noticed the bridge at Havre DeGrace, De.
It seems unusual to see the bridge structure under the rails. On a river, I assume putting the structure on top provides clearance for boats underneath. No need in this case, it's an island in the foreground of the picture and there is a longer span on the other side
Is there some advantage to building it underneath: cost, ease of construction, ... ?
other photos
greg - Philadelphia & Reading / Reading
With the deck style (underneath), the bridge is narrower. That uses less steel. Saves money. Also saves deadweight. Which means the bridge can also be designed lighter. Saving more money. Also, there is no need to allow for the through portal that is needed for the through style. Generally, if there is no need for clearance under a bridge, a deck style is used.
The interesting thing about the picture is the use of the through bridge over the shoreline. Usually, the through bridge would be more towards the center to allow clearance for traffic. But. Closer examination of the shoreline under the through bridge shows pilings and a dock. Of sorts. I expect the existence of the dock somehow is related to having a through bridge immediately adjacent. In other words, if there hadn't been such shoreline usage, they likely would have used a deck bridge there, also. Or, optionally, that side of the waterway is the navigable section. Kinda weird seeming, but maybe???
Ed
The navigable channel is behind the photographer. That's the Perrysville side of Garrett Island.
I should add that the Eastern channel is hypothetically navigable, but the NEC Bridge to the south may prevent that now. Also, the Conowingo Dam renders a lot of that moot. There's nowhere to go upstream.
7j43kWith the deck style (underneath), the bridge is narrower. That uses less steel. Saves money. Also saves deadweight. ... Also, there is no need to allow for the through portal that is needed for the through style.
thanks, I never realized that and that is consistent with the design of the bridge on the other side of the island (below).
Deck structures usually don'thave wide load restrictions.
Dave H. Painted side goes up. My website : wnbranch.com
It's entirely possible the shoreline shown in the first photo was not like that when the bridge was built. Most likely, in fact. A quick following of the link provided indicates that the bridge was built 20 years before the dam. A lot could have changed after the dam went in. The Ohio River is a good example: it is entirely different since they completed the locks and dams in the mid fifties. The situation here could be similar. Interesting bridge, though.
Robert
LINK to SNSR Blog
ROBERT PETRICK It's entirely possible the shoreline shown in the first photo was not like that when the bridge was built. Most likely, in fact. A quick following of the link provided indicates that the bridge was built 20 years before the dam. A lot could have changed after the dam went in. The Ohio River is a good example: it is entirely different since they completed the locks and dams in the mid fifties. The situation here could be similar. Interesting bridge, though. Robert
I consulted a 1902 topo map and compared it to a 1958 map. Curiously, the opposite happened: they cut the shoreline back when they built the current bridge. Generally, the shoreline seems to be the same. I guess the Bay offset the reduced Susquehanna flow.
i guess i've never noticed an arched type of bridge underneath the deck.
why do you think they used that type of bridge instead of the non-arched type of bridge also underdeath the deck next to it?