The behaviour of reinforced concrete masonry beams using the H-block

Abstract

This research presents a study on the behaviour of reinforced concrete masonry beams using the double open-end masonry unit known as H-Block. The reinforced concrete masonry beams provide an effective and efficient solution to the construction industry when compared to the other flexural elements of different materials. Four main components are used for the construction of the reinforced concrete masonry beam; the masonry unit, mortar, steel reinforcement and concrete infill. Each respective material has its own mechanical properties, which affects the flexural stiffness and behaviour of such beams. Furthermore, the behaviour of reinforced concrete masonry beams act compositely since the concrete infill and mortar provide the bond between each subsequent material. The overall design procedure for reinforced concrete masonry beams is discussed through various research procedures and codes of practice. Moreover, the overall behaviour and failure modes of reinforced concrete masonry beams are described in conjunction with boundary conditions. The performance of the reinforced concrete masonry beams, using the H-Block unit, was further studied by testing full-size specimens of different spans, different tensile and shear reinforcement, but having the same height of two courses, concrete infill and mortar. The total load applied was plotted against the mid-span deflection, concrete and steel tensile strains. Furthermore, the experimental reinforced concrete masonry beams were compared to theoretical reinforced concrete masonry beams and reinforced concrete beams. This comparison provided reasonable conclusion for further research into the construction of reinforced concrete masonry beams. From experimental results, it was concluded that the addition of shear reinforcement resulted in a higher beam load and moment carrying capacity. In addition, when comparing different span beams with shear reinforcement, it was deduced that the load at which the deflection limit was reached was lower for the shortest span beam; which may be attributed to the difference in shear span to depth ratio. When comparing theoretical and experimental RCM beams with the same parameters, a linear behaviour was observed in the theoretical graphs, characterised by a constant flexural stiffness with a proportional increase in load and mid-span deflection. This result was obtained since the theoretical graphs do not factor the effect of beam cracking and the yielding of the steel tensile reinforcement. On the other hand experimental results showed an initially high flexural stiffness which then decreased as it approached the elastic limit as a result of the formation of cracks and yielding of the tensile steel reinforcement. When comparing theoretical RC beams with experimental RCM beams, it was concluded that theoretical RC beams showed a higher flexural stiffness and lower midspan deflection when compared to experimental RCM beams. However, the flexural stiffness of the experimental RCM beams changes with an increase in load since it experiences cracking, resulting in a reduction in the beam flexural stiffness. From the results obtained from this study, the use of RCM beams can be considered as a viable option to be adopted as a lintel typically used in small residential projects.