International Concrete Abstracts Portal

This paper presents pedagogical techniques used to teach detailing of reinforced concrete structures. Detailing includes the ACI 318 code specifications for reinforcement placement and layout in a structural component. Students sometimes view this topic as a set of rules and standards; however, students must also understand the reasons these specifications exist. Therefore, the authors include a variety of methods to address both how to apply detailing and why detailing matters. These methods allow students to make critical assessments and experience higher-order learning. The authors utilize a variety of active and student-centered learning methods to teach the topics of detailing. The specific approaches discussed within this paper include skeleton-style notes, case studies, field work, experiential learning opportunities, projects, and the inverted classroom. This paper presents the pedagogical significance of each method, provides examples of implementing each method, and includes lessons learned by the authors based on their own implementation of these methods in the classroom.

Reinforced concrete bridge columns built prior to the enactment of seismic design and detailing requirements of modern codes of practice are vulnerable to seismic damage due to i) insufficient shear strength, ii) lack of concrete confinement and buckling of compression reinforcement, as well as iii) improper splicing of longitudinal reinforcement in potential plastic hinge regions. An innovative bridge retrofit technology was developed at the University of Ottawa, consisting of transverse prestressing to overcome all three deficiencies. Tests of large-scale bridge columns with circular square and rectangular cross-sections, with a shear span of either 1.5 m or 2.0 m, were tested to develop the technology. The results indicate that transverse prestressing provides clamping forces to control diagonal tension cracks, provides additional shear reinforcement and lateral concrete confinement pressure. It also improves the performance of plastic hinge regions with insufficient splice lengths by eliminating or delaying reinforcement slippage. As a result, the performance of seismically deficient columns can be improved substantially by the technique employed. Design procedures were developed to overcome all three deficiencies. The same technique is shown to be also effective as a column repair strategy for columns that have suffered from seismic shear damage.

Flat slabs with shear reinforcement not properly detailed and anchored as stated by ACI have been used in practice due to simplicity and the gained construction speed. This paper presents the results of 12 tests on slab-column connections with closed stirrups with anchorage variation and prefabricated truss bars as punching shear reinforcement. The behavior of the slabs, in terms of cracking pattern, displacements, and shear reinforcement strains, were analyzed, and ultimate loads were compared with estimations by ACI 318-19. Comparisons with the reference slabs without shear reinforcement showed that these two types of shear reinforcement effectively increased the load-carrying capacity of the tested slabs. For tests on slabs with closed stirrups, it was observed that if ACI detailing rules are followed, improvements in response and ductility of the slab-column connections should be expected. In the case of the slabs with prefabricated truss bars, it was observed that they were able to reach levels of punching shear resistance close to those of a reference slab with well-anchored stud rails. In both cases, further experimental research is needed. ACI 318-19 presented safe strength predictions for the different types of shear reinforcement tested, and in the case of the prefabricated truss bars, this was due to the conservative limitations imposed for calculating the crushing strength of the concrete strut close to the column.

The probabilistic study of fire exposed structures is laborious and computationally challenging, especially when using advanced numerical models. Moreover, fragility curves developed through traditional approaches apply only to a particular design (structural detailing, fire scenario). Any alteration in design necessitates the computationally expensive re-evaluation of the fragility curves. Considering the above challenges, the use of surrogate models has been proposed for the probabilistic study of fire exposed structures. Previous contributions have confirmed the potential of surrogate models for developing fragility curves for single structural members including reinforced concrete slabs and columns. Herein, the potential of regression-based surrogate models is investigated further with consideration of structural systems. Specifically, an advanced finite element model for evaluating the fire performance of a composite slab panel acting in tensile membrane action is considered. A surrogate model is developed and used to establish fire fragility curves. The results illustrate the potential of surrogate modeling for probabilistic structural fire design of composite structures.

Fibre reinforced concrete (FRC) is becoming widely utilized in segmental linings due to the improved mechanical performance, robustness and durability of the segments. Further, significant cost savings can be achieved in segment production and by reduced repair rates during temporary loading conditions. The replacement of traditional rebar cages with fibres further allows changing a crack control governed design to a purely structural design with more freedom in detailing. Macro synthetic fibres (MSF) are non-corrosive and thus ideal for segmental linings in critical environments. Although fibre reinforcement for segments is relatively new, recent publications such as the ITAtech “Guidance for precast FRC segments – Volume 1: Design aspects” or the British PAS 8810 “Tunnel design – Design of concrete segmental tunnel linings – Code of practice” have now given more credibility to this reinforcement type and the basis for design. This paper presents and discusses the design methodology for precast tunnel segments and in particular the tasks associated with the use of MSF reinforcement. Temporary loadings as well as long term load behaviour will be addressed. A case history from the Santoña–Laredo General Interceptor Collector, currently under construction in northern Spain, will illustrate the specific benefits of MSF reinforcement for segmental linings.