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Solar Photovoltaic Systems Committee New SEAOC Documents on the Structural Design of Rooftop Solar Arrays November 1, 2012 Ronald LaPlante, S.E. Division.

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Presentation on theme: "Solar Photovoltaic Systems Committee New SEAOC Documents on the Structural Design of Rooftop Solar Arrays November 1, 2012 Ronald LaPlante, S.E. Division."— Presentation transcript:

1 Solar Photovoltaic Systems Committee 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 SEAOC Solar Photovoltaic Systems Committee New SEAOC PV Committee Reports Available for free download for members at:

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

4 SEAOC Solar Photovoltaic Systems Committee PV COMMITTEE AND SCOPE

5 SEAOC Solar Photovoltaic Systems Committee 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

6 SEAOC Solar Photovoltaic Systems Committee Solar Photovoltaic Arrays Types Flat Roofs Carports Ground Mount Sloped Roofs Parking Garages

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

8 SEAOC Solar Photovoltaic Systems Committee Which Wind Loading Provisions Apply? Flat Roofs – not flush mounted Ground Mount - Sheltering Parking Garages Pitched Roofs – not flush mounted

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

10 SEAOC Solar Photovoltaic Systems Committee PV2 REPORT ON WIND DESIGN

11 SEAOC Solar Photovoltaic Systems Committee 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

12 SEAOC Solar Photovoltaic Systems Committee 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

13 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report Understanding wind flow environment on roof

14 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report Wind tunnel data from CPP & UWO

15 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report

16 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report

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

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

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

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21 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report GCrn curves similar to ASCE 7 methodology Uses normalized wind area instead Interpolate

22 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report Factor to increase loads at perimeter of array

23 SEAOC Solar Photovoltaic Systems Committee 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 doesnt meet geometry in Figure Lower values allowed if qualified peer review

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

25 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Wind Report Example Problem in Appendix Provides wind pressures on each panel of the array

26 SEAOC Solar Photovoltaic Systems Committee PV1 REPORT ON SEISMIC DESIGN

27 SEAOC Solar Photovoltaic Systems Committee Contents Performance objectives Building SFRS Attached arrays Unattached arrays Seismic displacement Prescriptive displacement Friction testing NLRH analysis or shake-table testing

28 SEAOC Solar Photovoltaic Systems Committee Performance Objective Life Safety per IBC 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

29 SEAOC Solar Photovoltaic Systems Committee 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.

30 SEAOC Solar Photovoltaic Systems Committee Attached Arrays Use ASCE 7-05 Chapter 13 for seismic demand ( F p ) How to establish a p and R p Some frictional resistance may be permitted to contribute in combination with attachment strength.

31 SEAOC Solar Photovoltaic Systems Committee 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?

32 SEAOC Solar Photovoltaic Systems Committee 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…..

33 SEAOC Solar Photovoltaic Systems Committee Restrictions for Unattached Arrays Prescriptive displacement 3 degree roof slope I p = 1.0 Friction tests for SDC D, E, and F All unattached arrays 7 degree roof slope Height of C.M. 2x base and 3

34 SEAOC Solar Photovoltaic Systems Committee Required Separation Between arrays I p MPV Between array and a fixed object on the roof -- I p MPV Between array and roof parapet -- I e MPV Between array and roof edge without parapet I e MPV MPV is the maximum inelastic displacement expected in the design basis earthquake

35 SEAOC Solar Photovoltaic Systems Committee Seismic Displacement ( MPV ) Compute seismic displacement by one of the following 3 methods: 1.Prescriptive formula 2.Nonlinear response-history analysis 3.Shake-table testing

36 SEAOC Solar Photovoltaic Systems Committee 1. Prescriptive Displacement MPV = ( S DS – 0.4) 2 (60 inches) 6 inches Seismic Design Categories A, B, C MPV = 6 inches Friction testing not required if common roof type

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

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

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

40 SEAOC Solar Photovoltaic Systems Committee 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.

41 SEAOC Solar Photovoltaic Systems Committee Structural Interconnection Required interconnection strength within an array

42 SEAOC Solar Photovoltaic Systems Committee 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

43 SEAOC Solar Photovoltaic Systems Committee NEXT STEPS

44 SEAOC Solar Photovoltaic Systems Committee SEAOC Solar PV Reports into Code Current Efforts SEAOC Solar PV Systems Committee Solar ABC Technical Papers Wind Tunnel Studies ASCE 49 ASCE 7 (2016?) IBC (2018?) ATC, NCSEA, CBC Amendments Whats next?

45 SEAOC Solar Photovoltaic Systems Committee 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

46 SEAOC Solar Photovoltaic Systems Committee Acknowledgements

47 SEAOC Solar Photovoltaic Systems Committee WHAT IS DSA DOING?

48 SEAOC Solar Photovoltaic Systems Committee 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

49 SEAOC Solar Photovoltaic Systems Committee DSA Offices

50 SEAOC Solar Photovoltaic Systems Committee DSA IR 16-8 Updated in October 2012 to incorporate SEAOC PV reports Available at:

51 SEAOC Solar Photovoltaic Systems Committee 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 combos when checking uplift Rack design – ICC AC 428 PV Installations on Standing Seam Metal Roofs BIPV systems – ICC AC 365 Fire Life Safety requirements

52 SEAOC Solar Photovoltaic Systems Committee 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 1.5 I e MPV separation distance.

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

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

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

56 Solar Photovoltaic Systems Committee THANK YOU


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