The arch bridge is one of the oldest forms of bridge and was used by the Romans and throughout the middle ages. This tutorial will show you how to make a type of arch bridge called a hump back bridge out of card.
Draw the plan of the bridge on graph paper, mine is 28cm wide by 4cm and the diameter of the arch is 11cm and the bridge height 7cm.
For the bottom of the arch draw a rectangle 6cm high to calculate the width we will need to do some maths using pi.
Width = (π x diameter of the arch) / 2
Width = (3.14159265359 x 11) / 2 = 17.3cm
Mark lines 1cm up from the top and bottom and divide into 5mm sections, these will become tags to affix the arch bottom to the bridge arch.
For the bridge deck sections draw two more rectangles 6cm by 15cm and draw lines 11mm from the top and bottom and divide into 5mm tags.
Using the tracing paper transpose the plan of the four bridge sections onto the card by reversing the tracing and drawing on the opposite side.
With a craft knife cut out the sections of the bridge, lightly score the fold lines and cut and fold the tags on the bridge deck sections and arch base.
Spread a line of PVA glue around the edge of the arch and press the tags of the arch bottom section so that the tags are glued to the outside of the bridge, this will give a stone effect.
Repeat with the other side of the arch and leave to dry.
Glue the bridge deck sections to the inside of the bride with the tags upwards. Allow the deck to form a natural curve. Join the deck in the middle with masking tape. Trim the deck at both ends if too long and leave to dry.
Mix a small amount of Pollyfilla to a smooth consistency and apply to the bridge using a glue spreader and leave to dry for a few hours.
Mix the black and white acrylic paint to make a dark grey and paint the bridge.
Mix a lighter shade of grey and apply a small amount to the paint brush, lightly dust the bridge and create a mid-tone over the dark grey.
Now dip the brush in white paint and wipe the brush on some tissue then lightly dry brush the bridge so that it defines the texture of the bridge. This will create a stone effect.Keywords: model bridge, arch, stone, hump back bridge