PORTAL FRAMES BUILDING CONSTRUCTION B.ARCH
- 2. PORTAL FRAMES • Portal frames are 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. • This form of continuous frame structure is stable in its plane and provides a clear span that is unobstructed by bracing. Portal frames are very common, in fact 50% of constructional steel used in the UK is in portal frame construction. • 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. 2
- 3. Typical portal frame • A portal frame building comprises a series of transverse frames braced longitudinally. • The primary steelwork consists of columns and rafters, which form portal frames, and bracing. • The end frame (gable frame) can be either a portal frame or a braced arrangement of columns and rafters. 3
- 4. 4 Hinges can be introduced into a portal frame design at the base connections and at the centre or apex of the spanning member, giving three basic forms of portal frame: Fixed or rigid portal frame All connections between frame members are rigid. This will give bending moments of lower magnitude more evenly distributed than other forms. Used for small to medium-size frames where the moments transferred to the foundations will not be excessive. Two-pin portal frame In this form of frame, hinges are used at the base connections to eliminate the tendency of the base to rotate. The bending moments resisted by the supporting members will be greater than those encountered in the rigid portal frame. Main use is where high base moments and weak ground conditions are encountered. Three-pin portal frame This form of frame has hinged joints at the base connections and at the centre of the spanning member. The effect of the third hinge is to reduce the bending moments in the spanning member but to increase deflection. To overcome this latter disadvantage a deeper beam must be used or, alternatively, the spanning member must be given a moderate pitch to raise the apex well above the eaves level. IMPORTANCE OF HINGE S IN PORTAL FRAME
- 5. TYPES OF PORTAL ON SPAN LENGTHS RIGID PORTAL FRAME SPAN UPTO 15 M SPACING – 3 TO 5 M FOUNDATION – RIGID JOINT KNEE – RIGID JOINT APEX – RIGID JOINT 2 PIN PORTAL FRAME SPAN 16 TO 35 M SPACING – 4 TO 8 M FOUNDATION – HINGED JOINT KNEE – RIGID JOINT APEX – RIGID JOINT 2 PIN PORTAL FRAME SPAN 36 TO 50 M SPACING – 8 TO 12 M FOUNDATION – HINGED JOINT KNEE – RIGID JOINT APEX – HINGED JOINT 5
- 6. 6 BENDING MOMEMT DIAGRAM FOR PORTAL FRAME
- 7. 7 Concrete portal frames are invariably manufactured from high-quality precast concrete suitably reinforced. In common with all precast concrete components for buildings, rapid advances in design and use were made after the Second World War, mainly because of the shortage of steel and timber that prevailed at that time CONCRETE PORTAL FRAME Pocket connection -The foot of the supporting member is located and housed in a void or pocket formed in the base so that there is an all-round clearance of 25 mm to allow for plumbing and final adjustment before the column is grouted into the foundation base. Baseplate connection- A steel baseplate is welded to the main reinforcement of the supporting member, or alternatively it could be cast into the column using fixing lugs welded to the back of the baseplate. Holding-down bolts are cast into the foundation base. Pin joint or hinge connection -A special base or bearing plate is bolted to the foundation, and the mechanical connection is made when the frames are erected FOUNDATION AND FIXINGS
- 8. 8 POCKET CONNECTION BASE PLATE AND HINGE CONNCETION
- 9. 9 MULTI SPAN PRECAST CONCRETE PORTAL FRAME
- 10. 10 TYPES OF SPLICE JOINTS IN PRECAST PORTAL FRAME
- 11. 11 The main advantages to using precast concrete portal frames are as follows *) Factory production will result in accurate and predictable components because the criteria for design, quality and workmanship recommended. *)Structural use of concrete can be more accurately controlled under factory conditions than casting components in situ. *)Most manufacturers produce a standard range of interchangeable components that, within the limitations of their systems, gives a well-balanced and flexible design range covering most roof profiles, single-span frames, multi-span frames and lean-to roof attachments. *) Maintenance of precast concrete frames is not usually required unless the building owner chooses to paint or clad the frames. *) Precast dense concrete products have an inherent resistance to fire, and therefore it is not usually necessary to provide further fire-resistant treatment. However, the amount of reinforcement concrete cover will vary depending on the fire resistance required . ADVANTAGES OF PRECAST CONCRETE PORTAL FRAMES
- 12. 12 *)The wind resistance of precast concrete portal frames to both positive and negative pressures is such that wind bracing is not usually required. *) Where members of the frame are joined or spliced together the connections are generally mechanical (nut and bolt), and therefore the erection and jointing can be carried out by semi-skilled operatives. *) In most cases the foundation design, setting out and construction can be carried out by the portal frame supplier or their nominated subcontractor.
