25 mm settlement origin
25 mm settlement origin
(OP)
I remember reading in an article that the 25 mm threshold came from observations of buildings that suffered some kind of settlement. The performance of the buildings that suffered settlements greater than 25 mm was deemed unacceptable. Is this true? Who made this observations? Terzaghi maybe? I can´t recall where I read this the first time. It could be great if you guys could share a reference.





RE: 25 mm settlement origin
RE: 25 mm settlement origin
If you look at the calculation of sub grade modulus, its SBC/0.04, that is the limit of settlement for 25mm.
So in a way Terzaghi has set the limit for using 25mm. WHY? for that I will have to read the paper to answer that question.
any other views plz..
RE: 25 mm settlement origin
Differential foundation movements and any limits should be based on the building's ability to accommodate those movements. There are limitless combinations of material types and geometries, so to come up with any set number that would apply to multiple situations would seem illogical.
I deal with foundation movements and causes of damage to homes every day. If someone has a wood-framed house with wood siding, and they have some differential foundation movements that have only caused some minor gyp board damage, I explain to them why they are lucky their house is built that way and can structurally accommodate the movements.
Other Example:
Pre-engineered steel building, all metal panel siding, slab used as a warehouse for storage: very tolerant to differential foundation movements
Three story office building with brick cladding all walls: not tolerant to foundation movements
RE: 25 mm settlement origin
Too often we get caught up in finding a computable number, rather than a concept.
RE: 25 mm settlement origin
Limits on differential settlement = limits on allowable deflection of members?
My code,EUROCODE is very cheap on giving informations on limiting member deflection.
A base value of span/250 is used but later on it is said that the maximum allowable deflection of any structural memeber should be based on the ductility of the "structure" siting on top of the member for wich the calculation is beeing done...a value of span/500 is mentioned.
I looked at Australian code, AS, since I wanted to see how other codes deal with this matter and they have named few values, and one of them is a limit od L/1000 if member is supporting a masonry partitions.
The last one seems to have the most logic since the masonry wall is brittle and suppose you have a beam or a slab of a span 600cm you should limit you deflection (differntial settlement "beam end" - "midpoint beam") to 600cm/1000=0,60cm.
Compared to European standard600cm/500=1,20cm 600cm/250=2,4cm.
Very large difference in values.
How is this defined in ACI?
This deflection parametar is basicly limiting deflection angle of end point on a member and its mid point.
span/1000 for L=1000cm max.def.=1,00cm for L=750cm max.def.=0,50cm for L=350cm max. def.=0,35cm. all different values but all have the same deflection angle wich is probaly based on a ductility of a member beeing suported.
I found this article that deals with differential settlements of foundations and the damage that is couses in the superstructure.
http://www.concrete.net.au/publications/pdf/TN61Ar...
Based on the material used you can find limiting values for dif.settle or lets call it deflections of bearing members - page 6.
Looking at the values it is clear that your brick partition walls will probably crack if there is a deflection greater then 1cm!
COnfusing thing is that in many foundation books there are values mentioned to allowable diferential settlements wich I think are mentioned for designing your members for their ultimate limiting state (a state before they break, bearing capacity of a member).
Todays design criteria have been updated are more or less all governed by the servicibility demands (cracking, deflections, limiting stresses im members).
RE: 25 mm settlement origin
RE: 25 mm settlement origin
RE: 25 mm settlement origin
One pint of (~3/8-1/2") gravel is NOT 473.2 mL
RE: 25 mm settlement origin
RE: 25 mm settlement origin
Luckily the staff are usually willing to consider it to be an editorial change, so it can get fixed without a reballot.
* And I believe it was "About 1 pint"