International Journal of Civil Engineering
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International Journal of Civil Engineering - Journal articles for year 2013, Volume 11, Number 2Yektaweb Collection - https://yektaweb.comen2013/6/11New graph products for configuration processing
http://www.iust.ac.ir/ijce/browse.php?a_id=689&sid=1&slc_lang=en
For the analysis of structures, the first step consists of configuration processing followed by data generation. This step is the
most time consuming part of the analysis for large-scale structures. In this paper new graph products called triangular and
circular graph products are developed for the formation of the space structures. The graph products are extensively used in graph
theory and combinatorial optimization, however, the triangular and circular products defined in this paper are more suitable for
the formation of practical space structural models which can not be generated easily by the previous products. The new products
are employed for the configuration processing of space structures that are of triangular or a combination of triangular and
rectangular shapes, and also in circular shapes as domes and some other space structural models. Cut out products are other
new types of graph products which are defined to eliminate all of the connected elements to the considered node to configure the
model or grid with some vacant panels inside of the model. The application of the presented graph products can be extended to
the formation of finite element models.A. KavehSize optimization of nonlinear scallop domes by an enhanced particle swarm algorithm
http://www.iust.ac.ir/ijce/browse.php?a_id=731&sid=1&slc_lang=en
The present paper focuses on size optimization of scallop domes subjected to static loading. As this type of space structures includes a large number of the structural elements, optimum design of such structures results in efficient structural configurations. In this paper, an efficient optimization algorithm is proposed by hybridizing particle swarm optimization (PSO) algorithm and cellular automata (CA) computational strategy, denoted as enhanced particle swarm optimization (EPSO) algorithm. In the EPSO, the particles are distributed on a small dimensioned grid and the artificial evolution is evolved by a new velocity updating equation. In the new equation, the difference between the design variable vector of each site and an average vector of its neighboring sites is added to the basic velocity updating equation. This new term decreases the probability of premature convergence and therefore increases the chance of finding the global optimum or near global optima. The optimization task is achieved by taking into account linear and nonlinear responses of the structure. In the optimization process considering nonlinear behaviour, the geometrical and material nonlinearity effects are included. The numerical results demonstrate that the optimization process considering nonlinear behaviour results in more efficient structures compared with the optimization process considering linear behaviour. .E. SalajeghehOptimization of high-performance concrete structures by variable neighborhood search
http://www.iust.ac.ir/ijce/browse.php?a_id=660&sid=1&slc_lang=en
This paper describes a methodology in designing high-performance concrete for simply supported beams, using a hybrid optimization strategy based on a variable neighborhood search threshold acceptance algorithm. Three strategies have been applied to discrete optimization of reinforced concrete beams: Variable Neighborhood Descent (VND), Reduced Neighborhood Search (RNS) and Basic Variable Neighborhood Search (BVNS). The problem includes 14 variables: two geometrical one material type one mix design and 10 variables for the reinforcement setups. The algorithms are applied to two objective functions: the economic cost and the embedded CO2 emissions. Firstly, this paper presents the application of these three different optimization strategies, which are evaluated by fitting the set of solutions obtained to a three-parameter Weibull distribution function. The Variable Neighborhood Descent with Threshold Accepting acceptance strategy algorithm (VND-TA) results as the most reliable method. Finally, the study presents a parametric study of the span length from 10 to 20 m in which it can be concluded that economic and ecological beams show a good parabolic correlation with the span length. V. YepesAn iterative process for pushover analysis of double unsymmetric-plan low- and medium-rise buildings under bi-directional excitation
http://www.iust.ac.ir/ijce/browse.php?a_id=577&sid=1&slc_lang=en
Double- unsymmetric-plan medium-rise buildings subjected to bi-directional seismic excitation are complex structures where
higher-mode effects in plan and elevation are important in estimating the seismic responses using nonlinear static or pushover
analysis. Considering two horizontal components of the ground motions makes the problem more intricate. This paper presents
a method for nonlinear static analysis of double unsymmetric-plan low- and medium-rise buildings subjected to the two horizontal
components of ground motions. To consider bi-directional seismic excitation in pushover analyses, the proposed method utilizes
an iterative process until displacements at a control node (centre of mass at the roof level) progressively reach the predefined
