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.The pushover curve of the “HFC wall with joint and sleeves” isvery similar to the curve of the “RC wall” with just the shape ofthe curve in the elastic deformation range being slightly differentbecause of the different cracking patterns. However, the bilinearapproximation of the two curves would be quite similar and,postulating a stable hysteretic behaviour, the seismic displacementdemand would also be similar for both walls [8].During the simulation with 500 mm long sleeves, the ultimatestrain of the longitudinal reinforcing bars was reached when thetop displacement was 100 mm (4.0% drift). Such a displacementcapacity, especially in terms of displacement ductility (12.5 in thiscase), is very large and it is unlikely to be required to survive even asevere earthquake. However, the displacement capacity of thewallcan be adjusted to the effective needs by changing the lengths ofthe sleeves,making thiswall very suitable for seismic applications.The intention of this short case study was to qualitativelydescribe the problems arising with the design of HFC structuralwalls and to suggest a strategy to overcome them. Parra-Montesinos and co-workers also investigated the behaviour ofstructural walls incorporating FRCC and they proposed a differentstructural solution which was better adapted to the mechanicalproperties of the FRCC they used and which differed noticeablyfrom HFC [9]. In the following Sections 2 and 3 the experimentalbehaviour of three HFC structural walls is presented while inSection 4 a numerical model for the simulation of such walls isdiscussed. A more detailed description of the experimental resultsand of the numerical model is available in [4].2. Test units2.1. Geometry and reinforcementThe test units represent approximately 1:3 scale models ofstructural walls that could be used to stabilise multi-storeybuildings. No specific prototype buildingwas defined. Aspect ratio,nominal axial load and reinforcement content were chosen basedon previous experience making the most of the proposed testsetup [10].Test Units W1 and W2 had a 900-mm-long and 100-mm-widerectangular cross-section as shown in Fig. 3. Test UnitW3 featuredan I-shaped cross-section with 190-mm-long and 100-mm-wideboundary regions; the web zone was 520 mm long and 52 mmwide. The flexural reinforcement was the same for all test unitsand consisted of 6 reinforcing bars D12 in the end regions of thecross-section and of 10 reinforcing bars D5.2 in the web region.The location of the flexural reinforcement of Test Units W2 andW3 close to the centreline of the section was chosen in order toallowfor a larger thickness of the cover concrete. The shear and theconfinement reinforcementwere provided by the fibres of HFC andno additional horizontal reinforcing barswere placed. In the plasticzone of Test Unit W1 500-mm-long plastic sleeves were usedwhile for Unit W2 and W3 200-mm-long steel sleeves were used.In the first unit the sleeves were located above the constructionjoint while in the other units the sleeves were embedded in thefooting over half of their length. The justification for this differencebetween the test units is discussed in Section 3.The units were all built in the same way. First the footing waspoured. After a curing time of about a week the rest of the wallwas poured creating a construction joint just above the footing. Thewalls were built in upright position and HFC was poured from thetop. Table 1HFC mix designsTest Unit W1 W2 W3Batch V3.3 V4.2 V4.3Short straight steel [% .kg=m3/] 1.5 (117) 3.0 (234)fibres .D0:15 6 mm/Medium straight steel [% .kg=m3/] 0.5 (39) 1.5 (117)fibres .D0:20 12 mm/Long crimped steel [% .kg=m3/] 1.5 (117) 1.5 (117)fibres .D0:60 30 mm/Cement CEM I 52.5R [kg=m3] 1000 961Fly ash [kg=m3] 168 161Silica fume [kg=m3] 95 91Aggregate 0/1 mm [kg=m3] 754 725Water [kg=m3] 215 218Superplasticizer [kg=m3] 20 19Water/binder ratio [–] 0.17 0.18Table 2Mechanical properties of HFC at day-of-testing (D.o.T)Test Unit W1 W2 W3Age [d] 48–50 69–91 70Cylinder strength f0c [MPa] 154 3.6 139 6.4 135 4.3Cube strength fcw [MPa] 157 6.2 158 6.7 158 9.13-pt. bending strength fct [MPa] 26.6 2.0 41.4 5.7 45.6 5.5Modulus of elasticity Ec [GPa] 41.4 1.0 39.9 0.6 39.9 0.22.2. Material propertiesThe HFC considered within this project was developed by theInstitute for Building Materials (IfB) at the ETH Zurich [11] and bythe Department of Design and Construction at the Delft Universityof Technology [12]. Themixes thatwere used to build the test unitspresented in the previous section were designed by the formerinstitution, and their detailed composition is given in Table 1. It isimportant to note, that despite the high fibre content, the HFC hadself-compacting properties. However, several trial batches wereneeded to adjust the rheology of HFC and avoid segregation [4].The mechanical properties of HFC were measured in a series ofdifferent tests and are summarized in Table 2. The compressivestrengths f0cand fcw were obtained from D150 300 mm cylindersand from cube specimens with 150 mm sides, respectively, andthe relevant stress–strain relationships are plotted at the top ofFig. 4. The tensile properties of HFC were characterized by meansof 3-point bending tests on 70 70 280 mm prisms using aspan of 220 mm. The force–deformation curves for the mid-spanvertical deflection of the prisms are plotted at the bottom of Fig. 4.The tensile strengths given in Table 2 were computed by simplypiding the mid-span bending moment by the elastic modulus ofthe section.For the reinforcement of the test units “Grade C” reinforcingsteel according to [13] and with the mechanical propertiessummarized in Table 3 was used.2.3. Test setup, instrumentation and loading historyThe test setup is depicted in Fig. 5. The test units were fixedto the strong floor by means of a steel footing. The lateral loadwas applied to Test Units W1 and W2 by a 250 kN, 250 mmservo-controlled hydraulic actuator. The actuator wasmounted ona reaction frame in line with the strong direction (North–South) ofthe test units and positioned 2500 mm (Aspect ratio of 2.8) abovethe footing of the test units. On the other hand, Test Unit W3 wasloaded bymeans of a 500 kN, 100mmservo-controlled hydraulicactuator positioned 1700 mm (Aspect ratio of 1.9) above the testunit footing. To prevent out-of-plane deformations a side restraintwas provided at the top of all structuralwalls. A constant axial loadof 200 kNwas applied to all test units bymeans of hollowcore jacksand two post-tensioning rods running fromthe steel footing to thetop of the units. The axial load was kept constant during testingbymeans of a load-follower that was connected to the hollow corejacks.The instrumentation of Test Unit W2 is shown in Fig. 6. Theinstrumentation of the other test units was similar and is givenin [4]. In total, 26 hard-wired devices were used to monitor thebehaviour of the test unit. In addition,