Why were Older Bridges Commonly Built so Low to the Water?

[DurableEfficientGood]

Why were so many pre-1970 bridges built so low to the water that they do not even allow a single-level stand-up boat (serving as water buses or small fishing/research vessels) to pass underneath without raising or swinging the span? If they're built so low with short spans anyway, why not make them a pontoon bridge by making their light-duty piers floating platforms to save tons of time, money, and difficulty? Examples include the Oregon Trunk Rail Bridge (also known as the Celilo Bridge), the old Biloxi Bay Bridge (1962-2005), Norfolk Southern Lake Ponchartrain Bridge, Lake Ponchartrain Causeway, the concrete arches of the old Seven Mile Bridge (originally for railroad), etc.?

Why not build the non-shipping channel portions as high as a boardwalk pier, so that small single-floor stand-up vessels can pass under with traffic simultaneously passing overhead, just like how all bridges built since the 1970s have [been built at least as high as the Burlington Northern Railroad Bridges 5.1 and 9.6 (also known as the BNSF Railway Bridge 5.1 and BNSF Railway Bridge 9.6, respectively) across the Willamette River and Columbia River (both in Portland, Oregon and the second one also being in Vancouver, Washington), respectively]?

For example, see how the lowest spans of the Chesapeake Bay Bridge-Tunnel are built significantly higher than those of the Lake Pontchartrain Causeway, the lowest spans of the replacement Biloxi Bay Bridge (2007-present) are built way higher than those of the original (1962-2005), and the lowest spans of the replacement Seven Mile Bridge (1982-present) are built significantly higher than the original (1916-1981). Also, this phenomenon isn't limited to just the United States alone or even when also including Canada -- it is a global phenomenon. For example, look at how the lowest spans of the Annai Indira Gandhi Road Bridge (1988-present) are way higher than the those of the Pamban Bridge (1914-present) in India. The video below shows how much higher the replacement bridge (estimated completion around late 2024) for the Hanshin Namba Line over the Yodo River in Osaka, Kansai, Japan is compared to the original (1924). Also, note how the Denpo-Ohashi Bridge (the tied arch bridge, estimated to have been completed in the 1930s) in the near background is significantly lower than the Shin-Denpo-Ohashi Bridge (completed in 1958 as part of National Route 43) right behind it. All of the bridges mentioned here for this video are level.

https://youtu.be/n9pBhmlQsQA

 

[1503-44]

Maybe ships are getting larger. You think ?
An English video would help here. I don't read whatever that is.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[LittleWheels]

Railways/ railroads don't like steep grades e.g. >1:100. If the river being crossed doesn't have high banks, high bridge decks require building long, high embankments to get the tracks up higher. That increases the amount of land, money and time needed for construction. None of that is popular unless there is a powerful regulatory requirement for additional 'air draft'.

 

[DurableEfficientGood]

Yes, ships are getting larger, but I'm only talking about portions of bridges that are low-level here, which pre-industrial ships can't fit under anyway. I'm just wondering why many bridges up until the early-mid 1960s were built at seawall height and not boardwalk/amusement pier height, which is so low that not only would small boats not be able to pass through, but also a high flood stage would inundate and wash the road/rail deck away. Also, I don't understand what that video is saying either. Just posted that for a visual reference.

 

[LittleInch]

My guess is simply that legislation has finally caught up with reality.

In other words if it wasn't required to get planning permission then build it as low as you can.


Also how high is high enough? If there was no water traffic there before they built the bridge then there would be no reasons to think in the future a demand might be there which costs me money now.

Floating pontoons tend to errr float and move with the tide and river levels. Not very good for a bridge which needs to be flat. OK maybe for military transport in times of war, but not much use for anything else.

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[DurableEfficientGood]

So, are you saying that you guess it took all the way until the mid- to late-1970s for legislation to catch up to the reality of forseeable storm surges and forseeable flood stages, which have been well-established concepts in meteorology and hydrology ever since the scientific method was discovered multiple centuries ago and universally known by the general public ever since the beginning of mankind?

