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

New SEAOC PV Committee Reports Available for free download for members at: http://www.seaoc.org/seasecure/member.html 2

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

PV Committee and scope 4

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

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

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

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

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

PV2 report on wind design 10

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

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

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

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

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

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

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

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

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

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

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

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 49-07 “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

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

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

PV1 report on seismic design 26

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

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

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

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

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

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 104.11 permits alternate (non-prescriptive) methods…..need to meet life safety objective….. 32

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

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 -- 1.5IeDMPV DMPV is the maximum inelastic displacement expected in the design basis earthquake 34

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

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

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

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

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

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

Structural Interconnection Required interconnection strength within an array 41

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

Next steps 43

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

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

Acknowledgements 46

What is DSA doing? 47

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

DSA Offices 49

DSA IR 16-8 Updated in October 2012 to incorporate SEAOC PV reports Available at: www.dgs.ca.gov/dsa 50

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

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

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

2013 CBC 2013 CBC Section 1613.5 – amendment to modify ASCE 7-10 Section 13.4 to allow unrestrained solar arrays. Next Slide 54

SEAOC Solar PV Paper indicates how to do this 2013 CBC 2013 CBC Section 1613.5 (continued). SEAOC Solar PV Paper indicates how to do this 55

THANK YOU ron.laplante@dgs.ca.gov