horizontal deflection of scissor joist spported on masonry wall

[Philboyd]

I am designing a gymnasium with load bearing masonry shear walls. the architect wants to use scissor joists with a 2-in-12 pitch for both the top and bottom chords. The joist span is 100 ft and the masonry bearng walls are approxomately 30 ft high to joist bearing. The joist manufacturer has informed me that the joist will deflect a total of 1-1/8 inches in the horizontal direction. I cannot allow a slip connection as the masonry walls need to be attached to the roof diaphragm for support.

I am concerned about the deflection of the joists cracking the masonry. I have considered allowing "slip" to occur at one end until the dead load is in place and then making a positive connection. I am still concerned that possible live load deflection added to possible uplift deflection in the opposite direction may cause cracking in the masonry over time, particularly near the corners where the masonry is very rigid.

Should I be concerned or can the masonry accommodate this movement without cracking? If the live load deflection can be limited to 3/4 inch that would only be 3/8 inch at each wall.

 

[ron9876]

Maybe a joint between the end walls and the side walls and don't make the final connections until all dead load is in place.

 

[SteveGregory]

Philboyd,
For your designer friend, if your live load is 2 or 3 times the dead load, the cracking may not show up until you have a big snow.