Structural Behaviour of Precast Concrete Sandwich Panels with Openings Under Axial Load

This research was conducted to study the structural behaviour of precast concrete sandwich panels with opening. Four types of sandwich panels involving panels without opening, panels with door opening, panels with window opening and panels with both door and window opening were studied. The size of the panels was 900mm x l000mm x 120mm thick. The 120mm thickness consists of two concrete layers with a sandwich insulation layer 40mm thick. The panels were tested under axial load until failure. During the experiment, the development of cracks was observed and the strain and dial gauges reading recorded. The values of experimental ultimate load for the panel without opening were compared to the theoretical ultimate load by a few researchers. For panels with opening, the experimental ultimate loads were compared to the theoretical equation for panels with opening by Saheb and Desayi. The theoretical equation used was actually meant to estimate the ultimate load of ordinary reinforced concrete walls with opening. It was used in sandwich panels with the assumption that the total thickness of the panels was equal to the thickness of the concrete layers only. From the calculations it was found that the theoretical equation by Saheb and Oesayi for the ultimate load of ordinary reinforced concrete walls with opening gave very close values to the experimental results for panels with opening. This showed that the ultimate load equation for ordinary reinforced concrete wall with opening by Saheb and Desayi could be used to estimate the ultimate load of sandwich panels with opening. Beside the ultimate load, the lateral deflection and the strain distribution in the reinforcement and concrete surface were also observed and recorded

Existence of fractal behaviour in ozone time series

Fractal has received a wide attention and has been used in many areas such as meteorology, stock market and also in medical field. It can be viewed as an object which has similar appearance when viewed at different scales which are known as self-similar. Thus, the scale invariance and scaling properties of the time series may be explored using fractal techniques. The aim of this study is to investigate the presence of fractal behaviour in the ozone time series. The presence of fractal behaviour can lead to the possibility of implementing the fractal approach in order to examine the properties of a time series. In this study, the daily average of ozone concentration from six selected air monitoring stations with different types of backgrounds in Peninsular Malaysia are used. From the autocorrelation function (ACF) plot obtained for the six stations, the slow decay in ACF values indicates that self-similarity are present where it shows that the series is having the property of fractal behaviour. In this paper, the existence of fractal behaviour is investigated by using the power spectrum method and the empirical probability distribution function. The result shows that the daily average of ozone concentration exhibits fractal behaviour for all the six monitoring stations considered

Faktor penulisan ilmu dakwah dalam Islam

Penulisan ini bertujuan untuk mengenalpasti faktor penulisan ilmu dakwah dalam kalangan para ulama. Perbincangan ini memfokuskan mengenai penulisan ilmu dalam pelbagai kecenderungan terutamanya penyebaran dan pembentukan pelaksanaan dakwah secara menyeluruh. Faktor mengenai penulisan ilmu dakwah dalam Islam ini boleh diaplikasikan dalam penerapan ilmu dakwah kepada masyarakat majmuk di Malaysia

Development of a new connection for precast concrete walls subjected to cyclic loading

The Industrialized Building System (IBS) was recently introduced to minimize the time and cost of project construction. Accordingly, ensuring the integration of the connection of precast components in IBS structures is an important factor that ensures stability of buildings subjected to dynamic loads from earthquakes, vehicles, and machineries. However, structural engineers still lack knowledge on the proper connection and detailed joints of IBS structure construction. Therefore, this study proposes a special precast concrete wall-to-wall connection system for dynamic loads that resists multidirectional imposed loads and reduces vibration effects (PI2014701723). This system is designed to connect two adjacent precast wall panels by using two steel U-shaped channels (i.e., male and female joints). During casting, each joint is adapted for incorporation into a respective wall panel after considering the following conditions: one side of the steel channel opens into the thickness face of the panel; a U-shaped rubber is implemented between the two channels to dissipate the vibration effect; and bolts and nuts are used to create an extension between the two U-shaped male and female steel channels. The developed finite element model of the precast wall is subjected to cyclic loads to evaluate the performance of the proposed connection during an imposed dynamic load. Connection performance is then compared with conventional connections based on the energy dissipation, stress, deformation, and concrete damage in the plastic range. The proposed precast connection is capable of exceeding the energy absorption of precast walls subjected to dynamic load, thereby improving its resistance behavior in all principal directions

Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete

In the current study, the size effects of SiO2 nano-particles on compressive, flexural and tensile strength of binary blended concrete were investigated. SiO2 nano-particles with two different sizes of 15 and 80 nm have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.%. It was concluded that concrete specimens containing SiO2 particles with average diameter of 15 nm were harder than those containing 80 nm of SiO2 particles at the initial days of curing. But this condition was altered at 90 days of curing. Also from the viewpoint of free energy, it can be concluded that the C–S–H gel formation around the particles with average diameter of 15 nm was more at the primary days of curing. This can be as a result of more nucleation sites that causes acceleration in early age strength. On the other hand, the growth probability of C–S–H gel around the 80 nm particles was more at 90 days of moist curing. This is due to the fact that the nucleus of strengthening gel could simply reach to the critical volume of nucleation that causes increase in the strength

Stabilization of Tropical Peat by Chemical Grout.

