Prefabricated components

UNIT II -
PREFABRICATED
COMPONENTS
Mrs.Sofia Rajesh
Asst.Prof,
AAA College of Engineering and Technology
This Presentation:
 Prefabrication systems
 Manufacturing Process
 Roof &Floor Slabs
 Waffle slabs
 Wall Panels
 Shear Walls
 Beams
 Columns
 Waffle slabs

Prefabrication systems
 Large- panel systems
 Frame systems
 Slab- column systems with walls
 Mixed systems

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

Frame systems
 Components are
usually linear
elements.
 The beams are
seated on corbels of
the pillars usually
with hinged- joints
(rigid connection is
also an option).
 Joints are filled with
concrete at the site

Lift Slab System (or)
Slab- column systems with walls
 Partially precast in plant (pillars) /
partially precast on- site (slabs).
 One or more storey high pillars
(max 5).
 Up to 30 storey high
constructions.
 Special designed joints and
temporary joints.
 Slabs are casted on the ground
(one on top of the other) – then
lifted with crane or special
elevators

Manufacturing Process of
components

Roof Slabs – for Ware house type
structure

Floor Slabs
 A floor slab (also called
plate slab or filigree slab)
is a reinforced concrete
slab with a minimum
thickness of 5–6 cm.
 Depending on the concrete
covering and
reinforcement, it can be up
to 7 cm thick. The floor
slab is a semi-precast
component that includes
the lower floor slab
reinforcement that is
required for structural
reasons.

 The floor slab is precast in the precast concrete
component factory under ideal conditions, and
contains the torsionally stiff reinforcement (truss) that
is required to give stiffness once installed, as well as
the flexural tension reinforcement, lengthways and
crossways, that is required for assembly and the final
state.
 The floor slab is made into a solid and monolithic
reinforced concrete floor by using mix-in-situ concrete
that is poured at the construction site. The thickness
of the finished floor slab is between 12 and 30 cm,
depending on the span and the loading.
 The protruding truss reinforcement and the concrete
surface itself provide the required anchoring, ensuring
good bonding and adhesion between the finished part
and the mix-in-situ concrete.
Floor Slabs

Floor Slabs
 Apart from some differences in
the measurement of the
pushing force, the floor slab
can be regarded from a
structural point of view as
being the same as a floor that
has been produced on site
with concrete poured into
casing. The floor slab thus
combines the major
advantages of prefabrication
with the advantages of floors
that have been produced on
site with concrete poured into
casing.

Analysis of Floor slab – as a deep
beam
Based on deep beam – mode of failure – Arch and
diagonal tie

Waffle Slab
 Waffle Slabs or Ribbed floors consisting of
equally spaced ribs are usually supported
directly by columns.
 They are either one-way spanning systems
known as ribbed slab or a two-way ribbed
system
known as a waffle slab.
 This form of construction is not very common
because of the formwork costs and the low fire
rating.
 A rib thickness of greater than 125 mm is
usually
required to accommodate tensile and shear
reinforcement.
 Ribbed slabs are suitable for medium to
heavy loads, can span reasonable distances,
are very stiff and particularly suitable where
the soffit is exposed.

Wall Panels
 Precast wall panel is an
independently supported vertical
member in a prefabricated structure
using an assemblage of metal
components and anchors. Joints
around each of the precast panels
are usually filled with sealant.
 There are generally four types of
precast panels used as part of
building envelopes:
• Cladding or curtain walls
• Load-bearing wall units
• Shear walls
• Formwork for cast-in-place
concrete

Shear Wall
 Shear walls are vertical structural components
meant for resisting horizontal forces and
counteract the lateral loads acting on the
structure like wind seismic forces etc.
 They are designed for the strength and
stiffness to resist the horizontal forces.
 They are designed to provide a safe
serviceable and economical solution for wind
and earthquake resistance.

Four factors influencing distribution
of lateral load to shear wall
 Supporting soil and footings – can be
neglected
 Stiffness of the floor and roof diaphragms –
D/Span – Small – flexible and deflect.
- large – rigid and not deflect.
 Relative flexural and shear stiffness of the
shear wall and of connections - proportional
to shear width of diaphragm
 Eccentricity of lateral loads to the centre of
rigidity of the shear walls -

Significance
 They are part of earthquake resisting building
design.
 They are rigid vertical diaphragm which can
transfer lateral forces acting on the exterior
walls, floors and roofs to the foundation in a
direction parallel to their planes.
 Shear wall panels are connected vertically and
at the corners to form a structural tube that
cantilevers from the foundation.

