Search for: All records

ABSTRACT This data paper presents data obtained from E‐Defense shake‐table tests of a full‐scale, steel moment‐resisting frame (MRF) supplemented with Spines. Herein, the Spines were pin‐based columns with sufficient stiffness and strength to distribute plastic deformation evenly over the height of the MRF. The specimen was tested under two configurations: first, with the Spine rigidly connected to the MRF; second, with the Spine connected to the MRF through force‐limiting connections (FLCs). Each specimen configuration underwent earthquake simulations using ground motions with two scale factors. The tests demonstrated the expected benefits of Spines as well as the disadvantage of inducing large floor accelerations in the structure and large shear forces in the Spines. The tests also demonstrated how the FLCs can mitigate these disadvantages. This data paper reports an overview of the tests, data archive structure, and potential use of the data. The data can be used, for example, to reproduce the observations presented by the authors, to compare the dynamic response of the specimen with building specimens tested in other shake‐table test programs, to validate numerical models against the measured specimen response, or to formulate classroom exercises on system identification of linear and nonlinear systems. 

Due to their ability to provide more uniform story drifts with building height, strongback braced frames (SBFs) have been proposed as enhanced-performance structural systems. Conventional design approaches, however, tend to underestimate force demands in strongback elements compared to nonlinear response history analysis (NRHA). To address this gap, alternative methods such as modal pushover analysis (MPA) have been suggested to obtain less computationally intensive estimates of seismic demands. This study presents a statistical assessment of MPA as an estimate of NRHA force demands for an 8-story SBF subjected to 44 far-field ground motion records scaled at the risk-adjusted maximum considered earthquake (MCE𝑟 ) intensity level. Unlike prior studies that compare MPA results to the statistics of the NRHA response, this work treats each ground motion as a separate test to characterize how MPA accounts for record-specific spectral characteristics. Accuracy in estimates of the force demands (i.e., how close the MPA estimates are to the NRHA “truth”) is characterized using root mean square error. Additional comparisons are made across the MPA parameters, such as the number of modes employed, as well as the use of initial versus elongated periods. Results provide a comprehensive statistical assessment of MPA, illustrating that the approach can be sensitive to spectral assumptions and is better suited to aggregated estimates from NRHA. 

Even with strong-column-weak-beam design requirements, story mechanisms have been observed in Moment Resisting Frames (MRF), resulting in concentrated drift demands that can result in severe structural damage to drift-sensitive components. Frame-Spine systems can redistribute demands with building height, but near-elastic higher-mode effects tend to contribute to floor accelerations, affecting damage to acceleration-sensitive nonstructural components. To mitigate this tradeoff, Force-Limiting Connections (FLCs) have been proposed to reduce accelerations through yielding components between the Frame and Spine, thereby limiting the magnitude of the forces. This study examines the sizing and placement of FLCs in a four-story Frame-Spine system using stochastic simulations. The T-shape yielding element dimensions in the FLC were modeled as random variables at each floor, and Monte Carlo simulations were used to explore their effect on drifts and accelerations. Results show the dominant role of the first-story FLC on balancing drifts and accelerations, while upper-story devices offered limited benefit. Design recommendations are provided to constrain first-story yielding element dimensions within effective bounds that reduce peak accelerations relative to the baseline Frame-Spine configuration. 

Concentration of drifts due to story mechanisms can lead to severe structural damage and economic loss. Frame-Spine systems have been proposed to mitigate these effects by redistributing drift demands with building height; however, systems can also exhibit near-elastic higher-mode effects, resulting in forces and floor accelerations that remain largely unreduced by inelastic behavior, thereby adversely affecting acceleration-sensitive nonstructural components and occupants. To address near-elastic higher-mode effects, Force-Limiting Connections (FLCs) have been introduced limiting force transfer between the frame and the spine and reducing acceleration demands through controlled yielding components. This study presents observations from full-scale shake-table testing of a four-story Frame-Spine and a Frame-Spine-FLC specimen at E-Defense. Results highlight higher-mode effects under strong shaking, with emphasis on (1) story shear resisted by the spine, (2) force–deformation behavior of the spine-to-frame connections, and (3) vertical distribution of forces. These findings provide experimental evidence of higher-mode participation in Frame-Spine systems and support the development of improved design guidance and controlling mechanisms. 

Abstract In light of the significant damage observed after earthquakes in Japan and New Zealand, enhanced performing seismic force‐resisting systems and energy dissipation devices are increasingly being utilized in buildings. Numerical models are needed to estimate the seismic response of these systems for seismic design or assessment. While there have been studies on modeling uncertainty, selecting the model features most important to response can remain ambiguous, especially if the structure employs less well‐established lateral force‐resisting systems and components. Herein, a global sensitivity analysis was used to address modeling uncertainty in specimens with elastic spines and force‐limiting connections (FLCs) physically tested at full‐scale at the E‐Defense shake table in Japan. Modeling uncertainty was addressed for both model class and model parameter uncertainty by varying primary models to develop several secondary models according to pre‐established uncertainty groups. Numerical estimates of peak story drift ratio and floor acceleration were compared to the results from the experimental testing program using confidence intervals and root‐mean‐square error. Metrics such as the coefficient of variation, variance, linear Pearson correlation coefficient, and Sobol index were used to gain intuition about each model feature's contribution to the dispersion in estimates of the engineering demands. Peak floor acceleration was found to be more sensitive to modeling uncertainty compared to story drift ratio. Assumptions for the spine‐to‐frame connection significantly impacted estimates of peak floor accelerations, which could influence future design methods for spines and FLC in enhanced lateral‐force resisting systems. 

