اتصال اعضاي خمشي بتن مسلح پيشساخته با استفاده از بتن فوق‌ توانمند (UHPC)

Connection of Precast Reinforced Concrete Flexural members using Ultra High Performance Concrete (UHPC)

در اين پژوهش، براي بررسي مقاومت پيوستگي بتن فوق توانمند، 36 آرماتور فولادي از بلوكهاي بتني بيرون كشيده شدند. علاوه بر اين، تعداد 9 تير آزمايشگاهي كه هر يك از اتصال دو تير خمشي پيشساخته‌ي مجزا تشكيل شده است و همچنين يك نمونه‌ي بدون وصله در مقياس واقعي ساخته و آزمايش شدند، و به كمك نتايج آزمايش بيرونكشيدگي اثر پارامترهاي مختلف در پيوستگي بررسي شدند. مقايسه‌ي شاخص شكلپذيري نمونههاي تيري وصلهدار نشان ميدهد كه استفاده از بتن فوق توانمند در محل اتصال قطعات پيشساخته‌ي اعضاي خمشي باعث سادهسازي جزييات اتصال شده است. در اين نوشتار، يك رابطه‌ي طراحي براي تعيين طول وصله و مقدار آرماتور جانبي مورد نياز وصله ارايه شده است. مقدار ميانگين نسبت مقاومت پيوستگي آزمايشگاهي به مقاومت پيوستگي حاصل از رابطه‌ي پيشنهادي در نمونههاي ساخته‌شده از بتن معمولي 10/1 با انحراف معيار 05/0 و در نمونههاي ساخته‌شده از بتن فوق توانمند 27/1 با انحراف معيار 10/0 بهدست آمده است.

Ultra High Performance Concrete (UHPC) is an excellent material for the creation of filigree components. Its high ductility and endurance make it the ideal replacement for other materials, such as steel, in many areas. Ultra high performance concrete has very high endurance due to its low capillary porosity. Its high resistance to deicing salt makes it an interesting choice for use in surfaces frequently exposed to deicing salt. Ultra high performance concrete (UHPC) has the potential to greatly simplify construction joints in accelerated bridge construction by reducing the development length of reinforcing steel. The use of UHPC in highway bridges has recently begun in the connection between modular precast components. The potential for increased safety and quality that comes from the use of prefabricated components is enticing; however, there is also the recognition that the use of these components frequently necessitates the use of field cast connection details. Conventional construction practices for such connection details can result in reduced long-term connection performance compared to joined components. In this study, the bond strength between UHPC and reinforcing bars is investigated using pullout and spliced beam specimens. Thirty six pullout specimens and ten beam specimens were manufactured and tested. The effects of different properties such as concrete cover and top bar effect on bond strength are studied by pullout tests. The strength and ductility of 9 full scale flexural beams fabricated from two precast components and joined together with UHPC are investigated. The bond strength of spliced bars in joints is the main parameter of this investigation. One beam without spliced bars was cast as a reference specimen. Mid-span displacement and the applied load were obtained using a hydraulic jack, a load-cell, a LVDT and a data logger set. The load versus displacement relationship of beams was determined using the experimental data. A ductility ratio was used to evaluate the ductility of the specimens. Comparison between the load-displacement relationship and the ductility ratio of different specimens indicates that using UHPC in the connecting region of precast members leads to simplification of the connection details without loss of ductility and flexural strength of the beams.