Steel Designers Manual - TheBestFriend.org

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Steel Designers' Manual - 6th Edition (2003)
lateral stability provided by portal action;
perimeter accommodation provides wind
shielding; longitudinal stability is provided
by portal action or braced frames
water run — off to new system
choice of sprinklers
and other fire
protection measures
could affect final form
of the structure
Fig. 5.40 Portal frame
panel propped top
and bottom but free
vertical and horizontal
dilferential movement
allowed
maisonettes
excluded from
enclosure to reduce
risk from fire
and smoke
ture is required to support a small proportion of the vertical load and relatively
small horizontal loads from wind and stabilizing forces for the new columns, which
does not generally pose a problem since there is usually some redundant horizontal
capacity due to the wind shielding effect of the new enclosure. The portal style
solution (Fig. 5.40) is substantially self-supporting.
Temperature effects are often a governing design consideration for an atrium
structure due to exposure to heating from sunlight. Temperatures in steelwork
painted black can be 30° higher compared with white where directly exposed to the
sun’s radiation. It is important to allow for movement of the structure, to prevent
locked-in stresses from building up. Releases of this sort are often incompatible with
providing horizontal stability. The choice of structural form needs to reflect these
opposing requirements. For example, a statically determinate structure such as a
three pinned arch can accommodate temperature movements and differential
settlements without generating secondary internal forces (see Fig. 5.41).
5.5.2.2 Type of cladding
Atria 209
Atria generally require transparent or translucent forms of cladding. Glazing is a
traditional solution but is relatively heavy. If the space beneath is heated the thermal
performance may dictate double-glazing, which is both heavy and costly. Other