Braceless Seismic Restraint for Suspended Nonstructural Elements: Concept, Design, and Numerical and Experimental Assessment

The economic and functionality losses generated by damage to nonstructural elements in recent earthquakes have called the attention of the engineering community to improve the seismic performance of such components, allowing for more resilient buildings. In this regard, seismic protection of nonstructural elements can benefit from the same principles of supplemental damping already used to increase the energy dissipation capacity of structures. This study proposes a novel, patent-pending, braceless seismic restraint for suspended nonstructural elements that control the seismic-induced lateral displacements by providing supplemental damping through rotary dampers. In addition, the braceless seismic restraint eliminates the need for bracing elements, simplifying the distribution of lateral restraints in congested layouts, and takes advantage of gravity loads to provide recentering forces into the system, reducing or even avoiding residual deformations. Conceptually, the proposed braceless seismic restraint resembles a damped pendulum composed of one vertical hanger connected to a rotary damper at its upper end that controls the maximum force and energy dissipation of the system. The rotary damper is attached to the supporting structure through a hinge connection, allowing free rotation of the restraint in the direction perpendicular to the damper rotation. The suspended nonstructural element is attached to a horizontal element connected to the bottom end of the vertical hanger. Two rotary damper typologies were explored to be implemented on the braceless seismic restraint, the first damper was based on a rotary friction damper, and the second one was based on a rotary viscous damper. A general displacement-based design procedure was developed for the seismic design of the braceless seismic restraint, which allowed for the detailing and sizing of both proposed configurations. A three-dimensional suspended piping system, located at the top floor of a nine-story steel moment-resisting framed building, was used as a case study to evaluate the seismic response of the braceless seismic restraints and a conventional restraint system based on braced channel trapezes. These suspended piping systems were subjected to nonlinear time history analysis, using floor motions generated from the FEMA P695 far-field ground motion set scaled to two increasing intensity levels. The seismic response was evaluated by comparing the horizontal lateral displacements of several points along the pipeline length. The results showed that the proposed braceless seismic restraint performed better than the conventional braced system in terms of median peak displacements, dispersion of the peak displacements, and residual displacements at both evaluated intensity levels. Finally, several prototypes of the braceless seismic restraint with a rotary friction damper were built and subjected to a fully reversed cyclic load test. The experimental results showed a stable hysteresis loop, exhibiting an almost elastic-perfectly plastic behavior. These results support the assumptions made for the numerical simulation of the braceless seismic restraint.