In-place mortar shear tests

[bouk715]

I'm working on a project in Massachusetts where the architect is proposing to gut the entire building (5-story building). Building construction generally consists of multi-wythe brick walls with wood-framed floors and roof. Per Massachusetts amendments to the 2009 IEBC, since this is Level 3 work we are required to provide anchors at all levels to tie the walls to the floor and roof construction. In general, we will be using thru-bolt anchors with a plate on the exterior. There is one level (2nd floor) where we are investigating using a different method on 2 exterior walls since there is a terra cotta veneer attached to the outer wythe of the brick (which may make the thru-bolt anchors appear unsightly). I'm aware that Hilti, Simpson, etc. have the 22.5 degree drill & epoxy anchors that could potentially be used, but they all carry the caveat that the mortar shear strength needs to be tested in accordance with IEBC Appendix A to indicate a minimum mortar shear strength of 50 psi. I took a look through Section A106.3.3.1 of Appendix A and came up with a few questions:

* Appendix A states that the outer wythes need to be tested. Since the outer face of the wall is terra cotta in this case, my preference would be to test from the interior. Does anyone know the reason for the outer wythe requirement? Is the assumption that the mortar would be weakest on the exterior due to weathering?

* It also states that there should be no less than 8 tests performed (A106.3.3.4 Item #3). My interpretation is that this would be necessary if we were doing a whole building lateral load analysis, not investigating the use of drill & epoxy anchors on just two walls of one floor. Item #1 of the same section indicates that there should be at least 2 tests per wall, so I'm thinking that this may be more applicable to our case (so 4 tests, not 8). Any experience someone has on the development of these requirements is appreciated.

* Am I going about this wrong? Is there a thru-bolt anchor that can be used that is a bit more aesthetically appealing for terra cotta?

Any feedback is greatly appreciated!

 

[dhengr]

Bouk715:
My argument would be..., You need a large enough number of test to be confident in the integrity of the wall areas involved, for the methods you are intending to use. And then, you need a less invasive inspection process, over the whole wall, to confirm that your test locations are truly representative of the whole wall involved. If we codified any more of this crap, nothing would ever get done, all for the ongoing argument about the correct number of tests and their exact locations. One side will always want fewer tests and the other will insist that more tests are needed. What ever happened to allowing a qualified and experienced engineer to exercise some good sound engineering judgement in these kinds of things. How can a code writer, from a distance, ever know what’s needed in the way of numbers of tests. After all, you are the one who must be convinced, it’s your stamp and licence on the line. And, the AHJ makes damn sure to fall back on that, if something goes wrong; however they codify it, so as to keep themselves employed and in the loop.

I would guess that you want to test the wythes you are loading, by the methods you are using. And, many bldgs. have four walls for enclosure, so min. two test per wall kinda gets you to their eight tests. I think your thinking is about right otherwise. A bigger question might be a complete survey of all of the walls and confidence in their condition, for this kind of gutting and continued use project. If the walls are good, why wouldn’t you use the same system everyplace, and save the contractor and inspectors the retraining on several methods. Another big issue is that you take a close look at the stability of the walls during the gutting and rebuilding process. These walls work fine when they are supported by each existing floor diaphragm, but less well when unsupported for several levels during the gutting. Finally, select repair mortar which closely matches the existing mortar in strength and stiffness. The newer mortar mixes are not flexible enough to perform well with the older softer mortars and bricks, and this mismatch can be detrimental to the final wall performance.

 

[bouk715]

Thanks dhengr...this is very good feedback. I was a bit surprised to see a number of tests specified in the code as that is usually left up to the EOR's discretion.

As far as using different methods of floor/roof attachment - I was coming at this from the direction that I am much more comfortable using thru-bolt "government" anchors, I guess that's just a personal preference. Drill & epoxy anchors in a situation like this require some level of skill by the installer. Given that it is a fairly isolated area that it is being used, I'm okay with them (with pull tests/special inspections of course).

 

[bookowski]

I have not interpreted 'outer wythe' to mean exterior, I think they just mean the outer wythe of a multi-wythe assembly so interior or exterior - just not inner wythe.

The problem with adhesive anchors that you run into is edge distance. I'm assuming you have joist pockets and are anchoring to the face of joist, this puts the anchor very close to the pocket which means little edge distance. There are ways to pad out the joist or do other details to avoid this but usually the hilti specd edge distances are hard to achieve. I think the 22.5 hilti config also specifies a min of 13 inch wall, i.e. 3 wythe, so your 2 wythe wall wouldn't satisfy this.

I agree with dhengr that you need to use judgement with these things. Hilti (or simpson) is not going to take any chances with something like historic masonry so they give you large edge distances, min thickness, and min material strengths that are going to be hard for you to achieve. Really difficult to codify this stuff.