تاثير الگوهاي بارگذاري جانبي بر روي ضريب رفتار سازه‌ي‌ فلزي با شكل‌پذيري متوسط

THE EFFECT OF LATERAL LOADING PATTERNS ON SEISMIC MODIFICATION FACTORS OF MOMENT-RESISTANT FRAMES WITH MEDIUM DUCTILITY

در اين نوشتار، تاثير الگوي بارگذاري بر اضافه‌ مقاومت، شكل‌پذيري، و ضريب رفتار قاب خمشي با شكل‌پذيري متوسط با استفاده از تحليل استاتيكي غيرخطي و با تجزيه و تحليل ديناميكي غيرخطي بررسي شده است. تاثير پارامترهاي موثر ديگري بر روي ضريب رفتار از جمله نوع مقاطع ايراني (IPE, IPB) و امريكايي (W) به‌كار گرفته‌شده در طراحي، تعداد دهانه‌ها، و ارتفاع سازه ارزيابي شده است. نتايج نشان مي‌دهند كه روند تغييرات مقادير به‌دست‌آمده از تجزيه و تحليل استاتيكي غيرخطي با نتايج تجزيه و تحليل ديناميكي غيرخطي بر هم منطبق است و مقادير شكل‌پذيري و ضريب رفتار سازه‌هاي طراحي‌شده با مقاطع امريكايي بيشتر از مقادير سازه‌هاي طراحي با مقاطع ايراني است. همچنين با افزايش ارتفاع، شكل‌پذيري، و ضريب رفتار سازه براي هر دو نوع مقاطع به‌كار گرفته‌شده در طراحي تحت كليه‌ي الگوهاي بارگذاري جانبي كاهش يافته است. ضمناً با توجه به نتايج متوسط شكل‌پذيري و ضريب رفتار به‌دست‌آمده براي سازه‌هاي طراحي‌شده با مقاطع امريكايي تحت الگوي بارگذاري مستطيلي اصلاح‌شده و براي مقاطع ايراني، الگوي بارگذاري مثلثي- مستطيلي بيشترين مقدار را از خود نشان داده است.

Many seismic codes permit a reduction in design loads, taking advantage of the fact that the structures possess significant reserve strength (overstrength) and the capacity to dissipate energy (ductility). Overstrength and ductility are incorporated in the structural design through a force reduction factor or a response modification factor. The factor represents the ratio of the forces that would develop under the specified ground motion if the structure were to behave elastically to the prescribed design forces at the strength limit state. Such a design concept is based on the assumption that well-detailed structures can develop lateral strength in excess of their design strength and sustain large nonlinear deformation without collapse. The role of the force reduction factor is essential in designing the earthquake load-resisting elements. In documents such as ATC-19 and ATC-34 [1], the behavior factor was calculated as the product of three factors: overstrength factor, ductility factor, and redundancy factor. Many researchers have studied parameter influence on the seismic modification factors of different systems. Since the loading pattern can affect the structure of the hinges of the formed plastic, it can also influence the seismic responses of the structure, such as the behavior factor. In this research, the effect of lateral loading patterns on overstrength, ductility, and the seismic modification factors of moment-resistant frames with medium ductility, is investigated by nonlinear static analysis (pushover) and nonlinear dynamic analysis. Also, the effects of any other parameters influencing the value of the R factor, such as type of consumer sector, are considered, i.e; Iranian (IPE, IPB), American (W)), number of bays and height. The results show that the value variations of nonlinear dynamic analysis generally matched well with those obtained from the pushover analysis. Also, the results show that the value of ductility and the R factor obtained from the frames made for the American sector was more than the Iranian sectors under the same condition. Finally, according to the analysis results, the modified rectangular and the rectangular-triangular loading patterns make the highest R factor for American sectors and Iranian sectors, respectively.