Tokyo Metropolitan University researchers conducted a detailed simulation of how a popular type of bridge falls during large-scale earthquakes. They examined the step-by-step method by which "I-shaped girder" bridges buckle and deform under lateral stresses, beginning at the ends.
Reinforcing ribs have been demonstrated to be effective against lateral forces and to improve load-bearing capacity. Their research directs bridge engineers toward rational design solutions for more resilient infrastructure.
Major earthquakes can be catastrophic to infrastructure. The consequences of a severely damaged bridge, for example, extend beyond the tragedy that occurs on it to how the loss of access impacts emergency services, evacuation operations, and the transport of critical supplies.
Understanding how seismic activity affects typical bridge structures is therefore critical, not only for building robust quake-resistant bridges but also for preventing the breakdown of existing ones by appropriate reinforcing. Though computer models exist to assess the durability of bridge superstructures, there are few examples that examine how each component of the entire bridge structure responds during large-scale earthquakes.
A team led by Tokyo Metropolitan University's Professor Jun Murakoshi has been exploring precise models that correctly reflect the real behaviour of complete structures, with an emphasis on how they might inform new design ideas.
They investigated the failure process and the impact on load-bearing capacity caused by lateral shaking of an "I-shaped girder" bridge, a common bridge type with a span length of 30m; supported steel girders shaped to resemble a capital "I" carry a flat "deck slab" over which cars and people can pass.
They subjected their model bridge to the lateral forces experienced during earthquakes, taking into account the response when the force was delivered to the girders in the longitudinal and transverse orientations.
The model provided a precise representation of how the bridge gives and deforms. When applied in the transverse direction, for example, the lower section of the vertical stiffeners on the support was the first to be impacted, followed by the yielding of the diagonal members of the end cross frame.
The vertical stiffeners continue to yield until the gusset plate (a steel plate that links the lateral members) begins to deform. Though this does not result in bridge failure, there have already been reports of deformations obstructing the passage of rescue vehicles following large-scale earthquakes.
The challenge now is how we can avoid this from happening in the future. The team then investigated the impact of reinforcing ribs on the structure: a model with reinforcing ribs demonstrated how stress acting on the girders and the end cross frame connecting them may be decreased.
As a result, the team's work provides rational insight into how bridge structures might be constructed and reinforced to make our infrastructure safer, as well as improved ways for assessing their safety.
( With inputs from ANI )
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