BRIDGE FAILURE CAUSES IN EXTREME FLOOD EVENTS

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 5, September-October 2016, pp , Article ID: IJCIET_07_05_023 Available online at ISSN Print: and ISSN Online: IAEME Publication BRIDGE FAILURE CAUSES IN EXTREME FLOOD EVENTS Azmat Hussain Department of Civil Engineering, Kurukshetra University, Haryana. Sumaira Jan Department of Civil Engineering, Bagwant University, Ajmer. ABSTRACT Bridges are important in modern world. Bridges add beauty to the roads. Bridge failures are one of the most infrastructure problems in the world. It often leads to the catastrophic consequences, loss of life, restricted commerce. Whenever there is a disaster there is loss of lives, damage to the public property. Road networks acts as viens. Without roads everything will come to halt. Therefore roads and bridges are to be maintained properly to keep them functional. The damage to the bridges will cost more and their rehabilitation will cost even more. Therefore to avoid such loss of money and lives, proper inspection for the bridges is necessary. Further we need to analyze the causes of the failure and need to overcome those causes so that in future we are prepared to save our infrastructure. Key words: Cause of failure of bridges, health monitoring, fault tree analysis. Cite this Article: Azmat Hussain and Sumaira Jan, Bridge Failure Causes in Extreme Flood Events. International Journal of Civil Engineering and Technology, 7(5), 2016, pp INTRODUCTION Engineers have studied many bridge failures, seeking the lessons from these failures, hoping to avoid the future demise and avoid costly repairs in the future. Proper inspection and necessary maintenance is necessary for the bridges to keep them functional. Apart from this, engineers accept that there are certain factors which cause distress to the structure over the years. Yet with the passage of the time, deterioration sets in the structure and finally when such a bridge faces natural disaster such as tsunami or floods, the bridge fails. Even though the structure may be designed and constructed to specifications, deterioration can set in or damages can occur during the service. By applying the failure theories and introducing preventive methods, the life of the structure can be increased by studying the reasons for failures and developing the methodology to minimize them. Also the practice of regular and periodic inspection is must.now days, there is less need for the engineers to go to the site and inspect the bridges on the site. Much software has been developed to detect the damages in the bridges. To some extent engineers can inspect the bridges using modern and advanced tools without going to the site. One of the tools is image processing which is now used for the health monitoring of the structures. The research paper published by Azmat Hussain, Sabah Bashir and Saima Maqbool on image processing in bridges clearly editor@iaeme.com

2 Azmat Hussain and Sumaira Jan indicated that these modernized tools can help a maintenance engineer a lot to monitor the bridges without personally going at the site. The American Highways have prescribed three types of inspection, viz.visual, routine and mechanical with appropriate machines. They have specified intervals at which these inspections are to be carried out depending upon the types of the structures. The inspections are being carried out in accordance with the manuals issued by the AASTHO for guidance of the inspectors. After detailed inspection, rating is done for each part of the structure and the grading is made as follows Good Rating 8 and 9 Element is new or in good condition with no repairs necessary Fair Rating 5,6 or 7 Element has minor or major defects Poor Rating 3 or 4 Element has potential for major rehabilitation or the element requires immediate repair. Critical Rating 0-2 Element has failed to perform the function intended for and is of critical nature that such a bridge should be closed and immediate repairs undertaken. Table 1 2. ROOT CAUSE OF THE FAILURE OF BRIDGES Engineering is usually avoiding failures and investigating why failures occur and ways to fix the problem. There is need to understand the reasons of the past failures and the ways to avoid such failures. The physical cause such as erosion, reversal of the stresses, impact, vibration, wind and extreme events are usually increasing the threat to the structutres. Usually it is a combination of the dead load stresses combined with one or more external transient forces resulting in a combined critical stresses.if dead load stress is already high and approaching the elastic limit of the member, any applied force or stress will exceed the allowable limit and will lead to the failure. The root cause for the purpose of the study as errors in designing, constructing, lack of proper maintenance, inspection or the insufficient consideration of an extreme event. Perhaps the extreme events like tsunami, floods hardly struck in the mind of an engineer. As we analyzed the bridges which fail during September 2014 floods in Jammu and Kashmir region, they failed due to negligence in inspection and proper maintenance and lack of proper designing. The bridges which failed during floods are studied and their cause of the failure is: Old Bridge Failures: Often we see these failures occur due to disintegration of the material over the period of time. Failure of New Bridges: These failures are few but occur due to design errors, construction problem or due lack of periodic maintenance or regular inspection. Design Deficiency: Due to design deficiency the newly constructed bridges can fail. Such an example in newly build prestressed concrete bridge which collapsed in Karachi in editor@iaeme.com

