From: Efren Allan Yango <engreay(--nospam--at)pacific.net.ph>
Date: Sun, 11 Mar 2001 22:55:02 +0800
To Engineers with braced frame experience :
I am doing a design check on a mall-type structure with some portions
3-storey high and others 2-storey high. All beams and girders were
assumed simply supported by the original designers (no moment frame
construction). The columns were designed for simple axial load and
minimal moment usually resulting from the beam connection eccentricity.
The lateral force resisting system adopted was an X-braced frame system.
The size of the whole structure is around 15,000 sq. m with beam spans
as long as 12m.
I have checked the path for the gravity loads and it met all the
criteria of our codes here. My questions are now related to the braced
1) Can the braced frame be located at the 2nd floor to 3rd floor
only? (One end of the digonal at the 2nd floor and the other at the
third floor). No braces
at the first floor were located. I believe that this would
create a soft storey. In terms of member forces, this would pass but I
have doubt on this type of
design. That's like terminating your shearwall at the second
floor instead at the foundation level.
2) Can flat bars (designed as tension-only members) be used as a
bracing system? I believe that tension-only design is discouraged by the
How about for low-rise structures? Is the slenderness limit
of 720/sqrt(fy) strictly followed?
For now, I don't want to conclude that the building has been improperly
designed. I would like to know first if I'm missing out on something. I
have other questions but I would like to limit them to these 2 for the
meantime. I hope engineers with experience in this type of structures