فهرست مطالب تقی مفید

Structural elements and systems experience a decrease in strength and stiffness throughout their lifetimes, called degradation. One of the most common types of degradation in RC (Reinforced Concrete) structures is the cyclic degradation caused by earthquakes. Structures that experience one or more earthquakes during their lifetime, experience a degree of degradation that affects their seismic response to subsequent earthquakes. Existing numerical models take into account the cyclic degradation of an earthquake, but many of these models neglect the effects of degradation caused by previous earthquakes; Recent studies show that this degradation has significant effects on the response of structural elements. In this study, the cyclic degradation of RC beams and their impact on the post-earthquake behavior of the beams is investigated experimentally. For this purpose, 12 RC beams are manufactured and subjected to displacement-control loading. Periodic loading with uniform amplitude is used to simulate the earthquake cyclic degradation. Three levels of slight, moderate and extensive degradation are selected to investigate the effect of cyclic degradation on the post-earthquake behavior of elements. After the experiment, the results of the hysteresis diagrams, strength degradation and energy absorption of the specimens are presented and discussed. The results of this study show that as the level of cyclic degradation increases, the energy absorption of RC beams decrease; Especially in the extensive level of degradation, the energy absorption of the beams is reduced by more than 40%.

A rehabilitation technique that utilizes a thin steel plateas a supplemental shear wall system for steel momentframes is described. In the proposed system, the plateand surrounding boundary elements are installed in themiddle of the bay, separate from existing columns (SW-TB =Steel Plate Shear Wall with Tension-Bracing). Thisgeometry intends to reduce the forces transferred to theexisting columns. In this paper, the behavior of steel mo-ment frames using the proposed system is investigated.Among the methods of retro tting of the steel frames,application of steel bracing system has been studied bysome researchers. The results of these studies show thatretro tting of steel frames by adding braces has dis-advantages such as increasing axial forces in adjacentcolumns, brittle behavior in the frame joints, bucklingthe bracing member, and creating a permanent deforma-tion on the frame. In order to remove these disadvan-tage researches such as the use of non-compression brace,buckling-restrained braces, dissipative bracing systems, displacement-restraint bracing and thin in ll panels areexamined. Steel plate shear wall systems have attractedmore attention in the past few years as one of the majorlateral-load resisting system in steel buildings. In thiscontext, many investigations have been conducted in dif-ferent countries. In this study, to eliminate the above-mentioned disadvantages, a SW-TB system is used toretro tting of a steel frame. Recent researches indicatethat this type of shear walls has a very good perfor-mance in comparison to its traditional form (i.e., SSW=Steel Plate Shear Wall). For this purpose, the Finite-Element Model (FE) of steel frame retro tted with steelshear walls and tension-bracing has been made. Theobtained results of this model are compared with Lab-oratory data. The comparison shows that the nite-element model produces similar results to those of theproposed method in the laboratory. After the experi-mental validation, this method is compared with threeother methods. The FE analysis results show that usingthis method causes the lateral resistance of the structureto increase as much as 50 percent with good ductility,and the need to enhance the lateral columns and foun-dations will be limited.