نشریه سازه و فولاد
سال پانزدهم شماره 31 (بهار 1400)

T-shaped joints are one type of beam-column connections in steel structures. Ease of construction, transportation, and installation, as well as suitable ductility, economy, and durability, are the advantages of this type of connection. However, bolting of the T-shaped flange to tubular columns is very challenging due to limited access. In this research, by using through bolts for connecting the T-shaped flanges and the column, the transfer of forces and the rigidity of the panel zone have been provided. This is especially effective in concrete filled tubular (CFT) columns where the passage of concrete through the panel zone is important. On the other hand, the direct transfer of stresses to the column, the stretch of through bolts under cyclic loads, which reduces their performance level, as well as accumulation of bolts, which is caused by large diameter, and four-way connection, especially at a long opening that interferes with the passage of concrete through the panel zone are controversial. Therefore, to provide a suitable solution, in an innovative action, the external diaphragm of the column with through bolts was used simultaneously and the performance of the connection was examined.
In this study, using ABAQUS software, one connection sample with a through bolt and another with an external diaphragm were investigated. The results show that the overall performance of both kinds of connection is quite good.

Capacity based design of vertical boundary elements with regard to resisting expected yield strength of the web plate could be led to large column size. This key problem leads to a lack of widespread implementation of steel shear walls. This research project aims to investigate the formation of tension field in steel shear wall with partial length connection of web plate to vertical boundary element which in this type of steel shear walls, reducing the length of the connection leads to a reduction in the flexure and stiffness demand on the vertical boundary elements. For this purpose, the finite element modeling methodology was initially established and validated based on a laboratory test. Nine FE models were developed based on the verified specimens, and various not connected infill plate values. Finally, based on assumptions confirmed by numerical modeling and complementary experimental investigation, two governing equations have been developed for this type of steel shear wall, including panel shear strength, tension field inclination angle in the web plate in case, not connected length ratio is less than 30%.

Conventional earthquake-resistant systems, often experience inelastic behavior in a part of the structure during a large earthquake and eventually causing residual deformation and damage to the structure. Repairing these damages are unaffordable and often leads to structure destruction. Therefore, the use of structures with the ability to focus damage on interchangeable elements, which leads to reduced earthquake damage, is very important. Due to the importance of the performance of self-centering structures to reduce their damage against various earthquakes, in this study, the repairability index of buildings with post-tensioned self-centering connections has been developed. According to the 12 models of the studied building, a building that can be repaired, that the maximum rotation in its connection after the earthquake does not exceed the rotation of the immediate occupancy performance. Based on this, the output data of IDA analysis in OPENSEES were drawn according to the connection rotation-spectral acceleration. According to the predicted performance levels of Garlock for each acceleration level, the value of the connection opening is divided by the opening of the DBE level. The resulting curve shows the repairability index according to spectral acceleration, which if less than one, the repairability target is achieved. To evaluate the damage of angles, the failure index of the angle is determined according to the fragility curve and the intensity of damage in each building is expressed according to an equation.

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 study of the effect of mechanical and geometric properties change on connections in steel moment frames against progressive failure in this research. In this regard, the variable parameters include the beam - column connection type (welded flange plate connection or WFP and welded unreinforced flange-welded web connection or WUF-W, reduce beam section connection or RBS, free flange connection FF), the type of steel used at the beam - column connection (St37 and Steel LY 160) and the column removal location in different stories (without removing and removing columns on the ground, first and second stories). Investigations on a three-storey steel frame using ABAQUS finite element software and alternative loads path method. Validation of numerical method was performed using numerical simulation of a steel frame and a suitable agreement was observed. The most important results show that in the frames which low-yielding steel is used at the connection point, the best performance from the demand-to-capacity ratio (DCR) of the beams around removal location belongs to the Free Flange and WUF-W connection frames.

This paper focused on the behavior of steel plate shear walls (SPSW) in high-rise buildings. The influence of essential parameters including number of stories, stress angles and openings and investigated. Comparison with moment resistant frame and alternative method of modeling the shear walls with Strip elements is investigated. Using finite element method, a four story steel plated shear wall which has been tested before was modeled and the results obtained were compared with the test data. Comparison of the results approved the numerical modeling. Then the 20-story, 15-Story and 10-story steel plated shear walls were designed in accordance with AISC-Seismic Provisions to make results more practical. Comparing steel pated shear walls with different heights with each other, it is noticed that with lowering SPSWs, its initial stiffness improves and its ultimate strength decreases; but the overall ductile behavior was maintained. Also to make it useful and practical, moment resistant frames were modeled similar to SPSWs but without infilling panels. This research showed that with lowering the SPSW height, its behavior gets closer to moment resistant frames. Also behavior of SPSWs with openings was studied. Four openings in a same position, same width and different height were modeled to see the effect of openings on the overall SPSWbehavior. Generally, it was observed that an opening in infilling panels reduces SPSW initial stiffness and final strength.

With development of communication infrastructure in cities, the use of bridges is increasing day by day due to existence of non-level intersections. Limitation of urban spaces has caused a significant part of these bridges to have a horizontally curved deck so that they can connect different routes in a low space. Therefore, recognizing the seismic behavior of these bridges is of great importance. The past earthquakes, such as 1994 Northridge and 2008 Wenchuan earthquake, also showed that these types of bridges are highly vulnerable under earthquakes and especially under near-fault earthquakes. Horizontally curved deck causes geometric irregularities, as a result, the seismic behavior of these bridges is complicated under earthquake. Analysis of these bridges is time consuming and costly using a finite element method. In recent years, many studies have been done on modeling of irregular bridges to obtain more precise results from the seismic response of bridges and also reduce analysis time. In this study, a horizontally curved bridge was modeled using a spine-line model and then verified by field-test and experimental results. The validation results showed that by using simple models such as the spine-line model for deck modeling, and taking into account the dimension effect in the connections and the pinching effect in the base of columns, can produce a real model of irregular bridges, such as horizontally curved bridges. The reason for this is the elimination of numerical analysis errors.