The Use of Tested Construction Materials - Essay Example

? Structural Fire and Structural Failures Full Structural Fires and Structural Failures Introduction Our ever changing living standards and development of our infrastructure is continuously updated to provide us with better living conditions. Our economy depends on the infrastructure; however, as our cities expand, the infrastructure becomes overloaded and in turn, susceptible to basic dangers as fire or even structural failures. In between 2007 and 2011, fire departments in the United States alone received an average of 366,600 calls per year for home structural fires (Ahrens, 2013, p.1). These fires resulted in over 2,500 casualties and cost $7.2 billion in damage on average every year. Efforts started in 1980 to keep track of fires and take measures to reduce structural failures and after three decades, the damages in casualties as well as property reduced by almost fifty percent. Structures were classified into different types to better access the parameters and predict the time the fire takes to consume the structure. This classification also gives firefighters better assessment to fight or counter fires. The speed by which fires spread throughout the structure depends on three major factors; oxygen source, fuel and the heat source. Oxygen is necessary for burning and air is the primary source, the interior of the structure provides fuel source for burning and different components burn with different speeds, and finally; some elements of the structure contribute towards the heat source which raises the air temperature to a point where everything bursts into flame and it is known as flashover. Structural fires reaching flash point are almost impossible to control and often lead to structural failure. Structure Types Structural fires are classified as per type of structures, depending on their external and internal composition of construction materials. Since every material burns with a different rate and in turn produces heat as well as smoke. Heat released contributes towards raising temperature of local air, which results in flash over. Every structure has different set of materials and that is why each structure takes different time to reach flash over. The structures are classified into five types with ascending rates of burning. Type I consists of structures with steel and concrete used to provide structural strength, making it the most resistant to fires. Type II uses steel to reinforce the structure of the roof, which provides additional support for the structure and in particular delays roof collapse. Type III is ordinary structures with exterior and interior made of brick and mortar, which are non-combustible. The interior may also have laminated or fire retardant wooden floors. Type IV is heavy timber structures which rely on timber to reinforce the structure, however, the exterior walls are made from bricks. Type V are wooden structures with wood used to form the basic frame of the structure, as well as, exterior and interior (Dunn, 2013). In simple, structures with steel and concrete, that is Type I and II, are the most resistant to fire as they are capable of handling heat generated for longer durations, whereas, structures with wood, either interior or exterior are destroyed at a faster rate, which includes Type IV and V. Occupancy Types Occupancy type involves type of activity the structure is designed for and therefore, classified accordingly for fire hazards. Structural fires are a result of human actions and the type of occupancy dictate regulations for a specific structure. Some of the groups among this classification include Assembly, Business, Education and Factories. These groups are subdivided depending on type of activities carried out within the structure. In general, fire hazard increase with increase in the number of occupants within the structure as well as the scope of activity. Factories are more susceptible to fires than any other group, because, they involve manufacturing and storage. The materials involved are much more hazardous and chances of fires are much higher. Assembly group with activities like cinema or theatre are hazardous as well, since they involve pyrotechnic films which burn rapidly. The group also includes restaurants and bars in which high concentration of people increases the chances of fires. Business as well as Education group is low hazard since activities like business transactions or educational classes are activities with fewer chances of fires. Station Nightclub Fire The Station Nightclub Fire of 2003 in Rhode Island can be taken as an example of structural fires. Hundred casualties were reported and it is the fourth deadliest fire in United States history. The fire started during concert of a local band and pyrotechnics were used to create sparks for the show. The walls were filled with polyurethane foam to absorb sound and the exterior of the club was cemented walls. Sparks from pyrotechnics during the concert ignited the polyurethane foam within the walls, which burnt rapidly and produced thick smoke. Within the first 7 seconds the flames reached the ceiling and in almost 90 seconds the smoke fills the structure from the ceiling till the floor (Tubbs and .Meacham, 2007, p. 85). In almost five minutes after the first flame, fire completely covered the building and flames reached the front and the back walls. The pace at which the fire spread throughout the structure was due to the burning rate of the polyurethane foam, which is estimated to burn one foot per second. Furthermore, the building was not equipped with water sprinkling system, which allowed the initial fire to grow unchecked. Polyurethane foam is a good burning fuel and also a good heat source. This contributed towards quick rise in air temperature and within minutes the structure reached flash over. The Station Nightclub had authorized capacity to hold 404 individuals, but at the time of the incident an estimate of 440 to 458 occupants were present at the event. Furthermore, the building had four main exits, which either blocked or were locked by the building staff. The main exit quickly crowded by people, resulted in a blockade. This caused the evacuation rate of almost one person per second. The other three exits were reported to be initially locked and unmarked. The fire escape through the stairs on the first floor was even locked by the management for security reasons. All these factors resulted in slow evacuation and resulted in hundred casualties. Regulations were changed after the incident to keep fire exits unlocked at all times. MGM Grand Hotel Las Vegas The 1980 MGM Grand Hotel fire in Las Vegas resulted in 85 casualties and is considered as one of the worst hotel fires in United States history. The hotel had 23 stories and the fire started in the casino or the second floor. Faulty electric system started the fire in the restaurant attached with the