Earthquake Engineering Research - HKU Libraries - The University ...

340
many research works that adequate strength does not have a decisive influence on expected structural
drift. Limit state can best be represented by deformation rather than by strength as damage that can be
directly correlated with displacement. Therefore, maximum displacements, rather than maximum
stresses, represent the proper design criteria. This differs from current force-based design that is based
on acceleration spectra, code performance factors that correlate poorly with damage potential, and
displacement checks to ensure that structural displacement limitations are not exceeded.
In this paper, nonlinear static method based on displacement is presented. The earthquake-resistant
performance of building structures is represented as a sequence of functions of the maximum
displacements that occur during strong seismic ground motions. The acceleration of ground motion
being monotonously increased by degree, maximum displacements can be estimated using the concept
of elastic displacement (or acceleration) spectra and be distributed using SRSS.
NONLINEAAR STATIC PROCEDURE
There are four levels of structural analysis procedures appropriate for the evaluation of existing
buildings and new design ones, as followed:
(1) The Linear Static Procedure (LSP), which is a basic procedure, and mainly applicable to buildings
whose respond is primarily in the elastic range;
(2) The Linear Dynamic Procedure (LDP), which has such characteristics as LSP;
(3) The Nonlinear Static Procedure (NSP), which can evaluate buildings loaded beyond the elastic
range, but does not fully reflect dynamic response of structures, specially the effects of higher
mode;
(4) The Nonlinear Dynamic Procedure (NDP), which is the most complete form of analysis,
modeling both dynamic effects and inelastic response, but which is sensitive to modeling and
ground motion assumptions.
The more advanced the form of analysis provides a more accurate model of the actual performance of
a building subjected to earthquake loads, but greater the time and memory space are required. So, The
Nonlinear Static Procedure (NSP) is a very practical analysis method, whose basic steps of are:
(1) Assume the nonlinear force-displacement relationship of individual elements of structure
(including yield strength, post yield stifmess and stiffness degradation, etc);
(2) Calculate the target displacement of structure;
(3) Select a reasonable lateral load pattern, and pushing the structure under this load pattern which is
monotonously increasing step by step, when a structural member yields, then its stiffness is
modified, until the roof displacement of structure is up to the target displacement or the structure
collapses.
At this time, the evaluation of seismic performance of structure is obtained. It is clear that the
Nonlinear Static Procedure (Pushover) is a force-based analysis method which adds checking
computation of displacement and deformation of structures by means of either base shearing force
versus peak displacement or seismic demand spectrum versus structural capacity spectrum.