International Journal of Steel Structures最新文献

In urban environments, in many cases, buildings with unequal story plan sizes are desired, resulting in non-uniform mass/stiffness distributions along the buildings’ height. In this study, three groups of 12-story steel buildings with uniform, ascending, and descending story plan size distribution (PSD) along their height, but having the same total architectural space, were investigated to determine how this distribution affects their seismic performance. First, three site conditions—stiff, medium, and soft—were considered, and all buildings were designed by considering moment frames with concentrical bracings as their lateral load-bearing systems. Then, for each site class, seven appropriate sets of accelerograms were selected, and using nonlinear time history analyses, the buildings’ seismic performance levels were compared based on the formation of plastic hinges (PHs). Results show that non-uniform PSD can be quite effective on the seismic performance of buildings’ structures, so that on hard and soft sites, the number of PHs exceeding the collapse prevention performance level in buildings with ascending and descending PSD, respectively, decreases by approximately 30–45% and 20–40% compared with the uniform buildings. Therefore, it is explicitly concluded that employing buildings with uniform plan sizes does not necessarily lead to a higher seismic performance level.

To investigate the the pull-out behaviors of wedge-grouted rockbolts and grouted rockbolts in strongly weathered and moderately weathered rocks, the rockbolts with lengths of 8.0 m, 10.5 m and 13.0 m were tested under freeze–thaw cycle and cyclic load. The test result shows that the minimum anchoring length of wedge-grouted rockbolt is less than 3.0 m and of grouted rockbolt is less than 4.0 m in the strongly weathered or moderately weathered rock. The effect of the wedge head on restricting the deformation of the rockbolt is not obvious when the anchoring length is less than 6.0 m. Freeze–thaw cycle had little effect on the stiffness and deformation of the two kinds of rockbolts. The wedge-grouted rockbolts have better deformation performance than the grouted rockbolts. The bonding force between the rockbolt and the grout or the grout and the surrounding rock is greater than the tensile strength of the rockbolt. Furthermore, the calculation models of shear stress and axial strain can provide reasonable predictions for two kinds of rockbolts, and the development trends of strain and shear stress under different pullout loads were calculated.

In the last few decades, there has been an increase in the popularity of helical piles in developed nations and their penetration in the construction field in developing countries. The multiple benefits of helical piles over conventional piles for smaller structures in densely populated or environmentally sensitive areas for both onshore and offshore construction have made it an obvious choice for many geotechnical engineers. Moreover, the development of high torque-generating machines has revolutionized the use of helical piles as their installation process has now become much easier and faster. Therefore, it is important to analyze the behavior of helical piles using modern and sophisticated techniques. Finite element method provides the flexibility of easy analysis of the working mechanism of helical piles by reducing cost, time, and effort and providing accurate results. Finite element analysis (FEA) incorporates more variables such as the stiffness properties, and soil-pile interactions and provides a load settlement curve, thus offering a more realistic result. In this paper, the characteristics and behavior of helical piles under different design parameters, loading directions, and soil conditions have been analyzed using finite element method in Plaxis 2D software. The parametric analysis demonstrates the influence of different design aspects and other conditions around the pile on its load-carrying capacity. The extent of influence zone formed around the pile upon loading and the deformation pattern at failure have been studied. The values of critical spacing ratio and critical embedment ratio have been determined for both cohesive and cohesionless soils.