Settlements : Upward or Downward???

[Raj Malhotra]

In all the text books concerned with Structural Analysis in dealing
with problems of support settlements they a;ways state the prolem as
“----- if the support at B settles downward by ----“ , I
want to know why use the word “downward” ? Can a support
settlement be upward??Is an upward support settlement possible???

[Mike Halloran]

- See 'gravity'.

- The word 'settlement' itself suggests a direction, so 'downward settlement'
is redundant. But language does not rule out the possibility of an upward
adjustment in a structure's support.

- Slab houses (e.g in flood- prone areas) can be elevated by pumping sand under
them. That would constitute an artificially induced upward support
settlement, I guess.

- I can conjecture a few natural processes that could produce similar effects.
One that occurs commonly is 'frost heaves', where water gets under a highway
and then expands on freezing. Drainage around building foundations in frost-
prone areas may be required for this reason.

-Mike-

[Raj Malhotra]

Post by Mike Halloran
- See 'gravity'.
- The word 'settlement' itself suggests a direction, so 'downward settlement'
is redundant. But language does not rule out the possibility of an upward
adjustment in a structure's support.
- Slab houses (e.g in flood- prone areas) can be elevated by pumping sand under
them. That would constitute an artificially induced upward support
settlement, I guess.
- I can conjecture a few natural processes that could produce similar effects.
One that occurs commonly is 'frost heaves', where water gets under a highway
and then expands on freezing. Drainage around building foundations in frost-
prone areas may be required for this reason.
-Mike-

Hello,
Thanx for the reply!!You said,"------ "frost heaves"where water gets
under a highway and then expands on freezing-----".
Can we say we , that consider a deck slab of a bridge which is
supported by beams then the beams in turn supported by columns.Here,
imagine that, if water gets accumulated below the deck slab so that
all the beams in turn get submerged . Then as the water freezes it
would cause the beams(the supports to the deck slab) to expand
resulting in upward settlement.
Is this example OK???

[Dan Tex1]

Settlement generally does refer to a downward movement. Generally, after you
put a heavy load onto the ground... the ground moves downward gradually over a
period of time as the soil compresses. However, upward settlement is possible
( though a bit of a misnomer if you ask me ).

If you want to refer to things in a more "exacting" and general way... you're
better off to describe such movements as displacements. At a structure
support... you can call it a support displacement. And, the term applies
equally no matter which direction the displacement is in.... upward
displacement, downward displacement, lateral displacement. To say that a
support has settled is to loosely describe the reason for the displacement.

Dan :-)

[Chuck]

Actually it would be a soil expansion that would cause an upward structure
displacement which would be analyzed using slab/beam on an elastic
foundation. Vertical loading on soil would be certainly be settlement
causing vertical downward displacement on the structure and mostly caused by
dead load of the structure since more than likely the full live won't won't
ever be realized at initial settlement.
CID...

Post by Dan Tex1
Settlement generally does refer to a downward movement. Generally, after you
put a heavy load onto the ground... the ground moves downward gradually over a
period of time as the soil compresses. However, upward settlement is possible
( though a bit of a misnomer if you ask me ).
If you want to refer to things in a more "exacting" and general way...

you're

Post by Dan Tex1
better off to describe such movements as displacements. At a structure
support... you can call it a support displacement. And, the term applies
equally no matter which direction the displacement is in.... upward
displacement, downward displacement, lateral displacement. To say that a
support has settled is to loosely describe the reason for the

displacement.

Post by Dan Tex1
Dan :-)

[Mike Halloran]

I'd say you're describing a bridge that's in, pardon the expression, dire
straits.

But Dan's answer is better; call it displacement, and allow 'settlement' to
imply displacement associated with natural compaction of the soil over time.

-Mike-