Performance-based seismic design of flexible-base multi-storey buildings considering soil–structure interaction

Abstract

The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractA comprehensive parametric study has been carried out to investigate the seismic performance of multi-storey shear buildings considering soil-structure interaction (SSI). More than 40,000 SDOF and MDOF models are designed based on different lateral seismic load patterns and target ductility demands to represent a wide range of building structures constructed on shallow foundations. The cone model is adopted to simulate the dynamic behaviour of an elastic homogeneous soil half-space. 1, 5, 10, 15 and 20-storey SSI systems are subjected to three sets of synthetic spectrum-compatible earthquakes corresponding to different soil classes, and the effects of soil stiffness, design lateral load pattern, fundamental period, number of storeys, structure slenderness ratio and site condition are investigated.The results indicate that, in general, SSI can reduce (up to 60%) the strength and ductility demands of multi-storey buildings, especially those with small slenderness ratio and low ductility demands. It is shown that code-specified design lateral load patterns are more suitable for long period flexible-base structures; whereas a trapezoidal design lateral-load pattern can provide the best solution for short period flexible-base structures. Based on the results of this study, a new design factor R F is introduced which is able to capture the reduction of strength of single-degree-of-freedom structures due to the combination of SSI and structural yielding. To take into account multi-degree-of-freedom effects in SSI systems, a new site and interaction-dependent modification factor R M is also proposed. The R F and R M factors are integrated into a novel performance-based design method for site and interaction-dependent seismic design of flexible-base structures. The adequacy of the proposed method is demonstrated through several practical design examples.

More adequate seismic design force pattern for yielding structures considering structural and ground motion uncertainties effects

“…In this investigation, steel building frames are modeled on the basis of the concept of FEMA‐440 for parametric study, which permits researchers to model special complex building structures as shear‐type buildings, representing multistory buildings having so‐called shear beams or those with relatively stiff diaphragms when compared with columns. In spite of some shortcomings, shear‐building models have been frequently utilized to evaluate the seismic behavior of multistory structures due to their simple forms and low computational efforts enabling a various ranges of parametric studies . In the steel shear‐building structures, beam‐column joints are modeled by bilinear elastic–plastic springs with 3% post‐yield strain hardening as representative of the story lateral stiffness.…”

Estimation of inelastic displacement demands of flexible-based structures on soft soils

“…The mass moment of inertia M θ and M φ (in the rotational degree-of-freedom φ) are used to account for soil incompressibility and frequency-dependency in the rocking degree-of-freedom θ; u ssi is the displacement of the structural mass relative to the ground, while u h is the foundation swaying displacement relative to the ground. The equations of motion for the SSI model and EFSDOF oscillators were solved in the time domain using the methods presented in Lu et al (2016). A suite of 20 ground motions recorded on soft soil deposits were employed in the study, as listed in Table 1.…”

“…This simplified SSI model enables the frequency-dependent global behaviour of the soil-foundation system (i.e., foundation swaying and rocking motions) to be solved in the time domain. The adequacy of this SSI model to predict the seismic performance of nonlinear systems on soft soil was investigated by Lu et al (2016).…”

“…Ghannad and Jahankhah (2007) studied the inelastic seismic demands of flexible-base structures and concluded that using the ductility reduction factor derived on the basis of the 'fixed-base' assumption for seismic design of SSI systems could lead to non-conservative design solutions. More recently, Lu et al (2016) proposed a performance-base design procedure for flexible-base multi-storey buildings, based on response-history analysis using synthetic spectrum-compatible earthquakes in accordance with code-specified soil site classifications. In their proposed procedure, they explicitly included the characteristic period, which is defined as the transition period from the acceleration-controlled to the velocity-controlled segment of a 5% damped design response spectrum of a design ground motion.…”

Estimation of inelastic displacement demands of flexible-based structures on soft soils

“…It was shown that a 0 generally varies from zero for fixed-base buildings, to a value of three for buildings located on very soft soil deposits (Lu et al, 2016).…”