1326
THEORY AND PRACTICE OF ENGINEERING.
Book II.
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PALAIS AT VERSAILLES.
At the Palais of Versailles is a roof of novel construetion, which has two collars, resting upon twiposts on each side, to allow of a passagethem.
Theatres admit of such an arrangement, tintween tne two upright posts on each side theusually devoted to the passage which conductsthe several boxes in front of the interior part. r lceiling of the pit is suspended to a kinstrengthened on each side byaslong strut that braces thewhole together.
At the Italian Theatre atParis , the roof was formedby a double arrangementof principal rafters, sostrutted and braced asto have strength enough tohold up the floor by meansof iron rods, which coveredthe entire width of thetheatre.
When roofs are constructedin this manner additionalstrength would be obtained bythe introduction of a St. An-drew’s cross between each pair of upright struts, framedbetween the upper and lower principal rafter; thesebol ted together would form a strong truss, and support orhold up a considerable weight; the abutments requireto be held firmly in their position, and inthe present example the lower strut wasintroduced to discharge aportion of the weight upon ^
the floor below, where theouter walls are tied together.
The collar or beam under theking-post alsoacts as a strut,to prevent thesagging of thetruss intowhich it is Iframed.
Fig. 2121. THEATRE EES ITALIENS, AT PARIS .
Roofs without tie-beams are frequently used where height is required in the buildingthey cover, but, with all the care possible, it is difficult to frame them so that they will
Fig. 2122.