DESIGN DATA FOR HEAVY VEHICLES

Vehicles which are required to carry very heavy concentrated loads, e.g. up to 400 ton, need to be designed to a minimum gross weight to enable them to operate as far as possible within the limitation of roads, bridges, etc. The basic vehicle weight could be minimised by using high strength materials. Welded joints in such materials tend to have the same fatigue strength as the lower strength materials, so that if fatigue strength is already a design criterion it might not be possible to take full advantage of high strength materials. The investigation described in the paper was carried out to measure fluctuating stresses on a trailer with a 300-ton load during a delivery movement. This required the installation of strain gauges and mobile recording equipment for retrieving full data over long periods of the journey which included a journey by sea. Assessment of the measurements required that the speed of travel was known accurately and it was found that existing devices were insufficiently accurate at the low speeds employed. A much more accurate speed measuring device was therefore developed for this operation. The results demonstrated the importance of correct loading and adjustment of the vehicle suspension system. The final conclusions of the exercise were that fatigue damage was unlikely to be a design criterion in respect of high strength materials. /Author/ /TRRL/