Scientia Iranica
Volume:19 Issue: 2, 2012

Many of the existing unreinforced masonry buildings are seismically vulnerable and require retrofitting. In this experimental study, the cyclic behavior of six, one-half scale, perforated unreinforced brick walls, before and after retrofitting, using Glass Fiber Reinforced Polymers (GFRPs), is investigated. The walls were built using one-half scale solid clay bricks and cement mortar to simulate the traditional walls built in Iran during the last 40 years of the 20th century. These walls had a window opening at their center. One brick wall was unreinforced and considered a reference specimen. Three walls were directly upgraded after construction using GFRPs. The fifth wall was first strengthened and tested. Then, the seismically damaged specimen was retrofitted, using GFRPs, and tested again. Each specimen was retrofitted on the surface of two sides. All specimens were tested under constant gravity load and incrementally increasing in-plane loading cycles. During the test, each wall was allowed to displace in its own plane. The key parameter was the strengthening configuration including the cross layout, grid layout, and combined layout. Strengthening by means of GFRPs significantly improved the strength, deformation capacity, and energy absorption of the brick wall. The increase in performance parameters was dependent upon GFRP layout.

This paper presents the performance of a single horizontal conventional Impact Damper (ID) in both wide range frequency and resonance excitations. The effects of the coefficient of restitution, e, mass ratio, μ, and clearance, d, on the performance of ID are investigated. The optimal parameters are numerically found by discretely varying the clearance and excitation frequency. The performance of optimal ID is discussed, with respect to different parameters, in both resonance and off-resonance modes. In addition, it is shown how the efficiency of the optimal conventional ID is deteriorated as a result of mistuning in the amplitude and frequency of excitation. This is estimated by suggesting a new criterion of post processing data. It is shown that an ID designed to resist high amplitude excitation is able to perform well at lower amplitude. However, the opposite trend can significantly deteriorate the efficiency of optimal ID. In regard to excitation frequency, the ID, optimized with respect to a wide range of frequency, is less sensitive to frequency mistuning. Finally, the vulnerability of the optimized ID versus uncertainties in structural parameters is clearly determined and it is illustrated that less robustness occurs when the performance of the controller is more efficient.

The soil permeability coefficient plays a key role in the process of numerical simulation of the liquefaction phenomenon. Liquefaction causes a considerable increase in soil permeability, due to the creation of easier paths for water flow. The work presented in this paper tries to investigate the effects of permeability coefficient on the results of numerical modeling of the liquefaction phenomenon. To do this, a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Two different versions of a well-calibrated critical state bounding surface plasticity model, which possesses the capability to utilize a single set of material parameters for a wide range of void ratios and initial stress states for the same soil, are used to model the behavior of saturated sand. To demonstrate the accuracy of the numerical model, two different finite element programs, which apply different numerical algorithms, are employed and validated by records of a centrifuge test. The obtained results indicate that by considering a constant value for the soil permeability coefficient, pore pressure variations and soil displacements cannot be simulated simultaneously. Therefore, variation of the permeability coefficient should necessarily be taken into account in the course of numerical analysis of liquefaction in order to achieve acceptable prediction of both pore pressures and displacements.

This study deals with the development of Artificial Neural Network (ANN) and Multiple Regression (MR) models for estimating the critical factor of safety (Fs) value of a typical artificial slope subjected to earthquake forces. To achieve this, while the geometry of the slope and the properties of the man-made soil are kept constant, the natural subsoil properties, namely, cohesion, internal angle of friction, the bulk unit weight of the layer beneath the ground surface and the seismic coefficient, varied during slope stability analyses. Then, the Fs values of this slope were calculated using the simplified Bishop method, and the minimum (critical) Fs value for each case was determined and used in the development of the ANN and MR models. The results obtained from the models were compared with those obtained from the calculations. Moreover, several performance indices, such as determination coefficient, variance account for, mean absolute error and root mean square error, were calculated to check the prediction capacity of the models developed. The obtained indices make it clear that the ANN model has shown a higher prediction performance than the MR model.

