بررسی آزمایشگاهی و تحلیلی تقویت اتصالات تیر به ستون بتنی آسیب دیده توسط ورقه‌های کامپوزیتی CFRP

نویسندگان
هاشم شریعتمدار 1
ابراهیم زمانی بیدختی 2
1 دانشگاه فردوسی مشهد
2 دانشگاه فردوسی مشهد- دانشکده مهندسی- گروه مهندسی عمران
چکیده
در این مقاله اتصالات خارجی تیر به ستون بتنی تحت اثر بارهای چرخه ای مورد آزمایش قرار گرفتند. پس از آسیب اولیه در نمونه ها، تقویت توسط ورقه های FRP انجام شده و اتصالات مجددا آزمایش شدند. سپس اتصال مبنا و اتصالات تقویت ‌شده با FRP توسط نرم‌افزار Opensees مدلسازی گردیده و نتایج با رفتار آزمایشگاهی آن‌ها مقایسه گردید. در ادامه تاثیر عواملی همچون افزایش بار محوری ستون و وجود دال عرضی متصل به تیر در حالت‌های با و بدون بار ثقلی بر روی کف بصورت تحلیلی با استفاده از نتایج مدلسازی مورد بررسی قرار گرفت. با توجّه به نتایج بدست آمده، با افزایش خسارت در اتصالات، ظرفیت باربری، سختی و استهلاک انرژی آنها کاهش می‌یابد. همچنین خسارت در اتصالات تا سطح آسیب اولیّه به میزان 1/5% دریفت طبقه با استفاده از ورقه‌های FRP قابل جبران می‌باشد. مقایسه‌ی پارامترهای لرزه‌ای اتصالات نشان می‌دهد افزایش بار محوری ستون از 5% به 10% ظرفیت فشاری اسمی مقطع ستون باعث افزایش 5 تا 12 درصدی ظرفیت باربری و سختی اتصال می‌گردد. بعلاوه، افزایش بار محوری اثرات چندانی بر افزایش انرژی تلف شده ندارد. همچنین وجود دال عرضی افزایش ظرفیت و استهلاک انرژی را در پی دارد. اثرات دال عرضی در حالت بدون بار ثقلی بیش از حالت وجود بار می‌باشد.

کلیدواژه‌ها

عنوان مقاله English

Experimental and analytical investigation of damaged concrete beam-column joints strengthened by CFRP composites

نویسندگان English

Hashem Shariatmadar 1
Ebrahim Zamani Beydokhti 2
1 Ferdowsi University of Mashhad
2 Ferdowsi University of Mashhad
چکیده English

The scope of this study is to investigation of the rehabilitation of concrete beam column joints retrofitted by use of carbon-fibre-reinforced plastics (CFRPs) to achieve a safe, economic and practicable level of seismic damage. This paper investigates analytically the efficiency of the strengthening technique at improving the seismic behaviour of damaged structures. 4 beam-column connections are tested under reversed cyclic load. The connections have none-seismic detailing of rebars, i.e. no transverse rebar and seismic stirrups are used in the joint core and beam and column critical end zones, respectively. The joints are damaged in different levels and then retrofitted by carbon fibre reinforced materials (CFRP sheets). The strengthened joints were tested again to reach the ultimate drift capacity. The experimental results show that the beam column joints could be retrofitted by external bonding of FRP sheets until a limited level. This level determined for tested joint approximately equal to 1.5% story drift. The specimens initially damaged until 1% and 1.5% drifts showed the capacity increase up tp 5% and 3%, respectively. If the damage level is higher than this repair-ability level, other rehabilitation methods may be useful. Then, to simulate the behaviour of joints, a numerical model was developed in the OpenSees framework version 2.4.0. The tested joints such as reference joint and retrofitted joints are analyzed by Opensees nonlinear software. The open source Opensees software has several models for concrete and reinforcement rebar materials possible for considering reloading / unloading stiffness deterioration and hysteretic energy dissipation during reversed cyclic loads. Also nonlinear beam-column elements with spread or concentrated plasticity make this nonlinear software capable for high accurate simulation. The analytical models are used to assess the efficiency of the CFRP rehabilitation to set an optimum level of damage that the seismic behavior parameters could be compensated, safely, economically and practicable. The results of joint analysis are compared with experimental behavior of specimens. The hysteresis curves of the modeled beam column joints had a high level of accuracy in terms of stiffness degradation, moment carrying capacity, capacity degradation and energy dissipation. So, the model is calibrated for each level of damage intensities. The results showed that the model had a good accuracy in terms of load carrying capacity, secant stiffness, energy dissipation and joint ductility and the error was less than 10% between analytical and experimental results. Then, the effct of some variables such as column axial load and existence of transverse slab connected to the beam was analytically investigated. The results showed that increasing the axial load on the column increased the load carrying capacity and stiffness from 5% to 12% (related to initial damage intensity of the joint), but it had negligible effect on dissipated energy. Also modeling of transeverse slab revealed an increasing effect on the capacity, stiffness and energy. The positive effect was higher in absence of gravity loads on the slab. So, existence of transeverse slab with gravity load had negative effect on secant stiffness in specimens with initial damage higher than 1.5% story drift.

کلیدواژه‌ها English

Beam-column connection
Rehabilitation
FRP sheets
Nonlinear Analysis
Performance level
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مهندسی عمران مدرس
دوره 16، شماره 5
آذر و دی 1395
صفحه 65-77