Roof trusses and purlins

                                                                                                                                                                                                          Brazil 2025, truss with purlins........................Thailand 2024, joint assembly with screws

Roof trusses and purlins are normally quite expensive items requiring high-end timber or metal profiles to meet the structural reliability. These components can easily be replaced by low-cost bamboo elements with their high tensile capacity, trimmed to a dimensional standard and combined with an efficient back-to-back gusset joint design.
Roof truss of recomposed bamboo and gusset joints

Steel plate gusset material can be sourced from scrapyards at very low cost. The 2 mm steel plate covering “white goods” like washing machines, refrigerators etc is perfect. That surface has a high-quality corrosion resistant coat and cuts can be bevelled and quickly recoated. If CNC equipment is available cutting can be efficiently organized for large scale production.
When mounting the bamboo culm halves with the steel gusset placed in position, drill right through all parts with a bit for metals. (See cross section) Small pieces of wood on the could be placed on the protruding screw on the other side to create pressure and anvil.
Purlins can be made using the same method of recomposing bamboo culm halves, hence the same section as for the truss. Mounting the purlins is then simply by inserting a sufficiently long wooden screw to first enter between the purlin halves and then reaching through the truss culm halves. With a common roof pitch of 27 degrees this method should be enough. For a steeper roof, purlin support of a small piece of wood or bamboo also stuck in between the truss culm halves, may be necessary. The center-to-center measure of the purlins is of course a matter of roof cover weight and wind pressure. and structural design.