Buildings designed according to modern seismic codes are expected to develop a controlled ductile inelastic response during major earthquakes, implying extensive structural damage after a design level earthquake, along with possibly substantial residual deformations. To address this drawback of traditional yielding systems, a new bracing system that can undergo large axial deformations without structural damage while providing stable energy dissipation capacity and a restoring force has recently been developed. The proposed bracing member exhibits a repeatable flag-shaped hysteretic response with full recentering capabilities, therefore eliminating residual deformations. The mechanics of this new system are first explained, the equations governing its design and response are outlined, and one embodiment of the system, which combines a friction dissipative mechanism and Aramid tensioning elements, is further studied. Results from component tests, full-scale (reduced length) quasi-static axial tests, and quasi-static and dynamic seismic tests on a full-scale frame system are presented. Experimental results confirm the expected self-centering behavior of the self-centering energy dissipative (SCED) bracing system within the target design drift. Results also confirm the validity of the design and behavior equations that were developed. It is concluded that the proposed SCED concept can represent a viable alternative to current braced frame systems because of its attractive self-centering property and because the simplicity of the system allows it to be scaled to any desired strength level.

Self-Centering Energy Dissipative Bracing System for the Seismic Resistance of Structures: Development and Validation

The seismic performance of a posttensioned energy dissipating (PTED) connection for steel frames is investigated analytically and experimentally. The PTED connection incorporates posttensioned high-strength bars to provide a self-centering response along with energy dissipating bars that are able to yield in axial tension and compression. The analytical study involves the development of an equivalent iterative sectional analysis procedure to predict the moment-rotation relationship of the PTED connection. Based on this analytical model, a simple design procedure for PTED connections is described. In the experimental study, a cyclic component test was performed on two energy dissipating bars and a cyclic test was conducted on a large-scale exterior beam-to-column PTED connection. The results of the tests show that the PTED test specimen was able to undergo large inelastic deformations without any damage in the beam or column and without residual drift. The proposed analytical model and design procedure wer...

Posttensioned Energy Dissipating Connections for Moment-Resisting Steel Frames

Development and experimental validation of a nickel–titanium shape memory alloy self-centering buckling-restrained brace

A recent study has shown that residual drifts after earthquakes that are greater than 05% in buildings may represent a complete loss of the structure from an economic perspective To study the comparative residual drift response of special moment-resisting frames (SMRFs) and buckling-restrained braced (BRB) frames, buildings between 2 and 12 stories in height are designed according to ASCE 7-05 and investigated numerically This investigation includes pushover analyses as well as two-dimensional nonlinear time-history analyses for two ground motion hazard levels The two systems show similar peak drifts and drift concentration factors The BRB frames experience larger residual drifts than the SMRFs; however, the scatter in the residual drift results is large Expressions are proposed to estimate the residual drifts of these systems as a function of the expected peak drifts, the initial recoverable elastic drift, and the drift concentration factor of each system When subjected to a second identical earth

Residual Drift Response of SMRFs and BRB Frames in Steel Buildings Designed according to ASCE 7-05

Two geometrically identical half-scale precast concrete cantilever wall units were constructed and tested under quasi-static reversed cyclic lateral loading. One unit was a code compliant conventionally reinforced specimen, designed to emulate the behavior of a ductile cast-in-place concrete wall. The other unit was part of a precast partially prestressed system that incorporated post-tensioned unbonded carbon fiber tendons and steel fiber reinforced concrete. Hysteretic energy dissipation devices were provided in the latter unit in the form of low yield strength tapered longitudinal reinforcement, acting as a fuse connection between the wall panel and the foundation beam. The conventional precast reinforced wall performed very well in terms of the ductility capacity and energy absorption capability, reaching 2.5% drift before significant strength degradation occurred. The precast partially prestressed wall unit achieved drift levels well in excess of 3% with no visible damage to the wall panel prior to failure. Test results and performance comparisons between the precast partially prestressed wall system and the precast conventionally reinforced unit are presented.

Seismic Performance of Precast Reinforced and Prestressed Concrete Walls

Steel moment-resisting frames (MRFs) with posttensioned connections are constructed by posttensioning beams to columns using high strength strands. Top and seat angles are added to provide energy dissipation and redundancy under seismic loading. This new type of connection has several advantages, including the following: (1) field welding is not required; (2) the connection stiffness is similar to that of a welded connection; (3) the connection is self-centering; and (4) significant damage to the MRF is confined to the angles of the connection. An analytical model based on fiber elements was developed for these connections. Experimental test results were used to calibrate the model. The model was used for inelastic static analyses of interior connection subassembages as well as dynamic time history analyses of a six-story steel MRF. A self-centering capability and adequate stiffness, strength, and ductility were observed in the results of these analyses. Time history analysis results show that the seismic...

Maria M. Garlock

Papers

Posttensioned Seismic-Resistant Connections for Steel Frames

Influence of design parameters on seismic response of post-tensioned steel MRF systems

Use of Post-Tensioned Friction Damped Connections for Seismic Retrofit of Steel Moment Resisting Frames

Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems (NEES-2005-0077)