Peats have low shear strength and high deformation characteristics. Cement, sometimes with other industrial binders, is widely used for the stabilization of peats by deep mixing. However, peats lack a favorable structure for the chemical reactions, coupled with high moisture content that is acidic in nature. So, the efficiency of the binders is low making it an expensive option. This paper presents the effectiveness of using calcium chloride and kaolinite in cement-sodium silicate grout for improving the strength of tropical peat. The change in shear strength of the treated samples was evaluated by the vane shear test and moisture content test. The microstructural changes were evaluated by scanning electron microscopy and energy dispersive x-ray spectrometer analysis. Calcium chloride seemed to have different effects on the shear strength of peat and was observed to play an important role in the effectiveness of the chemical stabilizers. Experimental results showed that kaolinite (more than 10%) has a crucial rule in increasing the shear strength of peat. It was observed that sodium silicate within 3% and cement has favorable effect on the shear strength of peat and induce a decrease in the moisture content of mixtures consisting of peat and themselves and also lead to some favorable changes in the microstructure

Contribution of rice husk ash to the properties of mortar and concrete: a review

In the last decade, the use of supplementary cementing materials has become an integral part of high strength and high performance concrete mix design. These can be natural materials, by-products or industrial wastes, or the ones requiring less energy and time to produce. Some of the commonly used supplementary cementing materials are fly ash, Silica Fume (SF), Ground Granulated Blast Furnace Slag (GGBFS) and Rice Husk Ash (RHA) etc. RHA is a by-product material obtained from the combustion of rice husk which consists of non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. It is used as pozzolanic material in mortar and concrete, and has demonstrated significant influence in improving the mechanical and durability properties of mortar and concrete. This paper presents an overview of the work carried out on the use of RHA as partial replacement of cement in mortar and concrete. Reported properties in this study are the mechanical, durability and fresh properties of mortar/concrete

Particle size effect on the permeability properties of nano-SiO2 blended Portland cement concrete.

In this study, nano-SiO2 has been used as a high reactive pozzolan to develop the microstructure of the interfacial transition zone between the cement paste and the aggregate. Mechanical tests of blended cement-based concretes exposed that in addition of the pozzolanic reactivity of nano-SiO2 (chemical aspect), its particle grading (physical aspect) also revealed considerable influences on the blending effectiveness. It was concluded that the relative permeability reduction (relative to the control concrete made with plain cement) is higher for coarser nano-SiO2 after 90 days of moisture curing. However, finer nano-SiO2 particles showed better effects in early ages. These phenomena can be due to the free spacing between mixture particles that was associated with the global permeability of the blended cement-based concretes. This article presents the results of the effects of particle size ranges involved in nano-SiO2 blended Portland cement on the water permeability of concrete. It is revealed that the favorable results for coarser nano-SiO2 reflect enhanced particle packing formation accompanied by a reduction in porosity and particularly in particle spacing after 90 days

The effects of lime solution on the properties of SiO2 nanoparticles binary blended concrete

In this study, the effects of SiO2 nanoparticles on both mechanical properties (compressive, split tensile and flexural strength) and physical properties (water permeability, workability and setting time) of binary blended concrete have been investigated. SiO2 nano-particles have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.%. Curing of the specimens has been carried out in water and lime solution for 7, 28 and 90 days after casting. For the specimens cured in water, the optimal replacement level of cement by SiO2 nanoparticles for producing concrete with improved strength, was set at 1.0 wt.%. However, by curing the specimens in lime solution, Portland cement could be advantageously replaced by 2.0 wt.% of SiO2 nanoparticles. It was concluded that the SiO2 nanoparticles can improve the filler effect and its ultra high pozzolanic activity causes more C–S–H gel formation when cured in lime solution. Although curing in the lime solution can reduce the strength of control concrete, Curing the specimens containing SiO2 nanoparticles in lime solution causes faster setting time together with higher strength and residence to water absorption