جستجوی مقالات مرتبط با کلیدواژه « shear » در نشریات گروه « عمران »

Corrugated steel plate shear wall system (CSPSW) is one of the lateral load resisting systems, which in some cases has better seismic performance than the steel plate shear wall system. In this study, the seismic performance of the corrugated steel shear wall system was investigated. The variables of the present study are the angle of corrugated steel plate (0 to 30 degrees), percentage of steel plate openings (10, 20, and 30), and the number of openings (1, 2, 3, and 4). Abaqus finite element software was used for modeling and analysis. A total of 91 steel shear wall models were subjected to 100 mm displacement and were analyzed by the pushover method. The behavior of steel materials is considered as elastoplastic. The results showed that as the angle of corrugation increased, the yield and ultimate strength increased. The initial stiffness decreased with increasing angle of corrugation. Secondary stiffness also increased initially but decreased afterward, but the ductility decreased. With the increase in the percentage of openings, the yield, and ultimate strength decrease. The initial and secondary stiffness decreased, and the ductility first decreased and then increased. As the number of openings increases, the yield and ultimate strength decrease first and then increase.

Due to their lightweight, high tensile strength, and ease to install on irregular surfaces, the use of FRP systems for the repair and strengthening of reinforced concrete structures has become an accepted practice within civil engineering community and codes. Extensive research has been conducted on structural members to identify the improvement in their flexural and axial capacity due to FRP strengthening. However, the analytical and experimental studies on shear strengthening with FRP systems, especially exact determining FRP contribution, are limited. This study provides a multi-layer artificial neural network and group method of data handling approach for predicting the shear contribution of FRP in RC beams strengthened by externally bonded FRP sheets. To achieve the main purpose; ultimate strain of FRP, thickness of FRP, elastic modulus of FRP, width, spacing and angle of FRP sheet, effective depth of FRP, width and of effective depth of beam, compressive strength of concrete, and shear span to depth ratio were considered as input parameters while the shear contribution of the FRP is calculated as the target one. In order to verify the validity of the proposed models, a comparative assessment was conducted between experimental results and predicted values obtained directly from the models and existing guideline equations such as ACI 440, fib-TG9.3, and JSCE. The results indicate that the proposed models could predict the shear contribution of FRP in RC beams strengthened by FRP sheets with a good degree of precision and can be used as a confident approach for pre-design concrete beams strengthened with externally bonded U-shape FRP plates.

The shear strength of deep beams of the reinforced concrete beams depends on the mechanical and geometrical parameters properties of the beam. Accurate estimation of shear strength in deep reinforced concrete deep beams of the reinforced concrete is one of the major issues in the design of engineering structures. However, some methods proposed to determine the shear strength in deep reinforced concrete beams do not have high accuracy. One method to accurately estimate shear strength is to use artificial intelligence (AI). Artificial intelligence has many different methods, one of which is the use of artificial intelligence based on the support vector machine method. In this study, the weighted least squares support vector machine (WLS-SVM), which is a relatively new and efficient method for predicting the shear capacity of reinforced concrete beams, has been used. In this study, a database containing experimental results on deep reinforced concrete beams was first collected. Then, after determining the input and output parameters using a training process in WLS-SVM method and using a part of the collected data, a model was developed to predict the shear strength of deep reinforced concrete beams. In order to determine the accuracy of the WLS-SVM method, the results were compared with those obtained by other AI methods and different regulations. Statistical analysis showed that WLS-SVM has the best performance in terms of statistical evaluation parameters (R^2 = 0.9887, RMSE = 0.107, MAE = 0.478 and MAPE = 9.48%) compared to the other methods.

This study examines the type, thickness, and the way of gridding and placement of FRP sheets with concrete slabs. Shear and bending failures are two major failures in concrete members. One of the ways to reinforce structural members is to use polymer plates that are used due to their low thickness, good effect and balanced price. In this study, eight samples of reinforced concrete reinforced slab reinforced single, double and different location of modeling and results were investigated, of which 2 samples were single FRP, 3 samples were double FRP and 3 were grid mode of Reinforced concrete slab. Reinforced concrete slabs with dimensions of 3400 mm in length, 2500 mm in width and 160 mm in thickness. Longitudinal and transverse rebars with a score of 12 and at a distance of 20 mm from the surface of the slab. After reviewing, it was found that in general, slabs reinforced with CFRP fibers performed better in terms of loading and breaking, and by doubling these plates, a better effect is observed. In the discussion of FRP placement, whatever the regular grid mode and the placement of the force, has a great impact.

