Effect of varying hysteresis models and damage models on damage assessment of r/c structures under standard design level earthquakes obtained using a new scaling method
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A seismic damage assessment of a real ductile framed structure of reinforced concrete requires not only realistic damage indices for members, storeys and the whole structure, but also a hysteresis rule simulating strength, stiffness and energy dissipation characteristics of the member hysteretic behaviour.
Many member damage indices and hysteresis models have been developed [Carr 1998]. Varying the member damage indices and the hysteresis models may result in significant variations in the predicted damage indices for storeys and structures subjected to design level earthquake excitations at ultimate limit state specified in New Zealand loading standard [NZS4203 1992]. This could greatly influence correct engineedng decisions of a structural design engineer, hence the effect of varying member damage indices and hysteresis models on the damage indices for the storeys and structures should be identified.
To this purpose, three main aspects studied include the earthquake scaling, the relationship between the member curvature ductility and structural displacement ductility, and the effect of varying hysteresis models and member damage indices on the damage indices for the storeys and structures respectively.
Three structures, four earthquakes, eight hysteresis rules and four member damage indices were employed in this study for structural models, earthquake inputs, modelling the inelastic behaviour in members and member damage respectively. The three reinforced concrete ductile frames are 6, 12 and 18 storeys respectively, designed according to the current New Zealand Standards [NZS4203 1992, NZS3101 1995] using the capacity design philosophy [Paulay 1992] with a structural displacement ductility of 5.0. The four different past earthquake excitations are Bucharest (1977-NS), El Centro (1940-NS), Northridge (Sylmar-949NW) and Kobe (1995-NS). The eight hysteresis models are the Elasto-Plastic, Bilinear, Modified Takeda (α=0.0, β=0.6), Degrading Bilinear (α=0.5), Clough, Modified Takeda (α=0.3, β=0.4), Q-Hyst (α=0.5) and Origin-Centred hysteresis models. The four member damage indices are the Park & Ang, Roufaiel & Meyer, Cosenza et al and Banon & Veneziano. The storey and structural damage indices, quantifying the storey and structural damage measures respectively, were calculated as the energy weighted average of all the inelastic member damage indices in the storeys and overall structures respectively (Park & Ang method).
To have appropriate scaled earthquakes matching design-level requirements, six different scaling methods are used to scale the four earthquakes for the three structures. By comparing the maximum responses (the maximum base shears, interstorey drifts and spectral accelerations), resulting from carrying out elastic dynamic time-history analyses to the scaled earthquakes with those at design level, a new procedure for earthquake scaling is proposed. To check whether the member curvature ductility demand to the design level earthquakes is less than the member curvature ductility capacity, the relationship between the member curvature ductility and the structural displacement ductility was studied and identified by carrying out inelastic dynamic time-history analyses. For this purpose, the Carr & Tabuchi trend-line approach for defining the structural yield displacements was used.
By comparative studies of the storey and structural damage indices for a specified member damage index and a specified hysteresis model, the effect of varying the hysteresis models and member damage indices on the storey and overall structural damage indices, i.e. damage evaluations, are identified.
Finally a procedure for the seismic damage analyses of reinforced concrete ductile framed structures to design-level earthquake excitations is proposed, which is illustrated by computing storey and structural damage indices for evaluations of 6- and 12-storey structures responding to the El Centro (1940-NS) excitation.