فهرست مطالب نادرفنایی

Concrete-filled tube (CFT) columns are a favorable and economical option for designing mid-height and tall buildings. However, using internal continuity plates in conventional moment frames will weaken the panel zone since infill concrete is present inside the steel tube column. Due to perforation of the continuity plate, stress distribution in this plate changes, and its strength and stiffness decrease. The proposed method in this study is aimed to strengthen the continuity plates with shear stud so as to transfer a part of the high force of continuity plates to the concrete. In this regard, two different full-scale specimens of rigid connections of I-shaped beam to CFT column were tested under cyclic loading. In the other part, using the finite element method in Abaqus software, the experimental specimens were modeled and analyzed. As a result of the stiffening of the continuity plates, the connection's bending capacity and cumulative dissipated energy increased by 7% and 4%, respectively. Additionally, the stiffening moved the highest rupture index by approximately 20% of the beam flange width from the outer edge of the flanges of the beam to the longitudinal axis of the beam. The proposed connection was approved for use in seismic zones' intermediate moment frames.

Previous studies have demonstrated the occurrence of brittle and early stage cracks in the connection between the link beam and the column, specifically in the vicinity of the groove welds  that connect  the flanges of the link beam to the column, when subjected to seismic activity. A similar type of rupture has also been observed in the end-plate connections of the link beam to the external link beam. This research explors the consept of utilizing a box-shaped link beam with a reduced cross-section in the Abaqus finite element software to magnitude the plastic strain demand generated at the flange ends of the box link beam. The objective is to prevent rupture in this specific region. The results indicate that the maximum equivalent plastic strain at the end of the link beam flanges can be reduced by up to 38% for short link beams, up to 41% for intermediate link beams, and up to 68% for long link beams. Consequently, this approach effectively prevents premature ruptures in the area adjacent to the groove weld connecting the beam flange to the end plate. The magnitude of the equivalent plastic strain at the end of the box link beam decreases as parameters "a" and "b" decrease, and parameter "c" (geometric parameters of the reduced cross-section) increases. Parameter "c" exhibits the most significant influence on this parameter, while parameter "b" has the least significant impact. Additionally, the adoption of a reduced cross-section in the box link beam results in an increase of up to 35% in the energy dissipation of the link beam due to enhanced participation of the flanges in energy dissipation for short link beams, up to 158% for intermediate link beams, and up to 250% for long link beams.

The purpose of this study is to investigate and improve the performance of energy absorption and dissipation system in the steel moment frames with short span lengths and deep beams. One of the challenges for designing a steel moment frame system is the existence of some code limitations such as minimum span length and beam depth that designers are required to follow in order to form the plastic hinges at both beam ends. By weakening a part of the beam in its middle, the mechanism of energy dissipation is changed from bending to shear, and this defect is practically eliminated. One of the studies on weakening the middle of the beams is to make circular holes in the beam web. By changing the shape of holes from circular to elliptic and changing the arrangement of the elliptic holes and the angles of the elliptical axes relative to each other and by maintaining constant the hole area reduced from the beam web, according to the models built in Abaqus software and comparing the response of different hole arrangements with circular ones, more ductility has been reported. Thus, in the models in which a combination of vertical and horizontal elliptical holes is used, more energy dissipation has been observed compared to other elliptical cases and 16% more energy dissipation has been calculated compared to the circular case.

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%.

The eccentrically braced frame has more ductility in comparison with concentrically braced frame and more lateral stiffness in comparison with moment resisting frame and involves the advantages of both moment frame and concentrically braced frame. Because of these reasons, this system has gained popularity in the last decades. I shaped and box-shaped beams are two usual link beams. In cases that lateral braces are hard to provide at both ends of the link beam, box link beam has some advantages comparing to the I-shaped beam because of its high torsional stiffness. Using transverse stiffeners in Box link beams, delays local buckling and leads to higher buckling stability and energy dissipation in links but increases the cost of construction and decreases the velocity of execution. In this research, low yield point steel, as a new material in seismic design of steel structures, has been used as web of link beam in order to enhance local buckling stability of links and eliminate intermediate stiffeners. Using low yield point steel in the web of link beam makes it possible to increase links web thickness and lowers the compactness ratio of the web as a result. Because of low yield stress, high ductility, and strain hardening, low yield point steel prevents buckling and fracture and increases energy dissipation of structure but using of low yield point steel as link web, leads to the about triple value of over-strength in comparison with usual steels that should be considered in the design of force-controlled members based on link beam capacity. According to this research, using Low yield point steel with a compactness ratio less than 16.5 and without intermediate stiffeners as link web, eliminate local shear buckling. Also using Low Yield Point steel in link beam may lead to a higher response modification factor.