Steel structures are one of the most used type of structures. Some of the steel structures may need to be strengthened due to different reasons. There are different methods for strengthening of this kind of structures. In recent years, strengthening of steel structures using Fiber Reinforced Polymers (FRP) has been most interested. This study investigates the shear strengthening of steel beams using one and both sides strengthening of the web by different angles of Carbon Fiber Reinforced Polymers (CFRP) strips. Five specimens were investigated in laboratory experimentally. The test method was four-point bending approach. The load was applied on a connector loading beam by a hydraulic jack, then the load was applied on the main beam through two equal point loads. The beams had two simple supports at the both ends. The loading type was the static gradual loading type. The dimensions of the beams were chosen in the way that beams behave most in shear. This means that beams fail first due to shear stress. One beam was not strengthened, and two beams were strengthened using vertical strips on one or both sides of the web, and two remained beams were upgraded using diagonal strips. Results of this research indicates efficiency of CFRP strips for increasing load-bearing capacity of the beams. Strengthening using diagonal strips on both sides of the web demonstrated the most increment in load-bearing capacity.

The use of fiber reinforced polymers, FRP, is one of the methods for strengthening and retrofitting concrete structures. In this research, the strengthening of reinforced self-compacting concrete beams against shear, torsion and bending has been investigated using GFRP. For reinforcing the beams against shear, bending and torsion, the strips of GFRP were used in the forms of U-shape, straight on the bottom surface and screwed around the beams respectively. In this study, the experimental results were compared with the results of the numerical models and their accuracies were confirmed. Then reinforcement sheets were applied in one and two layers on concrete beam models. By studying the numerical results obtained from Abaqus software, it was observed that with the increase of cracks in the concrete beams, their stiffness decreased and then the stresses were tolerated by the adhesive layers and the GFRP sheets, which has led to an increase in the bearing capacity of the beams. The results of numerical finite elements modeling show that by reinforcing the concrete beams with one layer of GFRP, the load bearing capacities of the beams improved in shear and torsion about 32% and 47% respectively. Moreover, if two layers of reinforcement sheets were used, the shear and torsion capacities of the beams increased about 45% and 61% respectively. The bending capacities of the concrete beams strengthened with one and two layers of GFRP increased up to 32% and 48% respectively.

In this paper, the mechanical properties of special concrete with magnetic heavy weight aggregates and steel fibres, from 24 different mixed designs with 0, 50, 100% of heavy weight aggregates replacing with regular aggregates, 0.52 and 0.4 water-cement ratios and 0, 1, 1.5 and 2% of steel fibers, totally 300 specimens including cubic, cylindrical, and beam was investigated. The results showed that the compressive, tensile and shear strenghts were improved with using special aggreagate and fibres particularly with 50% high weight aggreagate and 2% steel fibres.

In this paper a new method is proposed to estimate the seismic lateral acceleration response in tall buildings. Evaluation of lateral acceleration response in the stories of the structure will allow measures to be taken to reduce the damage on non-structural elements sensitive to lateral acceleration. In this article seismic acceleration response of the structure is obtained by combining mode-acceleration approach with shear-flexural cantilever beams method, and by estimating dynamic components of tall buildings. Quick proposed solutions and equation to calculate the seismic lateral acceleration response, require less information about the structure, which makes analysis easier and faster. The accuracy of the proposed equation is examined by calculating lateral acceleration of 10, 15 story structures during 3 earthquake records using the proposed equation and analyzing the same structures in finite element software, OpenSees. The results show that the proposed equation which does not need simulation and software analysis, offers a good estimation.