To obtain wider openings than those provided by Chevron bracing, the braces are cranked and connected to the frame corner by an additional brace to form double y-shaped bracings. However, y-bracings are prone to instability and out of plane buckling, accompanied by low hysteretic energy absorption. An experimental research program, focused on y-bracing, was conducted at the BHRC structural engineering laboratory. Specimens presented in this paper include three full-scale single bay frames, with symmetric y-bracing of different cross sections and connection types. In addition, one specimen with Chevron bracing was tested as a reference. A quasi-static cyclic loading was applied increasingly until yielding and failure occurred in the specimens. The results show that out-of-plane buckling is the governing mode of behavior, despite differences in the detailing of cross sections and connections. Hysteretic energy dissipation and damping of y-bracing are remarkably improved due to the flexural deformation of brace members. The seismic performance of the three y-braced frame specimens and a reference Chevron-braced frame was assessed using the capacity spectrum method. The results show that the y-braced frame, with double gusset plates, can carry almost 60% more weight than y-braced frames with single gusset plates.

Retempering of concrete is a common practice in ready-mixed concrete industries for adjusting the workability that might adversely affect strength and durability properties in hot climates. In this paper, the effects of retempering with melamine sulphonate naphthalene-based superplasticizer (RS), water (RW) and withhold water (RWW) on the compressive strength and water permeability (WP) of concrete, are experimentally investigated. The results of this study indicated that the compressive strength of concrete retempered with superplasticizer and withhold water, enhanced by increasing the delay in casting, while retempering with water, resulted in a substantial decrease. Moreover, it was found that RS improved the water permeability of retempered concrete much more than RWW, whereas RW diversely increased this parameter. Although RWW imposed a slight slump loss, RWW and RS are generally proposed for the retempering of concrete, due to the suitable strength and permeability results.

Time history analyses of structures typically require some accelerograms of strong ground motion expected at the site. They should be scaled, avoiding the average response spectrum, to fall below the target design spectrum given by the employed seismic-code procedure within a given period range. In this paper, a harmony search, as a recently developed meta-heuristic, is utilized and adapted to solve the problem of the optimal selection and scaling of such recorded accelerograms. Treating a number of ground motion records, close agreement between the scaled-average spectra and the design target were achieved, identifying the proposed algorithm as an acceptable and efficient technique to generate a spectrum compatible set of records for further dynamic structural analyses.

Higher-order effects in three-wave resonant interaction of a surface wave, with a pair of interfacial waves in a two-layer fluid, are studied theoretically. Following an initial rapid growth, the interfacial waves approach a steady state of constant amplitude. An explicit solution is presented for transition to the ultimate state of the interaction. It is shown that for interaction in a wave flume, it is necessary to include a 2nd pair of the interfacial waves, resulting from a reflection of the original pair in the analysis. The effects of different parameters on the dynamics of the interaction are investigated. The results indicate that a faster initial growth does not necessarily lead to larger ultimate amplitude. Also, there are two angles, at which the interfacial waves continue to grow at an initial growth rate, possibly leading to wave breaking. The results are in qualitative agreement with previous experimental observations.

The main objective of this study is to develop a new design methodology that controls damage to Reinforced Concrete Moment Resisting Frames (RCMRFs). For this purpose, first, a static damage criterion is developed and, then, the new design procedure is presented. The proposed method is applied to the design of two reinforced concrete frames subjected to seven earthquake acceleration records. To confirm the accuracy of the proposed method, inelastic damage analysis is performed on the frames. It is demonstrated that the proposed methodology can be very effective and practical for the design of RCMRFs with damage control.

In this paper, the Artificial Neural Network (ANN) and the Adaptive Neuro-Fuzzy Inference System (ANFIS) are used to predict the shear strength of Reinforced Concrete (RC) beams, and the models are compared with American Concrete Institute (ACI) and Iranian Concrete Institute (ICI) empirical codes. The ANN model, with Multi-Layer Perceptron (MLP), using a Back-Propagation (BP) algorithm, is used to predict the shear strength of RC beams. Six important parameters are selected as input parameters including: concrete compressive strength, longitudinal reinforcement volume, shear span-to-depth ratio, transverse reinforcement, effective depth of the beam and beam width. The ANFIS model is also applied to a database and results are compared with the ANN model and empirical codes. The first-order Sugeno fuzzy is used because the consequent part of the Fuzzy Inference System (FIS) is linear and the parameters can be estimated by a simple least squares error method. Comparison between the models and the empirical formulas shows that the ANN model with the MLP/BP algorithm provides better prediction for shear strength. In adition, ANN and ANFIS models are more accurate than ICI and ACI empirical codes in prediction of RC beams shear strength.