- 13. 13 *)Steel portal frames can be fabricated from standard universal beam, column and box sections. *)Alternatively a lattice construction of flats, angles or tubulars can be used. Most forms of roof profiles can be designed and constructed, giving a competitive range when compared with other materials used in portal frame construction. *)The majority of systems employ welding techniques for the fabrication of components, which are joined together on site using bolts or welding. *) An alternative system uses special knee joint, apex joint and base joint components, which are joined on site to square-cut standard beam or column sections supplied by the main contractor . STEEL PORTAL FRAMES
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- 15. 15 TYPICAL SKETCH OF A STEEL PORTAL FRAME
- 16. 16 FABRICATION OF STEEL PORTAL FRAME IN DIFFERENT STEEL SECTIONS
- 17. 17 *)The foundation is usually a reinforced concrete isolated base or pad foundation designed to suit loading and ground-bearing conditions. The connection of the frame to the foundation can be by one of three basic methods *) Pocket connection -The foot of the supporting member is inserted and grouted into a pocket formed in the concrete foundation, as described in precast concrete portal. FOUNDATION AND FIXINGS IN STEEL PORTAL FRAME *) Baseplate connection -Traditional structural steelwork column to foundation connection using a slab or a gusset base fixed to a reinforced concrete foundation with cast-in holding-down bolts. *) Pin or hinge connection -Special bearing plates designed to accommodate true pin or rocker devices are fixed by holding-down bolts to the concrete foundation to give the required low degree of rigidity at the connection
- 18. 18 DETAIL AT APEX AND KNEE OF A RIGID STEEL PORTAL FRAME
- 19. 19 SPLICING DETAILS & HINGED END AT FOOTING IN STEEL PORTAL FRAME
- 20. 20 *)The main advantages of factory-controlled production are a standard range of manufacturer’s systems, a frame of good wind resistance, and the fact that the ease of site assembly using semi-skilled operatives attributed to precast concrete portal frames can be equally applied to steel portal frames. *) A further advantage of steel is that, generally, the overall dead load of a steel portal frame is less than that of a comparable precast concrete portal frame. However, steel has the disadvantage of being a corrosive material, which will require a long-life protection of a patent coating or regular protective maintenance, generally by the application of coats of paint. *)Steel has a lower fire resistance than precast concrete, but if the frame is for a single- storey building structural fire protection may not be required under the Building Regulations . ADVANTAGES OF STEEL PORTAL FRAME
- 21. 21 BRACING AND THEIR IMPORTANCE IN DESIGNING OF STEEL PORTAL FRAME TYPE OF BRACING –1)WIND BRACING 2)STRUCTURAL BRACING
- 22. 22 TYPES OF PURLINS AND SHEETING RAILS. 1) MILD STEEL PURLIN 2) G.I STEEL SIGMA PURLIN 3) G.I ZED SECTION PURLIN
- 23. 23 FIXING DETAILS OF BRACING MEMBERS AT THE SIDE AND THE ROOF OF STEEL PORTAL
- 24. 24 TIMBER PORTAL FRAME Timber portal frames can be manufactured by several methods, which produce a light, strong frame of pleasing appearance that renders them suitable for buildings such as churches, halls and gymnasiums where clear space and appearance are important. Types of Timber portal frames *) Glued laminated portal frames. *) Glued and nailed portal frames. *) Plywood-faced portal frames. *) Timber portal frames using solid members.
- 25. 25 GLUED LAMINATED PORTAL FRAME
- 26. 26 *) The main objective of forming a laminated member consisting of glued layers of thin-section timber members is to obtain an overall increase in strength of the complete component compared with that which could be expected from a similar-sized solid section of a particular species of timber. *) This type of portal frame is usually manufactured by a specialist firm, because the jigs required would be too costly for small outputs. *) The selection of suitable-quality softwoods of the right moisture content is also important for a successful design. In common with other timber portal frames, these can be fully rigid, two- or three-pin structures. *) Most glued laminated timber portal frames are fabricated in two halves, which eases transportation problems and gives maximum usage of the assembly jigs. *) The frames can be linked together at roof level with timber purlins and clad with a lightweight sheeting or decking; alternatively, they may be finished with traditional roof coverings
- 27. 27 GLUED AND NAILED TIMBER PORTAL FRAME
- 28. 28 *) These frames are suitable for small halls, churches and schools with spans in the region of 9.000 m. *) The portal frames are in essence boxed beams, consisting of a skeleton core of softwood members faced on both sides with plywood, which takes the bending stresses. *) The hollow form of the construction enables electrical and other small services to be accommodated within the frame members. *) Design concepts, fixing and finishes are as given above for glued laminated portal frames PLYWOOD FACED TIMBER PORTAL
- 29. 29 SOLID TIMBER AND PLYWOOD GUSSET PORTAL FRAME
- 30. 30 *) These frames were developed to provide a simple and economic timber portal frame for clear-span buildings using ordinary tools and basic skills. *) The general concept of this form of frame varies from the two types of timber portal frame previously described in that no gluing is used, the frames are spaced close together (600, 900 and 1200 mm centres), and they are clad with a plywood sheath so that the finished structure acts as a shell, giving a lightweight building that is very rigid and strong. *) The frames can be supplied in two halves and assembled by fixing the plywood apex gussets on site before erection, or they can be supplied as a complete frame. *) The foundation for this form of timber portal frame consists of a ground beam or, alternatively, the frames can be fixed to the edge of a raft slab. A timber spreader or sole plate is used along the entire length of the building to receive and distribute the thrust loads of the frames. Connection to this spreader plate is made by using standard galvanised steel joist hangers or by using galvanised steel angle cleats.
