The well-known modal superposition method for the evaluation of seismic response by the complete quadratic modal combination rule (CQC) is revisited. The most widely used version of the CQC rule utilizes correlation coefficients derived for white-noise excitation and neglects the influence of peak factor variation on the response. Here a simplified procedure for evaluation of correlation coefficients and peak factors consistent with the power spectral density of seismic excitation is proposed. The procedure is based on an approximate analytic expression for direct evaluation of the power spectral density of the excitation consistent with any prefixed response spectrum, and the evaluation of the consistent correlation coefficients and peak factors by using analytical expressions. The ranges of system dynamic parameters for which the correlation coefficients derived for white-noise excitation are not adequate are pointed out. Then the influence of the assumptions for CQC rule derivation on the evaluation of...

Purpose: The paper illustrates a viaduct collapse due to corrosion phenomena. Moreover, a contribution to the issues related to both the control of existing structures and design methods to be followed for the construction of new buildings is provided. Design/methodology/approach: The objectives were achieved by in situ observations and numerical analyses. The effects of corrosion phenomena are investigated, and the progressive collapse analysis is provided to be helpful in this case. Findings: The damages induced by corrosion phenomena have caused the collapse of the viaduct taken in to account. The performed numerical analyses were able to reproduce the effects of corrosion in terms of reduction of wires diameter. Research limitations/implications: The research is limited to prestressed concrete viaduct with post-tensioned cables. Practical implications: A monitoring plan, subdivided in several phases, is suggested, to avoid critical situations as these described. Originality/value: The case study brought useful information on the effects of corrosion on the decks section, showing how the technology in post-tensioned cables is usually insidious and prone to the issues relating to corrosion of the wires

A simple physical model, for prediction of ultimate shear strength of steel fiber-reinforced concrete (SFRC) beams is developed on the basis of a plastic approach originally proposed for reinforced concrete beams without stirrups. It is founded on the hypothesis that cracks can be transformed into yield lines, and thus is know as crack sliding model (CSM). First, the CSM is improved to take into account the shear strength increase for deep beams, due to the arch effect. Then, the effectiveness factors for fibrous concrete under biaxial stresses are evaluated, taking into account the postcracking tensile strength of SFRC and its ability to control slippage along shear cracks. With the aim of providing a handy and fast tool for design of SFRC beams without stirrups, a simplified design model is also derived. Finally, the proposed models are validated by the results of a large set of experimental tests taken from literature.