casino. The items in the casino and interior turned into fuel source for the fire. These included the casino equipment, interior fabrics, plastic piping and the wallpaper as well. The smoke created more problems than the fire itself. It spread through the stair cases and the elevator shafts. The ventilation system further assisted in distributing the smoke throughout the building. Hotel guests evacuating their rooms through the corridors had to pass through thick smoke. An estimate of 300 guests reached the roof and was evacuated by helicopters (Craighead, 2009, p.130). Some were evacuated from terraces by firefighters with ladders reaching till the eighteenth floor. The fire at the originating floor was controlled by firefighters. The sprinkler system was not enough to control the initial flame and fire alarm was shut down by hotel staff misinterpreting it as a false call. This caused delay in fire notification and evacuation as well. Furthermore, at the time of the fire, the elevators could not reach the bottom floors and many of the guests could not take elevators to evacuate the building. Structure Failure - Resonance At times when a structure is overloaded or tested beyond its structural capabilities, it may lead to failure or collapse. Every structure relies on some key points which provide it the structural rigidity, which in turn is dictated by the material used or the architectural design. Every structure has a natural vibrating frequency which it gets from composition of material and design elements. The principles of resonance, that is, increase in amplitude when two waves of almost similar frequencies overlap in such a way that their high and low points align to give increased vibrational amplitude. This effect can be seen in particular with bridges. Wind can induce vibrations in bridges and its front and back motion is the vibrational frequency. The natural frequency of a structure can match with the induced vibrational frequency (Biggs, .2012) In case of bridges, induced vibrations from external factors like wind can match up with the natural structural frequency which causes two waves to overlap and result in increased amplitude. This increased vibrational amplitude can exceed structural rigidity and cause failure. The Tacoma Narrows Bridge collapse in 1940 is an example of structural collapse by resonance. The natural frequency of the bridge matched the frequency of motion induced by the wind which resulted in drastic increase of amplitude. The structure collapsed because the vibrations exceeded its design limits. Resonance is also the reason that soldiers are told to break off the marching steps so that their march cannot induce vibrations which can match natural frequency of the bridge. Design Flaw Structure failures can also occur due to design faults. Due to architectural design, a single component or a specific area may have to sustain extra load. An example of design flaws can be taken for an overhanging walkway collapse of Hyatt Hotel in 1980. The three walkways were supported by steel support rods. The walkways on different floors were connected to the roof with two different support rods. The first connected the top walkway with the ceiling, whereas, the second connected the lower walkway with the top walkway. With this design flaw the walkways could only hold 30 percent of their designed weight (“The Hyatt Regency Walkway Collapse” 2013). This design flaw forced all weight to be supported by the first support rod only, which was overstressed by presence of large crowd witnessing the floors below and resulted in a structural failure causing 114 casualties. Materials Materials used can contribute towards structural rigidity. At times structures are not strong enough to support the load capacity because of use of substandard materials during construction. This may result in failure or collapse when the load capacity is pushed to the limit. Collapse of a garment factory in Dhaka in 2013 can be taken as an example. The factory housed thousands of workers. Heavy machinery including power generators were placed on the first floor along with workers which was beyond the structural strength provide by construction materials (Yardley, 2013). The load on the first floor induced vibrations and shook the structure. The roof construction along with supporting walls was made from substandard material which resulted in cracks and subsequently the roof collapsed, killing thousand workers. Foundation Failure Foundations are the basis for any structure. The foundations may fail because of faulty design, substandard materials or more importantly change in subsurface conditions. Foundations need to be designed according to the surface conditions of the particular construction area. Construction or design errors in structure foundation may result in a leaning structure or a complete collapse. Leaning tower of Pisa can be taken as a glaring example of foundation failure. In 2004, an apartment building collapsed because of foundation failure. The foundations shifted because of foundation dug for neighboring building. The building leaned since its foundation could not support the weight and ultimately collapsed. Conclusion Fire hazards and structural failures cost lives and we are learning ways to reduce the damage. Safety regulations for fires are for our protection and these have matured over time. Incidents like the Standard Nightclub and the MGM Hotel fire have had significant impacts on these regulations. The system in place to check safety regulations were tested and lessons learnt from these incidents enable us to better protect and regulate future projects accordingly. In a way, structural failures have taught us to come up with better structural designs and the importance of regulating the use of tested construction materials. All these measures and regulations eventually aim to better protect us from future fires or structural hazards. References Ahrens, M. (2013). Home Structure Fires. Quincy, MA: NFPA Fire Analysis and Research Division. Biggs, B., (2012). How Can Resonance Collapse Bridges?. Retrieved from http://www.howitworksdaily.com/science/how-can-resonance-collapse-bridges/ Craighead, G., (2009). High-Rise Security and Fire Life Safely. Burlington, MA: Butterworth-Heinemann. Dunn, V., (2013). April Newsletter by Vincent Dunn Deputy Chief FDNY. Retrieved from http://vincentdunn.com/dunn/newsletters/april/FDNYHP_12.html Tubbs, J., & Meacham, B., (2007). Entress Design Solutions: A Guide to Evacuation and Crowd Management Planning. Hoboken, NJ: John Wiley and Sons Inc. Yardley, J., (2013). Report on Deadly Factory Collapse in Bangladesh Finds Widespread Blame. Retrieved from http://www.nytimes.com/2013/05/23/world/asia/report-on-bangladesh-building-collapse-finds-widespread-blame.html?_r=0 (2013). The Hyatt Regency Walkway Collapse. Retrieved from http://www.asce.org/Publications/ASCE-News/2007/01_January/A-Question-of-Ethics/ Read More