Re: Wood underframes and truss rods - a few questions

Some logging railroads did use a type of car known as a skeleton car or connected trucks, as opposed to disconnected trucks. With this type of car the trucks were connected with a heavy wooden beam, but there was no car body or deck. The bunks holding the logs were directly over the bolsters and no weight was carried by the connecting beam, hence no truss rods were needed. This also allowed for the use of air brakes, which the disconnects did not. The trade off was greater empty weight to be hauled back to the woods, and reduced flexability as to log lengths.

For those who might not know, a disconnected truck is a single truck with couplers on each end, and a log bunk where the car body bolster would set. They were used in pairs, and when loaded the logs formed the connection between them. They were coupled togather for the trip back to the woods. These reduced the weight on the (usually uphill) return trip and allowed logs of any length to be hauled. They also precluded the use of air brakes and train were brought down some very steep grades with hand brakes only, which resulted in some spectacular runaways. Disconnects were used in the Pacific Northwest until the late 1950's.