تعيين ضريب شبه استاتيكي ديوارهاي خاك مسلح بر اساس عملكرد لرزه‌يي

Determination of MSE wall pseudo static coefficient based on seismic performance

برتري ديوار هاي خاك مسلح نسبت به ساير روش هاي پايدار سازي سبب گسترش روزافزون اين گونه سازه ها شده است. صرف زمان زياد و هزينه‌ي نسبتاً بالاي انجام تحليل هاي ديناميكي مبتني بر تاريخچه‌ي زماني سبب شده است تا روش تحليل شبه استاتيكي علي‌رغم نداشتن دقت مناسب، از اهميت و جايگاه خاصي برخوردار شود. عدم وابستگي اين روش به پارامترهاي موثر در عملكرد لرزه ‌يي سازه و درنظرنگرفتن مشخصات بار گذاري ديناميكي، از جمله نقاط ضعف اين روش به‌ شمار مي روند. اين پژوهش با كمك مدل سازي عددي تفاضل محدود كوشيده است تا با درنظرگرفتن مشخصات بارگذاري، ميزان تغييرمكان سازه‌ي خاك مسلح و مشخصات هندسي ديوار خاك مسلح، روش شبه استاتيكي اصلاح را اصلاح كند و درنهايت ضريب شبه استاتيكي به‌منزله‌ي تابعي از سطح عملكرد لرزه ‌يي و شتاب بيشينه معرفي شود. نتايج حاصله، نمايان‌گر دست بالابودن روش هاي طراحي موجود در مقايسه با روش هاي مبتني بر پايه‌ي تغييرمكان است.

The supremacy of reinforced soil walls in easy installation, flexibility and economical aspects in comparison with other stabilization technics has caused the widespread use of these structures. Observation of these walls during the earthquakes and also the experimental studies have shown their appropriate behavior and flexibility. Since these walls have adaptable flexibility, using them in seismic areas has widely developed. Therefore recognition of the seismic behavior of these structures is mandatory. The high costs and needed time of dynamic analysis based on Time-History analysis has caused that pseudo static method become more desirable in spite of lacking suitable accuracy. Independency of pseudo static analysis to effective parameters on seismic behavior of structures, and ignoring dynamic loading characteristics, are some of the deficiencies of this method. The current study, by finite difference numerical modeling, tries to suggest a design method based on displacement. In this case, loading characteristics, such as magnitude, frequency, peak ground acceleration and geometrical characteristics of reinforced soil structure are considered to correct the pseudo static method and finally introduce the pseudo static coefficient as a function of seismic performance level and peak ground acceleration. In addition, the authors have tried to simply suggest the equivalent harmonic load of selected acceleration records. Considering the loading parameters, mechanically stabilized earth wall parameters and type of the site have caused that the used method in this study leads to most efficient design in comparison with other current methods suggested in regulations that are usually based on limit-equilibrium concept. The outputs shows the over-estimation of current design method in comparison with displacement based method.