week 7

• Structural steel construction is any work to erect assembled portions and single components of structural steel, such as columns, beams, bracing, bridging, fly bracing, rafters, purlins, and girts

  
• Standards for structural steel construction

  • AS 4100 Steel Structures
  • AS/NZS 4600 Cold-formed Steel Structures
  • AS/NZS 5131 Structural steelwork – Fabrication and erection

  
• Universal columns (UC)


  • I or H shape
  • Available in five basic sizes with a variety of section and flange depths as well as different thicknesses and radii
  • Light steel columns come in three designation sizes: 100 mm, 150 mm, and 200 mm
  • Heavy steel columns come in two sizes: 250 mm and 310 mm
  • The section mass ranges from 14.8 kg/m for the lightest columns to 158 kg/m for the heaviest columns
  • Larger welded columns come in 3 sizes: 350 mm, 400 mm, and 500 mm
• Universal beams (UB)


  • Range in size from 150 mm to 410 mm, including 180 mm, 200 mm, 250 mm, 310 mm, and 360 mm
  • Heavy Universal Beams are available in three sizes: 460 mm, 530 mm, and 610 mm
  • Standard section lengths vary from 9 m to 20 m with 9 m, 10.5 m, 12 m, 13.5 m, 15 m and 18m lengths available
• Taper flange beams


  • Similar in shape to the "I" shaped Universal Beams except that they have tapered flanges
• Channels (PFC)


  • Hot-rolled carbon steel made in a "C" shape with a vertical web and top and bottom horizontal flanges with inside radius corners, available in a wide range of sizes and thicknesses
• Structural Angles


  • Formed by bending a single angle in a piece of steel, 'L' shaped with the legs of the "L" can be equal or unequal in length
• Purlins and girts


  • Typically cold formed steel, hot dip galvanised, "Z" (able to be lapped) or "C" sections (unable to be lapped), range in depths from 100 to 350mm
  • Purlin and girt capacity often dictates the frame spacing
  • Connection to portal frame is via a simple cleat
  • Purlins and girts may require bridging to provide lateral stability against buckling
• Purlins


  Roof members used to support roof sheeting, run perpendicular to and supported on rafters
• Girts


  Wall members used to support wall sheeting, run perpendicular to and supported on columns and mullions
• Basic framing systems


  • Two-way rigid frames
  • One-way rigid frames
  • Two-way braced frames
• Two-way rigid frames


  • Two planes of rigid frames intersecting at right angles
  • Columns at frame intersections
  • Loads resisted by frame action in both directions
  • All rigid connections
  • No requirement for bracing or shear panels (usually)
• One-way rigid frames


  • Rigid connections in unbraced plane
  • Flexible connections in braced plane
  • Planning flexibility is reduced - some bays between column will be required for bracing or shear panels
• Two-way braced frames


  • All flexible connections
  • Stability in both planes is dependent on bracing or shear panels
  • Bracing or shear panels required in both directions
  • Lowest cost solution (usually)
  • Low to medium rise rectangular frames, can be used up to 50 storeys utilising cores as bracing elements and composite floors (steel beam + concrete floor) to transmit lateral forces
• Buildability considerations for structural steel framing

  • Stability at all stages of erection and effect of erection sequence on stability
  • Safe access, working environment and safe erection procedure
  • Hold down bolts and cast-in fittings installation method
  • Requirement of temporary bracing
  • Handling, lifting, storing, stacking and transportation of components
  • Assembling on ground to reduce fixings & connections at heights
  • Standardise as much as possible
  • Adopt simple detailing
  • Minimise number of bolt diameters and categories
  • Use only one bolt size and category in a joint
  • Corrosion protection of bolts should match the structure
• Factors for site management to consider in planning structural steel erection

  • Isolating other trades from the erection works
  • Risks of falls from heights
  • Falling objects
  • Scheduling duration for shop drawings, fabrication and erection
  • Ground conditions - ensuring safe working platform
  • Maximum permissible wind speed for erection
  • Frequent meetings to review safety issues
  • Consulting Structural Engineer's approval for modifications
  • Accuracy of installing holding down bolts and cast-in fittings
• Factors to consider for steel fabrication

