بررسي آزمايشگاهي رفتار شالوده‌هاي ساخته‌شده با بتن سبك و مسلح‌شده با ميلگرد بسپاري (GFRP)

Experimental Investigation of the Behavior of Lightweight Concrete Footing Reinforced With GFRP Rebar

در اين نوشتار، كاربرد بتن سبك سازه‌يي در شالوده‌هاي پيش‌ساخته‌ي مسلح‌شده با ميلگردهاي بسپاري مورد مطالعه قرار گرفته است. براي اين منظور، 4 نمونه شالوده با مقياس واقعي مسلح‌شده با ميلگرد بسپاري )G‌F‌R‌P( بر روي بستر ماسه‌يي تحت آزمايش قرار گرفتند. يكي از اين شالوده‌ها با بتن معمولي و3 نمونه‌ي ديگر با بتن سبك سازه‌يي ساخته شدند. همچنين براي كنترل عرض ترك در يكي از نمونه‌هاي ساخته شده از بتن سبك از الياف پليمري )بتن سبك اليافي( استفاده شده است. با توجه به نتايج، كرنش ايجادشده در ميلگردهاي شالوده با بتن معمولي، به‌دليل پيوستگي بهتر بتن شالوده با ميلگرد بسپاري )G‌F‌R‌P(، تقريباً به 55% كرنش نهايي ميلگرد مي‌رسد، در صورتي كه در شالوده با بتن سبك، كرنش بيشينه به 27% كرنش نهايي ميلگرد مي‌رسد.

The subject of pre-fabrication plays an important role in the construction of standard structural members. To this end, it is needed to reduce the weight of these pre-fabricated members for ease of transportation. The application of lightweight concrete (LWC) and Fiber Reinforced Polymer (FRP) bars instead of normal concrete and steel bars inside the foundations is helpful in reducing the weight of pre-fabricated foundations. Application of Glass Fiber Reinforced Polymer (GFRP) bars in construction practices has been developed because of its unique properties, including corrosion resistance, high tensile strength, ease of performance and availability. Furthermore, the GFRP shows different behavior in concrete members, compared with normal steel reinforced bars. This behavior needs more consideration to show accuracy by appropriate testing methods. In this study, four specimens of full scale concrete footing reinforced by GFRP bars on the soil bed have been investigated. One of the specimens is made of normal weight concrete and three others are made of structural lightweight concrete. One of the lightweight footings contains polymer fiber, too. The constructed foundations were placed under compressive force, then the data related to LVDTs and strain gauges was recorded using a data logger; after that, it was analyzed. The results of this study indicate that further study is needed for real application of ACI relations to estimate the ultimate strength of lightweight concrete footings reinforced by GFRP bars. It was also concluded that the concrete mix can affect the maximum bearable load of footing, while adding fiber to concrete mix can be useful in order to control crack width. According to results, strain in normal weight footing bars gets almost 55% of the ultimate strain of the bar, because of the better band between the footing concrete and the GFRP bar. In lightweight concrete footing, the maximum strain gets 27% of the ultimate strain of the bar.