نشریه سازه و فولاد
سال هفدهم شماره 39 (بهار 1402)

Unreinforced masonry (URM) buildings are rather popular around the globe due to low construction costs, even although they can be prone to substantial damage caused by even moderate earthquakes. In many cases, reconstruction is not the best choice because of financial and time restrictions. Shotcrete reinforced with steel mesh (SRS) is a cheap and simple yet effective method of repair/retrofit. This paper presents the results of experimental study with the aim of evaluating the effects of construction imperfections of steel reinforced shotcrete, as a retrofit method for URM walls, on the rebar pull-out resistance. For this purpose, a total of full scale URM speimens with one-sided 50 mm-thick shotcrete layer having a single steel rebar were made and tested. The results show in the case the wall’s finishing is not removed, the steel reabr cover is not sufficient, the plain steel reabrs is used, and , use of rebar without a tread, there is 57.8%, 55.2%, 25% and 7.5% decrease in the pullout resistance of the specimens, respectively.

One of the most widely used analytical methods to investigate the bending behavior of joints is the component method, which is mentioned in Eurocode 3. However, this method has some shortcomings such as a large amount of calculation, its reliability-low and its weaknesses in the post-yield behavior of the moment-rotation curve. In this research, to make the component method more efficient and reliable, this method was developed in the three mentioned aspects in such a way that the calculations of the method became more compact, the post-yield part of the moment-rotation curve was developed beyond the concept of Eurocode 3 and then it was used for fully welded and end plate connection. In the following, the obtained moment-rotation curves were verified by comparing them with the curve extracted using the laboratory method and finite element method in ABAQUS. In the end, parametric investigations within sensitivity analysis framework were carried out on these connections using advanced component method. The findings indicated that the advanced component method (the method developed in this research) compared to the conventional component method in Eurocode 3 can accurately predict the plastic part of the moment-rotation curve of the two connections. So that the difference percentage of the ultimate moment for the six-bolt extended end-plate connections in the comparison of the laboratory model with the outputs of conventional and advanced component method was obtained as 31.56 and -2.46 percent, respectively. compared to the outputs of the finite elements approach using ABAQUS, the difference percentage of initial stiffness and the moment of the connection is -14.75 and 5.55 percent respectively for the fully welded connection has been examined and -2.98 and 20.09 percent for the eight-bolt extended end-plate connections. Furthermore, it became clear that among the geometrical parameters studied for the two connections, the beam depth has the greatest effect on the change of the initial stiffness and the moment of the connection, as in the end plate connection has been examined, reducing the beam depth by 20 percent decreases the initial stiffness and the moment of the connection by 27.53 and 21.54 percent, respectively, while by increasing the beam depth by 20 percent, the initial stiffness and the moment of the connection increases by 28.65 and 21.54 percent, respectively.

Use of passive control systems causes reduction in seismic demand and prevents damage to the main components of the structure. Yielding dampers are among the common tools used for dissipation of earthquake energy entering the structure. The main goal of the present research is introduction of a novel pseudo elliptical yielding damper for improvement of the seismic performance of the existing steel structures. Considering the impact of geometric parameters of the pseudo elliptical damper on its stiffness and strength, a precise numerical study was performed on the ratio of diameter to thickness and other dimensions of the damper in this research.  For evaluating the impact of proposed damper on the seismic performance of existing steel buildings, use was made of three benchmark structures with 3, 9 and 12 stories which were retrofitted by this type of dampers. Also, the nonlinear time history analysis has been performed using the near field and far filed accelerometers to evaluate the analyses results at different seismic states. The results of numerical analyses indicated the good performance of propose pseudo elliptical yielding damper in terms of dissipating the earthquake energy entering the structure and reduction in the seismic responses of retrofitted benchmark buildings by this type of dampers. It was found that on average, the maximum inter-story drift in the 3, 9 and 20 story benchmark buildings were reduced by 66, 69 and 67%, respectively.

One of the systems resistant from to lateral load is the flexible from. The joints of the flexible frame are designed as rigids in these flexible frames, the purpose of the design is so that the plastic joint is removed from the connection point and placed on the beam. For this purpose and create a plastic joint in the beam, systems such as Reduce section are used.by weakening the beam in the critical area, causes the plastic joint to come out of the connection point on the beam. In this article, a replaceable connection has been achieved by using the Reduced section method and the patch system with up and underskirt sheets. That many problems in the reduced section have been solved and the behavior of the system has been improved. By using replaceable system, the structure has been repaired at a high speed after the earthquake and also its cost is very low. In this article, eight models have been evaluated numerically with Abaqus finite element software. Good results have been achieved by examining the cyclical and functional diagrams obtained from the models. In addition to the fact that the plastic joint has been removed from the connection point and placed on the beam, the possibility of being replaceable has also been added to the designed model, which has improved the problems to some extent

Steel moment frames have been known as one of the most reliable structural systems for many years. These structures were being designed and used as an alternative to masonry structures. It was assumed that these structures are very robust and will not collapse. However, some historic events such as the 1994 Northridge earthquake and subsequent tests proved otherwise. As a result, researchers tried to find ways to improve the seismic behavior of these structures. One of these methods is creating an opening in the beam web to move the plastic hinge to a region far from the connection welds. The purpose of this research is to analyze and investigate the dynamic behavior of steel moment frames with openings in the beam web and secondly to compare their behavior with the conventional moment frames. To achieve this goal, two four-story special moment frames with and without beam web openings have been modeled in OpenSees software, and nonlinear dynamic analysis has been performed on them. Finally, IDA curves, fragility curves and drift distribution in the height of structures are presented and compared. The results showed that the creation of beam web opening, increases the seismic collapse capacity of the steel moment frames and reduces their probability of failure during a seismic event. On average, the collapse capacity of a moment frame with beam web openings is almost 25% higher, and its collapse probability at different acceleration levels is 25% to 30% lower than the frame beam web openings.

One of the ways to reduce damages caused by earthquakes is to concentrate the damage in predetermined members (fuses). By absorbing a major part of the earthquake force, these members minimize the damage to other members of the structure. In this article, the performance of the fuse element with simple replaceability in eccentrically braced frames is studied. The proposed fuse element consists of three steel sheets that connect the link beam to the out-of-link beam through a joint connection, in the form of tongue and pin. When the loads are repeatedly applied to the divergent frame, the fuse causes the concentration of force in the connecting beam with the occurrence of shearing action and thus dissipates the force of the earthquake. In this study, ETABS software was used for frame design and ABAQUS was used for finite element analysis. The results show that the damage was limited to the fuse section, and there was no damage to other components of the structure. Also, this system has shown similar hysteresis behavior in tension and pressure, and the coefficient of behavior of this system is higher than conventional diverging frames, which indicates better performance and malleability of this system. On the other hand, since the damage is concentrated on a relatively small element, and the connection of this member to the frame is through pins, after a large