- 31. 31 ADVANTAGES OF TIMBER PORTAL FRAME The advantages of all timber portal frame types are as follows *) Constructed from readily available materials at an economic cost. *) Light in weight and easy to transport and erect and can be trimmed and easily adjusted on site. *) Protection against fungal and/or insect attack can be by impregnation, or surface application. *) Pleasing appearance either as a natural timber finish or painted.
- 32. APPLICATION OF PORTAL FRAME • Bridge Structures • Frames for Buildings • Large Span Entrances • Below Ground Waterways • Pedestrian Subways 32
- 33. TYPES OF PORTAL FRAMES BASED ON MATERIAL – CONCRETE / STEEL STEEL PORTAL FRAME CONCRETE PORTAL FRAME STEEL PORTAL FRAME Basic material used for taking load is Reinforced Cement Concrete. Basic material used for taking load is Steel. In Rcc portal frame, the cross Section areas of structural elements are large. In steel portal frame, the Cross Section areas of structural elements are small. The structure is less resistant to Earthquake and Wind. The structure is more resistant to Earthquake and Wind. In Rcc portal frame, the tensile strength of RCC structural elements is less as compared to Steel structural elements. In steel portal frame, the tensile strength of Steel structural elements is more as compared to RCC structural elements. Rcc portal frame is more skilled labor intensive. Steel portal frame is less labour intensive and much work can be done in workshop. Speed of construction is less. Speed of construction is more. Rcc portal frame is less prone to corrosion. Steel portal frame is prone to corrosion. Cost of repair is more and repair are cumbersome. Cost of repair is less and repair are comparatively easy. Skilled as well as non skilled workers are needed for its construction. Only Skilled worker are needed for its construction. The structure is fire resistant. The structure is not fire resistant. Economical where form work and labor are easily available. Costly form of construction. Maintenance is less It has to be maintained regularly CONCRETE PORTAL FRAME 33
- 34. TYPES OF PORTAL FRAMES BASED ON MATERIAL - TIMBER 34 Disadvantages: • Traditional procurement process • Additional design and engineering time • Lack of experienced builders and erection crews • Exposure to weather before enclosed • Deficiency of site quality control • Combustibility of timber requires vigilant quality control to achieve required fire rating Advantages: • Recyclable/ Renewal • Low embodied energy if constructed in local timber • Reduced construction waste through efficient controlled manufacturing • Low volume of waste on site requiring removal
- 35. TYPES OF PORTAL FRAMES 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 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. 35
- 36. TYPES OF PORTAL FRAMES 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. 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). 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. 36
- 37. TYPES OF PORTAL FRAMES Mansard portal frame 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. Curved rafter 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. 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. 37
- 38. CASE STUDY - SUTTON GAULT POTATO STORE, ELY 38 Introduction: Architect : Thurlow Nunn Standen Structural engineer : Frirth Blake Steel work contractor: AC Bacon Engineering Client: PJ Lee and Sons Using two mobile cranes, the steel frame was erected during a six week programme with the main central span installed first. All of the columns are spaced at 6m centres and the tallest of these members are 8m-high sections located in the middle of the building. Roof rafters were brought to site in two sections (each 15.5m for the outer spans and 17m sections for the mid- span), bolted together on the ground and then lifted into place as one member. The main frames are spaced approximately 15m apart, and secondary rafters span between the main frames. At each frame, the secondary rafters are generally at a level aligned with the apex of the primary frames, meaning that towards the eaves of the primary frames, the secondary rafters are supported on stools a significant distance above the primary rafter.
- 39. CASE STUDY -SIEMENS WIND TURBINE BLADE MANUFACTURING FACILITY, HULL 39 Introduction: Architect : Pringle Brandon Perkins+ Will Structural engineer : Waterman Structures Steel work contractor: Caunton Engineering Client: Siemens The (northern) manufacturing area of the Siemens factory has four bays with two 40t electric overhead travelling (EOT) cranes travelling on runway beams supported by double lattice columns. This arrangement conveniently allows the runway beam vertical reaction to be transferred to the ground directly through one leg of the double column. The estuary-side site requires piled foundations and this allows overall building stability in the direction perpendicular to the runway beams to be provided by fixed base columns. The double lattice columns are laterally stiff by virtue of acting as the tension and compression booms of a vertical cantilever truss. The push-pull in the columns is transferred via pile caps into the piles. The column leg not supporting the crane runway beams continues upward to support the roof trusses which are simply supported between columns. In the orthogonal direction, K bracing is provided to stabilize the building.
- 40. Source :- SteelConstruction.Info Advanced building construction –Chudley.