I have viewed other threads over the years about discussions on this matter and have read/researched information with respect to this and my conclusion is there is very limited information available. The item I am trying to better understand is thermal expansion in roof systems and how to properly detail this expansion joint. From the 1974 publication "Expansion Joints in Buildings", it gives guidance on this matter and it seems this is what everyone discuses/references. I have attached a generic example and based on an expansion joint at the midpoint of the building sidewall, there would be nearly 3.5" of movement. I am having a hard time picturing this:
1) If there was 3.5" of movement, it would seem to me this is a result of the deck corrugations deforming and flattening out. If this is the case, wouldn't the roof deck fasteners start elongating holes in the deck or spot welds tear through the deck that the diaphragm loses capacity and does not function properly? Bar joists have axial strength which would seem to want to resist this thermal expansion movement (parallel with the joist) and make the roof system act as the intended diaphragm with the exterior walls perpendicular to the expansion joint (shear walls) minimizing this movement from occurring.
2) Many details I see in references/publications talk about slotting holes in bar joists and/or using Teflon pads for slip movement. If the deck/joist framing act as a diaphragm system, where is the 3.5" of movement occurring? Are all elements actually moving as one so you only see movement at the expansion joint? It would seem with expansion and contraction of materials, you are going to have equal and opposite forces occurring at all elements where there is a rigid connection (ie: bar joist to joist girder), not just the expansion joint locations.
3) At expansion joint locations, many publications reference utilizing (2) lines of vertical bracing elements; one on each side of the expansion joint which essentially makes (2) separate buildings. If only a single line is utilized with one side being rigid and the other having a slip style connection/surface, how are diaphragm shears taken into the joist girder properly with only snug tightened bolts at the bar joist?
4) If this much movement is actually occurring, how are expansion joints handled in the opposite direction? Is this merely just (2) bar joists adjacent to each other allowing perpendicular movement when the deck is broken and then use a horizontal x-brace system to transfer load across the expansion joint (assuming no vertical bracing system below).
1) If there was 3.5" of movement, it would seem to me this is a result of the deck corrugations deforming and flattening out. If this is the case, wouldn't the roof deck fasteners start elongating holes in the deck or spot welds tear through the deck that the diaphragm loses capacity and does not function properly? Bar joists have axial strength which would seem to want to resist this thermal expansion movement (parallel with the joist) and make the roof system act as the intended diaphragm with the exterior walls perpendicular to the expansion joint (shear walls) minimizing this movement from occurring.
2) Many details I see in references/publications talk about slotting holes in bar joists and/or using Teflon pads for slip movement. If the deck/joist framing act as a diaphragm system, where is the 3.5" of movement occurring? Are all elements actually moving as one so you only see movement at the expansion joint? It would seem with expansion and contraction of materials, you are going to have equal and opposite forces occurring at all elements where there is a rigid connection (ie: bar joist to joist girder), not just the expansion joint locations.
3) At expansion joint locations, many publications reference utilizing (2) lines of vertical bracing elements; one on each side of the expansion joint which essentially makes (2) separate buildings. If only a single line is utilized with one side being rigid and the other having a slip style connection/surface, how are diaphragm shears taken into the joist girder properly with only snug tightened bolts at the bar joist?
4) If this much movement is actually occurring, how are expansion joints handled in the opposite direction? Is this merely just (2) bar joists adjacent to each other allowing perpendicular movement when the deck is broken and then use a horizontal x-brace system to transfer load across the expansion joint (assuming no vertical bracing system below).
