Inertial Force Limiting Floor Anchorage Systems for Seismic-Resistant Building Structures

Project Overview

The objective of the proposed research is to develop new knowledge of the dynamic behavior of building structures with an innovative floor anchorage system that reduces inertial forces while maintaining a centered floor. With this knowledge, the research will determine the appropriate design parameters for this system to produce optimal seismic performance for a variety of building geometries and properties. The ultimate goal of the research is to produce feasible prototype designs for one or more candidate structures that can be used in dissemination of the concept to the practice.

The concept is an inertial force-limiting self-centering floor anchorage system for seismic resistant building systems. In this system, different than floor isolation systems as have been proposed previously, the connection to the primary lateral force resisting system (LFRS) is initially stiff and strong, and intended to transfer the ground motion excitation to the structure without relative movement of the floor. However, at a predefined force level, the primary transfer mechanism “cuts-off”. At this point, the anchorage dissipates energy through the relative motion of the floor to the primary LFRS elements (e.g. walls, frames). The relative movement of the floor is limited (targeted at ~10cm) and ultimately removed through an elastic restoring force in parallel with the ductile connection, along with the inherent resistance of the gravity load resisting system columns.

The system has the potential to:

Reduce structural damage by lowering the seismic forces acting on the building
Reduce non-structural damage to contents and equipment by lowering floor accelerations
Eliminate the potential for non-ductile shear failure in core walls and shear walls
Mitigate the potential for floor diaphragm failures

Analytical Study

The trade-off occurs as increased relative motion of the floors, which will require seismic joints, special architectural details, and attention to stability of the gravity system. The performance targets are:

Reduce floor accelerations from~4X to no PGA amplification
Reduce LFRS damage tominimal or none
Floor relative movement within an acceptable range (2”-4”) in the DBE and MCE
Gravity system drift demands within 2% drift in DBE; 3% drift in MCE

Large Scale Test at NEES@Lehigh RTMD Facility

Phase	Position of Shear Wall	Loading	Energy Dissipation Devices
Ia	Fixed Vertical	One direction cyclic dynamic in plane	BRB + Rubber Bearings
IIa	Rotated out of plane 0.02 rad	One direction cyclic dynamic in plane	BRB + Rubber Bearings
Ib	Fixed Vertical	One direction cyclic dynamic in plane	LFD + Rubber Bearings
IIb	Rotated out of plane 0.02 rad	One direction cyclic dynamic in plane	LFD + Rubber Bearings
IIIb	Free to rotate out of plane – dynamic motion	Two directions cyclic dynamic in plane and out of plane	LFD + Rubber Bearings
Ic	Vertical	Hybrid Simulation Test – One direction cyclic dynamic in plane	LFD + Rubber Bearings