Impact behaviour of model prestressed concrete beams
This research work investigates the impact behaviour of prestressed concrete beams. A total number of forty 1000 mm long model beams with a rectangular section of 44 x 65 mm were cast. The beams were divided into four with ten beams in each series. Each beam was prestressed by four 1.6 mm diameter piano vire3 and the shear reinforcement va3 varied from series to series. The test rig available was modified so that the beam could have pin-end supports with a span of 600 mm and a static or impact load could be applied at the midspan. A total number of 40 static tests (8 static and 32 post-impact-static) and 32 impact tests were performed. The static load was applied by a screw jack via a one meter long steel pressure bar. The impact load was produced by the impact of a 350 mm steel cylinder projected at velocities of 4 to 17 m/s by compressed air onto the same pressure bar. In each impact test, the impact force-time history was recorded by the electrical resistance foil strain gauges attached on the pressure bar. The transient deflections at various positions along the span were measured by linear variable differential transducers and the reaction was measured by aluminium load cells on which electrical resistance strain gauges were fixed. A dynamic plastic model proposed by Ezra(90) was developed and applied in conjunction 'with the one-degree of freedom system to evaluate the maximum dynamic midspan deflection, reactions, energy absorption capacity and the initial impact beam velocity. A comparison was made between the predicted and the experimental results.