Anthony, You have to think about annual rain/snow fall in your dry parts of OZ vs N.America. But I do have to agree that we have wooden railroad tressels that last way over 10 years (100?) I think the sheds are snow protection. When you get 4-5 feet of fresh snow on a bridge, removal is problematic, especially in the horse drawn era. Regards, Bob S.
On Sat, Oct 18, 2008 at 10:25 PM, Anthony Farr <[EMAIL PROTECTED]> wrote: > That's a good explanation, except that wooden bridges have proliferated > worldwide while covering them seems quite limited. If weather protection > for the bridge structure was the issue then bridge covering would be > universal, it's reasonable to think, but it is uncommon except where heavy > snow falls. However, pedestrian comfort is usually the only justification > for footbridges to be covered. > > Here in Australia are many wooden bridges of great age, often over a century > old, that have survived uncovered with basic maintenance, giving the lie to > Wikipedia's claim that, "Wooden bridges tended to deteriorate rapidly from > exposure to the elements, having a useful lifespan of only nine years. > Covering them protected their structural members, thus extending their life > to 80 years or more." > > The Straight Dope writer unfairly debunks snow protection by claiming that > it's the weathering effect of snow that's being argued. AFAIK and have > read, it's the WEIGHT of the snow, not it's weathering nature, that bridge > covering seeks to deter. A bridge deck, being flat, could pile up with a > destructive weight of snow faster than it could be cleared. In a severe > blizzard, with everyone confined indoors, a bridge could collapse under the > load of snow before the storm cleared and the snow plough could arrived to > remove the burden. Putting a pitched roof above the deck prevented snow > from piling up. Simple as that. > > Regards, Anthony > >> -----Original Message----- >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of >> Derby Chang >> Sent: Sunday, 19 October 2008 8:09 AM >> To: Pentax-Discuss Mail List >> Subject: Re: PESO: Covered Bridge >> >> >> A Straight Dope classic >> > http://www.straightdope.com/columns/read/1136/why-are-covered-bridges-covere > d >> >> Nice series too, Jack >> >> D >> >> > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
