Hani Melhem

Fourier and wavelet analyses for fatigue assessment of concrete beams

We investigate damage detection in a simply-supported pre-stressed beam. A crack was propagated by fatigue loads, which were applied up to two million cycles. Both fast Fourier transform (FFT) and continuous wavelet transform (CWT) are used in the analysis of the structural response to impulse loads. The acceleration response of the full-scale beam was measured each time a certain number of cycles of fatigue loads were applied. The results of this study show that both methods can clearly identify the crack growth induced by fatigue loads. The natural frequencies found by FFT are sensitive to the crack progression. The results from the CWT analysis show a clear difference in structural responses between the initial and damaged states of the structure. The response accelerations are de-noised by a soft-thresholding method before they are analyzed by CWT. In addition to the frequency components, the CWT shows the moment in time when particular frequencies occur. Therefore, wavelet analysis has the potential of becoming an effective tool for damage detection and health monitoring of structures for which the natural frequencies are irregularly changing. As the crack grows, the magnitude of ridges obtained by CWT analysis decreases significantly, which indicates the reduction in structural stiffness.

Signal pattern-recognition for damage diagnosis in structures

In this article, a signal-based pattern-recognition approach is used for structural damage diagnosis with a single or limited number of input/output signals. The approach is based on extraction of the features of the structural response that present a unique pattern for each specific damage case. In this article, frequency-based features and time-frequency-based features were extracted from measured vibration signals by Fast Fourier Transform (FFT) and continuous wavelet transform (CWT) in order to form one-dimensional or two-dimensional patterns, respectively. Three pattern-matching algorithms including correlation, least-square distance, and Cosh spectral distance were investigated for pattern matching. The results showed that features of the signal for different damage scenarios could be uniquely identified by these transformations, and suitable correlation algorithms could perform pattern matching that identified both damage location and damage severity. Meanwhile, statistical issues for more complex structures as well as the choice of wavelet functions are discussed.

Monitoring bridge health using fuzzy case-based reasoning

Case-based reasoning (CBR), one of the artificial intelligence (AI) learning approaches, is drawing the attention of many researchers in Civil Engineering. However, due to vagueness and uncertainties in knowledge representation, attribute description, and similarity measures in CBR-especially when dealing with similarity assessment-it is difficult to find the cases from a case base which exactly match the query case. Therefore, fuzzy theories have been incorporated into CBR allowing for more robust, flexible, and accurate models. In this study, two fuzzy membership functions (trapezoidal and step-wise) and fuzzy numbers are used to measure the similarity between attribute values. They are integrated into CBR to develop a model used to monitor highway bridge health. This models learning capabilities have been validated using five different error-metrics, based on the cross-validation method. The code is implemented using the programming language C++, and all the cases used for both training and testing are extracted from the electronic bridge database of the Kansas Department of Transportation. It is shown from the experimental results that it is feasible to apply fuzzy case-based reasoning to monitor bridge health.

RIGOROUS PROCEDURE FOR CALCULATING DEFLECTIONS OF FIBER-REINFORCED POLYMER-STRENGTHENED REINFORCED CONCRETE BEAMS

The need to upgrade the capacity of structural members is growing due to the aging infrastructure elements and the expanding volume of traffic. The use of external fiber-reinforced polymer plates bonded to the tensile face of beams has proven to be effective in increasing the ultimate strength. With this in mind, this paper develops a rigorous analytical procedure for calculating the deflection of simple beams at any load stage. A parametric study is conducted to examine the relevance of the ACI original and modified equations for a wide range of geometric and material properties as well as different loading conditions.

Critical Success Factors in an Agency Construction Management Environment

AbstractThis study aims at differentiating construction project critical success factors based on organizational backgrounds of project participants: contractor, construction manager (owner representative), and design firms. Construction professionals from diverse locales were asked to rate a list of 53 potential factors for the objectives of schedule, budget, and quality, and additionally compare the objectives for overall project success. The set of 53 factors was enriched by eliminating 13 factors that could not prove their statistical significance for even one of schedule, budget, or quality performances for any of the three organizations. Commissioning the 40 significant factors, an analytical hierarchy process was used to determine organization-based factor rankings for overall project success. Spearman’s test on rankings of the 40 significant factors for overall project performance results in a highest level of correlation between the managers and contractor personnel (rs=0.54), followed by that be...

