ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2009 | Volume:10 | Issue:6|Papers Count:8

This article presents a heuristic particle swarm ant colony optimization algorithm to solve engineering optimization problems. Although PSO has simple principle and ease to be implemented and can eventually locate the desired solution, however, its practical use in solving engineering optimization problems is severely limited by the high computational cost of the slow convergence rate. Here, ant colony and harmony search principles are employed to speed up local search and improve precision of the solutions. A modified feasible-based mechanism is described which handles the problem-specific constraints.Benchmark optimization problems are used to illustrate the reliability of the proposed algorithm.

In recent years, the Information Technology (IT) has been utilized in various fields of civil engineering. Especially, trials have been made to utilize optical fibers as sensors to measure strain of civil engineering structures, ground deformation, temperature, etc., and they have been installed for measuring in the civil engineering structures including tunnel, river embankment, and cut-slope soil structures. In order to make such optical monitoring systems of civil engineering structures more general and organic systems, it would be effective to combine them with such comprehensive telecommunication systems. The infrastructure structure measurement and maintenance system is accumulation and collection system and processing/offering/exchanging system, and the network where information is additionally transmitted is needed. We investigate the construction of general monitoring systems of civil engineering structures which can perform thorough management from monitoring to maintenance utilizing telecommunication networks technology.

Mechanically Stabilized Earth Walls (MSEW) and Reinforced Soil Slopes (RSS) are usually considered as cost-effective soil-retaining structures. By inclusion of tensile reinforcing elements in the soil, the strength of the soil can be improved significantly such that the vertical face of the soil/reinforcement system is essentially self supporting. Based on limited data, reinforcement accounts for 45 to 65 percent of total cost. This paper couples a complete MSE wall design routine with a highly efficient optimization model for optimum design of mechanically stabilized earth walls. The design algorithm benefits from limit equilibrium technique to calculate the external and internal stability of the wall considering common safety factors. The proposed safety factors are treated as constraint to the problem.The optimization model uses GA to search for optimum combination of the design variables to satisfy the required safety factors. Integration of simulation-optimization approaches for optimum design of MSE walls is the first in its kind which has been overlooked in the literature. Application of the model in few case examples shows that up to 15 percent may be saved in design specific cost in relatively high walls.

The dynamic stability is studied for thin-walled structural elements with variable stiffness subjected to periodically alternating axial force in this paper. Here, the variation stiffness means that it changes with periodically alternating axial force as for nonlinear geometry stiffness matrix of thin-walled member. Damping is considered and the governing equations are expressed in terms of a system of two second-order differential equations of the Mathieu type, with periodic coefficients.MATLAB package is used to determine the stability boundary. Numerical example is presented for the dynamic stability boundary of a simply supported beam with I-shaped cross section. Comparison is made with finite element analysis. Considered damping, some conclusions are drawn out: Excited zone of thin-walled member is continuous, the dynamic instability is highly dominant in the first region while the second and third instability regions are of much less practical importance, The larger the ratio of damp, the less the dynamic instability region, The larger the ratio of damp, the more time dependent components of the load wanted, absorption of damping is commonly of no effect to prevent parametrically excited vibration from dynamic instability, Parametrically excited vibration considering damping is much more different from damped forced vibration in nature.

Sulfate attack and its effects are important from both scientific and industrial viewpoints. It is perceived that cements containing pozzolan have better performance in sulfate solutions, since the pozzolanic reactions reduce the quantity of Calcium hydroxide and increase Calcium silicate hydrate. This paper investigates the physical/mechanical properties of concretes made by blended cement containing Tuff natural pozzolan, and Portland cement.The microstructure of mortars under sulfate attack is studied using SEM analysis and reaction products are characterized using EDS analysis.The results suggest that, contrary to previous opinions, mortars containing pozzolan show more expansion and unsatisfactory performance in sulfate solution.

The use of Recycled Concrete Aggregate (RCA) is gaining importance throughout the globe due to the depleting sources of natural aggregate and disposal problem of demolished waste.The advancement in the prestressed concrete technology and multistoried structures has given impetus for making concrete of high strength. Also, it is well established that the fibers make concrete ductile. The aim of this research work is to determine the suitability of glass fibers for use in structural recycled aggregate concrete of high strength. The fresh and hardened state properties of partially replaced recycled aggregate concrete, with varying percentages of glass fibers, are compared with the corresponding conventional aggregate concrete. The compressive, split tensile and flexural strengths of M50 grade concrete with 0% RCA and 50% RCA have increased as the fiber content increased. The maximum values of all these strengths were obtained at 0.03% of fiber content for both the concretes of 0% RCA and 50% RCA. Large deflections of beams before failure indicated improved ductility with the addition of fibers.

This paper highlights the importance of selection of a suitable ductile composite, incorporating it into the predefined locations, for better seismic performance. Replacement of normal concrete with ductile composites at plastic hinge locations is an idea, which can be well thought for in the conceptual approach to structural design. A simple experimental investigation was carried out to establish this concept. The ability of the structure to sustain levels of inelastic deformation implicit in ductility values is dependent on the material and detailing used. Concrete, which is inherently brittle and weak in tension, were modified by incorporating polymeric materials like natural rubber latex and steel fibers. This improves ductility, strain at peak load and energy absorption capability. The validity of the scheme is proved by a couple of experiments including the stress- strain characteristics of the material as they play a significant role in ductile response of structural elements. Three point bending tests were conducted on four types reinforced concrete beams with different concrete matrixes at the central region and high strength concrete at other regions. As ductility and damage modeling of structural components plays an important role in achieving the performance objectives, they have been quantified using the experimental data by suitable methods. Damage index evaluation was done using one of the well-known damage models, which takes into account the hysteretic energy dissipation along with ductility. A response factor directly related to the damage index is found out in order to get the major design variable displacement ductility, thus helping the design stage calculations.

The response of a multi-story space frame structure resting on non-linear base isolation system, subjected to bi-directional harmonic and seismic ground motions are studied. A four-storey space frame structure with consistent mass system having six degrees of freedom (three translations along x, y, z-axes and three rotations about these axes) at each node is considered for study. The effect of isolation damping and the excitation frequency on the response of a base isolated structure is investigated. The effect of excitation frequency, isolation period, superstructure time period and superstructure damping on the optimum isolation damping is also studied in this paper. It is shown that the above parameters have significant effects on optimum isolation damping. The response of isolated system is found to be less in comparison to the corresponding response without isolation system, implying that the isolation is effective in reducing acceleration and forces of the system.