International Concrete Abstracts Portal

Editors: Carlos E. Ospina, Denis Mitchell and Aurelio Muttoni

fib Bulletin 81 reports the latest information available to researchers and practitioners on the analysis, design and experimental evidence of punching shear of structural concrete slabs. It follows previous efforts by the International Federation for Structural Concrete (fib) and its predecessor the Euro-International Committee for Concrete (CEB), through CEB Bulletin 168, Punching Shear in Reinforced Concrete (1985) and fib Bulletin 12, Punching of structural concrete slabs (2001), and an international symposium sponsored by the punching shear subcommittee of ACI Committee 445 (Shear and Torsion) and held in Kansas City, Mo., USA, in 2005.

This bulletin contains 18 papers that were presented in three sessions as part of an international symposium held in Philadelphia, Pa., USA, on October 25, 2016. The symposium was co-organized by the punching shear sub-committee of ACI 445 and by fib Working Party 2.2.3 (Punching and Shear in Slabs) with the objectives of not only disseminating information on this important design subject but also promoting harmonization among the various design theories and treatment of key aspects of punching shear design. The papers are organized in the same order they were presented in the symposium. The symposium honored Professor Emeritus Neil M. Hawkins (University of Illinois at Urbana-Champaign, USA), whose contributions through the years in the field of punching shear of structural concrete slabs have been paramount.

The papers cover key aspects related to punching shear of structural concrete slabs under different loading conditions, the study of size effect on punching capacity of slabs, the effect of slab reinforcement ratio on the response and failure mode of slabs, without and with shear reinforcement, and its implications for the design and formulation in codes of practice, an examination of different analytical tools to predict the punching shear response of slabs, the study of the post-punching response of concrete slabs, the evaluation of design provisions in modern codes based on recent experimental evidence and new punching shear theories, and an overview of the combined efforts undertaken jointly by ACI 445 and fib WP 2.2.3 to generate test result databanks for the evaluation and calibration of punching shear design recommendations in North American and international codes of practice. Sincere acknowledgments are extended to all authors, speakers, reviewers, as well as to fib and ACI staff for making the symposium a success and for their efforts to produce this long-awaited bulletin. Special thanks are due to Laura Vidale for preparing the bulletin for publication.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-315

Information is summarized on the behavior, evaluation and design of slab-column connections and flat plate/flat slab systems for three levels of structural performance: strength, strength combined with ductility, and strength combined with ductility and robustness.

Punching shear failure of reinforced concrete slabs has been examined by many researchers through laboratory experiments. However, the existing punching shear testing database cannot address all aspects of the punching shear stress transfer mechanism. Advanced 3-D finite element analysis (FEA) can be used to supplement the existing testing background and for parametric investigations. In this way, different aspects of punching shear failure may be explored in detail, to enable understanding of the phenomena that control the response and to support drafting design code requirements. This paper describes research on calibrating constitutive and finite element models in ABAQUS to capture punching shear behavior of concrete slabs. The coupled damaged-plasticity model is used for modeling the concrete. Two interior reinforced concrete slab-column connections previously tested under static loading are presented: one slab is without shear reinforcement (SB1) and the other slab is with shear bolts (SB4). The developed formulation is calibrated using the results for specimen SB1, where the tension stiffening response, the damage parameters and the support conditions are examined. Then, the adopted FEA and concrete model are used for the analysis of slab SB4, which was retrofitted with shear bolts. Finally, both test and numerical results are compared to the ACI 318-14 provisions.

Local yielding of the top flexural reinforcement above a column can induce punching failure. Slabs supported directly on columns without beams or shear capitals (flat plates) are vulnerable to flexure-induced punching failure when the amount of the flexural reinforcement above the column is not adequate. Provisions of ACI 318-14 and CSA A23.3-14 give the value of the nominal shear strength as function of specified concrete strength, geometry of slab and column and the shear reinforcement. The present research specifies the minimum amount and layout of flexural reinforcement that takes flexure-induced punching into account. These requirements are satisfied in current code design for many practical cases. A code change is proposed to cover all cases.

The two-way shear response of slab-column connections has been evaluated by a significant number of experiments. These experiments provide physical tests to examine and calibrate design methods. This paper documents an updated database of slab-column connection tests in the literature using consistent criteria for selecting key response parameters including the limiting lateral drift capacity and gravity shear ratio. The collected test results include interior reinforced concrete (RC) and post-tensioned (PT) concrete slab-column connections with and without shear reinforcement under combined lateral and gravity shear demands. The laboratory test data and specimen parameters are compared to current ACI design requirements and recommendations and trends are noted. As observed in previous studies, the laboratory test data indicates that the gravity shear ratio has a significant influence on the limiting lateral drift for both RC and PT slab-column connections without shear reinforcement. In general, the presence of shear reinforcement and prestressing improve the lateral drift capacity of slab-column connections. The ACI 318-14 relationship to evaluate the design lateral deformation demand for slab-column connections is reviewed with respect to the updated data. Possible modifications to this relationship for both RC and PT slab-column connections are presented.