H. Abdul Razak

The effect of corrosion on the natural frequency and modal damping of reinforced concrete beams

An experimental investigation to study the effect of general corrosion on the modal parameters of reinforced concrete beams was conducted. The full scale beams were subjected to reinforcement corrosion until an appreciable amount of steel corrosion damage was introduced. The states of damage in the test beams were assessed through measurement of crack width and spalling. Modal tests were performed on the test beams after corrosion damage and the modal parameters extracted were compared against that from a control beam. The results obtained showed changes in the modal parameters especially natural frequencies and damping ratio. The trend in the measured natural frequencies was sensitive to the deterioration state of the beams. Changes in modal damping ratio for the transfer function method and the normal mode method were also observed. However, the changes were inconsistent with the changes in natural frequencies, as concluded by previous researchers, but a trend was observed which was rather mode dependent. Furthermore, the load carrying capacity of the beams was determined through static load test and the results were correlated with the state of corrosion damage and changes in the modal parameters. This investigation provides further insight on the use of modal parameters to detect damage in structural concrete elements which can be useful for structural appraisal and assessment purposes when applied to full scale structures.

Experimental investigation and finite element modelling of the effects of flow velocities on a skewed integral bridge

This paper presents finite element modelling of the effects of different flow velocities on the structural behaviour of a skewed integral bridge. Flow velocities affect the scour depths at the piles of a bridge and thus affect its structural behaviour. Laboratory tests on a scaled-down hydraulic model along with numerical modelling were performed to simulate the structural behaviour of the scoured integral bridge. A finite element package was used for the numerical modelling work, and the displacements and strains corresponding to the measured locations on the physical model were extracted. The experimental and numerical results for the case of maximum scour depths were compared.

Toughness Characteristics of Arenga pinnata Fibre Concrete

Abstract This paper reports the results of an investigation on the toughness characteristics of concrete containing Arenga pinnata fibre. Three fibre lengths of 15 mm, 25 mm, and 35 mm were used in two volume fractions, i.e., 0.6% and 0.8%. The values of toughness, first crack deflection, first crack toughness, toughness indices, and residual strength factors are presented for ages up to 180 days. It was observed that the addition of Arenga pinnata fibre increased the toughness characteristic of concrete. However, it was observed that the positive effects of the fibre become less significant after 28 days, but still sufficient to give the concrete better toughness properties compared to the plain concrete.This is due to reaction of the fibres with the alkaline pore water in the cement matrix.

A wavelet-based approach for vibration analysis of framed structures

In this paper, an explicit time integration scheme is proposed for structural vibration analysis by using wavelet functions. Initially, the differential equation of vibration governing SDOF (single-degree of freedom) systems has been solved by wavelet operators, and later the proposed approach has been generalized for MDOF (multi-degrees of freedom) systems. For this purpose, two different types of wavelet functions have been exemplified including, complex Chebyshev wavelet functions and simple Haar wavelet functions. In the proposed approach, a straightforward formulation has been derived from the numerical approximation of response through the wavelet definition. Emphasizing on frequency-domain approximation, a simple step-by-step algorithm has been implemented and improved to calculate the response of MDOF systems. Moreover, stability and accuracy of results have been evaluated. The effectiveness of the proposed approach is demonstrated using three examples compared with some of the existing numerical integration schemes such as family of Newmark-@b, Wilson-@q and central difference method. In all the procedures, computation time involved has also been considered. Finally, it is concluded that the vibration analysis of structures is improved by lesser computation time and high accuracy of proposed approach, particularly, in large-scaled systems.

Weatherability of coated fabrics as roofing material in tropical environment

The weatherability of PTFE- and PVC-coated fabrics under tropical climate was evaluated based on outdoor exposure test for a period of 2 years. This study is confined to the examination of the surface characteristics of 10 different types of fabric which include dirt repellency, discolouration and coating condition. The results indicate that the dirt repellency of PTFE-coated fabrics is generally more superior. However, the surface treatment for some of the PVC-coated fabrics, do provide excellent dirt repellency as well. Morphological examinations using the scanning electron microscope revealed that cracking and peeling of the coating were more evident on the PVC-coated as compared to the PTFE-coated fabrics. The hot and humid conditions prevalent in a tropical environment were very conducive for the growth of fungi, which adhered on the surface of some of the PVC-coated fabrics. Generally the degree of surface degradation on all the fabrics was more severe due to the much harsher tropical climate in comparison with other exposure tests conducted in the past.

