چكيده به لاتين
Revision of seismic design provisions into the establishment of the more efficient strategies for structures design is considered during the last decades. In this regard, performance based design procedure is developed by the researchers and investigators from around the world. From the point of selecting analysis procedure or on the other hand determining of parameters as the performance index, the mentioned approach should be investigated and discussed. Self-determination of performance purposes regarding to various risk level could be considered as an advantage of applying the performance based analysis and design that plays a key role in optimized economical designs. The bridges are the most important civil structures that are constructed in the form of national projects and their quality and quantity is considered as an index of development of the countries. In addition to what was mentioned, considering damages to this type of strategic structures and determine the amount of during strong ground motion and even time spent on repairing process as purpose function through the performance based design procedure.
This study investigates the effects of effective duration of earthquakes on performance indexes as a topic, which has been less considered. To meet the purposes of this study, the structure of a four span box girder bridge with span length of 31.0 meters and the width of 17.0 meters is simulated. This is done through the powerful nonlinear analyzing educational software called OpenSees. Nonlinear time history analysis considering two different risk levels is preformed, as a collection of 100 records of earthquakes with various effective duration was applied. The performance indexes such as drift ratio, rebar strain, concrete strain and ductility of bridge piers were monitored and the maximum amount of are extracted during 200 series analysis.
Result establishes that the effect of increasing the effective duration of an earthquake on the performance level of a concrete box girder bridges is highly depended on the approach of duration determination. Macro properties of bridge structures such as ductility demand and their performance level are not affected by increasing the effective duration of strong ground motion, and this is regardless of not only the level of risk even effective duration determination approach, whereas micro properties such as strain levels of concrete and steel rebar and their performance level are severely affected by increasing the effective duration of strong ground motion. It should be mentioned that the latter case is also regardless of not only the level of risk even effective duration determination approach.
Keywords: Performance level analysis, Effective duration, Concrete box girder bridges, Significant time duration, Bracket duration
