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VBKN01 > EXAM > Flashcards

EXAM Flashcards

1
Q

Requirements for Plastic Analysis

A

Section Class 1 - no local buckling occurs

- therefore plastic hinge occurs

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2
Q

Static Method

A
  • assume shear force, axial force and torsional couples have no effect on carrying capacity
  • collapse load depends on fully plastic moments
  • choose a moment distribution
  • correct or understimated load capacity
  • “lower bound solution”
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3
Q

Kinematic Method

A
  • based on equilibrium of internal and external work
  • Advantage: simple to use for more complicated systems
  • Disadvantage: overestimates capacity
  • choose collapse mechanism
  • correct or overestimated load capacity
  • “upper bound solution”
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4
Q

Welding defects

A
  • cracks (in base material or weld)
  • loss of contact
  • lamellar tearing
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5
Q

Defects due to sloppy welding

A
  • had contact between consecutive welds
  • pores due to gases
  • scum
  • root defect
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6
Q

How to check welds

A
  • xray
  • ultrasound
  • penetration
  • magnetism
  • ocular/by eye
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7
Q

Bolted or welded connections?

A

welds at workshop

bolts on site

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8
Q

Slip Resistant Connections

A
  • in some structures, want to limit distortions in SLS
  • normal bolted connections have quite large distortions due to slack in joints
  • 2 methods to reduce:
    1. fit bolts
    2. slip resistant connections / friction gap joints
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9
Q

Reasons for Bolt spacing requirements

A 
minimum distances:
- so we can use existing eqns
- so we can assemble the joint
maximum distances:
- due to corrosion and prevention of local buckling
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10
Q

Friction Grip Joints

A
  • carry load by friction between plates

- after overcoming friction, the joint carries load by bearing capacity

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11
Q

Advantages of Friction Grip Joints

A
  • prestress with a torque
  • more even load transfer
  • higher fatigue strength due to lower stress concentrations
  • bolt may have threaded part within the prestressed length
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12
Q

Disadvantages of Friction Grip Joints

A
  • higher cost for bolts and washers

- needs surface treatment of surfaces that should transfer load via friction

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13
Q

Normal Joint loaded in shear

A

shear transferred by contact between bolt and steel plate

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14
Q

slip resistant joint loaded in shear

A

shear transferred by friction between plates

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15
Q

Brittle failure modes not included in Johnasens theory

A
  • row shear
  • block shear
  • plug shear
  • splitting
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16
Q

Embedding strength of timber influenced by:

A
  • friction between dowel and timber
  • moisture content of wood
  • reinforcement of timber perp. to grain
  • predrilling of holes
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17
Q

Rope Effect

A

increases if:
- dowel is threaded
- washers and nuts used
be careful with this effect, particularly with nails, not many test results on long term behaviour

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18
Q

Issues to be investigated in glulam elements

A
  1. Bending stress distribution in cross-section of a curved beam
  2. Stress distribution along span
  3. Effect of sawn taper cuts
  4. Tensile stress perpendicular to grain at apex
  5. Bending of laminations
  6. Volume effect
  7. Holes and notches
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19
Q

Bending stress distribution in cross section of curved beam

A 
straight beam:
- Bernoullis principle (plane sections remain plane)
- neutral axis located in middle
- equilibrium respected
curved beam:
- neutral axis moves downward
- equilibrium only possible if stress distribution is non-linear
- max stress achieved at inner fibre
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20
Q

Effect of Sawn Taper Cuts

A

bending stresses parallel to tapered side

  • generate compression perp. to grain if tapered side in compression
  • tension perp. to grain if tapered side in tension
  • tapering slopes larger than 15 deg on compression side, and 5 deg on tension side should be avoided
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21
Q

Tension perpendicular to grain

A
  • occurs in apex zone

- steeper slope = higher perpendicular tension

22
Q

Methods to reduce cracking risk (tension perpendicular to grain)

A

1) Leave non-glued “hat” at apex
2) Glued in rods
3) Plywood sheets glued on each side of beam at the apex zone

23
Q

Volume Effect

A

the larger the volume of the wood, the larger the possibility that the volume contains a defect (e.g. knot)

24
Q

Where to place holes in beam

A
  • highest bending stresses at beam edge, min at neutral axis –> place at mid height
  • for shear stresses, whole cross section needed
  • largest shear force close to supports –> no holes at supports
25
Q

Effects of different hole parameters

A
  • bigger holes = lower load capacity
  • curved beams have lower capacity than straight beams
  • high beams have (relatively) lower load-carrying capacity
26
Q

