This research studies the behavior of the soft story in RC structures using
static analysis and dynamic analysis, where studying models of RC
structures containing soft story where this story results from increased
hieght of story than the rest st
orys, was conducted static analysis using
Nonliner pushover analysis and dynamic analysis using Nonliner time
history analysis
: Nonlinear response history evaluation is becoming a practical tool due to availability of high performance computing and recommendations of the new seismic guidelines, and due to the increase of available strong ground motion database. When testing
the selected and scaled ground motions, it’s a standard procedure to use the time history analysis to validate the results in terms of structural responses and their variation. this proves the efficiency of the presented procedure.
In this study the selection and scaling criteria of real time history records to satisfy the Syrian design code are discussed. Ten set of records have been selected and scaled, every set consists of seven records of available real records, to match the Syrian design spectra. The resulting time histories are investigated and compared in terms of suitability as input to time history analysis of civil engineering structures, by mean of time history analyses of SDOF systems which are conducted to examine the efficiency of the scaling method in reducing the scatter in structural response. The nonlinear response of SDOF systems is represented by bilinear hysteretic model. Assuming 5 different Periods, α=3% post-yield stiffness, a number of 700 runs of analysis are conducted. And a number of 280 runs of analysis are conducted for MDOF systems.
Design ground motions are typically prescribed by smooth response spectra. Engineers often prefer to use a time history that matches the target design spectrum rather than evaluate a structure for a sit of time histories that are representative of th
e target spectrum in an ensemble average.
Generally, scaling actual time histories to match a given design spectrum can be made by two preferred methods: First, ground motions uniform scaling in time domain which is simply scaled up or down the ground motion uniformly to best match the target spectrum within a period range of interest, without changing the frequency content. Second, spectral matching in time domain which produces only localized perturbations on both the time history and the its response spectrum, where small adjustments can be made to a time history to change its response spectrum from jagged to smooth, if done properly the resulting time history can be “realistic”.
The realistic nature of a time history should be judged in the time domain in terms of the non stationary character of acceleration, velocity and displacement, for that the effectiveness of the two methods is examined by applying them to adjust actual earthquake time histories to much the design spectra while minimizing perturbations on their characteristics.
The procedures are utilized to scale 15 set of records, every set consists of seven records of available real records to match the Syrian design spectra. The resulting time histories are investigated and compared in terms of suitability as input to time history analysis of civil engineering structures
The European Standard, the New Zealand Standard, the U.S. Standard, the Syrian Standard and the Iranian Standard define a criterion for selecting ground motion records for time-history analysis by similarity between the seismological signature of ear
thquakes used for the analysis and those earthquakes that are expected to happen at the given location. But these standards follow different methodologies. The New Zealand Standard proposes that the spectrum of each selected record should match the design spectrum over a range of periods related to the fundamental period of the structure investigated. The energy of at least one of these record’s spectra must exceed the energy of the design spectrum. The European Standard recommends that the average spectrum of the selected records should be always higher than 90% of the design spectrum in a defined range of periods, and the value of the average spectrum at period equal zero should be larger than the value of the corresponding design spectrum. The U.S. Standard, also the Syrian and the Iranian Standard; advise that in a defined range of periods, the average spectrum of the selected records should be 40% and higher than the code spectrum.
This study illustrates the differences between selecting approaches, and how these differences affect the resulting ground motion records. Some resulting recommendations for record selecting procedures are presented, and advised to be used in addition to the Syrian Standard recommendations.
