The Hindu Business Line : Spans of safety for Oregon bridges

The Oregon rebuilding of bridges is a warning signal for India where a large number of bridges, under the control of the Highways Department and the Railways, are in bad shape and require renovation before it becomes too late.

THE STATE of Oregon, US, has drawn up a massive scheme for the renovation of hundreds of bridges to restore them to their original glory.

The restoration has become a matter of much concern because of alarming reports from national inspection agencies that more than 309 out of a total of 500 spans have revealed cracks, corrosion-based deterioration and telltale signs of fatigue.

The Oregon Transport Department is thus tied up with a huge task of renovation that may take at least a year to complete.

In deciding on priority attention the choice between city-owned bridges and those on hard-pressed Interstate Highways has to be carefully made.

What matters most is the extent of lurking danger to safe passage under the escalating mess of defects and decline in the strength of the structures.

Already, load limitations and curtailment on movements over many of them have raised fears of throwing the State off the economic track.

Hence, the urgency to proceed with the project and facilitate a smooth flow of commercial traffic.

Officials have estimated that the total renewal may cost nearly $3.1 million, not all of which is ready and available for the constructional needs.

Fund raising has assumed even more importance in view of the fact that the target set for full restoration of the last of the bridges remains unaltered.

Planning

Difficulties and delays are the norm in any major project. And so, working out the minute details towards fixing repairs on such a gargantuan scale is no small assignment.

The exercise gets more complicated because no two structures would involve the same pattern of repairs and therefore the recommendations have to be made only on a case-to-case basis.

While major repairs seem to abound, wholesale replacement of one or more spans is also found unavoidable.

The grand plan thus covers strengthening of members only affected slightly, partial replacement of some sections and total replacement of spans.

But the dangerously deplorable condition of those bridges that carry heavier commercial traffic has prompted the idea of building new ones in the place of the old and weakened ones.

But such a decision would turn the planning exercise itself into a lengthy engineering engagement and push the cost of execution to a staggering $700 million.

`Futuristic' is the catchword in all the construction plans and the new look of the overhauled bridges will incorporate features such as wider sidewalks and distinct lanes for bikers, walkers and joggers.

A task force in Oregon is already chalking out the number of activities involved, well set on a programme of handling the enormous number of activities involved, laying particular emphasis on the worst-affected bridges first. The effort which would soon

Harnessing technology

In resolving the logistics for the comprehensive renewal programme, the application of hi-tech ideas plays an important role.

The most common problem threatening the life of bridges, especially on the coastal belt, is corrosion.

To help combat this, experts prescribe a concept called Impressed Current Cathodic Protection (ICCP), which not only protects the bridge from corrosion but also gives it longer life, perhaps even a century.

The method begins with sandblasting every inch of the bridge surface, followed by a zinc rich coating or spray galvanising.

The idea is to nullify the electro-chemical reaction by passing current in the opposite direction, says The Oregonian. A fantastic maze of wires bunched together under the deck forms the main feature of the low-voltage electrical system.

The set-up is rather straightforward in steel fabrications but in RCC (roller-compacted concrete) structures, continuity for current flow would require jointing of reinforcement bars.

Likewise, road-laying by deploying modern equipment guarantees a smooth and level finish that enables heavily-laden trucks to pass without creating undue impact stress.

Aesthetics is combined with sophisticated technology in the renovation proposal of bridges. This departure from functional design to one incorporating state-of-the-art features is likely to set the trend in future constructions.

At this juncture, let us take a look at the scenario in India where almost all bridges are in the control of the National Highways Department or the Railways. Whether they have similar arrangements through national inspection agencies to conduct meticulous examination and report on dangers posed by weakened bridges is not clear.

A survey of the railway system to establish safety hazards will be of a potentially greater magnitude because of the high utilisation factor of its network.

But the large number of bridges built of steel or RCC and the countless culverts on the highways would also call for equal attention to assess deterioration levels.

The Oregon example would surely serve as a warning signal to these government controlled organisations to initiate measures for renovating all bridges before it becomes too late.

(The author, an engineering consultant, is a freelance writer.)