The importance of non-structural components in seismic Performance Based Design of buildings is well known nowadays. In this research calculation of absolute acceleration applied on non-structural components located on floors of moment-resisting، eccentric braced and concentric braced frames subjected to earthquake ground motions has been studied. The results of nonlinear time-history analyses of 3، 5 and 7-story steel frames with 8 different periods and 5 reduction factors subject to 15 records of near-field earthquakes and 15 records of far-field earthquakes has been used to investigate the effects of different parameters on absolute acceleration induced in each floor of the structures. The effect of inelastic behavior of system، natural periods of primary and secondary systems، structural system type and near-field ground motions have been studied with use of modified shear-building models of steel frames. The shear building models are set to have an equivalent lateral force-deformation behavior in each story to the one’s of given steel frames. Reliability of these models to estimate the maximum roof displacement and the maximum inter-story drift of steel frames has been investigated elsewhere through probabilistic analysis of the results obtained from comprehensive incremental dynamic analyses. The relationships that are presented in building codes to calculate the force applied on non-structural components has been usually expressed as a ratio of peak ground acceleration. This method of calculating of input acceleration to non-structural elements ignores the effect of frequency content of design ground motion. The results of the present study have been used to introduce a new method for calculation the force applied on non-structural components based on ground acceleration spectrum. In this method the input acceleration to non-structural components has been expressed as a ratio of earthquake response spectrum (instead of the peak ground acceleration). For this ratio which is entitled as “spectral amplification factor” two different expressions have been proposed for use in structures with linear and nonlinear behavior. This approach explicitly accounts for the frequency content of design earthquake in calculation of peak floor acceleration. The results of this study show that Euro-code 8 and ASCE 7-2010 recommendations need to modify specially for the precise location of the non-structural element and inelastic behavior of the structure. It has been demonstrated that structural system type does not significantly affect the amount of induced acceleration on each floor of steel frames.

Inversion analysis of dispersion curves for surface waves is one of recent and important applications in surface soil explorations. This is a challenging problem for linear inversion procedures to be used in evaluation of surface soil mechanical properties due to a highly non-linear nature of soil and to the possibility of large numbers of local minima and maxima of the objective function (multi-modality) in any inversion procedure. As the important outcome of the current study, Genetic algorithm (GA) method is utilized in optimizing the inversion of measured dispersion curves. The main objective of application of Genetic Algorithm in this study is to estimate unknown shear-wave velocity profile of soils in such a manner that the most conformity achieves between experimental dispersion curve obtained by Array measurements of microtremors and the theoretical dispersion curve obtained by the relations which are presented by Haskell (1953) based on wave-propagation theory in layered medium. GA firstly assumes random values for unknown parameters and then by using Selection, Crossover, Mutation and Elitism operators and producing new estimation for these parameters improves the results so that the results in each generation becomes more accurate. The effectiveness of the presented method is considered by an example presented in this study. The results of provided example show acceptable coincidence between the theoretical and experimental dispersion curves. Also, the shear-wave velocity profile of the example site obtained by the new method agrees well with the profiles which are obtained by another alternative method of determination of shear-wave velocity profile.

The instrument performs protection, preservation and control dam behavior, failure detection and timely treatment to prevent the occurrence of the risks and increase the longevity of the dam during construction and operation. In this paper, Zayandeh-Rud dam instrumentation data were analyzed and the stability condition of the dam, foundation and abutments are evaluated. Finally, considering the position of the instruments the distinct element method was employed. The effect of shear and normal stiffness on body and foundation displacements was investigated and the actual values of the shear and normal stiffness were selected as the input model. In this study, Mohr-Coulomb criterion are used for joint behaviors, which are defined as boundary between rock foundation and dam body and boundary between concrete arch blocks, and comparison between measured and calculated values by numerical models has been investigated and good agreement between the results obtained. Results of numerical modeling and measurements have shown that the dam body and foundation are stable. Due to poor geological condition of right wall of dam, the displacements obtained in comparison with the left wall are higher. Also demonstrates that stress and deformation of dam body and foundation, strongly influenced by variation of lake water level.

Dowel action and aggregate interlocking are the main mechanisms for shear transfer at RC joints and cracks. Dowel action is the only transfer agent across precast joints like those in some kinds of RC pavements. Behavior of RC pavement is affected by the load transfer capability at the joint. Efficiency of such a structure is directly related to the transferred loads. Therefore, analyzing joint and crack performance in pavements has an important role and also depends on using proper behavioral models to simulate load transfer mechanism. In this paper, shear transfer mechanism through dowel bars in RC pavements has been investigated based on the beam on elastic foundation theory (BEF) and has been extended to beam on inelastic foundation (BIF) to take account of the nonlinear interaction between concrete and reinforcement bars. In fact, the main objective is to provide a method which significantly reduces the calculation and analysis time whilehaving acceptable accuracy. Model verification has been carried out in two parts (RC interfaces and RC pavements) in comparison with experimental results.