During an earthquake, reinforced concrete members in a building will suffer cracking that oscillates as the building dynamically deforms. Equipment that services the building, such as mechanical and electrical items, are anchored to these components, and therefore will be subjected to this dynamic environment. Despite understanding this practical loading situation, as well as recognizing that anchor load capacity is significantly reduced when an anchor is embedded in cracked concrete, there remains a gap in knowledge regarding the effect of anchorage behavior on nonstructural component response. In particular, the effect of dynamic cyclic cracking coupled with inertia-generated tension load cycling on the anchor and component response has not been studied to date.
A new methodology involving experimental equipment and simulation tools is developed for investigating the seismic behavior of anchored nonstructural components and systems that accounts for the effects of simultaneous anchor tension load cycling and crack cycling on anchor behavior and anchored component response. To support the experimental ingredient of this work, a Cyclic Cracked Inertial Loading Rig (CCILR), Weighted Anchor Loading Laboratory Equipment (WALLE) system, and cracked concrete slabs, are designed and fabricated. Mounting the CCILR and WALLE onto a shake table results in a system that is able to simulate a concrete beam or slab from a building supporting an anchored nonstructural component. System-level shake table tests are conducted on floor mounted model nonstructural components anchored in cyclic cracks using epoxy, expansion, drop-in and undercut anchors to study the effect of a range of anchor types.
A nonlinear, lumped hysteresis anchor model is implemented and used to simulate anchor load-displacement response for tension load cycling dominant applications. The anchor model is calibrated against single anchor tests and subsequently extended for use in a system model of the anchored nonstructural components for predicting maximum system response.
It was determined that the load-displacement behavior of the anchorage, in particular, the ultimate displacement capacity of the anchor, plays an important role in the seismic response of tension load cycling dominated floor mounted nonstructural components. The experimental results also support the current code design philosophy for anchors, which specifies that either the anchor or the attachment should be ductile, or the anchor should be designed for a multiple of the expected load demand.
