International Concrete Abstracts Portal

Editors: Denis Mitchell and Abdeldjelil Belarbi

This Symposium Volume reports on the latest information related to shear in structural Concrete. The volume contains 14 papers that were presented at the ACI Convention held in Salt Lake City on March 27, 2018. The symposium was sponsored by ACI/ASCE Committee 445 “Shear and Torsion”. This event honored Professor Michael P. Collins (University of Toronto) whose enormous contributions in the development of rational behavioral models for shear and torsion of structural concrete have been paramount.

The papers cover different aspects related to shear in structural concrete including: the size effect in shear for both structural concrete and reinforced masonry; developments of the Modified Compression Field Theory; aspects of shear strengthening using FRP strips; the role of experimental measurements in understanding shear behavior; accounting for shear deformations; sustained loading effects on shear in members without transverse reinforcement; crack-based assessment of shear; key aspects in the design of concrete offshore structures, behavioral models for coupling beams; finite element modeling of punching shear in slabs; and seismic design for shear.

Sincere acknowledgements are extended to all authors, speakers and reviewers as well as to ACI staff for making this symposium a success.

Nonlinear finite element analysis (FEA), when properly calibrated based on experimental results of reinforced concrete slabs, can be useful to perform parametric studies for the investigation of structural behavior and for the development of future design code provisions. In this paper, a study is presented on how certain modeling decisions influence the FEA results for punching shear analyses of reinforced concrete slabs. The “Concrete Damaged Plasticity” model which is offered in the commercial FEA program ABAQUS is considered to simulate the concrete slabs, where the calibration was conducted based on already tested slab-column connections. The calibrated model is further investigated to discuss the impact of numerous modeling parameters including the boundary and loading conditions, finite element mesh type and size, and the constitutive modeling of concrete. Selected parametric studies are presented and recommendations for each of the investigated parameters are provided to better understand the punching shear behavior of reinforced concrete slabs. The results from the analysis of tested slabs and the subsequent parametric studies using the calibrated model show that that the FEA can be used to predict the punching shear strength, deformation capacity and crack pattern of the slabs.

Professor Michael P. Collins has always stressed the need for proper and consistent design. He emphasized the need for understanding the overall structural response, and to apply first principles. I remember, from the University of Toronto many years back, his emphasis on free body diagrams, a tool for establishing an overview of the stress resultants in the structure.

For floating concrete structures, these aspects are even more important than for land based structures, as over conservatism may lead to a structure that does not float.

Structures in the sea will be increasingly important in the future.

Two research efforts supervised by the author of this paper and the significance of the findings of those research projects are used to facilitate the discussion to explain a couple of the challenges that the structural engineers faced in the recent past. These research programs are (i) development of the new Strut-and-Tie design provisions of AASHTO LRFD Bridge Design Specifications, and (ii) development of a new prestress loss calculation procedure.

This paper was prepared with the aim of contributing to a session organized to honor Professor Michael Collins of the University of Toronto. The discussion provided within this paper is founded on the teachings of Professor Michael P. Collins and on the experiences of the author as a graduate student. More specifically, the author of the paper had the privilege to learn from Professor Collins (i) the importance of accuracy in calibrating design provisions and (ii) the significance of reducing the design expressions down to the essential parameters. Thus, the research projects summarized in this paper serve to present examples for those important concepts and are from the personal experiences of the author.

Short coupling beams are susceptible to brittle shear failures that need to be suppressed with dense transverse and diagonal reinforcement. To reduce the amount of shear reinforcement and improve the service behavior, researchers have proposed a solution with steel fiber-reinforced concrete (FRC). However, while this solution is promising, there are no sufficiently simple mechanical models capable of describing the complete shear behavior of short FRC coupling beams. This paper proposes such a model based on first principles: kinematics, equilibrium, and constitutive relationships for the mechanism of shear resistance. The model is compared with tests from the literature and with a significantly more complex finite element model (FEM). It is shown that, while the proposed kinematic approach requires a straightforward input and negligible time for computations, it also provides a similar (or better) accuracy as the FEM with excellent shear strength predictions.