Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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CHAPTER 6
Shores and
Scaffolding
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General Information
Shores
Vertical shores, or posts, and scaffolding are used with formwork to
support concrete girders, beams, floor slabs, roof slabs, bridge decks,
and other members until these members gain sufficient strength to be
self-supporting. Many types and sizes of each are available from
which those most suitable for a given use may be selected. They may
be made from wood or steel or from a combination of the two materials.
Aluminum shores and scaffolding are also available.
In general, shores are installed as single-member units that may be
tied together at one or more intermediate points with horizontal and
diagonal braces to give them greater stiffness and to increase their
load-supporting capacities.
If shores are to provide the load capacities that they are capable of
providing, at least two precautions must be taken in installing them.
They should be securely fastened at the bottom and top ends to prevent
movement or displacement while they are in use. Because the
capacities of shores are influenced by their slenderness ratios, two-way
horizontal and diagonal braces should be installed with long shores at
one or more intermediate points to reduce the unsupported lengths.
Concrete is usually pumped or placed from buckets, which permits
the concrete to fall rapidly onto a limited area. The use of either
method may produce a temporary uplift in the forms near the area
under the load. If this should happen, it is possible that a portion of
the forms will be lifted off the tops of one or more shores. Unless the
tops of the shores are securely fastened to the formwork which they
support, their positions may shift. For the same reason, the bottom
ends of shores should be securely held in position. There are reports
that forms have collapsed because the positions of shores shifted
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