Plate 83:  View looking west at the underside of the elevated girders along the north face of the layout
(This plate added SEP 2003)

Two horizontal girders support the roadbed at the north face of the layout: the "high-level north girder" and the "mid-level north girder". These two girders are made from furring strips cut to a length of about 55 inches. --more--

Girders are used wherever the roadbed must span a distance that should not be interrupted by closely spaced columns (such as long spans for bridges or viaducts). If thick girders were not used to help span these distances, the thin plywood roadbed across the span would lack strength and rigidity. The high-level north girder, composed of two parallel furring strips supported by three columns, carries the roadbed at the upper level (12 inches). The "Flying Scotsman" can be seen standing upon the high north girder in this view. The mid-level north girder is made from a single furring strip supported by two projecting cantilevered beams attached to the outer two of the three north columns (a cantilever beam is a horizontal structual element that is supported at one end, but not at the other end). The mid-level north girder carries the roadbed of the outer spiral at the middle level (4-1/2 inches). Go to top of page