Is you house deck safe for partying and dancing ? Does it show signs of rot or insect infestation ? Serious injury mat result.

1. HOUSE DECK
Structural Analysis
12/31/2015
Don Blanchet
3B Associates

2. Assumptions
 New construction to MA codes
 No break out stress cracks
 No insect damage

3. Model – 12 foot x 12 foot
floorplan
Lumber
2x12 framing
4x4 support posts
8” dia footings
6x1 planking
2x4 railings
2x2 spindles

4. Model

5. Model

6. FEA mesh

7. Assumed Wood
mechanical properties

8. Loading
 Self weight gravity
 Snow loading
 Dense party static load
 Dynamics dancing at natural frequency

9. Dancing loading
approximation
 Apply harmonic force wavelets to
areas of the deck planking over the
range of 40 to 200hz. Peak force of
500 lbs.

10. Self weight

11. Dynamic analysis

12. Mode 1 - 29hz

13. Mode 9 – 70hz
deck surface springing

14. Dancing dynamic loading
response ringing at 75 hz

15. Snow load maximum
stress location

16. Results Summary: 12x12 deck
loading
Max
Deflection
inch
Max
Stress
psi
Factor of
safety
Gravity
1G
.003 22.0 154
severe
Snow
(2 psi)
41,000 lbs
.188 1194.0 2.84
Party
10 people
(1800 lbs)
.010 70.0 49
Party
dancing .060 400.0 8.5