Calculation mode for dynamic load allowance of negative bending moment of short and medium-span continuous girder bridge under design load

To clarify the dynamic load allowance (DLA) of negative bending moment of short and medium-span continuous girder bridges under design load, theoretical derivation and numerical simulation were adopted to conduct the research on the DLA of negative bending moment of short and medium-span continuous girder bridges. Based on the Euler-Bernoulli girder theory, an analytical expression for the DLA of negative bending moment of a two-span continuous girder under multiple moving concentrated forces was derived. Continuous girder bridges with different standard spans were selected as research objects, and a spatial three-axis vehicle model was applied. Based on the principle of equivalent load effect in the negative bending moment section, the design load of lanes was equated to the heavy vehicle load spectrum in a quasi-design state. The vibration analysis model of coupled vehicle and bridge numerical simulation was established by ANSYS software. The significance analysis of the influence of bridge frequency, deck roughness, and vehicle speed on the DLA of negative bending moment was carried out. Plenty of numerical simulation results were counted. With the frequency of bridge structure as the independent variable and the deck roughness as the sub-standard, a calculation mode of DLA of negative bending moment and its suggested value were proposed, and they were compared with the standard values in China and abroad. Research results show that the maximum difference between the DLA of negative bending moment of short and medium-span continuous girder bridges with the same span but different span numbers is 38%. The DLA of negative bending moment gradually increases as the deck roughness class decreases. The average DLA of negative bending moment for deck roughness of Class B and Class C is 2.07 times and 4.15 times the corresponding average value for roughness of Class A, respectively. Vehicle speed has a great influence on the DLA of negative bending moment, but the relationship is not clear. When the deck roughness is Class B and Class C, the DLA of negative bending moment in the specifications of various countries are underestimated. The design value of the DLA of negative bending moment of the short and medium-span continuous girder bridge is suggested to be 0.335.