نشریه سازه و فولاد
سال چهارم شماره 6 (بهار و تابستان 1389)

A new approach for design of roof system due to the effect of explosion in confined explosion structures for the missile workshops Abstract This paper discussed a new method for estimation of the behavior and required weight of roof for the confined explosion structures. The behavior of explosion in confined explosion structures affected by different parameters such as reflected pressure, duration of reflected pressure, gas pressure and duration of gas pressure. The main idea for these types of structures that will use as the missile rehabilitation workshops is to protect and creating life safety for the other parts of the workshop. The roof of this structure should fly after an explosion to decrease the gas pressure. On the other hand, this will be a weak point during an attack. In this case, these types of roofs could not resist against any strike. This paper discussed a mathematical modeling for the roof behavior. Finally the paper shows the new method for fabrication of these roofs without a frangible behavior considering the vent opening function. The known behavior of roof and designed mechanism for it could help the workshop structure to be protected by another shelter structure to present of any strikes.

Studying the behavior of asymmetric structures in past earthquakes shows that torsion was one of the main factors of failure of the buildings. One of the methods of reducing the responses of a structure is using energy dissipation devices. The main contribution of this study is determining of effective parameters and their values of friction dampers load to reduce the adverse effects of torsion in stiffness eccentric structures. For this purpose steel building models have been analyzed in OpenSees program for various stiffness and strength eccentricity and different distribution and properties of frictional dampers. Finally the responses of the structure have been compared for different cases of damper distribution and change in effective parameters that influence suitable distribution and optimum slip load of frictional dampers.

Different researches show that during an earthquake, the seismic input energy of structures strongly affects the seismic destructive which foresight them completely is not possible only by strength nonlinear response spectrum or drift methods. Because of the recent studies show that energy concepts be able to explain about all effective parameters on seismic behavior of structures, therefore in some recent decades, energy balance idea in structures was considered by optimum distribution of damage in structures. Since almost all structures will have nonlinear behavior under strong ground motions, therefore study on such behavior of structures is necessary. Purpose of this paper is assessment of damage distribution quality, drift and hysteretic energy in stories of concentrically braced frames which have designed based on Iranian Earthquake Code No. 2800 (Third Edition). The results show that the maximum stories drift and the ratio of hysteretic energy to input energy under near field to far field records have been increased to two and three times, respectively and despite of uniform distribution of strength in frames height, damage and hysteric energy distribution's diagrams are not uniform and centralization of energy and damage are indicated in first story, which with increasing the number of stories, this centralization is decreased and it appear the more uniform distribution of this energy in frames height.

This paper presents an experimental study about applicability of Buckling-restrained braces (BRBs) by polyethylene sheets. Buckling-restraining unit (encasing member), whose function is to prevent the brace from buckling, is almost tube that is filled by concrete or mortar and has many problems and difficulties as concreting, shuttering, curing, reinforcing, transporting and wasting of time. This research shows that polyethylene can be used as Buckling-restraining unit instead of steel tube and concrete or mortar. And also they can be used as a reducer of compressive forces at steel braces for strengthening the existing building. The advantages of this innovative and new method are save the time, light weighting, economic, easy and quick installation, decreasing the construction problems, no need to shuttering and curing.

The seismic vulnerability of a steel-concrete composite slab-on-girder bridge has been assessed in this paper.Firstly quantity assessment of the bridge has been done and through an in-depth inspection program all the defects were detected. Then based on the purposes of this study appropriate Finite Element (FE) model hasbeen created and the vulnerability assessment of the bridge has been carried out. In between the above mentioned phases some destructive and non-destructive tests were carried out in order to find the mechanical properties of the materials as-well-as the characteristics of the surrounding soils. It has been tried to use a rational modeling for the expansion joints of "balanced type" as-well-as for the special steel bearings of the bridge. Two different FE models with different levels of accuracy and different element types have been used to increase the reliability of the models and the FE models of the bridge has been updated in a procedure with comparing the modal results of the above mentioned models. Finally the seismic vulnerability of the bridge has been assessed through the standard procedure of seismic spectral analysis of the bridge. Capacity-demand ratios for all the bridge components and elements have been calculated. The results showed that the bridge have adequate seismic performance against Iranian seismic code (standard 2800). It was found that the bridge has a low level of seismic vulnerability. The study showed that the bridge still enjoyed relatively appropriate strength reserve and proper dynamic performance despite some minor cracks and steel corrosion suffering from carbonation and poor maintenance.

The Northridge earthquake on 1994 was a turning point in the design of rigid beam to column connection and revealed some major weaknesses in those types of connections that were being implemented in that time. Connection with side plates is a kind of improved connection which was proposed after the earthquake and can lead to healing those major weaknesses. According to the experiments it was observed that during the loading as a result of stress concentration the beam flange and its welds that are close to the side plate are the starting point to crack and failure. In this research in order to overcome these weaknesses, a new method has been proposed and new parts have been modeled and nonlinearly analyzed both materially and geometrically using programming in Ansys software. Also in order to validate the results obtained from modeling an experimental work has been done to backup the conclusion. The results verify that the new shape of connection would overcome the existing weaknesses as well as increasing strength capacity and better performance of the connection is achieved. According the results the experimented connection is accounted as a connection of special moment frame (SMF).

In this paper, results of experimental and analytical studies on a new type of infilled frames, having high ductility are presented. The studied infilled frames, regarded Engineered, had frictional sliding fuses at their midheights. The fuse could be regulated for a desired sliding strength in longitudinal direction, but was restrained transversally. In the first part of the paper, experimental results of two engineered infill specimens, with different sliding strengths of their fuses, are presented. Cyclic loads were applied to the specimens. It is shown that such infills have more stable hysteresis loops as well as higher ductilities, in comparison with regular infill panels. After having the experience of failure by in-plane loads, the specimens were tested again; one of them was repaired by grout and reloaded by the same loading protocol. The other one was loaded transversally to evaluate the out-of-plane strength of the engineered infills after being failed by in-plane loads. Results show that such infills have high transversal strengths and they can be efficiently repaired by grout. In the second part, behavior of the engineered infilled frames (EIFs) in real earthquakes are studied and compared with ones of bare frame and regular reinforced concrete infilled frame. For this, some nonlinear time-history analyses of a three bay frame with 1, 3, 5 and 7 stories were conducted by IDARC for five earthquake records. It is shown that the engineered infilled frames are efficient to improve seismic behavior of the considered buildings.

Each frame has a layout which may be different from the layouts of other frames. This difference may be stemmed from differences between bay lengths or frame dimensions in frames. So, investigation on how these differences can affect the parameters, which govern the design of structure, becomes very important. One of the effective parameters which reduce the elastic spectra into inelastic form is so-called strength reduction factor. In most codes, this factor is constant and does not depend on several factors such as differences between layouts. In this study some 5 story intermediate moment resisting frames with different bay layouts are designed, their over strength, ductility and strength reduction factors are calculated by performing triangular pushover analysis and the influence of different frame layouts on strength reduction factor is evaluated. The results indicated that bay length is an ignored significant factor that can affect the strength reduction factors and the major impact on strength reduction is due to the bay-span rather than to its number of bays. the difference between frames withlong bays and short bays is calculated to be as high as 35 percent.