性能进行了研究。试验结果作为钢筋混凝土基础现行冲切设计规定的依据，这些规定一般假定控制周边的剪应力呈对称分布。然而，在实践中，中心加载基脚是一个例外，因为非预期（如缺陷）和预期（如起重机轨道）的负载偏心适用于结构。为了考虑荷载偏心对冲切承载力的影响，各种冲切设计规定定义了增加施加荷载的系数。对不同规定的安全水平的最终声明是不可能的，因为迄今为止只对偏心荷载基础进行了少数冲压试验。对于点支承板，剪切应力和弯曲应力的叠加导致沿柱面沿着的多轴应力状态。中心加载板形成一个压缩环沿着柱面，这增加了剪切阻力相比，单向板。然而，随着荷载偏心距的增加，这种旋转对称的多轴应力状态不再完全可能在柱的非荷载侧形成，从而导致冲切承载力降低。此外，内部剪切裂缝的形成受到荷载偏心率的强烈影响。所要求的研究项目的主要目标是对偏心荷载基础的冲切行为进行基础研究。通过对单、双向偏心荷载作用下钢筋混凝土基础的试验和数值模拟，研究了不同荷载偏心率和基础几何形状下，柱面（受压环长度）沿着方向的多轴应力状态以及内部剪切裂缝的形成。主要研究结果用于推导一致的模型，该模型可以分别基本描述载荷偏心率与压缩环长度或内部剪切裂纹形成之间的关系。基于该模型，现有的冲切设计规定的中心加载基础偏心加载的情况下进行了扩展。

The punching shear behavior of centrically loaded footings has been investigated by various researchers in the past. The results of the tests served as the basis for current punching shear design provisions for reinforced concrete footings, which generally assume a symmetrical distribution of shear stresses in the control perimeter. In practice however, centrically loaded footings represent an exception, since unintended (e.g. imperfections) and intended (e.g. crane tracks) load eccentricities apply to the structure. To consider the effects of load eccentricities on the punching shear capacity, the various punching shear design provisions define factors to increase the applied load. A final statement on the level of safety of the different provisions is not possible, since only few punching tests on eccentrically loaded footings have been conducted so far.For point-supported slabs, the superposition of shear and bending stresses results in a multi-axial stress state along the column face. Centrically loaded slabs form a compression ring along the column face, which increases the shear resistance compared to one-way slabs. With increasing load eccentricity however, the formation of this rotationally symmetric, multi-axial stress state is no longer entirely possible on the non-loaded sides of the column resulting in decreased punching shear capacities. Also, the formation of inner shear cracks is strongly influenced by the load eccentricity.The main goal of the requested research project is the fundamental investigation of the punching shear behavior of eccentrically loaded footings. By means of experimental and numerical investigations of the behavior of reinforced concrete footings with uniaxial and biaxial load eccentricities, the multi-axial stress state along the column face (length of compression ring) as well as the formation of inner shear cracks is investigated for different load eccentricities and footing geometries. The main findings are used to derive a consistent model, which allows for the fundamental description of the relation between load eccentricity and length of the compression ring or inner shear crack formation, respectively. Based on the model, existing punching shear design provisions for centrically loaded footings are extended for eccentric loading situations.