International Concrete Abstracts Portal

The use of near surface mounted (NSM) fiber reinforced polymers (FRPs) is being increasingly recognized as a valid technique strengthening of concrete members. In case of elevated temperature or fire exposure however, the bond between the bars and the concrete will be lost very quickly due to the adhesive’s low glass transition temperature. Although recent studies have shown that the fire endurance of appropriately designed and insulated FRP strengthened RC members is satisfactory, the performance of FRP strengthening systems at high temperature remains largely unknown. To study the bond behaviour at elevated temperature between the NSM FRP bars and concrete a series of 18 double bond shear tests were performed at Ghent University. Results show that the failure load of NSM FRP strengthened concrete structures and the bond strength are influenced at values of temperature equal to or beyond the glass transition temperature. Failure mode changed by increasing the temperature.

Shear walls as an integral part of structures have revealed to be of prime concern following earthquake surveys over the past few years. It was observed that shear wall structures sustained less damage in comparison to structures that did not possess shear wall. Researchers on the basis of their post earthquake surveys concluded that shear wall buildings sustained damage as a result of design and construction work flaws. In this article test data of CFRP strengthened short RC walls is analyzed. Three RC shear walls, designed to fail in shear, were subjected to static and cyclic load tests in which the loading amplitude was gradually increased till specimen failure occurred. Two out of three walls were strengthened externally with the help of CFRP material and mesh anchors at the wall foundation joint. The experimental results analysis consists in cracking pattern, stiffness, ultimate load capacity, ductility and energy dissipation.

Review of previous experiments on brittle R.C. columns through FRP jacketing illustrates that the efficiency of FRP jacketing in strengthening applications is superior to that which is observed when jacketing is used as a repair means. Actually, performance of the repair appears to be related to the state of damage along the anchorage or lap splice of primary reinforcement sustained in the initial phase and whether these defects have been corrected or not, by additional measures such as concrete replacement in cases of cracked cover or by epoxy injections along the damaged anchorages, prior to FRP jacketing. Surprisingly, this type of repair proves more effective in elements that have failed in a brittle manner rather than in cases that have undergone extensive yielding; the reason for that is that brittle failure along the member length occurs before the anchorage of the reinforcement has sustained excessive yield penetration, which cannot be avoided in ductile member behavior. This issue is explored systematically through evaluation of the collective experimental evidence from tests on columns repaired with FRP jacketing after having sustained damage under combined axial compression and cyclic lateral displacement reversals.

Fiber reinforced cementitious mortar (FRCM) systems present a novel means of strengthening deficient concrete structures. They present a number of advantages over conventional externally bonded fiber reinforced polymer (FRP) systems. FRCM systems consist of open-weave polybenzoxozole (PBO) fabrics which are applied to structural elements, walls, domes, tunnels, or shells using cementitious mortars. They are breathable, non-combustible and non-flaming, and their performance in elevated service temperature environments is superior to common FRP systems. However, additional research on FRCM is needed, most importantly on their high temperature performance and their long term durability, before they can be widely applied with confidence. This paper reports on an ongoing experimental study into the performance of a specific FRCM system for concrete. Comparative tests on FRCM and FRP strengthened concrete prisms are presented. The superior performance of FRCM strengthening systems at temperatures between 50ºC (122ºF) and 80ºC (176ºF) is demonstrated. The effects of elevated service temperature environments on the bond between FRP strengthening systems and concrete are discussed.

Three fire tests were carried out on slabs reinforced with Glass Fiber Reinforced Polymer (GFRP) bars bent at the ends of the member and the results were compared to those of six tests conducted previously. The anchoring of the FRP bars in the zone of slab not directly exposed to fire at the end of the members, provided by bending the bar ends, revealed essential to ensures slab resistance once in the fire exposed zone of slab the glass transition temperature was attained and the resin softening reduced the adhesion at the FRP-concrete interface. Therefore similar good performances of some of the six concrete slabs previously tested were later obtained even if a shorter length of the anchoring zone not directly exposed to fire was adopted. The production process allowing the bar to be bent is easily implemented by FRP bars manufacturers owing technologically advanced systems.