Analysis of shear-transfer actions on one-way RC members based on measured cracking pattern and failure kinematics

Shear in one-way reinforced concrete (RC) members is transferred in cracked concrete members by a number of actions such as aggregate interlock, residual tensile stresses, dowelling action, inclination of compression chord and transverse reinforcement (if available). The amount of shear transferred by each action is significantly influenced by the cracking pattern (shape of shear cracks) and by the kinematics at failure (opening and sliding of the cracks). In this paper, the activation of the various shear-transfer actions is investigated for one-way RC members. This is done by using a set of detailed measurements on the cracking pattern and actual kinematics at failure recorded on a number of specimens (beams) with a very low amount of transverse reinforcement. The amount of shear transferred by each action is estimated on the basis of available physical models and compared for the various specimens. The results show rather good predictions in terms of strength by following this approach. Consistent explanations of the shear transferred by each action are provided.

An analysis of the shear-transfer actions in reinforced concrete members without transverse reinforcement based on refined experimental measurements

Francesco Cavagnis, Miguel Fernández Ruiz, Aurelio Muttoni

A traditional difficulty in the understanding of the role of the various shear transfer actions in members without transverse reinforcement has been a lack of detailed measurements on the development of shear cracking and their associated kinematics during the process of failure. In this paper, this issue is addressed on the basis of an experimental program on 20 beams investigated by means of digital image correlation. The measurements are shown to allow a clear understanding of the mechanisms leading to shear failure and their evolution (transfer of forces between the various potential shear-carrying actions) during the loading process. The amount of shear carried by the various potential shear-transfer actions is estimated for varying levels of load accounting for the cracking pattern and actual kinematics on the basis of fundamental constitutive laws for concrete and steel. The results are shown to be consistent and provide a rational basis for the understanding of the phenomenon of shear transfer in reinforced concrete members without transverse reinforcement.

2018

Shear failures in reinforced concrete members without transverse reinforcement: An analysis of the critical shear crack development on the basis of test results

Francesco Cavagnis, Miguel Fernández Ruiz, Aurelio Muttoni

Shear in concrete members without transverse reinforcement can be carried by various potential sheartransfer actions, whose activation depends much on the actual cracking pattern and kinematics at failure. Failures can occur in a progressive manner (at the end of a stable propagation of a critical shear crack) or in a sudden manner (by an unstable progression or development of a new crack). In addition, the development and shape of the failure crack may also be very different from case to case. These differences influence which shear-transfer actions may be governing for a given member and loading situation. Despite the large number of specimens tested in shear, almost no information on the actual crack development during the process of failure is yet available. This paper presents the results of an experimental programme consisting of thirteen beams. The tests were designed to investigate different structural systems and loading conditions commonly found in practice (cantilevers with concentrated and distributed loading, single span beams with distributed loading and continuous beams). The cracking patterns and their associated kinematics were tracked in detail by using photogrammetric techniques at high frequencies during testing and particularly during the process of failure, providing data on the actual crack development leading to shear failure. The observations show that very different cracking patterns may be found and that they might be also developed in different manners. The results are interpreted with reference to the measured crack kinematics and related to the various potential shear-transfer actions, with the aim of providing a useful material towards the development of rational approaches for shear design.

Engineering structures2015

From experimental evidence to mechanical modeling and design expressions: The Critical Shear Crack Theory for shear design

Miguel Fernández Ruiz, Aurelio Muttoni

Many research efforts have so far been devoted to the topic of shear design of members without transverse reinforcement since the first development in structural concrete. This has allowed a number of significant advances in the understanding of the phenomenon, which is currently acknowledged to depend upon a number of shear-transfer actions in cracked concrete such as aggregate interlocking related to crack opening and sliding, the residual tensile strength of concrete after cracking, dowelling of the reinforcement and the inclination of the compression chord. In the last years, independent teams of researchers have confirmed this by means of detailed measurements on tests performed with Digital Image Correlation and by integrating constitutive laws governing the transfer of shear. In agreement to the observed physical reality, clear and scientifically based theories have been developed allowing researchers to reproduce the shear response in a realistic manner and to perform more accurate predictions on the strength of members. One of these theories, grounded on experimental facts and supported by mechanical modeling, is the Critical Shear Crack Theory (CSCT). In this paper, the fundamentals of the theory are reviewed, linking them to the experimental response of beams in shear. Based upon these fundamentals, a general physical-mechanical model is presented to implement the CSCT basic ideas. On the basis of these results, the aptness of defining a criterion to assess failures in shear is justified, which can be formulated in a simplified manner and is suitable for design. The aim of this criterion is to lead to consistent design expressions, sufficiently simple to be used in practice. It is particularly interesting that the mechanical basis of the model allows natural reproduction of physical phenomena, such as size and reinforcement strain effects, that can be assessed in an accurate manner considering the nonlinear response of a potentially cracked reinforced concrete member. This approach is consistent with the underlying physics and is significantly more general than approaches followed in the past, where empirical formulas were corrected with a size effect term to account for this phenomenon (imposing an effect on a formula which is not necessarily consistent or valid outside its ranges of calibration). Based on the evidence reviewed, this article replies in a scientific, detailed, and transparent manner to a number of criticisms by A. A. Donmez and Z. P. Baant on the assumptions of the CSCT.

2019

From experimental evidence to mechanical modeling and design expressions: The Critical Shear Crack Theory for shear design

Miguel Fernández Ruiz, Aurelio Muttoni

2019