300 year old stone wall with crumbling morter 1

[eriksasha]

Hi guys,

This is a wall called Bourke House in Limerick Ireland. The actual house has disintergrated and only the front wall is left standing. The wall is 17 m long and 7.5 m high 0.735 m thick and I've been given the task of determining if a 1200 kg telecommunication box can be cantilevered at a height of 5 m. I've told the client that I don't want to hang anything on a crumbling wall but the client demands calculations and I'm stuck for determining Young's Modulus, Poissons ratio and so on for this wall.

Has anyone else had to calculate on such a wall and can give me some advice?

All the best

 

[dik]

I've had a fair amount of experience with historic masonry, but nothing 300 years old.

It appears that your problem with the wall is that the lime used for the mortar had insufficient hydraulic impurities and over the years most of these impurities have leached out.

Also over the years with derelict buildings, neighbours often borrow stones for their own use...

there is no sure fire manner to determine the strength of the wall without reconstructing it. In particular if the mortar is as badly compromised. The University of Leeds has done a pile of work related to historic masonry and they may be able to give you some local direction.

Reconstruction of the wall should be done using appropriate mortars... these are often lacking strength. Early masonry relied on the mass, thickness and low compressive stresses. Details were nearly always to minimize any flexural component. The wall might be able to be used for bearing, but not likely for flexure...

Dik

 

[HgTX]

Is the idea to reconstruct the wall, or give nice numerical analytical calculations of exactly how crumbly it is?

Hg

Eng-Tips policies: faq731-376

 

[UcfSE]

Is load testing an option?

 

[Ussuri]

Can you assume its a cracked section as the mortar is completely shot and do you calcs based on this scenario.

I can guarantee though that a free standing wall 7.5m high, with no returns, will fail under wind load if assessed using a current code.

I think short of getting testing done you might struggle to get any meaningful calcs.

Could you pragmatically suggest to your client that if the rest of the house has disintergrated the wall wont be long behind and what happens to his bit of plant?

I guess there must be a good reason why it needs to be 5m in the air and not at ground level?

 

[eriksasha]

The wall is the last part of The Wall of Limerick so it is a Heritage site. There is a pub on the other side and the clients wanted the communication boxes above that roof.

The Limerick County Council hadn't heard anything about this idea of building on the wall but I gave the clients an alternative solution and a part of Irelands heritage shall still remain for our children to see.

Thanx for all the replies!

 

[dik]

What was the alternative?

Dik

 

[eriksasha]

I placed the telecomunication boxes on top of a blockwork structure housing the toilets in the pub. I set up a steel frame punctureing through the roof and resting in the block work. I used BS5628 for determining the strength of the blockwork wall.

The old wall was not touched!

What did disturb me was the complete lack of interest from the client in preserving the wall. While I was working on this job Munster won the European rugby championships and were taken to this wall for the photo sessions with the politicians and all that. I shudder to thick of them arriving there and finding steel bracing plates on the outside!

Thank you very much for your replies!