Column Shortening in Tall Structures Prediction and Compensation

Column Shortening in Tall Structures Prediction and Compensation

The effects of column shortening, both elastic and inelas-
tic, take on added significance and need special considera-
tion in design and construction with increased height of
structures, Differential column shortenings are magnified
by the quest for optimum economy through use of high-
strength materials and, in some instances, the use of com-
pnsite structural systems. These, in turn, change the initial
pnsitions nf the slabs. As a consequence the partitions,
mechanical equipment, cladding, architectural finishes,
and built-in furnishings are also affected.The strains in the columns nf low as well as ultra-high-
rise buildings are similar if the stress levels are similar;
however, the overall column shortening is cumulative and
depends upon the height nf the structure. For example, in
an 80-story steel structure, the total elastic shortening nf
the columns maybe as high as 7 to 10 in, (180 to 255 mm)
due to the high design stress levels of modern high-
strength steels. 

The shortening of columns within a single story affects the
partitions, cladding, finishes, piping, and so on, since
these nonstructural elements are not intended to carry
vertical loads and are therefore not subject to shortening,
On the contrary, partitions and cladding may elongate
from moisture absorption, pipes from high temperature
of liquid contents, cladding from solar radiation, and so
on, Details for attaching these elements to the structure
must be planned so that their movement relative to the
structure will not cause distress.
The cumulative differential shortening of columns
causes the slabs to tilt with resulting rotation of parti-
tions, as shown in Fig. 2. Modern dry-wall partitions can
be detailed with sufficient flexibility along their peripher-
ies and at the vertical butt joints to permit their distortion
without visible distress


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