Special Topics

The publications listed below cover special topics including blast resistance and prestress losses. You can also check our engineering tools and/or submit your engineering inquiry.

Special Topics (prestress losses during pre-tensioning)

Khalia, M, Youssef, M.A., Alhadid, MMA, 2020, “Heat of Hydration Stresses in Stainless-Steel-Reinforced-Concrete Sections”, Sustainability (Special Issue: Sustainable Structural Design for High-Performance Buildings and Infrastructures), 12(12): 4852.

Stainless steel (SS) is increasingly used in construction due to its high strength and corrosion resistance. However, its coefficient of thermal expansion is different from that of concrete. This difference raises concerns about the potential for concrete cracking during the hydration process. To address this concern, a thermal-structural finite element model was developed to predict the stresses in SS-reinforced concrete (RC) sections during the hydration process. Different curing regimes were taken into consideration. The analysis was performed in two stages. First, a transient thermal analysis was performed to determine the temperature distribution within the concrete section as a function of concrete age and its thermal properties. The evaluated temperature distribution was then utilized to conduct stress analysis. The ability of the model to predict the stresses induced by the expansion of the bars relative to the surrounding concrete was validated using relevant studies by others. The model outcomes provide in-depth understanding of the heat of hydration stresses in the examined SS RC sections. The developed stresses were found to reach their peak during the first two days following concrete casting (i.e., when concrete strength is relatively small).

El Naggar, A, Youssef, MA, El Naggar, H, 2020, “Effect of Tunneling on Shallow Foundations”, ACEM20/Structures 20, GECE, Seoul, Korea, August.

Effect of tunneling on nearby structures must be assessed to eliminate the potential for structural failures. Such assessment requires a deep understanding of the soil-structure interaction (SSI) of buried and surface structures. This paper focuses on structures supported by shallow foundations and provides an assessment of the available numerical and finite element analysis techniques. The assessment is made based on the ability to capture: (1) the complicated nonlinear behavior of the soil and the tunnel, (2) the effect of surface settlement, (3) the development of earth pressure along the tunnel lining, and (4) the construction sequence. The paper also discusses the limitations and accuracy of the considered methods.

Alhadid M.M.A., Soliman A.M., Nehdi M.L., Youssef M.A., 2014, “Critical Overview of Blast Resistance of Different Concrete Types”, Magazine of Concrete Research, 66(2): 72-81. 

Past attacks against buildings and civil infrastructure highlight the need for blast-resistant structural materials. Numerous studies have been conducted on various related techniques and some design guidance has been developed to increase the resistance of structures to blast loading. Generally, a blast results in a high-amplitude impulse loading typically with a very short duration. Hence, the material’s response to such loading will differ from its response to regular types of loading. Consequently, the analysis and design of structures subjected to blast loads require a full understanding of the behaviour of materials and structural elements under blast loading. This paper presents an overview of the behaviour of concrete elements subjected to blast loads. A critical discussion of the state of the art on blast resistance of conventional and modern concrete materials is provided, along with an overview of effective retrofitting and strengthening techniques.

Robitaille S., Bartlett F.M., Youssef M.A., Tape W., 2009, “Evaluating Prestress Losses during Pre-Tensioning“, CD-ROM Proceedings, 2nd Canadian Society for Civil Engineering (CSCE) International Construction Specialty Conference, St. John’s, NL, 10 pp, DOI: 10.13140/2.1.2501.8885. 

Prestressing losses due to friction between strands and ducts are typically accounted for in post-tensioned concrete members. Similar losses that occur in pre-tensioned prestressed concrete members due to friction at hold-up and hold-down points are typically ignored. A clause in the recent AASHTO Bridge Specification, however, requires consideration of losses that may occur at hold-down devices without providing any guidance about how this should be done. This paper derives equations to predict losses at hold-up and -down points, describes the design and calibration of a unique load cell to measure prestressing strand forces, and presents typical friction losses measured for pre-tensioned members produced at the PSI plant in Windsor Ontario with predicted values. The observed losses can be accurately predicted using a simple pulley-belt friction model with a coefficient of friction of 0.29. Using this model, strand inclinations of more than 2.5 degrees would cause losses at the dead end of a single member of more than 5%.


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