traffic guard load distribution

[jagti]

i have a job whereby i have to account for vehicular barrier approx 4.5ft offset at p/l behind wall is approx 5.0ft high.

The owner Engineer has provided min 6000lbs load . My question is do i have to convert this concentrated load to lb/linear fit. The vehicular barrier wood post is encapsulated in a Concrete footing. How do i apply/disperse this load in my external stability calculation. The length of the wall is only 10.0ft

Without guard rail load my geogrid tie backs are approx 4.5ft long for a 5.5ft grading difference using LL surcharge 250psf.

 

[RFreund]

Well for guard rail design on segmental wall is a bit different and I'm not sure I fully understand it. Usually you can use the AASHTO standard detail which says the gaurdrail should be atleast 3' from the face of the wall and 5' deep (they may have changed this but I don't think so). This, according to AASHTO, ensures that the wall will deform but not fail.
If you were to design for the 6,000lb impact load I would use a 45deg distribution (in plan view) and apply it to that length of wall. So at 4.5' behind wall thats 2*4.5'=9', Then you'd have 6,000lb/9'=666plf of horizontal force.



EIT

 

[jagti]

Thanks RFreund,

So in my External Stability calculation i will apply 666plf force & check my MSE wall against Base Sliding, Overturning the depth of Post footing wouldn't matter in this case as we are spreading this load uniformly longitudinally along wall length.

My concern is more of how would i transfer this load to the buried backfill.

 

[RFreund]

I don't think I understand your question, what is 'buried backfill'.

My assumptions are that the reinforced backfill will distribute the lateral force applied at the the gaurdrail post at a 45 degree angle. The distribution is through the soil and will act on the back of the wall. The wall then be restrained by the geogrid.
Not sure if that helps.

EIT

 

[jagti]

Without impact load my composite wall width itself is 4.5ft (CMU facing + reinforced fill) so I am not sure if 45 deg distribution would be applied for External Stability calculations. I can understand 45 degree load distribution for Internal Stability calculation for checking geogrid connection & pullout.

I am wondering can i divide this load by depth of the post 6000lb/6ft=1000lb/ft assume this as a linear load & check for adequate external stability.

Thanks

 

[RFreund]

hmmm.... I see what your asking now and I will do my best to explain.

For your situation I would use the 45deg distribution along the length of the wall (in plan view) for external calculations. I am also assuming that the post (5'deep) will distribute to the total wall height, therefore I will use the total wall height to resit this force. I would apply the effective load (6,000lb/9ft) at the height of the gaurdrail and sum moments at the toe of the wall. I would not consider internal stability as the post is behind the reinforced zone. You could consider local unit connection or sliding but not pullout. I can go into more detail if I have time later today or tonight.

EIT

 

[bridgebuster]

Go to the Keystone wall website. Under their technical notes they have an example for a barrier design.