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

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Design of Wood Members for Formwork 89
The reference design values are the same under both sets of grading
rules for dimension lumber. The designer should use the lower reference
design value in designing structural members because he/she
does not have control over which set of grading rules will be used.
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Loads on Structural Members
A load is a force exerted on a structural member, such as a beam,
column, or slab. The loads may be concentrated or uniformly distributed.
A concentrated load is a point load at a particular location on
the member. For example, a column may have single concentrated
load acting along the axis of the column, or a beam may have one
load applied transverse to the axis of the beam. Often, there are several
concentrated loads acting on a beam. For example, a girder in a
building receives concentrated loads at the points where the floor
beams are placed on the girder.
A uniformly distributed load is a load of uniform magnitude per
unit of length that extends over a portion or the entire length of the
member. A floor joist that supports floor decking is an example of a
member supporting a uniformly distributed load. Concrete placed in
a wall form produces uniformly distributed pressures against the
formwork sheathing, which in turn produces a uniformly distributed
load along the studs that support the sheathing. For some structural
members, there is a combination of concentrated loads and uniformly
distributed loads.
Equations Used in Design
It is the responsibility of the designer to assess the conditions and to determine
the proper analysis and design equations. Design procedures must
comply with all codes, specifications, and regulatory requirements.
The equations presented in the following sections are the traditional
basic equations for bending, shear, and compression. The
designer must ensure that the appropriate adjustments are made in
the equations based on the conditions that are unique to each job.
Loads on structural members produce bending, shear, and compression
stresses. These stresses must be kept within an allowable
limit to ensure safety. In addition to strength requirements, limits frequently
are specified for the maximum permissible deflection of
structural members. Stresses and deflections are analyzed by the use
of basic equations shown in subsequent sections of this chapter.
The following symbols and units will be used in the equations
presented in this chapter:
M = bending moment, in.-lb
c = distance from neutral axis of beam to extreme fiber in
bending, in.
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