A new technique to enhance the earthquake resistance of tall reinforced-concrete bridges is introduced whereby the tall piers are allowed to ‘step’ during a severe seismic attack. This means that each pier is free to rock from side to side with vertical separation of parts of the pier from the supporting foundations. This stepping action limits stresses in the reinforced-concrete piers to values below the yield levels and this should lead to a substantial reduction in the cost of providing earthquake resistance
As part of a feasibility study, a 200 feet-high stepping pier is defined and its displacements are calculated for the ground accelerations of the 1940 El Centre earthquake, N-S component. With no damping present the computations give many ‘stepping’ separations of rather large extent. When the effects of internal structural damping are included in the analysis, there is little reduction in the stepping motions at the level of damping expected in the pier. However, when the computations include the effects of some energy-absorbing devices of a recently-developed type, installed between the pier and its foundations, the amplitude and number of the stepping cycles are considerably reduced.