M. Ridha

An Elongated Tetrakaidecahedral Cell Model for Fracture in Rigid Polyurethane Foam

A fracture criterion for rigid polyurethane foam is developed based on idealization of constituent cells by elongated tetrakaidecahedra. The ability of the proposed geometrical model to mimic the fracture characteristics of actual rigid polyurethane foam is examined and a fracture criterion derived analytically. In tandem, the fracture properties of an actual rigid polyurethane foam are obtained from mechanical tests. The fracture criterion based on the model exhibits correspondence with the behavior of actual foam. Consequently, this model constitutes a suitable basis for further investigation into the mechanical properties of actual polymeric foams.

Boundary Element Simulation for Identification of Steel Corrosion in Concrete Using Magnetic Field Measurement

Abstract A method to identify corrosion of steel in concrete is introduced by combining magnetic field measurement and a boundary element inverse analysis. A better sensitivity of corrosion identif...

Multistep Genetic Algorithm for Detecting Corrosion of Reinforcing Steels in Concrete

Abstract In this article, a multistep genetic algorithm is developed to overcome some difficulties of the inverse analysis method for accurately detecting a corrosion profile on the steel matrices from a small number of potential data, which are measured on the surface of the concrete structure. In this method, the corrosion profile, which represents the number, locations, and shapes of plural corrosion areas on the steel matrices, is modeled into a binary string instead of a set of unknown parameters. The binary string is defined by discretizing the steel matrices into a suitable number of segments using a certain resolution. Each segment is represented by one binary bit. The fitness value is inversely proportional to the cost function, which is a function of the difference between the calculated and measured potentials at some locations on the surface of the concrete structure. The calculated values of potential are obtained by solving Laplaces equation using the boundary element method (BEM). In gener...

Performance of Lifelines in Banda Aceh, Indonesia, during the December 2004 Great Sumatra Earthquake and Tsunami

The 26 December 2004 earthquake and tsunami significantly affected lifelines in Banda Aceh: (a) the water system sustained almost no damage due to shaking, but it had breaks at almost all aboveground stream crossings affected by the tsunami; (b) a waste disposal plant 1 km inland was estroyed by the tsunami; (c) electric utilities were not affected by shaking but were generally destroyed when impacted by the tsunami, and a floating generation barge was carried several kilometers inland; (d) a 70-m steel telecommunications tower at Lho Nga was destroyed by the tsunami; (e) the fishing port at Banda Aceh was totally destroyed, while the deep-water port at Kreung Raya (oil and dry cargo) lost half its piping and 3 of 9 oil tanks; (f) the airport at Banda Aceh is inland and had minor shaking damage to the control tower; and (g) one fire was reported on 26 December due to the earthquake. Significant lessons are (a) since the potential for this event was well known, the global earthquake community should better inform populations and decision makers; (b) urban master planning and building codes should include tsunami design as a standard and significant criterion; (c) the needs of lifeline operators should be considered in the design and development of tsunami warning systems; (d) building and other design codes should include tsunami design as a standard loading; and (e) extrapolation of the experience in this event to other situations is required.

Simulation of the Ill-Posed Problem of Reinforced Concrete Corrosion Detection Using Boundary Element Method

Many studies have suggested that the corrosion detection of reinforced concrete (RC) based on electrical potential on concrete surface was an ill-posed problem, and thus it may present an inaccurate interpretation of corrosion. However, it is difficult to prove the ill-posed problem of the RC corrosion detection by experiment. One promising technique is using a numerical method. The objective of this study is to simulate the ill-posed problem of RC corrosion detection based on electrical potential on a concrete surface using the Boundary Element Method (BEM). BEM simulates electrical potential within a concrete domain. In order to simulate the electrical potential, the domain is assumed to be governed by Laplace’s equation. The boundary conditions for the corrosion area and the noncorrosion area of rebar were selected from its polarization curve. A rectangular reinforced concrete model with a single rebar was chosen to be simulated using BEM. The numerical simulation results using BEM showed that the same electrical potential distribution on the concrete surface could be generated from different combinations of parameters. Corresponding to such a phenomenon, this problem can be categorized as an ill-posed problem since it has many solutions. Therefore, BEM successfully simulates the ill-posed problem of reinforced concrete corrosion detection.

CORROSION RISK ASSESSMENT OF PUBLIC BUILDINGS AFFECTED BY THE 2004 TSUNAMI IN BANDA ACEH

Banda Aceh region has a coastal environment and frequent earthquakes. The 2004 Sumatra tsunami caused many buildings to collapse and became submerged by seawater in the region. Thus, the buildings might become susceptible to corrosion, which will reduce their strength. Consequently, sudden failure might happen when even a small earthquake occurs. This study reports a corrosion risk assessment for some reinforced concrete (RC) public buildings in Banda Aceh region in order to understand how the tsunami has influenced the corrosion risk level. The assessment was performed by using half-cell potential mapping technique. Six buildings were chosen: three existing buildings, two newly constructed buildings in the tsunami-affected area and one building located outside that area. The assessments were carried out from 2009 until mid of 2010. The assessment results indicated that the corrosion risk to the existing buildings were at intermediate to severe level. In addition, newly developed buildings were at intermediate level, while outside building was still at low levels. Those findings showed that the RC buildings around the tsunami-affected area, either existing or new buildings, had become corrosive. Therefore, it is important to conduct regular corrosion assessments to prevent early failure due to the coexistence of rebar corrosion and earthquake.

