The structural insulated panel (SIP) is an engineered composite product composed of an insulating foam core sandwiched to provide the insulation and rigidity, and two face-skin materials to provide durability and strength. SIPs can also be used as permanent wood foundation (PWF) for basements in low-rise residential construction to save in the energy cost. The maximum deflection equation specified in the Canadian Standard for Engineering Design of Wood, CAN/CSA-O86.09 specifies expressions for the effects of short-term bending deflection on the PWF timber stud walls. Information on the long-term creep behavior of SIPs under sustained triangular loading, simulating soil pressure, including effect of the change in ambient temperature and relative humidity is as yet unavailable. The long-term creep deflection for permanent wood foundation panels that is characterized as viscoelastic materials is highly affected by the change in ambient temperature and relative humidity. This paper reported the results from flexural creep experiments performed on two sets of different sizes of PWF made of structural-insulated foam-timber panels. In these tests, deflection, temperature and relative humidity were tracked for an eight-month period. The experimental findings were examined against existing creep models in the literature. Then, a creep model incorporating the effects of temperature and relative humidity on creep deflection was developed. Correlation between the proposed model and the experimental findings provides confidence on using the proposed model in the determination of the capacity of the PWF under combined gravity loading and sustained soil pressure as affected by temperature variation and relative humidity.

1. 3rd Specialty Conference on Material
Engineering & Applied Mechanics
Montréal, Québec
May 29 to June 1, 2013
Presented by:
Mahmoud Sayed-Ahmed
introducing
Effect of Temperature and Relative
Humidity on Creep Deflection for
Permanent Wood Foundation Panels
Mahmoud Sayed Ahmed, Khaled Sennah
Department of Civil Engineering, Ryerson University
Paper #: MEC-34

2. Arrangement of presentation
Literature
Review
Experimental
Study
Results &
Conclusions
PWF is a better way to build a basement
2

3. Literature Review
SIP, Materials, design, mechanical behavior and modeling
3

4. Structural Insulated Panel
Definitions
• SIP is a sandwich-structured
composite building material.
• Prefabricated by attaching two
stiff skins, and thick core.
• Have structural properties as
I-Beam or I-Column.
• SIP used for floors, Roofs,
Partitions and Walls.
• PWF used for Basement Wall.
http://en.wikipedia.org/wiki/Structural_insulated_panel
4

5. Ultra-Efficient SIP Home Performance
• Supper efficient envelope
– R-Control SIP R-Values for EPS
Panel
– Add R-0.55 for OSB
Thickness
4 ½”
– Add R-1.41 for CSP
6 ½”
– Compared to R-14 for
8 ¼”
10 ¼”
Conventional Wall Frame
• HVAC System
– Air Changer Hour (ACH50)
• Energy Consumption
12 ¼”
R-Value at
75oF
14.9
22.6
29.3
37.0
44.7
R-Value at
40oF
16.0
24.3
31.6
39.9
48.3
Type of House
ACH50
SIP House
1.8
Wall Frame
5.3
5

6. Specification of PWF materials
Oriented Strand Board (OSB), 11 mm
Spruce-Pin-Fur (S-P-F) Lumber, 38x
Expanded Polystyrene (EPS),
Canadian Softwood Plywood (CSP), 15.5 mm, 5 plies
Galvanized nails
Structural adhesive
The assembly of permanent wood foundation PWF
G1: 1220x3048x260.3 , G2: 1220x2743.2x209.55 [mm]
6

7. Design codes and standards
Codes
• National Building Code of Canada (2010)
Standards
• Construction of Preserved Wood Foundation, CSA-S406
• Engineering Design of Wood, CSA-O86.09
Manual
• Wood Design Manual, CWC (2010)
Design equations are yet unavailable!
Slab Floor System
Standard design procedures (NBCC 2010):
• Evaluation of a given full-scale structure or a prototype
by a loading tester
• Equivalent Fluid Pressure of 4.7 kN/sq.m/m.depth
Testing References
• Acceptance criteria ICC-ES AC04
• Standard Test Methods of Conducting Strength Tests on
Panels for Building Construction, ASTM E72-02
7

