Impact Damage to a Structure

How often is a building struck by a vehicle? A lot more often than most people think.  It has been reported that a vehicle crashes into a commercial building as many as 60 times a day in the United States, and that number is much higher when residential buildings are included.  It is also not uncommon for bridges to be damaged from the impact of a moving vehicle.  Single-vehicle accidents, which are usually off-road accidents, account for nearly 20 percent of all traffic accidents, although not all single-vehicle accidents involve a building being struck.  Unfortunately, exact statistics concerning buildings being struck by vehicles are not available, as states, counties and cities compile and track accident information, including “off-road, fixed-object accidents”, in different ways.  Regardless, the frequency of buildings being struck by a vehicles is surprising, if not alarming.

Incidents by cause

There are numerous causes of vehicle-building crashes, with some of the more common including distracted driving, drunk driving, reckless driving, medical emergencies involving drivers, and vehicle defects. Although less common, vehicles are sometimes deliberately used to gain entry into a building in order to commit theft.  The chart on the right shows statistics gathered by the Storefront Safety Council (www.storefrontsafety.org).

After a building has been struck by a vehicle, there are various issues to be addressed: possibly personal injury, damage to the vehicle, damaged personal belongings, and legal considerations, along with the focus of this article, damage to the structure that was impacted.

In the vast majority of cases, the impacted building can be repaired, but one of the first things that must be determined is whether a residence can continue to be occupied or whether a commercial building can remain open during the repair process.  A structural engineer, sometimes in conjunction with public officials (fire rescue personnel, building department personnel), will typically conduct an initial investigation and evaluation of the building to make a determination as to whether the building is safe to continue to be used.  The utilities and mechanical / electrical / plumbing systems of the building also must be evaluated in some instances.

Vehicle Impact

While the occurrence of a vehicle impacting a building is not infrequent, the chance of impact on any particular building is typically so slight that the loading condition is one that is not normally required to be addressed by building codes. The existing building codes do not specifically require that structures be designed to withstand the forces from a vehicle colliding into a structure; however, there can be situations where an elevated risk is recognized or the importance of the building’s function is greater than normal, and in those instances the design of a building may include consideration of impact loads caused by vehicles colliding with the structure.  As is likely intuitively discerned, the magnitude of the force exerted by a vehicle colliding into a structure is primarily a function of the weight of the vehicle and the speed at impact.

After a vehicle impact event, it will also be necessary for a structural engineer to determine the extent of damage to the building, and prepare a scope of repair required to restore the structure to its pre-loss condition. A detailed investigation and analysis by an experienced structural engineer is necessary in order that the loss can be objectively adjusted, as well as to enable the engineer to assist in any possible future subrogation efforts.  The forces that are associated with vehicle impacts can be orders of magnitude greater than the typically designed for live loads; therefore, the damage that results can be severe.  While the damage to a structure in the immediate vicinity of the vehicle impact can be fairly obvious, the localized considerable force of the collision can be transferred through the structure and cause damage in areas not directly adjacent to the impact location.  The structural engineer should attempt to identify damage to all portions of the building related to the vehicle impact, and differentiate between damage that may have been present prior to the subject event.  The structural engineer will also need to consider whether it is necessary to include structural improvements in the scope of repair that involve current building code requirements and/or the elimination of dangerous conditions that may exist.  Depending on the party that has retained the structural engineer, the requested services may include determining a scope of repair that is used in establishing the monetary value of the loss, or determining a scope of repair and providing specific repair recommendations that are suitable for construction.

Damage to a building can be caused by the impact of something other than a vehicle, such as a falling tree, wind-borne debris, water-borne debris during a flood, and as is occasionally reported in the news, an aircraft; but the investigation and analysis process would be similar to that described above.

At Western Engineering & Research Corporation (WERC) we have licensed Professional Engineers (PEs) with decades of experience in conducting thorough forensic investigations in order to provide sound and substantiated opinions. If you are in need of structural engineering services related to impact damage to a structure, call WERC at (800) 303-9800; we are available 24/7.

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