World is witness to the dynamism in frequency and severity of natural hazards, leading to their dynamic occurrences. Previously defined as “Once in a hundred years event” have changed to “Once in few years event”. The upward trends in severity challenge conventional engineering designs. As societies confront escalating dynamism of natural hazards, the importance of resilience has surged. Resilience is the most conspicuous introduction to the vocabulary of decision-makers across the World. In India too, we are mute witness to this emergence of dynamism.
Aging Bridges: A Growing Concern
In India, like the world over, bridge demography indicates forty-five percent of bridge population is aging. These aging bridges experience severe levels of deterioration, leading to reduction in strength of bridge elements. Strength reduction leads to failure of Bridge structure. Seventy percent of aging bridges face this grim situation. Normally, designed bridges withstand the forces of natural hazards. Strength reduction induced due to deterioration drastically alters this scenario. Dynamism of natural hazards complicates the grimness. Together this creates an ideal recipe for an increment in the probability of bridge collapses.
The Vital Role of Bridges in Society
Today, Bridges are not mere physical structures; they are vital conduits bolstering connectivity, trade, and regional development. The contribution of bridges to regional growth, stability and security is understood well. This aspect of bridges makes it essential to enhance bridges’ resilience and sustainability. The importance of resilient bridges cannot be overstated. Resilience in bridges has multifaceted significance.
Understanding Resilience in Bridge Engineering
Federal Highways [USA] defines resilience as and we QUOTE “Resilience is the ability to anticipate, prepare for and adapt to changing conditions and withstand, respond to, and recover rapidly from disruptions.”
Having an understanding of this, the next question that pops in our mind is: What is being done in India by Bridge engineers on this front?
Researchers from India have consistently contributed majorly to the global efforts to bring newer technologies within the Bridge management system [BMS]. They successfully evolved the world’s first digital bridge management system. This Indian Bridge Management System went on to become the largest database of data for over 172,000 bridge structures. Every bridge collapse resulted in newer goals and changes. The integration of high-end innovative technologies within BMS was the next step.
Collapse of Morbi bridge resulting in the tragic death of over hundred people, forced the research focus to create a cost-effective and easy to use BMS. Every gram panchayat, micro or mega Municipalities, regional authorities should afford implementation of bridge management to avoid collapse and resulting deaths. Their research yielded the most cost-effective BMS.
Addressing the Dynamism of Natural Hazards
Present day challenges needed a solution for the dynamism of natural hazards occurrences and the consequent damage due to their occurrences. On the global front, United Nations office of Disaster Risk Reduction [UNDRR] under Sendai Framework for Voluntary Commitments [SFVC] made strides to ensure that every citizen of the world will have adequate warning about impending hazards. To address the needs of bridges, our own Indian Researchers made an ambitious not for profit commitment to SFVC to evolve a “Tool that could identify/ anticipate the response of the aging, deteriorated bridges to the forces of natural hazards”. This commitment given to the United Nations office of Disaster Risk Reduction under the Sendai Framework for Voluntary Commitment has now culminated. Conclusions of research aids integration of resilience and risk assessment, leading to resilience management of bridges. Probably for the first time, our scientists and researchers have delivered a Global solution to resolve the issue of resilience management of bridges.
Research focused on the “ANTICIPATE” aspects of the definition of Resilience, to identify/ anticipate the response of bridges to natural hazards. Aging bridges face the uncertainty of survival post occurrence of natural hazards. Earthquakes, Flooding, Cyclone, and Landslides are the Natural hazards that cause maximum impact, together or singularly, posing significant threats to bridge infrastructure, leading at times to catastrophic collapse. Worldwide, these four hazards caused the maximum number of bridge collapses.
Again the question persists:
What is Being Done in India by Bridge Engineers on This Front?
How Does This Research Bring Clarity to Our Understanding of the Impact of Natural Hazard Occurrence?
The research findings shed light to unveiling the myth relating to bridge collapse, thereby helping to define the boundaries of resilience that any bridge exhibits. Research identifies the principal causes leading to failure of bridge elements due to the four natural hazards. Historical study of previous collapses have identified that Collapse or failure of bridge elements arises from the Shear failure of sub and superstructure, Unseating and overturning of superstructure elements. Typically, failure of one element can lead to cascading effect leading to the collapse of the bridge. Horizontal force is found to cause all three failure modes. The origin of failure emerges from high velocity of flowing water causing scouring and horizontal force on the substructure.
