| Cars, Trucks, or Trees; Structural Impacts Need Careful Investigation |
| by |
| John B. Peterson, MS, PE |
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| Impacts to buildings can come from numerous sources and vary widely in severity, but the most common impacts Knott Laboratory investigates often involve either an out-of-control vehicle crashing into a wall (or walls) or a toppled tree impacting the roof and/or walls of the building, both of which can happen on a moment’s notice. Both impact types are capable of causing extensive damage to the structural system and finishes, not only in the immediate vicinity of the impact, but also to areas that may not be readily apparent at first glance. One doesn’t need to be a forensic engineer to determine where the original point of impact occurred – everyone sees the gaping hole in the side of the building. It’s the additional hidden or minor damage that is often overlooked which, in some instances, can have significance. |
| Ultimately, the forces created by an impact will find a path to get to the ground. How the force finds a path to the ground is highly dependent on several factors and the resultant damage can vary greatly depending on several combined factors including: |
| - Size and Velocity of Impacting Object – If a truck going 25 miles per hour crashes into a structure, there will be considerably more resultant damage than if a small motorcycle going 25 miles per hour impacted the same structure. |
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| - Location of Impact – Did the impact occur at a corner? On the roof trusses? At a shear wall or near columns supporting multiple levels? How are window and door openings affected? Depending on where the impact occurred, the transfer of load to nearby members may have occurred leading to subsequent damage away from the impact location, below or even above the level of impact. |
| - Size of Structure – If a tree impacts the roof at the north end of a 200 foot long commercial structure, is that lower-level wall cracking the owner sees in their office on the opposite end caused by the tree impact? |
| - Construction Style and Materials (Both Structural and Architectural) – Many materials react differently to impacts. How the load is transferred depends on the strength of material, its resistance to initial impact, the connections (or lack-thereof) and framing orientation (either vertical or horizontal). If a vehicle impacts a loadbearing, reinforced masonry shear wall, the resultant damage will be considerably different than had the same vehicle hit a non-loadbearing, 2×4 wood stud wall. |
| - Type of Lateral Resisting System – Exterior shear walls are a common lateral force resisting system, but a structure may contain alternative systems including rigid frames or diagonal braces for example, which are affected differently by impact forces and transfer the load to the foundation by different means than a shear wall system. |
| - Age of Structure – Deterioration of materials can occur over time potentially leaving some older structures more susceptible to damage due to an impact. The building codes were less stringent years ago allowing for some interesting framing and construction techniques to occur. On the other hand, advances in materials technology and engineering have allowed us to build structures taller and lighter with less material, but that same lack of material can potentially leave a newer structure more susceptible to impact style damage than older, stouter structures. |
| Knott Laboratory considers all of these factors together when determining the resultant damage caused by an impact. Often, what may seem like a minor impact with minimal localized damage at first glance, can be shown to have caused damage in areas away from the impact once all of the factors have been considered. On the flip side, damage that may be thought to be associated with the impact can actually be ruled out when considering the above-mentioned factors. |
| Unfortunately, the damage to structural components is not always readily visible, so the engineer must rely on notable signs of damage that can transmit through finishing materials, often in the form of cracks. Care must be taken when “reading” cracks in that cracks can occur in various materials due to numerous reasons, many of which are not associated with the impact in question. Settlement, differing material expansion and contraction, poor ventilation and lack of control joints are just some of the many contributors to cracks. Once an impact has occurred, the building owner will most likely be looking for what they believe to be signs of damage, typically in the form of cracks that, in many cases, have been present for years, but were never noted until the impact event occurred. |
| In summary, damage as a result of impacts on structures can come in many forms with a wide array of severity based on several factors, which should all be taken into consideration in order to get the whole picture rather than focusing solely on the immediate damaged area at the point of impact. |
| Company News |
| A recent case involving a truck vs. passenger vehicle collision on Colorado Hwy 93 settled for $8 million dollars. Dr. Ziernicki served as expert on behalf of injured party. |
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| Ben T. Railsback, M.S., P.E. achieved Senior Member status in the National Academy of Forensic Engineers (NAFE). |
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| Richard M. Ziernicki, Ph.D., P.E. is an invited speaker at the American Association for Justice 2012 Annual Convention in Chicago, IL on July 28 – 31, 2012. The title of Dr. Ziernicki’s presentation will be “Current Technology in Accident Reconstruction.“ |
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| Karen Mellentine has been elected to the Rocky Mountain Property Claims Association (RMPCA) board as Secretary. |
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| Ben T. Railsback, M.S., P.E. testified in trial in Missouri for plaintiff in a case where a forklift ran over a pedestrian. The defendant settled for $2.825 million during the trial and prior to jury deliberation. |
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| Mike Lowe joins Knott Laboratory as Director of Business Development. Mike comes to Knott Laboratory with a strong construction background. He owned and operated a construction company in the Chicago area for the past six years. |
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| Ricky Nguyen, B.Sc. joins Knott Laboratory as a Mechanical Engineer. Prior to joining Knott Laboratory, Ricky was working for BP in Houston, Texas as a gas engineer involved in hydraulic fracturing, coil tubing and wireline operations. Ricky is a graduate of the Colorado School of Mines. |
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| Knott Laboratory is Celebrating Our 30th Year in Business!Knott Laboratory is proud to announce our 30th anniversary since the company was formed. Over that time, Knott Lab has been fortunate to work with the nation’s best lawyers and highest profile cases. |
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| Knott Laboratory now has a YouTube channel where you can see our latest animations. |
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