Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems (Moment Resisting Frame)

Objectives

The overall project objective is to investigate a family of innovative self-centering (SC) steel frame systems with the potential to withstand the currently accepted design basis earthquake (DBE) for buildings without damage. This current project task is focusing on the design and experimental performance of a self-centering moment-resisting frame (SC-MRF). The SC-MRF test structure was designed using limit-state based design criteria to be undamaged under a median-level DBE and undergo controlled yielding under the Maximum Considered Earthquake (MCE). This expected performance will be assessed and the design criteria verified through hybrid-pseudo-dynamic experiments on a 0.6-scale 2-bay 4-story SC-MRF.

Earthquake Simulations

1. Introduction

The SC-MRF is a post-tensioned MRF with web friction devices (WFDs) as energy dissipating devices. The WFDs are positioned on the beam web to avoid interference with the floor slab. Using a performance based design (PBD) approach the SC-MRF is designed to be damage-free under the DBE to enable immediate occupancy, while also achieving the performance level of collapse prevention under the MCE. Figure 1(a) shows an SC-MRF with WFDs. The PT strands run parallel to the beams across multiple bays to precompress the beams to the columns. The WFDs are shown in more detail in Figure 1(b) and (c).

2. Experimental Program

Using the specific design criteria and the performance-based design (PBD) approach shown in Figure 2, a 7×7-bay 4-story prototype building shown in Figure 3(a) was designed. The building is located on stiff soil in the Los Angeles. The perimeter frames include SC-MRFs. Each perimeter frame has two 2-bay SC-MRFs with WFDs. Figure 3(a) also shows the floor diaphragm is attached to one bay of each SC-MRF in each perimeter frame to avoid restraining the post-tensioned connections from developing gap opening.

2.1. Test Structure, Test Setup and Test Matrix

The test structure for the experimental program is a 0.6-scale 4-story 2-bay SC-MRF as shown in Figure 3(b). A992 steel sections were used throughout the test structure. Figure (c) shows the test structure. The Table 1 summarizes the design demands for roof drift (θ_roof), story drift (θ_s), and connection relative rotation (θ_r) under the DBE and MCE levels. The hybrid pseudo-dynamic simulation uses an analytical model for the gravity load-carrying system of the building, along with the test structure in the laboratory. The simulation uses Rayleigh damping with 2% damping in the 1st mode and 5% in the 3rd mode. The explicit unconditionally stable CR integration algorithm is used to solve the equations of motion. The test matrix is shown in Table 1.

3. Related Publications

Lin, Y.C, Ricles, J.M. and Sause, R., ” Earthquake Simulations On A Self-Centering Steel Moment Resisting Frame With Web Friction Devices,” Proceedings, 14th World Conference on Earthquake Engineering, Beijing, China, Oct 12-17, 2008.

4. Participants

Graduate Research Assistant

Ying-Cheng Lin

Faculty Advisors

Richard Sause
James Ricles

Post-Doctoral Research Associates

Choung-Yeol Seo

Table 1 – Design demands (in radians)

θ_roof,DBE	θ_s,DBE	θ_r,DBE	θ_roof,MCE	θ_s,MCE	θ_r,MCE
0.026	0.039	0.031	0.039	0.059	0.047

Table 2 – Test matrix

Tests	Description	Ground Motion Record	Scale Factor	Test Method
Stiffness	Stiffness matrix determination	–	–	Static
Pushover	WFD connection behavior check	–	–	Static
FOE-1	1979 Imperial Valley	H-CXO225	0.700	Pseudo-dynamic
FOE-2	1979 Imperial Valley	H-CXO225	1.410
DBE-1	1979 Imperial Valley	H-ECC002	0.943
DBE-2	1989 Loma Prieta	SJTE315	-2.234
DBE-3	1994 Northridge	LOS000	1.182
MCE	1994 Northridge	STM090	2.071
Aftershock	1979 Loma Prieta	SJTE315	-2.234

Figure 1 – Schematic of (a) Elevation of a 2-bay SC-MRF with PT strands and WFDs, (b) and (C) Connection details

Figure 2 – Performance based design objectives

Figure 3 – Schematic of (a) Plan of prototype, (b) Elevation of 0.6-scale 4-story 2-bay SC-MRF test frame, and (c) Experimental test frame (the yellow frame).