فصلنامه رویکردهای نوین در مهندسی عمران
سال چهارم شماره 2 (تابستان 1399)

The Buckling Restrained Brace (BRB) is a type of high energy dissipation damper. The damper includes a thin steel core, a concrete cover designed to maintain the steel core and prevent it from buckling under axial compression, and a middle layer that prevents unwanted interactions between the steel brace core and the concrete sheath. Braced frames that use the BRB are known as buckling restrained braced frames, which have many advantages over conventional braced frames. In this study, the effect of geometric shape and number of holes on the core of the buckling restrained brace has been investigated by numerical simulation with finite element method. Six brace core types with rectangular and circular shaped with equal area with and without holes. The holes are placed one, three and five with full details in ABAQUS software and results in terms of failure modes, severity of damage and Hysteresis curve have been studied. To verify the modeling method and assumptions, an experimental sample is verified. The results of this study indicate the significant effect of more holes and the use of circular rather than rectangular holes on the cyclic performance of buckling restrained brace.

This study investigates the magnitude of damage index in irregular structure under the impact of progressive collapse base on measuring values of damage index with considering nonlinear material behavior and geometrical nonlinearity in static and dynamic methods. Progressive collapse in every element and magnitude of influences of column location in damage index for every element were investigated. The main aim of this study is how progressive collapse by removing a column effects on damage index of bearing element. For this reason, impacts of progressive collapse in steel structure and also removed column location in this structure were surveyed. A four story building with moment frames and irregular plans is chosen for investigation. Loading were conducted base on 6th issue of the national building regulations of Iran and 2800-Standard. Designing of structure was done base on 10th issue of the national building regulations of Iran and ETABS software. In second step, designed structure was simulated in ABAQUS software and with considering nonlinear material behaviour and geometrical Nonlinearity under load combination which proposed by GSA analysed in static and dynamic methods. In static approach, the ultimate capacity of structure under removing every column were checked by using push-down curve. Based on results it was seen that the corner column had the maximum failure potentially. In the next step structural responses to progressive collapse under present loadings were studying by nonlinear dynamic analyse in diverse column removing scenarios. Values of displacements in top of removing column and proportional of maximum rotation of every beam end node in critical region to yield rotation are investigated. The result is exactly in accordance with static results.

Nowadays, increasing population and, consequently, increasing water requirements is a serious threat to water resources. Due to the scarcity of water resources, issues related to the quality of water resources are of great importance. Due to the fact that surface water is more polluted than groundwater, one of the most important issues related to the operation and environment of dam reservoirs, which are considered as artificial lakes, is to check the water quality of dam reservoirs. In this study, using remote sensing techniques and using Sentinel-2 satellite images, the trend of spatial distribution changes of two parameters of turbidity and nitrogen was investigated. The results showed that rainfall (investigated events) caused changes in the amount of turbidity and nitrogen in the water of the Sepidrud Dam reservoir.

In this study, FRP effects on cyclic and push over behavior of locally and globally rehabilitated concrete frames were investigated. ABAQUS software used for modeling of frames. At first a 3 story-2 bay concrete building was modeled under gravity and earthquake loadings and then one of its frames was chosen as the base frame of this research. In the second step the base frame was weaken and rehabilitation carried out using three kinds of FRP named carbon, glass and aramid to compensate the lack of capacity. Strengthening of frames was done in two types of local and global manner and in each type three kinds of FRP were used. Force-displacement curve and stress-strain counter were determined for all of the models. Results showed positive effects of FRP using in rehabilitation of concrete frames. In local rehabilitation, all FRP improved the both of loading capacity and ductility but carbon FRP compensated all lack of capacity that was imposed to the model. In global rehabilitation, all kinds of FRPs showed satisfying performance in improving capacity of concrete frames. At the end, local strengthening by carbon FRP was showed the best performance among the others and glass FRP was presented the optimum behavior in global strengthening.

Concrete is the most important building material that is most used in the construction of various structures including residential buildings, infrastructure structures such as bridges, dams, roads, buildings, docks, dams and other structures. Generally, concrete is made of a mixture of cement with water and coarse aggregates, which in practice are referred to as sand. Determine the amount and weight of each of these materials to build a concrete to obtain the characteristic strength referred to as the concrete mixing scheme. In this study, we investigated the effect of silica and powder on polymeric cement concrete of styrenebutadiene (SBR) found in latex commercial market and for making samples of polymer weight percentages of 10,15 and 20 in cement with alternative 5, 10 And 15% mocrosilica and rubber powder used to replace cement. The results show that the supernatants with the addition of the samples show an increased resistance with the sample and at 42 and 28 days these samples have more than the resistance of the sample. The best resistance in the combination of microsilica and powder was between 6 and 7.5% with a 28-day increase of 15% over the control.