Rain cap system for fast modular structures

An apparatus for preventing weather elements from penetrating the assembly junctions of a temporary building structure, comprising an arched frame comprised of I beam segments joined end to end, wherein each I-beam segment is formed with a top, a pair of outer walls, and a bottom, the outer walls each having a longitudinally extending, outwardly opening rounded slot therein, and a rain cap conformably disposed on and covering the joined end-to-end I beam segments of the arched frame, the rain cap consisting essentially of a planar first portion spanning the top of the joined I-beam segments for face to face engagement therewith and a pair of planar side flanges integrally formed with the planar first portion and extending downwardly and perpendicular from the planar first portion for face to face engagement with the respective outer walls of the joined I-beam segments, each planar side flange extending to a distance just above the rounded slot in the respective outer walls of the joined I-beam segments, each planar side flange being terminated in a lip turned inwardly therefrom to engage an edge of the rounded slot in the outer walls of the joined I-beam segments, the rain cap extending along a longitudinal length of the arched frame for a distance less than a total length of the arched frame sufficient to cover the joined ends of the I-beam segments.