Seismic Testing

SunLink’s R&D program has brought new knowledge to bear in the design of ballasted roof top PV arrays (those that do not use connectors to the roof structure) to safely withstand seismic activity. SunLink undertook this R&D effort because the current U.S. standard ASCE 7, “Minimum Design Loads for Buildings and Other Structures,” does not consider the unique characteristics of these PV arrays in its prescriptive requirements for the design of earthquake-resistant attachments for building equipment such as HVAC and electrical equipment.

Structural Analysis Approach

The first phase of SunLink’s solar seismic R&D program began In 2008, when SunLink partnered with structural engineering firm Rutherford & Chekene (R&C) to investigate the earthquake performance of its ballasted roof top solar mounting products.

R&C built upon current industry standards, such as ICC-ES AC 156, to develop a proper structural analysis approach for studying this challenging problem. First, a representative set of actual, three-directional, earthquake recordings from building roof tops was selected from the California Strong Motion Instrumentation Program. These records were adjusted to match AC 156 recommendations, then used to study ballasted array behavior with SAP2000 Advanced response history analysis computer simulations.

The results of this effort allow SunLink to understand more than any other racking manufacturer the response of its roof mount products on different roofing surfaces, on a range of roof slopes, and in various seismic areas. This knowledge allows SunLink not only to design safer racking products, but also to document that our mounting systems meet the code level of earthquake safety performance on every project.

RD_SesimicSAPAnalysis
Software that models the impact of seismic activity on a given array.

Shake Table Validation

SunLink has been able to accomplish the second phase of its seismic R&D program with the help of a million dollar matching grant from the California Solar Initiative. In this phase, SunLink subjected full-size samples of its ballasted RMS products to shake table tests, again studying the effects of roof slope, roofing surface, and wet and dry conditions on system response. These tests were conducted in March 2012 on UC Berkeley’s Pacific Earthquake Engineering Research Center Shaking Table, the largest multidirectional shaking table in the US. To our knowledge, SunLink is the only racking manufacturer to undertake extensive seismic tests of this nature.

Core RMS Precision RMS
Polyvinyl Chloride (PVC)
roof, flat
heavy ballast,
dry surface
heavy ballast,
dry surface
heavy ballast,
wet surface
light ballast,
dry surface
Polyvinyl Chloride (PVC)
roof, 4% incline
heavy ballast,
dry surface
heavy ballast,
dry surface
light ballast,
dry surface
light ballast,
dry surface
Mineral Cap Sheet (MCS)
roof, flat
# of Inputs
heavy ballast,
dry surface
heavy ballast,
dry surface
light ballast,
dry surface
heavy ballast,
wet surface
Mineral Cap Sheet (MCS)
roof,4% incline
heavy ballast,
dry surface
heavy ballast,
dry surface
light ballast,
dry surface
light ballast,
dry surface

The results of these tests allowed for the verification and calibration of the computer analysis models developed in phase 1, making it much easier for building officials and other stakeholders to validate and approve SunLink’s seismic design approach.

RD_ShakeTable1
Testing the Core RMS System on a 4% incline polyvinyl chloride (PVC) roof.

RD_ShakeTable_SwitchingRoofs
Switching to the mineral cap sheet (MCS) roof.

RD_EarthquakeAccelerationRecord

Earthquake acceleration record.

Codes and Standards

A third phase of work is also underway. SunLink is involved in the development of industry standards by the Structural Engineers Association of California  that will lead to a wider understanding and acceptance of properly designed ballasted roof top PV arrays. As the industry leader in this area of research, SunLink is proud to be in a position to bring forward a new seismic design approach that will lead directly to less costly and more roof friendly, code compliant PV arrays in seismic areas.

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