Current Issue : July - September Volume : 2013 Issue Number : 3 Articles : 4 Articles
The seismic vulnerability of highway bridges remains an important problem and has received increased attention as\r\na consequence of unprecedented damage observed during several major earthquakes. A significant number of\r\nresearch studies have examined the performance of skew bridges under service and seismic loads. The results of\r\nthese studies are particularly sensitive to modeling assumptions in view of the interacting parameters. In the\r\npresent study, three-dimensional improved beam-stick models of two-span highway bridges with skew angles\r\nvarying from 0�° to 60�° are developed to investigate the seismic response characteristics of skew box girder bridges.\r\nThe relative accuracy of beam-stick models is verified against counterpart finite element models. The effect of\r\nvarious parameters and conditions on the overall seismic response was examined such as skew angle, ground\r\nmotion intensity, soil condition, abutment support conditions, bridge aspect ratio, and foundation-base conditions.\r\nThe study shows that the improved beam-stick models can be used to conduct accurate nonlinear time history\r\nanalysis of skew bridges. Skew angle and interacting parameters were found to have significant effect on the\r\nbehavior of skewed highway bridges. Furthermore, the performance of shear keys may have a predominant effect\r\non the overall seismic response of the skew bridges....
In this paper, three artificial neural networks are presented using the experimental results from bolted moment\r\nconnections among cold-formed steel members and the software MATLAB in order to predict the rotation at the\r\nconnections. A common neural network which has a multilayer perceptron along with back propagation learning\r\nalgorithm is applied in this research. Each of the networks consists of four layers including two hidden ones. The\r\nnumber of neurons in the first hidden layer is changed from 1 to 10 to achieve optimal results. The best results\r\nare obtained when the networks had 10, 10, and 9 neurons in the first hidden layer for column base and beam\r\ncolumn connections (in positive and negative rotations), and they had the performance of 0.0001371, 0.00044, and\r\n0.00047, respectively, after being trained in the software MATLAB. Thirty percent of the data from each test series\r\nwere omitted randomly in order to verify the networks. The Mannââ?¬â??Whitney P value tests are 0.9933, 0.9393, and\r\n0.9653 for column base and beam column connections (in positive and negative rotations), respectively....
According to seismic design codes, nonlinear performance of structures is considered during strong earthquakes.\r\nSeismic design provisions estimate the maximum roof and story drifts occurring during major earthquakes by\r\namplifying the drifts computed from elastic analysis at the prescribed seismic force level with a displacement\r\namplification factor. The present study tries to evaluate the displacement amplification factors of conventional\r\nconcentric braced frames (CBFs) and buckling restrained braced frames (BRBFs). As such, static nonlinear (pushover)\r\nanalysis and nonlinear dynamic time history analysis have been performed on the model buildings with single and\r\ndouble bracing bays, and different stories and brace configurations (chevron V, invert V, and X bracing). It is\r\nobserved that the displacement amplification factors for BRBFs are higher than that of CBFs. Also, the number of\r\nbracing bays and height of buildings have a profound effect on the displacement amplification factors. The\r\nevaluated ratios between displacement amplification factors and response modification factors are from 1 to 1.12\r\nfor CBFs and from 1 to 1.4 for BRBFs....
Flat-slab building structures exhibit significant higher flexibility compared with traditional frame structures, and\r\nshear walls (SWs) are vital to limit deformation demands under earthquake excitations. The objective of this study is\r\nto identify an appropriate finite element (FE) model of SW dominant flat-plate reinforced concrete (R/C) buildings,\r\nwhich can be used to study its dynamic behavior. Three-dimensional models are generated and analyzed to check\r\nthe adequacy of different empirical formulas to estimate structural period of vibration via analyzing the dynamic\r\nresponse of low- and medium-height R/C buildings with different cross-sectional plans and different SW positions\r\nand thicknesses. The numerical results clarify that modeling of R/C buildings using block (solid) elements for\r\ncolumns, SWs, and slab provides the most appropriate representation of R/C buildings since it gives accurate results\r\nof fundamental periods and consequently reliable seismic forces. Also, modeling of R/C buildings by FE programs\r\nusing shell elements for both columns and SWs provides acceptable results of fundamental periods (the error does\r\nnot exceed 10%). However, modeling of R/C buildings using frame elements for columns and/or SWs overestimates\r\nthe fundamental periods of R/C buildings. Empirical formulas often overestimate or underestimate fundamental\r\nperiods of R/C buildings. Some equations provide misleading values of fundamental period for both intact and\r\ncracked R/C buildings. However, others can be used to estimate approximately the fundamental periods of\r\nflat-plate R/C buildings. The effect of different SW positions is also discussed....
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