Abstract
The starting point of the proposed procedure for seismic evaluation of existing structures is that the yield displacement of a structure in flexure is constant and that it depends only on the yield strain of the yielding material and the geometrical characteristics of the structure, not on the yield strength of that structure. The fundamental vibration period of the structure is, thus the dependent variable derived from the estimated yield strength and yield displacement of the structure. To facilitate an evaluation of the maximum inelastic deformation of an existing structure using a corresponding single-degree-of-freedom system approach, a new relation between the yield strength (defined using a new yield strength reduction factor) and the displacement ductility demand of a corresponding single-degree-of-freedom system is proposed. This relation is consistent with the constant yield displacement assumption and characterizes the relevant properties of the structure using the yield strain of its yield material, its aspect ratio and its size. The proposed Constant-Yield-Displacement-Evaluation (CYDE) procedure for seismic evaluation of existing structures has four steps. Given an existing structure, its seismic hazard environment, and an estimate of its strength, the CYDE procedure estimates the displacement ductility demand, i.e. the maximum inelastic displacement, the structure may experience at the examined seismic hazard levels. The proposed CYDE evaluation procedure is similar to the current constant-period procedures, but provides a more realistic estimate of the displacement ductility demand for stiff structures, enabling a more accurate seismic assessment of numerous existing structures.
Highlights
Evaluation of existing structures to examine their seismic behavior and assess their performance and safety at various seismic hazard levels is a difficult task
Based on the values of the yield displacement and the yield strength of the CYD SDOF model of an existing structure and the seismic hazard it is evaluated for, the Constant Yield Displacement Evaluation (CYDE) procedure provides an estimate of the displacement ductility demand the structure is likely to experience
The approximate μ–R*–H/B relations for CYD SDOF models make it possible to develop a displacement-based seismic performance evaluation procedure for existing structures that respond to ground motion excitation predominantly in flexure, the Constant Yield Displacement Evaluation (CYDE) procedure
Summary
Evaluation of existing structures to examine their seismic behavior and assess their performance and safety at various seismic hazard levels is a difficult task. The constant-period assumption used to generate the Ry–μ–Tn relations leads to unrealistically small yield displacements of the corresponding constant-period SDOF model (Fig. 1) that, in turn, result in unrealistically large ductility demand values (Eq 2) even though the maximum inelastic displacement of the SDOF model may not vary significantly This effect is even more pronounced for seismically isolated superstructures, as pointed out by Sollogoub (1994), Vassiliou et al (2013), Tsiavos (2017) and Tsiavos et al (2013a, b, 2017) as a result of the small forces exciting the isolated superstructures that, according to the CP approach, lead to unrealistically small yield displacements. Based on the values of the yield displacement and the yield strength of the CYD SDOF model of an existing structure and the seismic hazard it is evaluated for, the CYDE procedure provides an estimate of the displacement ductility demand the structure is likely to experience. The benefits and shortcomings of the CYDE procedure are discussed
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