Collapse of the Multi-Span I-35W Mississippi River Bridge on August 1, 2007 - Coursework Example

Forensic Engineering The collapse of the multi-span I-35W Mississippi River Bridge on August 2007 INTRODUCTION In the everyday decisions that people make safety is paramount considering that it is the essence of having constructive and not destructive programs. Compared to monetary gains, a person’s safety is more important and hence, should be ensured at all times. Of particular interest would be the public support utilities such as bridges, canals, dams among others. These are indispensible given that they serve a large population of individuals; hence, a failure recognized on them would likely translate to loss of lives and properties (Ramachandran, 2005.p.115-120). This would then be a threat to safety, which was the original intent for developing such structures. Objectives and Scope As a part of the Forensic Engineering coursework, this study is a prerequisite for the attainment of a Civil Engineering Master’s degree. Therefore, the author in this case is appointed and mandated by the relevant academic staff to carry out and prepare an independent forensic report into the into the events that led to the breakdown of the I-35W bridge transversely the Mississippi river (Structures Congress, & Griffis, 2009.p.95-102). This shall be in harmony with the established Terms of Reference below. Terms of Reference The engineering structure under investigation is the Interstate-35W Mississippi Highway Bridge, and the matters under investigation in this study are as follows: a. Detailed review of the schematic plan and the construction of the bridge. b. The detailed review of the construction repair plan that was being carried out on the bridge before its collapse. c. The impacts of any alterations that could have been made on the bridge before or during the repair that could have led to the collapse. This can either be structural or non-structural. d. An assessment of the failures of the bridge prior to and after the collapse. e. Probable causes of failure on the bridge basing on the information I shall gather. f. Conclusions, reflections and recommendations. Purpose of the Study Many times, there have been failures witnessed in the constructions set up to aid mankind live a fulfilling life. In this study, I seek to provide a critical analysis of failure as presented in the failure of I-35W Mississippi River Bridge on August 1, 2007. This study will seek to provide further and detailed information that can act as roadmaps for the improvement of strategies to prevent such failures again from occurring (Senauth, 2007.p.98-105). Background Information I-35W Mississippi River Bridge also known as Bridge 9340 was built in the form of eight lanes and majorly intended to connect the two sides of Mississippi River in Minneapolis, Minnesota. Built in the form of arches and of steel truss, the bridge carrying Interstate 35W appeared to have been the most strongest and modern engineering structure to have been built. However, all this perceptions about the bridge were to change with the collapse of it on the fateful evening of August 1, 2007. Around 6.05 p.m. central time, the 1,907 foot long, I-35W eight-lane Highway Bridge experienced a high catastrophic failure when the span of its main deck truss collapsed (Ebling, 2012.p.206-211). The result of the deck failure was an ultimate collapse of the 1,000 feet deck truss and a greater section of the main span fell into the 15 foot deep river. An approximation of the length of the bridge destroyed was 108 feet. Records from the National Transportation Safety Authority indicated that about 100 cars were over the bridge at the tragic time of collapse and that 145 people were injured while additional 13 died on the pot awaiting the arrival of the emergency help. A devastating disaster to be ever recorded in the history of the US was this and is as shown in the figure below (Ratay, 2010.p.105-111). Figure 1: I-35W Mississippi River Bridge before the collapse. Figure 2: I-35W Mississippi River Bridge after the collapse. Source: http://abcnews.go.com/Blotter/bridge-collapse-anniversary-safe-drivers-now/story?id=16907710 On the fateful day of the collapse, reports indicate that construction work was going on in the bridge as usual and that four lanes (two outside northbound and two inside southbound) were closed from the traffic. Construction equipment (sand and gravel) were witnessed positioned for work in the closed lanes. However, as shown in the figure above, a motion-activated video camera for surveillance located at Lower St. Anthony Falls Lock and Dam, recorded that the center of the bridge span separated from the rest of the bridge and fell into the river. As such, from a forensic engineering point of view, it would be noted that the failure could be attributed to a simple flaw in the design of the gusset/metal plates of the bridge, connecting one beam to another (Markow & Hyman, 2009.p.130-136). STRUCTURAL ANALYSIS Factual Analysis of the Failure The main cause of failure in the bridge that probably led to its collapse was the nature of the gussets/metal plates that had been used to form connections to the members of the truss bridge. Ideally, from a forensic