Fada C. AL-Subaei Master Theses
Theses Title : GEOMETRIC DESIGN OF CORES IN CONCRETE HOLLOW BLOCKS FOR OPTIMUM WEIGHT.
The main objective of this study is to determine the optimum geometric design of cores of concrete hollow block that satisfy the strength and dimension requirements of the ASTM Standards. A total of ten common shapes of concrete hollow blocks (400 x 200 x 200 mm) with different core geometries were collected from forty-two factories in Riyadh City. The shape and size of cores of four blocks of common concrete hollow blocks were modified to enhance the performance of the blocks in terms of compressive and shear strengths.
A non – linear three-dimensional finite element analysis was used as a tool to investigate the behavior of the masonry units under axial compression and pure shear forces. The finite element model had cracking and crushing capabilities. The available blocks in the local market were evaluated first, and then new blocks with modified shapes and sizes of cores were studied.
Four cylindrical specimens of the same mix design of concrete hollow blocks were used to determine the mechanical properties of the concrete experimentally. Two types of common concrete hollow blocks with different geometry were tested under axial compression to determine the compressive strength. The Experimental results were used to standardize the finite element program by selecting realistic parameters.
Two finite element Programs (ANSYS and ADINA) were investigated for reasonable modeling of such type of problems. ANSYS program underestimates the ultimate compressive strength of the concrete blocks by about 45% with respect to the experimental results. However, ADINA predictions are close to the experimental values. Therefore, ADINA program was considered as the analysis tool in this study.
The comparison criterion for blocks efficiency in this study is the strength / weight ratio. The concrete hollow blocks with large size cores have the lightest weights. In general, as the number of cores increases and hence number of webs, the blocks weight increases.
Since the objective of this study is to optimize the geometric design of cores in concrete hollow blocks, the shape and size of cores of four blocks of common concrete hollow blocks were modified. The selected blocks either have relatively large net area, or have good potentional of extra reduction in the web and face shell thickness by changing the shape and size of the cores. The reduction in net area of the modified shapes was in the range of 13 –38 %. The ratio of the compressive and shear strengths to the weight was increased in the range of 19 – 41 %, and 19 – 43 %, respectively. This study showed that the concrete hollow blocks with two cores is the optimum shape available in the local market. The modified shapes presented in this study are also recommended for increaseing the effeciency of the block factories as well as reducing the dead load on the building elements.