• Structural Engineering and Mechanics
• /
• v.14 no.3
• /
• pp.287-306
• /
• 2002

The assessment of structural performance of transfer structures under potential seismic actions is presented. Various seismic assessment methodologies are used, with particular emphasis on the accurate modelling of the higher mode effects and the potential development of a soft storey effect in the mega-columns below the transfer plate (TP) level. Those methods include response spectrum analysis (RSA), manual calculation, pushover analysis (POA) and equivalent static load analysis (ESA). The capabilities and limitations of each method are highlighted. The paper aims, firstly, to determine the appropriate seismic assessment methodology for transfer structures using these different approaches, all of which can be undertaken with the resources generally available in a design office. Secondly, the paper highlights and discusses factors influencing the response behaviour of transfer structures, and finally provides a general indication of their seismic vulnerability. The representative Hong Kong building considered in this paper utilises a structural system with coupled shear walls and moment resisting portal-frames, above and below the TP, respectively. By adopting the wind load profile stipulated in the Code of Practice on Wind Effects: Hong Kong-1983, all the structural members are sized and detailed according to the British Standards BS8110 and the current local practices. The seismic displacement demand for the structure, when built on either rock or deep soil sites, was determined in a companion paper. The lateral load-displacement characteristic of the building, determined herein from manual calculation, has indicated that the poor ductility (brittle nature) of the mega-columns, due mainly to the high level of axial pre-compression as found from the analysis, cannot be effectively alleviated solely by increasing the quantity of confinement stirrups. The interstorey drift demands at lower and upper zones caused by seismic actions are found to be substantially higher than those arising from wind loads. The mega-columns supporting the TP and the coupling beams at higher zones are identified to be the most vulnerable components under seismic actions.

• Journal of Korean Society of Steel Construction
• /
• v.18 no.2
• /
• pp.173-180
• /
• 2006

The seismic responses of a building are affected by the base soil conditions. In this study, linear time-history seismic analysis and nonlinear pushover static seismic analysis were performed to estimate the base shear forces of 3-, 5-, and 7-story steel buildings, considering the rigid and soft soil conditions. Foundation soil stiffness, based on the equivalent static stiffness formula, is used for the damper, one of the Link elements in SAP 2000. The base shear forces of the steel buildings, estimated through time-history analysis using the general-purpose structural-analysis program of SAP 2000, were compared with those calculated using the domestic seismic design code, the UBC-97 design response spectrum. and pushover static nonlinear analysis. The steel buildings designed for gravity and wind loads showed elastic responses with a moderate earthquake of 0.11 g, while the elastic soft-soil layer increased the displacement and the base shear force of the buildings due to soil-structure interaction and soil amplification. Therefore, considering the characteristics of the soft-soil layer, it is more reasonable to perform an elastic seismic analysis of a building's structure during weak or moderate earthquakes.