PORTAL FRAME

G r a c e H e n r y&

M i d h u n a S u r e s h

INTRODUCTION• Developed during second world war,

but now the most common form of enclosure for spans of 20 to 60 m.

• Driven by the need to achieve low-cost building envelope.

• They are usually made from steel, but can also be made from concrete or timber.

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.

Portal Frames are generally used for single storey construction which require a large unobstructed floor space i.e.,A.FactoriesB.Shopping CentresC.Warehouses 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.

TYPES OF PORTAL FRAMEPitched roof symmetric portal frame Generally fabricated from UKB 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

Portal frame with internal mezzanine Floor Office accommodation is often provided within a portal frame structure using a partial width mezzanine floor. 

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

Pitched Roof Symmetric Portal FrameLancashire Waste Development

Portal Frame With Internal Mezzanine FloorWaters Meeting Health Centre, Bolton

Tied portal frameIn a tied portal frame the horizontal movement of the eaves and the bending moments in the columns and rafters are reduced.

Mono-pitch portal frameIt is a simple variation of the pitched roof portal frame, and tends to be used for smaller buildings (up to 15 m span).

Propped portal frameWhere 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.

Rebottl ing Plant, Hemswell 

Mansard portal frameA 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.

Curved rafter portal framePortal frames may be constructed using curved rafters, mainly for architectural reasons.

Cellular beam portal frameRafters may be fabricated from cellular beams for aesthetic reasons or when providing long spans.

Hayes Garden World

BASIC COMPOSITION• The portal structure is designed in such a way that it has no

intermediate columns.• A portal frame building comprises a series of transverse

frames braced longitudinally. • The primary steelwork consists of columns and pitched rafters. • The light gauge secondary steelwork consists of side rails for

walls and purlins for the roof. • The roof and wall cladding separate the enclosed space from

the external environment as well as providing thermal and acoustic insulation.

FIRST PORTAL FRAME IN HISTORYAt the EXPOSITION UNIVERSELLE in Paris 1878, the engineer HENRI DE DION progressed the science of vaulting with the first portal frame of lattice girders where the forces were transmitted directly to the foundations without tie bars. This Galarie des Machines had a span of 35m and its pitched roof shape was a forerunner of many sheds to follow.

ROOFING• A high percentage of roofs are

covered with composite profile metal sheets with a coloured external skin.

• These composite sheets have approximately 50mm of insulation sandwiched between two thin metal sheets or aluminium sheets.

• Galvanised steel purlins span between the steel rafters.

INTERNAL VIEW OF A PORTAL FRAMED WAREHOUSE

• Clear unobstructed floor area is available.

• With single storey buildings natural lighting is gained by placing clear sheets in roof layout. These sheets will run from eaves to ridge at suitable intervals.

BASE JOINT FOR PORTAL FRAME• The legs or stanchions of the

portal frame need connecting at the bottom to a foundation.

• Here we can see the base joint connection in place.

RIDGE JOINT FOR PORTAL FRAME

Shown here is a ridge joint or apex joint. It is Important that this joint is strong hence the use of wedge shaped pieces called gusset pieces to strengthen and increase the bolt area.

KNEE JOINT FOR PORTAL FRAME

Again the knee joint must be strong to support the roof loads and prevent bending. Gusset pieces will be used to increase strength, give greater bolt area and prevent deflection under load.

DIAGONAL BRACING FOR PORTAL FRAME

With all types of frameworks we must think on stability i.e. movement. To help strengthen the framework and prevent movement diagonal bracing will be used.

CLADDING RAILS FOR PORTAL FRAME

• This slide shows the cladding rails for attaching the external metal cladding panels to.

• These rails can be fixed horizontal or vertical depending on the way the cladding panels are fixed.

TIE CABLES FOR PORTAL FRAME• These wire and tubular

ties are used to prevent sagging of the cladding rails which can add considerable force unto the joints of the external cladding.

EXTERNAL WALL DETAIL• Here we see the finish

of the external cladding panels with the lower level facing brickwork.

• The blockwork behind creates a protective wall or firewall.

ADVANTAGES

Speed and ease of erection

Building can be quickly closed in and made water tight.

Framework prefabricated in a workshop and not affected by weather.

Site works such as drainage, roads etc can be carried out until framework is ready for erection.

No weather hold up during erecting the framework.

Connected together in factories by welding and site connections should be bolted.

• Cost effectiveness• Sustainability

• Saves time• Capable taking loads

immediately

DISADVANTAGES

Although steel is incombustible it has a poor resistance to fire as it bends easily when hot.

Subject to corrosion

CONSTRUCTION METHOD

Foundation –in situ concrete, concrete slab

COLUMN INSTALLATION

• Pinned base.

• From left to right.

RAFTER INSTALLATION

• Rigid connection

• Haunches and stiffener installed

PURLIN AND GIRT INSTALLATION

BRACING INSTALLATION

SHEET INSTALLATION

FINAL DESIGN- CRANE INSTALLATION

MODERN ART GLASS WAREHOUSE, THAMESMEAD.

NORMAN FOSTER AND ANTONY HUNT

THANK YOU!