As part of the EU-research project, called REDUCE, a load test to failure on a demountable composite cellular beam was carried out at Bradford University on 18th June, which proved to be successful. The 11.2m span cellular beam used a 305 x 305 x 97 kg/m UC bottom Tee and a 305 x 165 x 46 kg/m UB top Tee, which had an asymmetry of 2.4:1 in its flange areas.
The cellular beam was 427mm deep and had regular 300mm diameter openings at 450mm centre-centre spacing. The span: depth ratio of the cellular beam was 26, which is typical of composite construction designed for optimum serviceability performance. The test beam at its maximum test load is shown in Figure 1.
The composite beam used 20mm diameter bolted shear connectors cast into a 150mm deep composite slab. The bolts were connected by nuts above and below the top flange and so could be detached with the slab by un-tightening from below. To facilitate re-use of the slab and the beam, a 120mm deep double edge trim was also cast into the slab along the centre-line of the beam and the bolted shear connectors were placed either side in a staggered pattern. The double edge trim provided a cut-line in the slab that could be demounted by being sawn into segments and unbolted, and then re-assembled for a second cycle of use as a composite beam of the same dimensions and properties.
The test objectives were to show that long span composite beams could be designed for a low degree of shear connection using this new type of demountable shear connector and also that local composite action could be achieved at the openings to resist Vierendeel bending. The test load at failure was an equivalent uniform load of 24.1 kN/m2 (760 kN total load) plus the self-weight of the slab and beam, which was 10% higher than the predicted load based on the steel strengths and a shear connector resistance obtained from push tests.
The test failure mode was in pure bending by tension yielding of the bottom Tee. The degree of shear connection was 38% based on measured material properties, which is less than to the minimum to Eurocode 4. The measured slip in the bolted shear connectors was 8.3mm at failure, which demonstrated their high deformation capacity and showed that their longitudinal shear resistance was achieved.
SCI will prepare guidance on demountable composite construction based on this and other tests performed under REDUCE. For more information on demountable composite construction, contact Ana Girao-Coelho at SCI.
Figure 1: 11.2m span composite cellular beam tested to failure at Bradford University