BEHAVIOUR OF FIBRE REINFORCED CONCRETE JOINT UNDER OPENING BENDING MOMENTS

Abstract

Beams and columns are major components in most Civil Engineering Structures. Their roles are complementary as they influence each other at the joints. Besides beams and columns, joints are also formed by the intersection of structural members in open channels and basins, tanks, folded plates, staircase lodgings, retaining walls and bridge abutments etc. Depending on their location, in general, joints may be classified as interior joints, exterior T joints, and comer joints. Also depending on the mode of structural action, joints may be subjected to closing bending moments (negative moments) or to opening bending moments (positive moments). The principles of detailing and the structural behaviour of simple members such as beams and columns are well established. On the other hand, the detailing, strength and behaviour of corner structures has not been conclusively determined. Detailing system 4 (See Fig. 3.2) was adopted for all specimens because of the confining effect of the loops on concrete in the corner zone. Tests have shown that opening corners in reinforced concrete structures have significantly reduced efficiency, ductility and unacceptable cracks at service loads. A substantial increase in post cracking tensile strength, toughness, ductility and crack control can be achieved by adding steel fibers to the concrete. In the present study, a total of four specimens had been tested to investigate the effect of two variables, namely the bar diameter at a given percentage of tension steel and the addition of silica fume (10% by weight of cement) to the matrix on the ultimate strength and behaviour of SFRC corner joints under opening bending moment. iii From tests, it has been found that the lowering of bar diameter at a given percentage of tension steel has a significant effect on the efficiency of the SRFC corner. 5-124 bars and 8-104 bars have similar percentages of tension steel but exhibit quite different modes of failure with the load-deflection curves for these two specimens having significantly different characteristics as well as the associated crack patterns. The increase in nominal efficiency due to lowering the bar diameter was as much as 30%. The addition of silica fume increased the ultimate strength, ductility and improved the efficiency considerably by allowing for greater energy absorption. ry