Aluminium Design and Construction John Dwight

Nominal loading. Nominal loads are the same as ‘working loads’.
They are those which a structure may be reasonably expected to
carry in normal service, and can comprise:
dead loads (self-weight of structure and permanently attached items);
imposed loads (other than wind);
wind loads;
forces due to thermal expansion and contraction;
forces due to dynamic effects.
It is beyond the scope of this book to provide specific data on loading.
Realistic imposed loads may be found from particular codes covering
buildings, bridges, cranes, etc. Wind is well covered. Often the designer
must decide on a reasonable level of loading, in consultation with
the client.
Factored loading is the factored (up) loading on the structure. It is
obtained by multiplying each of the individual nominal loads by a
partial factor � f known as the loading factor. Different values of � f can
be taken for different classes of nominal load. See Table 5.1.
Action-effect. By this is meant the force or couple that a member or
joint has to carry, as a result of a specific pattern of loading applied
to the structure. Possible kinds of action-effect in a member are axial
tension or compression, shear force, bending moment, and torque. In
a joint, the possible action-effects are the force and/or couple that
has to be transmitted.
Calculated resistance denotes the ability of a member or joint to resist
a specific kind of action-effect, and is the predicted magnitude thereof
needed to cause static failure of the component. It may be found by
means of rules and formulae given in codes or textbooks, in applying
which it is normal to assume minimum specified tensile properties
for the material and nominal dimensions for the cross-section. Suggested
rules are given in Chapters 8, 9 and 11, based largely on BS.8118.
Alternatively the calculated resistance may be determined by testing,
in which case the word ‘calculated’ is something of a misnomer.
Testing procedure is well covered in BS.8118.
Factored resistance is the factored (down) resistance of a member or
joint. It is the calculated resistance divided by a partial factor � m
known as the material factor (given in Table 5.1).
In discussing limit state design, we use the following abbreviations to
indicate quantities defined above:
NA =action-effect arising under nominal loading;
FA =action-effect arising under factored loading;
CR =calculated resistance;
FR =factored resistance (=CR/� m ).
In Chapters 8, 9 and 11 the suffix c is used to indicate calculated resistance.
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