Surface Modification of Pure Titanium by Nitrogen Ion Implantation at Different Beam Energy and Dose

The implantation of nitrogen ion is one of the important techniques for modifying the surface characteristics to improve wear and corrosion resistance of commercially pure (cp) Titanium. Although nitrogen ions implanted titanium in various dose demonstrated significant changes of the wear and corrosion resistance, the variable energy implanted is still not yet fully studied. Nitrogen ions were implanted in cp Titanium surface with varies of both dose of 0.5; 1.0 and 2.0 x1017 ions cm-2 and energy of 80, 100 and 115 keV. The nitrogen ion implanted cp Titanium demonstrated an increase in the surface hardness and improvement in corrosion behavior. The maximum surface hardness was delivered by the specimens implanted with the dose of 2.0x1017 ions cm-2 at energy of 80 keV. Grazing incidence x-ray diffraction studies indicated that TiN phase was formed on near surface substrate. Electrochemical tests in 3.5%-wt NaCl solution depicted significant improvements in corrosion resistance for specimens implanted with dose of 0.5x1017 and 1.0x1017 ions cm-2 at energy of 80 keV, dose of 1.0x1017 and 2.0x1017 ions cm-2 at energy of 100 keV. The dose of 2.0x1017 ions cm-2 and energy of 100 were the best implantation parameter in this study.

Comparison of GA and PSO in boundary element inverse analysis for rebar corrosion detection

This paper presents the comparison of the two optimization methods, particle swarm optimization (PSO) and genetic algorithm (GA) in boundary element inverse analysis that applied to detect the corrosion location of rebar in the concrete. This comparison focuses at analyzing the performance of both methods in reaching the global optimum, considering that both heuristics are based on population search techniques. The model of 2-dimension rectangular reinforced concrete was used as a case example to compare both methods in boundary element inverse analysis. The boundary element inverse analysis was developed by combining Boundary Element Method (BEM) and PSO or GA. The inverse analysis is carried out by means of minimizing a cost function. The cost function is a residual between the calculated and measured potentials on the concrete surface. The calculated potentials are obtained by solving the Laplaces equation using BEM. The GA or PSO is used to minimize the cost function. Thus, the corrosion location of reinforcing steel in concrete can be detected. The numerical simulation results showed that one of PSO or GA can be used for the inverse analysis for detecting rebar corrosion by combining with BEM. However, it shows that PSO seem numerically superior compared to GA in term of consistency and accuracy in finding global optimum solution for such a problem.

Infinite Boundary Element Formulation for the Analysis of CP System for Submersible Pump

The effectiveness of the cathodic protection system is very important to be maintained for the submersible pump structure. Early damage of the infrastructure can be caused by improper design of the protection system. However, nowadays the effectiveness of the cathodic protection system could not be evaluated before the system applied in the field. This study is conducted on development of 3D infinite domain boundary element method (BEM) to evaluate the cathodic protection system for submersible pump structure using aluminum sacrificial anode. In this study, the potential in the domain was modeled using Laplace equation. The equation was solved by applying BEM, hence the potential distribution and current density on the metal surface and at any location in the domain can be obtained. The numerical analysis result shows that the 3D infinite domain BEM can be used to simulate the cathodic protection system. Moreover, the execution time for infinite domain BEM is less than the finite domain for the evaluated case.

The Influence of Inertia Weight on Particle Swarm Optimization in Boundary Element Inverse Analysis for Rebar Corrosion Detection

Particle Swarm Optimization (PSO) has been applied as optimization tool in various engineering problems. Inverse analysis is one of the potential application fields for PSO. In this research, the behavior of PSO, related to its inertia weight, in boundary element inverse analysis for detecting corrosion of rebar in concrete is studied. Boundary element inverse analysis was developed by combining BEM and PSO. The inverse analysis is carried out by means of minimizing a cost function. The cost function is a residual between the calculated and measured potentials on the concrete surface. The calculated potentials are obtained by solving the Laplace’s equation using BEM. PSO is used to minimize the cost function. Thus, the corrosion profile of concrete steel, such as location and size, can be detected. Variation in its inertia weight was applied to analyze the behavior of PSO for inverse analysis. The numerical simulation results show that PSO can be used for the inverse analysis for detecting rebar corrosion by combining with BEM. Also, it shows different behavior in minimizing cost function depending on inertia weight.