point of view, it is easy to note that these gussets were not thick enough hence, could have not withstood the load of the bridge plus those of traffic that passed through it. Before the collapse day, the design of the bridge looked safe and in actual sense, the bridge’s overall design appeared reliable, safe and effective (Nunnally, 2011.p.130-136). Figure 3: The main truss node as used in the I-35W Brdige As is shown in figure 3 above, the gusset plates and the truss node were not thick enough to sustain the load, which the bridge was constructed to contain. Therefore, this being true of the bridge, it can be noted that the failure to detect such an anomaly in civil engineering concepts by the original contractors of the bridge could have been the main cause of failure and a threat to safety on the road (Cronn-Mills, 2009.p.85-89). The likely reason for this could be that the engineers could have failed to perform the necessary and requisite calculations that were needed to check whether the gussets were of the correct sizes fit for the bridge. Therefore, the mismatch in the gussets was the main cause for the failure witnessed. Outcomes of the National Transportation Safety Board (NTSB) According to the NTSB, the probable cause for the collapse that was witnessed on I-35W Bridge was as a result of the design error made by the company that had been contracted to carry out the initial construction process. The collapse resulted because the bridge lacked the adequate load capacity that it needed to carry itself plus the additional load impacted on it by the daily traffic (Levinson et al, 2012.p.11-26). Considering that the accident occurred in the evening during a rush hour, there were possibilities of a large fleet of vehicles crossing the bridge. Sverdrup & Parcel and Associates Inc. the company tasked with the construction failed in the identification of appropriate gussets for the U10 nodes thus, leading to the failure under a combination of several factors as listed below. a. There was a significant intensification in the bridge’s weight as a result of the previous modifications that had been done on it. b. There was an aggregated load on the bridge on the day of collapse as a result of the heavy rush hour traffic and the construction materials that had been put on the bridge. c. Failure of the procedures used to check the quality by Sverdrup and Parcel Inc. in ensuring that the calculations for the truss and gussets were appropriate. d. The inadequate review of the design of the bridge by the State and Federal officials from the transportation sector. Instead, the officials’ general practice of accepting and giving inadequate attention during the inspection procedures, could have led to failure, as well. They should have determined the conditions that could have caused distortion early in time and had them rectified. Safety issues identified In another report by the NTSB, the collapse could have been initiated by other factors such as the corrosion of gussets at the L11 nodes thus, causing them to be damaged, movements by the pier, temperature effects on the steel, preexisting cracks on the bridge. In alternative instances, the possibilities could be that the technologies used to assess the conditions of the gussets were not accurate enough (Lemaître & Desmorat, 2005.p.201-210). Consequently, the exclusion of the gusset plates in the rating guidance of the load and the unavailability of required guidance from the designers in relation to placement of loads and repair were lacking. The insufficiency in the procedures for controlling quality in the planning of the bridge, and the inadequacy of inspection procedures by the State and Federal Agencies to review and approve the designs and plans of the bridge and calculations could have been the main safety problems identified (Delatte, 2009.p.412-423). Personal Analysis of the failure and Findings i. Causes Taking a personal analysis of the situation with I-35W Mississippi Highway Bridge, I would like to note that this concur with some of the investigative reports and information therein, given that I find the collapse of the bridge to have solely resulted from the load imbalance brought about the weak gussets used. In my view, the collapse could have been prevented had the designers and contractors engaged in its initial construction and repair and maintenance procedures, conducted adequate feasibility tests to measure the viability of the construction material and the strong points of the bridge. It is quite possible that the load weight for the bridge could have been determined in prior so as to influence the decision on the type of truss and gussets to use in the nodes (Lepatner, 2010.p.114-123). ii. Design structures and capacity In my findings, I note that the U10 node gussets were all fractured into pieces thus, clearly explaining the ultimate collapse of the center floor of the bridge immediately after the failure from the nodes. In differentiating the damage that resulted from the impact with the ground/river and the damage caused before the impact, I learnt that there was a substantial displacement of the L9, L10 and the U10 nodes, as well as the trusses before the collapse impact (Maranian, 2010.p.87-92). Engineering