W30 column unbraced lengths?

[rfied112]

Existing one story building, full diaphragm at roof from metal deck and horiz bracing, some column lines have vertical bracing, others have CMU wall tied into steel columns. Question is: on outer column line there are W30x124 columns that have full height CMU walls (shear wall assuming) tied into web of columns with straps every 24", inside face of wall is 22 inches from inside flange of column, wall is 20 inches thick. At the roof in the columns major axis a 4.5 feet deep truss that spans 45 ft frames into the column flange, truss chords WT12x55 T & B.
Can KLy be taken that minor axis is continuosly laterally braced, no sidesway, Ly=0 ?; can KLx be taken as 1.0 times height to underside of truss.

 

[JAE]

20" thick CMU? Don't follow your description as to what the main, structural portion of the wall is. Please expand a bit. Thanks.

 

[rfied112]

3 wythes thick, 12 inch CMU in middle, a four inch thick veneer on inside and outside face according to drawing

 

[jike]

The Kx would depend upon how the trusses are connected to the column. Do the columns and trusses work together as lateral frames to resist lateral loads?

I would normally not count on the masonry ties to provide bracing in the y direction.

 

[JAE]

jike is right - I would consider the CMU to brace in the Y direction only if I had confidence that the wall to column connections were strong enough to resist some level of tension/compression - say 2% of the axial load of the column. Strap ties to CMU just don't "feel" reliable to me and someday the owner may remove a wall or two with an addition, etc.

If the truss to column connection is intended to work as a moment frame, then the kx would be 2.0. Assuming that the base is assumed pinned.

 

[DaveAtkins]

I would not consider the column braced in the y direction for a different reason--the inside flange is too far (22") from the inside face of the masonry.

DaveAtkins