الفهرس 
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Abstract
This study aims to investigates the structural behavior of structural precast lightweight sandwich panels. The main objective of this research is to approach the theoretical fully composite state by changing many of parameters to determine the effect of each parameter. The other objectives are: obtaining high load/weight ratio (by increasing the strength of concrete with thin thickness of two concrete wythes and overall relative lightweight) and measuring heat transfer between the two wythes. The parameters that changed during this study were: concrete grade (80, 70 and 37 MPa), concrete densities (2660, 2440 and 1800 kg/m3), thicknesses of concrete face wythes (2.5, 3.5 and 4.5 cm), insulation core material (high density foam, polyethylene foam and palm bark), shear connectors’ material (steel, carbon fiber rods and carbon fibers strips) and finally the shear connectors’ angle (45°, 60° and 90°). A total number of 25 specimens with the dimensions of (50*50) cm and height of 12 cm were prepared. The thermal conductivity coefficient was obtained for all specimens by measuring heat transfer through the specimens. Three-point flexural test was carried out on all specimens to get the ultimate experimental load. The results were compared with the predicted loads from ANSYS software and theoretical extremes of fully-composite and non-composite states to determine the degree of composite action was obtained for each specimen. In addition, the effects of changing every component in specimens were studied also to determine the optimum components and effect of each parameter. The SPSS software was used to get the significant correlations of each parameter. The results indicated that increasing grade of concrete caused decrease in thermal conductivity coefficient for all grades of concrete, also decreasing the thickness of face wythes (specially with steel rods shear connectors) had a positive effect on thermal conductivity coefficient due to increasing thickness of core layer (about 13% per cm of thickness). It was confirmed that decreasing thickness of concrete face wythes had a positive effect on load/weight ratio (although the ultimate loads decreased) which enhanced the performance of panels as light weight structural panels and the optimum face wythe thickness is 2.5 cm which has high (load/weight), although it has relative low ultimate capacity. It was also found that adding carbon fiber strips in specimen has a high positive effect in degree of composite action and the specimens contain carbon strips obtained high percent of predicted ultimate loads from ANSYS software. Adding polyethylene foam as a core material resulted positive effect on structural sandwich panel. Using carbon fiber strips and rods as shear connectors was the best shear connectors’ type with light high strength concrete in thermal conductivity, degree of composite, load/weight ratio and overall ultimate strength. The thermal conductivity of specimens containing carbon fiber material were less than the specimens containing steel rods by about 30%. In addition, it was verified that the structural behavior of slabs enhanced with the decrease of shear connectors installing angle from 90° to 60° then 45° with steel and carbon fiber shear connectors. Angle of 45° is the optimum angle in ultimate load, degree of composite action and load/ weight ratio. It also obtained the highest percent of predicted ultimate loads from ANSYS software. The great advantage of carbon fiber shear connectors is insulation between two concrete wythes relative lightweight. That because the steel shear connectors work as thermal bridges between two face wythes. The analysis with SPSS software program showed that all parameters correlations in this research were significant.