رفتار ساختاری نمونه عرشه پل تقویت شده تحت بارگذاری خستگی

The deterioration of concrete bridge decks that have been directly damaged by traffic loads affects their durability, safety, and function. It is therefore necessary to strengthen the damaged concrete structures. Even though there have been many experiments performed to investigate the static behavior of strengthened structures, few experiments or analyses have considered their fatigue behavior. In this study, fatigue tests were conducted on bridge decks strengthened using various fiber-reinforced polymer plastics, such as carbon fiber sheet, glass fiber sheet, and grid-type carbon fiber reinforced plastic. All of the strengthened specimens were shown to have an improved resistance to crack propagation and better stress distributions. The Weibull distribution was adopted to analyze the fatigue life of the decks. The fatigue life limits of the strengthened bridge decks were determined at higher stress levels, and the grid-type carbon reinforced plastic specimens proved to be the most effective.

Reinforced concrete bridge decks receive traffic loads directly. Structural damage can increase, such as residual deformation and numerous cracks, which eventually decreases the life of the deck as well as its load carrying capacity [1], [2], [3], [4] and [5]. In South Korea, there are many deck panels that have deteriorated after almost 20 years of service and which must now be rehabilitated. Many of these were designed for relatively low traffic loads rather than the heavy traffic (over HS25) found nowadays, and are only 18 cm thick. When such decks are strengthened, the overall structural performance must be improved, including their serviceability and fatigue resistance as well as the load carrying capacity. The flexural strength of a deck can be improved easily by applying external bonding techniques, using materials such as carbon fiber sheet (CFS) and carbon fiber reinforced plastic (CFRP) attached to the tension side of the concrete. However, it is fairly difficult to rehabilitate the fatigue resistance of a deck because the shear strength that has been decreased by repeated loads must be improved with the flexural strength. Previous research by the authors experimentally verified that the fatigue resistance of a deck that was externally strengthened with CFSs was improved even if no additional sectional enlargements of the deck were made [6]. This result presented the possibility of extending the life cycle of a deck panel without adding deadloads by using either mortar overlay or an additional internal stiffener. Although numerous research programs over the past decade have attempted to understand fatigue response and to establish a fatigue model for concrete subjected to repeated loads, the fatigue failure characteristics of strengthened concrete structures are not yet systematically established on a scientific foundation [7], [8], [9], [10], [11] and [12]. Much of the research for concrete structures has been limited to either a simple S–N relationship or a mechanical approach, because the analysis is too complicated to extend to an entire structural system from either the microscopic element or material points of view. The experimental and theoretical work presented in this paper is the result of successive research programs conducted at the Hanyang University in Korea to verify the structural efficiency of various fiber reinforced polymer (FRP) composites for strengthening concrete structures [6], [12] and [13]. The authors have persisted in developing rehabilitation techniques for deteriorated concrete structures for the past decade [6], [12] and [14]. A recent focus has been how to achieve additional benefits by applying FRPs to a deteriorated concrete member, either by extending its fatigue life or enhancing its serviceability. Improvements to both the fatigue and flexural resistance must be considered when rehabilitating a deteriorated concrete bridge deck. The experiments reported in this paper were conducted to find structural differences and efficiencies between slabs strengthened with various FRPs and subjected to cyclic loading [13]. We also attempted to verify the theoretical S–N relationship of strengthened deck panels through a probabilistic approach based on the test results. In this paper, CFS, glass fiber sheet (GFS) and grid-type carbon fiber reinforced plastic (GCFRP) were used as the strengthening materials.

Strengthening concrete bridge deck panels with various FRP materials can substantially increase fatigue life. The strengthening effect in fatigue loading was mainly influenced by the bonding characteristics between the strengthening material and the concrete surface. The compliance of strengthened decks when materials delaminated from the concrete either due to stress concentration or damage accumulation increased abruptly. The S–N relationship obtained from the tests and probabilistic analyses was used to predict the fatigue life of the decks. A probabilistic approach based on the Weibull distribution yielded appropriate results when compared with the actual fatigue responses of the deck specimens. The fatigue behavior of decks strengthened using GCFRPs and CFSs was more effective than that of the deck strengthened by GFSs. Therefore, the choice of strengthening material should depend on whether the purpose of the strengthening is to extend the fatigue life or to raise the design traffic loads of the bridge deck.