Abdullah Zawawi Awang

Slenderness effect and upper-bound slenderness limit of SSTT-confined HSC column

In designing the HSC columns confined with steel-straps tensioning technique (SSTT), safe and economic are two important aspects. The designed member should not be too expensive but guarantee minimum safety. Generally, the effectiveness of confinement became less pronounced as the slenderness of column increased. This is mainly due to the flexure-dominated behaviour of slender column and the non-contribution of the confinement to the flexural stiffness of the concrete. In this paper, a numerical analysis was conducted in the view to establish the upper-bound slenderness limit of SSTT-confined HSC columns. The utilisation of SSTT beyond this limit is not recommended. The slender SSTT-confined HSC column is considered to reach its upper-bound slenderness limit when the ductility enhancement is less than 5%.

Elastic Design of Slender High-Strength RC Circular Columns Confined with External Tensioned Steel Straps

This article proposes a design approach to calculate the capacity of slender high-strength concrete (HSC) columns confined with a cost-effective Steel Strapping Tensioning Technique (SSTT). The approach is based on results from segmental analyses of slender SSTT-confined circular columns subjected to eccentric loads. A capacity reduction factor analogue to that proposed by Kwak and Kim (2004) accounts for the effect of slenderness in design. P-M interaction diagrams computed using rigorous nonlinear P-Δ analyses are compared to those calculated by the proposed approach to assess its accuracy. The results indicate that the proposed approach predicts conservatively the ultimate capacity of slender HSC circular columns confined using the SSTT, and therefore it can be used in the design of modern reinforced concrete (RC) structures.

A Review on Repair of Damaged Concrete Column Under Cyclic Loading by Using Confinement

The earthquake stroke Sabah in 2015 have given an alarm to structural engineers on the importance of ensure concrete structures to resist seismic load. The damaged column due to the seismic load needed to be repaired. Research and development of rapid repair techniques have emerged as one of the most critical researches globally as the money spent on repairing damaged structures are more than the cost of building new structures. Confinement is one of the popular and effective rapid repairing of damaged concrete under cyclic loading. This paper reviewed the uses of confinement as a repairing technique to facilitate the research development in this field. The findings have proven that confinement repair techniques are effective and can restore the original capacities of damaged concrete members.

Modeling of high-strength concrete-filled FRP tube columns under cyclic load

The behavior of high-strength concrete (HSC) - filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs) column subjected to cyclic lateral loading is presented in this paper. As the experimental study is costly and time consuming, a finite element analysis (FEA) is chosen for the study. Most of the previous studies have focused on examining the axial load behavior of HSCFFT column instead of seismic behavior. The seismic behavior of HSCFFT columns has been the main interest in the industry. The key objective of this research is to develop a reliable numerical non-linear FEA model to represent the seismic behavior of such column. A FEA model was developed using the Concrete Damaged Plasticity Model (CDPM) available in the finite element software package (ABAQUS). Comparisons between experimental results from previous research and the predicted results were made based on load versus displacement relationships and ultimate strength of the column. The results showed that the column increased in ductility and able to deform to a greater extent with the increase of the FRP confinement ratio. With the increase of confinement ratio, HSCFFT column achieved a higher moment resistance, thus indicated a higher failure strength in the column under cyclic lateral load. It was found that the proposed FEA model can regenerate the experimental results with adequate accuracy.The behavior of high-strength concrete (HSC) - filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs) column subjected to cyclic lateral loading is presented in this paper. As the experimental study is costly and time consuming, a finite element analysis (FEA) is chosen for the study. Most of the previous studies have focused on examining the axial load behavior of HSCFFT column instead of seismic behavior. The seismic behavior of HSCFFT columns has been the main interest in the industry. The key objective of this research is to develop a reliable numerical non-linear FEA model to represent the seismic behavior of such column. A FEA model was developed using the Concrete Damaged Plasticity Model (CDPM) available in the finite element software package (ABAQUS). Comparisons between experimental results from previous research and the predicted results were made based on load versus displacement relationships and ultimate strength of the column. The results showed that the column increased in ductility and abl...

The Effect of Pre-Damaged Level on Repair Damaged Columns by Using Steel Straps Tensioning Technique

To date, repair of damaged columns has become increasingly more significant. The failure of columns structure contributes to the serious consequences in structural stability. Most of the existing repairing techniques are based on lateral passive confining pressu re. However, this passive-type of confinement is ineffective in restoring the performance of damaged concrete columns. In this regards, active confinement was selected in this study to repair damaged concrete columns which can actively confine concrete in this study. Ste el strapping tensioning technique (SSTT) allows pre-tensioning low-cost recycled steel straps around the damaged column was chosen herein to represent active confinement. A total of 12 columns were prepared and loaded axially to certain degree of their respective ultim ate strength. Hence, a pre-damage level of the columns was developed. Then, the damaged columns repaired by using mortar and confined with SSTT. Finally, the repaired columns were then tested under monotonic uniaxial load. The structural performances of the confined repaired columns were compared with those of the repaired columns without confinement. It is expected that as the concrete compressive strength increases, the effectiveness in restoring the load carrying capacity of the damaged column becomes more significant.

Design of steel-strapped, high-strength concrete columns subject to unequal end moments

A new equation is proposed for practical flexural design of high-strength concrete columns confined externally with tensioned steel straps. The proposed equation is based on the simplified approach of the equivalent moment factor adopted by existing design codes. It also accounts for non-linear behaviour of the materials, which is usually neglected in the codes. The equation was derived using results from rigorous theoretical analyses of 120 simulated strap-confined columns subjected to short-term ultimate loads and unequal flexural moments at the column ends. The theoretical simulations accounted for parameters shown to influence the design of strap-confined columns, such as load eccentricity, longitudinal reinforcement ratio, free concrete cover and volumetric confinement ratio. The proposed equation was found to predict the strength of strap-confined columns with sufficient accuracy, making it suitable for practical design and rapid assessment of such structures.

Compressive strength models of repaired concrete structures

Application of confinement as repairing technique can improve the strength and ductility of concrete significantly. This paper compares the existing models of repaired concrete, and describes the differences between these models. Over recent years, a great number of studies have been done to develop the models to define the stress-strain behaviour of repaired structures. The considered variables are the cross-sectional area, types of confinement, types of materials used and type of the strength models. Subsequently, the limitations were discussed and significant conclusions on the strength and weakness of each existing models were highlighted. This paper presented the state of the art design strength models available for repaired concrete structures and indicated a direction for future development.

Artificial neural network models for FRP-repaired concrete subjected to pre-damaged effects

Confining damaged concrete columns using fibre-reinforced concrete (FRP) has proven to be effective in restoring strength and ductility. However, extensive experimental tests are generally required to fully understand the behaviour of such columns. This paper proposes the artificial neural networks (ANNs) models to simulate the FRP-repaired concrete subjected to pre-damaged loading. The models were developed based on two databases which contained the experimental results of 102 and 68 specimens for restored strength and strain, respectively. The proposed models agreed well with testing data with a general correlation factor of more than 97%. Subsequently, simplified equations in designing the restored strength and strain of FRP-repaired columns were proposed based on the trained ANN models. The proposed equations are simple but reasonably accurate and could be used directly in the design of such columns. The accuracy of the proposed equations is due to the incorporation of most affecting factors such as pre-damaged level, concrete compressive strength, confining pressure and ultimate confined concrete strength.