8. Combined Axial Force-Bending Interaction
Engineering Design of Wood,
CSA-O86.09
𝑀 𝑓 + 𝑃𝑓 𝜟
𝑴𝒓
1
𝑃𝑓
1− 𝑃
𝐸
𝑃𝑓 2
+ [
] ≤ 1.0
𝑷𝒓
Mf = maximum applied factored
moment due to soil pressure,
Pf = factored applied axial load on the
wall,
Δ = deflection due to lateral load at
point where Mf is calculated,
Mr = factored bending moment
resistance of the wall,
Pr = factored compressive resistance
of the wall, and
PE is the Euler buckling load in plane
of the applied moment.
8

9. Mechanical behavior and modeling
Know-How?
Initial strain obeys Hooke’s law (σ = Eε), while the viscoelastic response
𝒅ɛ
𝑑𝜀
(long-term deformation) obeys Newton’s law ( 𝜎 ∝
= 𝜂 ).
𝒅𝒕
Rheological Models;
Maxwell, Kelvin-Voigt, Zener, Burgers
𝑑𝑡
ACI 209R defined the
creep as a constant stress
under condition of steady
relative humidity and
temperature, assuming
the strain at loading
(nominal elastic strain) as
the instantaneous strain
at any time.
9

10. Gravity Load
Lateral
Loads
Combined Loads
The Permanent Wood Foundation works as
shear wall, load bearing wall, retaining wall,
and designed for simultaneous loads:
-
Earth
pressure
Gravity loads
Environmental loads
Earth pressure
10

11. Experimental Study
Loading, creep models, short-term and long-term deflection
11

12. It’s not just about the visuals, but strengthening for
SERVICE LIFE DESIGN.
12

13. Equivalent Fluid Pressure (EFP)
4.7 kN/sq.m/m.depth
Group I:
20,563.20 N [714 Bricks]
Loading area; 1220 x 2700 mm
Group II:
16,243.20 N [564 Bricks]
Loading area; 1220 x 2400 mm
8
8
7
7
6
Number of Layers
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14
Number of Piles
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10 11 12
Number of Piles
13

14. Creep-deflection; loading for BW1, BW2
14

15. Creep-deflection; loading for BW3, BW4
15

16. Creep-deflection; loading for BW4, BW6
16

17. Creep-deflection; curves
12.00
12.00
Creep deflection, mm
14.00
Creep deflection, mm
14.00
10.00
BW1-1
8.00
BW1-2
BW2-1
6.00
BW2-2
4.00
BW2-3
BW3-1
2.00
BW3-2
PWF# BW 1,2,3; Size
0.00
1,000.00 2,000.00 3,000.00 4,000.00 5,000.00 6,000.00 7,000.00
BW4-1
8.00
BW4-2
BW5-1
6.00
BW5-2
4.00
BW6-1
BW6-2
2.00
0.00
0.00
1,000.00 2,000.00 3,000.00 4,000.00 5,000.00 6,000.00 7,000.00
Time, Hours
Time, Hours
0
Deflection, mm
0.00
10.00
-2
0
500
1000
1500
2000
2500
3000
-4
-6
Group I, ID
Group I, FD
Group II, ID
Group II, FD
-8
-10
-12
Height, mm
17

18. Creep-deflection, table
Table 1: Recorded creep deflection and creep recovery of the tested panels
Deflection Creep
Creep
Recovery
-to-span constant
Panels
ID (mm) FD (mm)
IRD (mm) PD (mm)
ratio
BW1
7.69
10.99
1/396
0.43
7.42
2.73
BW2
BW3
8.02
11.27
1/380
0.41
6.51
4.45
8.39
11.08
1/363
0.32
7.86
2.62
Average
8.03
11.12
1/379
0.39
BW4
8.14
11.35
1/337
0.39
7.71
3.31
BW5
7.24
10.02
1/378
0.38
7.01
2.34
BW6
8.71
11.11
1/314
0.28
8.31
2.14
Average
8.03
10.83
1/341
0.35
Notes: ID = Instantaneous deflection, FD = Final deflection,
IRD = Instantaneous recovery deflection, PD = Permanent deflection.
18

