Wooden bridges of all types exist in all cultures.But how we design them and how we think about them,varies between cultures and over time.Such differences in design thinking leads to different concepts of structure，and these structural concepts influence the final result. An example is the combined structural types that were built in wood and were common in Europe before the Industrial Revolution and later in North America.In combined structures each structural form supports loads on its own，but at the same time each helps support all other parts.Each form either carries part of the total load,as in the case of anarch superimposed on a truss，or each of the forms can be specialized to carry a specific type of load like when a stiffening truss is superimposed on a suspension bridge.