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Xavier Magazine | July 28, 2014

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Behind the…Bellarmine Chapel Roof

Behind the…Bellarmine Chapel Roof
By France Griggs Sloat

• Construction of St. Robert Bellarmine Chapel was completed in 1962, replacing the previous chapel, which was located in Schmidt Hall. 

• Its roof is a freestanding hyperbolic paraboloid that is unsupported by its exterior walls.

• Horizontal beams embedded into two buttresses anchored several feet into the ground are the roof’s main support.

• These four steel beams, each 89 feet long, stretch front and back, meeting at the roof’s two apex points.

• A lattice of rebar connects the beams side to side across the roof. The rebar is what gives the roof its smoothly curving shape.

• The curve of the roof continuously changes because it’s a geometric shape created by the intersection of two parabolas—curved planes created from conical cross-sections. 

• Looking at the roof from the side, its curve is convex—dipping then rising from front to back. But from the front, the underside of the roof is concave—rising in a bell curve from one buttress to the other.

• The apex of the roof at the rear of the chapel is higher than the apex over the front entrance.

• The roof, made of reinforced concrete, is only 3.5 inches thick. 

• The length of the roof span from front to back is 153 feet, 3 inches; the height is 47 feet, 7 inches at the highest point—the rear.

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