Application of CFRP sheets with high fiber density in strengthening RC slabs subjected to fatigue load

H. K. Chai, H. Onishi, S. Matsui

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

Research and development on the strengthening of deteriorated reinforced concrete (RC) slabs of highway bridges by carbon fiber reinforced plastic (CFRP) sheets have been extensively carried out in recent years. One important property of the CFRP sheets that affects the effect of the strengthening work is the tensile stiffness, which is determined by their Young's modulus and unit cross sectional area. Therefore, it is anticipated that CFRP sheets with normal Young's modulus but high fiber density (high unit cross sectional area) can achieve strengthening effect equivalent to those with higher Young's modulus but lower fiber density. In other words, the low Young's modulus of the CFRP sheets can be compensated by its high cross sectional area to acquire desire effect of strengthening. The CFRP-concrete bond behavior determines the effectiveness of the strengthening. Thus, in the case of strengthening RC slabs subjected to fatigue loading, it is essential to investigate the durability of the bond and to clarify the debonding phenomenon. In this paper, investigations are carried out on the strengthening effect of the CFRP sheets with fiber density of 600 g/m2, which is higher than those of the commonly used CFRP sheets. The high-fiber-density CFRP sheets have two different knit structures, namely the laminate structure and the warp-knit structure, as shown in Figure 1. The warp-knit structure is introduced to increase the penetration of epoxy resin into the gap between bundles of wrapped carbon fibers, so that a stronger bond can be formed. Small-scale bond tests were carried out to investigate the durability of the CFRP-concrete bond. The testing instrument as shown in Figure 2 applied flexure load to the concrete prisms bonded by CFRP sheets. Under repeated loading, failure of the specimens was characterized as complete detachment of sheet at one of the concrete prisms of the specimens, which occurred abruptly when the debonding area became considerably large. Experimental results verified the excellent bond durability by single layer of the 600 g/m2 warp-knit type CFRP sheet, in which the fatigue cycles was approximately 3.3 - 5.0 times that of bond by double layers of the 300 g/m2 laminate type CFRP sheets. To investigate the effectiveness of the high-fiber-density CFRP sheets in strengthening RC slabs, fatigue tests on full-scale slab specimens were carried out by using the wheel running machine as (Figure Presented) presented in Figure 3. The testing machine simulates repeated horizontally moving wheel load similar to traffic load by heavy trucks on slabs. In the full-scale slab fatigue tests, the slab specimens failed in the form of punching shear of concrete. The debonding of the CFRP sheets from the tension surface of the specimens occurred as shown in Figure 4. By comparing the strain results of the CFRP sheets in small-scale prism tests and those of slab fatigue tests, it is concluded that the debonding of the CFRP sheets did not occur under flexure during the fatigue loading. It was actually initiated by peeling stress due to punching shear of concrete at the ultimate failure. The high-fiber-density CFRP sheets generally exhibited an excellent strengthening effect with fatigue life extension ratio of RC slabs at least equivalent to that of the slabs bonded with double layers of 300 g/m2 laminate type CFRP sheets. Furthermore, the extension in fatigue life of the strengthened slabs increases substantially if the concrete properties are good. Besides, equivalent strengthening effect can be obtained by CFRP sheets of different Young's modulus and fiber density, with the condition that they have similar tensile stiffness.

Original languageEnglish
Title of host publicationAdvances in Bridge Maintenance, Safety Management, and Life-Cycle Performance
Subtitle of host publicationProceedings of the Third International Conference on Bridge Maintenance, Safety and Management, 16-19 July 2006, Porto, Portugal - IABMAS '06
PublisherTaylor and Francis - Balkema
Pages1023-1025
Number of pages3
ISBN (Print)0415403154, 9780415403153
Publication statusPublished - 2006
Event3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost - Porto, Portugal
Duration: 16 Jul 200619 Jul 2006

Publication series

NameProceedings of the 3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost

Conference

Conference3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost
Country/TerritoryPortugal
CityPorto
Period16/07/0619/07/06

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