stone veneer on bridge 2

[RRBegin]

Howdy folks-

I am designing a bridge widening for an historic stone arch bridge in the northeast. We are going to use a stone veneer on both precast concrete and cast-in-place concrete elements on the bridge. Can anyone point me in the direction of A)details for attaching the veneer (should it be detailed like a brick veneer on cmu wall with flashing, etc.?) and (B) a generic spec for the stone veneer itself.

And I might as well throw in a (C): any things that I should watch out for or be careful of or check or...well, you get the point.

Any input will be appreciated.

Thanks in advance

Ron

 

[dik]

I think that you may want to avoid using a bonded masonry veneer and do a conventional cavity complete with a non-corroding basecourse flexible flashing. I would likely avoid using a 'shelf-angle' approach at the base and support the base coursing on a concrete ledger. This can be coloured or patterned to match the existing stonework as much as possible (in any event, it should be executed in an attractive fashion) and maybe duplicate the arch geometry and first voissoirs or ring in concrete including 'fake' stones.

The veneer can be attached to the concrete backing 'arch' using stainless dovetail anchors or other adjustable ones. The stone or concrete cap can have a drip cut or cast into it, overhanging the stone veneer by an inch or two. A proper stainless steel 'cap flashing' should be installed.

Reinforcing should be such that it won't stain/bleed.

Materials chosen for the veneer should closely mimic the existing and the veneer may be 8" thick or whatever (not necessary to think in 4" nominal). Mortars can be modern but coloured to match the existing or what the existing would look like in 10 years. Restoration of the existing mortar should reflect the existing mortar and have similar constituents and be a similar mix.

The concrete contractor should be skilled and the spec should be tight to prevent 'screw-ups'. It may be prudent to have the contractor provide sample concrete components(generally two approved and the resulting product being within the range of the samples). Careful about the approval process, you may have to live with it!

All attachments and fasteners should be detailed using materials that will not drip or stain. The existing stone may have chemicals that do that (often stones have iron or sulpher based compounds that darken).

I would likely get a 'restoration' architect involved because my aesthetics are terrible (he would likely be technically adept). He may be able to design the underside of the arch (intrados) in concrete so that it will be attractive.

You will likely have more fun verifying the strength of the existing structure. I can email you a number of articles on arch design in *.pdf format if you need them.

 

[RRBegin]

Thanks for the input!

We are using conventional bridge elements (precast box beams and CIP retaining walls)with stone veneer. This was as required by the historic people who have final say in all of the elements.

We currently have the CIP walls detailed with "brick" shelves, and the box beams detailed with shelf angles. I hadn't thought of using a concrete shelf on the beams until you mentioned it. I like the idea. I imagine that the added cost of forming in the casting beds will be the deciding element; although I have been told that casting inserts into precast elements is not a favored detail for the precasters.

We are limited to 4" thickness for the veneer for structural reasons. If we use a rubble pattern for the veneer, how do we locate the anchors in the cip concrete; its not like brick work where you have nice 16" increments that you can use. Should I call for an anchor below each stone? And what about with the precast elements? There are two different trades involved, masons and precaster.Is there a drilled anchor product? This leads to another question: if we do drill, how do we avoid the strands in the precast boxes?

Phew! Enough already!(But I can't promise that I'm done)

Thanks for the advice so far, most of which is very helpful. I would really like to see a detail that has been used by others, if possible.

 

[dik]

I would avoid using a 'shelf angle', generally they have a limited life, are ugly and are inappropriate for restoration work.

The use of a concrete ledger can be problematic due to honeycombing (more likely at the exposed corner, the contractor should be aware of the concern address this in his formwork and proper vibration. The use of dovetail anchors can alleviate the problem of spacing. The anchor slots are vertically continuous and can secure a 'rubble' ashlar pattern. I would avoid drilling if pre/post tensioning is involved.

The samples prepared by the contractor may include a ledger condition to check for honeycombing. They can be sufficiently large (maybe 4'x4') to permit the cast-in dovetail channel (stainless).

Maintaining heritage can be pricey... I've seen too many poorly executed 'additions'. Feel free to pass the comments on to your local 'Historical People&quot;... I'm on one of the local heritage committees in these enviorons... (tekkie plebe <G>)

 

[dicksewerrat]

Have you looked at casting the 'rubble' rock right into the concrete and painting it to look like the original bridge? There are contractors that can copy the rock pattern of the original bridge and put it in the forms.

 

[DaveAtkins]

I would talk to the Indiana Limestone Institute about your questions. First, I disagree with dik about using mortar in the limestone joints. Normally a flexible sealant is used, to prevent restraining the individual pieces from expanding thermally. Second, limestone veneer is most often SHOP attached to precast concrete, not field attached. DaveAtkins

 

[dik]

I guess we disagree...

