Surcharge and Soil Safety Factors, Retaining Wall.

[Jay17]

I am design a soil retaining wall with 3 rows of tiebacks. I have a surcharge on the top of the wall of 95 KPa (2000 lb/ft2). This is load is from a water storage tank. Should i be factoring my surcharge load by 1.5? Also, should I be factoring my soil loads by 1.25?

 

[ishvaaag]

Hmmm, the rationale for factoring live loads and dead loads remains in place whatever their nature. So except the code makes explicit exception, the ordinary safety factors should be employed.

As an example; floors made of just a plate of concrete, here, Spain. Everyone knows that with proper caution on not exceeding the thickness, the load rarely will exceed the normative value. Yet anyway a on dead load safety factor of 1.35 must be used factoring the loads.

Now, a structural code is a system of getting in reliable way a targeted level of safety, and any works on the scope of one should be following its clauses.

There is another important aspect of codes, comparing them and their practical effects, tu pursue betterment of construction.

Separate clauses use also to be used where no extant enforceable information is standing, always caring of the way of application and the intent, being then basically another source of technical information explicitly sanctioned by some government or technical body.

 

[Boondog]

Refer to the AASHTO LRFD 2007 Bridge Design Specs. It provides a chart with specific load factors for specific load types. Chapter 11 is specific to MSE walls.

 

[fattdad]

I would present the unfactored loads to the structural engineer and let them properly design the structure using the safety factors required for the structure (and the codes).

f-d

¡papá gordo ain’t no madre flaca!

 

[apsix]

The code I use (AS1170) allows a factor reduction from 1.5 to 1.2 if 'the liquid type and density is well defined and design liquid height cannot be exceeded'.

 

[jdonville]

Jay17,

Use factored or unfactored loads as required by the code you are using and the calculation methodology for the resistances.

Do not mix factored and unfactored loads!

Jeff