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1. Analyzing the inelastic response of wind-excited steel tall buildings through a reduced-order model incorporating strength and stiffness degradation along with P-Delta effects

   https://doi.org/10.1016/j.engstruct.2024.119268  

   Huang, Jinghui; Chen, Xinzhong (January 2025, Engineering Structures)

   When wind-excited tall buildings undergo vibrations beyond their linear elastic range, it becomes imperative to account for both strength and stiffness degradation and P-Delta effects. This study investigates the influence of the degradation and P-Delta effects on the inelastic response of wind-excited tall buildings through a reduced-order building model, wherein the alongwind and crosswind building responses are presumed to be contributed by the fundamental modes. The backbone curves of the hysteretic relationships between the generalized restoring forces and displacements are developed through monotonic static modal pushover analysis utilizing a high-fidelity finite element building model with consideration of P-Delta effect. A cyclic modal pushover analysis is performed to ascertain the degradation of generalized building stiffness and strength in both translation directions, stemming from the deterioration of steel material in stiffness and strength. Subsequently, a biaxial hysteretic force model is employed to depict the hysteretic relationships between generalized forces and displacements, factoring in degradation and P-Delta effects. The inelastic response of a 60-story steel building subjected to both alongwind and crosswind load excitations is quantified through response history analysis to assess the accuracy of the reduced-order building model and to evaluate the influence of degradation of material strength and pre-yield stiffness and P-Delta effects on various responses. 

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2. Rolling-Type Isolation: An Experimental Characterization and Numerical Parametric Study

   https://doi.org/11244/53085  

   Casey, Corey (December 2017, The University of Oklahoma Libraries)

   null (Ed.)

   Building contents and nonstructural components are known to be vulnerable during seismic events. Of particular concern is computer and network equipment that is critical in the post-earthquake recovery process. A solution for mitigating the seismic hazard to such systems is rolling-type isolation systems (RISs), but the characterization of RISs with realistic loading conditions and system setups is not well documented. An experimental parametric case study was performed varying the mass eccentricity, the number of cabinets, and the damping to simulate in-service conditions. A series of free response tests was performed using an abrupt shake table displacement (pulse) along with forced response tests utilizing the VERTEQ-II Zone-4 waveform. An array or string potentiometers and accelerometers measured the longitudinal, transverse, and rotational responses of the systems. Supplementally damped systems were found to have increased rotations when a mass eccentricity was present. The increase in system size and mass reduced the overall rotations due to an increased restoring moment arm and higher mass moment of inertia. Increased damping decreased the displacement demand on the isolator but increased the overall accelerations slightly. However, the systems without the supplemental damping had such large displacements that impacts were experienced causing excessively high accelerations. Durability was an issue for lightly damped systems due to increased contact stress between the ball and concave rolling surface. A physics-based mathematical model was developed for the prediction of the response of multi-unit RIS arrays with mass eccentricity. The model was first calibrated to the experimental free response tests and then validated with the forced response tests. The validated model was then used to perform a numerical parametric case study. Configurations with one, two, four and eight cabinets were modeled, and the eccentricity was varied. The VERTEQ-II waveform was applied in both the front-to-back and side-to-side directions under varying ground motion scaling. Impacts are predicted at lower ground motion scaling with larger mass eccentricity due to the initiation of rotations. The ground motion scaling for which impacts occur is increased due to the systems higher resistance to rotations from increased number of isolated cabinets. Finally, capacity design curves for the impact point were determined, which can be used to establish the required configuration (number of cabinets and eccentricity) for a given ground motion intensity. 

