Stone masonry wall 5

[Guern]

Refurbishing a stone masonry dwelling by removing the original floors, and building a timber framed building inside. The floors used to provide lateral support to the walls, but the new internals provide no lateral support. A new roof spans onto the external walls to provide lateral support at eaves level. Now the external walls will need to span vertically about 8 metres to resist wind loads. Walls are 450 mm thick. How can the walls be strengthened?

 

[kieran1]

Why don't you tie the walls to the new timber frame?

I am not sure what country you are based but 450mm thick walls would easily span 8.0m high and resist wind load where I'm from.

Kieran

 

[Guern]

Thanks Kieran.
The wall has window openings which halve the width of wall effective in bending, without reducing the width exposed to wind loads. The windows also prevent the wall from spanning horizontally. The masonry is old, and cannot resist bending tension. I have not been able to show that the walls resist wind loads.
My initial approach was that the original walls should be provided with the same support that they had from the original floors, i.e. compression connection to the wall facing the wind at floor levels to collect wind loads, and shear connections to the side walls. I am having difficulty designing suitable connections.
Can you suggest anything?

 

[msquared48]

So the walls are about 18" thick, 26 feet high, and are in a deterioratd condition?

Sounds like you need wood compression struts from the post frame to the wall, and thru the wall brick masonry ties with exterior metal plate rosettes, all at the two interstitial floor levels.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ishvaaag]

Furthermore, masonry and wood stabilizing it make dissonant companyons. Wood moves from higrothermal seasonal changes, something not comely if you want to stabilize the masonry with wood.

You will need to make wood, masonry and connections resist the higrothermally caused forces, something that can be far too dear to do. You can then let the wood structure slip loose but then no restraint, and walls need be made then auto-stable, either by themselves or other structural additions.

 

[shobroco]

There are thousands of stone buildings with timber floor structures that brace the walls and have done so for hundreds of years; the minimal amount of seasonal movement is easily handled by the walls. You are removing the existing floors (presumably wood) and the bracing, why can't you simply connect your new structure to the walls to replace the existing bracing the way that MM said? It is possible to embed a connection if you don't want to see external rosettes. I have refurbished an 1846 5 storey stone mill into residential and commercial use and the 60' high stone walls are still braced with wood the way they have always been.

 

[CJPW]

you could cast in a rc ring beam to the wall head and cast in threaded rods to tie in the wall plate.
Use 30x5 galvanised mild steel vertical restraint straps @ 1.5m c/c along length of wall plate(s) (bolted to wall plate, resin anchored into stones @ min. 150mm from bottom of strap).
Tie the roof rafters to the wall plates with twisted tie clips, the joists (assuming a framed roof structure) can be tied in horizontally using restraint straps cast into the rc ring beam.

when you say stone, what is the finished face like? dry stone walling like the West Country? rubble filled core? any signs of freeze/thaw cracking in the stones? is there any mortar present/left? and if so is it a lime based?
you could chase in steel 50 x 50 SHS windposts to frame the window openings (full height of the wall)or use traditional timber.

depending on the condition of the stone resin injection into the stone wall core can be used to increase the stiffness of the wall, although I personally would not rely on this as a prevention of wind bending stresses more a serviceable requirement for excessive deflection.

 

[Guern]

Thanks CJPW. The top storey is in the pitched roof. The floor of this storey (the third floor) will be supported on the internal timber frame.
I will bear the roof on to ring beam, and use a horizontal restraint connection between the third floor and ring beam that allows vertical movement for shrinkage. This will give stability to the timber frame.
The stone is mainly granite with some brick, rendered on the outside. The mortar is lime based, and of poor quality. No freeze thaw cracking.
I will try inserting wind posts. The difficulty will be fitting them in unobtrusively.

 

[ishvaaag]

There is risk in stabilizing masonry structures with wood. This of course is far more true when neglecting higrothermal change, and with thin masonry walls.

Even in the old structures, usually with thick walls, ruptures at the supports are common, where the stabilization as understood in a modern way is jeopardized.

So you may have reasonable stabilization prior to slip caused by mechanical forces (wind) on the standing time moment of higrothermal equilibrium, and you may get even strong enough stabilization at limit states through cleavage of properly solidary floors.

In the intermediate states some unwanted things may develop. If not, the walls have enough degree of auto stabilization for the matter.

It is entirely an altogether different problem rehabilitation where the structural system is to be respected and design of a new structure.

For masonry work to be stabilized through wood structures, I would closely inspect these matters, be it as a project author or a reviewing party.

 

[ishvaaag]

I may add (and I have not developed my ideas from it) stabilization of masonry walls through woodwork diaphragms is intently excluded from the typified structures in the structural code for masonry in Spain (not a country without tons of old buildings using masonry walls and wood supported floors) CTE. Since the code is performance based, either you have autostable walls or you show the performance of the system is adequate, which is exactly to what I have been refering in my two previous entries to this question.