3 Bridge Failure Causes in Extreme Flood Events Failures after Construction: These failures occur after the construction, due to lack of the proper maintenance. Many times the designers and construction engineers are not responsible for the failure but the public is also responsible for these hazards. No engineer would like to face difficulty after constructing a structure. But in Kashmir an engineer is helpless before the Government and public. As such an example of the bridge is located at Chadoora called Chadoora bridge in J and K where the linear waterway of the bridge was considerably reduced leading to the scour failure of the bridge during September 2014 floods. 3. ENABLING CAUSE OF THE FAILURE Enabling cause can be defined as that cause that can be identified as internal weakness or deficiencies that can lead to the failure of the bridges. The design defects, construction faults, maintenance problems which can lead to the failure of the structure. Better design, careful construction and proper maintenance can decrease the enabling cause. Enabling cause may or may not the same as the root cause but it can make the conditions that can lead to the failure. 4. TRIGGERING CAUSE OF THE FAILURE These are often related to the external events such as tsunami, flooding, earthquakes etc.triggering cause can be disastrous if the enabling cause or root cause are not overcome. Such bridges which are structurally deficient like they have design deficiency, lack of proper maintenance and material also, them the triggering cause can be disastrous. An example of the triggering cause of the failure is indicated in below figure. Figure 1 The above figure clearly indicates how scouring of the abutments are taking place leading to the failure of the bridges. Due to lack of proper river training works and due to construction faults these failures often occur. The figure clearly shows that there are no proper guide banks or any other river training work across the stream which can protect the bridge and can protect the breaching of the water during floods. The triggering causes are harder to predict and sometimes engineers can t do anything but only to watch how structure will fail. The triggering causes which are investigated in this study are hydraulic and that cause which could not save the bridges during floods. The basic or principal cause of the failure is the basic cause. Enabling and triggering causes are the only means of the failure. If a bridge is properly designed and properly maintained, then enabling and triggering causes will be low or will be zero. In enabling or triggering causes, the failures can be total or partial. Total collapse or total failure means when bridge is unserviceable to the traffic and needs editor@iaeme.com

4 Azmat Hussain and Sumaira Jan replacement. Thereby leading to huge loss of the money. An example of the total collapse of the bridge is depicted in below picture Figure 2 The above picture clearly tells us that the bridge is completely damaged and is unserviceable to traffic. This bridge needs to rebuild completely in order to restore the traffic again. The bridge is 150 metre long. This bridge is located at Roomshi Nallah of Pulwama district and the discharge recorded on 9 September 2014 was 3882 (Q) cusecs. Partial collapse means there is only need to retrofit or repairmen of the bridge. Not much amount of the money is wasted and the bridge can be used within short span of the time. An example of this type of failure can be shown in below figure. Figure 3 In the above figure it is clearly seen that there is only need to retrofit the bridge. There is no need for the replacement of the bridge. The foundation of the bridge is safe, only the girders are washed away in floods. So, this bridge can be build quickly to restore the traffic. A fault tree method which is shown in this context will offer the level of damage to the structure and allow the identification of the probability of the bridge closure at given intensity of an extreme event. This will also help to understand the damage assessment to the bridges in floods editor@iaeme.com

5 Bridge Failure Causes in Extreme Flood Events Bridge failure Damage to superstructure Damage to substructure Beam Approaches Deck Surface Pier or column Abutment or girder Time effects or Aging Induced by extreme events Overload Unseating Flood loading Debris impact Damage to the bearings Bearing missing Movement of Bearings Fault Tree Analysis

6 Azmat Hussain and Sumaira Jan 5. CONCLUSION There are many causes of the failure of the bridges and all are dangerous. If the proper study is not conducted to analyze the past failures, future can t be saved. In future we again have to waste huge money to rehabilitate the bridge. So, by studying past failures, future planning can be done with some best techniques. REFERENCE [1] Ichiro Ario, Yuki Chikahiro: A New Type of Bridge, Mobile bridge to Super-Quickly Recover a Bridge. [2] Yogen Sadashiv Masurkar, Abdul Rashid Chand Attar: Investigating the Causes for Failures in Construction by Taking a Case Study. [3] Dr. Abdul-Hassan K. Al-Shukur and Zaid Hadi Obeid, Experimental Study of Bridge Pier Shape to Minimize Local Scour. International Journal of Civil Engineering and Technology (IJCIET), 7(1), 2016, pp [4] Azmat Hussain, Sabah Bashir, Saima Maqbool: Damage detection in bridges using image processing. [5] Johnson Victor: Essentials of bridge engineering. [6] Dr. K.V. Ramana Reddy, Aerodynamic Stability of a Cable Stayed Bridge. International Journal of Civil Engineering and Technology (IJCIET), 5(5), 2014, pp [7] Punnoswamy: Bridge Engineering. [8] Wesley Cook: Bridge failure rates, consequences and predictive trends editor@iaeme.com