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.

Presents the background to Canadian Standard CSA A23.3 requirements for design of concrete wall buildings for seismic shear. Design provisions are simplified versions of general procedures that can be used to do refined calculations when needed. Design of squat walls utilizes a variable angle truss model with shear resistance of cracked concrete V_c=0 and inclination of diagonal compression θ chosen freely. Contribution of distributed vertical reinforcement to overturning resistance depends on wall height-to-length ratio. For flexural walls, θ used to determine steel contribution Vs depends on axial compression applied to wall, while V_c and maximum shear force to prevent diagonal crushing depend on inelastic rotation of wall. Thus, drift capacity of flexural walls may be limited by shear failure modes. CSA A23.3-2014 permits a lower-bound estimate of higher mode shear demand because analysis procedures do not account for shear ductility, maximum shear demand occurs during a single short pulse, and maximum shear force demand usually does not occur at the same time as maximum flexural demands. Shear strains of flexural walls may significantly increase interstory drifts at lower levels of a building where gravity-load columns are less flexible. CSA A23.3-2014 requires that gravity-load frames be design for the increased interstory drift demands.

An experimental program was carried out on full-scale precast pretensioned I-girders to study the influence on the shear response of carbon fiber reinforced polymer (CFRP) shear strips epoxied to the sides of the girders. The test program demonstrated that the CFRP shear strips were effective in increasing the shear strength of the webs and in controlling the shear crack widths. The shape of the I-girders makes it difficult to properly anchor the vertical shear strips. The curved epoxy transitions between the web and the flanges at the re-entrant corners together with the use of horizontal CFRP strips in the regions of the re-entrant corners helped to improve the anchorage of the vertical CFRP strips. The shear resistance components from the concrete, the stirrups and the CFRP shear strips, were determined experimentally and compared with analytical predictions. The results from this experimental study are compared with the test results from other researchers. The design approach of the 2014 Canadian Highway Bridge Design Code provides conservative estimates of the shear strength of the webs.

Much of the post-war reinforced and prestressed concrete infrastructure in North America and Europe is reaching its design life and engineers are in need of tools that can be used to assess the shear behavior of these structures. The Compression Field Theory (Collins, 1978) and the Modified Compression Field Theory (Vecchio and Collins, 1986) form the basis of a suite of design procedures and software that engineers can use to assess concrete structures subjected to shear. The complexity of these tools varies from simple hand calculations, such as the sectional design procedures or strut-and-tie procedures in CSA A23.3-14 and AASHTO-LRFD, to sectional software tools, such as Response-2000, and full finite element programs such as VecTor2. This paper describes how such tools can be used to evaluate shear-critical structures in the context of assessing inventories of bridge structures. A preliminary crack assessment procedure, capable of providing estimates of the residual capacity of bridge girders based on crack slips and crack widths, is also presented. This procedure is based on the Pure Mechanics Crack Model and builds on existing compression field approaches. The tool is envisioned as a means of moving from traditional bridge inspection procedures to more complex methods, based on the theoretical advancements that have been made over recent decades.

The cross-section and reinforcement in a concrete beam must be selected to provide sufficient strength at the ultimate limit state while limiting the service deflection to an acceptable magnitude. ACI 318 analytical models for flexural capacity and deflection of slender beams assume that plane sections remain plane after bending and perpendicular to the longitudinal axis, but this hypothesis ignores the presence of diagonal cracking and related deformations associated with the imposed shear. This paper reports on an analytical deflection model developed using simplifications to the Modified Compression Field Theory that superimposes contributions from the flexural deformations arising from member curvatures and the shear deformations arising from diagonal cracking. The model is shown to be in better agreement with test data than the ACI 318 deflection model that only accounts for curvatures. A parametric study was completed using the model to gain insight into the influence of beam span-to-height ratio and the longitudinal and transverse reinforcement ratios on beam deflection. Recommendations are made on using a holistic design approach to satisfy both strength and serviceability requirements for a given span-to-height ratio.