Post Local Buckling Behavior and Ultimate Capacity of H–section Beam
Abstract This paper presents a study on the ultimate capacity (maximum strength and plastic deformation capacity) of a thin–walled H–section beam. An experimental study is adopted by subjecting beams under cyclic loading to a large range of deformations with large depth–thickness ratios, which are over or close to the limit value of the current standards. The objectives of the present paper are to reveal the post local buckling behavior and to propose a handy method to evaluate the ultimate capacity. Instead of the commonly used parameter of width and depth–thickness ratio, the normalized thickness ratio WF developed in this study based on the author's previous studies can be regarded as the major parameter to evaluate the ultimate capacity. The relationship between WF and ultimate capacity is examined. The improved criteria for assessing the maximum strength and plastic deformation capacity of an H–section beam is proposed using normalized thickness ratio WF and is shown to be in good agreement with the experiment results.
Characteristics of Overburden and Ground Failure in Mining of Shallow Buried Thick Coal Seams under Thick Aeolian Sand
Mining can lead to overburden failure and ground damage, which are more severe in mining shallow buried thick coal seams (SBTCS) under thick aeolian sand (TAS). We attempted to discover characteristics of mining in this particular geological condition through theoretical derivation and numerical simulation, and field monitoring. Theoretical methods, combined with numerical simulation and field monitoring methods, reveal the essence of the development and distribution of surface cracks caused by mining SBTCS and depth to thickness ratio (DTR) to be 13.43, less than 15. The findings show that, when mining SBTCS, the overburden breaks down periodically, the initial collapse distance is greater than the collapse step, approximately 55 m on average, and the collapse step is approximately 45 m, on average, in the Daliuta Coal Mine. The collapsed blocks are stacked into goaf and form “masonry beams”, and many cracks and pores are generated between the blocks. The weak stress of the aeolian sand layer causes the movement angle in the aeolian sand layer to be smaller than that in the bedrock, and leads to much sheer, tension and compression failure on the ground, and the main forms of cracks are compression uplift, tensile cracking, shear step.
Behavior of Thin-Walled Steel Box Columns Under Biaxial Loading
Ultimate strength tests on welded thin‐walled steel box columns simply supported at the ends and subjected to biaxial loading are reported. A series of 28 large‐scale box columns of square and rectangular cross section were tested to failure. The parameters that were varied include plate slenderness ratio, column slenderness ratio, cross‐sectional shape, and eccentricity of loading. A description of the specially built test rig along with end fixtures and experimental procedures are also presented. Extensive measurements of welding residual stresses and initial column deflections were made. Stub‐column tests were also carried out. The test results show that the ultimate load‐carrying capacity of columns dropped with an increase in the plate slenderness ratio and an increase in the load eccentricity. The experimental failure loads of the tested columns are compared with the corresponding theoretical values obtained by the method proposed earlier by the writers.