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Running head: STRUCTURAL FAILURE OF PALAU BRIDGE Structural Failure of Palau Bridge Structural Failure of Palau Bridge Palau Bridge is located in Singapore. The Bridge provided a link between two major islands in Singapore, Koror and Babelthuap Islands. The latter connects to the country’s airport and holds close to 70% of the total population of the country (Nunnally, 2011). Palau Bridge 1 STRUCTURAL FAILURE OF PALAU BRIDGE collapsed primarily owing to poor architectural design. Constructed in 1977, the bridge collapsed in 1996, after approximately 20 years of operation. The original design was symmetric, where each side comprised a main pier with cantilevers extending over the water and meeting at the centre. The main pier provided the horizontal support while the end piers maintained the vertical positioning of the bridge. After the completion of the bridge, it remained subserviced for a period of 18 years. As a result, it experienced shrinkage and prestress loss of the levers, which led to the eventual collapse of the Bridge. The collapse occurred towards the side that is close to Koror Island. Evidently, the bridge’s collapse was mainly because of human error. According to Nunnally (2011), the cantilevers deflected owing to shrinkage and reduced prestress. Importantly, the sag of the centre line of the bridge intensified to 1.2m towards 1990. Therefore, the bridge’s appearance changed noticeably, which caused uneasiness to its users. It also prompted some users to seek other means of transport. The turn of events prompted the government of Palau to commission the assessment of the safety of the bridge. A group of two construction experts involved in the study maintained that the Bridge was in good condition for use. However, the duo warned the government over another 0.9m deflection of the central part in the next hundred years. Yet, the tips of the centre levers came into contact within some few months, which induced increased stress on the bridge. As a result, the remediation works committee designed a strategy to correct the sag and prevent further deflection. The committee accepted a proposal by the VSL International Company to repair the bridge. However, the committee called for the correction of the bridge by local civil engineers. The contracted engineers removed the central hinge and added eight external post-tensioned prestressing cables beneath the top slab and the deviator beams on either side of the bridge. The strong anchorage intended to reduce the deflection by 0.3m. The beams, 2 STRUCTURAL FAILURE OF PALAU BRIDGE however, could not eliminate all the sag and the continuous wearing off the upper layer of the bridge owing to the heavy weight it was carrying. The bridge eventually collapsed in 1996, which led to its redesign and reconstruction. Burgoyne & Scantlebury (2008) outline several reasons that led to the failure to control or prevent the destruction of the Palau Bridge. According to the duo, the area experienced high humidity, which facilitated the carbonation of the concrete. Further, the area experienced very heavy summer rainfalls, which combined with the industrial pollutants, especially carbon dioxide producing the carbonic acid, which continuously eroded the concrete. Any attempt by the civil engineers to maintain the thickness of the main pier was futile. Consequently, the high salinity of the seawaters provided sufficient media for the reaction, which limited the chances of preventing the collapse. Additionally, the poor quality of grout specifications coupled with high water/cement content and few admixtures contributed to the collapse of the Palau Bridge. The bridge experienced high evaporation and shrinkage rates, which created voids within the ducts. Besides, some grouts generated excess heat, hardened prematurely, and eventually prevented the flow of grout into the ducts upon the addition of fresh cement. The situation led to the development of joints in segmental construction, which reduced the anchorage strength of the bridge (Burgoyne & Scantlebury, 2008). Notably, most of the architectural experts involved in the construction of the Palau Bridge possessed limited knowledge and experience on the process of grouting and bridge construction. Moreover, the lack of supervision by experts of the progress of the bridge contributed greatly to the collapse of the bridge. Further, several people in charge of constructing and servicing the bridge contributed to the collapse of the Palau Bridge. However, the 3 STRUCTURAL FAILURE OF PALAU BRIDGE architectural experts, who designed and drew the plan for the Palau Bridge, are the first group of the people responsible for the collapse of the bridge for proposing the wrong design. Secondly, the two expert groups that reviewed the condition of the Palau Bridge, when it showed post tension signs of sagging and recommended that the Bridge could serve another 100 years, should also account for providing the wrong information. In addition, the committee reviewing the repair of the bridge should be responsible for recommending lowly experienced civil engineers to handle the repair works (Åkesson, 2008). Without doubt, the collapse of Palau Bridge was preventable. Indeed, understanding the topographical characteristics of the region and the expertise required for the construction would have prevented the collapse of the bridge. The design and construction of a bridge essentially determine its longevity. In this regard, structural renovations only maintain the strong foundation of the bridge. Given the opportunity, I would have prevented the collapse of Palau Bridge by involving the best experts in civil engineering in the construction process. Further, I would have maintained continuous servicing of the bridge to limit the chances to grouting. In addition, I would have incorporated a committee of experts in the continuous management of the bridge to prevent unnoticed changes or defects on the bridge. 4 STRUCTURAL FAILURE OF PALAU BRIDGE Figure 1: The structure of Palau Bridge before collapse (Åkesson, 2008). Figure 2: Structure of the Palau Bridge after collapse (Åkesson, 2008) References Åkesson, B. (2008). Understanding bridge collapses. London: Taylor & Francis. Burgoyne, C., & Scantlebury, R. (2008). Lessons learned from the bridge collapse in Palau. Proceedings of the ICE - Civil Engineering, 161(55), 28-34. 5 STRUCTURAL FAILURE OF PALAU BRIDGE Nunnally, P. (2011). The city, the river, the bridge: Before and after the Minneapolis bridge collapse. Minneapolis: University of Minnesota Press. 