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a b s t r a c tHybrid Fibre Concrete (HFC) is a self-compacting high-performance cementitious composite materialwith a high-strength mortar matrix reinforced by steel fibres. HFC structural walls are characterized bythe presence of conventionalmild steel flexural reinforcement and the absence of shear and confinementreinforcement. The function of the last two reinforcements is taken over by the fibres of HFC. This paperpresents the experimental and numerical investigation of the hysteretic behaviour of threeHFC structuralwalls and shows that the proposed structural system is able to provide large inelastic deformationcapacity while ensuring a superior post-earthquake functionality compared to conventional reinforcedconcrete.The test units were cantilevers featuring either a rectangular (Test Units W1 and W2) or a barbelledcross-section (Test Unit W3). 53196
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The fibre volume fraction of the HFC used for the construction of the testunits ranged between 3.5 and 6%. In order to ensure the formation of a suitable plastic hinge at the baseof the cantilevers, the flexural reinforcement of all three units was artificially debonded from the HFCby means of steel pipes (sleeves) that were slid onto the reinforcing bars. In order to prevent slidingshear deformations at the construction joint between the footing and the wall, the steel sleeves werepartially embedded into the footing acting as dowels. HFC prevented spalling of the concrete cover,hence preventing buckling of the flexural reinforcement. Despite the absence of shear reinforcement,the test units failed in flexure. Because not only shear but also confinement reinforcement was not usedand because of the self-compacting properties of HFC, the construction of the test units was a lot easiercompared to conventional reinforced concrete structural walls.The proposed numericalmodelswere able to predict the global behaviour of the test unitswhile at thelocal level the agreement between the experimental results and the numerical simulation was not verygood. The main reason for this disagreement is the lack of accurate information about the cyclic tensilebehaviour of HFC. 1. Introduction1.1.
Statement of the problemThe ability of the capacity design method to ensure depend-able ductile behaviour of reinforced concrete (RC) structures isproven by a large amount of evidence worldwide [1,2]. However,the ductile behaviour of such structures entails some disadvan-tages. To ensure enough inelastic displacement capacity, exten-sive transverse reinforcement for shear, confinement and stabilisa-tion of the longitudinal reinforcement is required in plastic regions,which often results in expensivemanufacture and time-consumingplacement of the transverse reinforcing bars, in reinforce-ment congestion and in concrete casting difficulties. The post-earthquake functionality of conventional ductile RC structures is also problematic because their plastic zones are typically affectedby spalling of cover and architectural concrete already at relativelyminor plastic deformations and because residual deformationsafter an earthquake are potentially large.The use of high-performance fibre-reinforced cementitiouscomposites (FRCC) to improve the seismic performance ofstructural elements has been investigated by many researchers inthe past and a comprehensive summary of possible applicationscan be found in [3] or in the literature survey presented in [4].As a further contribution towards the development of structuralsystems incorporating FRCC and in an attempt to reduce thedisadvantages of ductile reinforced concrete structures; this paperinvestigates the replacement of concrete with self-compactingHybrid Fibre Concrete (HFC) in the construction of structuralwalls. HFC is a FRCC featuring a high-strength mortar matrixreinforced by steel fibres of different dimensions and shapes. HFCis characterized by a high strength, a strain hardening behaviourand a smooth and controlled post-peak softening behaviour bothin compression and in tension. 1.2. Hybrid fibre concrete structural wallsThe behaviour of Hybrid Fibre Concrete (HFC) structural wallscan be better understood by making a comparison with thebehaviour of conventional reinforced concrete (RC) structuralwalls. Fig. 1a displays a conventional RC wall that was taken as abenchmark to assess the behaviour of different configurations ofthe HFC wall shown in Fig. 1b. For this purpose, the monotonicpushover curve of four different cantilever walls was computednumerically. The walls all had the geometry shown in Fig. 1.The footing was fixed to the ground, a constant axial load N D200 kN was applied and the pushover curves were computedby increasing the horizontal displacement at the location of theload V in order to track global softening of the walls. The mainproperties of the four walls are: (1) The “RC wall” is a conventionalRC wall with longitudinal reinforcement, shear reinforcement andconfined boundary elements for plastic deformation capacity. Thebehaviour of this wall was predicted using the software Response-2000 [5]. (2) The “HFC wall, no joint, no sleeves” is a HFC wallwith longitudinal reinforcement only. The shear transfer and theconfinement of the boundary elements are ensured by the HFC.The wall and the footing are cast at the same time and there areno sleeves on the longitudinal reinforcing bars. All HFC walls weremodelled using the well-known FE code ABAQUS [6]. (3) The “HFCwall, with joint, no sleeves” is a HFC wall similar to wall no. (2).However, it is cast in two lifts.