How to Make Models of a Beam Bridge

Construct the land that the bridge will span with the cardboard sheets. Glue triangular cardboard tabs on the underside of the cardboard sheets to support the landscape model. Use glue sparingly by applying only a thin line or small dots, called tacks, to the cardboard. Too much glue will not set properly and create a model with poor craftsmanship.

Create the land with stacked sheets of cardboard glued sparingly between each sheet of cardboard. Apply pressure from above with your hand, a clamp or a stack of books. This will prevent the cardboard stack from bowing or bending from the wet glue.

Cut the length of one side of the bridge with a craft knife, using wood structural shapes or square dowels to the correct length. Make multiple passes with the craft knife to ensure the cut is clean and precise. If you are creating a truss, determine the truss type. There are many beam bridge trusses you can use, including Warren, Pratt, Howe, truss leg and K-truss structures. Cut the top and bottom truss chords first, then cut the diagonals. Cut the diagonal members accurately to create a stronger truss with high craftsmanship.

Glue the structural shapes or pin the truss chords with straight pins. Push the pins through the top and bottom chords and through the axis of the vertical and diagonal chords. Sparingly glue the intersections of the truss chords. Let one side of the bridge dry for 24 hours.

Cut and glue the second side of the beam bridge. The second side will be the exact mirror image of the first side. Turn over the first side and build the second over the finished, dried side, following the instructions in Steps 1 through 3. Let the second side dry for 24 hours.

Cut lateral members to span between the two completed sides of the bridge. The lateral members can be wood structural shapes, braced frames or small trusses. Account for the desired clear opening between the bridge sides when determining the desired overall dimensions. Cut the members with multiple passes of the craft knife to ensure the cut is precise. If the lateral members are braced frames or trusses, glue the lateral member assemblies together, apart from the completed sides of the bridge. Let the glue dry for 24 hours.

Span and glue the lateral members between the two sides of the beam bridge. Pin the braced frames or trusses to the sides of the bridge. Use the glue sparingly, whether the lateral members are structural shapes, braced frames or trusses. Let the glue dry for 24 hours.

Glue balsa or bass wood sheets across the usable or top plane of the beam bridge for use by people or vehicles. Ensure the width of the wood sheets is equal to or less than the clear opening of the beam bridge lateral span. Glue wood square dowels along both edges of the wood sheets to act as model guard rails for the usable surface of the model beam bridge. Let the glue dry for 24 hours.

Glue the wood beam bridge model to the cardboard land model. Add scale vehicles, people and cars to create realism and show the scale of the bridge.