6 RUNNING HEAD: ENGINEERING 1 Engineering Failure of bridges is one of the most devastating incidents as it leads to injury, loss of life and property. Failures always result from careless mistakes, which the engineers fail to recognize or neglect. Old bridges often collapse due to the flaws in the in the building materials or incorrect assessment of the stability of the bridges. However, the failure of the new bridges is due to the ENGINEERING 2 complicated construction methods and negligence of minor aspects. One of the recent and famous structural failures of bridges was the collapse of the Maumee River Bridge in Toledo, Ohio on 16th February 2004 (Kassabian, McCall, Dusenberry, & Konicki, 2011). The length of the largest span of the bridge is 167 feet, while the total length is 846.2 feet. The width of the deck is 23.6 feet and the length of the vertical clearance above the deck is 15 feet. After completion, the cable-stayed concrete bridge expects to carry six lanes of interstate 280, with an average traffic on the bridge per day as 10,890. The disaster occurred due to the collapse of one of the two identical launching gantries, utilized for the parallel construction of the approach viaducts for the bridge. The accident resulted in the death of four workers and the injury of four others. Each gantry had two overhead trusses and box girders under bridge made of steel. The engineers involved in the construction spanned the trusses between contiguous piers and strengthened the pre-cast concrete segments for the purpose of post tensioning. After the post tensioning of the concrete span, the forward movement of the trusses across the new span and the underbridge advanced before the consequent span (Kassabian, McCall, Dusenberry, & Konicki, 2011). The process repeated throughout the construction. From the review of the two launching gantries and the records, it was evident that certain modifications took place to the procedure and magnitude of grounding the gantries to the newly completed bridge. The failure of the bridge was due to the failure of the engineers to install the pre-stressed rods at the stools, which support the legs of the trusses of the gantry at the back. In other words, there was no sufficient resistance to movement upon the reversal of the under bridge backwards into the pier. Another major reason for the failure of the bridge was the improper use of the launching gantry by the Fru-Con construction company. The sole responsibility of the failure of ENGINEERING 3 the bridge is due to the negligence of the engineers of the construction company who failed to anchor the tail properly, in spite of the instructions to anchor the legs with threaded bars after pre-stressing to 135,000 lb. As a result of the failure of the bridge, the construction company had to pay $280,000 towards penalties as announced by the federal government (Clark, 2005). The Occupational Safety and Health Administration took serious measures upon the failure of the bridge as it resulted in deaths and serious injuries. The construction company denied mentioning the cause for the collapse of the bridge, but the officials assumed that there were multiple causes for the structural failure of the bridge. It is important to understand that a majority of structural failures of bridges arise due to false assumptions, poor supervision, material defects, instability and disregard of fatigue rather than calculation errors. The reasons for the collapse of the bridge might be one of those mentioned above. Due to the failure of the bridge, the officials had to detour the traffic through other possible routes, which caused inconvenience to the general public. Most of the traffic was dependent on the Craig Memorial Bridge due to which there was an increase in the load of the bridge (Kassabian, McCall, Dusenberry, & Konicki, 2011). In spite of the collapse of the bridge, the engineers of the construction company promised to complete the construction of the bridge on schedule. One of the best approaches that I would suggest in order to prevent the bridge failure is to dismantle the launching gantry and no longer use it in the construction. I would also develop a simple and distinct means to complete the construction of the approach span, such as constructing the pylon and producing segments at the casting yard. The bridge collapse would not have happened had the company taken care to secure the truss properly before the collapse. I would also suggest an independent consultant for the bridge project who would review the ENGINEERING 4 construction at every stage instead of the construction company taking the entire responsibility of the project (Clark, 2005). I would also recommend a review committee that examines the construction at each phase and makes sure that the construction is carrying out according to the plan and the budget. I would recommend the implementation of new systems, designs, manufacturing methods and materials in the construction of bridges to ensure a safe and accurate structure. The engineers responsible for the construction should gain adequate mastery in the span lengths, widths and loads. All the participants involved in the construction should take great care of the work to avoid accidents caused by negligence or minor mistakes, which cause huge losses in terms of both people and property. The hydraulic press is another issue, which the engineers should consider during the construction of the bridge as it is one of the major causes of bridge collapses (Scheer, 2011). Engineers should also take the responsibility of paying attention to instability, which is one of the frequent incidences of failure, especially in truss bridges. Cantilever break off during erection is another crucial issue that requires care in the case of prestressed concrete bridges. Thus, following the instructions carefully according to the plan and the budget would prevent a majority of bridge failures. Fig: Maumee River Bridge before Collapse ENGINEERING 5 Fig: Maumee River Bridge after Collapse ENGINEERING References Clark, S. (2005). OSHA Settles with Ohio Bridge Builder. Laborer's Health and Safety Fund of North America . Kassabian, P., McCall, M., Dusenberry, D., & Konicki, W. (2011). Collapse of the I-280 Maumee River Bridge Launching Gantry in Toledo, Ohio. Structures Congress 2011 , 1570-1582. Scheer, J. (2011). Failed Bridges: Case Studies, Causes and Consequences. Hannover: John Wiley & Sons. 6
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