Dilum Fernando

Preparation and characterization of steel surfaces for adhesive bonding

AbstractIn fiber-reinforced polymer (FRP) strengthened steel structures, debonding of the bonded FRP reinforcement from the steel substrate may result from adhesion failure at the steel/adhesive interface or the FRP/adhesive interface, cohesion failure in the adhesive, or a combination of these two modes. Of these failure modes, cohesion failure in the adhesive is the preferred mode of failure as it facilitates the development of a design theory based on the adhesive properties; the other two failure modes should be avoided if at all possible. This paper presents a systematic experimental study to identify a surface-adhesive combination that will avoid adhesion failure at the steel/adhesive interface. Different steel surface preparation methods, including solvent cleaning, hand grinding, and grit blasting, and different commonly used adhesives were examined in the study. Surface characterization using three key parameters (namely surface energy, surface chemical composition, and surface roughness and topo...

Behavior of CFRP Laminates Bonded to a Steel Substrate Using a Ductile Adhesive

Strengthening of steel structures with adhesively bonded carbon fiber–reinforced polymer (CFRP) laminates (or plates) has received extensive research attention over the past few years. Existing studies have revealed that debonding of CFRP plates from a steel substrate is one of the main failure modes in such CFRP-strengthened steel structures. To better understand and model debonding failures, the behavior of CFRP-to-steel bonded joints needs to be well understood. Recent tests conducted by the authors’ have demonstrated that the bond strength of such bonded joints depends significantly on the properties of the adhesive used, and more specifically on the interfacial fracture energy rather than the tensile strength of the adhesive. The study has also showed that the bond-slip curves for nonlinear ductile adhesives have an approximately trapezoidal shape. This paper resents an analytical solution for the full-range behavior of CFRP-to-steel bonded joints with a ductile nonlinear adhesive. Predictions from the analytical solution are presented to explain the different stages of debonding failure and are compared with test data to demonstrate the validity of the analytical solution.

Treatment of Steel Surfaces for Effective Adhesive Bonding

In the FRP strengthening of steel structures, cohesion failure in the adhesive is the preferred mode of debonding failure at FRP-to-steel interfaces so that the design theory can be established based on the properties of the adhesive. In this paper, results from a systematic experimental study are presented to examine the effects of steel surface treatment and adhesive properties on the adhesion strength between steel and adhesive. The test results show that adhesion failure can be avoided if the steel surface is grit-blasted prior to bonding and the treated surface can be characterised using three key surface parameters.

A methodology for the prediction of structure level costs based on element condition states

The determination of work programmes for bridges that maximise benefit to all stakeholders requires consideration of not only the condition of the elements of which a bridge is comprised, but also the performance of the structure as a whole. This is required because although some costs can be related to the condition of the elements, others, such as the costs of travelling over the bridge, cannot. One possible methodology to do this involves linking relevant costs to structure performance states (SPS) that are determined from the element condition states (CSs). However, even a bridge with a moderate number of elements and element CSs results in a large number of possible SPSs and an unwieldy amount of required work to estimate the costs associated with each. This work can be drastically reduced, however, by exploiting the almost linear system behaviour of the bridge that can occur between many combinations of element CSs. This article presents a methodology for relating SPSs to element CSs for the purpose of determining structure level costs. This methodology is demonstrated in several examples, wherein the effects of exploiting the linearity of the system behaviour to reduce the computational effort are also explored.

Total Cost-Benefit Analysis of Alternative Corrosion Management Strategies for a Steel Roadway Bridge

This paper describes a methodology for evaluating alternative corrosion management strategies for a steel roadway bridge based on a total cost-benefit analysis. In this analysis, the impacts of girder type and preservation intervention selection on the bridge owner, users, and public are considered. The methodology is demonstrated for a steel girder bridge in Wallis, Switzerland. Painted carbon steel and unpainted weathering steel girders are investigated. The investigated preservation interventions are the following: protection by painting, protection by metalizing, and replacement. Deterioration of the girders by corrosion is modeled probabilistically. Following the methodology demonstration, sensitivity studies are performed, wherein the corrosion environment, traffic volume, and detour length during interventions are varied. The effects of these variations on the various benefit types are then discussed and the conditions under which the various corrosion management strategies may be optimal are identified.

Fatigue strengthening of cracked steel beams with CFRP plates

Externally bonded FRP systems offer an attractive method to improve the fatigue life of steel beams. The fatigue performance of such a strengthened beam can be further enhanced by prestressing the bonded FRP reinforcement. While a number of studies have been conducted on the fatigue strengthening of steel beams using FRP, they have generally been concerned with the overall performance of the strengthened beam, with limited attention to the behaviour of the FRP-to-steel interface and its effects. Against this background, this paper presents the preliminary results of an ongoing experimental program aiming at investigating the behaviour and fatigue failure mechanism of FRP-strengthened cracked steel beams under fatigue cyclic loading, with particular emphasis on the debonding process of the FRP reinforcement and the effect of debonding on crack propagation. The effects of prestressing and debonding on the fatigue performance of the strengthened beam are clearly demonstrated by the test results.