  • Workshop drawings preparation, review, and Consulting Engineer's approval
  • Sequence for delivery
  • Marking of steel components for erection sequence
  • Indicating the weight of steel members
  • How members will be supported to prevent uncontrolled movement
• Factors to consider for steel erection

  • Erector is required to be a certified 'rigger' experienced in steel erection
  • Erection methodology
  • Bracing bays & temporary bracing
  • Plant, equipment & crane including access, working radii and boom clearances
  • Stability requirements for all components
  • Methods for handling components
  • Possibility of pre-assembly on ground
• Portal framed structures


  • Generally constructed from structural steelwork
  • Provides clear open space inside the building
  • Quick and easy construction
  • Cranes can be included in design
  • Wall types - Concrete or Steel
• Portal framed structures - clear span

  • Up to 30m - portal framed structures made from UB steelwork tend to be the most economical
  • 30 - 70m - portal tapered frame (BUP) designed systems usually more economical, depending on the design criteria and region (i.e. cyclonic region)
  • Over 70m - space frame (three dimensional truss) systems or truss rafter systems (Aircraft Hangars)
• Typical portal framed building

  • Typically consist of universal members (e.g. universal beams 200UB25.4)
  • Connections usually bolted sometimes may be welded
  • Spans up to 20m - uniform column and rafter section most economic (usually)
  • Spans over 20m - haunching of rafter more economical (usually)
• Portal frame components


  • Rafter
  • Ridge
  • Knee joint
  • Column
  • Haunch
  • Mullions
  • Purlins
  • Girts
• Rafter


  Transfers load from roof sheeting and self weight to column to foundations
• Ridge


  A moment-resisting connection provided at the crown to resist lateral and gravity loadings
• Knee joint


  The main design area is to resist the moment of wind
• Column


  Vertical frame member that transfers load from roof to column then foundations
• Haunch


  Haunching the rafter is done in lieu of a bolted connection and increases the section strength. Higher moments at haunch and wind is resisted by the haunch and portal frame
• Mullions


  Supports the end wall girts where the frame span is too large for the girt to span between main columns
• Bracing in portal framed buildings

  • Portal frames are typically one-way rigid frames - provide lateral strength parallel to the frame through frame action, but unable to provide lateral strength perpendicular to the frame
  • Bracing required in this perpendicular direction, usually by triangulation (cross bracing)
  • Bracing required to transmit lateral forces to foundation level, in the roof and walls
• Portal frame members are subject to failure by buckling due to lateral instability from compressive forces
• Fly bracing


  Provides lateral restraint to the inside flanges of portal frame members that are in compression, transmitting lateral forces via the bracing to the purlins and girts
• Erection options for portal frames

  Assemble in place - crane location not critical, but guys must remain until sufficient steelwork erected to allow permanent bracing to be installed, time consuming but permits careful progress
• Fly bracing


  1. Portal frame members are subject to failure by buckling

  2. Outside flanges in compression have lateral restraint provided by purlins and girts

  3. Inside flanges in compression use fly bracing to provide restraint

  4. Lateral forces transmitted via bracing to purlins and girts

  5. Fly bracing is required before compression can develop in the internal flange of the members prior to fixing the sheeting
• Portal Frame Structures


  • Lateral instability due to compressive forces
  • Not necessarily required at each purlin or girt
• Erection option 1: assemble in place

  1. Crane location not critical

  2. Guys must remain until sufficient steelwork erected to allow permanent bracing members to be installed

  3. Time consuming but permits careful progress
• Erection option 2: assembled on slab and erected as unit


  1. Portal assembled on slab clear of erected work

  2. Two crane lift if portal cannot withstand compression forces

  3. Rubber tyred cranes should not travel with load
• Crane selection


  • Cranes kept as close as practicable
  • Sketch required to detect clashes
  • Always provide temporary bracing to existing work
• Levelling and aligning option 1

  1. Styrene foam cores

  2. Grout cores

  3. Grout under base plate

  4. Pack and wedges to height
• Levelling and aligning option 2


  Extra thread on bolt to permit second nut for levelling
• When things go wrong - see appendix one of this lecture