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
New SEAOC PV Committee Reports
Available for free download for members at:
http://www.seaoc.org/seasecure/member.html
SEAOC Solar Photovoltaic Systems Committee
Outline
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PV Committee and Scope
SEAOC Solar PV Wind Report
SEAOC Solar PV Seismic Report
Next steps
What is DSA doing?
SEAOC Solar Photovoltaic Systems Committee
PV COMMITTEE AND SCOPE
SEAOC Solar Photovoltaic Systems Committee
Formation of Committee
 Formed in September 2011 as subcommittee
of SEAOC Wind Committee
 Composed of:
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Structural Engineers
Code Enforcement Agencies
Wind Tunnel Experts
Solar PV Industry Members
NCSEA & ASCE 7 Wind Committee Members
SEAOC Seismology Members
SEAOC Solar Photovoltaic Systems Committee
Solar Photovoltaic Arrays Types
Parking Garages
Flat Roofs
Sloped Roofs
Carports
SEAOC Solar Photovoltaic Systems Committee
Ground Mount
Which Wind Loading Provisions Apply?
ASCE 7-05
What about
other
installations?
Enclosed Buildings – C&C
(ASCE 7-05 Figure 6-11)
Open Buildings (ASCE 7-05 Figure 6-18,19)
SEAOC Solar Photovoltaic Systems Committee
ICC AC 428
Which Wind Loading Provisions Apply?
Parking Garages
Flat Roofs – not flush mounted
Pitched Roofs – not flush mounted
Ground Mount - Sheltering
SEAOC Solar Photovoltaic Systems Committee
Wind Tunnel Procedure
ASCE 7
Wind Tunnel Procedure (WTP)
What’s 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?
Roof zoning?
Etc…
Does building need
to be modeled?
Is there a minimum
wind load?
SEAOC Solar Photovoltaic Systems Committee
PV2 REPORT ON WIND DESIGN
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
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
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Understanding wind flow environment on roof
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Wind tunnel data from CPP & UWO
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Roof zoning for open elements on roof
different than C&C
Components & Cladding
SEAOC Solar Photovoltaic Systems Committee
Solar PV Arrays
SEAOC Solar PV Wind Report
 Geometry selected based
on most common
application and
supported by data
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Defined roof zones similar to ASCE 7
 Clarified steps, angled corners, reentrant corners
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 GCrn curves similar to ASCE 7 methodology
 Uses normalized wind area instead
Interpolate
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Factor to increase loads at perimeter of array
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 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
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Example Problem in Appendix
 Aid in interpretation and application of method
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Wind Report
 Example Problem in Appendix
 Provides wind pressures on each panel of the array
SEAOC Solar Photovoltaic Systems Committee
PV1 REPORT ON SEISMIC DESIGN
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
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SEAOC Solar Photovoltaic Systems Committee
Performance Objective
Life Safety per IBC 101.3
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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
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.
SEAOC Solar Photovoltaic Systems Committee
Attached Arrays
 Use ASCE 7-05 Chapter 13
for seismic demand (Fp)
Fp 
0 . 4 a p S DS
Rp
(1  2 z )W p
h
Ip
 How to establish ap and Rp
 Some frictional resistance
may be permitted to
contribute in combination
with attachment strength.
SEAOC Solar Photovoltaic Systems Committee
Unattached Arrays
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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?
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 104.11 permits
alternate (non-prescriptive)
methods…..need to meet life
safety objective…..
SEAOC Solar Photovoltaic Systems Committee
Restrictions for Unattached Arrays
All unattached arrays
Prescriptive displacement
 ≤ 7 degree roof slope
 Height of C.M. ≤ 2x base and 3’
 ≤ 3 degree roof slope
 Ip = 1.0
 Friction tests for SDC D, E, and F
SEAOC Solar Photovoltaic Systems Committee
Required Separation
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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
SEAOC Solar Photovoltaic Systems Committee
Seismic Displacement (DMPV)
Compute seismic displacement by one of the
following 3 methods:
1. Prescriptive formula
2. Nonlinear response-history analysis
3. Shake-table testing
SEAOC Solar Photovoltaic Systems Committee
1. Prescriptive Displacement
0.5m
Peak displacement (cm)
relative to roof
70
60
50
0.67m
40
30
m
20
10
0
0.25
0.5
0.75
1
SDS (g)
1.25
DMPV = (SDS – 0.4)2(60 inches)
≤ 6 inches
1.5
Seismic Design Categories A, B, C
DMPV = 6 inches
Friction testing not required if
common roof type
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
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.
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.
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.
SEAOC Solar Photovoltaic Systems Committee
Structural Interconnection
 Required interconnection strength within an array
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
SEAOC Solar Photovoltaic Systems Committee
NEXT STEPS
SEAOC Solar Photovoltaic Systems Committee
SEAOC Solar PV Reports into Code
What’s next?
Current
Efforts
• SEAOC Solar
PV Systems
Committee
• Solar ABC
• Technical
Papers
• Wind Tunnel
Studies
• ASCE 49
ATC, NCSEA,
CBC
Amendments
ASCE 7
(2016?)
SEAOC Solar Photovoltaic Systems Committee
IBC
(2018?)
Next Steps for SEAOC Solar PV Committee
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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
SEAOC Solar Photovoltaic Systems Committee
Acknowledgements
SEAOC Solar Photovoltaic Systems Committee
WHAT IS DSA DOING?
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
SEAOC Solar Photovoltaic Systems Committee
DSA Offices
SEAOC Solar Photovoltaic Systems Committee
DSA IR 16-8
 Updated in October 2012 to incorporate SEAOC PV
reports
 Available at: www.dgs.ca.gov/dsa
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 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
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 1.5IeDMPV separation distance.
SEAOC Solar Photovoltaic Systems Committee
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
SEAOC Solar Photovoltaic Systems Committee
2013 CBC
 2013 CBC Section 1613.5 – amendment
to modify ASCE 7-10 Section 13.4 to
allow unrestrained solar arrays.
Next Slide
SEAOC Solar Photovoltaic Systems Committee
2013 CBC
 2013 CBC Section 1613.5 (continued).
SEAOC Solar PV Paper
indicates how to do this
SEAOC Solar Photovoltaic Systems Committee
Solar Photovoltaic Systems
Committee
THANK YOU
ron.laplante@dgs.ca.gov