FINITE ELEMENT MODELLING OF RC BEAMS WITH LARGE OPENING AT CRITICAL FLEXURE AND SHEAR STRENGTHENED WITH CFRP LAMINATES

Pipes and ducts are provided to accommodate essential services that are required in a building, namely power supply, sewerage, air-conditioning, water supply, telephone cable and computer network. Traditionally, pipes and ducts are usually hung below the beams and formed a “dead space” in a building. An option is to pass these pipes and ducts through openings in reinforced concrete (RC) beam. In the design stage, design engineers provide sufficient strength and ensure serviceability in beams with opening. However, M&E contractors usually request to drill an opening in order to simplify the pipe arrangements during construction stage which were not considered in the design. This causes problem to structural engineers especially when the required opening is located at critical section in an existing beam. This paper presents a two dimensional non-linear finite element analysis to study the behaviour of externally strengthened RC beams with large opening at section with critical flexure and shear using carbon fiber reinforced polymer (CFRP) laminates. The numerical results were validated with the experimental testing of nine beams which included a control beam, four un-strengthened and four strengthened beams. The numerical modelling was conducted using a non-linear finite element (FE) program, ATENA. In this FE program, tensile behaviour of concrete is modelled by nonlinear fracture mechanics combined with the crack band method in which smeared crack concept is adopted. All the beam specimens had a cross section of 120x300 mm with an effective span of 1800 mm. The beams were loaded to failure under four point bending. The parameters included the size, location and shape of opening. The crack patterns, load deflection curves at mid-span and ultimate load were compared with the experimental results. Generally, good agreement has been obtained between the numerical analysis and experimental results. The finite element analysis can be useful to design a suitable strengthening configuration for RC beams with large openings at critical location by optimal application of CFRP laminates.