Chau Khun Ma

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%.

Evaluation of new spiral shear reinforcement pattern for reinforced concrete joints subjected to cyclic loading

Using continuous spiral reinforcements can greatly improve the seismic performance of reinforced concrete columns, in terms of ductility and energy dissipation capacity. The simultaneous incorporation of this method in beams and columns might influence the behaviour of beam–column connections as wide spectrums of brittle failure were observed in this region. A new proposed beam–column connection introduced as ‘twisted opposing rectangular spiral’ was investigated in this research in both experimental and numerical manners along with comparing its seismic performance with both normal rectangular spiral and conventional shear reinforcement systems. The design of three full-scale beam–column connections was performed according to Eurocode (EC8-04) for high ductility classes, and the quasi-static cyclic loading recommended by American Concrete Institute Building Code (ACI 318-08) was hired to conduct the seismic tests. Finally, the experimental results were validated by numerical results obtained from the finite element analysis of the three specimens. The results revealed improved ultimate lateral resistant, energy dissipation capacity and ductility for the new proposed connection.

An excavatability classification system for surface excavation in sedimentary rocks

This paper describes the development of an excavatability classification system for surface excavation of weathered sedimentary rock based on practical excavations and statistical analysis. Extensive field and laboratory studies were undertaken on three sedimentary rock sites with a range of weathering and strength conditions in the Iskandar region, South Johore, Malaysia. Rock mass descriptions were made in the field and rock material tests were carried out in the laboratory. Statistical analysis was used to study the correlation between the rock parameters and the productivity of excavation. A classification rating system based on the analysis results is proposed. The proposed classification system incorporates rock parameters such as point load strength (Is50), Schmidt Rebound hammer value (R), uniaxial compressive strength (UCS), density of rock (γ), indirect tensile strength (ITS), second-cycle of slake durability index (Id2), joint number (Jn), joint spacing (Js), joint length (JL), joint direction (Jd), existence of iron pan (IP), moisture content (Mc) and existence of bedding. The proposed model was then verified against further excavations on another sedimentary rock site. It was found that the productivities recorded correlated well with the proposed system when tested on a fourth site.

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.

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.