By Edward L. Fronapfel, M.S.C.E., P.E. and Alan D. Gillan, P.E./P.L.S.
We often examine building structures that show signs of failure or have already failed. This part of our work allows us to see first hand how structures fail and examine the factors that contributed to the failure. An example of this type of work is a structural failure on which we consulted.
Initial Investigation
We received a phone call regarding the collapse of a roof canopy of a hotel, as shown in the photograph. No one was injured, but the city inspector was considering shutting down the hotel. The hotel manager needed an engineer's help so the hotel could remain open. Above all, the safety of the building occupants needed to be assured while we provided construction failure analysis and a repair design.
The porte cache canopy that collapsed is about 30 feet wide by 50 feet deep and is covered by a low-slope corrugated metal roof. The canopy is framed with steel joists running along its width. A steel I-beam at each end of the joists runs from the front of the building to freestanding masonry columns located at the front end of the canopy. Each beam is supported on masonry columns embedded in the building's masonry wall.
Analysis
Our analysis of the structure first needed to find the cause of the failure and determine if other portions of the structure were likely to fail. Our evaluation of the structure determined that the problem was limited to the area of the roof collapse; other portions of the structure showed no signs of structural stress. We then narrowed our investigation to the damaged area.
Why had the porte cache collapsed when other portions of the structure showed no signs of structural stress and appeared to be adequately constructed? Further investigation revealed the cause was the direct result of the installation of a window two years earlier. The wall was originally constructed without a window, and the portion of the wall removed for the window contained the support columns for one of the steel I-beams. This means that whoever installed the window cut through the masonry column containing concrete and steel bars and removed the support for the steel I-beam. The top of the window was about two masonry blocks below the steel beam. Consequently, for two years, this steel beam rested on two rows of concrete block held together by mortar. But why had it taken two years for this beam to collapse?
Since the canopy is a low-slope roof located in a mountain region, it was designed to hold snow loads up to 100 pounds per square foot of roof area. The concrete blocks left supporting the steel I-beam could not support this load. At the time of the collapse, the area had received a great amount of wet, heavy snow. The weight of this snow exceeded the snow load from the previous winter and finally overwhelmed the canopy to a point of collapse. This had led the building owner to believe the collapse was merely a result of the snow load. The owner had filed a claim with its insurance company for damages thought to be caused by the snow.
Conclusions
Our review of building department records for the original construction showed that the canopy was originally designed and constructed with sufficient support for each steel I-beam. So, the original architect, engineer and contractor could not be held liable for the failure.
Building department records did not show any record of the installation of the window. The contractor who installed the window had not checked with the building department or original architect and engineer before installing the window. Consequently, the contractor who installed the window was fully liable. The snow was only the catalyst in this failure; the beam would not have failed if its support had not been removed.
Because of our findings, the building owner's insurance company was able to entirely subrogate the claim to the contractor's insurance company.
Copyright 1999 Professional Investigative Engineers. All rights reserved.
Ed holds a Bachelor of Science in Civil Engineering, and a Master of Science in Civil Engineering with an emphasis in structural engineering. He is a Certified Level 2 Infrared Thermographer, a Certified 3rd Party EIFS Inspector, and a Certified Forensic Claims Consultant (CFCC.) Ed's background includes geo-hydrology, hydrology, hydraulics, civil engineering, structural engineering and extensive work in construction forensics for building envelope sciences including asphalt work to the roof. Clients include construction companies, management companies, insurance companies, attorneys, homeowners, and homeowner associations. Ed's work has included deposition testimony, expert witness testimony, and mediations and arbitrations. He is a registered engineer in the States of Colorado, Florida, North Dakota, Wyoming, New Mexico, Texas, Nevada, Mississippi, and Nebraska. Ed's dedication to the community is demonstrated by being an active member of over 25 professional organizations. He is a published writer in "The Journal of RCI," "Building Integration Solutions," "The Forensic Engineering Task Force," "The Investigative Engineer," "The I-ENG-A Report," “Inframation, Proceedings Volumes 4, 5, 6, 7, 8,” “Colorado Claims Guide,” and "Building Integration Solutions."