strcteng 201 - test 1
For steel what two reinforcement grades are used?
- Grade 300E (fy = 300MPa)
- mild steel
- Grade 500E (fy = 500Mpa)
- alloyed or tempered
What are the three types of Grade 500 reinforcement?
- Grade 500L (low ductility)
- Grade 500N (normal ductility)
- Grade 500E (earthquake)
Chracateristics of why 500E reinforcement should be used in NZ
- yield strength of N/L grades not tightly controlled
- low ultimate strain
- low ratio of ultimate to yield strength
How to prevent corrosion in steel?
- Prestressing (prevent cracks)
- very low porosity concrete (SCMs, low w/c ratio)
- galvanised rebar
- stainless rebar
- cathodic protection
- non-metallic reinforcement
What is non-metallic reinforcement?
- Not a routine product
- Useful for:
1. Very corrosive environments
2. Situations where steel cannot be used
- GFRP most common alternative
Wood is truly sustainable if.....?
The forest are managed responsibly, i.e. The volume used is less than the volume grown (use less)
50% of wood is...?
carbon
What are the two types of woods?
Softwoods & Hardwoods
What is in a softwoods forest?
Coniferous / Evergreen plants
What is in a hardwoods forest?
Deciduous / Broad-leaved plants
What are all the NZ native species?
- Rimu
- Totara
- Taraire
- Tawhai
- Kauri
- Puriri
- Matai
- Towai
- Tawa
- Pukatea
- Rewarewa
- Rata
- Tawhero
What NZ native species supply is not abundant enough to sustain the timer construction industry?
Puriri & Rewarewa
Which out of the two (hardwoods/softwoods) grow faster?
Softwoods
Softwoods vs Hardwoods
Softwoods:
- Faster
- Cheaper
- Timber industry relies on softwood species more
Hardwoods:
- Used in limited cases
How to calculate the strength of wood?
By using its density value as density is the indicator of strength. Related to such things as; hardness, ease of machining and nailing resistance.
Specific gravity is....?
The ratio of the density of wood to the density of water. It is customary to use oven-dry weight and current volume.
Structural defects of wood:
- knot
- slope of grain
- resin pocket
- check
- split
- compression wood
- wane
What are the 3 main frame types?
- Moment Resisting Frame
- Concentrically Braced Frame
- Eccentrically Braced Frame
Types of Open Cross Sections?
- I section
- C or Channel Section
- Tee section
- Angle section
Types of Closed Cross Sections?
SHS = Structural/Square Hollow Section
RHS = Rectangular Hollow Section
CHS = Circular Hollow Section
Manufacture Stage 1: Production of Pig Iron
- Iron ore and carbon mixed at 1600 degrees celcius
- Reduction reaction gives pig iron
- Pig iron contains up to 5% carbon and other elements
- Slag residue used in road making, aggregate etc
- Excess Co2 bottled for industrial use
- Electricity cogenerated from iron and steel making process: 60% of total used for NZ steel
What yields from the brace first, concentrically or eccentrically braced frame?
Concentrically braced frame
Manufacture Stage 2: Production of Steel
- Oxygen is pushed through pig iron to remove most of the carbon
- Excess oxygen is removed by adding aluminium and silicon
- killed steels = all oxygen removed
- Molten steel then rolled into final shape
- Controlled rolling
pros and cons of fillet weld
good for static & earthquake, bad for fatigue loading
What are the 3 basic categories of hot rolled section?
1. Beams
2. Columns
3. Piles
incomplete penetration butt weld vs complete penetration butt weld
plate to plate connection, full strength not required, weaker, bad in fatigue vs expensive, full strength of weakest member, good for static/earthquake/fatigue
What are the principal elemnts of steel?
- Principal two elements are iron & carbon
- Carbon content for structural steels < 0.8%
- Max carbon content for any steel < 3%
(Carbon content strongly influences behaviour)
What are the cayses of residual stress for steel members?
