Asad Esmaeily

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.

BEHAVIOR OF REINFORCED CONCRETE COLUMNS UNDER VARIABLE AXIAL LOADS

Six large-scale reinforced concrete circular columns were tested to study effects of variable axial load on the seismic behavior of bridge piers. The primary experimental parameters were axial load levels, lateral as well as axial loading patterns. The axial loading patterns included constant and variable loading, either proportional or nonproportional to the lateral forces. Experimental evidence revealed the significant effects of the magnitude and loading pattern of axial force on seismic behavior of columns. Main effects of the variable axial load are reflected in the distinct physical failure patterns, hysteresis loops, and load-carrying capacities, compared with the case of constant axial load. Test results also provide experimental data useful for calibrating and evaluating analytical models. It is suggested that analytical tools, like the plastic hinge model, should be modified to account for the effects of variable axial load.

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...

A new eccentricity-based simulation to generate ultimate confined interaction diagrams for circular concrete columns

Abstract The analysis of circular concrete columns using unconfined concrete models is a well established practice. However, there is a necessity to develop realistic analysis and design tools that predict the extreme ultimate capacity of such columns since modern codes and standards like AASHTO LRFD are introducing extreme load events. The increase in strength and ductility due to full axial confinement is not applicable to pure bending and bending plus axial load simply because the area of effective confined concrete is reduced. The higher the eccentricity the smaller the compressed portion of the confined core. Accordingly, the ultimate confined strength is gradually reduced from the fully confined value fcc′ (at zero eccentricity) to the unconfined value fc′ (at infinite eccentricity) as a function of eccentricity to diameter ratio. A numerical analysis algorithm is developed using the finite layer procedure and the secant stiffness approach within a framework of incremental-iterative moment of area computations. The resulting nonlinear section analysis requires radial loading in which the eccentricity is kept constant or the axial load is proportional to the applied moment. The results are compared with existing experimental data and the widely used Mander model to benchmark the present predictions.

An Overview of Signal-Based Damage Detection Methods

Deterioration of structures due to aging, cumulative crack growth or excessive response significantly affects the performance and safety of structures during their service life. Recently, signal-based methods have received many attentions for structural health monitoring and damage detection. These methods examine changes in the features derived directly from the measured time histories or their corresponding spectra through proper signal processing methods and algorithms to detect damage. Based on different signal processing techniques for feature extraction, these methods are classified into time-domain methods, frequency-domain methods, and time-frequency (or time-scale)-domain methods. As an enhancement for feature extraction, selection and classification, pattern recognition techniques are deeply integrated into signal-based damage detection. This paper provided an overview of these methods based on two aspects: (1) feature extraction and selection, and (2) pattern recognition. Signal-based methods are particularly more effective for structures with complicated nonlinear behavior and the incomplete, incoherent, and noise-contaminated measurements of structural response.

Analytical Performance of Reinforced Concrete Columns using Various Confinement Models

Accuracy of various stress-strain relationship models for concrete confined by lateral steel reinforcement in prediction of the moment-curvature response of a section under various loading patterns was investigated. Fiber model was implemented in a computer program developed for flexural analysis of reinforced concrete columns. Both monotonic and hysteretic analysis were performed. Each confined concrete model was used in the analysis for several loading cases on a circular, and a loading case on a rectangular section, keeping all other parameters fixed. Results were compared to each other and also validated against experimental data from six large-scale reinforced concrete circular columns and a rectangular section tested under the analyzed loading cases. In general, analysis underestimated the moment and overestimated the curvature capacities under a high level of axial load regardless of the model used, and there was a better agreement between analysis and test for low level or no axial load. Results from various models were close to each other, though different from test results, for cases with a constant or proportionally variable axial load. For a monotonic curvature with non-proportionally variable axial load, predictions by some recent models had a better agreement with experimental data. Evidently the level of axial load, and in turn the depth of compression zone, is related to the degree of confinement-utilization, and affects the confined concrete behavior. This is rarely addressed by the models.

A Realistic Theory of Soils Consolidation

The consolidation behavior of soils is usually predicted by making use of the convectional theory of consolidation proposed by Terzaghi.Laboratory observations of the consolidation behavior exhibit discrepancies between the theory and the results. These discrepancies are usually attributed to the secondary effects that occur during primary consolidation. On the other hand, Terzaghi’s theory presupposes the constancy of permeability and compressibility of the soil. In this study, the effect of variable permeability and compressibility on the consolidation behavior is investigated. For this objective, mathematical treatment of the behavior is presented. Subsequently, laboratory consolidation tests with mid-plane pore pressure measurements are conducted on soft, remolded, pre-consolidated and undisturbed samples of clay. The test results, when compared with the theoretical findings, indicate that most of the inherent discrepancies may be explained via the use of the theory developed in this study.

Parametric Study of Posttensioned Inverted-T Bridge System for Improved Durability and Increased Span-to-Depth Ratio

Rehabilitation of the existing bridges is one of the most pressing needs in maintenance of the transportation infrastructure. As an example, more than 2,000 bridges in Kansas alone need to be replaced during the next decade. The majority of these bridges have spans of 30 m (100 ft) or less, and shallow profiles. The inverted-T (IT) bridge system has gained increasing popularity in recent years due to its lower weight and relatively larger span-to-depth ratio compared to the prestressed I-girder bridges. However, there are some limitations in replacing the existing cast in place (CIP) bridges with IT system. Implementation of posttensioning, which is the focus of this paper, is a promising solution for these limitations. This leads to a higher span-to-depth ratio and reduces potential transverse cracks in the CIP deck which is a major concern for corrosion of the reinforcement. An analytical research was conducted to identify the major parameters influencing the performance of a posttensioned IT bridge system. This was followed by a parametric study to explore the scope of these parameters and specify the design limits in terms of posttensioning stages, timing scenarios, and posttensioning forces. Concrete strength and different methods for estimating time-dependent restraining moments were addressed in this parametric study.

Evaluation of shear design provisions for shear-critical concrete beams

Shear provisions of ACI 318-11, general procedure and simplified procedure for prestressed and non-prestressed concrete beams using AASHTO LRFD (2008. Bridge design specification and commentary. Interim 2008. Washington, DC: AASHTO LRFD, 5.59–5.84) are comparatively studied. Experimental results from 34 simply supported and continuous non-prestressed shear-critical beams were selected to assess the accuracy of Response-2000 as an analytical tool implementing the Modified Compression Field Theory. On average, the shear capacity of simply supported beams was slightly underestimated while that of continuous beams was quantified accurately. Shear provisions of all of the three aforesaid procedures were examined using a variety of reinforced and prestressed concrete beams. These beams included six simply supported prestressed double-T with harped strands, continuous prestressed bulb-T having both straight and harped strands, simply supported and continuous reinforced deep rectangular beams with or without longitudinal crack control reinforcement. Results of this comparative study considering critical parameters, such as minimum transverse reinforcement, design spacing of the transverse steel and longitudinal crack control reinforcement are detailed in the conclusions followed by some recommendations.

Behaviour of RC beams under combined shear and torsion according to AASHTO LRFD and ACI equations

In this study, the AASHTO LRFD provisions for combined shear and torsion have been investigated and their accuracy has been validated against experimental data. AASHTO LRFD (2008) provisions on combined shear and torsion have also been compared to the pertinent ACI code requirements for the behaviour of reinforced concrete beams subjected to combined shear and torsion. In this comprehensive comparison, different sections with high strength and normal strength concrete as well as over-reinforced, moderately-reinforced and, under-reinforced solid and hollow sections were analysed. This study resulted in findings on the applicability of both code procedures to different sectional material and geometry values under these load combinations.