اثر تيپ‌بندي اعضا روي رفتار لرزه‌اي قاب‌هاي

Investigation of Grouping Effect in Seismic Behavior of R. Concrete Frames

از عوامل موثر بر رفتار لرزه‌اي سازه‌ها كه طراحي، به آن وابسته است، تيپ‌بندي المان‌هاي سازه‌اي هنگام آزمايش و طراحي است. تيپ‌بندي كه بيشتر به خاطر آساني اجرا و سادگي كار انجام مي‌شود، روي رفتار لرزه‌اي سازه اثر مي‌گذارد. در اين پژوهش اثر تيپ‌بندي ستون‌هاي بتن‌ آرمه روي رفتار غيرخطي سازه‌هاي 4، 8 و 12 طبقه بتن‌آرمه و پاسخ‌هاي سازه مانند بيشينه تغيير مكان و شاخصهاي خسارت (با تيپ‌بندي و بدون تيپ‌بندي) بررسي شده است تا نتايج مثبت و منفي اين تيپ‌بندي‌ها كه اكنون در طراحي و اجراي سازه مرسوم است، روشن شود. سازه‌هاي مورد نظر با ركورد زلزله طبس با شتاب‌هاي بيشينه (PGA) گوناگون ارزيابي ديناميكي غيرخطي شد و شاخص‌هاي خسارت برپايه‌ي المانها، طبقات و نيز شاخص‌هاي كلي خسارت بر پايه‌ي شاخص خسارت Park-Ang-Wen، محاسبه و ارايه شده است. نتايج ارزيابي،گوياي كم بودن اثر تيپ‌بندي در PGAهاي كمتر از 0.5g بر خسارت كلي سازه است و از روي ديگر نشان مي‌دهد كه در PGAهاي بزرگ‌تر، سازه هاي تيپ‌بندي شده دچار خسارت‌هاي بيشتري مي‌شود. تيپ‌بندي المان‌هاي سازه‌اي باعث تمركز انرژي و خسارت در المان‌هايي مي‌شود كه نسبت نيرو به ظرفيت المان (DE/CE) در تراز بالاتري قرار دارد؛ اين پديده باعث ايجاد طبقات نرم در سازه و بيشتر مواقع افزايش خسارت كلي سازه مي‌شود.

One of the problems that influence on seismic behavior of structures and associate designing to itself is the grouping of structural element within analyzing and design of structures. Generally this grouping is due to facilitate of performing the structures. This paper investigates these grouping effects on behavior of concrete structures with RC bending frame systems andmoderate ductility scale. Study cases that is used for assessment of these grouping effect contains buildings with 4, 8 and 12 story RC structures. Each of these buildings designed one time without grouping and several times with grouping consideration about columns of structures in the height direction of buildings.Codes that are used for design purposes are Iranian Seismic code and RC structure design code. IDARC program V7.0 is utilized for estimation of damage indices, maximum story drifts or displacements and energy dissipated by building structural systems to comparing thenonlinear seismic behavior of column grouped and non-grouped structures. Damage indices calculated by this program is based on modified Park-Ang-Wen model and represented individually by elements, stories and a total damage index. The selected structures are analyzed with nonlinear dynamic analyzing method under Tabas earthquake record using several peak ground accelerations (0.35g, 0.50g, 0.75g and 0.90g) and pushover analysis with force-control and displacement-control methods. Maximum responses such as maximum displacements, damage indices(with grouping and non-grouping design method) were used to realization result of this designing method.Comparing the result of nonlinear analysis showed increasing of damage with increasing of PGA. This is due to a better distribution of forces in the elements of structures in case of non-grouped designed structures. Analytical results showed that the effect of grouping in PGA less than 0.5g is not sensible, but in larger PGA the grouped designed structures suffer more damages. The grouping of structural elements causes to concentration of energy in elements that their demand to capacity ratio (DE/CE) is greater than others.This causes that these elements embroil more damage and save other element from greater damage.One of the other results of this designing method (Grouping of element) is formation of soft stories in the structure. Also the reason of this behavior is due to lumping of hysteretic energy on these stories. This subject causes to generate soft and weak story in the structure and increase the overall damage indices.Furthermore result of pushover analysis showed that grouped element structures have a more stiffness and so in a weak earthquake (a low PGA) have a less or equal damage index in comparison to non-grouped element structures. As an overall result determined when DE/CE for all elements is close to each other distribution of damage is uniform and vice versa.