P. B. R. Dissanayake

An approach to multicriteria fuzzy optimization of a prestressed concrete bridge system considering cost and aesthetic feeling

In practical structural design problems, the designer should take into account several objectives, such as economics, safety, serviceability, aesthetic feeling and so on, and relative evaluations among these different characteristic objectives have some tolerances or fuzziness. For these reasons, the practical optimum structural design process concerning multiobjectives can be defined as a kind of compromising optimum decision-making process with fuzziness. In this paper, a rational, systematic and efficient fuzzy optimum design method for structural systems is developed by combining a suboptimization concept and fuzzy decisionmaking techniques at the discrete combinations of common design variables. The design method is applied to an optimum design problem of a large scale prestressed concrete bridge system considering two objectives; the total construction cost and aesthetic feeling. The rationality, the systematic design process and the efficiency of the proposed method are demonstrated.

Structural Appraisal-based Different Approach to Estimate the Remaining Fatigue Life of Railway Bridges

The current fatigue life estimation methods of railway bridges are generally based on combinations of measured strain histories, Miner’s rule, and railway code provided fatigue curve. Even though the past measured strain histories are available for major bridges, most of the old bridges do not have past strain measurements. Furthermore, in case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. These reasons hinder the usage of current methods to estimate the realistic remaining fatigue life of most of the existing railway bridges. Therefore, a new method is presented in this article to estimate remaining fatigue life of riveted railway bridges. The method mainly consists of predicted stress histories, recently developed sequential law and fully known Wöhler curve. Here, it is essential to use the fully known Wöhler curve as the related fatigue curve. Hence, the technique, which utilizes transfer of the partially known Wöhler curve to fully known curve, is also discussed in this article. Further, this method describes a reasonably accurate procedure to obtain the past stress histories from present day measured strains. Initially, the article describes the proposed method for remaining fatigue life estimation. Then the sequential law and associated fully known S-N curve determination procedure are verified by comparing theoretical fatigue life, damage behavior with real fatigue life and damage behavior of few materials. Finally, the remaining fatigue life of an existing railway bridge is estimated. Hence, validity and merits of the proposed method is confirmed by comparing the results with previous method-based fatigue lives.

Reliability Index for Structural Health Monitoring of Aging Bridges

This paper presents a reliability-based methodology for health monitoring of aging bridges. Initially, critical failure criteria are proposed depending on the type of bridge. Safety margins are then defined based on these criteria. It is assumed that quantities in the failure criteria are random variables that are normally distributed. Based on this assumption, elementary reliability indices and thereby elementary failure probabilities are estimated for each critical failure mode. Having found the elementary failure probability values, system failure probability of the bridge is calculated for the period under consideration. Finally, the system failure probability is used to obtain a system reliability index of the bridge. The system reliability index is a quantative way to express the condition of the bridge for the period under consideration. As a case study to illustrate the proposed reliability procedure, a wrought iron railway bridge was selected from the national railway bridge network of Sri Lanka. For this bridge, fatigue and corrosion were selected as the most critical forms of failure. Application of the proposed methodology showed that the present condition of bridge was satisfactory for current loading conditions. Predicting reliability, as opposed to damage, is a positive outlook approach to health monitoring that is useful for infrastructure management.

Development of an Efficient Maintenance Strategy for Corroded Steel Bridge Infrastructures

The potential for structural capability degrading effects caused by corrosion is of profound importance and must be both fully understood and reflected in bridge inspection and maintenance programs. As the number of steel bridge infrastructures increases throughout the world, it is an exigent task to conduct regular and detailed corrosion surface investigations to evaluate their residual strength capacities and to develop analytical models to understand their current conditions and critical locations, as well as yield and ultimate behaviors. This paper presents a simple, accurate, and rapid assessment method and an effective maintenance management strategy developed by using the results of tensile coupon tests conducted on numerous corroded plates obtained from a steel plate girder used for about 100 years with severe corrosion and an finite element method (FEM) analytical approach proposed by measuring only the maximum corroded depth, which can be used to make reliable decisions affecting cost and safety.