Research helped bridge engineering understanding of the boundaries and factors contributing to these failures. Two boundaries identified being: Average Bridge Structural Rating Number [BSRN], and water flow velocity / magnitude of horizontal force. Velocity being in case of water flow during floods and magnitude of force being during earthquakes. The progressive transgression from stable condition to that of failure occurs, as velocity starts to exceed 15 kmph. The substructure will show signs of moving from being Safe to Marginally Safe, finally transgressing to all three modes of failure mechanism. This occurs when velocity exceeds 20 – 22 kmph. Regarding the boundary for the second factor, namely Avg. BSRN, initiation for failure is witnessed when this increases and exceeds 3.5. The probability of collapse increases sharply when Avg. BSRN exceeds 4.25. Similarly, for Earthquakes above 6.5 on the Richter scale, the response is identical.
Does the Shape of Bridge Elements Affect Resilience and Sustainability?
The answer to this can be summarized by one statement. “Increasing the volume of concrete and reinforcement will result in enhanced resilience”. Robustness is the key to sustainable structure. Our present system of awarding key infrastructure projects on “Design and Construct” impedes and motivates the bidders to compromise on constructing robust structures. Closer scrutiny of this critical policy is essential for bringing the culture of Resilience in our National outlook. Research points that resilience demands are satisfied only when the situations do not force an opposing view. A Pro-active approach is essentially required backed by adequate funding to enhance resilience planning. It is critical for authorities to redefine all criteria of decision-making that force opposite actions.
For the same geometry, the bridge with lower deterioration and strength reduction are probably safe for velocity of flow below 23 kmph / earthquake below 7 on Richter scale. In all rivers originating at elevations above 5000 meters above MSL, water flows from higher elevations, leading to higher normal flow velocity. During Floods and flash flood water can traverse 5 to 7.5 meters per second. This translates to a velocity range from 18 to 25 kms per hour. Such high velocity are dangerous for aging bridges unless immaculate precautions and Proactive approach is adopted to ensure Resilience. Similar scenario exists for bridges in high seismic zones.
The Urgent Need for Enhanced Strategies
Researchers brought out a very concerning and fearful reality: “The inevitability of bridge collapse”. Most of the bridges constructed in the late 20th century are nearing the end of their designed lifespans and face this reality / situation. Accelerated dynamism in frequency and severity of natural hazards, add fuel to fire. Neglecting aging infrastructure has resulted in a scenario, where the numbers of dilapidated bridge infrastructure is increasing, further heightening the risk of bridge collapse. Adequate funding for proactive enhancement in resilient bridges is essentially required to stop bridges from collapsing.
The research provides a crucial insight into the significance and critical aspect of enhancing the resilience of reinforced concrete bridges. It highlights the urgent need for enhanced strategies to address aging infrastructure. Time lost now to enforce enhanced resilience will result in frequent collapse and increased loss of connectivity resulting in derailment of economic growth and stability.
Aging bridges have very similar geometrical and design parameters. Research also reveals that flood velocity, water height, and earthquake forces are crucial factors affecting bridge survival. Research urges a shift from mono-criterion approaches focused on distress in bridges and advocates for a transition to multi-criteria decision-making processes to address the complexities of resilience effectively.
Addressing this issue requires a multi-faceted approach, which requires proactive allocation of funding for resilience, policy reforms to enforce and prioritize infrastructure resilience. It is a long but indispensable journey.
A Call to Action
The inevitability of bridge collapse is a wake-up call for society. We can prevent catastrophic failures and ensure the safety and reliability of our bridges for future generations. The time to act is not tomorrow, but today.
UN Secretary-General Antonio Guterres recently made a statement which we QUOTE “It is We the Peoples versus the polluters and the profiteers. Together, we can win. But, it is time for leaders to decide whose side they are on. Tomorrow it will be too late. Now is the time to mobilise, now is the time to act, and now is the time to deliver. This is our moment of truth”.
We hope that these research findings will not fall on deaf ears and sway the opinion from short sightedness to a long-term strategy to enforce enhanced resilience in infrastructure.
Authored by;
Sachidanand Joshi, Head- UBMS Research Group (URG)
Atharvi Thorat, Mayuri Tundalwar, Researchers @ UBMS Research Group
Image Sources: CNN, BBC, The Guardian
