International Journal of Civil Engineering
Volume:10 Issue: 3, Sep 2012

Endurance Time (ET) method is a response history based analysis procedure that can be used for estimating seismic response of structures at different excitation levels in each response history. This method of seismic analysis utilizes specific intensifying acceleration functions for seismic analysis. One of the potential applications of the ET method is in the seismic assessment of shell structures. In this paper, a procedure for linear seismic analysis of shell structures is proposed and application of this method to several cases of shell structures is investigated. These structures is analyzed under three ET acceleration functions in one direction and results is compared to time history analysis considering seven actual earthquake records. Also the results of ET method compared to response spectrum analysis method. Outcomes of the study show that ET method predicts the linear seismic performance of shell structures with acceptable precision and significant reduction in time of analysis. Also it is conluded that scattering of results of three ET analysis is very low and it can be used one analysis instead of three, And the comparison between THA and RSM results show that response spectuarm method is a conservative method that sometimes has problem to evaluate bending stresses of shell structures.

Due to the algorithmic simplicity, Cellular Automata (CA) models are useful and simple methods in structural optimization. In this paper, a cellular automaton based algorithm is presented for shape and topology optimization of continuum structures, using five-step optimization procedure. Two objective functions are considered and the optimization process is followed by using weighted sum method. The design domain is divided into small triangle elements and each cell is considered as the finite element. The stress analysis is performed by the constant strain triangles (CST) finite elements method. The CST finite element method is developed in this paper to perform analysis. The thicknesses of the individual cells are taken as the design variables which for the purpose of this paper are continuous variables. The paper reports the results of several design experiments, comparing them with the currently available literature results. The outcomes of the developed scheme in this paper show the accuracy and efficiency of the method as well as its timesaving behavior in achieving better results.

In this paper a discrete Big Bang-Big Crunch algorithm is applied to optimal design of reinforced concrete planar frames under the gravity and lateral loads. Optimization is based on ACI 318-08 code. Columns are assumed to resist axial loads and bending moments, while beams resist only bending moments. Second-order effects are also considered for the compression members, and columns are checked for their slenderness and their end moments are magnified when necessary. The main aim of the BB-BC process is to minimize the cost of material and construction of the reinforced concrete frames under the applied loads such that the strength requirements of the ACI 318 code are fulfilled. In the process of optimization, the cost per unit length of the sections is used for the formation of the subsequent generation. Three bending frames are optimized using BB-BC and the results are compared to those of the genetic algorithm.

One important application of fiber reinforced polymer (FRP) is to confine concrete as FRP jackets in seismic retrofit process of reinforced concrete structures. Confinement can improve concrete properties such as compressive strength and ultimate axial strain. For the safe and economic design of FRP jackets, the stress-strain behavior of FRP-confined concrete under monotonic and cyclic compression needs to be properly understood and modeled. According to literature review, it has been realized that although there are many studies on the monotonic compressive loading of FRP-confined concrete, only a few studies have been conducted on the cyclic compressive loading. Therefore, this study is aimed at investigating the behavior of FRP-confined concrete under cyclic compressive loading. A total of 18 cylindrical specimens of FRP-confined concrete were tested in uniaxial compressive loading with different wrap thickness, and loading patterns. The results obtained from the tests are presented and examined; based on analysis of test results predictive equations for plastic strain and stress deterioration were derived. The results are also compared with those from two current models, comparison revealed the lack of sufficient accuracy of the current models to predict stress-strain behavior and accordingly some provisions should be incorporated.

Self-desiccation is the major source of autogenous shrinkage and crack formation in low water-binder ratio (w/b) concretes which can be reduced by internal curing. In this paper performance of high strength self consolidating concrete (HS-SCC) with w/b of 0.28 and 0.33 including autogenous shrinkage, drying shrinkage, compressive strength, and resistance to freezing-thawing was investigated. Then, for the purpose of internal curing, 25% of normal weight coarse aggregate volume was replaced with saturated lightweight aggregate (LWA) of the same size; and its effects on the material properties was studied. Two modes of external curing, moist and sealed, were applied to test specimens after demoulding. Autogenous shrinkage from 30 minutes to 24 hours after mixing was monitored continuously by a laser system. The initial and final setting time were manifested as a change of the slope of the obtained deformation curves. Shrinkage after initial setting was 860 and 685 microstrain (με) for 0.28 and 0.33 w/b mixtures, respectively. The saturated LWA reduced these values to 80 and 295 με, respectively. By LWA Substitution the 28-day compressive strength of 0.28 w/b mixture was reduced from 108 to 89 and 98 to 87 MPa for moist and sealed cured specimen, respectively. The corresponding values for 0.33 w/b mixture was 84 to 80 and 82 to 70 MPa. Shrinkage of 0.28 w/b mixture without LWA after moist and sealed cured specimen dried for 3 weeks was about 400 με. Shrinkage of moist and sealed cured specimen containing LWA was reduced 9% and 25%, respectively. On the contrary for 0.33 w/b mixture an increase was noticed. Freezing-thawing resistance was improved by sealed curing, decreasing w/b and substituting LWA.

The application of fuzzy algorithms in the response control of a base isolated building with MR dampers is investigated in this work. Most of researches in this field have been focused on fuzzy algorithms with linear membership function but in the current study; the membership functions are assumed to be Gaussian and their effectiveness is studied. For this purpose, an eight-story building model with regularity in plan and height is prepared. The adopted base isolation system includes linear bearings and control devices. MR dampers are used to reduce base displacements and have the capacity of 1000 kN with the maximum applied voltage of 10 V. In order to verify the control procedure and analyzing the structure, a simulation procedure is developed. This procedure performs linear analysis of the structure in presence or in absence of the base isolation system. Moreover, the simulation procedure is able to appropriately determine the MR damper voltage using fuzzy logic algorithms and then analyzing the whole system. Finally, seven near-field earthquake records are chosen in the simulation of the structure response and the obtained results validate proposed control procedure.

The torsional capacity of unreinforced masonry brick buildings is generally inadequate to provide a stable seismic behavior. The torsional strength is believed to be the most important parameter in earthquake resistance of masonry buildings and the shear stresses induced in the bed joints of such building’s walls is an important key for design purposes. Brick buildings strengthened with wire-mesh reinforced concrete overlay are used extensively for building rehabilitation in Iran. Their quick and simple applications as well as good appearance are the main reasons for the widespread use of such strengthening technique. However, little attention has been paid to torsional strengthening in terms of both experimental and numerical approach. This paper reports the response and behavior of two single-story brick masonry buildings having a rigid two-way RC floor diaphragm. Both specimens were tested under monotonic torsional moment. Numerical work was carried out using non-linear finite element modeling. Good agreement in terms of torque–twist behavior, and crack patterns was achieved. The unique failure modes of the specimens were modeled correctly as well. The results demonstrate the effectiveness of reinforced concrete overlay in enhancing the torsional response of strengthened building. Having evaluated the verification of modeling, an unreinforced brick building with wall-to-wall vulnerable connections was modeled so that the effect of these connections on torsional performance of brick building could be studied. Then this building was strengthened with reinforced concrete overlay and the effect of strengthening on torsional performance of brick buildings with vulnerable connections was predicted numerically.