老顶的初次断裂步距和周期断裂步距

本文应用板的极限分析法求老顶的断裂步距,从而解决了按板模型周现有的方法不能计算老顶周期断裂步距的问题这种方法的另一个显著的优点是它不但适用于矩形采空区而且也适用于非矩形采空区。作者导出了几种常见开采边界老顶的初次、周期断裂步距的表达式,并通过算例说明了公式的用法。本文最后讨论了工作面长度和开采边界对老顶断裂步距的影响,提出了对坚硬顶板控制有实际意义的工作面临界长度的概念。图5,表1,参6.

Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

Variation analysis of ultimate pullout capacity of shallow horizontal strip anchor plate with 2-layer overlying soil based on nonlinear M-C failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule,a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed.The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced.When the 2-layer overlying soil is degraded into single-layer soil,the model of ultimate pullout force could also be degraded into the model of single-layer soil.And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method.Based on that,the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed.The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly.Thus,it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.

Analytical model for ultimate loading capacities of continuous composite slabs with profiled steel sheets

Composite slabs with profiled steel sheet are widely applied in practical structures now. Plenty of literatures can be available about simply supported composite slabs with single span. However, continuous slabs always exist in high-rise building structures. In order to obtain the ultimate loading capacity of continuous composite slabs, the full scale test on slab specimens with high cost need to be carried out. This paper presented an analytical model for calculating the ultimate loading capacity of continuous composite slabs. Only the small-scale slide block test needed to be carried out for determining some mechanical parameters, resulting in less cost, compared with the conventional m-k test method. Various load conditions and parameters were considered in the analytical model. The comparison between test results and predicted results showed that the proposed method had enough precision. Furthermore, the simplified method was also proposed for practical design.