Load-Bearing Walls, Steel Skeleton, Skyscrapers and Otis Safety Elevator

Posted by PITHOCRATES - May 22nd, 2013

Technology 101

Because there is no Elevator in a Brownstone the Lower Floors are more Valuable

If you live in Manhattan on the Upper West Side you may have a view of the Hudson River.  Depending on how high you live.  For the higher you are the better your view.  Which is why the best apartments are on the top floors of our high rises.  Interestingly, though, if you live in a 5-story brownstone the prime real estate in those buildings are on the lower floors.  Why?  Because they don’t have an elevator.

Early buildings had a limit on height.  Because they had load-bearing walls.  And as the buildings grew taller the walls grew thicker.  To support the weight of the buildings above them.  Consider the pyramid.  Large, tall structures made of stone.  Part of the reason why they were pyramid shape was the weight of these heavy stones.  Supporting these heavy stones above the ground required a wide stone base below them.  So as a building got taller the walls got thicker on the lower floors.  So thick that they had less useable space than the upper floors.

It’s also more difficult to put windows in load-bearing walls.  As an opening reduces the strength of those walls.  In your typical 5-story walkup brownstone you’ll have small window openings facing the street.  Making it hard to flood these spaces with natural light.  So buildings with load-bearing walls have a few drawbacks.  Thick walls shrink living space.  And reduce the amount of natural lighting.  Not to mention having to hoof it up all of those steps.  Which is why the lower floors are more valuable in a brownstone.  For no one wants to walk up and down 5 flights of stairs every time you leave the apartment.

With a Steel Skeleton replacing Thick Load-Bearing Walls we can Enclose a Building with Glass Curtain Walls

In the 19th century new building technologies addressed these problems.  Thanks to Henry Bessemer and his Bessemer process.  The first cost-effective way to produce large amounts of steel.  Steel is stronger than iron.  But early steel was brittle.  Because of a high carbon content.  So we used iron.  For our train rails.  And our boilers.  But we could not harden iron as much as steel.  Because of a lack of carbon in iron.  Which is why iron boilers had a tendency to explode.  And iron rails failed.

Henry Bessemer changed that.  By blowing oxygen through the molten steel.  Which removed impurities.  And excess carbon.  Andrew Carnegie used the Bessemer process on a grand scale.  Producing the steel that built America.  Mass producing the structural steel that changed the way we built buildings.  Bringing the word ‘skyscraper’ into the lexicon of building.  As Carnegie’s steel sent our buildings soaring to the sky.

Instead of building thick load-bearing walls we built a rigid steel skeleton.  We anchored it to the earth with some steel-reinforced concrete piers deep underground.  And steel piles driven down to bedrock.  Giving us a tall, sturdy structure to build around.  The structure being so strong we can support up to a hundred (or more) concrete floors from it.  With useable space on every floor.  And without thick load-bearing walls we can hang glass curtain walls from this steel skeleton.  Wrapping the exterior of the building in glass.  Flooding these floors with natural light.

Before Elisha Otis and Andrew Carnegie the Top Floor of any Building was the Hardest to Let

So the steel skeleton allowed us to build buildings taller than ever.  But it took something else to allow those buildings to reach skyward.  For people were just not going to walk up and down a hundred flights of stairs every time they left their home or office.  They may walk up and down 5 flights of stairs in exchange for a cheaper rent in a brownstone on the Upper West Side.  But no one is going to walk up and down a hundred flights.  Even if they don’t have to pay rent.  So it was the elevator that really allowed today’s skyscraper.  Tiny little cars suspended by a few cables in a very long vertical shaft.

Elevator safety evolved over time.  At first it was not that uncommon for people to fall to their death in an elevator car that broke free from its cables.  Elisha Otis solved that problem.  He attached the elevator cable to a flat-leaf spring attached to the car.  The tension on the cable from the weight of the elevator car compressed the flat-leaf spring.  Drawing in mechanical linkages.  If the cable broke the energy in the compressed spring released and pushed down on the mechanical linkages.  Which forced arms outward and into saw-tooth safety rails that ran the length of the elevator shaft.  Bringing the elevator car to an immediate stop if the cable broke.

This revolutionized elevators.  And allowed our buildings to reach skyward.  As people no longer feared getting into an elevator.  Thanks to Elisha Otis.  Who went on to found the Otis Elevator Company.  If you see the word ‘Otis’ in the elevator car you’re in you can thank Elisha Otis.  For you’re in one of his elevators.  And you can thank Andrew Carnegie.  For giving us tall buildings.  And whose company may have even built the steel of the building you’re in.  Before Otis and Carnegie the top floor of any building was the hardest to let.  Because no one wanted to climb up all of those stairs.  But with tall steel and a safe elevator the top floor in a building now commands the highest rent.  Because of the view.  And the ease at which we could enjoy that view.



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