Fully Grouting and Pinning Existing Masonry Walls

[TylerM94]

Hi,

I'm working on a project that is a building re-model. The building is an early nineteenth century brick masonry structure (4 stories) with timber framing at the interior. The building is being transformed to a library and will use the "box in a box" approach where the existing three-wythe masonry walls will be maintained and all new steel framing will be dropped in as the primary gravity structure.

The brick construction is made of two wythes at the exterior with a 1" air gap and a third wythe at the interior tied together with header bricks every 6 courses. The engineer I am working on feels hesitant about the air gap, even though my calculations show the wall works just fine as a two wythe wall for gravity and out of plane bending based on the unbraced length of the wall.

I'm curious if anyone has experience fully grouting and pinning walls. What pitfalls are there? What are the major challenges? I am assuming we want to drop steel columns all around the perimeter to fully brace the walls during construction. What other work would be involved?

Are there any engineering articles from trade magazines or journal articles you could point me to?

Thanks in advance for your consideration.

 

[r13]

Not sure I know how to do it, just a few notes and questions here. Old brick can be tricky, take good samples and test the strength. I think the air gap needs to remain as is, the brick needs breath. What is the share of loads between the masonry wall and the wood frame, how they tied together? Do you have information on the existing foundation, soil strength/condition? I think it is better to work on the foundation with the existing framing stays intact, and provide more bracings as required.

 

[TylerM94]

Thanks for your response retired13. What do you mean by share of the load? Heavy timber girders run north-south and land on bearing plates in the brick wall. 2x10 joists span the opposite direction and pocket into the walls with “fire cuts” at the end.

The existing foundations are rubble walls. Geotechnical studies were performed and there are no issues with the soil in terms of required bearing capacity / no improvement of the soil is required. It’s interesting you say the brick needs to breath. Is there evidence for this I could use to push back on my pm in a professional way, explaining why grouting is not the preferred approach?

 

[masonrygeek]

There are a few FEMA and ASCE documents that can assist:
FEMA 547 - Techniques for the Seismic Rehabilitation of Existing Buildings (Chapter 21)
FEMA 774 - URM and Earthquakes: Developing Successful Risk Reduction Programs
ASCE 41 - Seismic Rehabilitation of Existing Buildings

The FEMA 547 document will probably be the most helpful. It may also give you some alternatives to your box in a box idea. There are pros and cons to any rehabilitation scheme and a lot will depend on the quality of the existing masonry.

 

[r13]

TylerM94,

"Breath" is not the appropriate word. The air space provides thermal protection, and keep moisture/condensation out. It is commonly provided between brick veneer and brick bearing wall. I don't think it should be grouted solid.

 

[MotorCity]

If the brick has been there since the 19th century, why do you want to change it now (assuming its sound)?

I would not grout the airgap for two reasons:
1. It is most likely a drainage path for any moisture that finds its way into the wall. Filling it could direct moisture elsewhere and create water problems.
2. Unless the wall is shored, the brick will have to act as formwork. Doable, but probably not a great idea

What do you mean by "pinning"....pin what to what?

 

[GC_Hopi]

Simpson makes some post installed ties that are to be used for multi wythe walls. Might be worth a look and it would save you from grouting which contractors hate.
Link
Structure Mag Article

 

[phamENG]

I don't have any good technical documents to share at the moment, but the bricks that comprise that wall are likely softer than modern bricks, or at least less uniform. Much depends on how they were molded and fired. I've dealt with several colonial era brick structures here in the mid-Atlantic for which the bricks were made on site with clay dug up from the foundation excavation and fired in site built furnaces. Needless to say, quality control was questionable if existent at all. Also, there can be variations within each individual brick (one end of the brick was closer to the fire) much less variations between lots. So you typically have one face that is harder and less porous, and one face that is softer and more porous. In modern bricks, the design of the ovens is a lot more advanced and the bricks tend to be heated more evenly and with a much greater level of quality control. Porosity plays into moisture movement within the wall.

Mortar is also an issue. A building form the early 1800s will have a lime mortar. Lime mortars are also very porous and allow for a lot more movement of water than more modern masonry cements and portland based mortars. If you start repointing with a modern mortar or filling voids with modern grouts, you're likely going to trap moisture somewhere it doesn't belong. I see you're in Massachusetts. When winter comes, that trapped water will freeze and expand - and you'll be getting some irate phone calls form the owner.

It's important to understand how the evolution of energy codes, moisture/water management, and even air conditioning has impacted structural design and the materials with which we build. In a building like this, the structural brick is as much an architectural element as it is a structural one. When the building was built, structural engineering wasn't really a thing yet, at least not the way we think of it now. In fact, architecture was still in it's infancy in the US in the early 1800s. When you make a change to this wall, you need to think like an architect, engineer, builder, and conservator all at the same time.