STRUCTURAL DESIGN FOR ARCHITECTURE

Fig. 4.44 Composite in situ and precast concrete. Precast

units of complex shape are used here in conjunction with

in situ concrete to form a composite floor deck with an

efficient 'improved' cross-section.

fit' problem and the provision of structural

continuity. In situ concrete can also be used to

allow more complex or irregular overall forms

to be adopted.

4.4.2 Structural forms - cast-in-situ forms

4.4.2.1 Introduction

Reinforced concrete cast-in-situ forms are used

principally for multi-storey buildings in which a

frame-type structure is required. The form of

the structure is determined by the same factors

as influence the design of all structures, which

are the need to provide effective resistance to

Fig. 4.45 Four basic types of reinforced concrete struc-

ture.

(a) Two-way-spanning ribless flat-slab.

(b) One-way-spanning ribbed flat-slab.

(c) One-way-spanning slab supported on rigid frame.

(d) One-way-spanning slab supported on loadbearing

walls.

both gravitational and lateral load, and to

achieve reasonable economy in the use of

material. Although the mouldability of

concrete theoretically gives the designer a wide

choice of frame geometries, the need to

minimise costs normally favours the use of

rectilinear arrangements which require simple

patterns of reinforcement and formwork. The

variety of multi-storey forms which are used in

Structural Design for Architecture

134

Table 4.1 Span ranges and size requirements for the four basic types of in situ reinforced concrete

structure

Structure type Span range (m) Span/Depth Column/wall

Reinforced Pre-stressed Reinforced Pre-stressed slendemess

One-way-span slab 4X6 to 8X11 8X11 to 8X14 25 36 15 to 20

Two-way-span slab: solid 4X4 to6 X 6 6X6to10X10 25 to 30 30 to 35 15to20

coffered 6X6 to 18X18 8X8 to 20X20 35 30 15 to 20

Beam/Column frame:

one-way-span slab 3X6 to 6X12 6X12 to 8X15 slab 36 36 15 to 20

beam 15 to 20 20 to 25

two-way-span slab 4X4 to 8X8 8X8 to 15X15 slab 36 36 15 to 20

beam 15 to 20 20 to 25

Loadbearing wall:

one-way-span slab 3 to 12 36 15 to 20

two-way-span slab 3X3 to 12X12 36

(b)

(a) (c)

(d)