ويژگي هاي مهندسي نانو- بتن سبك و اثر آن در رفتار لرزه‌يي سازه‌هاي ساختماني

Engineering Properties of Nano-lightweight Concrete and its Effect on Seismic Behavior of Building Structures

كاهش وزن ساختمان‌ها ضمن كوچك‌تركردن ابعاد اعضاي سازه ‌يي، موجب كاهش نيروي ناشي از زلزله نيز مي شود. براي كاهش وزن سازه مي‌توان از بتن سبك در اعضاي سازه ‌يي و غيرسازه‌يي استفاده كرد. به‌كارگيري بتن سبك در اعضاي سازه‌يي‌، نيازمند تامين كمينه‌ي مقاومت آيين‌نامه ‌يي است. براي تامين مقاومت كاهش‌يافته‌ي ناشي از سبك‌دانه، مي توان از نانوسيليس به‌منزله‌ي يكي از تقويت كننده ها استفاده كرد، كه علاوه‌بر افزايش سرعت هيدراسيون سيمان و واكنش با هيدروكسيد كلسيم، ژل سيليكات كلسيم هيدراته (C-S-H) تشكيل مي دهد، كه به مراتب مستحكم تر از هيدروكسيد كلسيم است. در اين نوشتار، ويژگي‌هاي مكانيكي بتن سبك ساخته‌شده از سبك‌دانه‌ي رس منبسط‌شده براي دو نوع بتن بدون نانوسيليس و با نانوسيليس مورد آزمايش قرار گرفته‌اند. نتايج نشان داده است كه در صورت افزودن نانوسيليس، ميانگين مقاومت فشاري 47%، مقاومت خمشي 57%، مقاومت شكافتگي 26% و مدول ارتجاعي 79% افزايش مي‌يابد. همچنين بررسي عملكرد سازه‌يي بتن سبك در اعضاي سازه‌يي و غيرسازه‌يي و بتن سبك داراي نانوسيليس در اعضاي سازه‌يي نشان داده است كه تغيير چشم گيري در رفتار لرزه‌يي ساختمان‌هاي بتن مسلح ايجاد نمي شود.

The weight of structural and nonstructural building elements is the main part of dead loads, which have a direct and considerable effect on the lateral load induced by earthquakes. The lower the dead load is, the lower are the structural element dimensions, which results in a lower lateral load induced by earthquakes. This is an important design key factor for high seismic countries like Iran. One of the methods to reduce structural weight is the use of lightweight concrete (LWC) for structural and non-structural members. LWC used for structural elements needs to attain the minimum strength recommended by the code of practice. Additives may be used in the mix design to recover the strength reduction caused by the use of light weight aggregates (LWA). To enhance the mechanical properties of LWC, it is recommended to add nano-silicate, which increases the cement hydration rate and reacts with calcium hydroxide to form hydrate calcium silicate gel (C-S-H). This is much stronger than calcium hydroxide. This paper reports the results of experimental and analytical investigation into the mechanical properties of LWC and nano-silicate lightweight concrete (NLWC), with optimum water-cement ratio, and the use of NLWC for structural members of four reinforced concrete moment resisting frames, with medium ductility, of six story building structures. All structures were analyzed according to the Iranian standard for seismic design of buildings (IS-2800) and designed on the basis of the Iranian concrete code of practice (ABA). Results indicated that mechanical properties were improved with nano-silicate material. Over 28 days, the compression, flexibility, splitting tensile strength, and the elastic modulus increased by 48, 57, 26 and 79 percent, respectively. Also, the results of nonlinear analysis of all structures with NLWC structural members show that their seismic behavior does not significantly change compared to that of similar normal weight RC structures. Finally, it is recommended to pursue research in this field to produce relevant seismic regulations.