New models for reinforced concrete precast hybrid deep beams under static loads with curved hybridization

Abstract

In this study, two innovative proposals of hybrid precast deep beams are suggested making of the arching action, tied arch and Strut-and-Tie (STM) models. The first one which is called as the “curved hybrid” that consisted of two type of concrete with curved layers while the second, which is termed as “arched hybrid”, consisted of using three layers of concrete that constitute a high strength concrete arch within the beam. The proposed models incorporated reducing weight with keeping capacity without significant drop and, may result in cost minimization. Eleven deep beam specimens with dimensions of (180 × 450 × 1700) mm have been tested experimentally up to failure under two systems of static loading. Several variables have been considered including; loading configuration, type of hybridization, density of concrete at the tension face and quantity of shear reinforcement. Results revealed that using the conventional hybrid model tested under two-point loading system improved the ultimate load by 27%. For the first proposal of arched hybridization, the improvement was 39%. For the second proposal of arched hybridization, the improvement was 45%. When testing deep beams under one-point load, the improvement was reduced by a range of (1–5) % relative to the control beam. Moreover, it is found that using lightweight concrete under the curved interface line instead of normal weight concrete resulted in reducing capacity by 1% for both systems of loading. Regarding ductility and toughness, enhancements ranged in (33–108) % and (140–375) % respectively under two-point loading. When testing under one-point load, the respective values are (7–48) % and (28–180) %.