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This Symposium Volume reports on the latest advancements related to the various facets of modeling and performance assessment of concrete structures. The volume contains 10 papers that were presented at the ACI Convention held in Toronto on April 1st, 2025. The symposium was dedicated to celebrate Prof. Frank J. Vecchio’s extraordinary research contributions and accomplishments in the development of behavioral models and analytical tools for the assessment of concrete structures. The papers cover different aspects related to modeling and performance assessment of concrete structures including developments of the Modified Compression Field Theory, finite element modeling of punching shear in slabs, behavior and modeling of steel fiber reinforced concrete members subjected to torsion, modeling of concrete structures subjected to impact loading, behavior and modeling of slender walls, modeling of concrete frame elements, behavior and modeling of GFRP reinforced members, crack-based assessment of concrete structures, and advancements in modeling deterioration mechanisms and repaired concrete structures. Sincere acknowledgements are extended to all authors, speakers and reviewers as well as to ACI staff for making this symposium a success. Anca-Cristina Ferche, Editor Vahid Sadeghian, Editor

The limited availability of research studies related to the behavior of Steel Fiber Reinforced Concrete (SFRC) members subjected to torsion has hindered the development of clear and reliable design guidelines. Recent efforts by various researchers have been devoted to the development of analytical models for predicting the torsional response of SFRC members, supported by experimental results which have highlighted the efficiency of steel fibers in improving the torsional resistance and stiffness. For beams subjected to moderate or low levels of torsion, steel fibers, even at moderate dosages, have demonstrated the potential to replace minimum conventional torsion reinforcement, thus providing significant advantages for practical applications. This paper presents a discussion of the recent developments in research related to testing SFRC members under pure torsion. A comprehensive database of experimental test data is collated to provide a state-of-the-art in this respect. Additionally, the manuscript delves into analytical prediction models for the torsional capacity by some European code-oriented models, recently introduced by the Eurocode 2 as well as by the Authors of this paper. The results of model predictions are compared with available experimental data to assess the effectiveness and reliability of the models.

As glass fiber-reinforced polymer (GFRP) reinforcing bars become more widely used, there is a need to better understand the behavior of GFRP reinforced members. GFRP reinforced deep beams are one example of concrete members that are not currently well understood. Besides the linear elastic behavior of GFRP material, another significant difference between GFRP and steel reinforcement is the difference in surface treatment. While deformation requirements are prescribed for steel reinforcing bars, FRP bars may have different surface treatments depending on the manufacturer. The different surface treatments lead to different bond characteristics and, ultimately, a difference in performance. This research explores the effect of bond through both an analytical study using VecTor2 and a series of large-scale deep beam tests reinforced with GFRP bars. Analytically, VecTor2 was able to capture the behavior of published experiments from the literature, reinforced with sand-coated GFRP bars. An alternative surface preparation consisting of machined indentations was introduced as a parameter in this study, resulting in significant changes in the performance and behavior of the deep beams. VecTor2 was also able to capture the behavior of these beams when adjustments were made to the bond model to match the observations of the experiments.

Developed 40 years ago by Frank Vecchio and Michael Collins, the Modified Compression Field Theory (MCFT) and its successor, the Disturbed Stress Field Model (DSFM), have proven to be robust methodologies in modeling the response of concrete structures. Originally developed for newly designed concrete structures, they have been refined over the years to expand their applicability to various engineering problems, including modeling deteriorated and repaired structures. This paper reviews the evolution and application of MCFT in modeling and assessment of deteriorated and repaired concrete structures. The first part focuses on the application of MCFT to advanced field structural assessment, including stochastic analysis procedures that incorporate field data. The second part discusses the evolvement of MCFT to account for two of the most common deterioration mechanisms, reinforcement corrosion and alkali-silica reaction. The last part explores the application of the model to structures repaired with fiber-reinforced polymer composites. It is concluded that the extension of the MCFT formulation has enabled it to reliably predict the behavior of both deteriorated and repaired concrete structures.

This theoretical study discusses the serviceability of reinforced concrete beams retrofitted with near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strips. Particularly, the research aims to understand the tension stiffening of the strengthened beams under varying degrees of steel corrosion. Five beams are modeled and analyzed, which represent different levels of deterioration up to 100 years. The effects of tension stiffening are evaluated at service and yield loads. Results show that the tension stiffening of the beams decreases as the cross-sectional area of the steel reinforcement reduces. Likewise, the yield and ultimate capacities of the beams diminish with the reduced steel reinforcement. The effective moment of inertia formula stipulated in ACI 318-19 appears to be applicable to the NSM CFRP-retrofitted beams.