target displacements in both horizontal directions. In the case of medium-rise buildings, continuous implementation of modal
pushover analyses is used to take higher-mode effects into account. To illustrate the applicability and to appraise the accuracy
of the proposed method, it is applied to the 4- and 10-storey torsionally-stiff and torsionally-flexible buildings as representative
of low- and medium-rise buildings, respectively. For the purpose of comparison, modal pushover analysis (MPA) is also
implemented considering the two horizontal components of the ground motions. The results indicate that the proposed method
and the MPA procedure can compute the seismic demands of double unsymmetric-plan low- and medium-rise buildings with
reasonable accuracy however, seismic responses resulting from the proposed method deteriorate at the flexible edge of the
torsionally-flexible buildingsM. PourshaEffects of higher modes on vertical distribution of isolated structures under near field earthquakes
http://www.iust.ac.ir/ijce/browse.php?a_id=536&sid=1&slc_lang=en
It has been pointed out the static lateral response procedure for a base-isolated structure proposed in International Building Code (IBC) somewhat overestimates the seismic story force. That is why in the current paper, vertical distribution of base shear over the height of isolated structures considering higher mode effects under near field earthquakes is investigated. Nonlinear behavior of isolation systems cause variation of frequencies transmitted to the superstructure and consequently higher modes effects should be considered. In this study base shear distribution obtained from nonlinear dynamic analysis is compared with that achieved from IBC for assessment of the international building code. This investigation has been conducted in two parts, in order to have an appropriate base shear distribution formula for isolated structures under near field earthquakes. In the first part using three first mode shapes of isolated structure and introducing coefficient corresponding to each mode, extracted from nonlinear dynamic analysis under near field earthquakes, a new formula has been derived. In the second part, the mode shape coefficients have been obtained theoretically and consequently a new base shear distribution over the height of isolated structures including the isolation system properties under near field ground motions was proposed. F. KhoshnoudianPresenting asphalt mixtures flow number prediction model using gyratory curves
http://www.iust.ac.ir/ijce/browse.php?a_id=750&sid=1&slc_lang=en
Pavement permanent deformations due to lack of shear strength in mixture are a major reason of rutting. Any simple test to determine mixtures resistance to permanent deformation isnâ€™t distinguished in the 1st level of SUPERPAVE mix design method and prevalent methods for evaluating mixture rut resistance are expensive and time-consuming. Two aggregate types, gradations, asphalt cements and filler types were used in this research to present a prediction model for rutting based on flow number. A mathematical model to estimate flow number of dynamic creep test was developed using model parameters and gyratory compaction slope. The model is validated using Neural Network and Genetic Algorithm and makes it possible to evaluate mixtures shear strength while optimum asphalt content is being determined in laboratory. So not only there is no need to expensive test instruments of rutting or dynamic creep but a remarkable time saving in mix design procedure is achievable. H. ZiariGeomatics applied to dam safety DGPS real time monitoring
http://www.iust.ac.ir/ijce/browse.php?a_id=681&sid=1&slc_lang=en
New advances in geomatics and communications technologies are enabling the development of Automated Auscultation System for structure monitoring. In particular, Differential GPS (DGPS) technique allows real-time monitoring of structures with millimetre accuracy after an appropriate mathematical treatment. The results of real-time DGPS monitoring of a pilot dam over 15 months are presented and compared with the results of pendulums and angular collimation. DGPS monitoring was established to control two points at the top of the dam with reference to an external and stable station. Communications were critical, evolving from initial GPRS connections to more reliable ASDL line in the last months. Real-time DGPS positions were filtered to reach millimetric accuracy through Kalman filter. Two configurations of the filter were tested, one more adapted to predictable and uniform velocity deformations (low frequency) and another more suitable for sudden and large movements (high frequency). Root mean square errors were calculated taking pendulums as a reference. Results show that both DGPS and angular collimation allow monitoring with millimetric accuracy. In the last period, where communications with processing server were stable, a global accuracy of 1.44 and 1.86 mm was reached for real-time DGPS monitoring. RINEX post-processing yielded millimetric results, validating real-time observations. We can affirm that the DGPS system is very useful for dam auscultation and safety as it detects adequately absolute deformations, being a complement to existing methods which should be considered in new safety plans. M. MARCHAMALO