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

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Shores and Scaffolding 165
allowable loads on shores that are 6 ft long. The information applies
to wood with the allowable unit compressive stress parallel to grain
and the modulus of elasticity as shown.
The pattern of dramatic reduction in allowable load with increase
in effective length applies to wood members having other physical
properties and also to materials other than wood and to patented
shores.
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Wood Post Shores
Although the common practice today is to use patented shores, there
are some instances where wood shores are fabricated for use on a
particular job. Wood shores have several advantages and several disadvantages
when they are compared with patented shores.
Among the advantages are the following:
1. The initial cost is low.
2. They are usually readily available.
3. They possess high capacity in relation to their weight.
4. It is easy to attach and remove braces.
Among the disadvantages are the following:
1. It is difficult to adjust their lengths.
2. The cost of labor for installing wood shores may be higher
than for installing patented shores.
3. Unless they are stored carefully, they may develop permanent
bows, which will reduce their load capacities.
4. They may develop rot or permanent bows.
If wood shores are too long for a given use, they must be sawed
to fit the required length, which results in additional labor costs and
waste of materials. If they are too short, it is necessary to splice them,
which may result in a weakening of the shores when compared to the
strengths of unspliced shores. Also, the cost of the labor required to
make such splices may be substantial.
Usually the final adjustment in the height of the top of a wood
shore is made with two wood wedges driven under the bottom of the
shores from opposite sides. Because of the higher allowable unit
stress in compression perpendicular to the grain, wedges made of
hardwoods are better than those made of softwoods. Both wedges
should be nailed to the mud sills, or other boards on which they rest,
to prevent displacement.
Field-constructed butt or lap splices of timber shoring should not
be used unless the connections are made with hardware of adequate
strength and stability. To prevent buckling, splices should not be
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