نشریه آنالیز سازه - زلزله
سال هفدهم شماره 4 (زمستان 1399)

The buildings equipped with buckling restrained brace (BRB) are earthquake resistant structures that have two properties of high lateral stiffness and ability to absorb and dissipate energy at the same time In this study, a parallel double core mechanism with the same core length and with different yielding stress was used to investigate the seismic performance of buckling restrained brace of single core and double core. Therefore, in this research, three 3-dimensional 3, 6 and 9-story buildings equipped with concentric buckling restrained braces were designed according to AISC-LRFD Code along with the controlling of the seismic criteria based on standard 2800 version 4th in ETABS 2017 software. Then, the two dimensional perimeter frames equipped with buckling restrained brace were modeled in SeismoStruct 2018 software in two states of single core and double core. In order to investigate the behavior of these structures, the adaptive pushover nonlinear static analysis and time history nonlinear dynamic analysis were performed under three far fault earthquakes. The results presented that the use of a parallel yielding double core increased the elastic stiffness of the structures but does not cause a noticeable change in the lateral strength of the prototypes. Also under applied earthquakes, the hysteresis curves were obtained and these figures showed that the use of a parallel double core increased the earthquake energy dissipation. In general, the use of the double core buckling restrained brace reduced seismic responses such as roof displacement, roof acceleration, drift and base shear by approximately 20%.

Over recent decades, regarding the spread of unusual events such as fires, explosions, and vehicle collisions, the study of the behavior of structures subjected to abnormal loadings has been taken into account by the researchers and structural engineers. In this study, 2 and 5-story steel moment-resisting frame structures have been considered under the heavy vehicle collision impact. They are modeled in OpenSees software two-dimensionally with regarding to uncertainty in materials and applied loads and the sensitivity based reliability analysis of the studied random parameters is performed in Matlab software. Then, the effect of each of the variables is investigated using simulation-based methods according to limit state functions based on the maximum permitted beam rotation of damaged bay of frames. The results of this study presented that the random variables such as mass and velocity of vehicle and yield strength of material were the most influential parameters in calculating the failure probability in representative structures. Also, the control variates-based subset simulation (CSS) method compared to Monte Carlo Simulation (MCS) approach estimated the failure probability with permissible error rate, less sample number and the minimum computer processing time duration. Furthermore, the results of this research indicated that by increasing the number of stories of the building, the probability of its failure due to vehicle collision increased. According to the results of this study, the value of beam rotation of damaged bay parameter of the 5-story frame compared to 2-story one has increased by 55, 18 and 33% under the LSF1, LSF2 and LSF3 functions, respectively

Based on the importance of explosion of the specific structures with composite steel shear wall and concrete-filled steel box columns (CFT), this study investigates the effect of explosion on such a structures. An 8-story steel structure with steel shear wall as a lateral resisting system and CFT columns was designed, then was modeled under blast loading in the air. This study presents that by addition of two concrete layers to the composite shear wall, with respect to the case with one layer, considering the constant amount and distance of the explosive material TNT from the structure the average out-of-plane displacement of the shear plate is decreased by 63% and also the type of damage has changed from the failure of the shear plate to buckling of the shear plate. As well the stress concentration is transferred from the plate and boundary elements connection to the center of the plate and the absorbed energy has increased by 380%.

In recent years, most of the experimental studies have been performed on the mechanical behavior of reinforced concrete with recycled and industrial steel fibers in foreign countries, and it is necessary to conduct studies on fiber reinforced concrete made from existing materials in our country. In this paper, experimental and numerical research on the mechanical behavior of the fiber concrete has been conducted. In the experimental program, first, by modeling the mix design presented in previous research for recycled fiber concrete, two mixing designs were determined in accordance with the available materials of the country, so that by adding two different types of steel fibers, the desired slump flow is obtained. The effect of industrial fibers and recycled metal chips on the compressive and splitting tensile behavior of fiber reinforced concrete was investigated by performing compressive and tensile tests. The addition of industrial fibers and recycled metal chips has slightly reduced the indirect compressive and splitting tensile strength of the concrete. In the simulation and modeling of finite element compression tests, the formation of cracks in the concrete elements surrounding metal chips elements, confirmed the occurrence of stress gradients in these concrete elements, which led to a reduction in the compressive strength of the fibre reinforced concrete.

With the use of pozzolans and additives, today, a huge change has been made in mortar technology to achieve high strength and durability. The purpose of this study is to make two-component and three- component mortars and compare their rheological and mechanical properties. In this research, compressive, flexural and tensile strength tests were performed on reference mortar, two-component mortars as well as three-component mortars. Slag utilized in making of research mortars was produced in Ahvaz Steel plant. Compressive strength tests were conducted at 7, 28, 56 and 91 days and flexural and tensile strength tests were performed at 28 and 91 days. In the mentioned resistance tests, cubic specimens with dimensions of 50 mm, prismatic specimens with dimensions of 160 × 40 × 40 mm and standard bow-tie specimens were applied, respectively. The results presented that the replacement of microsilica up to 10% by weight of cement increased the compressive, flexural and tensile strengths of two-component mortars, which were significant at all ages compared to the sample without microsilica. With increasing cement substitute microsilica up to 15%, changes in compressive, flexural and tensile strengths follow an inverse nonlinear behavior. Optimal microsilica and slag replacement percentages of 5% and 10%, respectively, increased the three strengths in the three-component mortars, which are significant at all ages compared to the reference sample. With increasing the percentage of replaced microsilica, the flowability of the mortars decreased and with increasing the percentage of slag, the flow increased.

Smart concrete refers to structural materials that can sense and respond appropriately to changes in their environment. This is done by changing one or more parameters. The smart properties of concrete are usually achieved by modifying and upgrading the concrete mix design and matrix. It is mainly obtained by improving the composition of initional materials or adding functional materials to concrete. This concrete also has bionic (biological) characteristics. Compared to conventional concrete, properly designed smart concrete can be utilized to optimize the safety, durability and proper performance of infrastructure and reducing of the maintenance costs. The costs of use, resource consumption and environmental pollution, which are the basic parameters for construcction, will be reduced. Over the past few decades, significant efforts have been made to research smart concrete and many innovative achievements in the development and application of smart concrete are obtained. Thirteen types of smart concrete, with emphasis on their capabilities, are systematically investigated in this article, which is based on the principles, composition, construction, properties, research development and structural applications. In addition, some perspectives on the development of smart concrete are discussed. Finally, thirteen compositions of smart concrete were organized into a Table.

In the modern characteristics of concrete design based on daily needs, the use of recycled materials is an important and basic principle. Therefore, in the present study, PET (Polyethylene Terephthalate) has been substituted for fine aggregates in self-compacting concrete. The aim of this study is to produce and optimize the mechanical and rheological properties of environmentally friendly self-compacting concretes. Input variables in the mixtures include (PET) as a substitute for a percentage of fine aggregates, steel fibers, powder stone as a substitute for a percentage of cement weight, and lubricant as a percentage of powder material weight. The studied responses are slump flow, L-box ratio (H2 / H1), compressive and tensile strengths. Mixing schemes were designed and studied using the Central Composite Design (CCD) method, which is one of the RSM (Response Surface Methodology) methods. The results demonstrated that with increasing PET, the rheological and mechanical properties of the mixtures decreased while the fibers effectively improved the reduction of strengths. Applying mathematical models provided by ANOVA, multi-objective optimizations were performed to maximize compressive strength by the RSM method and an optimal mixing scheme based on experimental results was proposed.