Kamyar Kildashti

A case study on the assessment of response modification coefficient and earthquake-induced collapse potential of a high-rise setback tower

Abstract This paper evaluates response modification coefficient (R-factor) and collapse potential of a high-rise tower with setback irregularity under spectral-matched ground motion records. The tower is comprised of two legs with three distinct lateral bearing systems in elevation and curved configuration in plan. Furthermore, it has a setback in elevation, recognised by inclined columns joining two legs of the tower in uppermost stories. These characteristics cause the tower to classify as a complex irregular structure in which using code-based R-factor is highly dubious. In this paper, initially, an analytical model of the tower was subjected to a suite of ground motions to estimate collapse potential and equivalent R-factor in accordance with FEMA P695. Alternatively, structural performance parameters including inter-storey drift ratios, residual drift ratios and plastic hinge rotations were compared to TBI acceptance criteria. To achieve consistent safety margin against collapse, the value of 8 was suitable for R-factor. In spite of satisfactory threshold in accordance with FEMA P695 and TBI guidelines, for a structure with irregular configuration and multiple bearing system, damages can be localised close to zones of change in lateral bearing system that may lead to partial collapse.

A case study on the soil–pile–structure interaction of a long span arched structure

Abstract Different concepts for modelling of soil-foundation in complete dynamic interaction analysis for a 110-m height 70-m span arched structure on 180 piles were investigated in this paper. The modelling approaches consisted of a sophisticated procedure to account for soil compliance and foundation flexibility by defining frequency-dependent springs and dashpots; namely, flexible-impedance base model. The results of this model were compared with those of the conventional modelling procedures; namely, fixed base model and flexible base model by defining frequency-independent springs. In the flexible-impedance base model, the substructure approach was employed through finite element modelling. To account for the kinematic interaction, the numerical model of the soil, foundation and piles were developed using a verified finite element model in ABAQUS. The free field time history and design spectrum were modified to obtain the foundation input motion. The impedance of pile groups with different length was obtained by the finite element model to assess the inertial interaction. The comparison of the results of the employed models showed that rocking and torsional responses were greatly affected by soil–structure interaction, indicating redistribution of seismic demands. It was also proven that the internal demands of the conventional model considering frequency-independent Winkler springs might be higher than those of the model including pile–soil–structure interaction effects.