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7
Cladding and Curtain Wall
Construction
The structural frame provides the possibility of endless variation in the form and appearance
of buildings that no longer need to be contained inside a loadbearing envelope. A
large variety of walling materials are available to meet the changing needs of use, economy
and architectural trends. The external walls of framed buildings differ from traditional
loadbearing walls, because the structural frame has an aesthetic effect and hence influences
the design of the wall structure that it supports. To the extent that the structural frame may
affect the functional requirements of an external wall, it should be considered as part of
the wall structure. The use of the various materials for the external wall is, to an extent,
influenced by the relative behaviour of the structural frame and the wall to accommodate
differential structural, thermal and moisture movements, which affect the functional
requirements of a wall. The finished appearance of the external wall is another significant
consideration, and it is possible to create some highly creative buildings with the use of
cladding, as illustrated in Photograph 7.1.
7.1 Functional requirements
Under load, both steel and concrete structural frames suffer elastic strain and consequent
deflection (bending) of beams and floors, and shortening of columns. Deflection of beams
and floors is generally limited to about one three hundredth of span, to avoid damage to
supported facings and finishes. Shortening of columns by elastic strain under load can be
in the order of 2.0 mm for each storey height of about 4 m, depending on the load. Elastic
shortening of steel columns may be of the order of 1 mm per storey height. The comparatively
small deflection of beams and shortening of columns under load can be accommodated
by the joints in materials such as brick, stone and block and the joints between panels,
without adversely affecting the function of most wall structures.
Unlike steel, concrete suffers drying shrinkage and creep in addition to elastic strain.
Drying shrinkage occurs as water, necessary for the placing of concrete and setting of
cement, migrates to the surface of concrete members. The rate of loss of water and consequent
shrinkage depend on the moisture content of the mix, the size of the concrete
members and atmospheric conditions. Drying shrinkage of concrete will continue for some
weeks after placing. For the small members of a structural frame, drying out of doors in
summer, about half of the total shrinkage takes place in about one month and about three
Barry’s Advanced Construction of Buildings, Third Edition. Stephen Emmitt and Christopher A. Gorse.
© 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.
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