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Parabolic profile of cracks is well known in fracture mechanics, which typically develops in metallic systems. The profile of Interfacial delamination cracks in polymer foam cored sandwich composite structure is being investigated in this work using a procedure of embedded fiber Bragg grating sensor array with wavelength division multiplexing. The observed arbitrary nature of the crack profile in the mode I dominated loading condition, raises questions on the parabolic crack profile as well as on the assumption of numerous variables for numerical simulations of crack propagation problems especially for polymer foam-cored sandwich materials.

Given that both ACI 318-08 provisions and 352R-02 recommendations have been developed based on quite limited experimental data, an extensive database was assembled by Kang et al. [12] , which contains most of the available test data of reinforced concrete exterior beam-column connections with headed bars subject to load reversal. In this study, the database has been further expanded by adding the recent data focusing on the investigation of design parameters of clear bar spacing and head size, and re-evaluated using a variety of statistical and empirical techniques. An effort has been made to find a statistical model linking quantitative design parameters and qualitative connection response. In this study, binomial logistic regression methodology has been applied. The statistical methodology quantifies the effect of each design parameter in determining the performance of the connection. A reliable and robust goodness-of-fit test, the log-likelihood ratio test, was performed to evaluate the developed logistic regression model. Finally, the recent connection data were used to validate the predictive capability of the developed statistical model.

The results of previous experimental tests indicate that reinforced concrete interior beam column joints may exhibit significant strength and stiffness loss under earthquake loading, and the results of post-earthquake reconnaissance indicate that joint failure may result in structural collapse. Thus seismic evaluation and design of reinforced concrete frames requires accurate prediction of the potential for joint failure. This paper presents a binomial logit model, developed using data from 110 experimental tests, which define the probability that a reinforced concrete interior beam–column building connection, with a specific set of design parameters, will exhibit either a non-ductile joint shear failure prior to beam yielding or a ductile failure that initiates with beam yielding. The calibrated model identifies the relative importance of various design parameters in determining the connection’s response mechanism. The model can be used by an engineer designing a new connection, constructed of normal or high-strength materials, to estimate the likelihood of joint failure initiation. The model can also be used by an engineer evaluating an existing structure to estimate the likelihood of joint failure, determine the factors that most significantly affect this likelihood, and, thereby, develop a suitable and efficient retrofit strategy.