Defn of Minimum Gauge Length
Defn of Minimum Gauge Length
(OP)
One of the recent changes to ASCE 7-10 (15.7.5 Seismic Anchorage) and ACI 318(App D Eqn D-3) require that anchor bolts have a minimum gauge length of 8 diameters.
I haven't been able to find the explicit definition for "Minimum Gauge Length" in the context of concrete anchor bolts, either in the ASCE 7 or ACI 318.
Surely this is a simple question, but I haven't found the simple answer.
Is it simply the minimum depth of the anchor in the concrete, below the threads? ????
(I've seen other past comments indicate a minimum anchor depth of 6 diameters was preferable, but never to exceed 8 diameters. I still am not explicitly clear on the intention.)
Any help is appreciated.
I haven't been able to find the explicit definition for "Minimum Gauge Length" in the context of concrete anchor bolts, either in the ASCE 7 or ACI 318.
Surely this is a simple question, but I haven't found the simple answer.
Is it simply the minimum depth of the anchor in the concrete, below the threads? ????
(I've seen other past comments indicate a minimum anchor depth of 6 diameters was preferable, but never to exceed 8 diameters. I still am not explicitly clear on the intention.)
Any help is appreciated.






RE: Defn of Minimum Gauge Length
BA
RE: Defn of Minimum Gauge Length
RE: Defn of Minimum Gauge Length
"Ductile bolts should only be relied upon as the primary ductile mechanism of a system if the bolts are designed to have adequate gauge length (unbonded strained length of the bolt) to accommodate the anticipated nonlinear displacements of the system at the design earthquake."
RE: Defn of Minimum Gauge Length
On the other hand, I also read commentary elsewhere placing a guide of 6 diameters, and never to exceed 8 diameters. The ASCE 7-10 revision, though, states minimum of 8 diameters, so I'm not fully clear as to why this minimum condition is being made.
Would this imply the bolt needs to be sleeved, so it's ability to strain isn't influenced by adjacent concrete bonding or friction? ...to insure the bolt is able to handle the pure tensile forces in the design?
The ACI AppD Eqn D-3 is actually in AppD Section 5, Design Requirements for Tensile Loading. I suspect other commentary recommending no greater than 8dia are looking to avoid lengths which might bend or distort, as the material strength of a homogenous material is approached from a different geometry, loading shear stresses along with the tensile design.
Generally the bolt or bolt group will also have a moment being transferred to the concrete foundation, but the code section is only focusing on tensile design, so I suspect there is something practical in mind with this constraint.
RE: Defn of Minimum Gauge Length
See my presentation at http://civilbay.com/download/eng/ASCE-Anchor-Bolt-...
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com