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

12 Chapter Two
Downloaded From : www.EasyEngineering.net
in the quantity of concrete required for columns, it may not reduce
the cost of a structure; actually, it may increase the cost. Often, the
large column size from the lower floors can be used for the upper
floors with a reduction in the amount of the reinforcing steel in the
upper floor columns, provided code requirements for strength are
maintained. Significant savings in labor and form materials can be
achieved by reusing column forms from lower to upper floors. If a
change in the column size is necessary, increasing one dimension at a
time is more efficient.
The column strategy of the structural engineer has a significant
impact on formwork efficiency and column cost. By selecting fewer
changes in column size, significant savings in the cost of column
formwork can be achieved. Fewer changes in sizes can be accomplished
by adjusting the strength of the concrete or the reinforcing
steel, or both. For example, to accommodate an increase in load,
increasing concrete strength or the reinforcing steel is preferable to
increasing column size.
Columns that are placed in an orientation that departs from an
established orientation cause major formwork disruptions at their
intersections with the horizontal framing. For example, a column that
is skewed 30° in orientation from other structural members in a building
will greatly increase the labor required to form the skewed column
into adjacent members. A uniform, symmetrical column pattern
facilitates the use of high-productivity systems, such as gang or flying
forms for the floor structural system. Scattered and irregular positioning
of columns may eliminate the possibility of using these costeffective
systems. Even with conventional hand-set forming systems,
a uniform column layout accelerates construction.
The option to use modern, highly productive floor forming systems,
such as flying forms or panelization, may not be feasible for
certain column designs. The designer should consider adjacent structural
members as a part of column layout and sizing. Column capitals,
especially if tapered, require additional labor and materials. The
best approach is to avoid column capitals altogether by increasing
reinforcement within the floor slab above the column. If this is not
feasible, rectangular drop panels, with drops equivalent to the lumber
dimensions located above columns, serve the same structural
purpose as capitals, but at far lower total costs.
ww.EasyEngineering.n
Beam and Column Intersections
The intersections of beams and columns require consideration of both
horizontal and vertical elements simultaneously. When the widths of
beams and columns are the same, maximum cost efficiency is attained
because beam framing can proceed along a continuous line. When
beams are wider than columns, beam bottom forms must be notched
Downloaded From : www.EasyEngineering.net