Portal frames, its types and a case study on portal frames. Link to Download: https://dimpstrail.gumroad.com/l/vpdve

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ABCM REPORT
PORTAL FRAMES
DIMPLE B PODDAR
SEM 09 | DATE: 30 JUNE 2020
SMT.K. L. TIWARI COA

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PORTAL FRAMES
What are Portal frames?
 Portal frames are generally low-rise structures, comprising columns and
horizontal or pitched rafters, connected by moment-resisting
connections.
 Resistance to lateral and vertical actions is provided by the rigidity of the
connections and the bending stiffness of the members, which is increased
by a suitable haunch or deepening of the rafter sections.
 They are very efficient for enclosing large volumes therefore they are
often used for industrial, storage, retail and commercial applications as
well as for agricultural purposes.
Figure 1: Cross-section of a typical portal frame

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Figure 2: Components of a portal frame building Figure 3: Multi-bay portal frame construction
Types of portal frames
1. Pitched roof symmetric portal frame:
• Generally, fabricated from UB sections with a substantial eaves haunch
section which may be cut from a rolled section or fabricated from plate. 25
to 35 m are the most efficient spans.
Figure 4: Components of a pitched roof Figure 5: Lancashire waste development
symmetrical portal frame

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2. Portal frame with internal mezzanine floor
 Office accommodation is often provided within a portal frame structure
using a partial width mezzanine floor.
Figure 6: Portal frame with internal mezzanine floor Figure 7: Waters Meeting Health Centre, Bolton
3. Crane portal frame with column brackets
 Where a travelling crane of relatively low capacity (up to say 20 tonnes) is
required, brackets can be fixed to the columns to support the crane rails.
Use of a tie member or rigid column bases may be necessary to reduce
the eaves deflection.
Figure 8: Sketch of Crane portal frame

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4. Tied portal frame
 In a tied portal frame, the horizontal movement of the eaves and the
bending moments in the columns and rafters are reduced. A tie may be
useful to limit spread in a crane-supporting structure.
The high axial forces introduced in the frame when a tie is used
necessitate the use of second-order software when analyzing this form of
frame.
Figure 9: Sketch of a tied portal frame
5. Mono pitch portal frame
 A mono pitch portal frame is usually chosen for small spans or because of
its proximity to other buildings. It is a simple variation of the pitched roof
portal frame, and tends to be used for smaller buildings (up to 15 m span).

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Figure 10: Mono pitch portal frame
6. Propped portal frame
 Where the span of a portal frame is large and there is no requirement to
provide a clear span, a propped portal frame can be used to reduce the
rafter size and also the horizontal shear at the foundations.
Figure 11: Sketch of propped portal frame Figure 12: Rebottling plant, Hemswell
7. Mansard portal frame

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 A mansard portal frame may be used where a large clear height at mid-
span is required but the eaves height of the building has to be minimised
Figure 13: Mansard portal frame
8. Curved portal frame
 Portal frames may be constructed using curved rafters, mainly for
architectural reasons. Because of transport limitations rafters longer than
20 m may require splices, which should be carefully detailed for
architectural reasons.

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Figure 14: Curved portal frame
9. Cellular beam portal frame
 Rafters may be fabricated from cellular beams for aesthetic reasons or
when providing long spans. Where transport limitations impose
requirement for splices, they should be carefully detailed, to preserve the
architectural features.
Figure 15: Cellular beam portal frame Figure 16: Hayes garden centre

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DESIGN CONSIDERATIONS OF A PORTAL FRAME
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
1.5m
 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.
Figure 17: Dimensions used for analysis and clear internal dimensions

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LOADS ACTING ON PORTAL FRAME
 Permanent actions: Permanent actions are the self weight of the structure,
secondary steelwork and cladding.
 Service loads: Service loads will vary greatly depending on the use of the
building. In portal frames heavy point loads may occur from suspended
walkways, air handling units etc. It is necessary to consider carefully where
additional provision is needed, as particular items of plant must be treated
individually.
 Imposed roof loads: This load depends on the roof slope and material
used for construction of roof.
 Snow loads: Snow loads may sometimes be the dominant gravity loading.
 Wind load: Wind actions are inherently complex and likely to influence the
final design of most buildings.
 Crane loads: The most common form of craneage is the overhead type
running on beams supported by the columns. The beams are carried on
cantilever brackets or, in heavier cases, by providing dual columns.
Figure 18: Gantry girders carrying an overhead travelling crane

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Fire protection
When a portal frame is close to the boundary, there are several requirements
aimed at stopping fire spread by keeping the boundary intact:
 The use of fire resistant cladding.
 Application of fire protection of the steel up to the underside of the haunch.
 The provision of a moment resisting base (as it is assumed that in the fire
condition rafters go into catenary).
Figure 19: Collapse mechanism of a portal frame
CONNECTIONS
Figure 20: Eaves connection Figure 21: Apex connection

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Figure 22: Connection at the column base
CASE STUDY
The Pavillion

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The atmospheric and successful garden center "The Pavilion Garden Centre", with a
strong focus on greenery and interior, wants to expand because of their success. In the
spring we will start the construction of the ± 1,500 m2
extension.
Most modern techniques
We are building a new, modernized the Venlo construction on the site of the old
cold greenhouse, where everything has been adapted with modern
technology. In order to have the maximum amount of light inside, our special
glass construction with tempered glass with a column height of 4 meters was
chosen and with maximum ventilation for good ventilation.
Figure 23: Multi-bay pitched roof portal frame