Safe loads on hangers for timber joists
Dr J. B. Bellamy believes that there is a need for the clarification of the criteria for designing joist hangers, and explains how he sees the design considerations:
There appears to be a widespread misunderstanding among suppliers of builder’s metalwork as to what is the safe working load on built-in joist hangers. It is common to see figures in sales literature which are many times those set out in the relevant Code of Practice, BS 6178: Part I 1990. For example, one supplier quotes loads ranging from 14.7 to 37.8 kN compared with l.9 to 3.1 kN in the standard. At first sight, this could be taken as being due to improved designs, but closer examination suggests that the majority of suppliers offer very similar products. A few minutes spent calculating
stress levels reveals that, in normal applications, the factor governing capacity is the crushing strength of the masonry, not the strength of any element of the metalwork.