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One of the ways medieval cathedral builders overcame this problem was by propping up

the walls from the outside with an inward pushing masonry brace, called a buttress.  The

buttress resisted the outward thrust of the roof.  This caused its load to shift more towards

the centerline of the wall which helped stabilize the structure.  Additional weights, such as

statues, were often placed on top of the buttress to help direct the outward thrusting forces

downwards nearer the centerline.

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However, the height attainable by masonry wall bearing construction was limited by the

sheer massiveness of the structure.  As land values in the hearts of the cities increased and

steel prices dropped around the start of the last century, the desire to build up rather than

out caused engineers to turn to steel skeleton structure for a solution.

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Skeleton construction

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In skeleton construction the live and dead loads are supported by a structural framework

skeleton.  Unlike wall bearing construction, the exterior walls do not bear any of the load.

Instead the walls are hung from the skeleton. Therefore, they are called curtain walls. The

floor and roof loads are dissipated to the girders, beams, and columns of the skeleton. The

structure is comprised of right-angled boxes interconnected with each other. Since the box

lattice structure is inherently unstable, the joints of the skeleton framework must be rigidly

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