![]() ![]() ![]() The failure point would be the section of the rafter outside of the triangular shape. Pressure on the collar tie going sideways will want to push the entire rafter and tie, and the rafter on the other side of the "roof." Pressure downward at that point will pull at the tie, trying to make it longer, which then will then instead pull the junction at the other end of the tie inward, which is resisted by the rafter on the other side of the roof. Imagine a roof section made of toothpicks glued together, and then a finger pressing in various ways against the construction. Primarily, a collar tie works as a response to wind load.Ī collar tie DOES create a limited resistance to downward loads. Deflection of one side of a triangle is minimized, and since a side cannot change in length, it creates a stable form. A chord is a geometric term, or one used in music to denote relationships between notes.Ī collar tie creates a triangle. Your best bet would be to get all of the specifications/weight on the panels and then have a engineer review the existing conditions to determine if additional framing work will be necessary.Ĭhord, not cord. If it is necessary to strengthen the rafters, you would need to add to the ceiling joists and then add cords or a cord at center span of each rafter which would dramatically shorten the span of the existing rafters adding to their strength. Collar ties do add to the resistance of the rafters and walls laterally (to spread) as mentioned above, so they basically are not necessary since the ceiling joists provide the same function.
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