Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars

This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy （SMA） link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitie SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%-12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly.

Numerical analysis of seepage flow characteristic of collapse column under the influence of mining

Based on the importance of fractured rock mass seepage research, in order to analyze seepage flow characteristics of collapse column under the influence of mining, a method by embedding fractured rock mass flow solid coupling relationship into FLAC3D internal flow models is presented according to fluid-solid coupling theory and strength criterion. A calculation model of numerical analysis was established, and the influences of mining pressure and plastic damage to pore water pressure and seepage vector change rule were studied. The results show that collapse column is the main channel of confined water seepage upward. The impact is not big when the workface is away from the collapse column. But when the workface is nearing a collapse column, there will be a seepage channel on a side near the workface, in which seepage vector and head are comparatively large. With workface pushing through collapse column, the seepage channel transfers to the other side of the column. In addition, when the plastic damage area within the collapse column breaks through, a "pipeline flow" will be formed within the column, and seepage field will change remarkably and the possibility of water bursting will be greater.

Cost-effective post-tensioned bridge pier with internal dissipation

This paper presents the development and testing of a novel internal dissipation connection for the use of post-tensioned rocking columns.The solution is one of the many referring to the dissipative controlled rocking(DCR)bridge design philosophy.The internal dissipaters are carefully designed to be cost-effective and reduce the over-all construction cost.The dissipaters are fully threaded,Grade 300 bars connected to the permanent column and foundation longitudinal reinforcement with threaded couplers.In this research,a DCR column is subjected to subsequent earthquake events,and the dissipaters’strain design limits are chosen such that there is no need for replacing after a significant seismic event.The result is a recommended design strain limit of 1.5%for the dissi-paters that guarantees the structural integrity of the DCR column after a seismic event.Additionally,a cumulated strain of 5%is recommended for the dissipaters before replacement is suggested.The proposed connection de-tailing with replaceable internal dissipaters,combined with post-tensioned high strength bars and well-confined concrete,provided self-centring capabilities(no residual displacement),dissipation capacity and significantly less damage in the bridge column than a traditional reinforced concrete solution.