Eco-friendly paper bridge

Load on the bridge is taken up by the manila ropes.  

THE STUDENTS of IIT Madras with the help of their professors, recently constructed the world's longest paper footbridge, as a part of SHAASTRA 2002, the technical festival of IIT-M. The bridge with a total length of 11m and a height of 5 m was made entirely out of 1800 newspapers and 250 m of manila rope.

A cable-shaped bridge system was adopted where the load on the bridge is taken by the ropes. These ropes are supported on top of the towers made of paper and hence transfer the load from the deck to the towers.

The challenge was to build an unconventional and eco-friendly bridge made with old newspapers and ropes. The bridge had 2 towers spaced 5 m apart along its length. About 45 sheets of paper were rolled up tightly to make a cylindrical unit. These units were integrally connected using ropes to form a 5 m long tower.

The towers had to be so constructed that the only forces coming on them were tensile and compressive. The tower was x-braced so that the ropes took tension and the paper units took compression — exploiting each element to its best.

The deck, also made of paper and rope, was parabolic in shape. If it were horizontal, any load acting on it would cause it to sag.

To prevent sagging the deck was given an initial upward curvature.

Before the mass production of rolled paper, work on basic units were started and a column was made and tested for failure.

All units — two towers, twenty-odd deck members — were prefabricated. Everything being ready the construction of the entire bridge right from marking of the site to the time of the last knot was done within seven hours, with nearly 100 students participating at one stage.

The final test was when more than 10 people (average weight of 65 kg) walked over the bridge one at a time with no single unit failing.

This proved beyond doubt the strength of the paper bridge. Engineering of this unique paper bridge was an exhilarating experience and created great enthusiasm at the campus.

Anita Rao

Department of Civil Engineering IIT, Chennai