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.

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.

The Modified Compression Field Theory (MCFT) was introduced almost 40 years ago as a simple and effective model for calculating the response of reinforced concrete elements under general loading conditions with particular focus on shear. The model was based on a smeared rotating crack concept, and treated cracked reinforced concrete as a new orthotropic material with unique constitutive relationships. An extension of MCFT, known as the Disturbed Stress Field Model (DSFM), was later developed which removed some restrictions and increased the accuracy of the method. The MCFT has been adapted to various types of finite element analysis programs as well as structural design codes. In recent years, the application of the method has been extended to more advanced research areas including extreme loading conditions, stochastic analysis, fiber-reinforced concrete, repaired structures, multi-scale analysis, and hybrid simulation. This paper presents a brief overview of the original formulation and its evolvement over the last three decades. In addition, the adaptation of the method to advanced research areas are discussed. It is concluded that the MCFT remains a viable and effective model, whose value lies in its simple yet versatile formulation which enables it to serve as a foundation for accurately solving many diverse and complex problems pertaining to reinforced concrete structures.

Recent advancements in measurement technologies make it possible to record the full field displacements and strains on the surface of test specimens, as well as to examine internal composition including the progression of cracking and other forms of damage. This data can greatly advance design code provisions, as well as support the creation, calibration, and validation of more complete analytical and numerical models. This paper presents the authors experience in the use and development of increasingly sophisticated measurement technologies over the duration of the 30 years that he has been conducting experimental research on structural concrete. The most advanced technologies that are discussed include coordinate measurement machines, digital photogrammetry, digital image correlation, and X-ray-micro-tomography. The paper will also introduce advancements and challenges to the post-processing of this complex and voluminous data for advancing models and practice.

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.