R Gravina

Deterioration Prediction of Timber Bridge Elements Using the Markov Chain

AbstractTimber bridges require high accumulated maintenance costs, which can be many times greater than their initial cost. Infrastructure managers need deterioration models to assist with making appropriate decisions concerning repair strategies and program maintenance schedules by accurately predicting the future condition of timber bridge elements. Markov chain–based models have been used extensively in modeling the deterioration of infrastructure facilities. These models can predict the condition of bridge elements as a probabilistic estimate. This paper presents the prediction of future condition of timber bridge elements using a stochastic Markov chain model. Condition data obtained from the Roads Corporation of Victoria, Australia, were used to develop transition probabilities. The percentage prediction method, regression-based optimization method, and nonlinear optimization technique were applied to predict transition matrices and transient probabilities from the condition data. The most suitable ...

An Evaluation of the Learning of Structural Engineering Concepts during the First Two Years of a Project-Based Engineering Degree.

In the modern working environment it is essential for a structural engineer to have an understanding of abstract concepts in structural behaviour and an ability to use them qualitatively. This paper presents the findings of a study on how effectively students acquire such conceptual understanding within a new project/design focused degree course. The new degree programme is described. The first-year students experience a mixture of learning opportunities, including model building/testing, laboratories, workshops/tutorials, and lectures. In the second year there are two design exercises but no formal structural theory course. Specific concepts-based learning material was introduced into the first-year course at mid-semester and the effectiveness of this examined by tests and interviews. The performance of the first-year students is compared to that of the second-year students. The findings show that there is good student engagement and satisfaction with the course and that basic skills are successfully being acquired throughout both years. However, the study highlights areas where concepts are not being adequately developed in the first year and subsequently show little enhancement in the second year.

Interfacial bond strength of resin-impregnated fibre-reinforced polymer laminates bonded to concrete using vacuum and heat: Experimental study

Two processing techniques commonly used in the repair of concrete structures via bond of fibre-reinforced polymer (FRP) onto the substrate are known as the pultruded plate and wet lay-up systems. The pultruded FRP plate and wet lay-up systems both involve the curing of resins of up to several days under ambient conditions to achieve full load capacity and rely on workmanship to achieve good bond. Hence, new techniques for the application of FRP that adopt a vacuum consolidation process and heat to impregnate FRP fibres with resin to improve the curing process, bond strength and speed of application are being developed. In this article, the interfacial bond behaviour of pre-impregnated FRP laminates attached to concrete in the presence of vacuum and heat is studied and compared to more conventional methods of FRP strengthening systems. Further the effects of bondline thickness on the bond performance of pre-preg FRP laminates are also studied whereby three different bondline thicknesses are examined. The interfacial bond thickness was changed by application of resin films between FRP plates and concrete surface.

Application of Heat/resin Injection in the Presence of Vacuum for FRP Attachments on the Concrete Substrate

Advanced processing techniques for the application of Fibre Reinforced Polymer (FRP) materials to repair concrete structures include the adoption of a vacuum consolidation process coupled with heat and/or resin injection to improve the curing process, bond strength and speed of application. The vacuum can contribute to the penetration of the resin into the surface around the exposed aggregates in order to achieve higher bond in strengthened elements. Since, debonding of FRP materials from the substrate is a brittle failure, it is essential to study this phenomenon and propose significant ways to improve the behaviour of the bondline. In this article, the interfacial bond behaviour of FRP laminates attached to concrete in the presence of vacuum and heat/resin injection is studied. The results of single lap shear tests have been utilized to investigate the capability of this system in strengthening of concrete elements. In this regard, several FRP-bonded concrete prisms will be examined in a single lap shear test set-up. Further, the effects of bondline thickness on the bond performance of adhesively bonded joints are studied.

Extraction and analysis of bond-slip characteristics in deteriorated FRP-to-concrete joints using a mechanics based approach

AbstractAdhesively bonding fiber-reinforced polymer (FRP) composites to reinforced concrete members is a simple and highly effective method to restore strength, increase loading capacities, and ext...

