STRUCTURAL DESIGN FOR ARCHITECTURE

4.4 Structural forms for reinforced

concrete

4.4.1 Basic elements

Beams

Reinforced concrete beams are normally either

rectangular in cross-section or combined with

the slab which they support to form T- and L-

shaped cross-sections (Fig. 4.37). The normal

span range for reinforced concrete beams is 4.5

to 10 m. Spans of up to 20 m are occasionally

used but depths of around 1.5 m and upwards

are required for this, and a large volume of

concrete is therefore involved. Spans greater

than 20 m are possible but other types of

structure will normally perform better in this

span range. The depth which is required for

beams depends on the span and the load

which is carried. It is frequently determined

from deflection rather than from strength

requirements and in the normal span range a

depth of around one twentieth of the span is

required for a simply supported beam and one

twenty-sixth of the span for a beam which is

continuous across a number of supports. The

breadth of a rectangular beam is usually

around one third to one half of its depth.

Columns

Columns are constructed with a range of cross-

sectional shapes, the most common being

square, rectangular and circular. The primary

reinforcement in columns is longitudinal

reinforcement which contributes to the resis-

tance of the compressive load and therefore

reduces the required size of the cross-section.

Transverse reinforcement, in the form of links,

is also provided to give lateral support for the

longitudinal reinforcement to prevent a burst-

ing-type compression failure (Fig. 4.38). As in

all compression elements, the principal factor

which determines the dimensions which must

Fig. 4.37 T- and L-beams. Where reinforced concrete

beams support a reinforced concrete slab the elements are

normally cast together and act compositely to form T- and

L-beams.

Fig. 4.38 Reinforcement in a column. Columns are

provided with longitudinal reinforcement, to increase their

compressive strength, and links to prevent buckling failure

130 of the very slender reinforcing elements.

Structural Design for Architecture