Abstract
The dynamic effect of bridges under moving vehicles must be investigated to the decision of impact factor in the rational design of highway bridges, This dynamic effect is defined by the word of the dynamic factor in this study, and is distinguished between the dynamic factor and impact factor written by design specifications. The dynamic factor of single-span bridges under the equivalent vehicle load to design live load (L-20) is calculated, Numerical examples are presented to obtain the information of the dynamic factor of highway bridges consolidated the multi-span continuous bridges and the single-span bridges. Finally, the dynamic factor based on the response of deflection and bending moment of highway steel girder bridges is suggested by a function with the parameters of span number and span length.
