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RE: Retaining Wall Design Methodology

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I haven't heard of the third option; I use option 2 when I want to be
realistic and save material and I use option 1 when I want to save time and
can accept conservatism. 

> -----Original Message-----
> From: Caldwell, Stan [mailto:scaldwell(--nospam--at)halff.com]
> Sent: Wednesday, July 12, 2000 10:22 AM
> To: 'SEAINT Listserv'
> Subject: Retaining Wall Design Methodology
> Importance: High
> 
> 
> Cantilevered retaining walls are probably one of the most 
> easily understood
> types of structures, and are routinely analyzed and designed 
> by engineers
> all over the world without any great difficulty.  
> Nevertheless, there is at
> least one aspect of retaining wall design that is still open 
> for debate.  My
> colleagues and I have identified three different methodologies for the
> design of the heal footing, and we are currently debating 
> which alternative
> to adopt as our future standard.  As described below, the 
> issue is how to
> treat (upward) bearing forces when designing the heal footing 
> for shear and
> moment.  For short walls, this does not make much difference. 
>  However, for
> tall walls, the difference can be quite significant.  For a 
> modest 15 ft.
> high wall, the resulting heal footing design can vary by as 
> much as 40% in
> concrete thickness, and 25% in reinforcement area.  If you 
> are designing
> hundreds of feet of retaining walls, that soon adds up to 
> "real money"!
> 
> Here are the three alternative methods, all of which appear to be code
> compliant, within the realm of good engineering practice, and 
> in common use:
> 
> 1)  For determining soil bearing pressure, the full width of 
> the footing is
> used and results in a trapezoidal (sometimes triangular) soil pressure
> distribution.  In designing the footing, however, the soil pressure is
> applied only under the toe.  No soil pressure is assumed 
> acting under the
> heal.  This leaves the heal being conservatively designed as a heavily
> loaded cantilever.  This method is described in many popular texts,
> including the 5th Edition (1992) of Reinforced Concrete 
> Design by Wang &
> Salmon.  It is the only method available in Daystar software, 
> and is an
> optional method in Enercalc (and RetainPro?) software.
> 
> 2)  For determining soil bearing pressure AND for designing 
> the heal and toe
> footing, the full width of the footing is used and results in 
> a trapezoidal
> (sometimes triangular) soil pressure distribution.  Some 
> believe that this
> method is not always conservative.  This method is described 
> in several
> popular texts and manuals, including the 4th Edition (1988) 
> of Foundation
> Analysis and Design by Bowles, and the 1996 CRSI Design 
> Handbook.  It is an
> optional method in Enercalc (and RetainPro?) software.
> 
> 3)  For determining soil bearing pressure AND for designing 
> the heal and toe
> footing, a uniform soil pressure distribution is applied over 
> a portion of
> the footing, excluding a width of "2e" at the end of the 
> heal, where "e" is
> the eccentricity between the center of the footing and the resultant
> vertical force.  This method is the newest, and appears to be strongly
> supported by the research of G. G. Meyerhof, and others.  
> This method is
> described in the 5th Edition (1996) of Foundation Analysis 
> and Design by
> Bowles.  Although this method might well be the most logical 
> of the three,
> it does not appear that it is currently supported by any commercial
> software.    
>           
> My question to all of you (and especially to the software 
> authors) is very
> simple:
> 
> What method do you use, and why do you use it?
> 
> I look forward to any and all responses.
> 
> Regards, 
> 
> Stan R. Caldwell, P.E.
> Vice President
> *************************************
> HALFF ASSOCIATES, INC.
> Engineers+Architects+Planners
> 8616 Northwest Plaza Drive
> Dallas, Texas    75225
> Phone:  (214)346-6280
> Mobile:  (214)236-9696
> Fax:      (214)739-0095
> Email:   scaldwell(--nospam--at)halff.com 
> Website:  http://www.halff.com
> *************************************
>  
>  
> 
> 
>      
> 
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