STRUCTURE AND STEEL
Year:2017 | Volume:14 | Issue:21 |Papers Count:7

Utilization of reducing brace’s section in concentrically steel braced frame to cope with seismic loads and raising ductility and its impact on the base shear variations is studied in this research. In this study, two types of fuses are created by reducing brace’s cross sections. The first fuse is created by reducing the cross-section of tubox bracing in certain areas. This type of brace has been used in the frames of 3& 7 story buildings with various openings. The second fuse is created by reducing the cross-section of angles in X bracing steel frames of 2 - 9 story buildings. Therefore, sections are designed such that the tensile capacity of bracing is lower than the capacity of connection. The above tasks were simulated using ETABS & ABAQUS software. Performance of the frames were examined under lateral loads.Results show that the braced frame with reduced sections dissipate applied energy from seismic loads and ductility of structure is increased. The formation of plastic hinges on the fuses prevent yielding of connections without the need for retrofitting. Transitional forces to main structural members and base shear of structures is decreased with good performance of fuses, which is an indication of optimal performance of the system and its preference.

There are various factors in the analysis and design of steel frames that uncertainty of them can have a significant effect on the structural safety. Accordingly, study of these factors to understand the actual behavior of the structure are important. Meanwhile, the initial stiffness of beam-to-column connection, can be considered as one of these variable.Therefore, in this paper, the effects of uncertainty in the initial stiffness of BUEEP, WFP and BSEEP connections, from rigid connections pre-qualified of Iran steel codes, on drift of simple steel frame are evaluated. In the firstly, the initial stiffness of mentioned connections based on the mechanical method of the European Code (EC3) and numerical method based on the finite element method by using of the commercial software ABAQUS obtained. By evaluating the responses of the two methods with experimental findings, stiffness obtained from finite element method selected as appropriate stiffness. Then, the probabilistic analysis performed by using of the Monte Carlo simulation method. It should be added, for stiffness of any connections, uniform distribution, normal distribution and lognormal distribution with coefficient of variation from 5 up to 20 percent are considered and drift of frames for thousands simulation are calculated. Results that exceed the allowable drift of Iran code, indicating count of failure of structure. Accordingly, the structure analysis performed 72000 times and probability of the failure will be evaluated. For all connections, the probability of failure for different distributions and coefficients of variation graphically displayed. In the following, reliability of the frame obtained from graphs of cumulative distribution function (CDF). Moreover, for any of the connections and in all investigated cases, a reduction coefficient to achieve 100% reliability and coordination of lateral displacement of with allowable drift with Iran codes becomes available.

In this new type of steel plate shear wall, called semi-supported steel plate shear wall, steel plates are connected to secondary columns which are responsible for undergoing post-buckling force of plates while in the traditional steel plate shear walls, steel plates are connected to main columns. Fiber polymers can be utilized to improve the functionality of semi-supported steel plate shear walls. The effect of yield stress, plate thickness, and fibers thickness and orientation on semi-supported steel plate shear walls reinforced by glass fiber polymers has been investigated in this study. The results exhibit that the behavior of system as well as its energy absorption and ductility can be enhanced by using plates with lower amounts of yield stress. Increasing each of plates thickness or yield stress improves ultimate resistance although the effect of plates thickness is much more remarkable than that of yield stress.Moreover, increasing the fibers thickness increases seismic parameters of the supposed system up to an optimal limit.

The study of seismic safety of buildings is one of the basic requirements for its implementation. In recent decades, structural reliability theory to be allocated very extensive research. Monte Carlo simulation is a suitable method for structural reliability analysis. In this paper, a new method of Importance Sampling is proposed to reduce the number of limit state function computations. A feature of the proposed algorithm doesn’t need to know the position of the design point or shape of limit state function. The main idea of the proposed algorithm is that the average amount of sampling probability density function is changing in the simulation process. Accordingly, the concentration of sampling will be on the areas of problem space’s importance. One of the methods for calculating seismic structural reliability taking into account the structural uncertainties against deterministic earthquake records. Reliability analysis of crossing the structural threshold level for given earthquakes, will be determined as analysis of the level crossing is likely to exceed the structural response of a threshold value. Monte Carlo simulation method based on the importance sampling is one of the most powerful statistical methods for calculating reliability index, which improves and reduce the number of samples and increasing the speed of the operation. Due to the dependence of structural system capacity to the material properties and dimensions of the members, evaluation of uncertainties involved in any of these parameters is important.

Researchers and engineers used steel plate shear walls in recent decades. In general design of this system, the total story shear assigned completely to infill plate. then, peripheral frame designed for transferred tension field forces from steel plate in this procedure, the contribution of frames ignored in shear transfer. In this research, a design procedure based on capacity of both steel plate and peripheral frame. Then, steel plates designed according to plate-frame interaction (PFI) theory for different percentages of story shear and their seismic parameters compared using numerical tools and softwares. It is found that using conventional design of this system, design of steel walls for total story shear and ignoring peripheral frame capacity may lead to conservative design of system. While the proposed design philosophy for consideration of both steel wall and peripheral frame leads to more engineering and economical system.

Structural control methods are aimed to decrease structural responses and improve the dynamic behavior against lateral loads such as wind or earthquake. These methods are classified to three main category of passive, semi active and active. Semi active control possesses both adjustability of active control and reliability of passive control. Semi active control needs a small power source such that lack of electricity during earthquakes cannot disturb its function. In this study a tuned liquid damper (TLD) with baffles is used. TLD is a damper with low installation and maintenance costs and can simultaneously be utilized as a water tank. The used TLD has 4 baffles in two rows that can rotate during excitation. The semi active control algorithm is implemented using the optimal linear control method with time delay compensation. Four far fields and four near field earthquake record are used to study effects of baffles’ rotation.Results show that semi active TLD improves structural behavior more than passive one. Also, the performance of semi active TLD under near field earthquakes are better than that under far field earthquakes.

Lightweight steel frame construction system is one of the building systems that has been good development in recent years in the world. The possibility of prefabrication of LSF systems and the development of building Industrialization in Iran, has led to greater attention to this system. Cold-formed steel shear wall with steel sheathing is one of the lateral load resisting systems in this building system. In this paper, the cyclic lateral behavior of steel sheathed Cold formed steel shear wall has been studied. The effect of steel sheathing thickness and double sided sheathing in lateral behavior of steel sheathed CFS shear wall has been investigated. The failure modes of CFS shear walls and shear strength of them is described in detail.