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Re: COLUMN STRIP WIDTHS FOR VARIOUS BAY LENGTHS

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Brian,
 
Because we're talking about minor differences in the distribution (as opposed to the total quantity) of reinforcing, I think the answer to the question (which of the two methods of computing the width of the column strip is superior?) is that in so far as the performance of the completed structure is concerned it probably doesn't matter.  I would therefore argue that in so far as code compliance is concerned, either satisfies the intent of providing for safe design.
 
Practically however, the first method is more sensible.  This is because adopting the second, which creates a "jog" in the column strip, would theoretically require the designer to detail a "jog" in the column strip top steel.  I suppose you could approximate this effect with skew and/or hooked bars, but you would be adding cost without adding strength and possibly reducing effective continuity.
 
IMHO, the answer is found by reference to the age-old rule in regard of simplicity (KISS).  In your example, I would use straight top steel distributed across a N-S column strip 4.5' wide.
 
Drew Norman
SE (CA), PE (CA, MI, TX)
 
Drew A. Norman and Associates
Consulting Structural Engineeing
and Project Management
 
Betraying the Engineering Profession
by leaving it to study Law
at the University of Pennsylvania
Philadelphia, Pennsylvania
----- Original Message -----
From: Brian Hsi
Sent: Wednesday, July 23, 2003 8:53 AM
Subject: COLUMN STRIP WIDTHS FOR VARIOUS BAY LENGTHS

 

I would appreciate any it if anyone could give input on how setting CS widths in ACI 318, section 13.2 should be interpreted.

I have a question on setting column strip widths for an interior column with various L1 and L2 values.  Let?s say the L1 span south of the column and L1 span north of the column are 10? and 14? respectively.  The L2 span west and L2 span east of the column are 8? and 12? respectively.  There are differing opinions throughout the office on how the CS width should be determined. 

Let?s assume we are determining the width of the CS for the span that runs north and south.

For the CS width east of the column, some would compare the two L1 spans, find the smallest and compare that to the L2 east, giving me 10?/4=2.5?.  It would be done the same for the west side, giving 8/4=2?, for a total CS width of 4.5?.

Others in the office would compare the L1 and L2 length at each quadrant to determine the CS width, which would create a ?jog? in the CS at the center line of the column.  The south-east width of the CS would compare the smallest of L1 south with L2 east, giving 10/4=2.5?.  The north-east width of the CS would compare the L1 north with L2 east, giving 12/4=3?, creating a .5? jog.  Again for the west side, the south-west CS width would equal 2? and the north-west CS would equal 2?.

 

Again, I would appreciate any input that could clarify how to determine column strip widths.

 

Thank you,

Brian Hsi