نشریه آنالیز سازه - زلزله
سال هفدهم شماره 1 (بهار 1399)

Undoubtedly, one of the main and effective members in building structures is the ceiling, and the type of execution of this part of the structure will play a significant role in the speed and quality of the entire structure. The application of old materials and traditional construction methods no longer meets the desired speed and design needs. In this study, in addition to introducing the structure of U-Boot roof, an attempt has been made to provide a comparative approach in terms of structural performance with other common roofs such as steel deck roof, concrete slab and Cobiax roof. For this purpose, after ensuring the results of modeling using Abacus software, modeling of numerical samples and comparing them with other common ceilings have been done. The results indicate that by comparing concrete slabs, when increasing the compressive strength of the specimens, the amount of final yield load is increased, but after the yield point, the failure of the specimens was immediate. Then the load capacity has remained constant for the same displacement, and with a decrease of 30% in the number of U-Boots and a 20% increase in compressive strength, the amount of load capacity has increased by about 22.32%. Comparing these specimens with the state without reducing the number of U-Boots, it is determined that for each similar sample, the load bearing capacity has increased by 10%. The U-Boot roof also has higher hardness and load-bearing capacity than other roofs and the concrete slab has the lowest load-bearing capacity in the same displacements. The performance of the steel deck roof and the Cobiax roof is also close in terms of bearing capacity, but in terms of the hardness or gradient of the force-displacement curve, the Cobiax roof has shown more hardness.

One of the effective factors in the designing process of buildings is how to control and manage the seismic force to achieve the optimal seismic resistance while maintaining proper ductility. In this regard, the application of various bracing systems in the construction of high-rise buildings, such as steel and concrete shear walls is a common solution. Therefore, in this research, once considering the soil-structure interaction and again without considering the impact of this interaction on two 10 and 15-story structures, different models of ABAQUS software were presented in the presence of steel and concrete shear walls. The nonlinear analytical method was investigated. For this purpose, by modeling the structures mentioned in the software, the effect of using steel and concrete shear walls was analyzed in terms of the impact of soil-structure interaction and without it. The results of modeling for 10-story structures showed that the performance of the structure with steel shear wall is better than concrete shear wall. In addition, the results obtained for the 15-story structure showed that the performance of this structure with steel shear wall was better than concrete shear wall. In general, the results present that the steel shear wall exhibits better behavior than the concrete shear wall. In general, it was found that by taking into account the soil-structure interaction in the modeling performed for both types of structures, the outputs are closer to reality.

As the population grows, the importance of creating more buildings in the short term and at low cost, such as prefabricated structures, becomes more apparent. For this purpose, in this research using SAP 2000-14 software, three kinds of 2, 4 and 6-story RC frames were designed by considering connection rigidity. Three types of connection rigidity including pinned, semi-rigid and rigid precast RC connections were applied to estimate response modification factor (R) of designed frames. It is worth mentioning that each of the frames has five bays and the length of each of the bays is 5 meters with the exception of median bay that is 4 meters strengthened with X-steel bracing. Then the nonlinear static analysis was applied to evaluate the effect of frame’s height and connection rigidity on response modification factor of designed frames. The results presented that with increasing the rigidity and frame’s height R factor is increased.

In the seismic design of structures, determination of the number and position of braced frames, according to the architectural scheme of projects, is usually encountered with obstacles. This has made it difficult in some cases to choose the best location and number of braced bays and especially in dual frames, has led to differences in the design forces of their adjacent members (columns). One of the seismic design requirements of lateral resisting system is to control the columns adjacent to braced bays for load combinations of intensified seismic load, which is a function of over-strength factor of the structure. This research aims to present and introduce the best structural model regarding the number and position of braced frames in a structural system, such as steel moment resisting frame and eccentric braces dual system. Though the intensified seismic load function is controlled in models which columns are connected to the braces in 2 directions, and seismic loads are applied in those 2 directions, the number of damaged hinges (Exceeding CP) is significantly increased in comparison with the models with straggly braces. Since the increase in axial force of these columns reduces their moment capacity (despite controlling the amplified seismic load provision), columns in dual systems that resist flexure, would be damaged and exceed the collapse threshold much sooner than other columns. Therefore, it is suggested that, like the publication 360, the control of these columns in an amplified earthquake should not be based solely on axial force, but on the interaction of forces.

Connections have a significant effect on the energy depletion of the structure and its behavior against unusual loads, which often lead to the phenomenon of progressive deterioration.  Therefore, the effect of changing the mechanical and geometric characteristics on the connections in steel moment frames against progressive failure has been studied in this research. In this regard, the variable parameters include the type of beam-to-column connection (reduced beam section connection or RBS, free flange connection FF), the type of steel used at the beam-to-column connection (St37 and Steel LY 160) and the column removal location in different stories (without removing and removing of the columns on the ground, second and fourth stories). Research on a six-story steel frame is performed using ABAQUS finite element software and alternative loads path method. Validation of the finite element method was performed using numerical simulation of a steel frame and a suitable fit was observed. The most important results present that in the frames where low-yielding steel is used at the connection point, the best performance in terms of demand-to-capacity ratio (DCR) of the beams around the removal location belongs to the Free Flange connection frames.

Nowadays, it is recommended to use non-stiffened steel plate shear wall. One of the innovations that can be applied to the steel plate shear wall is the use of corrugated sheets instead of flat sheets. Therefore, corrugated sheets are utilized to delay the occurance of buckling. In this study, regarding to the importance of the subject, to ensure the accuracy of the modeling, a laboratory sample of Choi and Park was selected for verification and after ensuring the accuracy of the results, 8 samples of corrugated sheet steel plate shear wall were modelled by ABAQUS software. In these samples, parameters such as thickness of the steel sheet, the length-to-width ratio of the sheet (a/ b) and change in the geometric characteristics of the perimeterial elements are investigated. Numerical results presented that the stability of the hysteresis curve cycles in the specimen with a plate thickness of 8 mm was not constant, as observed in the final loading steps, loss of resistance and local buckling in the loading cycles. Numerically, it can be said that the sample with a sheet thickness of 8 mm has the highest bearing capacity compared to the samples with a sheet thickness of 4 and 6 mm. The effect of boundary elements on the performance of the specimens was negligible. Finally, it was revealed that with increasing the length of the sheet relative to its height, the amount of plasticity has significantly increased.