Connections

Question 1

Wood connection design variables

Answer 1

• Load-carrying capacity of connector
• Species of wood
• Type of load
• Condition of wood
• Wood fire treatment
• Service conditions
• Angle of load to the grain
• Misc: critical net section, type of shear at joint, spacing of connectors, end & edge distances to connectors

Question 2

Timber connector classification

Answer 2

• Timber connectors designated to groups A thru D
• Other connectors designated groups I thru IV
• Each group has allowable connector loads

Question 3

Species of wood

Answer 3

• Wood density is the biggest factor
• Design values for connectors in groups differ by species, and apply to all grades of said species UNO

Question 4

Load type

Answer 4

• Wood max loads over short durations are greater than max loads over long durations
• Tables for allowable connector loads usually cover 10 years

Question 5

Multipliers for Loads on wood

Answer 5

• Permanent loading for 10 yrs: 0.9
• 2 months: 1.15
• 7 days: 1.25
• Wind/earthquake loads: 1.6
• Impact loads: 2.0

Question 6

Service Conditions

Answer 6

• Any service condition other than dry or continuously wet will reduce the holding power of the connector.

Question 7

FRT Wood

Answer 7

• FRT Wood doesnt hold connectors as well as non-treated wood
• Allowable design values for treated wood must come from manufacturer

Question 8

Angle of Load

Answer 8

• Angle between direction of load acting on member & the longitudinal axis of member.
• Wood can carry more load parallel to grain than perpendicular to it

Question 9

Angles other than parallel/perp

Answer 9

Hankinson Formula must be used

Fn = (Fg*Fc)/ (Fg(sin^2)(theta) + (Fc(cos^2)(theta)

Question 10

Critical Net Section

Answer 10

The section where most wood has been removed (for connections, except for nails & screws). Member sizing must account for area lost to connectors.

Question 11

Connector spacing minimums

Answer 11

Can be found in building codes & NDS

Question 12

Nails

Answer 12

• Tables provide allowable withdrawal & shear resistance values for engineering applications
  – Engineered applications: each nailed joint is specifically designed
• Lateral loading in side grain better than withdrawal from side grain
• Withdrawal from end grain not permitted
• 25% bump in design values if metal side plate used

Question 13

Screws

Answer 13

• Wood screws range from size 6 t 24
• Lengths up to 5in
• Flat & round heads most common
• Design tables give withdrawal & lateral values
• Lateral loading side grain better than withdrawal from side grain
• Withdrawal from end not permitted
• 25% bump in design values if metal side plate used
• Lead holes required

Question 14

Lag screw

Answer 14

• Threaded, pointed end with bolt head
• Lead holes drilled & screwed with wrench
• Washer between head & wood member
• .25” to 1.25” diameter (measured at nonthreaded shank portion)
• 1” to 12” length

Question 15

Lag screw design value factors

Answer 15

• Wood species
• Angle of load to grain
• Screw diameter
• Thickness of side member
• Length of screw
• (unlike screws & nails) if angle of load is not 0 or 90, Hankinson formula must be used
• Spacing, end distance, edge distance same as bolts

Question 16

Bolts

Answer 16

• Most common for moderate to heavy loading
• Typically used in single & double shear applications
• Design values reduce by 60% if separate side plates not used for each row of bolts parallel to load
• Standard design tables assume side members are 1/2 width of main member
• If side members widths differ from above, NDS provides guides for modifying design values