Flexible sealant would be OK for any vertical control joints, as encountered with normal veneer construction and I've even used it for 'toothed' masonry where the architect did not want a definite vertical line. I don't think it would fare well on the horizontal joints, in particular those at the bottom where it would be supporting the full weight of the stone above, or is there another method for vertical load transfer? How would you transfer vertical loads?

Shop application of the veneer as a 'wall panel' may be a good possibility depending on the size and configuration of the arch. I've seen this done for new construction with small panels but not for restoration 'type' finishes.

I didn't know they had an Indiana Limestone Institute... great idea to contact them.

 

[mrbridge]

Have you looked into using precast elements with a form liner texture? Form liner has come a long way in recent years and can be stained to accurately mimic real stone. My experience shows that you will have fewer problems during construction and reduce the maintenance by using precast. Precast can be lighter weight than real stone veneer, you will have more control over the final product, and cost is competetive with real masonry veneer.

 

[RRBegin]

Thanks everyone so far...

Some general responses:

Form liners are out; the historic people generally don't want to use them, and I personally am not a big fan of making one material look like another (I think this was some subliminal message from a college professor that I had back in the day...)

I will probably go with two different details: one for the cast in place concrete where the veneer will be one stone thick with a reinforced concrete &quot;fill&quot; behind; another for the precast elements where the detail will utilize cavity wall details with dovetail anchors, etc. (after my original post, I consulted a masonry catalogue for attachment hardware and &quot;discovered&quot; the cast in vertical anchor slot -thanks to those who suggested it.

How can I contact the Indiana Limestone Institute? Sounds like a good source for information.

Any other opinions on the mortar vs flexable sealant? I am leaning toward the mortar (masonry structures have been built this way for hundreds of years, sucessfully, I presume from the number still around).

I will enquire with the precaster's if they can accomodate a brick shelf, seems like the best way to go to me.

Finally, it has been my experience (and the experience of countless engineer's spouses, no doubt) that if you put four engineers in a room and ask for the best way to do something, you'll get a MINIMUM of four answers, and probably six or more (you know, the &quot;Wellllll...it depends,...&quot; folks who never have a straight answer for anything). Thanks for your input so far, and feel free to disagree, it beats me finding out the hard (spell that L-A-W-S-U-I-T)way!

 

[dik]

If the veneer has the appearance of 'cut stone' then you can use 1/4&quot; dia. stainless steel pins from the lower stone to the upper stone passing through a hole in the dovetail anchor. Where the bedding plane is not horizontal, the dovetail anchor can be twisted to accommodate the sloped surface.

 

[RRBegin]

I'm not sure that I follow the last post. What are the pins for? Are they vertical? I thought that the anchors were located in the joint, under the stones. Can you please clarify?

Thanks

 

[dik]

The stainless pins are from stone to stone and pass through a hole in the anchor. They are vertical. The anchors can be embedded in the mortar or alternatively, steel pins can be used to secure the anchor to the veneer.

The dovetail anchors have a hole in them. A pin is inserted into the lower stone, the dovetail anchor fits over the pin and then the stone above fits over the pin. Very positive anchorage and often used for stone veneer.

d
o
v |stone | pin |
e |________|_________|
--------------|---- <-------anchor
t ---------|----------
a |stone | |
i | | |
l

I'm not sure how that's going to print... ASCIIArt...you may have to reformat the sketch. I'm glad I didn't try 'hatching' the stone <G>.

 

[dik]

Proportional spacing messed it up... capture it and use a non-proportional font...

 

[RRBegin]

Thanks for the, ahh, sketch.

I get the picture (sorry for the awful pun). The pin is located perpendicular to the bedding joint, and is inserted into a hole in the stones directly above and below. The anchor is placed on the pin before the top stone is placed (or the pin is passed through the anchor, I suppose).

Sounds expensive and time consuming. What has been your experience? (Don't get me wrong, it also sounds very secure.)

Well, I went and did it! I asked the historic folks for a recommendation regarding ashlar vs rubble stone veneer, and guess what? They were surprised to see that the stone facade was going to be a veneer rather that the existing stone reconstructed into the new parapet. Should I be surprised? It has been shown this way through 14 revisions (no kidding) of two reports that they have seen, commented on, and finally approved over the last five years of local, state, and federal review.

I'll keep you posted when the dust settles.

 

[dik]

It's pricier but within limits for stonework... and great for larger stones... of the 2'x2' and larger. It's very positive. I've also used it for actual cut stones and have used it for securing veneers in lesser seismic zones. I wish there was a way to embed sketches in the messages... I cold have knocked it off faster by autocad... and it would have made more sense.