Experimental analysis of the shear strength of composite concrete beams without web reinforcement

• Published in: Engineering structures 2021-02, Vol.229, p.111664, Article 111664
• Main Authors: Rueda-García, Lisbel, Bonet Senach, José L., Miguel Sosa, Pedro Fco, Fernández Prada, Miguel Ángel
• Format: Article
• Language: English
• Subjects: Building codes; Cast in place; Composite beam; Composite beams; Composite materials; Concrete; Concrete slabs; Concrete structures; Cross-sections; Differential shrinkage; Failure analysis; Failure modes; High strength concretes; Horizontal shear strength; Precast construction; Reinforced concrete; Reinforcement; Shear strength; Shrinkage; T shape; T-shaped beam; Vertical shear strength; Webs (structural)
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2020.111664

•Shear in monolithic and composite concrete beams without stirrups was studied.•Slab width, interface, concrete strength and differential shrinkage were analysed.•The interface between concretes modified the critical shear crack direction.•The slab contributed to increase the shear strength of the composite specimen.•An over-strength of the T-shaped composite beams due to arching action was noted. Composite concrete members without web reinforcement are often used in precast construction. The contribution of the cast-in-place concrete topping slab to vertical shear strength has been traditionally disregarded. However, significant cost savings can result from designing and assessing these structures if this contribution is considered. This paper presents the experimental study of a series of 21 monolithic and composite (precast beam and cast-in-place slab) specimens without web reinforcement, and with rectangular and T-shaped cross-sections, failing in shear. The vertical shear strength was analysed by the following test variables: cross-section shape, the existence of an interface between different aged concretes, strengths of the two concretes and the differential shrinkage effect. From these experimental tests, it was concluded that the slab contributed to shear strength, the use of high-strength concrete slightly increased specimens’ shear strength and the differential shrinkage did not reduce shear strength. Specimens’ failure modes were analysed based on their shear transfer mechanisms, noticing that the arching action in the slab was considerable after critical shear crack formation. The vertical shear strength experimental results were well predicted by the codes’ formulations (Eurocode 2, Model Code 2010 and ACI 318-19) when composite beam depth was taken for the calculations instead of beam depth. Codes significantly underestimated the horizontal shear strengths of the composite specimens.