This dataset contains data from E-Defense shake-table tests of a full-scale, steel moment-resisting frame (MRF) supplemented with spines. Herein, the spines were pin-based columns with sufficient stiffness and strength to distribute plastic deformation evenly over the height of the MRF. The specimen was tested under two configurations: first, with the spine rigidly connected to the MRF; and second, with the spine connected to the MRF through Force-Limiting Connections (FLCs). The two structural systems were subjected to two ground motions adjusted to two different scales. The tests highlighted the expected benefits of spines as well as their drawbacks of inducing large floor acceleration in the MRF and large shear forces in the spines themselves. The tests also highlighted how the FLCs can mitigate such drawbacks of spines. The data may be used, for example, to reproduce the observations presented by the authors, to compare the dynamic response of the specimen with building specimens tested in other shake-table test programs, to validate numerical models against the measured specimen response, or to formulate classroom exercises on system identification of linear and nonlinear systems. 

Mid-rise moment resisting frames (MRF) which utilize supplemental pinned-base spines (spine) to prevent the formation of story mechanisms experience higher mode accelerations at near elastic spectral values. Force Limiting Connections (FLC) can be introduced to reduce the floor accelerations from the higher mode responses while having small impact on first-mode response and maintaining the story mechanism prevention from the spine. Results from nonlinear response history analysis (NRHA) of a 4-story MRF-Spine system show how floor accelerations for higher modes are reduced with the addition of FLC placed between the MRF and spine. Peak effective pseudo accelerations are utilized to show how pseudo spectral accelerations are reduced by the introduction of FLC. Full-scale testing of the 4-storyMRF-Spine structure supports the numerical results of theMRF-Spine andMRF-Spine-FLC numerical analyses. These results show the potential benefits of adding FLC to MRF-Spine systems. 

Advancements in seismic hazard mitigation and resilience have spurred the exploration and development of lateral-force resisting systems with enhanced performance goals. In this context, brace frames coupled with elastic spines offer a more uniform drift distribution with building height that reduces the concentration of damage in a few stories and therefore reduces the likelihood of a story mechanism. However, properly sizing the spine, along with selecting and placing the energy dissipators, remains challenging and lacks standardized procedures due to 1) the kinematic and force compatibility between the pivoting spine and the energy dissipators and 2) the near-elastic higher-modes demands that are present in this type of system; both closely governed by the selection of the spine strength and stiffness. This study investigates the nonlinear static response of 8-story Strongback Braced Frames (i.e., brace frames where the elastic spine is composed of a pivoting truss called strongback) using a first and second-mode force pattern. The archetypes have different variations in the implementation of the strongback; e.g., keeping the strongback in a separate bay from the main brace frame or embedding the strongback into the frame. In pushing the archetypes with a first-mode force pattern, the strongback imposes more uniform drifts, without a significant increase in the system’s ultimate capacity. In pushing with a second-mode force pattern, the strongback delays the formation of a mechanism and increases the system’s ultimate capacity to values comparable to expected elastic demands under MCE intensities. The distribution of story shears between the main frame and the strongback is assessed, and the implications of higher-mode demands in sizing the brace and ties of the strongback are highlighted. It is expected that results from this paper may begin to inform future code-based provisions in adopting the use of near-elastic spines in enhanced performance systems. 

Abstract. A novel structural system is being investigated collaboratively – by an international team including three U.S. universities, two Japanese universities and two major experimental research labs – as a means to protect essential facilities, such as hospitals, where damage to the building and its contents and occupant injuries must be prevented and where continuity of operation is imperative during large earthquakes. The new system employs practical structural components, including (1) flexible steel moment frames, (2) stiff steel elastic spines and (3) force-limiting connections (FLC) that connect the frames to the spines, to economically control building response and prevent damaging levels of displacement and acceleration. The moment frames serve as the economical primary element of the system to resist a significant proportion of the lateral load, dissipate energy through controlled nonlinear response and provide persistent positive lateral stiffness. The spines distribute response evenly over the height of the building and prevent story mechanisms, and the FLCs reduce higher-mode effects and provide supplemental energy dissipation. The Frame- Spine-FLC System development is focusing on new construction, but it also has potential for use in seismic retrofit of deficient existing buildings. This paper provides an overview of the ongoing research project, including selected FLC cyclic test results and a description of the full-scale shake-table testing of a building with the Frame-Spine-FLC System, which represents a hospital facility and includes realistic nonstructural components and medical equipment. 

Numerical modeling is widely used in structural engineering to represent buildings response under seismic loading conditions. However, even though numerical modeling is a common tool to characterize the behavior of structures, modeling uncertainties can lead to a broad range of expected response, particularly when representing the behavior of novel systems or components. Addressing different modeling choices can provide more informed insights into the response of structures, especially prior to conducting experimental tests or participating in blind prediction contests. Herein, blind response prediction of a novel steel system was conducted before testing at the E-Defense facility in Japan. The full-scale specimen consisted of a weak Moment-Resisting Frame (MRF) retrofitted with steel spines and force-limiting connections (FLC). The set of pre-test predictions involved addressing of different modeling choices to overcome the many sources of epistemic uncertainties and to provide greater confidence in the design and experimental testing program. Several models were subjected to the records specific to the testing program (Northridge Sepulveda and JMA Kobe) to estimate drift and acceleration responses. Numerical results were compared to the experimental data from the shake-table tests. Although all the models were able to represent general trends in drifts and accelerations and enabled proper development of the testing plan, peak response varied significantly depending on the modeling choices, especially those altering the system’s natural periods or those leading to different yielding patterns.