In analysing cracked Reinforced Concrete (RC) flexural members at the service level, some of the simplifying assumptions commonly made in the literature are poorly justified and do not properly account for the significant disturbed strain regions in the neighbourhood of the cracks. This may lead to misunderstandings and poor interpretations of the in-service behaviour of RC structures. For instance, in determining the contribution to flexural stiffness of the intact concrete between primary cracks, it is usual to assume a linear variation of strain despite warping of these cross-sections. Another example is the use of an effective area of tensile concrete to assess the flexural stiffness of a cracked member. It is unlikely that a single value of the effective concrete area could accurately model the stiffness of a cracked tension zone without due consideration of the spacing of cracks and the complex strain field that arises in the concrete around the embedded bars. This paper presents an analytical model for the estimation of instantaneous flexural stiffness of cracked RC members, making use of the results of two Finite Element (FE) studies of disturbed strain regions near cracks.
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