calculations performed on the decks, and trusses revealed that the D/C ratio was slightly higher than the recommended ratio of 1 thus, a likely indication of the inadequacy of the design capacity. Therefore, there could have been an assumption that the gussets are stronger than the members that they connected thus, the reason as to why load ratings were not conducted on them. Subsequently, there had been no bridge collapse recorded in history of this magnitude that involved gussets hence, the laxity in measuring the load rates. iii. Emergency response Relating to the emergency response, my findings reveal that there was a rapid reaction from the police and relevant agencies with the first rescue team arriving nearly four minutes after the collapse. CONCLUSION AND RECOMMENDATION The main concern to structural and civil engineers in the world today is the prevention of such collapses of important structures, more so based on the preventable factors such load ratings. However, from the analysis point of view, the initiation of the collapse on the I-35W Bridge was as a result of the lateral shifting of the upper diagonal members and the subsequent failure of the gussets in the center nodes of the deck truss. The total collapse of the deck truss was achieved immediately after the gussets failed to support the joints. Subsequently, the collapse as is indicated in the findings could have resulted from the failure to make accurate calculations of the effects of stress upon the gussets (Macalevey, 2010.p.145-148). It is also evident that the collapse or at least the failure could have been attributed to the inadequacy of the procedures set forth by the Federal and State agencies in relation to structural engineering. Based on these circumstances, it would be appropriate to recommend that the Federal Highway Agencies develop and implement a quality assurance program that can be used by the contractors, bridge owners and the state to detect and make a correction to any defects and design errors. Such a program should be engaged to ensure that all errors are identified and eliminated before the final structures can be made (Bijen, 2003.p.125-130). Subsequently, I would recommend that all bridges to be constructed in the future be assessed for the types of trusses kept in the inventories by the owners before they can be put to use in construction. It is on record that the bridge collapsed and it is quite sure that had the gussets been checked properly, and the right calculations made the appropriate sizes would have been used in the construction. I would also recommend that construction load materials deposits on the bridges unfinished and finished be reduced as the same would lower the load weight to the bridge especially if the bridge is of truss. Reference List BIJEN, J. (2003). Durability of engineering structures: design, repair and maintenance. Boca Raton, Fla. [u.a.], CRC Press. CRONN-MILLS, K. (2009). Collapse!: the science of structural engineering failures. Mankoto, MN, Compass Point Books. DELATTE, N. J. (2009). Beyond failure: forensic case studies for civil engineers. Reston, Va, ASCE Press. EBLING, G. (2012). Collapsed: A survivors climb from the wreckage of the Interstate 35W Bridge. Minneapolis, MN, Two Harbors Press. INTERNATIONAL SYMPOSIUM ON TRANSPORTATION NETWORK RELIABILITY, LEVINSON, D. M., LIU, H. X., & BELL, M. (2012). Network reliability in practice selected papers from the Fourth International Symposium on Transportation Network Reliability. New York, Springer Science+Business Media, LLC. http://dx.doi.org/10.1007/978-1-4614-0947-2. LEMAÎTRE, J., & DESMORAT, R. (2005). Engineering damage mechanics ductile, creep, fatigue and brittle failures. Berlin, Springer. http://public.eblib.com/EBLPublic/PublicView.do?ptiID=303940. LEPATNER, B. B. (2010). Too big to fall Americas failing infrastructure and the way forward. New York, Foster Pub. http://site.ebrary.com/id/10425225. MACALEVEY, N. F. (2010). Structural engineering failures: lessons for design. S.l, s.n. MARANIAN, P. (2010). Reducing brittle and fatigue failures in steel structures. Reston, Va, American Society of Civil Engineers. MARKOW, M. J., & HYMAN, W. A. (2009). Bridge management systems for transportation agency decision making. Washington, D.C., Transportation Research Board. NUNNALLY, P. (2011). The city, the river, the bridge: before and after the Minneapolis bridge collapse. Minneapolis, University of Minnesota Press. RAMACHANDRAN, V. (2005). Failure analysis of engineering structures methodology and case histories. Materials Park, OH, ASM International. http://www.books24x7.com/marc.asp?bookid=42641. RATAY, R. T. (2010). Forensic structural engineering handbook. New York, McGraw-Hill. http://www.accessengineeringlibrary.com/html/viewbookdetails.asp?catid=C&bookid=2001a27e. SENAUTH, F. (2007). The collapse of the I-35W Mississippi River Bridge: victims of the dark. Denver, Colo, Outskirts Press, Inc. STRUCTURES CONGRESS, & GRIFFIS, L. G. (2009). Dont mess with structural engineers expanding our role : [Proceedings of the 2009 Structures Congress : April 30-May 2, 2009, Austin, Texas. Reston, VA, American Society of Civil Engineers. http://ascelibrary.aip.org/dbt/dbt.jsp?KEY=ASCECP&Volume=341&Issue=41031. Read More