AASHTO Rock Socket Side Resistance

[jdonville]

The formula given in Article 4.6.5.3.1 of AASHTO HB-17 (page 85) for ultimate side resistance reads as follows:

Qsr = (pi)*Br*Dr*(0.144*qsr)

Yet the label on the y-axis for Figure 4.6.5.3.1A indicates that qsr is the unit side resistance.

Should the formula read:

Qsr = (pi)*Br*Dr*(144*qsr)

to make the units work out?! Or do they intend to reduce Qsr by a factor of 1000 for some reason?!

All responses welcome.

Note: Originally posted in AASHTO Code Forum.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[Panars]

I think the equation is correct. qsr is in psi (lb/in^2), but the other units are in kips or feet. So the conversion factor of 0.144 is equal to

(12 in/ft)^2
---------------
1000 lb/kip

The notation and the units for each symbol can be found in Sectino 4.6.2 on page 79.

 

[jdonville]

Panars,

Thanks for the explanation. I had not considered that the units of Qsr would be specified.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[RJ62]

jdonville,

I posted the thread "DS Uplift Capacity with Socket". Does the AASHTO HB-17 publication address total side resistance (soil resistance + socket resistance) and the resistance distribution along the shaft? I'm looking at uplift capacity from soil and socket contribution.

Is the publication available on-line?

Jefferys

 

[jdonville]

jefferys,

HB-17 is the AASHTO Standard Specifications for Highway Bridges, 17th Edition (2002). It is most definitely not free (unfortunately)! Copies are available from AASHTO (

http://www.aashto.org).

However, Amazon.com and ebay might have 3rd-party (used) copies available. Note that this version will be officially deprecated for highway structure design in a year or two when the LRFD version will be the "official" design basis for federally-funded projects (and likely many state projects, too).

Unfortunately, the document does not give any specific guidance on this topic - which I am pained to admit that I don't know as much about as I should. I am currently looking at DSs with rock sockets for a current project, but they are fortunately short (<15 ft OA) and I will assume negligible contribution from the soil for skin friction.

Off the top of my head, I don't know of any source giving explicit design guidance. But please do let us all know if you find some.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com