Report - PEER - University of California, Berkeley

(7) a method of performance evaluation based probability of exceeding limit states.The guidelines consist of the following three volumes in Japanese:(i) Level 1 documents: Evaluation concept(ii) Level 2 documents: Evaluation methods in practice(iii) Level 3 documents: Evaluation exampleThe full provisions and most of the commentaries are being translated into Englishtowards publication in the near future.3. PERFORMANCE OBJECTIVESServiceability and safety are the two basic performance objectives, as commonlyadopted in performance-based design codes for buildings in the world.Serviceability is the performance objective so as to keep functional use withoutrepair normally under moderate earthquakes. Therefore, the serviceability limit stateshall be corresponded to the so-called slight or no damage levels. In the BSL of Japan,the allowable stress design is to deal with this, although the relationship between thecriteria and the damage level is not clear. A procedure is presented in the Guidelinesfor verifying that the residual crack width is sufficiently small.Safety is the performance objective so as to protect human life, and correspondsto the ultimate limit state or the safety limit state. Therefore, the design objective maybe selected so that the structure can bear gravity loads and would not collapse. Interms of structural damage, the state may be just before collapse at the loss of gravityloadcarrying capacity or P-δ deformation limits. In the Guidelines, the ultimate limitstate of members is to be evaluated similarly by past AIJ guidelines[1][2], where theso-called inelastic deformability (ductility) limit is defined, while the deformability isdefined as the point where the lateral resisting forces starts to decrease. For structuresdesigned by the inelastic displacement concept possess a large margin up to the actuallimit of collapse. However, a general method of evaluating the collapse limit is notyet established and the response with strength deterioration is not clear.In addition to these two performance objectives, restorability or reparability areidentified in the new Guidelines. This might not be a basic performance objectiveconceptually, because most of the damage less than near collapse may be regarded as"anyhow restorable." However, it has often been pointed out after the experiences ofrecent major earthquake disasters in urban areas such as Northridge and Kobe, thatthe reparability, which means whether economically reparable or not, could also beone of the most explicitly important performances for the owners and often be criticalperformance objective for the designers.Ideally, the criteria should be established by quantifying the damage level ofstructural and nonstructural members such that economically allowable repair ispossible, i.e., by taking into account estimated cost for restoration after earthquakes,where the diminished basic performance of safety and serviceability caused by theearthquake shall be restored to the required levels. In the Guidelines, the reparabilitylimit state is mainly defined based on the residual crack widths instead of repair cost.29