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Title: Cracking Mode And Shear Strength Of Lightweight Concrete Beams
Keywords: Beams, Cracking, Lightweight Concrete, Reinforced Concrete, Shear, Tests
Issue Date: 21-Jan-2011
Citation: KUM YUNG JUAN (2011-01-21). Cracking Mode And Shear Strength Of Lightweight Concrete Beams. ScholarBank@NUS Repository.
Abstract: Lightweight concrete is a high performance material with advantages for a myriad of applications. It has the potential to be used in sophisticated structures like prefabricated high-rise construction and architectural icons, to simple low-cost housing and rapidly erected semi-permanent structures. There however remains significant lacunae in engineering knowledge with regards to shear response of reinforced concrete. This is especially true of lightweight concrete with and without aggregates which remains a maturing engineering material. While lightweight aggregate concrete has been introduced and successfully used in specialized environments, it has yet to generate mainstream acceptance as an alternative to normal weight concrete. An experimental program including 64 lightweight concrete beams without transverse reinforcement and 22 companion normal weight concrete reference beams were tested under monotonically increasing third point loading until ultimate physical failure. The results were analyzed and compared with empirical equations in the literature as well as international reinforced concrete building codes. Within the scope of this study, it was found that lightweight aggregate concrete beams without transverse reinforcement behaved in a similar manner to the reference normal weight concrete beams until the onset of diagonal cracking. Thereafter, while normal weight concrete beams were able to continue resisting shear until a flexural mode of physical failure occurred, lightweight aggregate concrete was unable to develop sufficient resistance and physically failed in a brittle shear mode. Foamed concrete and lightweight aggregate-foamed concrete also responded to loads like normal weight concrete. Diagonal cracking occurred at lower loads than both normal weight concrete and lightweight aggregate concrete due to its tensile strength being much lower than the reference concrete although having comparable compressive strengths. Nevertheless, after the onset of diagonal cracking, foamed concrete and lightweight aggregate-foamed concrete was able to continue resisting a significant amount of shear prior to physical ultimate failure. This ability was found to be due to the irregular and angular cracking plane at the macro level compared to the smooth crack surface at the micro level. Using the diagonal cracking and ultimate shear capacity data generated from this test program and the rigorous observations recorded, a prediction equation was derived for shear strength of lightweight concrete beams without transverse shear reinforcement based on the parametric behavior model of Russo et al. (2005). This diagonal cracking equation was then tested against the results of a set of rectangular lightweight concrete beams as well as data from the literature and found to be in good agreement across the range of parameters tested including with and without shear reinforcement. Comparison of the performance of these lightweight high-strength concrete beams with and without transverse reinforcement against design equations of the American Concrete Institute and the British Standards Institute show that the design equations can be used with confidence. Diagonal cracking of lightweight concrete beams only occur beyond the design loads and deflection limits imposed. However, caution should be exercised when considering the behavior of lightweight concrete beams beyond service loads as the physical shear capacity of the material may be exhausted prior to its flexural capacity.
Appears in Collections:Ph.D Theses (Open)

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