Civil Engineering Reference
In-Depth Information
Figure G5-3
Example of a cantile-
vered roof girder
system.
is commonly the primary effect, in arches there are two primary effects:
moment and thrust. The problem is further complicated if the arch material
has different allowable (or ultimate) tensile and compressive stresses. Com-
pressive stress is largest when both moment and thrust are large, whereas
tensile stress is largest when moment is large and thrust is small. Since arches
are often shaped so that dead-load moments are reasonably small, intuition
suggests that the controlling partial load would correspond to a full bal-
anced load on one side of the crown and a half balanced load on the other
side. The degree to which unbalanced arch loads (discussed in Chapter 6)
account for or serve as a conservative proxy for partial loading on an arch
is currently unknown.
A cantilevered roof girder system with drop-in simply supported spans
is shown in
Figure G5-3
. For the exterior girder (continuous over one sup-
port) and the interior girder (continuous over both supports), two partial
load cases are investigated. In both cases, the cantilever and the adjoining
drop-in span are considered as one region, and the portion of the cantile-
vered girder between the supports is considered to be another region.
In
Figure G5-4,
Case A maximizes the moment, shear, and defl ection
for the region between the girder supports. In
Figure G5-5,
Case B maxi-
mizes the same quantities in the cantilever and drop-in span. Note that a
partial load (i.e., variations of load between the two links at either end) is not
required for the drop-in span because the drop-in span is simply supported.
The ASCE 7-10 Commentary also mentions snow-removal operations
and melting as possible causes of partial loading. The issue of appropriate
Figure G5-4
Partial load Case A for
a cantilevered roof
girder system. (a) Exte-
rior girder. (b) Interior
girder.
(a)
(b)
