A model is descriptionbed whereby the optimum loading time and the concomitant production and cost of a scraper Fleet may be accurately and very rapidly ascertained on site by means of a pocket calculator. The requisite equations are given and the pertormance of a program Implementing the model Is discussed.
The response of prestressed concrete sleepers to torsional loading is Investigated. A theoretical prediction of the ultimate torsional resistance moment of a type F4 prestressed concrete sleeper is given, using the space truss model for reinforced concrete beams under torsional loading. The results of an experimental investigation Into the structural behaviour of prestressed concrete sleepers under torsional loading and a combination of torsional and flexural loading are reported. Even with the required design flexural moment an adequate resistance to combined moment and torsion was obtained.
A new simplified method for long-term deflection calculations of reinforced concrete members was presented. The method defined a modular ratio for creep conditions based on laboratory verified strain distributions In beams for both immediate and long-term conditions. A simple formula was derived for the ratio of long-term to immediate deflections. A value for the creep factor has to be assumed but a series of curves was recommended that relates the creep factor to ambient relative humidity, age of loading and surface area to volume ralio of the member. Calculated deflections using the method were compared with laboratory measured values reported in the liIerature.