Cracked Section Properties for Walls
Cracked Section Properties for Walls
(OP)
I am using ETABS to model a concrete shear wall building. Section 1910.11.1 of the UBC provides modified properties to be determine lateral story drift. How do I determine if I should use the value for a cracked or uncracked section? Thanks!






RE: Cracked Section Properties for Walls
RE: Cracked Section Properties for Walls
RE: Cracked Section Properties for Walls
Supposedly everyone in a seismic zone ignores cracked sections and uses 0.7Ig. This includes our peer reviewer (Saiful Bouquet- the "AUTHORITY" on seismic design despite us being the EOR on the most recent tallest buildings in the world.. work including 101 Taipei, Petronas Towers, Burj Dubai, Soldier Field, 1180 Peachtree (great website btw), 181 West Madison, Shanghai Plaza 66 etc..)
RE: Cracked Section Properties for Walls
Most buildings are really straight-forward.. And ETABS 9 has made some really great improvements.
RE: Cracked Section Properties for Walls
RE: Cracked Section Properties for Walls
If we use 0.7Ig for wall design, which is really conservative (attracts more force). In the same analysis, if we assign 0.5Ig for coupling beams/frame members, then it is fine because it is going to effect distribution of forces.
Cracked sections should be arrived for serviceability and limit state in all the structural members(horizontal/vertical), which is really tedious.
Any more thoughts...
RE: Cracked Section Properties for Walls
suppose i have shear wall section formed of 4 shell elements and stress in one or more shell element forming the shear wall section exceeded cracking limit then the four shell elements must be assigned reduction factor for tension cracked section.
In Most analysis cases when modification factors are used to allow for cracking this lead to increase stress in walls and columns sections than analysis done by using uncracked section.
What are the great improvments ETABS 9 has?
RE: Cracked Section Properties for Walls
ALL uniformity in geometry was neglected in SD phase.
IMHO today's software does not have the capability of assigning cracked section properties.. period. Hence the value of the structural engineer and my position (i.e. not quite ready to get fired..) in determining the approximate behavior of the system.
For instance, with all of the proper algorithms, I got an estimate from one of the FEA software teams.. a perfect, fully automated analysis and design of the said project would take until 2015 with out current capabilities- and current design locked in.
Headline- the project WILL be finished fall 2009. (hell or high-water..)
RE: Cracked Section Properties for Walls
RE: Cracked Section Properties for Walls
I need a quick answer. Under ultimate state, though wall is not cracked, 0.7Ig need to be used in the analysis. How do we modify the stifness in ETABS. Are they f11 & f22.
Please let me know
We are currently using UBC code as a reference for analysis purpose. Stiffness modifiers as stated in UBC 1997 are for ultimate. It doesn't clearly indicate what to be used for wind tunnel study and vibration studies. But ACI has got the right direction. But we need to satisfy the UBC requirements.
Do i get any reference or cross reference from UBC to ACI with respect to stiffness modifiers?
Thanks
Murali G