Stiffness demand of self-centering dual systems under near-field pulse-type ground motions based on spectral analysis

Aided by rocking mechanism and energy dissipation mechanism, self-centering dual systems can control the degree of drift concentration while simultaneously reducing the response of interstory drift ratio, and thus making the primary system (frame structure) quickly restore its occupancy function by concentrating damage on the replaceable secondary system (rocking components). To investigate the relationship between the stiffness demand and dynamic responses, an extended coupled-two-beam model was proposed. The primary system and the secondary system are simplified as a cantilever shear beam and a flexural beam with variable base rotational constraint, respectively. Its dynamic characteristics are defined by two dimensionless parameters: the stiffness ratio between the shear beam and the flexural beam (α), the stiffness ratio between the flexural beam and its base rotational constraint (Rf). The generalized interstory drift spectra and drift concentration factor spectra are derived by solving dynamic equations and obtaining closed-form solutions of modal shapes and their corresponding modal drifts. A one-sided fling-step pulse and a two-sided forward directivity pulse are both generated with simplified pulse models. Then, the effect of these two dimensionless parameters on generalized interstory drift spectra and drift concentration factor spectra were studied under the two pulses. It is found that within the identified range of 1≤α≤5and 0<Rf≤5, the degree of drift concentration and the interstory drift ratio of mid-rise and low-rise frame structures are effectively and stably controlled, and these two spectra can be used as tools to quantify the relationship between the stiffness demand and targeted response so as to facilitate preliminary performance-based design of the self-centering dual system. © 2018, Editorial Office of Journal of Building Structures. All right reserved.