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Shear and Torsion Design Review – Australian and International Standards
Published in Nigel Powers, Dan M. Frangopol, Riadh Al-Mahaidi, Colin Caprani, Maintenance, Safety, Risk, Management and Life-Cycle Performance of Bridges, 2018
T. Hossain, S. Mikhael, A. Chaudry, S. Mohanakumar
The Modified Compression Field Theory, MCFT, is a shear model developed by Vecchio and Collins (1986), which is based on a variable angle truss model. The MCFT is a behavioral model that can be used to predict the shear stress and shear-strain response of an element subjected to in-plane shear and membrane forces. The formulation of MCFT includes equilibrium, strain compatibility, and a constitutive relationship for diagonally cracked concrete that enable determination of the state of stress (fx, fy, vxy) in structural concrete corresponding to a specific state of strain (εx, εy, γxy). Using these principles, the MCFT accounts not only for Vs, but also the combined effect of the complex shear resistance mechanisms that contribute to Vc without having to consider each mechanism individually. The theory considers cracked concrete as a material with its own stress-strain characteristics and accounts for tensile stresses in the concrete between cracks from the aggregate interlock mechanisms.
On the use of MCFT per AS 5100.5 for the assessment of shear capacities of existing structures
Published in Australian Journal of Structural Engineering, 2020
Colin C. Caprani, Mayer M. Melhem
The modified compression field theory (MCFT) was developed at the University of Toronto by Vecchio and Collins (1986). The theory assumes cracked concrete can be treated as a new material with its own stress-strain behaviour. MCFT considers concrete tension stresses, the effect of aggregate interlock, dowel action, and the presence of steel reinforcement on the behaviour of the cracked concrete. In a full MCFT analysis, 15 equations of equilibrium, strain compatibility, and constitutive relationships, shown in Figure 1, require an iterative process to obtain the shear capacity of a given concrete member.
Computational modeling of high performance cementitious thin shell elements under in-plane shear
Published in Mechanics of Advanced Materials and Structures, 2018
Apostolos Koukouselis, Euripidis Mistakidis
Over the years many researchers have developed theories and methods for calculating the ultimate shear strength of reinforced concrete (R/C) panels and predicting their behavior under pure shear or combined axial and shear stresses. For many years, the design of such elements was governed by the assumption that the inclination of the cracks with respect to the loading vector was equal to 45 degrees. The Compression Field Theory (CFT) [1–2], a significant landmark in shear relevant research, introduced the idea of the correlation of the inclination angle θ of the crack with respect to the loading axis, to the strain conditions of the element. Then, Vecchio and Collins [3], based on an experimental program, developed the Modified Compression Field Theory (MCFT) introducing the contribution of concrete by its tensile stress in the ultimate shear resistance of the element. Due to the complexity of its equation, MCFT, although an excellent theory for use by the aid of appropriate software, was found by engineers to be a very cumbersome method to be used in hand calculations. The simplified MCFT (SMCFT) by Bentz et al. [4] simplified the calculations of MCFT and provided, as the authors mention, a good method for “back of the envelope” calculations. Their simplification is based on various assumptions, one of which is the lack of axial stress in the transverse direction. Similar limitations, as Rahal [5] mentions, also apply in the proposed equations of building regulations such as the ACI code [6]. A very effective calculation method was proposed by Rahal [5] termed SMCS (Simplified Model for Combined Stress resultants). Combined with the calculation method proposed by the same author [7] regarding the determination of the postcracking shear modulus of the reinforced concrete panel, SMCS can effectively describe the behavior of R/C membrane elements under in-plane shear.