huangyhg

historical restoration
the walls are masonry or stone? if so your first job should be re-mortaring and re-pointing the walls to full height. you presumably would do this anyway as part of the finished job.
then look at your final design solution. can you introduce some masonry (or even concrete) piers which will not detract from the final job? if so these should be built next and will give you structural support as well as location points for temporary braces etc. you could also provide location points ("strong ponts") in such a 15 inch wall, once it has been re-pointed, for attachment of temporary braces. these can almost always be hidden afterwards (eg within depth of a new floor etc etc.)
many more ideas but not the time. hope this helps!!
adt
i would strongly suggest you demolition and reconstruction one floor at a time and even each floor by sections, depending on house size and shape. i know that this will be complicating, but is the safest way.
prex
some years ago, we did some preliminary design on an 1800's era five story convent house that was not capable of meeting code with its wood floors. with renovation, the floors would have to be replaced with steel framing, but the exterior was such a "public treasure" according to the hysterical society (oops, i meant historical society) that we had to a least find a way to salvage the exterior load bearing brick walls.
what we came up with was a series of vertical (temporary) trusses, tied to the existing brick walls which would be erected first. then, interior floors and roof would be gutted one at a time until there would be a complete shell, open inside.
the new floors could then be installed from the bottom up with the new roof finishing off the work. i agree with adt that re-pointing could be considered as a preliminary effort if it is determined that the wall condition required it.
as it turned out, doing this work was so expensive that the sisters told the historical society to go fly a kite (not their words) and demolished the entire building. we did replace it with a close replica of the original, though. the difference was about a million dollars us.
in lisbon, reconstruction of ancient buildings considered with historical/architectural value must preserve the exterior masonry walls, wich are temporarly reinforced by a bracing system.
this bracing sistem is always made of steel elements. it is placed outside (of course) and must have very heavy foundations for its global stability. the connection between the bracing system and the masonry walls are usually made by wood plates - something like masonry sandwich - to spread the tensions that can appear, due to wind or instability.
windows openings are usually used to connect the wood plates from both sides of the original wall, so that it wouldn't be necessary to damage it.
finally, i think this system makes the demolition process safer.
to ricardo, what on earth do you do with the masonry walls? lisbon was the site of a tremendous earthquake in the 1700's was it not? is there any mandate to somehow improving the performance of these structures once they are rehabilitated?
trying not to be too long, i should say that, in fact, in 1755 there was a huge earthquake followed by a devastating fire.
since then, buildings were made with a wood structure inside the mansonry, knowned by 'cage' buildings (that's the best translation i could find), wich brings flexibility to the all building.
i believe it was, eventually, at the time, the first effective anti-sismic construction technic.
actually, the reason to maintain those ancient walls is only political.
if the contractors completely demolish a building, they eventually won't re-build it the same way. the city hall prefers not having problems afterwards, with the harm allready done.
(law procedures take many, many yars).
so, in that kind of buildins, the resistance of those mansonery wall is not considered, only its weight.
the resistance is assured by the structural concrete.
in fact we are talking about a completelly new concrete structure with some weights coupled, and not reinforced masonry walls.
it's much more expensive, but it's the price we have to pay.
thanks ricardo, its always good to here what others are doing with their historical buildings in light of seismic hazards.
hello bigdog,
restorations are tricky and you need to assess the failures correctly. i would first work on the supporting elements. you need to render/plaster the walls straight away. sika have a product called sikacem810. it is a reactive bonding agent and mortar improver. you add that to the pointing/render/plaster. it will increase flexural-tensile & compressive strength of the wall. the additive also allows for the plaster's greater resistance to wear and abrassion that may result from demolition works.
furthermore, i would allow for prop supports to slab at 1 metre from the walls. this will assist in ensuring that the floors do not shear on to the walls.
i believe that the 15" wall is of stone/rubble construction.
hope this is useful.
riz

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