External bonding of fiber-reinforced polymer (FRP) plates or sheets has recently emerged as a popular method for the strengthening of reinforced concrete (RC) structures. The behavior of such FRP-strengthened RC structures is often controlled by the behavior of the interface between FRP and concrete, and this interfacial behavior is commonly studied through a pull test in which an FRP sheet or plate is bonded to a concrete prism and is subject to tension. In this paper, a meso-scale finite element (FE) model implemented with the MSC.MARC program is presented for the simulation of interfacial debonding failures in a pull test. In this model, very small nearly square elements (0.25-0.5mm in size) are used with the fixed angle crack model (FACM) to capture the development and propagation of cracks in the concrete layer adjacent to the adhesive layer. The effect of element size is taken into account in modeling both the tensile and shear behavior of cracked concrete. Comparisons between the predictions of this model and test results are presented to demonstrate the capability and accuracy of this FE model. The debonding mechanism is also examined using results obtained with the FE model. Finally, a method for the determination of the local bond-slip curve of the FRP-to-concrete interface from the FE results is described.

An accurate local bond-slip model is of fundamental importance in the modelling of FRP-strengthened RC structures. In this paper, a review of existing bond strength models and bond-slip models is first presented. These models are then assessed using the results of 253 pull tests on simple FRP-to-concrete bonded joints, leading to the conclusion that a more accurate model is required. In the second half of the paper, a set of three new bond-slip models of different levels of sophistication is proposed. A unique feature of the present work is that the new bond-slip models are not based on axial strain measurements on the FRP plate; instead, they are based on the predictions of a meso-scale finite element model, with appropriate adjustment to match their predictions with the experimental results for a few key parameters. Through comparisons with the large test database, all three bond-slip models are shown to provide accurate predictions of both the bond strength (i.e. ultimate load) and the strain distribution in the FRP plate.

利用动力有限元程序LS-DYNA，对纽约世界贸易中心受飞机撞击后的倒塌，进行了力学分析和仿真，并根据计算结果进行了参数讨论。仿真计算的结果与真实倒塌过程非常接近，说明通过适当的选取计算参数和计算模型，可以对这种特殊的复杂破坏过程进行模拟分析和仿真。计算结果说明，世界贸易中心倒塌的直接原因，是火灾导致的钢材软化和楼板塌落冲击荷载引起的连锁反应。如果能够提高结构的抗火能力或者提高结构的延性，将有可能避免结构倒塌，避免惨剧再次发生。