A Process for the Development and Evaluation of Preliminary Construction Material Quantity Estimation Models Using Backward Elimination Regression and Neural Networks

During the early stages of a project, it is beneficial to have an accurate preliminary estimate of its cost. One way to make those estimates is by determining the amount of construction material quantities that are required and then multiplying the estimated construction material quantities by the corresponding unit cost. One advantage of making estimates in this way is that it allows for the segregation of quantities and costs. This way they can be updated separately as new information becomes available. They can also be tracked separately allowing decision makers to make better decisions about the project during its conceptual phase. There are several techniques that can be used to develop estimation models. The most common include regression analysis and artificial intelligence, such as neural networks. Work has been done, however, in a non-standardized way, leaving practitioners without guidance as to how to develop and evaluate models for their specific purposes. This can be seen in particular in the many different types of metrics used for the evaluation of models. The goal of the work presented in this article was to create a process to (1) develop models to be used to prepare preliminary estimates of construction material quantities taking into consideration the available data during the early stages of a project, and (2) evaluate the developed models using the Akaike information criterion. The proposed process is illustrated with an example in which data from 58 storage buildings was used to develop models to estimate the amount of concrete and reinforcement required using backward elimination regression analysis and neural network techniques. The developed models were then evaluated using a second-order correction Akaike information criterion (AICc) to select the most accurate model for each construction material quantity. The proposed process is useful for practitioners in need of developing robust estimation models in a consistent and systematic way, and the AICc metric proved to be effective for selecting the most accurate models from a set.

A hybrid methodology to estimate construction material quantities at an early project phase

Preliminary project cost estimates are the first serious estimates made on a project. They play an important role during the decision-making process, and are the benchmark with which future estimates are expected to agree. This paper concentrates on the estimation of construction material quantities (CMQs) and presents a methodology to accurately estimate them during an early project phase. We make use of existing data and utilize regression analysis, neural networks and case-based reasoning to provide accurate results. It encompasses data collection, model development and evaluation, and the integration of different techniques. The use of the methodology is demonstrated by estimating CMQs of relevant structures. The accuracy of the methodology is investigated and compared with three state-of-practice approaches. The results obtained show a significant improvement over the state of the practice, and would improve the accuracy of preliminary project costs estimates. Through partial automation, it would likely reduce the time required to make estimates.

A model for the evaluation of intervention strategies for bridges affected by manifest and latent deterioration processes

Markov models are often used in bridge management systems to evaluate intervention strategies (ISs) for bridges affected by manifest deterioration processes (MnDPs). These models do not directly take into consideration the effect of latent deterioration processes (LtDPs) on the object, i.e. the deterioration that might occur due to natural hazards (e.g. earthquakes and floods). In cases where there is a negligible probability of the occurrence of natural hazards, this is justified, otherwise it is not. In this paper, a model is proposed that can be used to evaluate ISs for bridge elements and bridges considering both MnDPs and LtDPs. The model is an extension of the Markov models, and includes condition states (CSs) that can occur due to both MnDPs and LtDPs, as well as the probabilities of transition (p.o.ts) between them. The contributions to the p.o.ts due to MnDPs are initially estimated using well-established methods and adjusted for the contributions to the p.o.ts due to LtDPs, which are estimated using fragility curves and adjusted considering element dependencies, i.e. how the elements of a bridge work together. The use of the model is demonstrated by predicting the future CSs of a bridge affected by both MnDPs and LtDPs.

Behavior and Modeling of CFRP-Strengthened Rectangular Steel Tubes Subjected to a Transverse End Bearing Load

The end bearing capacity of a rectangular hollow section (RHS) steel tube can be substantially increased through local strengthening using bonded carbon fiber reinforced polymer (CFRP) plates. This paper presents a combined experimental and numerical study into the behavior of such CFRP-strengthened RHS steel tubes with particular attention to debonding failure in such tubes. The results of an experimental study are first presented, which showed that debonding failure occurred in all the CFRP-strengthened steel tubes and the effectiveness of strengthening depended significantly on the slenderness of the webs. A finite element approach for modeling the behavior of such CFRP-strengthened steel tubes is next presented, in which a coupled cohesive zone model is employed to depict the response of FRP-to-steel bonded interfaces with a linear or a nonlinear adhesive. The finite element approach, which is shown to provide close predictions for CFRP-strengthened RHS steel tubes under an end bearing load, offers a valuable tool for understanding the behavior of these CFRP-strengthened steel tubes.