ANALYTICAL AND EXPERIMENTAL STUDY ON REPAIR EFFECTIVENESS OF CFRP SHEETS FOR RC BEAMS

AbstractThis paper presents the results of both analytical and experimental study on the repair effectiveness of Carbon Fibre Reinforced Polymer (CFRP) sheets for RC beams with different levels of pre-repair damage severity. It highlights the effect of fixing CFRP sheets to damaged beams on the load capacity, mid-span deflection, the steel strain and the CFRP strain and failure modes. The analytical study was based on a Finite Element (FE) model of the beam using brick and embedded bar elements for the concrete and steel reinforcement, respectively. The CFRP sheets and adhesive interface were modelled using shell elements with orthotropic material properties and incorporating the ultimate adhesive strain obtained experimentally to define the limit for debonding. In order to validate the analytical model, the FE results were compared with the results obtained from laboratory tests conducted on a control beam and three other beams subjected to different damage loads prior to repair with CFRP sheets. The res...

Damage Detection Based on Wavelet Packet Transform and Information Entropy

In this study, a new approach for damage detection in beam-like structures is presented. Damage feature such as relative wavelet packet entropy (RWPE) based on the decomposed component is used to identify the damage location and evaluate the damage severity. RWPE describes present information of relative wavelet energies correlated with different frequency ranges. It is should be noted that the acceleration measured in the all three directions should be used in computation of RWPE. Numerical and experimental results are used to verify the practicality of this method. Results show that the damage index technique has great potential in detection of location and depth of cut in a steel beam. The procedure can be applied for health monitoring of other complex structures.

Mechanical properties of black sugar palm fiber-reinforced concrete

This article reports the results of an investigation on the engineering properties of concrete containing black sugar palm fiber. Three fiber lengths of 15, 25, and 35 mm in four volume fractions, namely 0.2%, 0.4%, 0.6%, and 0.8%, were utilized in this investigation. The values of compressive, flexural, toughness, first crack deflection, first crack toughness, and toughness indices are reported for ages up to 90 days. It was observed that the addition of palm fibers slightly increased the flexural strength of concrete. The incorporation of the fibers had no significant effect on the compressive strength. The mix with 0.8% volume fraction and 35 mm length fiber gave higher toughness and ductility compared to other mixes.

Application of artificial neural network on vibration test data for damage identification in bridge girder

Structures are exposed to damage during their service life which can severely affect their safety and functionality. Thus, it is important to monitor structures for the occurrence, location and extent of damage. Artificial neural networks (ANNs) as a numerical technique have been applied increasingly for damage identification with varied success. ANNs are inspired by human biological neurons and have been used to model some specific problems in many areas of engineering and science to achieve reasonable results. ANNs have the ability to learn from examples and then adapt to changing situations when sufficient input-output data are available. This paper presents the application of ANNs for detection of damage in a steel girder bridge using natural frequencies as dynamic parameters. Dynamic parameters are easy to implement for damage assessment and can be directly linked to the topology of structure. In this study, the required data for the ANNs in the form of natural frequencies will be obtained from experimental modal analysis. This paper also highlights the concept of ANNs followed by the detail presentation of the experimental modal analysis for natural frequencies extraction. ©2011 Academic Journals.

Damage Detection Optimization Using Wavelet Multiresolution Analysis and Genetic Algorithm

In this study, an optimized damage detection using genetic algorithm (GA) in beam-like structures without using baseline data. For this purpose, a vibration-based damage detection algorithm using a damage indicator called ‘Relative Wavelet Packet Entropy’ (RWPE) was applied to determine the location and severity of damage. To improve the algorithm, GA was utilized to optimize the algorithm so as to identify the best choice of wavelet parameters. To examine the robustness and accuracy of the proposed method, numerical examples and experimental cases with different damage depths were considered and conducted.