Timber and Steel Framing Lecture Notes

Structural Loads

  • Framing members must be designed and joined to withstand dead, live, wind, and earthquake loads.
  • Must also meet serviceability requirements.
  • Buildings are constantly moving due to various forces.
  • Dead Loads: Stationary weights (structure itself).
  • Live Loads: Movable weights (people, furniture).
  • Gravity Loads: Dead and live loads acting downwards.
  • Wind Uplift Loads: Forces from wind, including side pressure, suction (uplift), and internal pressure.
  • Other Forces:
    • Racking or wall deformation loads.
    • Overturning and rotational forces.
    • Sliding and uplift forces.

Timber Framing

Pros

  • Often harvested sustainably.
  • Easy to work with on-site (cutting, drilling, nailing).
  • Relatively lightweight.
  • Readily available and easy to recycle.
  • Many skilled laborers.
  • Goal is to use timber framing as much as possible, using steel only when required.

Cons

  • Can be heavy for larger beams.
  • Natural imperfections can cause weaknesses.
  • Prone to termite attack, movement, and fire.

Softwood vs. Hardwood

  • Distinguished by tree species, not density.
  • Softwood (e.g., pine): Common for framing due to availability, light color, lightweight, and ease of use.
  • Hardwood (e.g., jarrah, ironbark, spotted gum, ash): More expensive, harder to source, color varies, relatively heavy.
  • Often use softwoods in the frame and hardwoods in the finishes
    *Hardwoods may have some degree of fire resistance.
Examples
  • Cypress pine (softwood flooring):
    • Density: 480kgm3480 \frac{kg}{m^3}
    • Janker rating: 1.6kN1.6 kN
  • Vic ash (hardwood cladding):
    • Density: 650kgm3650 \frac{kg}{m^3}
    • Hardness: 4.5kN4.5 kN
  • Ironbark (hardwood):
    • Density: 1120kgm31120 \frac{kg}{m^3}
    • Hardness: 14kN14 kN
Durability
  • Class 1 (very durable) to Class 5 (non-durable).
  • Pine is non-durable (less than 5 years if exposed).
  • Jarrah and Ironwood are very durable.
Rough Sawn Timber
  • How a log is cut affects the wood grain.
  • Cutting methods: straight grain, quarter sawn, plain sawn.
  • Grain profile affects durability, strength, and finish.
sustainably harvested plantation forest
  • Using sustainable means for harvesting timber is obviously crucial and not cutting down old growth forests for using construction.
  • A massive proportion of the timber that Australia grow and harvest goes to The US and then we get our timber from overseas.

Stress Grading

Grading Systems

  • S Grading: Visual stress grading; S1-S7 (unseasoned), SD7 & SD8 (seasoned).
  • F Grading: Mechanical stress grading; F4-F34.
  • Aesthetic Grading: Select (minimal knots), Standard, or Character (rustic).

Strength Groups

  • Represents timber's ability to maintain stress without failure.
  • 7 groups for unseasoned, 8 for seasoned.
  • S = unseasoned (green), SD = seasoned (dried).
  • Seasoned timber has better stiffness and less movement than unseasoned.
    *There are a lot of timber that is coming out very green.

F Grades

  • Structural timber is generally sold as stress graded product.
  • F14 indicates basic working stress in bending is 14MPa14 MPa.
  • Native forest timbers often use F grading.

MGP Grades

  • MGP (Machine Graded Pine): MGP10 and MGP15.
  • MGP10 indicates a minimum stiffness of 10,000MPa10,000 MPa.
  • Exotic plantation softwoods (e.g., pine) use MGP system.

Practical Application

  • Timber must meet required stress grade for its application (architect/engineer).
  • Australian Standards provide graphs for joist and bearer sizing based on timber grade and span.
    *When buying timber these abbreviations will make more sense.

Example

  • 70×4570 \times 45 structural pine, KD (kiln dried).
  • 90×4590 \times 45 structural hardwood F17 KD.
    There are also technical advisory brochure advisory brochure on structural timber.

Terminology

  • Essential for architects to know.
  • Floor Framing:
    • Stump (concrete or timber) with ant cap.
    • Bearer.
    • Floor joists.
  • Wall Framing:
    • Bottom plate.
    • Common studs.
    • Noggings (prevent twisting).
    • Top plate.
  • Wall Frame Anatomy: Top plate, bottom plate, studs, noggings.
  • Openings:
    • Sill trimmer (bottom of window opening).
    • Jack studs (below window).
    • Jam stud (next to window).
    • Lintel (above window, transfers load around the opening).
    • Rafter
    • Hanger Beam Hanger
    • Fascia

Preservative Treated Timber

H System

*The h system refers to how the product is treated.

  • H1: Indoor, above ground, no wetting (minimal infestation risk).
  • H6: Prolonged exposure to marine water (jetty piers).
  • Treatment depends on location and infestation threat.
Example
  • 90×35H390 \times 35 H3 MGP10 treated pine (outdoor timber framing).
    • H3: Suitable for outdoor above ground periodic wetting, resists decay, bores, and termites.
    • MGP10: Machine graded pine (structural characteristic).

