Elevated Solar PV Bolted Joint Failure

Problem Statement:

Matrix Engineering Consultants (Matrix) led an evidence-based root cause investigation of an elevated solar photovoltaic structure bolted joint, which failed during a high wind event. The work aimed to identify the potential root and contributory causes for the bolted joint failure(s) and develop a list of interim actions to allow the system to be brought online quickly.

Methodology and Analysis:

A Matrix Consultant visited the site and interviewed the system owner, maintenance staff, and event witness. Detailed pictures and samples of failed bolts were taken, and hardware and structural members were removed from the site and placed into a secure crib. The failed bolts were sent to a collaborating laboratory for metallurgical analysis. 

Based on observations made during the site visit, interviews, and results from the metallurgical analysis, it was concluded that two bolts were missing from joints on the eastern end of the structure before the high wind event versus those bolted joints failing during the wind event. The missing bolts caused the structural member to be unsupported, resulting in a shear overload and fractures of the remaining bolts on the western end of the member, triggering a cascading series of events and ultimately resulting in the supporting structure and related PV modules becoming detached.

The focus of the investigation shifted to understanding why the critical hardware was missing before the wind event. Torque audit data from the site at commissioning indicated that all bolted joints were assembled correctly initially but, apparently, loosened incrementally over time and eventually fell out, but it was unclear why.

Recommendations and Results:

At this point, the system was reassembled, video cameras installed, and a periodic torque audit plan was implemented to confirm that the joints were loosening and to understand better why.

Based on those torque audit results and video evidence, it was concluded that the bolted joints under review were loosening due to self-loosening caused by shear overload in the joint during moderately high wind load events when a natural frequency of the structure was excited. Our evidence-based approach and meticulous investigation provided a clear understanding of the root cause and potential solutions. If you’re facing similar challenges and need expert bolted joint consulting, don’t hesitate to contact us. If you have a problem that you think that we can assist you with, please contact us.