International Concrete Abstracts Portal

This paper describes a simplified methodology to design masonry and concrete walls retrofitted with fiber-reinforced polymer (FRP) products to resist blast load. The wall is analyzed as an equivalent single-degree-of-freedom (SDOF) system responding in flexure to a spatially uniform blast load. The methodology provides specific guidance on how to define all the relevant properties of the equivalent SDOF system based on flexural and shear properties of the retrofitted wall using equations similar to those for static properties of retrofitted walls in ACI 440.2R responding in flexure. The methodology also provides response limits that give correlations between the calculated maximum dynamic response and the corresponding blast damage level to the retrofitted wall. The response limits can be used to design a blast resistant wall for a given amount of acceptable damage. This paper discusses the SDOF-based procedure, summarizes available blast test data on retrofitted walls, and shows comparisons between maximum deflections calculated with equivalent SDOF models of the test walls and measured values. Also, the development of the response limits is described with photographs of observed wall damage levels in shock tube tests.

Carbon Fibre reinforced Polymers (CFRP) have become an effective solution to upgrade and strengthen existing box girder bridges in flexure, shear and torsion. The introduction of CFRP strain limitations to prevent premature delamination together with the increasing strengthening demands and the necessity for use of fibres of increasing stiffness and thickness has resulted in a very poor CFRP material utilisation levels achieved in practice. An effective method to increase CFRP material utilisation is by appropriately anchoring the ends of the CFRP. In this paper, a study into CFRP end anchorage solutions is presented which formed the basis of the experimental program. Both uni-directional and bi-directional fabric was applied to the ends of CFRP laminates and tested under direct shear loading. Uni-directional fabric was oriented both horizontally across and parallel to the direction of the laminate. In all cases it was found that the anchorages solutions tested resulted in a distribution of fibre-to-adhesive bond stresses over a greater length, width of concrete and could potentially result full CFRP utilisation and laminate rupture.

Masonry buildings form significant part of the cultural heritage in the world. One of most important aspects for old and historical buildings is the vulnerability to lateral loads such as earthquake and wind loads and the need for appropriate strengthening. Fiber reinforced polymer (FRP) composite materials are developed options for strengthening of masonry buildings. The application of FRP composites as externally bonded reinforcement in repairing and strengthening the masonry walls has becoming more attractive than the traditional methods which are based on steel elements. Their excellent strength-to-weight ratio, easy installation and minimized damage for the existing structure made them the best option for strengthening of listed buildings and structures. In this research, an experimental study has been conducted to show the out-of-plane behavior of FRP strengthened large-scale masonry walls. The wall panels made of clay bricks have been investigated and the effectiveness of different type of FRP elements used for strengthening is analyzed.

Creep tests have been conducted on six commercial GFRP bars, pertaining to three different manufacturers, under two levels of sustained service load (nominally 15% and 30% of the ultimate tensile strength). The test duration was 10000 hours (417 days). At the end of the test duration, the samples were tested statically to infer upon their residual tensile properties. It is evident that GFRP bars with lower fiber content and/or bigger diameter exhibit higher levels of creep strain than their counterparts of high fiber content and smaller diameter. Residual tensile property tests show barely any change as to the bars’ longitudinal tensile properties. Microstructural analysis indicates that there is no degradation in the matrix or the fiber-matrix interface, within the GFRP bars after the lengthy duration.

Different strategies can be used to repair, rehabilitate and strengthen existing structures. Techniques based on Fiber Reinforced Polymer (FRP) materials appear to be innovative alternatives to traditional solutions because of their high tensile strength, lightweight, and ease of installation. One of the most common and useful FRPs is Carbon Fiber Reinforced Polymer (CFRP) sheets and anchors attached to strengthen the section through addition of tensile capacity. The purpose of this study was to develop a technique for assessing the strength of anchors for quality control. A method for assessing the quality of CFRP anchor installation was developed using plain concrete beams reinforced externally with CFRP sheets attached with epoxy and CFRP anchors. Under loading on the beam, a tensile force was developed in the CFRP sheets and a shear force on the CFRP anchors. The forces in the CFRP anchors were defined by the load applied to the beam and compared with forces based on measured stress in CFRP sheets.