Influence of Surface Crack Width on Bond Strength of Reinforced Concrete

This paper reports the results of an experimental program to investigate the changes in the bond characteristics of deformed mild steel reinforcing due to chloride-induced corrosion. The principal parameters investigated are the cover depth, bar diameter, degree of corrosion, and the surface crack width. The results show a strong relationship between the average surface crack width and the average bond strength; the degree of corrosion does not demonstrate such a clear relationship. The bars with a 1 C/F (cover/diameter) show an initial increase in bond strength at the first visible crack; no similar initial increase is observed for the bars with 3 C/F. The bottom-cast bars display a higher bond strength with no corrosion, but a similar bond strength is observed for both top- and bottom-cast bars once cracking is observed.

Influence of the Processing Techniques on the Bond Characteristics in Externally Bonded Joints: Experimental and Analytical Investigations

AbstractThis paper investigates the bond characteristics between the concrete substrate and fiber-reinforced polymer (FRP) material processed with advanced manufacturing techniques. Tests provide further understanding regarding the interface behavior of the joints manufactured with a heated vacuum bag only (HVBO), vacuum-assisted resin infusion (VARI), wet lay-up, and pultrusion techniques. A specific criterion, the equalization of the processing techniques, is proposed to compare the characteristics of the joints. Based on the outcomes, the advanced processing techniques such as HVBO and VARI can be successfully applied to achieve a high-quality bond in strengthening of the reinforced concrete structures. Furthermore, a new analytical approach is presented to determine the interface behavior, which can be applied to any type of the FRP processing technique.

Review of the Performance of High-Strength Rubberized Concrete and Its Potential Structural Applications

Partially replacing concrete aggregates with recycled materials could help to combat the decreasing availability of some natural resources (like natural sand) and at the same time help to utilize growing quantities of waste material like used tires. This idea has been put into practice to develop a more sustainable concrete material called rubberized concrete or crumbed rubber concrete (CRC). CRC has improved structural ductility and impact resistance but can have lower strength than traditional concrete. Most research to date has focused on low strength CRC and its non-structural applications. However, recent research has shown that high-strength CRC (HSCRC) can be achieved through rubber pre-treatment, using various additives, optimal rubber content, or good grading of combined rubber sizes. This paper reviews the research undertaken to date in HSCRC (defined as compressive strength over 30 MPa), focusing primarily on the material properties but also considering the potential structural applications of HSCRC. Finally, the future research necessary to prove the viability of HSCRC for structural reinforced concrete applications is discussed.

Review of near-surface mounted FRP plates in the strengthening of continuous flexural members and bond behaviour

ABSTRACT Bonding carbon fibre-reinforced polymers (FRP) to reinforced concrete (RC) flexural members has become a popular means to enhance load carrying capacity and prolong service life. Considering the type of FRP strengthening system, the near-surface mounting (NSM) technique of embedding FRP strips in saw-cut grooves within the concrete cover of RC members to flexurally strengthen beams and slabs is known to have desirable bond behaviour benefits over external bonded FRP plates. Further the NSM technique has attracted growing attention in strengthening of statically indeterminate RC members. However, little is known about the durability of the critical bond between the embedded FRP and the concrete when installed using this technique. In this paper, experimental results of continuous flexural members strengthened with NSM FRP is collated and reviewed to investigate failure modes, ductility and moment redistribution capability. Ductility and moment redistribution characteristics of strengthened RC members relies on the bond performance of reinforcement to concrete and hence this paper also reviews durability testing of NSM joints. Regression analysis shows that concrete compressive strength and steel reinforcement ratios are paramount to maintaining ductility under all strengthening schemes.

Evaluating time-dependent reliability and probability of failure of reinforced-concrete bridge components and predicting residual capacity after subsequent rehabilitation

AbstractThe load-carrying capacity of reinforced concrete bridges can degrade over their service life through the initiation of deterioration mechanisms induced by fatigue, corrosion, cracks, and s...