محسن عقابی

Reduced Beam Sections (RBS) provide ductility for rigid connections in steel moment frames by reducing the load imposed on the panel zone and driving the location of the plastic hinge away from the column. Despite these advantages, RBSs are accompanied by a number of drawbacks, among which are the impracticality of some of the proposed models, early local buckling in the beam’s flange/web, and lateral torsional buckling brought on by the transverse reduction in the flange’s width. The objective of the present study is proposing a new RBS detail that has the minimum number of these weaknesses, while benefitting from the advantages of reduced sections. In the first step, a number of numerical models were constructed inside the ABAQUS finite element software. After analyzing the models using pushover analyses and interpreting the results, three beam models were selected. One of these models was an AISC-approved RBS model, which was used as the basis of comparison to evaluate the performance of the proposed specimens. In the three models proposed, the reduction was in the form of decreasing the thickness of the beam’s flange. In one of the models, thickness reduction in the flange was done by creating shallow grooves. In the remaining sample, a rectangular area on the surface of the flange was shaved off to create the reduced section. The plastic section moduli of the proposed samples are equal to the thinnest section of the RBS specimen. The experimental RBS samples were full-scale, and tested under cyclic loading. The results of all of the samples showed that plastic hinge was created in the expected region. The seismic criteria for the special moment connection were satisfied by all of the proposed samples. The sample with the shaved flange was superior to the RBS specimen in terms of ductility and energy dissipation.

In the past years, the use of steel structures with Saddle (khorjini) beam to column connections was one of the common construction methods in Iran. But the behavior of steel buildings with this type of connection in earthquakes such as Manjil 1369 and Bam 1382 showed the failure of connections before the failure of beams and columns. Considering the advantages of this connection, if new details and proper performance are provided, The Saddle connection can be used as a suitable connection in modern steel structures. For this purpose, in this paper, a new rigid saddle connection with reduced beam sections (RBS) for earthquake-resistant steel structures is presented. In the rigid saddle connection, two beams pass continuously on both sides of the column and are connected to the column by vertical plates. The RBS method has disadvantages such as local buckling of the web and lateral torsional buckling, to avoid these weaknesses and improve the performance of the connection, diagonal stiffeners were used in the beam web. Three laboratory samples were made and tested using IPE 140 profiles. According to the results obtained from these experimental tests, it was found that the sample with a reduced cross-section can withstand a rotation of 0.06 radians and the sample with stiffeners can withstand a rotation of 0.07 radians without any significant drop in the strength, which shows that both connections have an acceptable performance considering the Requirements of the AISC standard, and are placed in the category of rigid connections that can be used in the special moment frame systems. Also, the use of diagonal stiffeners increases energy dissipation and plastic rotation capacity of the connection.

Investigation of the nonlinear behavior of SPSWs requires complex non-linear finite element analyses. These analyses have some drawbacks namely convergence problems, time-consuming, and the need for expertise. Therefore, it is necessary to propose a comprehensive method that can solve the problems of current methods. In this research, a novel approach based on the use of axial members to evaluate the nonlinear behavior of SPSWs with any arbitrary configuration is developed. The innovation of the proposed method is that the obstacles in modeling of shear walls with different shapes and aspect ratios have been solved. Moreover, due to the low computational cost of this method, i.e., a 60% reduction in modeling time, and a saving of 92% and 66% in analysis time in static and cyclic loading, respectively, full-scale structures can be analyzed with acceptable accuracy. In addition, owing to its comprehensiveness, this method can be placed in existing commercial software, or it is possible to be developed as software. To evaluate the efficiency of the proposed method, 4 different SPSWs with different mechanical and geometric characteristics were analyzed using the proposed method. The results showed a good agreement between the outputs of the proposed method and the actual behavior of the SPSW, which verifies the suitable performance of the method. The results of analysis using the proposed method indicated that the maximum shear stress ratio occurs at the lower H/L and thickness. In addition, increasing the thickness and H/L of the infill results in an increase in the shear that can be tolerated by the section as well as a reduction in the stress ratio. The average of reduction for an increase in thickness and H/L is 61.8% and 72 %, respectively.

Pipe behavior under fault displacement is complex. In the past earthquake fault displacement of 2.1, 3 and 4 meters has been reported. Literature review shows understand failure modes of buried pipelines subjected to big fault displacement, is a challenge. In this paper, the influence of the thickness of the pipe on the response of the pipe under the fault displacement greater than 1 meter is studied. The quasi-static analysis by taking into pipe-soil interaction, by finite element simulation was performed with the ABAQUS software. Pipe and soil Dimensions and material properties of the soil and pipe is fixed in all analyzed. The fault displacement (0.2 to 3 meters) and the pipe thickness (from 8.2 to 20 mm) variable parameters of this article. For variable displacement faults and the thickness of the pipe, the pipe deformation After removing the fault, the thickness of the pipe and the amount of displacement of the fault on the behavior of pipe strain exists in the pipeline wall is extracted and discussed is located. The displacement of less than 1 meter, the pipes like the letter S and local buckling occurs in the pipeline. The displacement of 1.5 meters and more like the letter Z-pipe deformation and wrinkling occurs in the pipeline. The displacement of more than 1.5 meters, distortion, and wrinkling pipe is deformed. The displacement of more than 1 m by increasing the thickness of the pipe, the strain is reduced. Change the thickness of the pipe, the pipe failure mode changes.