We dedicate this issue of The Forensic Engineering Report (FER) to the subject of wind, which is an environmental factor in all of our lives. Gentle winds can provide us great comfort and pleasure but fierce winds can cause us pain and destruction. Our heartfelt condolences go out to those who lost loved ones or were in the path of destruction during the recent series of tornados in the US. The Investigative Engineers Association and its Catastrophe Response Team is here to help put the pieces back together should we be called upon to assist.
Wind is the flow of gases on a large scale. On earth, wind consists of the bulk movement of air. The two main causes of atmospheric air circulation (wind) are the differential heating between the equator and the poles, and the rotation of the planet (called the Coriolis Effect). Specifically, wind is caused by a difference in atmospheric pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure zones. Wind is the kinetic energy of the air in motion and wind force is proportional to the third power of wind velocity.
In today's science of meteorology, wind speeds (velocity) and forces can be measured and sometimes predicted. But even in the age of modern weather technology, some major wind events (i.e. tornadoes) cannot always be accurately pinpointed to timely provide ample warning for those in the path of destruction.
In human civilization, "good winds" have inspired mythology, influenced events of history, expanded the range of transportation and warfare, and provided a source of power. And yet, "bad winds" have sometimes proven to be problematic for safe air travel and destructive to some land features. As we continue to enjoy the good aspects of wind, we need to be ever aware of the bad aspects of wind, and keep our eyes to the sky and our ears to the weather channel.
While relatively unknown to the general public, wind turbine fires are not as rare as one might expect. In today's newer wind turbines, they are not only larger (2.4MW and up), but contain the switchgear, inverter, and transformer within the nacelle (power house). The primary causes of fires include lightning strikes, machinery breakdown, electrical malfunction, and resonant circuits. Capacitors can be damaged due to poorly designed circuitry. Explosions due to breaking mechanism failure during high winds. If your insured's wind turbine or wind farm experiences a fire, it isn't necessarily a lightning strike.
Last month's tornados in the south are proving to be among the most damaging storm events in U.S. history. We have seen entire cities wiped off the face of the map. Billions of dollars of property damage, as well as injuries and loss of lives have resulted from these horrific storms.
While there is now considerable debate as to why so many major weather events are occurring around the world, our country has historically been subjected to severe seasonal weather events. With our population increases and concentrations, the physical impact of major storm events today is more problematic. And the media coverage of tragedies like we experienced last month certainly creates a stronger awareness of these dramatic conditions. Whether it is an EF 5 tornado, a category 5 hurricane or a 9 point earthquake, we have been reminded again that the fury of Mother Nature is among the most power and destructive forces on the planet.
Over the years, design standards have been modified to address nature's major forces and engineers have upgraded their designs to account for some degree of abnormal forces. But the fact remains that engineers cannot practically design and build structures and facilities to totally withstand some of the major forces of nature.
When a catastrophic event occurs in this country, the insurance industry is challenged to address the multitude of claims that arise from the event. In many instances, as was the case last month, the damages are significant and very wide spread. Typically, it will take months, if not years, for the insurance companies to properly adjust these claims. And in some instances, engineering assistance is required.
The Investigative Engineers Association (I-ENG-A), comprised of a large group of engineering firms located across the nation, have provided technical assistance to insurance companies on a wide range of claims, during and after tornado and other major storm events.
Also, the I-ENG-A Catastrophe (CAT) Response Team is designed to deploy a number engineers to loss areas where a large volume of claims require technical input. Typically, this occurs after major catastrophic events, such as the cent tornados.
A few brief examples of how I-ENG-A members have provided investigative engineering services after past tornado events are as follows:
In many major storm related investigations, I-ENG-A is asked to determine the origin and cause of specific damages. Some of these investigations are commissioned shortly after the event, while other claims arise after considerable time has elapsed. In either event, our local member firms stand ready to assist with its CAT Response Team to provide local insurance adjusters with engineering investigations and evaluations of questionable or problematic claims.
In the meantime, as we all hold our collective breaths and hope that this year's current trend for U.S. tornado activity does not persist. Please join with our entire organization in sending our heart felt best wishes to the victims of nature's most recent fury.
Large buildings, commonly known as "Pole Structures", are found throughout the landscape of our country. These structures are common in farming and other industries, as well as for commercial and private use. They are generally used for storage of large equipment and/or large quantities of materials or supplies. Pole Structures are typically very large buildings and in many cases are built with random construction materials and with little or no engineering input. Many times, these buildings do not have properly sized structural elements and are not properly braced. With the size and sometimes fragile construction of these structures, they are commonly prone to damage from wind (straight and swirling wind forces).
When investigating potential wind related damage to these unusual structures, engineers typically follow a prescribed protocol of investigation, including:
During a recent insurance company commissioned investigation of a damaged Pole Structure, these procedures were generally followed to determine if the damage(s) was indeed caused by wind forces.
The four year old structure being investigated was noted to be 150 feet long, 60 feet wide (a very long span) and 20 feet tall (a very high structure). The numerous long wood-supporting poles for the structure were observed to be six to eight inches in diameter, and were reported to have been purchased from a local electric company. The roof system was noted to consist of a series of light weight pre-fabricated wood trusses. The roof and wall systems of the structure were observed to consist of various wood support and bracing members, covered by light weight corrugated sheeting.
The site investigation revealed numerous conditions. There was noted evidence of wind related damages on surrounding properties, but none of the damage was as significant as the Pole Structure damage. Inspection and documentation of the Pole Structure revealed various damage conditions. Many of the supporting poles were observed to be bowed and tilting. Some of the roof trusses were noted to have experienced out-of-plane bowing with numerous failed connections. These damages were particularly evident in areas of the trusses that had experienced previous repairs (reportedly done by the truss installer during initial construction). Considerable bending, twisting and broken member patterns were observed in the roof and wall systems. Some of the support and bracing members/systems were noted to have failed, especially near the corners of the structure (corner areas of these type structures are cited to receive the highest loads and pressures according to codes). The metal sheeting which covered a large portion of the structure displayed localized bending and buckling. Generally, the overall structure was measured to be significantly racked and out of level and plumb. Also, the overall pattern of damages to the Pole Structure was noted to be consistent with the direction of the recent documented wind event.
Although there were numerous "red flags" concerning the preexisting condition of the structure and it's methods of construction, after assessment of all information and damage evidence it was concluded that the primary causal factor in the damage to Pole Structure was indeed abnormal wind forces. It was further concluded that the structure was salvageable but extensive repairs and reinforcements were recommended. A detailed cost estimate for the repairs was developed as a part of this investigation.
Pole Structure owners and engineers who investigate damage to these unusual structures should take heed in these findings. By their size and very nature of construction, Pole Structures are very susceptible to wind forces, both normal and abnormal. In essence, these structures could be likened to a large kite, getting ready to fly. While it is very difficult to economically build these structures in a total fail-safe manner, it is probably prudent to take extra pains with the initial construction of your Pole Structure, in order to minimize the risk for wind damage and very costly future repairs.