Due to the rapid increase in traffic volumes, existing infrastructure demands proper assessment and in some cases rehabilitation is needed. Prestressed concrete (PC) I‐shaped girders are widely used in prefabricated girder bridges. With sequel generations of shear design provisions their shear capacity might need to be increased in the framework of assessing safety of aging bridges. Earlier attempts in shear strengthening this specific type of girder with fiber reinforced polymers (FRP) has shown early debonding along the concrete surface at the web‐flange corner so that the increase in shear strength was very limited. This study presents the results of full scale PC I‐girders strengthened with CFRP through epoxy bonded concrete in‐fill blocks that locally transforms the I‐section to a rectangular section at the position of CFRP strips. This transformation eliminated the early debonding of CFRP shear reinforcement and for the studied configurations a 30%–40% increase in shear capacity was obtained with respect to the unstrengthened control specimen, without and with additional CFRP spike anchors, respectively. In comparison, similar configurations without in‐fill blocks reached 5% and 12% increase in shear capacity, respectively. As such, the use of in‐fill blocks appeared more effective than local anchorage of the CFRP at the web‐flange corner. Analytical verification of the experimental results confirmed that existing formulations lack ability to predict the shear capacity of strengthened I‐girders, and further work is needed in this respect.

A number of attempts were made by different researchers in the last couple of decades to strengthen prestressed concrete (PC) I-girders in shear using externally bonded FRP (fibre reinforced polymer) reinforcement. The unanimous observation reported in the literature is the early debonding of FRP shear reinforcement around the internal angles of the I-section. Because of this undesirable phenomenon, the strength of the FRP is utilized inefficiently. This paper gives an overview of the techniques utilized in the past and their relative performance in order to develop a rational solution to the debonding problem, particularly for I-sections. The anchoring techniques used in the past includes different types of FRP anchors as well as mechanical anchors to protect FRP shear reinforcement from debonding on the I-section. It can be concluded that the definite solution to the debonding problem on I-sections has not been obtained yet. This is because of the complex failure modes of FRP shear reinforcement and PC I-girders.

Seeking optimal material distribution in a nuclear system to maximize a response function of interest has been a subject of considerable interest in nuclear engineering. Examples are the optimal fuel distribution in a nuclear reactor core to achieve uniform burnup using minimum critical mass and the use of composite materials with an optimal mix of constituent elements in detection systems and radiation shielding. For such studies, variational methods have been found to be useful but, they have been used for standalone analyses often restricted to idealized models, while more elaborate design studies have required computationally expensive Monte Carlo simulations ill-suited to iterative schemes for optimization. Such an inherent disadvantage of Monte Carlo methods changed with the development of perturbation algorithms but, their efficiency is still dependent on the reference configuration for which a hit-and-trial approach is often used. In the first illustrative example, this paper explores the computational speedup for a bare cylindrical reactor core, achievable by using a variational result to enhance the computational efficiency of Monte Carlo design optimization simulation. In the second example, the effect of non-uniform material density in a fixed-source problem, applicable to optimal moderator and radiation shielding, is presented. While applications of this work are numerous, the objective of this paper is to present preliminary variational results as inputs to elaborate stochastic optimization by Monte Carlo simulation for large and realistic systems.

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively.