Structural engineering assessment and property damage investigation is one of the areas of expertise at AEI Corporation. Recently in the news we heard and read about roof collapses that occurred in Western New York during the historic lake effect snowstorm.
One type of structural forensic investigation AEI performs is to determine if damage to a structure was in fact caused solely by weather conditions, or if there were other design, construction, or maintenance factors at play.
Structures should be designed and constructed to withstand very large snowstorm events. The first question we need to ask is “Was the snow load at the time of the event greater than the load anticipated in the design?” When providing emergency response to catastrophic collapses, our engineers can take actual snow depth and density measurements to determine the loads on the roof at the time of the event. More often, weather data that has been reviewed and is supported by regional climate centers and state climatologists are used to substantiate weather conditions in the area of question during the date of the claimed damage. Temperatures, wind speeds, and conditions favorable for accumulation of precipitation over a number of days are reviewed and can be an important part of the investigation. From these reports an approximate ground snow load in the geographical area in question can be calculated and with the application of appropriate factors, the rooftop loading can be estimated.
Next we ask, “Did the existing conditions conform to the design and were there any unforeseen or poorly maintained aspects of the construction that could have contributed?” In new construction, missing blocking and bracing or holes and notches cut through structural members for plumbing penetrations must be ruled out. In older buildings, drifted snow from altered rooflines or additions, insulation and ventilation problems that lead to ice damming, and chronic moisture infiltration that has deteriorated the interior structural components are common contributing factors that must be assessed.
As I have discussed in previous “Yeah We Do That” articles, scene photographs are always a part of the investigation. The photographing and inspecting the interior walls and the roof structure, including trusses and truss plates, must be completed in order to verify damage patterns and rule-out other causes such as foundation movement. But that is a story for another day….