1. New SEAOC Documents on the Structural Design of Rooftop Solar Arrays November 1, 2012 Ronald LaPlante, S.E. Division of State Architect – State of California

2. New SEAOC PV Committee Reports
Available for free download for members at: 2

3. SEAOC Solar PV Wind Report SEAOC Solar PV Seismic Report Next steps
Outline
PV Committee and Scope
SEAOC Solar PV Wind Report
SEAOC Solar PV Seismic Report
Next steps
What is DSA doing? 3

4. PV Committee and scope 4

5. Formation of Committee
Formed in September 2011 as subcommittee of SEAOC Wind Committee
Composed of:
Structural Engineers
Code Enforcement Agencies
Wind Tunnel Experts
Solar PV Industry Members
NCSEA & ASCE 7 Wind Committee Members
SEAOC Seismology Members 5

6. Solar Photovoltaic Arrays Types
Parking Garages
Flat Roofs
Sloped Roofs
Carports
Ground Mount 6

7. Which Wind Loading Provisions Apply?
ASCE 7-05
What about other installations?
Enclosed Buildings – C&C
(ASCE 7-05 Figure 6-11)
ICC AC 428
Open Buildings (ASCE 7-05 Figure 6-18,19) 7

8. Which Wind Loading Provisions Apply?
Parking Garages
Flat Roofs – not flush mounted
Ground Mount - Sheltering
Pitched Roofs – not flush mounted 8

9. Wind Tunnel Procedure Should the WTP be peer reviewed?
ASCE 7
Wind Tunnel Procedure (WTP)
What’s an appropriate wind tunnel study?
Should the WTP be peer reviewed?
ASCE 7 WTP is written for specific building modeling, not generalized buildings with solar panels.
Does building need to be modeled?
Roof zoning?
Etc…
Is there a minimum wind load? 9

10. PV2 report on wind design10

11. Goals for Solar PV Wind Report
Develop report to address wind design provisions for low-profile solar PV arrays on flat roofs
Establish wind design coefficients similar to those in ASCE 7 figures 11

12. Goals for Solar PV Wind Report
Define Effective Wind Area for unique aspects of solar PV arrays
Define minimum Wind Tunnel Procedure modeling requirements and minimum design loads
Example Problem 12

13. SEAOC Solar PV Wind Report
Understanding wind flow environment on roof 13

14. SEAOC Solar PV Wind Report
Wind tunnel data from CPP & UWO
Cermak Peterka Petersen, Inc
University of Western Ontario 14

15. SEAOC Solar PV Wind Report
Cermak Peterka Petersen, Inc
University of Western Ontario 15

16. SEAOC Solar PV Wind Report
Cermak Peterka Petersen, Inc
University of Western Ontario 16

17. SEAOC Solar PV Wind Report
Roof zoning for open elements on roof different than C&C
Components & Cladding
Solar PV Arrays 17

18. SEAOC Solar PV Wind Report
Geometry selected based on most common application and supported by data 18

19. SEAOC Solar PV Wind Report
Defined roof zones similar to ASCE 7
Clarified steps, angled corners, reentrant corners 19

21. SEAOC Solar PV Wind Report
GCrn curves similar to ASCE 7 methodology
Uses normalized wind area instead
Values shown for sheltered panels in middle of an array
Formulas for lines in Example
Normalized wind area is same as effective wind area at 10 meters / 33 feet
Interpolate 21

22. SEAOC Solar PV Wind Report
Factor to increase loads at perimeter of array 22

23. SEAOC Solar PV Wind Report
Wind tunnel model requirements
Promote consistency
Model array on building, must consider:
Roof zones, effective wind area, panel geometry, tilt angle, spacing, height above roof, roof shape
ASCE “Wind Tunnel Testing for Buildings and Other Structures”
Minimum design wind loads from wind tunnel
50% of values in Figure (no arbitrary 10 psf minimum)
65% of values in Figure if doesn’t meet geometry in Figure
Lower values allowed if qualified peer review
No 10 psf min 23

24. SEAOC Solar PV Wind Report
Example Problem in Appendix
Aid in interpretation and application of method 24

25. SEAOC Solar PV Wind Report
Example Problem in Appendix
Provides wind pressures on each panel of the array
Sensitive to effective wind area
Note edge panels 25

26. PV1 report on seismic design26

27. Contents Performance objectives Building SFRS Attached arrays
Unattached arrays
Seismic displacement
Prescriptive displacement
Friction testing
NLRH analysis or shake-table testing 27

28. Performance Objective
Life Safety per IBC 101.3
Stay on the roof
Stay on supporting members
Do not block roof drainage
Do not cause electrical fire
Do not impede fire-fighter roof access
Other damage that would endanger life 28

29. Existing Building Structures
Represent 95%+ of commercial solar installations
Design per IBC chapter 34
Increase lateral loads by no more than 10%
Increase gravity loads by no more than 5% (concentrated loads)
Where panels are placed, roof live load is not assumed to act. 29

30. Attached Arrays Use ASCE 7-05 Chapter 13 for seismic demand (Fp)
How to establish ap and Rp
Some frictional resistance may be permitted to contribute in combination with attachment strength. 30

31. Unattached Arrays
Installation option that has no attachments to roof structure.
Array is free to slide on roof during seismic event
Need to provide seismic separation around roof and objects
How to go about it? 31

