5. STEEL PORTAL FRAMES
Portal frames are generally low rise structures, comprising columns and horizontal or pitched
rafters, connected by moment-resisting connections.
Portal frames can be defined as two-dimensional rigid frames that have the basic characteristics
of a rigid joint between column and beam.
The main objective of this form of design is to reduce bending moment in the beam, which
allows the frame to act as one structural unit.
The transfer of stresses from the beam to the column results in rotational movement at the
foundation, which can be overcome by the introduction of a pin/hinge joint.
For warehouses and industrial buildings, sloping roof made of purlins and ac sheet roofing
between portals is provided. For assembly halls, portals with R.C slab roof cast monolithically
is used.
Portal frames are designed for the following loads:
roof load
wind load
While designing, care should be taken for proper
joints
foundation
bracing
If the joints are not rigid, they will "open up" and the frame will be unstable when subjected to
loads. This is the pack of cards effect.
1. Vertical loading results in the walls being pushed outwards. If the foundation cannot
resist horizontal push, outward movement will occur and the frame will lose strength.
2. Wind subjects the frame to uplift forces. Overturning forces on the sides and ends of the
building. Drag forces on the roof and sides.
3. These destabilizing forces are resisted essentially by the weight of the building and in
this regard, the foundations contribute significantly to this weight. The foundations are
regarded as the building's anchors.
6. CHOICE OF MATERIAL AND SECTIONS
Steel sections used in portal frame structures are usually specified in grade S275 or S355 steel.
MAIN FRAME:
The main (portal) frames are generally fabricated from UB sections with a substantial eaves
haunch section, which may be cut from a rolled section or fabricated from plate. A typical frame
is characterised by:
A span between 15 and 50 m
An clear height (from the top of the floor to the underside of the haunch) between 5 and
12 m
A roof pitch between 5° and 10° (6° is commonly adopted)
A frame spacing between 6 and 8 m
Haunches in the rafters at the eaves and apex
A stiffness ratio between the column and rafter section of approximately 1.5
Light gauge purlins and side rails
Light gauge diagonal ties from some purlins and side rails to restrain the inside flange of
the frame at certain locations.
7. STEEL PORTAL FRAMES – TURBHE RAILWAY STATION (LIVE CASE STUDY)
Specifications: - Material: - Steel Design: - Customize
Conventional steel structures are basically fabricated at site. This steel structure is highly
acclaimed for longer service life and high tensile strength. It is 84-m roof with a semi circular
shape
8. Turbhe Railway Station Navi Mumbai
Turbhe Railway Station, designed by Hafeez Contractor and conceptualised with a gigantic
arch roof, is the new Gateway for the grand entry into the city of Navi Mumbai.
Turbhe is the fifth railway station with Rail Corridor, a 23-km-long corridor connecting
Thane with Navi Mumbai. It is at a distance of 15 km from Thane railway station and 3 km
from Vashi railway station.
The station occupies a total length of 65.4 m x 27 m, across the five platforms and the tracks.
The station spread over an area of 15,000 sq m has a parking capacity for 175 cars and 250
bikes.
ROOF STRUCTURE:
The station stands apart because of its massive 84-m roof with a semi circular shape.
An innovative ribbed arch roof design spans across all platforms and its sheer size and
magnitude makes an imposing assertion.
Large strip skylights, integrated with the structural system, establish light-filled
platform spaces.
Resilient galvalume sheets made of aluminum and zinc are used for the roof.
The roof is distinctive because of the clips that have been used for fixing joints instead
of drilling
