Tendon Elongation in foundation ground anchors
Tendon Elongation in foundation ground anchors
(OP)
Hi all,
We have installed and proof loaded a test ground anchor for a tower pre-cast foundation.
I am trying to get a handle on how much of the extension recorded (24mm) is due to elongation of the tendon?
The bar is a MacAlloy 1030 40mm. 3m un-bonded, 8.5m bonded. Loaded up to 530kN. Bar secant modulus of elasticity = ~170MPa
Any thoughts anyone.
Thanks in advance.
We have installed and proof loaded a test ground anchor for a tower pre-cast foundation.
I am trying to get a handle on how much of the extension recorded (24mm) is due to elongation of the tendon?
The bar is a MacAlloy 1030 40mm. 3m un-bonded, 8.5m bonded. Loaded up to 530kN. Bar secant modulus of elasticity = ~170MPa
Any thoughts anyone.
Thanks in advance.





RE: Tendon Elongation in foundation ground anchors
P = test load
L = unbonded length of tendon plus jacking length = total length from bottom of unbonded length to top of testing jack. Actual L could be more if/as load transfers down into the bond length.
A = crtoss section area of tendon
E = Modulus of Elasticity of tendon
www.PeirceEngineering.com
RE: Tendon Elongation in foundation ground anchors
The interface intrigues me, suppose that the entire load is transferred in say 10 units of length, one tenth goes into the first unit and nine tenths of the load continues down the tendon, but for it to continue, there must be strain, strain that should break the bond in the first unit. I don't see how these things don't just "unzip".
Okay, I know they don't but...
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Tendon Elongation in foundation ground anchors
I think the OP knows this, but is asking for opinions on acceptance/failure criteria.
RE: Tendon Elongation in foundation ground anchors
Only really looking for a back-of-the-fag-packet ball park assessment, so PEinc's reply is spot on.
Cheers
RE: Tendon Elongation in foundation ground anchors
RE: Tendon Elongation in foundation ground anchors
You raise a point that, unfortunately, many engineers choose not to think about. The short answer is that the bond between the anchor and soil and/or rock is not inelastic. As load is transfered to the soil/rock strain occurs both at the bond and within the soil/rock. That strain accounts for some portion of the load being developed by the anchor.
Additionally, the amount of load at any given point in the bonded length of the anchor may change with time. This is very true of anchors in clay soils. The only way to know how much load the anchor is developing at any point is by placing strain gauges on the anchor bar at different depths and that only gives an approximate value.