Asian journal of civil engineering
Volume:5 Issue: 3, July & October 2004

This paper presents a hybrid optimization algorithm based on a modified genetic algorithm(GA). The algorithm includes two stages. In the first stage, a global search is carried outover the design search space using a modified GA. In the second stage, a local search isexecuted that is based on GA solution using a discretized form of Hooke and Jeeves method. The modifications on basic GA includes dynamically changing the population sizethroughout the GA process, utilizing variable penalty multiplier and the use of a square root form of the penalty function in constraint handling. The hybrid algorithm and themodifications to the basic GA are examined on the design optimization of a well-known test problem (10 bar truss). The effect of different parameters and techniques of handling GA operators on the performance of the proposed algorithm is investigated. The hybrid algorithm is employed for the design optimization of a reinforced concrete flat slab building and the results are compared with those of using the GA only.

Plastic analysis using kinematic approach is quite conventional. A C++ program has beendeveloped which computes the collapse load factor of planar frames using combination ofelementary mechanisms and Genetic algorithms. The program has the capability ofgenerating the frames visually and observing the results by simple clicks on appropriateicons. Elementary and combined collapse mechanisms could be viewed on screen instead of having to interpret the results from the rush of outputs. Many examples presented here show how easy it is to create the model from scratch, perform the loading, and complete the analysis.

A computer-based systematic approach for optimizing material cost in reinforced concreteelements is presented. This approach considers the current material cost in the trade-off and selection of member dimensions and reinforcement design of concrete elements such as beams and columns. The theoretical framework is to design reinforced concrete structure based on the cost of available materials and not just on the availability of materials. The windows-oriented computer program developed for this purpose would also be beneficial to owners, designers and contractors interested in cost optimization of reinforced concrete elements.

The paper presents a study on the fatigue strength of steel fibre reinforced concrete (SFRC) containing different volume fractions, aspect ratios and types of steel fibres, for various levels of the fatigue stress. The fatigue test data available in literature has been used for analysis. The test data is used to generate the S-N curves and an Equation is proposed by regression analysis to predict the flexural fatigue strength of SFRC. A probabilistic approach is used to predict the fatigue reliability of SFRC. The fatigue-life distributions of SFRC at a given stress level, is shown to approximately follow the two-parameter Weibull distribution. The S-N relationships have been used to obtain the parameters of the Weibull distribution. Mean and Design fatigue lives have been computed for different stress levels for SFRC with different combinations of fibres, corresponding to different probabilities of failure.

The plastic behavior of an elastoplastic cylindrical shell with circular and rectangular cutoutsunder bending moment loads was investigated numerically and experimentally.A testing device (pure bending measurement) was designed and made to perform experiments on bending moment tests. The ratio of diameter to thickness of the stainless steel 304 specimens was 40.4 and the ratio of length to diameter was 7.94. The shape of the cutout on the shell was circular or rectangular. The tested specimens were categorized into five dissimilar groups. The effect of size, position and numbers of the cutout on the plastic moment is discussed. In order to investigate the strain distribution around of cutout, nine strain gauges were mounted in the longitudinal and circumferential directions on two specimens with different type of cutout.To investigate the accuracy of analytical and experimental results, numerical analysisconsidering the behavior of elastoplastic material were performed and good agreement was obtained between them. The strength of bending moment of cylindrical shells was decreased with increasing of sizes of cutout and it was increased with changing the location of the cutout from compression side to tension side. The effect of the number of cutouts (increasing from 1 to 3 (axisymmetrical)) on bending strength of tubes is negligible.

Arches, vaults and domes were the most important elements in Iranian buildings until thebeginning of the 20th century. These forms are one of the main features of traditionalbuildings in small cities and villages in the neighborhood of the desert. The present paperinvestigates the general performance of arches and domes during the Bam earthquake(December 2003, Ms=6.6). In this earthquake, wide damages to such traditional buildingswere observed, especially those located in the vicinity of the fault. The paper reviews themain reasons of failures of such buildings. It also discusses the suitability of these structures in earthquake hazard areas and reviews the main points of weakness of the current construction practices.