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Dowel action of the longitudinal reinforcement in RC beams without and with small amounts of shear reinforcement is typically considered a constant shear contribution determined from the splitting strength of the concrete cover. However, in a recent experimental investigation by the authors, it was shown that the shear force transferred by dowel action for beams without shear reinforcement should be determined from the dowel displacement and a linear elastic model and a rigid plastic dowel model. This article is aimed at extending this model to also cover members with small amounts of shear reinforcement. To that aim, a novel approach to calculate the shear force carried by dowel action of the longitudinal reinforcement in both beams with and without shear reinforcement is presented. The model is derived by establishing an equilibrium of work between the internal stored elastic or dissipated plastic energy and the external work performed by the shear force in the dowel. Additionally, a method to determine the displacement of the dowel from DIC measurements is presented. For the remaining shear‐transfer actions, reasonable constitutive models from the literature are adapted. On the basis of DIC measurements, the shear force carried by each of the shear‐transfer actions is calculated for 16 shear tests of beams without and with small amounts of shear reinforcement. The sum of shear force carried by each of the shear‐transfer actions is shown to predict the applied shear force fairly well, from the development of the critical shear crack until failure. Additionally, it is shown that for beams with shear reinforcement below the minimum requirements according to the current design standards, the shear capacity is governed by aggregate interlock, residual tensile stresses, and the inclination of the compression chord. While for beams with shear reinforcement above the minimum requirements, the shear capacity is governed by the shear reinforcement and dowel action. [ABSTRACT FROM AUTHOR]

Small amounts of shear reinforcement are often assumed to increase the shear capacity of RC beams, compared to an identical beam without shear reinforcement. However, in a recent experimental campaign, the shear capacity of beams with a shear reinforcement ratio below the minimum requirements according to the design standards turned out to be similar to identical beams without shear reinforcement. This paper presents a detailed analysis of why the shear capacity may be similar for beams without‐ and beams with small amounts of shear reinforcement. This includes the influence of small amounts of shear reinforcement on the shear behaviour and shear‐transferring mechanisms. The analysis shows that the crack development is more severe at the ultimate load for beams with a small amount of shear reinforcement compared to beams without shear reinforcement. This more severe crack development is shown to cause an overestimation of the shear contribution from aggregate interlock when applying a well‐known constitutive model often used for beams without shear reinforcement. Therefore, a new expression for the aggregate interlock stresses is proposed. A comparison of the proposed expression with Mixed‐Mode crack opening tests shows a good agreement with the test for both small and large crack openings. By applying the proposed expression on the measured crack kinematics it is shown that for a large shear contribution from aggregate interlock the shear contribution from the shear reinforcement is very limited and as the aggregate interlock stresses decrease the shear contribution from the shear reinforcement increases. This shift in the governing shear‐transferring mechanism can help to improve the requirements for the minimum shear reinforcement often found in the design standards. [ABSTRACT FROM AUTHOR]

Dowel action is a well-known phenomenon in shear-related problems within structural concrete. The tests previously reported in the literature to evaluate this contribution in reinforced concrete beams without shear reinforcement were conducted without any initial activation of the tensile reinforcement. This paper presents the experimental results of dowel tests, performed in a novel experimental test setup. The test setup reflects more realistically the conditions of the tensile reinforcement in reinforced concrete beams without shear reinforcement. The test setup enables a realistic tensile activation of the longitudinal reinforcement before applying the dowel force. The tests show that even a low activation of the tensile reinforcement results in the development of horizontal- and inclined cracks, even before the dowel force is applied. This shows that the contribution from dowel action of the tensile reinforcement is not just simply governed by the splitting strength of the concrete cover. A method to determine the displacement of the dowel from photogrammetric measurements is presented. In addition, a linear elastic- and a rigid-plastic mechanical model are presented for estimating the shear force transferred by the tensile reinforcement in RC beams without shear reinforcement. The estimates are based on measurements of the dowel displacement. Comparison of the presented model and the experimental results shows fairly good agreement. • Presents a novel dowel test setup with a tensile activation of the reinforcement • The tensile activation induces cracks before the dowel force is applied • The shear force carried by dowel action depends on the dowel displacement • An elastic- and a plastic mechanical dowel model is proposed • Comparison of proposed models with the experimental results shows a good agreement [ABSTRACT FROM AUTHOR]

• A novel carbon-efficient 3DCP beam design with a 200% higher strength-to-weight ratio than a full 3D printed beam. • Data-transfer tool from the digital modelling environment to the Finite Element Analysis workspace. • Finite Element Analysis which accurately predicts the capacity and failure mechanism found from structural testing The paper presents a workflow for the design, material testing and numerical simulation of shape-optimised reinforced 3D Concrete Printed (3DCP) beams tested structurally in three-point bending. Building upon previous research on structurally optimised toolpath planning for 3DCP, the presented work suggests a method for the computational design optimisation process based on material efficiency principles and the parallel development of a lossless data transfer tool from the 3D modelling environment to a Finite Element Analysis (FEA) workspace taking into account the layered process characteristic of 3DCP and the consequent weak interactions generated between adjacent printed concrete filaments. The proposed FEA model was calibrated through cored cylindrical specimens and then applied to the design, fabrication and experimental testing of a proof-of-concept shape- and infill-optimised 3-metre simply supported beam. The comparative analysis of simulation and structural testing proves the reliability of the numerical model, which correctly estimated peak load and damage patterns for 3DCP. The tests highlight how, with a shear failure mode, the dominant cracks start from the support region and reach the area of load application. The presented work advances the research in 3DCP by developing 3DLightBeam+, a carbon-efficient reinforced concrete beam design with a 200% higher flexural strength-to-weight ratio than a full comparable beam. The beam is conceived through a seamless workflow for its FE analysis and structural verification that accurately predicts structural capacity and behaviour without destructive testing methods. [ABSTRACT FROM AUTHOR]