19. Creep Modeling
Mathematical modeling:
Power Model
Logarithmic Model
Rheological modeling :
Maxwell Model
Kelvin-Voigt Model
Zener Model
Burgers Model
Refined Burgers Model
19

20. Total deflection
Simple Beam: Load increasing uniformly to
one end
∆ 𝑆ℎ𝑜𝑟𝑡
𝑇𝑒𝑟𝑚 =
∆ 𝐵 + ∆𝑆
𝑤 𝑓 (𝐿 − 𝑥)
𝑤 𝑓 𝐿𝑥
𝑥2
=
𝐾 +
1− 2
360𝐸 𝑠 𝐼𝐿𝐻 ∆
6𝐴𝐺
𝐿
𝑏𝑑 2 𝐸1 𝐸2 𝑡1 𝑡2
𝑏
3
3
𝐷 = 𝐸𝑠 𝐼 =
+
(𝐸1 𝑡1 + 𝐸2 𝑡2 )
𝐸1 𝑡1 + 𝐸2 𝑡2
12
𝐾 = (∆ 𝑓,𝑡 − ∆ 𝑆ℎ𝑜𝑟𝑡
𝑡𝑒𝑟𝑚 )
∆ 𝑆ℎ𝑜𝑟𝑡
𝑡𝑒𝑟𝑚
Where;
Δ long term is immediate deflection under dead
load + long-term portion of live loads;
Δ short term is deflections under short-term
portions of design load (Δo).
Δ Total = K (Δ long term) + Δ short term
20

21. Creep-deflection with Burgers Model
Group I
Group II
12.00
Creep-Deflection, mm
14.00
12.00
Creep-Deflection, mm
14.00
10.00
BW1-1
8.00
BW1-2
BW2-1
6.00
BW2-2
BW2-3
4.00
BW3-1
BW3-2
2.00
10.00
8.00
BW4-1
BW4-2
6.00
BW5-1
BW5-2
4.00
BW6-1
BW6-2
2.00
Burgers Model
Burgers Model
PWF# BW1, BW2, BW3
PWF# BW4, BW5, BW6
0.00
0.00
0.00
2,000.00
4,000.00
6,000.00
8,000.00
Time, Hours
Coefficient of determination = 92%
0.00
2,000.00
4,000.00
6,000.00
8,000.00
Time, Hours
Coefficient of determination = 89%
21

22. Flexural Creep Constant – 8 months
Group I
Group II
0.5
0.4
Experimental Data
Power Model
0.3
Maxwel Model
Kelvin Model
0.2
Zener Model
Flexural Creep Constant
0.6
0.5
Flexural Creep Constant
0.6
0.4
Experimental Data
Power Model
0.3
Maxwel Model
Kelvin Model
0.2
Zener Model
Burgers Model
0.1
Burgers Model
M.Burgers Model
0.1
M.Burgers Model
Log. Model
Log. Model
0
0.00
2,000.00
4,000.00
Time, Hours
6,000.00
8,000.00
0
0.00
2,000.00
4,000.00
Time, Hours
6,000.00
8,000.00
22

23. Flexural Creep Constant – 75 years
Group I
Group II
1.4
1.4
1.2
Flexural Creep Constant
1.6
Flexural Creep Constant
1.6
1.2
Log. Model
1
Kelvin Model
0.8
Log. Model
1
Kelvin Model
0.8
Zener Model
0.6
Burgers Model
0.4
Refined Burgers
Model
0.2
0
Zener Model
0.6
Burgers Model
0.4
Refined Burgers
Model
0.2
0
0
15
30
45
60
75
Time, Years
Two phases
• Phase 1: 0 – 5 years
• Phase 2: 5 – 75 years
0
15
30
45
60
75
Time, Years
ASTM D6112 defines creep as the progressive
deformation of a material at constant load (stress)
applied to a specimen in selected loading
configuration at constant temperature where the
deformation is measured as a function of time
23

