The Structural Systems oF Tall Buildings - Tall Buildings: Structural Systems and Aerodynamic Form - page 18

reinforced concrete or composite in the structural system. In North America, steel
construction, while in the Asia Pacific (Far East), reinforced concrete or composite
construction is generally used.
With the progress in technology, the increase in the strength of concrete and the
ability to pump concrete to high levels, the use of reinforced concrete and composite
structural systems increases day by day.

3.2 rigid frame systems

Rigid frame systems, also called moment frame systems, are used in steel and
reinforced concrete buildings. This system consists of beams and columns ( Figure 3.3 ).
A rigid frame is an unbraced frame that is capable of resisting both vertical and lateral
loads by the bending of beams and columns. Stiffness of the rigid frame is provided
mainly by the bending rigidity of beams and columns that have rigid connections.
Rigid framing is based on the principle that beam-column connections have adequate
rigidity to hold the original angles between intersecting members unchanged under
the effect of both vertical and lateral loads. Thus, reinforced concrete is an ideal
material for this system by virtue of its naturally monolithic behaviour, resulting with
inherent rigidity at connections. For steel buildings, rigid framing is achieved by
reinforcing beam-column connections.
The structural stiffness of rigid frames is directly proportional to the cross-sectional
dimensions and bending rigidity of the beams and columns, and inversely propor-
tional to their length and spacing. In this system, columns are placed in locations that
least restrict architectural planning. At the same time, columns should be of sufficient
length to provide minimum storey depth. To obtain effective rigid frame behaviour, it
is necessary to have closely spaced columns, and for the beams connecting them to
be sufficiently deep.
For buildings constructed in regions of high seismic activity in particular, the
details of the connections between structural elements are very important because of
the need for ductile behaviour in the rigid frame due to the large lateral drift during

Figure 3.3

Rigid frame system