IntroductionIn the last six decades, several experimental and analytical researches have been carried out to investigate the structural effects of the infill panels, especially in seismic loads. These studies showed that infill panels have considerable effects on the performance of infilled frames that should not be neglected in a safe and realistic design.In most of the buildings that require seismic retrofit, beams are not sufficient for the dead and live loads, and therefore, part of the vertical load is transferred to the ground through the walls. However, in most of the researches on infilled frames, the vertical load is not considered. In other words, very few studies investigate the effect of vertical load and its influence on the behavior of an infilled frame. These researches show that vertical load can have considerable effects on the strength and stiffness of masonry infilled frames.Research ProcedureThispaper presents a numerical study concerning the effects of vertical loads on the behavior of masonry infilled steel frame in seismic events. In this regard, an experimental study is selected that includes two identical infilled frame specimens [1]. One ofthe specimens is only subjected to lateral loading and the other one is subjected to lateral and vertical loading. Finite element method is employed to simulate and analyze the infilled frames. The specimens are modeled and verified based on the corresponding experimental results. Micro modeling method has been used, instead of modeling the mortar, half of its thickness is added to adjacent bricks. Concrete damage plasticity (CDP) approach was used to model the inelastic behavior of the masonry.ResultsThe analysisresults showed that the finite element modeling is well capable of predicting the behavior of the infilled frames. The initial stiffness of the analytical model matches with the experimental stiffness; however, as the loading continues, the strength of the finite element models is greater than that of the experimental specimen. This difference is due to the fact that the experimental specimen is subjected to cyclic loading and therefore experiences more strength degradation than the finite element model that is under monotonic loading. Based on the finite element study, the vertical load applied to the infilled frame is distributed in two ways, part of it (approximately 40%) is transferred through beam to column connection and the other part (approximately 60%) is applied to the wall. When the vertical load raises from zero to 200 kN (in which the vertical loading of 128 kN that is equivalent to 6.7% of compression capacity of the masonry prism is transferred to the masonry wall), strength and stiffness are increased 15% and 50%, respectively. The strength reduces when the vertical loading raises reach from 200 to 300 kN, and the stiffness remains constant approximately after vertical loading of 300 kN. It can be stated that up to a certain point, vertical load results in the increase in the stiffness and strength of the infilled frame, and after that point, the stiffness approximately remains constant and ultimate strength decreases.This occurrence can be justified as until a particular values vertical load increasesthe friction between the bricksandthus increases the strength. However, after this value, the vertical load turns into a destructive factor in combination with the lateral load effects. Ductility of the specimen with vertical loading of 200 kN is less than that of the specimen without the vertical loading.

There are few actual records of near fault ruptures with features dierent from those of far elds. These features are mostly aected by forward directivity in near eld earthquakes. So, investigation into this eld of study by using methods such to simulate records would be essential Until now, dierent methods have been used by researchers to simulate strong ground motion. Stochastic simulation is a method widely used for simulating high frequency ground motion in recent years. This method, which considers a point source, was presented by Boore (1983). The seismic source is considered to be a rectangular fault plane divided by some sub-faults in its longitudinal and traversal directions. Bersneve and Atkinson (1998) have introduced earthquake stochastic simulation based on nite fault modeling. In such simulations, each subfault is considered a point source, using the source model presented by Brune, with a corner frequency and a constant stress drop. The target accelerogram is obtained by summation of accelerograms generated by each subfault and by considering their corresponding delay times. This new modeling considers rupture geometry and the directivity eect; therefore, its results will be more appropriate. The stress drop parameter is one of the most important parameters in stochastic simulation that has a high uncertainty. This parameter is studied here, based on both stochastic point source and nite fault modeling. For this purpose, the stress drop is calculated for 7 Iranian earthquakes with at least one near eld record. Then, these earthquakes have been simulated by using the results of the stress drops. Finally, several parameters, such as nu, t0, gamma, and the impulse peak, which affect near eld records and directivity pulses, have been investigated.

For centuries, mathematicians have used recurrence relations, such as the famous Fibonacci recurrence sequence, and their produced functions for solving mathematics problems. The Fibonacci sequence is named after Leonardo of Pisa, who was also known as Fibonacci. The Fibonacci sequence is a set of numbers that start with a one or a zero, followed by a one, and proceeds based on the rule that each number is equal to the sum of the preceding two numbers. Unfortunately, this amazing aspect of mathematics has not been considered in the analysis of structures. This article is, therefore, particularly focused on using recurrence relations as an innovative method in the analysis of structures. In this research, rst, a continuous multi span beam with equal lengths under end, xed end and sliding end conditions is considered subjected to a concentrated bending moment at the beginning of the beam. Then, the function of the support moments is calculated and moments are obtained. In this regard, one - and two- story frames with equal span lengths have been considered in order to present the applied procedure. Accordingly, torsional springs have been used instead of columns, ignoring their axial stiness. The bending moments are then computed again at the connection of the beam and column using recurrence relations. Analyzing the sub-frame by this method is one of the products of using recurrence sequences for approximate analysis of the frames subjected to gravity loads. Finally, the eect of shear deformations has been considered for continuous multi span beams with equal span lengths and the structure is analyzed again. In all above mentioned cases, the structures have been analyzed by software as well. The results obtained from analyzing the structures using recurrence sequences are strongly in accordance with those using software. This article shows that the distribution of internal forces follow recurrence sequences in structures, like many other proportions seen in natural phenomena, such as the arrangement of leaves in plants.

Gate bracing system is a form of concentric bracing systems which is similar to chevron (inverted V) bracing. To provide enough space for openings، the members are not direct and joined together with different slope in one point. Bracing is joined to connection joint of beam and column in its other end. In this paper، overstrength factor، ductility factor and response modification factor of steel frames with gate bracing are evaluated. To do it، buildings with different story numbers on soil type II are considered. Static push over analysis، linear dynamic analysis and nonlinear incremental dynamic analysis are performed using Opensees software. To consider the uncertainties associated with earthquakes and to perform Incremental dynamic analysis procedure، 10 records of sever earthquakes ever happened including records of Bam and Tabas earthquakes are selected. Finally ductility factor، overstrength factor and response modification factor for gate bracing system are calculated and values of 3. 5 and 5 has been suggested for ultimate limit state and allowable stress design method.