Performance of Lag Bolts Under Base Plate

[lager]

How would this lag expansion bolt perform when they are used in base plate anchoring...

It looks like this:

When installed under base plate:

When you use 16mm lag screw, the housing that needs to get inside or drilled must be 22mm.. so when you insert the housing inside, there is a gap between the bolt insert and surrounding concrete (22mm-16mm= 8mm) on the upper part.. only the bottom is in contact.. how does the tension breakaway mechanism of this bolt look like.. how does this kind of bolt perform?

 

[Ron]

That is a very light duty anchor. Do not use it for anything that requires more than a small load.

The base plate shown in the graphic is not like a base plate for a column!

 

[lager]

When the bolt is inserted, the housing opens inside concrete that secures it in place. Is the mode of failure you envision breakage of the bolt itself (yielding at 36 ksi) or slip from the housing? but note in anchor bolts.. it is the concrete that is the limitation because it breaks before the bolts get into tension. So how does it differ to the Hilti dynabolt that has same expansion mechanism?

 

[thaidavid40]

One way in which these lag-shield types of anchors differs from Hilti expansion-type anchors is that the Hilti anchors have testing results to back them up. I've never seen any test results published for simple lag-shield type anchors. I wouldn't use them for anything more critical than a dog house, myself.
Dave

Thaidavid

 

[XR250]

They seem to work nicely in brick for light duty applications. Other than that no.

 

[lager]

That is a very light duty anchor. Do not use it for anything that requires more than a small load.

The base plate shown in the graphic is not like a base plate for a column!

Oh, by the way I drew that graphic using photoshop. I was showing that there was no contact on the upper part.. just the bottom part. I was wondering how its tension breakout and shear breakout differs to that of dynabolts in which only the bottom part expands.. dynabolts have same effect of almost no contact on the upper part. In tension, the lags bolts would be poor.. but for shear.. what would happen if only the bottom part of the concrete are engaged.. would it have the same shear breakout pattern as fully embedded anchors?

 

[Ron]

Those anchors do not have enough capacity to break out the concrete. The shield that expands is very malleable and will deform to the extent that the bolt will pull out before the concrete breaks.....and again, as thaidavid40 points out, there is likely no reliable test data on the performance of the bolts in tension or shear. Stick with the "tried and true" products.

 

[lager]

Those anchors do not have enough capacity to break out the concrete. The shield that expands is very malleable and will deform to the extent that the bolt will pull out before the concrete breaks.....and again, as thaidavid40 points out, there is likely no reliable test data on the performance of the bolts in tension or shear. Stick with the "tried and true" products.

Ok. The malleable shield that expands is very well noted. But what would happen if the hollow portion are filled with non-shrink grout? Then it's like you have the entire bolt embedded in concrete with the tip hold by malleable shield. But then in dynabolts like the following. The expansion sheet is as weak!

So it seems only epoxy anchors makes sense in addition to cast-in-anchors.

 

[Ron]

No. No. No. !!!

You have no space to fill effectively with anything between the bolt and the concrete. Use tested materials with a valid record of service. Don't experiment with life safety.

 

[Agent666]

For tension the breakout surface of concrete is the same whether or not the upper part of the bolt is in contact with the concrete or not. In simplistic terms think about a cone of concrete being ripped out from the base for a mechanical anchor.

For shear, yes there is a gap, but its doesn't matter too much at the ultimate capacity. You will get some movement to take up this tolerance to engage the concrete in shear. Additionally there is some friction between the basepate and concrete which may limit any movement at lower levels of load.

Think about a standard steel to steel bolted connection with typically 2mm oversized holes. Does this gap cause any concerns/reduction to the bolt capacity in shear, I would say no as the connection slips and/or the plate plys deform to engage the bolts. Similar concept really in your scenario.