Engineered Timber

  • Timber products that have gone through an engineering process
  • Examples include plywood and other composite materials.

Examples

  • Posi Joists: timber top and bottom plate with a chipboard interior.
  • Achieves higher structural performance through cross-lamination or other techniques.
    *LVL: Lots of thin layers of timber that is rotated and this gives it the composite strength of that grain of the timber changing.
  • Plywood
    *CLT is used in mass timber construction and is a serious alternative for concrete due to environmental benefits
    *Glulam: Often used as sort of an oversized beam in large scale projects.

Steel Framing

Pros

  • Durable.
  • Consistent dimensions.
  • Relatively lightweight.
  • Recyclable and non-combustible (but deforms under heat).
  • Greater span with smaller sections.

Cons

  • Not easy to work on-site (cutting, drilling, welding are costly and cause delays).
  • Susceptible to rust.
  • Deforms under high temperatures.
  • Can be noisy (creaking).
  • More expensive than timber.
  • Difficult to change on-site; limited builder experience.

Lightweight vs. Heavyweight Steel

*Offices are built with thin steel studs whereas heavy constructions have thicker steel.

  • Steel columns and beams come in standard sizes (e.g., the C1 89×8989 \times 89 SHS = square hollow section column).
Hot Rolled vs. Cold Rolled Steel
  • Hot rolled: made in high temperatures, cheaper, used where exact dimensions are not needed.
  • Cold rolled: rolled at low temperatures, more costly, gives exact dimensions.

Universal Column

  • Steel column with an H profile.
  • Fixing to concrete slab requires a base plate and cast-in bolts with anchors.
    *Steel framing can also be used for decking.

Floor Framing

Components

  • Floor bearers, floor joists.
  • Stumps: Concrete stumps embedded in concrete pads.
  • Adjustable legs can support the bearer.
  • Ant cap prevents ants from climbing onto bearers.
    *Differences between concrete slab and timber floor structure.

Wall Framing

Conventional Framing

  • Bottom plate, top plate, studs. Sheet bracing and strap bracing.
  • Sheet bracing is more effective, strap bracing's much more convenient because you can run cabling and services through that wall without having to punch holes through the sheet bracing.
  • Wall Intersections:
    • Corners built up with studs and blocking.
    • Australian Standards document has examples of corners and intersections.
      *When it comes to a wall intersection the wall is fixed to the nogging as opposed to a double stud

Noggings

  • Maximum height requirement from the bottom plate.

Lintels

  • Jack studs are notched around lintels.
    *Used lightweight steel studs for Classic office context.

Roof and Ceiling Framing

Types

  • Timber (rafters or trusses) vs. steel.
  • Rafters: Ridge beam installed first, then individual rafters (more time-consuming).
  • Trusses: Prefabricated with nail plates (efficient).
  • Most houses built with truss roofs over individual rafters.

Bulkhead

  • Lowered section of roofing/ceiling.
    *Whenever we need to lower a ceiling, generally speaking, we would leave the main roof structure where it is at that high level, and then we would build down with 90 by 45 framing to create that bulkhead structure.

Bracing

Types

  • Plywood, strap, and rod bracing.
  • Structural engineer specifies the type and location of bracing.
  • Strap bracing must have a specific angle (30-60 degrees) and be nailed at each stud.
    *Three d software is used in large commercial projects to design structures

Case Study Project

Ground Floor

  • Ply bracing in green, strap bracing indicated.
  • Steel:

Steel Beams

1B2 is steel beams. The structural engineering drawings use codes. 1B2 (goes to a point) and 1B3 are 300PFC300 PFC (parallel flange channel) beams.

  • 1B3 spans from PC1 (portal column 1) to a dropper post supported by 1L3.
    One can read this by find the code in the structure and checking what that member is. PC1 likely an 89×8989 \times 89 SHS (engineer oversight).
  • 1L2 is a 200PFC200 PFC forming a portal frame over the bi-fold door.
    *One needs to also add amended pergola design.

Upper Story

  • Cross bracing around the walking rope; ply bracing in corners.
    You need to make sure you check the building is not conflicting with the bracing of the three d model when adding things or engineering. Upper story, there is timber flooring made of 400 Posi joists. The stair is not a structural element of the building.
  • Infill roof in the original front part of the house.
    When drawing the roof you must include what the original roof looked like and add the extra infill design. The skylights are framed out specifically on the south side.
    These detail also have the specific measurements Discrepancies between architectural, structural, and site photos.
    1B2 has been drawn in the wrong location and there’s differences in how parts are measured such as R1.

Notes from Site Photos

  • Studs may not be evenly spaced; construction variations exist.

Ground Floor

*Little blocking pieces that seem unusual. * Concrete stumps, bearers, floor joists.

  • Infill pieces around shower area (lowered section).

Upper Story

  • Wall framing (P1 post part of timber frame).
  • Diagonal pieces were temporary supports during construction.
  • Framing with posies floor joists, r ones and framed Skylights.
    There’s differences such as r one sits lower as opposed to engineer drawings.
    *Nail plates show the use of trusses which are prefabricated.