Exploratory study of small timber trusses constructed with through-bolt and cross-pipe heel connectors

Abstract

Throughout the world, there is a need for simple, strong, yet inexpensive connectors that can be used to fabricate trusses from natural small-diameter tree stems as well as squared stems without extensive premachining of the joint area. A connector that might satisfy these requirements is the through-bolt with cross-pipe heel connector. Tests were conducted, accordingly, to determine the load carrying capacity of a variety of trusses constructed with these connectors. The primary purpose of the tests was to obtain first estimates of the peak load carrying capacity of representative trusses constructed with through-bolt and cross-pipe heel joints and to determine the modes of joint failures to be expected. Cross pipes were cut from commercially available 1-1/2-, 2-, and 4-inch diameter schedule 40 and 80 black pipe. Truss members measured a nominal 2 by 4, 4 by 4, or 4 by 6 inches. A number of trusses were also fabricated from round small-diameter tree stems. Load carrying capacities of the trusses ranged from 4,500 to 30,000 pounds. Overall, results of the tests indicate that trusses with useful load carrying capacities can be easily constructed with relatively inexpensive cross-pipe heel joints. Of particular importance, the trusses do not fail catastrophically when the cross pipes begin to yield but continue to carry load. Trusses in which the top chords frame into the bottom chord are able to carry substantially higher loads than are those in which the bottom chord frames into the top chords. Use of close-fitting pipe inserts or wood disk inserts provides a simple and effective way of reinforcing cross pipes.