The Bridge on the River Phairuang : a Model Built With Paper

Making a model of the Suspension Bridge on the River Phairuang has been on my mind for a very long time, but due to some reason or other I have been postponing the idea. It is almost 33 years since we constructed that Bridge, and now only I get to make the model in paper.

Though it may be not be that much interesting to all, I feel that this Instructable will be incomplete without a brief history and specifications of the original bridge.

Step 1: The "Not So Interesting" Part : History and Specifications of the Bridge

Phairuang River is situated in Lungleh district of Mizoram, India. Though the normal water level remains at 2 to 3 feet, it rises to more than 60 feet during heavy rains. Prior to construction of this bridge, all the villages located across this river remained cut-off most of the time during the lengthy monsoon (from April to October). Construction of the semi-permanent bridge started during 1969-70 but without any considerable progress due to so many unfavorable conditions: the main factor being the bridge site is located about 400 kilometers away from Silchar in Assam, the nearest Rail head. In those days only a single lane road through Aizawl and Lungleh connected Phairuang and it took three days to reach the site.

During 1977, I was asked to take over the charge of the Bridge site. The remaining concrete works and protective / river training works were completed by 1978. We planned to launch the superstructure before the monsoon and we got only 5 months for this (from November 1978 to March 1979). Stretching the schedule beyond March would be dangerous as heavy floods would wash away the scaffolding and other supporting structures. More than one thousand people were engaged for the task. A temporary platform with local timber was erected covering the entire span of the bridge and we constructed the superstructure with the help of whatever equipment available to us.

Here is an old photograph of the Bridge  taken by me on March 1979, after commissioning for traffic. You can also see my name on the Bridge in the second photograph. We named it as "Ranjit Bridge" in memory of a worker died during construction.

I also came across a recent photograph of the Bridge taken during 2010 by one Mr. Malsawma Chhangte, from the link below:

http://www.panoramio.com/photo/45213198

Specifications of the Bridge :

• Total length of the Bridge : 270 feet
• Spans : Three spans of 90 feet each
• Type : Stiffened Girder suspension Bridge
• Designed by : Garden Reach Shipbuilders & Engineers Ltd, Kolkata, India
• Total Steel used : About 200 metric ton

Let us start building the Bridge with paper to the scale of 1 inch = 10 feet

Step 2: Materials and Tools

Tools Required

• A steel ruler
• Craft knife
• Pencil
• Eraser
• Scissors
• Fine tweezers

And for applying glue in very small quantities, I have used a piece of coconut leaf stem

Materials required

• 5 pieces of A4 sized matte art paper used in Inkjet printers
• Fevicol synthetic resin adhesive or Gorilla wood glue

Step 3: The Bridge Parts

The main bridge parts required for the span are as below. I have given a brief description for easy understanding of the parts. Please refer to the photos also for the part names

• Cross girders : The main load bearing members laid perpendicular to the center line of bridge
• Stringers : five of them connect cross girders and forms a bay
• Bottom diagonal bracings : Used diagonally at the bottom of cross girders
• Bottom chords : used at the ends of cross girders through out the length of bridge
• Vertical chords : Vertical members erected at the ends of cross girders
• Diagonal chords : Diagonal members connecting the top of top chords with ends of cross girders and bottom chord
• Top chords : connects the top of all vertical chords and diagonals

I have drawn all these parts (other than bottom and top chords) in matte paper to the scale of 1 inch = 10 feet, cut them to size and stored separately in a cookie container. Bottom chords and top chords can be made as a single piece on each side of the span.

Step 4: Constructing the Spans

Each of the three spans can be constructed separately and joined together later. Here I have constructed the bays with cross girders and stringers

• Attach two cross girders with a stringer with glue and keep them separately for curing
• After the glue dries up, join the cross girders with stringers to form one span
• Add all the stringers to each bay with glue and allow them to dry
• Use a thin wooden stick like the stem from the coconut leaf to apply the glue in small quantities
• A pair of tweezers helps in adding the parts to the exact location
• After completing the stringers you can add the bottom chords at both sides of the span. I have used a single piece of paper cut to the correct size for the entire span on both sides.

Now all three spans are completed with cross girders, stringers and bottom chords

Step 5: Add Bottom Bracings

To add the bottom diagonal bracings, turn over entire span upside down. Using little amount of glue, fix the bottom bracings with the cross girders as shown. Allow the glue to completely cure

Step 6: Add Vertical, Diagonal and Top Chords

• After the glue used for fixing bottom bracings dries up, the span can be turned over to its normal position
• Attach the verticals on both ends of the cross girders as shown
• Using the tweezers, place the diagonal chords and glue them to bottom and top chords
• A single piece of paper cut to the correct size can be used as top chord on both the sides

All the three spans are now completed and ready for final assembly.

Step 7: Join the End Span and Middle Span

• Place the two completed spans on a piece of press board or any other suitable material
• The two spans need to be connected together with stringers in-between
• Apply glue and attach the stringers using the tweezers

Step 8: Towers

Here, I have drawn the towers to scale and cut to the required shape using a craft knife. We need two towers, one on each end. However, as the paper can not withstand the load, I have made four pieces and glued two of them together to form one single tower.

The towers can be attached to the end spans as shown in the picture.

Step 9: Piers

Both the ends of the end spans and towers rest on concrete piers. Here I have cut the shape of pier to scale and glued the sides around with paper. The completed piers can be attached to the sides of any firm support like the piece of press board I have used here

Step 10: Anchor Blocks

Anchor blocks of heavy mass concrete are used to anchor the suspension cables firmly at both ends.

• Mark the position of anchor blocks with reference to the spans and towers
• Roughly measure the angle of the ropes from bottom to the top of towers
• With reference to this angle, draw the sketch of the anchor block to scale
• We need to make only the portion of the anchor blocks above ground level
• here, I have cut the shape of the anchor blocks. folded and glued together to form the anchor blocks
• Mark the position of anchor blocks behind the piers on the press board
• Apply glue and fix the blocks to the support

Step 11: Suspension

Initially, I thought of making the suspension cables from paracord strands or cotton thread, but when I tested those materials, they formed a visible sag. So, I have used the same matte paper for the ropes also. here you can see the ropes made with from the paper.

• Measure the distance from top of tower to position where the cables will be joined.
• Trim the paper pieces to the required length
• Attach the suspension ropes to the top of tower towards the span with glue
• After the glue dries up, attach the cables to the span
• Make thin slots in the face of the anchor blocks and glue the cables
• After drying, attach these cables to the top of tower

When attaching the suspension cables, I found that the paper tower is not able to withstand the downward pressure. So  I glued some additional support to the towers

Step 12: Decking and Hand Rails

We need to add the decking and hand rails to the bridge. I have used a single piece of paper for each span separately and drawn the same to scale. After cutting and removing the unwanted portion, the hand rails can be folded upwards to 90⁰ and glued. There is no need to fix the decking permanently to the span.

Step 13: Mount on a Base and Complete the Bridge

Now our bridge is completed in all respects. We need to mount the whole bridge to a firm base. I have used a suitable piece of press board and glued both the end pieces to the base

Step 14: The Completed Model of the Bridge

This is the completed model of the bridge in paper, which I displayed over the small garden fish pond I constructed earlier. It took me about a month to recollect and design the bridge from my memory which I have constructed 33 years ago. I was just 24 years old when I completed the bridge over River Phairuang...

Your comments and suggestions are most welcome