32. Code Equivalence
ASCE-7 Section 13.4 : “Components and their supports shall be attached (or anchored) to the structure … Components and their attachments shall be bolted, welded, or otherwise positively fastened without consideration of fractional resistance produced by the effects of gravity.”
IBC Section permits alternate (non-prescriptive) methods…..need to meet life safety objective….. 32

33. Restrictions for Unattached Arrays
All unattached arrays
≤ 7 degree roof slope
Height of C.M. ≤ 2x base and 3’
Prescriptive displacement
≤ 3 degree roof slope
Ip = 1.0
Friction tests for SDC D, E, and F 33

34. Required Separation Between arrays -- 0.5IpDMPV
Between array and a fixed object on the roof -- IpDMPV
Between array and roof parapet -- IeDMPV
Between array and roof edge without parapet IeDMPV
DMPV is the maximum inelastic displacement expected in the design basis earthquake 34

35. Seismic Displacement (DMPV)
Compute seismic displacement by one of the following 3 methods:
Prescriptive formula
Nonlinear response-history analysis
Shake-table testing 35

36. 1. Prescriptive Displacement
DMPV = (SDS – 0.4)2(60 inches)
≤ 6 inches
Seismic Design Categories A, B, C
DMPV = 6 inches
Friction testing not required if common roof type 36

37. 2. Nonlinear Response-History Analysis
Design-basis roof motions consistent with ASCE-7 Chapter 13 demands.
Account for friction and roof slope 37

38. Option A Input roof motions Spectrally matched roof motions
Per ICC AC 156 with additional requirements; include motions with T > 0.77 seconds, taken proportional to 1/T. 38

39. Option B Input roof motions
Apply ground motions to a building model and extract roof motions
Recommended to bracket the assumed properties of the building model. 39

40. 3. Shake-Table Testing Vertical motion to be included
Minimum filtering of motions
If motions are high-pass filtered, supplemental analysis required.
2D tests require 3D supplemental analysis. 40

41. Structural Interconnection
Required interconnection strength within an array 41

42. Friction Testing Per ASTM G115, and:
Worst case conditions for each roof surface, e.g., wet or dry
Independent test agency
Measured under continuous movement of at least 3 inches
Loading velocity 0.1 to 10 inches per second, adjust to minimize stick-slip 42

43. Next steps 43

44. SEAOC Solar PV Reports into Code
What’s next?
ATC, NCSEA, CBC Amendments
Current Efforts
SEAOC Solar PV Systems Committee
Solar ABC
Technical Papers
Wind Tunnel Studies
ASCE 49
ASCE 7
(2016?)
IBC
(2018?)
Solar ABC’s – Technical papers to guide engineers.
Technical Papers – describe proper wind tunnel studies, CFD use, etc. 44

45. Next Steps for SEAOC Solar PV Committee
Roof live load
Special Inspection
PV tracking systems
Impacts on MWFRS
Wind loads for high profile systems on roofs
Existing building issues
Airflow effects on PV around rooftop equipment
Provide a simplified alternate for low profile systems
State-owned essential service building fall under DSA jurisdiction under the ESB Act, and these same code provisions and procedures will similarly apply. 45

46. Acknowledgements 46

47. What is DSA doing? 47

48. Authority of DSA
DSA has the authority for plan review and supervision of construction for:
Elementary and secondary schools (K-12)
Community Colleges
Essential Service Buildings
Plan review and construction oversight by licensed CA Structural Engineers
Emphasis on Seismic Safety
State-owned essential service building fall under DSA jurisdiction under the ESB Act, and these same code provisions and procedures will similarly apply. 48

49. DSA Offices 49

50. DSA IR 16-8 Updated in October 2012 to incorporate SEAOC PV reports
Available at: 50

51. DSA IR 16-8 DSA IR 16-8 addresses:
Dead load – Check roof, keep mass increase below 10%
Live load – No need to include where covered by panels < 24” or signs
Wind – SEAOC PV paper, Wind tunnel requirements, peer review
Seismic – ASCE 7 loading, unrestrained systems per SEAOC PV paper
Load combinations – Apply load combo’s when checking uplift
Rack design – ICC AC 428
PV Installations on Standing Seam Metal Roofs
BIPV systems – ICC AC 365
Fire Life Safety requirements 51

52. What is DSA doing?
IR 16-8 accepts both SEAOC papers with some exceptions:
Does not allowing friction concurrent with anchorage to resist seismic loads unless testing and analysis performed.
Maximum slope for unattached systems is limited to 1:12 (4.8 degrees) instead of 7 degrees to be consistent with 2015 IBC and 2013 CBC HCD Amendment (following slides).
A qualifying parapet, which is used to reduce the separation distance around the perimeter of the roof, must be checked for the PV sliding impact load concurrent with out-of-plane wall inertial load. SEAOC PV paper does not require any structural check. No need to check parapet if ignoring it and using 1.5IeDMPV separation distance. 52

53. 2013 CBC 2013 CBC Amendment to 2012 IBC Section 1509.7
Effective wind area should NOT be based on effective wind area of a single unit frame
DSA and HCD co-adopt Exception 53

54. 2013 CBC
2013 CBC Section – amendment to modify ASCE 7-10 Section 13.4 to allow unrestrained solar arrays.
Next Slide 54

55. SEAOC Solar PV Paper indicates how to do this
2013 CBC
2013 CBC Section (continued).
SEAOC Solar PV Paper indicates how to do this 55

56. THANK YOU