24. Permanent Wood
Foundation panel acts as
beam under bending,
acts as strut under axial
forces
PWF satisfies the
NBC2010: instantaneous
bending deflection (ID)
for span/300
SIP carrying elephant
PWF satisfies the SIP Design Guide (NTA,
2009), where FD is less than 4 for SIP
loaded with lateral earth pressure.
http://www.structall.com/residential/content/pages/sips/SIPA_article.htm
The fractional deflection
(FD) after ninety (90)
days (minimum) for
each surviving specimen
shall not be greater than
2.00 to evaluate the
acceptance of the woodbased products for longterm load behavior
according to ASTM
D6815-09
24

25. Green Buildings
What about The
influence of humidity and
temperature on creep?
Humidex
25

26. Humidex
26

27. Humidex
Recorded temperature
and relative humidity
with time during creep
testing for specimens
BW1, BW2, BW4 and
BW5
Recorded temperature
and relative humidity
with time during creep
testing for specimens
BW3 and BW6
27

28. Humidex
Effect of Humidex on
creep displacement for
tested panels BW1,
BW2, and BW3
Effect of Humidex on
creep displacement for
Tested Panels BW4,
BW5,and BW6
28

29. Proposed Model
Proposed Creep Model for Group I
Proposed Creep Model for Group II
29

30. Proposed Model
Measured and predicted Flexural Creep
Constant (K) versus time for Group I
Coefficient of determination = 87%
Measured and predicted Flexural
Creep Constant (K) versus time for
Group II
Coefficient of determination = 94.2%
30

31. Humidex in Toronto
(5 cases extended up to 75 years)
Climate Effect on Long-term Flexural Creep Constant
Two phases
• Phase 1: 0 – 5 years
• Phase 2: 5 – 75 years
ASTM D6112 defines creep as the progressive
deformation of a material at constant load (stress)
applied to a specimen in selected loading
configuration at constant temperature where the
deformation is measured as a function of time
31

32. Results & Conclusions
Experimental and theoretical findings
32

33. CONCLUSIONS
• After 8 months of sustained soil pressure, the panel experimental deflection increased
by about 38 and 35% for groups I and II, respectively.
•
Results for the Power and Maxwell models beyond the 8-month test period show
significant increase in the total deflection that makes it realistically unacceptable for
long-term creep deflection. Other creep models performed well in predicting the creep
deflection within the creep test period when correlating the results with the
experimental findings.
• Creep deflection results up to 75 years showed that Burgers model predicts the most
reliastic increase in deflection due to creep effects. A creep constant of 1.43 is
proposed for PWF made of SIPs for the application of combined bending-compressive
force interaction equation for ultimate limit state design.
33

34. CONCLUSIONS
• The proposed model in this paper predicts the creep deflection constant after 75 years
as 1.43 for the average readings of the temperature and relative humidity during the
tested period.
• It is recommended to conduct creep tests on PWF panels beyond the 8-month period
to validate the proposed creep model over a considerable number of years.
34

35. Acknowledgments
35

36. References
Sayed Ahmed, M. 2011. Flexural Creep Effects on Permanent Wood Foundation made
of Structural Insulated Foam-Timber Panels. M.A.Sc. Thesis, Ryerson University,
Toronto, Ontario, Canada.
Sayed Ahmed, M. and Sennah, K. 2012. Flexural Creep Effects on Permanent Wood
Foundation Made of Structural Insulated Foam-Timber Panels. 3rd International
Structural Speciality Conference (pp. STR-1007). Edmonton: Canadian Society of Civil
Engineering (CSCE).
36

37. Thank you
Your Questions?
37