ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2008 | Volume:9 | Issue:3|Papers Count:7

The spacing between the longitudinal and transverse beams of a grillage system has an important effect in the minimum weight design of these systems. In this study this effect is investigated using an optimum design algorithm which is based on recently developed harmony search algorithm. The optimum design problem of a grillage system is formulated implementing LRFD-AISC (Load and Resistance Factor Design-American Institute of Steel Construction) limitations. It is decided that W-Sections are to be adopted for the longitudinal and transverse beams of the grillage system. 169 W-Sections given in LRFD code are collected in a pool and the optimum design algorithm is expected to select the appropriate sections from this pool so that the weight of the grillage is the minimum and the design limitations implemented from the design code are satisfied. The solution of this discrete programming problem is determined by using the harmony search algorithm. This algorithm simulates jazz improvisation into a numerical optimization technique. Design example is presented to demonstrate the effect of beam spacing in the optimum design of grillage systems.

In the recent years heuristic algorithms such as genetic algorithms, ant colony algorithms and simulated annealing have found many applications in optimization problems. The essence of these algorithms lies in the fact that they do not depend on the specific search space to which they are applied and consequently this extends their generality. In this paper, genetic and ant colony algorithms are used to find the collapse load factor of two dimensional frames and their efficiency is compared to a direct approach. It is shown that when these algorithms are tuned finely and their parameters are adjusted carefully, very good results can be obtained. Four examples are presented to illustrate the efficiency of algorithms.

In practical applications, it is difficult to link dashpot absolutely rigidly between the structure and the mass blocks of the multiple tuned mass dampers (MTMD). In order to cope with this practical issue, Maxwell damper based multiple tuned mass dampers (referred to as the MD-MTMD) have been presented for attenuating the response of structures excited by the ground acceleration. By resorting to the formulated transfer functions of the MD-MTMD structure system, the dynamic magnification factors (DMF) are then defined of the MDMTMD structure system. The criterion for the optimum searching can thus be selected as the minimization of the minimum values of the maximum DMF (min. min. max. DMF).Employing this criterion, the effects of the normalized relaxation time constant (NRTC) are investigated on the optimum parameters and effectiveness of the MD-MTMD. Likewise, the effects of the RTC on the stroke of the MD-MTMD are estimated in terms of maximizing the dynamic magnification factors (DMF) of each MD-TMD in the MD-MTMD. The numerical results have indicated that the MD-MTMD is a feasible solution for the practical issue mentioned above of the traditional MTMD.

Empirical ground motion models for the average horizontal component of peak ground motion and acceleration response spectra from shallow crustal earthquakes are derived using near-source database. These models were derived using a worldwide dataset consisted of corrected and processed accelerograms of 646 strong-motion records recorded with 60 (km) of the surface projection of earthquakes between Mw 5.2 and 7.8. Model is function of earthquake mechanism, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, depth-to-top of rupture, hanging wall effects and faulting mechanism. Non-linear site effects are constrained by equivalent linear models. An important additional source parameter, depth to the top is also included. The hanging wall effect is included with an improved model that varies smoothly as a function of the source properties, such as magnitude, dip, distance, depth, and the site location.

The present work is aimed at studying the effect of re-vibration on the compressive strength of concrete using 53 grade Ordinary Portland Cement, with wide range of w/c ratios varying from 0.35 to 0.7 and with more number of re-vibration time lag intervals ranging from ½ hour to four hours. The effect of re-vibration on the density of concrete is also studied. The results have shown that the compressive strength of the concrete with various w/c ratios have increased up to certain time lag interval i.e. within the initial setting time (IST) and decreased thereafter. The percentage increase in the compressive strength also nearly followed the above trend.

Biogenic sulfuric acid corrosion is often a problem in sewer environments. Also in certain industrial activities sulfuric acid is used during the production process. İt can lead to a fast degradation of the concrete structures. Therefore there is a substaintial need for construction of durable concrete structures in such environments. The porosity of concretes plays an important role in harsh environments. For production of low porosity or high density concretes, optimization of aggregate and cement grading and their proporations is necessary. The size distribution of aggregates and cement materials determine the compactibility and highest local density of particles. Dense packing of concrete particles in the mixes lead to low cement content and high-strength of low porosity mortar and concretes. A research program was under taken to improve concrete resistance against sulfuric acid attack. Five concrete mixtures were investigated, first mix contains Type 2 portland cement as a control mix and the second one contains Type 2 portland cement and super fine Quartz powder as a filler with particle size between 0 to 16 micron. Third mix contains Type 2 portland cement with 8% silica fume (SF) replacement and super fine filler. Other mixes contain Type 2 portland cement with 20% natural pozzolanas replacement namely Trass and Pumice and super fine filler. The dense packing of siliceous aggregates and cement materials were used to achieve the highest density of concretes. Fuller ideal grading curve for particle size distribution (PSD) of cement material was used. The PSD of the Quartz powder, silica fume, natural pozzolanas and cement were analayzed to explain the packing effect of super fine Quartz powder. Cementitious material content and water binder ratio were varried in this investigation. İn the experiment, concrete cubes and mortar plates were immersed in sulfuric acid with pH=1.0. They were periodically examined for appearance, measured for mass change and tested in compression and flexure up to 180 days. The performance of mortar and concretes containing Trass and ultra fine filler was better than the other mixes. Also performance of other mixtures was better than the control mixture.

The objective of the paper is to present the dependence of the wind profile of a monsoon on the depth of the layer, the ground surface roughness length, and the atmospheric stability. The paper also indicates that the wind profiles of the typhoon are composed of two layers, the upper one with the nearly constant velocity and the lower one in which the velocity decreases with the decrease in the height. The typhoon wind profiles are not stationary but changes abruptly.