Question on an example of designing retaining wall 3

[marslam]

with the attached file
I got some problem in the reinforcement section
In page 3
For the reinforcement of heel section, I dont understand the equation that calculates the design moment at point C
And I dont know where did the 51.8 appear in the same equation

 

[MotorCity]

You're going to have to give us a hint what page your question is on......nobody is going to look over a 16 page document trying to guess what you are referring to

 

[BAretired]

There are four terms as follows in the equation of Moment at C (see the diagram on page 3):
1. Contribution of the soil weight
2. Contribution of the concrete base weight
3. Contribution of p2 over 2.9m length
4. Contribution of varying pressure p3 - p2 over 2.9m length

51.8 is p3 - p2

BA

 

[masterthenight]

I glanced at it real quick.

Mc = 385.7*2.9/2 + 2.9*38.4*1.4*1.45/4 - 91*2.9*2.9/2 - 51.8*2.9*2.9/2/3

385.7*2.9/2 = M clockwise due to down force on right
2.9*38.4*1.4*1.45/4 = can't figure this term out, but lots of recognizable values in there
91*2.9*2.9/2 = M counter clockwise due to uniform upwards soil pressure on right, magnitude is p2 = 91
51.8*2.9*2.9/2/3 = M counter clockwise due to triangular soil pressure up on right, magnitude p3-p2 = 51.8 on left end (@ C) and 0 on right end

The diagram is a little confusing.
p1 is on the far left, p3 is @ c and p2 is on the far right.

Couldn't figure out the one term, you'll have to do that.
I won't be responding further because I'm not on here often, FYI.

Hope this helps!

 

[IDS]

2.9*38.4*1.4*1.45/4 = can't figure this term out, but lots of recognizable values in there

That's the moment due to the weight of the base x 1.4 (load factor)

The total base weight is 38.4 and total width is 4.0, so weight to the right of C is 38.4 x 2.9/4.0
Factored moment about C = (38.4 x 2.9/4.0) x 2.9/2 x 1.4

Note that the load factor is not applied to the anti-clockwise moments due to the soil pressure, since that would reduce the nett moment at C

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/