 

[LittleInch]

Yes

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[DurableEfficientGood]

Wow, that sounds very (and extremely) stupid to build a bridge like that to be intended to be used for 50-150 years but just to be destroyed only 15-40 years later (varies widely, so large range) when the next predicted large storm surge comes (that is totally expected and would be abnormal and unexpected if it doesn't come within that timeframe) according to the public open-source data from the meteorology office. I'm so glad they don't build them this way anymore! This is one example that "they don't build them like this anymore" is sometimes (and possibly often or even usually) a good thing.

 

[DurableEfficientGood]

I'm now willing to bet that Hanshin Electric Railway (private company that owns the line services and infrastructure) was forced by thw government to update the Namba Line bridge over the estuary of the Yodogawa due to flood risks (as well as earthquake risk, because it is Japan). It is a vital lifeline to the Kansai region, connecting Kobe and destinations beyond right to the heart of the cosmopolitan city of Osaka, so it is placed high in the priority of infrastructure upgrades. Since there was no way to feasibly upgrade the old bridge, they had no choice but to build a new bridge if they were really forced to upgrade.

Originally, I thought it was just that the original bridge was losing structural strength due to old age that warranted the replacement. However, now, I bet that even if the old bridge was in great condition, they would still have been forced to replace it anyway due to seismic and flood reasons.

 

[WinelandV]

LittleInch,

Only because I was tangentially involved with this project in my first job:

Washington State SR520 Pontoon Bridge

Sometimes they're used for more than military transport.

 

[LittleInch]

That's a pretty neat bridge.

Lakes are a bit different because their level is pretty much fixed. The transition piece allows no more than 24" change in level.

OK for road but rail wouldn't like it.

Also they had no other decent option....

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[btrueblood]

Pontoon bridges can sink (Lake Washington floating bridge, I-90).

The Celilo Falls railway bridge was built in a fast water (un-navigable) stretch of the Columbia River. The river became navigable when a downstream dam (The Dalles) was built some 40 years later; they added a drawspan to the Celilo Falls bridge to accomodate river barges.

There's currently a running debate for the I-5 bridge across the Columbia. Current drawspan can clear some 180 ft., but proposals are for a non-closing bridge (i.e. no drawspan to block road traffic). The US Coast Guard has blocked the proposed bridges, stating the bridge must have a clear passage for 180 ft. ships, to allow upstream businesses (shipyards) to continue operations. Construction costs would probably triple to build a high span on that stretch; it may well be cheaper to relocate said businesses downstream.

 

[BridgeSmith]

Once again, you're expecting engineers to be able to see the future. No, we don't know, and have never known, what the highest flood may be for any particular body of water in the next hundred years. The hydrologists make their best estimates, and sometimes they're wrong. Providing more clearance under bridges costs more money (bigger piers, more fill material, etc.), and there's only so much available. The priority is life-safety, which means when it comes down to spending money on providing more clearance than the bridge is ever expected need, or improving the railings on 20 bridges, the railings get the money.

Very few locations are suitable for a pontoon bridge.

By the way, ignorantly spouting off how stupid it is that things are designed the way they are, is not the way get on the good side of people you wish to ask questions of and learn from.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[IRstuff]

Rod,

They're not the only one. SWMBO often complains about traffic or parking; "Why didn't they foresee the need for more ...?"

TTFN (ta ta for now)
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[LittleInch]

Also the engineers of today tend to forget that the internet in its current form "open source etc" has only been around for about 25 years. Before that is was all paper based, with records held in various places, sometimes they would then get destroyed by war, fire, mould or just thrown out on purpose or by accident.

A record search was pretty laborious...

Also not many structure got designed for anything like 50 years. They just got built big and strong and survived longer than their designers on that basis (over design rather than design).



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[geotechguy1]

>Wow, that sounds very (and extremely) stupid to build a bridge like that to be intended to be used for 50-150 years but just to be destroyed only 15-40 years later (varies widely, so large range) when the next predicted large storm surge comes (that is totally expected and would be abnormal and unexpected if it doesn't come within that timeframe) according to the public open-source data from the meteorology office. I'm so glad they don't build them this way anymore! This is one example that "they don't build them like this anymore" is sometimes (and possibly often or even usually) a good thing.

People, including educated people / developers do insanely stupid / short sighted things like this all the time. 2 years after a major flood in a flood hazard area people have already forgotten about it and developers are trying to get standards changed to ignore the flood hazard.