Tests on a 120-ft Span Prestressed Concrete Beam

Tests to destruction have been carried out on a 120-ft-span prestressed concrete beam similar to the beams to be used in the construction of a four-span overpass at the Chiswick rotary junction. The tests showed that the design assumptions with regard to the loss of stress due to friction and short term creep, shrinkage, and relaxation were valid. The behaviour of the beam in the working-load range agreed excellently with the behaviour predicted. At ultimate load the beam failed by crushing of the concrete in the top flange at a deflection of 20 in. The calculated ultimate load was 6% less than the actual failing load; the assumptions, on which the ultimate load calculations were based, were thus fully vindicated.