On Tue, 20 Mar 2018 12:28:24 +0000, Tim+ wrote:

charles wrote:
In article , Max
Demian wrote:
On 19/03/2018 10:26, Brian Gaff wrote:
Well the earth is curved after all, so in reality nothing is flat or
level is it?

I wonder how big a thing (building? bridge?) has to be before
designers have to take into account the curvature of the earth?

It's certainly taken into account when predicting uhf tv coverage.


Humber bridge towers apparently diverge by 36mm due to curvature.

I tried to find out if they'd done something similar when building the
Severn suspension road bridge just over 50 years ago but the only
reference to 'tower divergence' was in relation to 388 millimetres[1] of
lean back to compensate for the weight of the suspension cables which has
nothing to do with the curvature of the earth over the one mile
separation distance.


I wonder what the *smallest* man made object is that has to take account
of the earths curvature?


I'd guess at something about a tenth of the size of the Humber Bridge
since the resulting 3.6mm 'curvature of the Earth allowance would likely
come within normal tolerances on a structure one tenth the size of the
Humber bridge but that's just a guess.

Sadly, I've not been able to find an "Earth's curvature compensation"
figure for the slightly shorter Severn bridge (1 mile span versus the
Humber bridge's 1.4 mile span), just that 388mm[1] 'lean back' on the
towers during construction to compensate for the suspension cable forces.
It might have been mentioned in the Timewatch/Timeshift documentary on
this record breaking bridge but I've not got the time right now to spin
through the recording just to find out whether or not a figure was
actually mentioned.

[1] AFAIR, the figure was 388mm BICBW.

--
Johnny B Good