γ-ray assisted synthesis of silver nanoparticles in chitosan solution and the antibacterial properties

In the present study, chitosan had been utilized as a “green” stabilizing agent for the synthesis of spherical silver nanoparticles in the range of 5–30 nm depending on the percentage of chitosan used (0.1, 0.5, 1.0 and 2.0 wt%) under γ-irradiation. X-ray diffractometer identified the nanoparticles as pure silver having face-centered cubic phase. Ultraviolet–visible spectra exhibited the influence of γ-irradiation total absorbed dose and chitosan concentration on the yield of silver nanoparticles. The antibacterial properties of the silver nanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (gram-positive) and Aeromonas hydrophila (gram-negative) bacteria. This work provides a simple and “green” method for the synthesis of highly stable silver nanoparticles in aqueous solution with good antibacterial property

Nonlinear finite element analysis of reinforced concrete tube in tube of tall buildings

The non-linear finite The non-linear finite element analysis (NLFEA) has potential as a readily usable and reliable means for analyzing of civil structures with the availability of computer technology. The structural behaviors and mode of failure of reinforced concrete tube in tube tall building via application of computer program namely COSMOS/M are presented. Three dimensional quarter model was carried out and the method used for this study is based on non-linearity of material. A substantial improvement in accuracy is achieved by modifying a quarter model leading deformed shape of overall tube in tube tall building to double curvature. The ultimate structural behaviors of reinforced concrete tube in tube tall building were achieved by concrete failed in cracking and crushing. The model presented in this paper put an additional recommendation to practicing engineers in conducting NLFEA quarter model of tube in tube type of tall building structures.element analysis (nlfea) has potential as a readily usable and reliable means for analyzing of civil structures with the availability of computer technology. The structural behaviors and mode of failure of reinforced concrete tube in tube tall building via application of computer program namely cosmos/m are presented. Three dimensional quarter model was carried out and the method used for this study is based on non-linearity of material. A substantial improvement in accuracy is achieved by modifying a quarter model leading deformed shape of overall tube in tube tall building to double curvature. The ultimate structural behaviors of reinforced concrete tube in tube tall building were achieved by concrete failed in cracking and crushing. The model presented in this paper put an additional recommendation to practicing engineers in conducting nlfea quarter model of tube in tube type of tall building structures

Seismic behaviour of engineered cementitious composites beam-column joints

Reinforced concrete (RC) beam-column joints are one of the most important components that may lead to collapse or major damage of an RC frame structure when subject to earthquake loading. Structural engineers tend to pay attention to the detailing of the joints, which may lead to reinforcement congestion and thus making it difficult to be constructed. The emergence of engineered cementitious composites (ECC), which features ultra-ductility and damage-tolerance, offers a potential solution to the abovementioned problem. Therefore this study evaluates the feasibility of using ECC in the joint cores as a means to enhance the seismic behaviour of the RC beam-column sub-assemblages. Two series of experimental tests were conducted on interior and exterior RC beam-column sub-assemblages under lateral cyclic loading. In the first series, two RC interior beam-column sub-assemblages were detailed to seismic design while another two were detailed to non-seismic design. The control specimens had normal concrete in the joint core while ECC was incorporated into the joint core of the seismic and non-seismic designed sub-assemblages. Joint stirrups were totally eliminated from the joint core when ECC was used in the beam-column sub-assemblages, to study the performance of ECC joints without joint stirrups. On the other hand, four exterior beam-column sub-assemblages were adequately designed to seismic in the second series of test. The effects of joint stirrups and column axial load on the seismic behaviour of the exterior beam-column sub-assemblages were investigated. Comparisons on the hysteretic response, failure mode, analysis of inter-story drift contribution, distribution of beam and column longitudinal bars strain, joint shear stress and energy dissipation were made between sub-assemblages with joint cores either made of ECC or RC materials. In order to study the bond-slip behaviour of steel reinforcement embedded in ECC, a series of pull-out tests was conducted on short and long reinforcement. Thereafter an analytical model for bond-slip was proposed based on experimental results to predict the force-slip relationship of long reinforcement either anchored in concrete or in ECC. Moreover, a series of parametric study was conducted to estimate required embedment length of reinforcement in concrete and ECC according to four types of failures. Finally, a beam-column joint model available in OpenSees was employed in simulating seismic response of the beam-column sub-assemblages. Bond strength of steel reinforcement embedded in ECC obtained from pull-out test was incorporated in the bar-slip component for ECC joints. Results of simulation were discussed.Doctor of Philosophy (CEE

Sufficiency of the Central Provident Fund in meeting healthcare and retirement needs : a comparison with selected countries.

This paper aims to ascertain the adequacy of Singapore’s Central Provident Fund in providing for the healthcare and retirement needs of Singaporeans by comparing it with schemes in other countries. Through this, we hope to get a better picture of the robustness of the current CPF system, and generate practical recommendations to improve it

Seismic behaviour of interior reinforced-concrete beam–column sub-assemblages with engineered cementitious composites

The feasibility of using engineered cementitious composites (ECC) in joint cores of reinforced-concrete (RC) beam–column sub-assemblages as a means to enhance seismic behaviour is evaluated. Four RC beam–column sub-assemblages are constructed and tested under lateral cyclic loading. One RC beam–column sub-assemblage with normal concrete in the joint and one RC sub-assemblage with ECC in the joint are designed to gravity loads; neither type has transverse reinforcement in the joint core. Similarly, one RC sub-assemblage with normal concrete in the joint and one with ECC in the joint are designed for seismic provisions, but the latter has no transverse reinforcement in the joint. The test programme thereby allows direct comparison of the structural performance of ECC joints with concrete joints for beam–column sub-assemblages for both gravity and seismic design situations. Results show that the use of ECC joints significantly changes the behaviour of the joint from brittle to ductile. Both ECC specimens exhibit superior damage tolerance, with limited shear distortion and multiple fine cracks in the joints, even though no transverse reinforcement is provided in the joint. Moreover, specimens with ECC joints demonstrate improved bond behaviour in early loading cycles.Published versio

Singapore ornamental fish trade : a new concept

For five decades, the ornamental fish industry has been shunning the lime light despite its illustrious performance. Due to the close guarded nature of ancestral family business, much of the art of this trade has been under wraps. This has resulted in a handful of veterans of the trade, dominating the industry. They have received more than adequate assistance from the government but have failed to fully exploit the potential of this highly lucrative business.ACCOUNTANC

Mechanical properties of engineered cementitious composites using local ingredients / Lee Siong Wee...[et al.]

This research focuses on the mechanical properties of Engineered Cementitious Composites (ECC). Few ECC mixtures were designed and tested under direct tensile test and compression test. The novelty of this research is the utilization of available local materials in Malaysia, which is significantly different from the ingredients employed by previous researchers in the US, Japan and other countries. The ingredients used for ECC mixtures in this research were Ordinary Portland Cement (OPC), ground granulated blast-furnace slag (GGBS), sand, water, superplasticizer (SP) and polypropylene (PP) fibers. Local ingredients such as river sand and GGBS were used to replace micro silica sand and fly ash in the standard mix of ECC. Test results demonstrated that tensile ductility and compressive strength in ECC improved as compared to normal concrete. The effect of cement replacement ratio and fibres content are discussed based on the performance in both tensile and compressive properties. Comparison with previous studies was carried out to identify the weaknesses of the current ECC mixture, so that improvement can be done in future studies. The best ECC mixture is proposed according to the performance in mechanical properties