An appeal for better support On several occasions, we have had letters giving account of problems with the bearings for precast units of various kinds. Mr. A. Tydeman is
concerned in this respect about the provisions made for precast floor slabs; essentially an appeal from the manufacturing side of the industry to the designer, Mr. Tydeman's letter was written on behalf of the Federation of Concrete Specialists:
We would be grateful if we could use your columns to put forward a plea on behalf of the manufacturers of precast concrete floor slabs for more thought to be given to bearings on shelf angles. The problems that are arising with ever increasing frequency are, firstly, that the units have inadequate bearings and, secondly, that the ends of the units have to be reduced to an unsatisfactory degree in order to be placed at all.
The first problem can be easily overcome by ensuring that the shelf angle projects sufficiently beyond the flange of the steel beam. When the end of the unit will slip between the top flange of the beam and the shelf angle, the amount of this projection can be obtained by using the formula (b/4) + 80 for the minimum length of the horizontal leg of the shelf angle, where b is the breadth of the top flange of the beam.