Evaluation of flexural strength of concrete beams reinforced with timber encased in permanent ferrocement forms

Abstract

A structural element must exhibit strength and stability for its intended use. This paper presents an investigation of a concrete beam reinforced with timber and encased in permanent ferrocement form for use as lintels for low-income housing. The 25 mm thick cement-sand ferrocement is reinforced nominally using a two-layered chicken mesh. The timber is placed in the tensile zone and the concrete cast around it is assumed to act in compression. The specimens were tested under a single-point flexural loading. The concrete design strength was 20 N/mm2 at 28 days. The induced loadings computed on the beam included the triangular load from the blockwalls and the self-weight of the concrete beam at the ultimate limit states which yielded a maximum bending moment of 0.22 KNm. However, the maximum carrying capacity based on first crack load yielded a maximum bending moments of 9.10 and 10.20 KNm for 50 x 50 mm and 50 x 75 mm timber reinforced ferrocement beams respectively. The computed maximum bending stress at the bottom of the fibre assuming uncased isotropic timber beams are 9.67 and 4.29 N/mm2 for the 50 x 50 mm and 50 x 75 mm timber respectively which is less than 10 percent of the ultimate bending strengths of the timber specimen. The results of the ultimate carrying capacity achieved would enable a choice of the size of timber beams positioned in the tensile zone of the permanent ferrocement forms to be made.