Report - PEER - University of California, Berkeley

where, T: natural period of structure(sec.), Sa: acceleration response spectrum atengineering bedrock without surface soil, h: damping coefficient. The earthquakeground motion is used as the standard for evaluating the seismic performance capacityof a structure, which includes the site amplification through the surface soil from thebedrock. A new and simple method of calculating the site amplification from thebedrock is presented in the Guidelines. The standard earthquake motion is basicallythe same as defined in the BSL and does not have an explicit conception of exceedingprobability and regional hazard.On the other hand, the site earthquake motion is the earthquake motion used forevaluating the seismic performance risk of a structure at the construction site. Thelevel and the characteristics are to be calculated based on the site-specific groundcharacteristics as well as the regional seismic activity.5. ESTIMATION OF RESPONSESA variety of analytical methods are supposed to be used for estimating responses ofthe structures, from equivalent linearization to time-history response analysis withdetailed structural models. The principles for the structural and response analyses areprescribed in the Guidelines.The response evaluation procedures covered in the Guidelines may be roughlyclassified as (a)-(d) below:(a) Static nonlinear (pushover) analysis and response estimation based onreduced SDOF system (equivalent linearization),(a) Pushover analysis and reduced SDOF time-history response analysis,(b) (a) and time history response analysis of multiple lumped-mass systems,(c) (a) and nonlinear time history response analysis at the member level,(d) Nonlinear time history response analysis at the member level.The method (a), which is a de facto standard procedure in the Guidelines, may bedescribed more in detail as follows:(1) Static nonlinear analysis of the structure with fixed foundation under anassumed load distribution (pushover analysis) is performed to obtain the equivalentload-displacement relationship of the reduced SDOF system, and the relationshipsbetween the equivalent displacement and the inter-story drift angle, memberdeformation angle (ductility factor) and member force.(2) The limit deformations on the relations corresponding to the limit states(serviceability, reparability I/II, safety) are calculated from damage rates based onmember deformations. The detailed evaluation methods are given in the level 2documents. Also possible errors in the analysis due to higher modes, material strength,shall be taken into account.(3) The earthquake response spectrum at the base of the building is evaluatedfrom the standard earthquake at the engineering bedrock taking into account the soilamplification.31