Jeffrey Erochko

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

A recent study has shown that residual drifts after earthquakes that are greater than 0.5% 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...

Design and Testing of an Enhanced-Elongation Telescoping Self-Centering Energy-Dissipative Brace

AbstractThe self-centering energy-dissipative (SCED) brace is a new steel bracing member that provides both damping and recentering capability to a structure, while reducing or eliminating residual building deformations after major seismic events. Previous SCED brace designs exhibited full self-centering capability over frame lateral deformations ranging from 1.5 to 2.0% of a typical building story height owing to the elongation capacity of the tendons comprising the system. To overcome this limitation, a new enhanced-elongation telescoping SCED (T-SCED) brace has been developed that allows for self-centering response over two times the range achieved with the original SCED bracing system. A prototype design of this proposed system was fabricated and tested quasi-statically and dynamically in a full-scale vertical steel frame. It exhibited full self-centering behavior in a single story frame that was laterally deformed to 4% of its story height. This new T-SCED brace also satisfied standard testing protoc...

Design, Testing, and Detailed Component Modeling of a High-Capacity Self-Centering Energy-Dissipative Brace

AbstractThe self-centering energy-dissipative (SCED) brace is an innovative cross brace for buildings that provides a nonlinear response with good energy dissipation and postyield stiffness while minimizing residual drift after an earthquake. This provides a high level of seismic performance by allowing structures to remain operational even after major seismic events. Recently, the SCED brace has been improved through the design and experimental evaluation of a high-capacity SCED (HC-SCED) that has an axial capacity similar to some of the largest available conventional cross braces for buildings. This prototype HC-SCED satisfied testing protocols for buckling-restrained braces and exhibited full self-centering behavior during cycles up to 1.5% drift. To characterize the hysteretic response of the brace in detail, a new analytical approach is developed. This new approach is necessary because simplified stiffness estimates do not provide good predictions of the low-amplitude displacement response and initia...

Self-Centering Energy-Dissipative (SCED) Brace: Overview of Recent Developments and Potential Applications for Tall Buildings

The self-centering, energy-dissipative (SCED) brace is an innovative cross-bracing system that eliminates residual building deformations after an earthquake while simultaneously dissipating energy to reduce drifts. Several recent studies are summarized which have confirmed and extended the capabilities of SCED braces. These include a multi-storey SCED frame shake table test, a high axial-capacity SCED brace prototype, and a telescoping configuration called the T-SCED brace which greatly increases axial elongation capacity. These recent advancements have improved the desirability of SCED braces for use in high-rise structures because the braces can now better accommodate the larger forces and elongations prevalent in tall buildings. SCED braces may also provide an increased level of performance compared to other damping systems for tall buildings because they are designed to return a structure to its original, undeformed position after an earthquake. This paper reviews several potential configurations for the use of SCED braces in tall buildings, including the use of SCED braces in tall braced frames, coupled with shear walls and with vertical outriggers.

DETAILED COMPONENT MODELLING OF A SELF-CENTERING ENERGY DISSIPATIVE BRACE SYSTEM

The self-centering energy-dissipative (SCED) brace is a new steel bracing member that provides damping to a structure and a re-centering capability, reducing or eliminating residual building deformations after major seismic events. Recently, the SCED concept has been extended through the design and construction of a new enhanced-elongation telescoping SCED (or T-SCED) brace that allows for self-centering behaviour over a range that is two times as large as the range that could be achieved by the original SCED bracing system. Pre- vious prototype tests of SCED and T-SCED braces have shown that the simplified estimates of the initial brace stiffness that were previously used do not predict the results from the proto- type tests well. To accurately model the mechanics of these new systems, a new software tool has been developed that is able to represent the detailed behaviour of SCED braces to deter- mine realistic brace stiffness and the effect of construction tolerances on the brace behaviour. In this paper, the inner workings of the software tool are described and its analysis results are compared to the test results from the two previous experimental studies to demonstrate the softwares ability to model SCED and T-SCED behaviour accurately.