Shear strength and fatigue crack propagation in concrete by energy method
Department of Civil and Environmental Engineering
Doctor of Philosophy
Hsu, C.T. Thomas
Spillers, William R.
Meegoda, Jay N.
Blackmore, Denis L.
The limit analysis methods have been commonly used to predict the ultimate flexure strength of reinforced concrete members over 50 years. However, current design formulas for shear in structural concrete are mostly empirical. In part one of this dissertation, attempts are made to apply the theory of plasticity to predict the shear strengths of reinforced concrete structures.
The modified Coulomb-Mohr failure criterion is used as the constitutive law of concrete, and the plastic flow is assumed to be associated with this failure criterion. A generalized formulation for energy dissipation in accordance with the failure criterion and associated flow rule is proposed in this dissertation. The upper-bound method is used to predict the shear strengths of reinforced concrete members, including push-off shear transfer, bracket and deep beams. The proposed method is also used to predict the torsional strength of reinforced concrete beams. The theoretical solutions show a good agreement with the existing experimental results.
A structural coefficient of plasticity is proposed to consider the effect of hydrostatic pressure on the ductility of concrete materials. This structural coefficient of plasticity, namely vs is found to be a function of reinforcement indexes and shear span ratios. Different Vs are given in this dissertation.
The fracture property of concrete structures becomes an increasingly important issue in the engineering practice because of the changing working of environment of reinforced concrete structures. Part two of this dissertation is designated to the study of the fracture and fatigue characteristics of structural concrete.
In part two, a generalized process zone theory based on the Paris' energy formula is proposed to study the inelastic fracture properties. This generalized process zone theory is capable of analyzing inelastic fracture characteristics of engineering materials in general. The so-called sized effect is formulated by this proposed generalized process zone theory for softening materials. A brittleness index is also proposed in this research based on the this generalized process zone theory. This brittleness index may be used to characterize the inelastic fracture properties of the structures.
A damage accumulation theory is proposed in this research to predict the fatigue crack propagation rate. The damage of the materials near crack tips caused by the cyclic load is characterized by the plastic component of J integral, or, the plastic fracture energy of the system. A fatigue crack propagation formula is proposed based on this damage accumulation theory. With the inelastic fracture properties predicted by the proposed generalized process zone theory, this fatigue crack propagation formula is capable of predicting the crack growth rate in metals and structural concrete. This theory is also able to predict the fatigue threshold of metals and concrete materials. Test results show that the proposed theory has a good accuracy in both metals and structural concrete.
njit-etd1995-012 (242 pages -- 9,279 KB pdf)
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