Fuzzy logic for bridge rating using an eigenvector of priority settings

To avoid possible inconsistencies in the inspection and rating of highway bridges, a fuzzy inference model based on a priority setting obtained through the solution of an eigenvector problem invoking a pairwise comparison matrix of importance is presented. This method and the associated solution technique, originally developed for general use in multi-attribute decision making, are used to implement a computer program written in CLIPS and C language in a knowledge-based expert system environment. The computer program was verified using actual bridge inspection data. The advantage of the proposed model is that, when applied to bridge rating, it provides priority settings of the individual elements of a bridge component in addition to the final rating of that component.<<ETX>>

An expert system/training aid for fatigue of steel bridges

Abstract The expert system FASTBRID (Fatigue Assessment of STeel BRIDges) is under development. A prototype (pilot) system has been developed and is currently being validated. The system is intended to serve as a training aid/consultant for inspection and rehabilitation of steel highway bridges with regards to fracture and fatigue, and to be made available for wide distribution. In this paper the development of the prototype, its architecture and usage are presented. Illustrative examples are given to demonstrate the system performance. When completely developed FASTBRID would constitute both an advisory system to be used by practitioners in real world evaluations, and a training aid to guide bridge engineers and inspector leaders in detecting and solving fatigue related problems in steel highway bridges.

Application of Fuzzy Case-Based Reasoning to Bridge Management

Case-based reasoning (CBR), one of the artificial intelligence (AI) learning approaches, is drawing the attention of many researchers in Civil Engineering. However, due to vagueness and uncertainties in knowledge representation, retrieval, and inference of cases in CBR, -- especially when dealing with similarity assessment -, it is difficult to find the cases in a case base which are exactly the same as the query case. Therefore, fuzzy theory h as been incorporated into CBR, which promises more robust, flexible, and accurate models. In this research, fuzzy case -based reasoning (FCBR) has been used to develop a model for bridge management. This model can deal with multiple objectives, namely, pr edicting the future health condition of a bridge deck, and recommending the appropriate maintenance, rehabilitation and replacement (MR&R) actions. The FCBR model’s learning capabilities have been validated using the cross-validation method. The code is implemented using the programming language C++, and all the cases used for both training and testing are extracted from the electronic bridge database of the Kansas Department of Transportation. In this paper, recommending MR&R actions, the second function of the developed bridge management model, is focused on.

MACHINE LEARNING AND ITS APPLICATION TO CIVIL ENGINEERING SYSTEMS

Abstract Todays state-of-the-art expert systems are plagued by four major problems: brittleness, lack of metaknowledge, knowledge acquisition, and validation. Knowledge acquisition by itself is a very time consuming and tedious process. The uncertainty of information and erroneous data have also caused knowledge engineers anxious moments. In order to address these problems, several machine learning techniques supported by well-formulated theories and algorithms, have been developed. In this article some of these techniques are reviewed along with examples of their application to civil engineering problems. The techniques presented either fall under the category “learning from examples” (commonly referred to as inductive learning) including the ID3 algorithm, the rough sets theory, and the PROTOS algorithm, or “learning from observations” (also known as conceptual clustering) including the COBWEB algorithm, or a combination of both.

Applications of Fuzzy Logic to Bridge Engineering

This article summarizes several attempts made to apply fuzzy logic to structural engineering and particularly to bridge engineering. Many of these attempts have been implemented in depth and are readily available for practical use. The major research activity has been in the areas of structural damage assessment, bridge condition evaluation, and structural rating. In the case of bridge rating, the inspection procedure currently being used suggested the need for a multi-attributive decision making model. Two fuzzy models previously proposed in the literature and a third model adopted by the authors are presented here. The later produces a priority setting obtained through the solution of an eigenvalue problem involving a closest discrete pairwise matrix indicative of the relative structural importance of the different elements of the bridge components considered.