- Uneven cooling of hot rolled sections
- Cutting of edges
- Welding of pieces together
What is a 'unit cell' ?
Is the smallest volume element of a space lattice
what are some advantages of comining steel and timber
concentrated and heavy long term compression load, earthquake resistance
When a metal is stressed below the elastic limit it....
- returns to its og dimension
- aka the target region for the design structures for in-service condition
When a metal is stressed above the elastic limit...?
- a permamant deformation remains.
- aka the target region for design structurs for the ultimate limit state condition
Brittle fracture is?
Characterised by a rapid crack proagation without significant plastic deformation
Ductile fracture is?
- Characterised by tearing of metal and signifcant plastic deformation
- Can be grey & fibrous
- Associated with overload of the structure or large discontinuities
What is a static load?
- Applied slowly so that ut cayses minimal dynamic effects in the structure (for eg - fatigue failure)
- Load is constant
- Building loads = static loads
What is a dynamic load?
= Repeatd load
- aka it fluctuates in magnitude over time
examples: trucks, trains, people, conveyor systens, cranes, furniture, warehouse material, snow & water
What is fatigue?
The deterioration of a material under repeated cycles of stress or/and strain, resulting in cracking & fracture
- Most significant = large number of cycles at small strains / stresses
How big of a problem is fatigue?
- 80-90% of all steel failures fatigue failure joints that are more susceptible to fatigue
- Fatigue failure occurs with tall signs due to the window force
Transition Temperature?
The temp at which the fracture behaviour changes from ductile to brittle
- 50% ductile & 50% brittle = transtion zone
Brittle Failure at low temps occur when....
in metals when these metals are below transition temp
3 Types of welds?
- Fillet weld
- Incomplete penetration butt weld
- Complete penetration butt weld
3 Types of connections?
- Simple (rotate under design actions without moment)
- Semi - rigid (carry moment but weaker than beams)
- Rigid (no rotation under design actions)
What happens in a beam-moment resisting splice?
- Flanges resist moment-induced and direct axial forces
- Web resists shear and moment due to eccentric shear transfer
- Bolt and weld failure suppressed
What are the 3 types of heavy timber?
- Sawn timber
- Glulam (glue laminated timber)
- LVL (laminated veneer lumber)
What are the 4 fire behaviours
- Ignition
- Growth
- Burning
- Decay
What is a rain screen?
Protects from the rain and allows air movement behind
3 Environment types?
- closed
- sheltered
- exposed
What is the durability clause?
requires that materials, components & construction methods allow the building to function for its specified intended life of not less than 50 years for structural and inaccessible elements.
What causes deterioration?
- insect & marine borers
- fungi
- moisture fluctuations
- ultraviolet light
- bacteria
- mechanical abrasion
- chemicals
What is a crosslam panel?
- panels made from boards
- laid in perpendicular pattern
- dimensionally stable
- good thermal resistance
- allows prefabrication of building components
What is LVL?
Laminated veneer lumber
- a derivative of plywood
- all laminations are laid in one direction pressed together
- very strong and stiff material (good for beams)
- not as good to connect
- some cross-ply LVL frabricated is better for members other than beams
Glulam
- laminations are glued together
- laminations are typically 45 mm - need to be thinner if theres curvature
- not all glue is of the same service class
What are all the wood products?
- sawn lumber
- glulam
- panelling (sheating)
- engineered wood poles
what is air-dried wood?
wood which moisture content is in equilibrium with the ambient air relative humidity
what is kiln - dried wood
wood which moisture content has been reduced to 15-19%
What is plywood?
- uses logs peeled
- veneer is laid at various angles
- gives stability & strength
- different grades for strength & visual finish
- used for flooring and lateral bracing, gussets in moment resisting frames and plywood boxed beams
Does timber deteriorate through age alone?
No
What is wood preservation?
extends the life of timber by modifying its resistance to agents
What are the hazard classes?
- Untreated
- H1.1
- H1.2
- H2
- H3.1
- H3.2
- H4
- H5
- H6