نشریه آنالیز سازه - زلزله
سال سیزدهم شماره 3 (پاییز 1395)

Bracing system is one of typical lateral bearing schemes in steel buildings. If just a limited length of ductile element becomes inelastic, a more controllable behavior is warranted. Knee Braced Frames, KBFs, are among such systems. In this paper, multistory frames (5 and 8-story frames) have been modeled with SAP2000 software and their lateral behavior has been studied. Meanwhile some of their properties have been introduced by using criteria such as target displacement, capacity curve (Force-Displacement), formation of plastic hinge and sample designed sections.
Better lateral performance of chevron knee braced frames compared to diagonal knee braced frames has been indicated due to more knee elements and thus higher damping. According to the results of chevron knee braced frames, when the height of the structure increases (from 5 to 8 stories), the target displacement increases 65%, base-shear and spectral acceleration decrease 10% and 40% respectively, while in diagonal knee braced frames the target displacement increases 70%, base-shear and spectral acceleration decrease 5% and 40% respectively.

More than a decade, the issue of improving the quality of building engineering knowledge infrastructure is considered as one of the most important cases. Deterioration and loss of columns and decks of bridges, beams, columns, walls of buildings are attributed to some cases such as the age of the structure, environmental destructive factors, weak design or implementation and also change of structures’ usage, and procedures of the old regulations or events such as earthquake. On the other hand, strengthening the location of the implementation of reinforced concrete structures is not usually taken into consideration. Therefore, strengthening the proper location of the structure and increasing the structural strength and reducing the cost of retrofitting have been of great importance to the attention of various researchers. The main purpose of this study is to investigate reinforced concrete structures in various modes of reinforcement of elements using FRP fibers. For this purpose, at first, three concrete structures with 5, 7 and 9 stories were designed according to the 2800 seismic regulations in SAP 2000 software and were subjected to static nonlinear analysis for which overlapping analysis has been carried out with a reverse triangular loading pattern. This structure is reinforced so that it can use the maximum structural capacity and also the columns enter the nonlinear stage after the beams. In the next step, we consider the structure in various ways such as strengthening the entire structure, reinforcing the frames, reinforcing the elements separately, strengthening the external frame of the structure, strengthening the internal frames (structural core), etc., so that through extracting the base cutting, floor drainage, the internal force of the elements and the amount of FRP consumed, we obtain the most optimal method for reinforcing the structure, which provides the functional level of LS safety with reinforcement by FRP.

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.

Steel is extensively used in the construction industry and, welded joint is a conventional type of steel joints. It is important that the welding quality should comply with standard terms and consistent with the contract. If the terms are not met and the quality of weld is poor, corrective actions (repairs) should be taken in accordance with the standard. Once the corrective actions (repairs) have been completed, the piece (the weldments) must be re-inspected, tested and checked in accordance with the requirements, and the conditions and causes of defect should be carefully reviewed and resolved. Fixing unacceptable welding defects is simply called "welding repair". This study, investigates the effect of repeated welding repairs on tensile properties of the component in the welding area. To this end, four samples (samples without repair, one repair, two repairs and three repairs) with thicknesses of 10 mm and 20 mm, were welded unilaterally (v shape), and an evaluation of tensile strength was implemented. The results show that for samples with the thickness of 10 and 20 mm, the mean yield stresses and the ultimate stresses of three repair welds increase compared to original welds. Furthermore, the failure in tensile often occurs out of the heat-affected zone and the tensile strength of mild steel (st37) subjected to three repairs is acceptable in the welding area.

This paper studies on active control of structures subjected to near field earthquakes. In order to evaluation of effects of earthquakes with different frequencies three steel structures of 4, 8 and 15 floors with different natural period have been desined using ETABS software based on allowable stress method then opensees software have been used for three dimentional modeling of structures. Considering the impact and frequency content complexity of new field earthquakes, these structures subseetes to new field earthquakes. The different softwares have been used to verify of structures modelling. In order to evaluation of frequency content of earthquake, all of records scaled to 0.6 g then applied to structures. Different dynamic analysis conducted using eleven near field earthquake records and then the results compared to non-controled model to indicate the effect of active tendons.

One kind of shear wall system is CSRCW which consists of two steel columns with stud and the column which is buried in reinforced concrete. This concrete cover can contribute to both load bearing and stiffness increasing. Studs are used to connect concrete to steel columns which have a very significant role in this regard. This research attempted to use the CFRP system in order to increase the load of the system. CFRP as a suitable method for increasing strength of structures has been the focus of research in recent decades. In 2012, D. Dan investigated the function of CFRP in reinforcing shear wall. After verifying the Abaqus software, the outlet will also be examined to reinforce CFRP. As such, the base model without FRP reinforcement and strengthening model A are crossed X shape and model B are crossed K shape and model C just overlaps at the corners. The results showed an increase in the load of about 18% compared to the Model A which is the base model.

The beam columns are under the influence of bending and compression, given that the buckling occurs in these members in one of the lateral, torsional and lateral-torsional forms, the bending moment and compressive axial force ratio have a significant effect on the behavior of the buckling. This paper investigates the performance of thin-walled closed box steel boxes under different loading conditions, concentrated load in the middle of the span, and a uniform distributed load with finite element method and with two-headed joint supported conditions in the range of elastic behavior. The tenth topic of the National Building Regulations, due to the large buckling limit moment from the yield limit buckling, does not occur in any global buckling, however, it mentions the probability of occurrence of lateral buckling in the range of post-elastic deformations for seismic beams. The results of this study show that in the presence of flexural loads, the buckling mode of the sections studied varies from the lateral buckling to the lateral-torsion, and the greater the ratio of the flexural loads to the axial loads, the torsional deformations will be greater. But, in the presence of bending loads on the buckling plane, the buckling mode of the sections in a certain amount of bending load will change from the global buckling to the local buckling. Compared to the three loading, the lowest M/P ratio, which leads to a global buckling, is related to the uniform distributed loading. By choosing the correct support condition in terms of the rotation around each of the fender members, and the appropriate shape of the box section, the strength of the member under the compression axial force-bending moment can be improved