Abstract
Abstract This paper investigates the laboratory test results of 12 deep beams available in the literature, where the longitudinal reinforcement was anchored into the support using short straight bar anchorages. Four different specimen groups with three different shear span-to-depth ratios (a/d) were selected and most of the deep beams failed by strut crushing after yielding of the main longitudinal reinforcement. In order to investigate the behavior of the selected deep beams, an enhanced strut-and-tie model assuming geometrical adaptability (possibility of update in the dimensions of the struts and ties as the main tie starts to yield) is proposed. The analytical results obtained using this approach may be considered as much as accurate than some conducted complex nonlinear analysis considering smeared fixed cracking model and bond-slip behavior. However, an improvement on the effective strength factor of bottle-shaped struts by means of an iterative strut-and-tie model is needed, once the effective strength factor prescribed by NBR6118 (2014) has shown to be over conservative for all ranges of span-to-depth ratio (a/d) investigated. Finally, the obtained results indicated that short bar anchorages did not seem to influence significantly the shear strength of the deep beams investigated, especially the strength of bottled-shaped struts when appropriate crack control reinforcement is present.
Highlights
Schlaich et al [1] suggested the idea of subdividing a structure into ‘‘B-Regions’’ and ‘‘D-Regions’’, in order to develop a rational procedure to design reinforced/prestressed concrete structures
This paper investigates the laboratory test results of 12 deep beams available in the literature, where the longitudinal reinforcement was anchored into the support using short straight bar anchorages
Strut-and-tie models are constructed using an assembly of compression and tension members connected at joints to represent the real stress field in a structural member in a simplified manner
Summary
Schlaich et al [1] suggested the idea of subdividing a structure into ‘‘B-Regions’’ and ‘‘D-Regions’’, in order to develop a rational procedure to design reinforced/prestressed concrete structures. The parameters included in NBR6118 [2] mainly pertain to the effective strength to be assumed for concrete struts under different stress levels The introduction of this minimum guidance follows provisions contained in other structural codes around the world, as for example: ACI318-14 [3], EC2 [4] and FIB MC [5]. For prismatic struts or nodes where only struts meet (CCC nodes), i.e., elements where the level of transverse tensile stress may be neglected, Brazilian code suggests the following effective strength for design: fcd1 = 0,85.a v2.fcd (1). For bottle-shaped struts (struts subjected to significant transverse tensile stress) or nodes where more than one tie under different directions meet (CTT nodes), Brazilian code suggests the following effective strength for design: fcd2 = 0,60.av2.fcd (3). Actual proposed value seems to be more appropriate for bottleshaped struts with no reinforcement or skin reinforcement below a minimum ratio
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