Force-Based Beam-Column Element With Multispring Models for Modelling Post-Tensioned Rocking Members

Abstract eng:
Post-tensioned rocking beams and columns are popularly used in earthquake-resistant structures because of their selfcentring and low-damage response characteristics. Rocking actions in these members arise from the open-and-close action at their two end joints. A post-tensioned prestressing tendon passing through the members and the joints provides the axial and moment continuity between the members and the joints. Rocking at member interior joints may also be provided for segmental rocking members, which are usually used as bridge piers. Because the plane sections of the rocking members at the joints do not remain plane during the rocking action, the traditional beam-column finite elements based on classical plane-section beam theories are no longer applicable to simulate the rocking motions. As a result, a new type of beamcolumn finite element is needed. In this paper, a new rocking beam-column element is proposed. The new element allows multiple rocking joints to be anywhere within the beam-column members, and, therefore, is applicable to both traditional end rocking members and segmental rocking members. It is derived based on the mixed formulation that interpolates the force field exactly but satisfies the strain-displacement compatibility weakly. The formulation allows the relaxation of plane-section assumption at the rocking joints using the idea of multispring models. The new element can be readily used to simulate the seismic response of a large-scale structures with multiple rocking beams and columns. The new element accurately simulates the experimental results of a rocking column undergone a series of bi-axial loading. To demonstrate its advantages in large-scale simulations, the new element is also used to model the dynamic response of a large-scale structure. The results indicate that this new element shows highly promising potentials for large-scale structural analysis.

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