The Kinematic Displacements of the Two-spans Single Lane Suspension Steel Footbridge and Their Stabilization

The behavior of the two-span single lane suspension footbridge is influenced not only by the loads, but by the structural solution of the middle bearer as well. If the middle bearer can move in the lateral direction then additional kinematic horizontal and vertcal displacements appear under the asymmetric load. The article presents an analysis of the behavior of the two-span single lane suspension footbridge under asymmetric loads. The kinematic displacements of the bearing suspension structures of such bridges are reviewed under an assumption that the suspending cable is flexible. The influence of the initial suspended cable sag on these displacements is analyzed. The analytical expressions of computing the kinematic horizontal and vertical displacements of the cable are introduced. It was ascertained that the kinematic displacements of the the two-span single lane suspension footbridge structure are directly dependent on the ratio of the symmetric and asymmetric loads and the value of the initial cable sag. The efficiency of stabilizing the kinematic displacements using the bending cable tightness is analyzed and the engineering methods for calculating the necessary bending stiffness of the cable while taking into consideration the ratio of the symmetric and asymmetric loads and the marginal displacement values. The results of the calculative test that showed the precision (which is sufficient for practical calculations) of the engineering computing methods of the cable kinematic displacements are presented. It was determined that the efficiency of stabilizing the kinematic displacements increases when the values of the cable bending stiffness and the initial cable sag grow.