International Concrete Abstracts Portal

Over the last few years, the use of composite materials has become anincreasingly popular method of repairing and strengthening ageing civil engineeringstructures. However, despite the efficiency and attractiveness of this technique, itsmarket progression has been impaired by the relative lack of knowledge on the long-term behavior of the FRP materials themselves and, by extension, on the behavior ofthe structures strengthened with such products. The authors are conducting a 10-yearexposure test program on FRP products, and this paper provides midway results fromthe first 5 years of exposure data. There was no significant change in the tensilestrength of the CFRP laminates after a 5-year exposure, however in-plane shearstrength showed a slight decrease. Bending strength of matrix resin also decreased inthe early exposure stage. The results suggest a reduction of the bonding propertiesbetween carbon fibers and resin.

This research program was initiated to examine the feasibility of assessingthe blast-resistant capacity of reinforced concrete (RC) slabs using the displacementbased design (DBD) method. In order to achieve this objective, five RC slabs weretested under real blast loads in the out-of-plane direction. One of the slabs was usedas the control unit to establish a baseline for comparison in terms of performance forthe other four slabs, which were strengthened with fiber reinforced polymer (FRP) andsteel fiber reinforced polymer (SRP). The explosive charge weight and stand-offdistance required to impose a given damage level were predicted by the DBD method.Test results showed that the blast loads were effectively estimated and the damagelevels observed from the field tests correlated well with the predicted levels. Inaddition, test results corroborated that the blast-resistant capacity of RC slabs can beeffectively increased by strengthening using FRP composites. The main conclusion thatcan be drawn from these tests using improvised explosive devices (IDE) is that RC slabsretrofitted on both sides have a higher blast resistance capacity than those slabsretrofitted only on one side. This paper discusses these experimental results alongwith the analysis steps used to predict the blast charge and standoff distance toimpose a given damage level.

Recently, ISIS Canada studied the durability of GFRP in concrete in severalfield structures across Canada. The objective of the study was to provide theengineering community with the results of the performance of GFRP materials that havebeen exposed to the concrete environment in built structures. Cores of GFRP-reinforcedconcrete were removed from five field structures. Analytical methods, namely opticalmicroscopy, scanning electron microscopy and energy dispersive x-ray, differentialscanning calorimetry and infrared spectroscopy, were used to determine thecomposition of GFRP after being subjected to the alkaline environment of concrete forfive to eight years. Three research teams from four Canadian universities performedmicroanalyses of the GFRP and surrounding concrete independently. Results indicatethat no deterioration of GFRP took place in any of the field structures. No chemicaldegradation processes occurred within the GFRP due to the alkalinity of the concrete.The overall conclusion of the study is that GFRP is durable in concrete. Also, it wasconcluded that the CHBDC was conservative in its first edition by not permitting GFRP asprimary reinforcement. As a result of the study, the second edition of the CHBDC,currently in the final stages of approval, permits the use of GFRP as primaryreinforcement.

In this paper, a non-linear 3-D finite element analysis (FEA) model usingABAQUS (Hibbit, Karlsson and Sorensen, Inc. 2003) was developed to predict the cyclicbehavior of shear wall structures. In this FEA model, SPRING element is used to simulatethe constraint deformation due to fiber reinforced polymer (FRP) wrapping, andimproved concrete stress-strain curve is considered to account for the improvement ofstrength and ductility of concrete under FRP confinement. A damaged plasticity-basedconcrete model is used to capture the behavior of concrete under cyclic loading.Method to identify shear failure due to FRP debonding and FRP rupture in FEA is alsoproposed. The model is validated using the results from the experimental study. It isshown that the proposed model can predict the shear failure and cyclic hysteresisbehavior of GFRP-wrapped shear wall reasonably well.

The SPEAR (Seismic PErformance Assessment and Rehabilitation) researchProject is specifically targeted at existing under-designed structures and, in itsframework, the core of the experimental activity is the series of full-scale pseudo-dynamic tests on a torsionally unbalanced three-storey RC structure, carried out at theELSA Laboratory of the Joint Research Centre. As one of the main goals of the project isto pursue a better understanding of the potential of seismic rehabilitation methods, theexperimental activity of the SPEAR project has foreseen pseudo-dynamic tests both onthe ‘as-built’ and the FRP-retrofitted full-scale structure. In the paper, the strategy ofthe retrofitting intervention, consisting in the application of glass fiber wrapping, isdescribed and the performance of the specimen in the two different configurationsduring the PsD tests is described. Through the experimental data, the effectiveness ofthe retrofitting strategy is thus assessed.