Notch on upper side of beam

A
  • only reduces load carrying capacity due to smaller cross-section
  • no effect on strength as no tension perpendicular to grain stresses
27
Q

Notch on lower side of beam

A
  • reduces strength, due to tension perpendicular to grain
28
Q

Assumptions in LTB

A
  • linear elastic material
  • small deformations
  • initially straight beam
  • no residual stresses
29
Q

Influence of cross-sectional dimensions on LTB

A
  • more effective to widen beam than to make it higher
30
Q

Factors affecting LTB risk

A
  • low bending stiffness in weak direction
  • low torsional stiffness
  • low warping stiffness
  • high loading point
  • long distance between braces
  • low lateral and torsional brace stiffness
  • shape of bending moment diagram
31
Q

How to reduce LTB risk

A
  • increase torsional stiffness (e.g. box section)
  • increase bending stiffness in weak direction (e.g. select wider beam)
  • bracing of compressed upper edge
32
Q

What is warping?

A
  • when torsion occurs, the cross-section is rotated but still plane “St Venants Torsion”
  • when warping occurs, the cross-section is rotated and distortions out of plane of the cross-section occur “Vlasors Torsion” (cross-section no longer plane)
33
Q

Platform Framing

A
  • slab resting on wall
  • walls erected for one storey, and floor constructed above
  • this is repeated with the next level constructed on that platform
34
Q

Balloon Framing

A
  • suspended slab
  • walls constructed few storeys at a time, then floors
  • better system (used in modern buildings)
  • continuous walls
35
Q

Stabilisation methods for multi-storey buildings

A

a) shear walls/centre core
b) rigid connections
c) cross-braces

36
Q

Problems in large span glulam structures

A
  • tension perpendicular to grain
  • sensitive to moisture changes
  • design of joints
37
Q

Plywood

A
  • log rotated and veneer peeled
  • veneer thickness 2 - 4 mm
  • veneers dried and glued together at 90 angles between neighbouring veneers
  • lower moisture content than structural timber
  • better shape stability than structural timber
38
Q

LVL

A

Laminated Veneer Lumber

  • fibre direction parrallel to beam/board direction
  • glued
  • boards, beams
  • same applications as structural timbers
  • high strength
  • low strength perpendicular to fibre direction
39
Q

Particle Board

A
  • fibres
  • dried to 3-4% MC
  • glue
  • pressed at 150 to 240 degrees
  • fibres not oriented
  • sensitive to cycling moisture (grows in thickness)
  • moisture and temperature have higher effect on strength and stiffness than in structural timber
40
Q

OSB

A

Oriented Strand Board

- board consisting of timber strands and glue

41
Q

Fibre Boards

A
  • moistened wooden fibres
  • pressed without glue
  • density variations
42
Q

XLAM

A
  • layers of structural lamellae are glued crossed to each other
  • same glue adopted for glulam
  • structural optimisation possible
43
Q

Why use engineered wood products?

A
  • structural timber has its limitations
  • limitations in dimensions e.g. size requirements vs size of tree
  • EWP have more homogenous properties than structural timber
  • EWP have better slope stability than structural timber
44
Q

Effect of Carbon Content on Steel

A

increasing carbon content….

  • decreases ultimate strain
  • increases tension strength
45
Q

Effect of production methods on strength

A

different cold production methods can result in increased strength

46
Q

Eigenstrain - residual stresses

A

develop due to non-uniform temperature in the steel

  • beam ends cool fast and are stiff “restraints” to the rest of the beam
  • thick parts cool slower
  • outer flange parts have compression, inner parts tension
  • residual stresses fo not ifluence load bearing capacity (as long as ultimate strain is not reached)
  • stress-strain curve only locally influenced
47
Q

Two different design methods to calculate the capacity of frame “columns”

A

1) Buckling Analysis

2) Second Order Analysis

48
Q

Buckling Analysis

A

linear method

a) Determine Ncr
b) Determine slenderness, lamda
c) Determine associated reduction factor
d) Find capacity

49
Q

Second-Order Analysis

A

non-linear

- takes into account that internal actions in a structure increase in a non-linear fashion with increasing applied loadT

50
Q

Failure modes of bolt in tension

A
  • thread in nut fails
  • thread in bolt fails
  • tensile failure of screw
  • prying failure
51
Q

Two methods to decrease tension stresses perpendicular to grain at apex

A
  1. increase the radius of curvature (flatten beam)

2. decrease height of section

52
Q

What to think of when designing welds

A
  • working space
  • avoid stress concentrations
  • avoid high loads perpendicular to surface (risk of lamellar tearing)

VBKN01 (1 decks)

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