24-11-2012, 12:08 PM
PRECAST CONCRETE STRUCTURES
1PRECAST CONCRETE.pdf (Size: 3.18 MB / Downloads: 353)
INTRODUCTION
The concept of precast (also known as “prefabricated”) construction includes
those buildings, where the majority of structural components are standardized and
produced in plants in a location away from the building, and then transported to the site
for assembly. These components are manufactured by industrial methods based on mass
production in order to build a large number of buildings in a short time at low cost.
The main features of this construction process are as follows:
The division and specialization of the human workforce
The use of tools, machinery, and other equipment, usually automated, in the
production of standard, interchangeable parts and products
Compared to site-cast concrete, precast concrete erection is faster and less
affected by adverse weather conditions.
Plant casting allows increased efficiency, high quality control and greater control
on finishes..
This type of construction requires a restructuring of entire conventional construction
process to enable interaction between design phase and production planning in order to
improve and speed up construction.
LARGE PANEL SYSTEMS
The designation “large-panel system” refers to multistory structures composed of
large wall and floor concrete panels connected in the vertical and horizontal directions so
that the wall panels enclose appropriate spaces for the rooms within a building. These
panels form a box-like structure. Both vertical and horizontal panels resist gravity load.
Wall panels are usually one story high. Horizontal floor and roof panels span either as
one-way or two-way slabs. When properly joined together, these horizontal elements
act as diaphragms that transfer the lateral loads to the walls.
FRAME SYSTEMS
Precast frames can be constructed using either linear elements or spatial beamcolumn
sub-assemblages. Precast beam-column sub-assemblages have the advantage that
the connecting faces between the sub-assemblages can be placed away from the critical
frame regions; however, linear elements are generally preferred because of the
difficulties associated with forming, handling, and erecting spatial elements. The use of
linear elements generally means placing the connecting faces at the beam-column
junctions. The beams can be seated on corbels at the columns, for ease of construction
and to aid the shear transfer from the beam to the column. The beam-column joints
accomplished in this way are hinged. However, rigid beam-column connections are used in
some cases, when the continuity of longitudinal reinforcement through the beam-column
joint needs to be ensured.