Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

ACI slender wall

Status
Not open for further replies.

ramihabchi

Structural
May 1, 2019
98
LB
hi,
It seems that ACI is not clear about slender walls as it is for columns.in aci 318-08 it is not clear which walls are considered slender walls and to which walls(slender or not or both)does empirical design method (14.5) apply.what is obvious is that slender walls with great out-of-plane moment could be designed with 14.8 ("alternative design for slender walls")but again I could not determine which walls are considered slender.it seems that walls where flexure is tension controlled are considered slender regardless of their height to thickness ratio.please correct me.
 
Replies continue below

Recommended for you

My opinion, a non-slender wall is the resultant force fall within middle third of wall depth (thickness) - eccentricity small, thus mainly subjects to axial forces.
 
@Retired13 you are right.in addition,for walls which are subject also to axial force without moment when they are at critical load they are subject to buckling so they need to take into acount this.
I have rechecked the code and I appologize i didn t notice it.the general way of design of bearing walls refer to 10.10 in which treats walls as columns in term of slenderness.my only remaining question is do we consider corewalls as a single element?I mean when a wall is connected to another wall in another direction it will somehow restrain its movement and change buckling load in such a case how would I know if it is slender or not?
 
I'll analyze/design the core-wall as one huge column, L, U, or fully enclosed shapes, since the elements are momently connected.
 
Thee walls in a core are not always connected adequately. You would have to look at each wall individually to make sure it has connections that control its slenderness if it would be slender by itself.
 
I disagree that slenderness is primarily related to the location of the axial load. It has traditionally been tied to the ratio of effective length divided by wall thickness being over some arbitrary limit in most codes. Even if the axial load is applied to the centre of the wall, it can still be unstable and buckle if it is too slender.
 
There are two considerations (IMO):
1) Traditional UBC considerations like section 1914 of the 1997 UBC which states that a slender concrete wall is anything with a h/t ratio greater than 25. That's the slenderness level that invokes the slender wall design procedures in the UBC. Think of this as akin to a when P-little delta moments will start to really affect column design in moment frames. I would never do a design of a wall with an h/t ratio greater than 25 without considering slenderness effects or moment magnification.

I should also point out that this is "sort of" in the new ACI code as well. Table 11.3.1.1 of the 2014 ACI specifies that the minimum wall thickness is 1/25 of the of the unsupported height (or length). Not quite the same, but pretty similar.

2) Any situation where moment magnification could be problematic. I'd take this as what retired 13 said. When the e = P/M is greater than 1/3 the thickness of the wall. Essentially the point where the extreme fiber is in tension or when the section may crack.... Reducing stiffness and amplifying any flexural bending. I.e. moment magnification.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Top