Advantages over masonry walls
Masonry walls
 Load bearing
masonry walls are
brittle.
 They collapse
instantly during
unpredictable
earthquake.
 No warning of
failure.
 No time for
Shear Walls
 Stable and ductile than
masonry walls
 No sudden collapses
minimizing loss of lives.
 They give enough warning
before failure like widening
of cracks , yielding of
reinforcing rods etc.
 Enough time for mitigation
before collapse.

Types of shear Walls
According to H/D ratio

According to the openings
provided

TYPES OF SHEAR WALLS BASED ON
MATERIALS
 RC shear wall
 Plywood shear wall
 Midply shear wall
 RC Hollow concrete Block masonry wall
 Steel plate shear wall

Functions
 To resist vertical load – gravity load
 To resist horizontal load – lateral loads
 To provide necessary lateral strength to
structure so as to transfer horizontal forces to
the next structural element in load
transmission pattern.
 They are structurally integrated with roofs/
floors and other structural components.

Basic principles of shear wall in
precast constriction
 Shear walls should be oriented to resist lateral
loads applied to the building along both of the
structures principal axes.
 There should be at least two shear walls
oriented to resist lateral loads along principal
axes.
 If only one shear wall is oriented along one
principal axis, two shear walls should be
provided along the orthogonal axis to resist to
resist diaphragm torsion.

Basic principles of shear wall in
precast constriction
 They should be designed as load bearing
panels always .
 The increase in dead load acting on the panel
is an advantage because it increases the
panel resistance to uplift and overturning.

Position of Shear Walls
Exterior Shear Wall Interior Shear Wall / shear
core

Shear Wall System
 Precast concrete structures are mostly
designed as simply supported shear wall
systems.
 Shear wall can be located on the interior or the
exterior of the structure.
 Structural core inside – Interior System
 Structural core at the envelope – Exterior
system

Advantages of exterior system
towards interior system
 Provides more efficient and flexible floor plans
than an interior shear wall system – eliminates the
need for structural core .
 Exterior walls do not affect the interior flow of
loads.
 They can be designed – to have both vertical
stability and horizontal connections.
 Horizontal connection permit the entire wall to
function as a single unit to mobilize the
overturning effect.
 They eliminate the need for exterior columns and
beams.

 Structural core or Interior Walls are provided.
 Here, lateral forces are not directly transferred
to the foundation. Instead wall panels distribute
the lateral forces to the floor diaphragms to the
structural core or the interior shear wall and
then to the foundation.
Interior Shear wall system

Shear Wall Vs Moment Resisting
Frame

Forces on shear wall
 Shear walls will be designed to resist two
types of forces , they are
 Shear forces
 Uplift forces

Design Guidelines
 Warehouse type structure- exterior wall as
lateral force resisting system.
 Parking structures- shear walls can be located
at stair , elevator tower , ramped bay
,perimeter of structure or combination of above
etc.

Preliminary design
 Provide atleast three non-collinear walls to
ensure torsional as well as direct lateral
resistance.
 Arrange shear walls to minimize restraint due
to volume changes.
 Determine if shear wall can also be bearing
wall – overturning as governing criterion.
 Consider whether walls to be individual full
height (vertical joins only )

Preliminary design
 Consider the practicality of transportation and
erection – to select size of wall panels.
 Balance the design requirement of shear wall
with the design requirement of the associated
diaphragms.

Vertical and lateral roads
 Vertical gravity load to be determined first.
 Appropriate seismic design criteria to be
adopted to determined magnitude of lateral
load for each floor and compare with wind
load.

Shear wall design – steps
involved
 Create preliminary load analysis.
 Determine over tuning moment at each base.
 Select appropriate shear wall.
 Review preliminary choice and modify the
number location and dimension to satisfy the
requirement of each base. (foundations not to
be subjected to uplift.)
 Determine final load analysis.

Shear wall design – steps
involved
 Perform final load analysis and vertical load
analysis to determine design load.
 Create final shear wall design.
 Design shear wall reinforcement and
connection for associated diaphragms.
 Design the diaphragms.

BEAM
 Beams can be designed as either full, semi or
shell sections depending on the fabrication,
joining details, handling and delivering and
lifting capacities of the crane.
 Design consideration:
 Section properties
 Construction methods
 Sequence of the loads applied to the beams
 Beam behavior at the serviceability and
ultimate limit state.

COLUMN
 Designer should be conversant with various
connection methods:
Column to foundation
Column to beam
Column to column
Joint behavior – moment rigid or pin
connected.
 Design of precast column is similar to in-situ
columns.
 Sufficient capacity to withstand failure from
buckling due to slenderness effect.

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