Development of Analytical Method for Predicting Residual Mechanical Properties of Corroded Steel Plates

Bridge infrastructure maintenance and assurance of adequate safety is of paramount importance in transportation engineering and maintenance management industry. Corrosion causes strength deterioration, leading to impairment of its operation and progressive weakening of the structure. Since the actual corroded surfaces are different from each other, only experimental approach is not enough to estimate the remaining strength of corroded members. However, in modern practices, numerical simulation is being used to replace the time-consuming and expensive experimental work and to comprehend on the lack of knowledge on mechanical behavior, stress distribution, ultimate behavior, and so on. This paper presents the nonlinear FEM analyses results of many corroded steel plates and compares them with their respective tensile coupon tests. Further, the feasibility of establishing an accurate analytical methodology to predict the residual strength capacities of a corroded steel member with lesser number of measuring points is also discussed.

Interval Reliability Based Condition Assessment of Bridges

Recent research indicates that small changes in input parameters of reliability models significantly affect outcomes of reliability computations. This is a considerable concern especially in reliability based condition assessments of old bridges which have lower reliabilities. To overcome such errors of input parameters, structural reliability can be combined with interval analysis (i.e., interval reliability). This paper presents an interval reliability based condition assessment procedure of bridges. Interval reliability of a component is introduced when resistance and load behave as: (1) normal variables; (2) log normal variables. Similarly, interval reliabilities of other components can be estimated. Finally, system interval reliability is estimated. Bridge condition is assessed by comparing with the acceptable reliability of the bridge. A case study, a steel girder bridge, is selected, and its interval reliability indices are estimated for possible errors of statistical parameters. The obtained results are then compared with an existing method without considering interval reliability. Results indicate that there are significant variations in reliability when interval reliability is considered.

Numerical Investigation of Residual Strength and Energy Dissipation Capacities of Corroded Bridge Members Under Earthquake Loading

Recent damage examples of aged steel bridge infrastructures around the world are so alarming. They intensified the importance of careful evaluation of existing structures for the feasibility of current usage and to ensure public safety. Corrosion and fatigue cracking may be the two most important types of damages in aging structures. Furthermore, recent earthquakes demonstrated potential seismic vulnerability of some types of steel bridges. Corrosion and its effects can trigger the damages caused by earthquakes, and it will be vital to understand the behavior of existing steel bridges which are corroding for decades in future severe seismic events as well. This article comprises the results of nonlinear FEM analysis of many actual corroded plates with different corrosion conditions and proposes a simple and reliable methodology to estimate remaining seismic strength and energy dissipation capacities by measuring only the minimum thickness of a corroded surface, which can be used to make rational decisions about the maintenance management plan of steel infrastructures.

Ground Penetrating Radar wave behavior under different corrosion levels of concrete

Corrosion of reinforced concrete structures is the most significant issue for its safety and lifetime. During the structural assessment of lifetime evaluation of structures, destructive tests might increase the damage size of the structure. This investigation attempts to identify the corrosion effect of the reinforcement in concrete and chloride contamination of the concrete using Ground Penetrating Radar (GPR) as a non-destructive testing method. A 300 mm wide, 600 mm long and 100 mm high three concrete slab panels were prepared using a 12 mm rebar. After 28 days of casting the concrete slab panels, reflection and common mid-point GPR surveys were performed using Pulse EKKO PRO system with 1000 MHz centre frequency transducers. The concrete panels were partly submerged in 5% NaCl solution and reinforcement bar was corroded using the impedance current technique. A 17.2 V DC current was applied to accelerate the corrosion of slab panels and kept it for 24 hours. The GPR surveys were repeated and the same procedure was performed after 48 h, 72 h and 96 h of submerged time intervals. With parallel to each GPR data acquisition steps, half-cell potential test was also conducted. The collected GPR data were analyzed separately using the EKKO Mapper, GFP Edit and EKKO View Deluxe software packages. Analyzed results clearly showed that the GPR wave velocity did not change with corrosion time, but the reflected wave amplitude decreases with increasing corrosion time which is in correspondence with the half-cell potential test.