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3. Development and Full-Scale Validation of Resilience-Based Seismic Design of Tall Wood Buildings: The NHERI Tallwood Project

   Pei, S. (April 2017, Proceedings of the New Zealand Society for Earthquake Engineering Annual Conference, April 27-29, Wellington, New Zealand, 2017)

   With global urbanization trends, the demands for tall residential and mixed-use buildings in the range of 8~20 stories are increasing. One new structural system in this height range are tall wood buildings which have been built in select locations around the world using a relatively new heavy timber structural material known as cross laminated timber (CLT). With its relatively light weight, there is consensus amongst the global wood seismic research and practitioner community that tall wood buildings have a substantial potential to become a key solution to building future seismically resilient cities. This paper introduces the NHERI Tallwood Project recentely funded by the U.S. National Science Fundation to develop and validate a seismic design methodology for tall wood buildings that incorporates high-performance structural and nonstructural systems and can quantitatively account for building resilience. This will be accomplished through a series of research tasks planned over a 4-year period. These tasks will include mechanistic modeling of tall wood buildings with several variants of post-tensioned rocking CLT wall systems, fragility modeling of structural and non-structural building components that affect resilience, full-scale biaxial testing of building sub-assembly systems, development of a resilience-based seismic design (RBSD) methodology, and finally a series of full-scale shaking table tests of a 10-story CLT building specimen to validate the proposed design. The project will deliver a new tall building type capable of transforming the urban building landscape by addressing urbanization demand while enhancing resilience and sustainability. 

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4. Evaluation of Rolling-Type Isolation Systems for Seismic Hazard Mitigation

   https://doi.org/11244/300332  

   Calhoun, Skylar Josef (August 2018, The University of Oklahoma Libraries)

   null (Ed.)

   Nonstructural components within mission-critical facilities such as hospitals and telecommunication facilities are vital to a community's resilience when subjected to a seismic event. Building contents like medical and computer equipment are critical for the response and recovery process following an earthquake. A solution to protecting these systems from seismic hazards is base isolation. Base isolation systems are designed to decouple an entire building structure from destructive ground motions. For other buildings not fitted with base isolation, a practical and economical solution to protect vital building contents from earthquake-induced floor motion is to isolate individual equipment using, for example, rolling-type isolation systems (RISs). RISs are a relatively new innovation for protecting equipment. These systems function as a pendulum-like mechanism to convert horizontal motion into vertical motion. An accompanying change in potential energy creates a restoring force related to the slope of the rolling surface. This study seeks to evaluate the seismic hazard mitigation performance of RISs, as well as propose and test a novel double RIS. A physics-based mathematical model was developed for a single RIS via Lagrange's equation adhering to the kinetic constraint of rolling without slipping. The mathematical model for the single RIS was used to predict the response and characteristics of these systems. A physical model was fabricated with additive manufacturing and tested against multiple earthquakes on a shake table. The system featured a single-degree-of-freedom (SDOF) structure to represent a piece of equipment. The results showed that the RIS effectively reduced accelerations felt by the SDOF compared to a fixed-base SDOF system. The single RIS experienced the most substantial accelerations from the Mendocino record, which contains low-frequency content in the range of the RIS's natural period (1-2 seconds). Earthquakes with these long-period components have the potential to cause impacts within the isolation bearing that would degrade its performance. To accommodate large displacements, a double RIS is proposed. The double RIS has twice the displacement capacity of a single RIS without increasing the size of the bearing components. The mathematical model for the single RIS was extended to the double RIS following a similar procedure. Two approaches were used to evaluate the double RIS's performance: stochastic and deterministic. The stochastic response of the double RIS under stationary white noise excitation was evaluated for relevant system parameters, namely mass ratio and tuning frequency. Both broadband and filtered (Kanai-Tajimi) white noise excitation were considered. The response variances of the double RIS were normalized by a baseline single RIS for a comparative study, from which design parameter maps were drawn. A deterministic analysis was conducted to further evaluate the double RIS in the case of nonstationary excitation. The telecommunication equipment qualification waveform, VERTEQ-II, was used for these numerical simulations. Peak transient responses were compared to the single RIS responses, and optimal design regions were determined. General design guidelines based on the stochastic and deterministic analyses are given. The results aim to provide a framework usable in the preliminary design stage of a double RIS to mitigate seismic responses. 

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5. Development of multi-directional real-time hybrid simulation for tall buildings subject to multi-natural hazards

   https://doi.org/10.1016/j.engstruct.2024.118348  

   Al-Subaihawi, Safwan; Ricles, James; Quiel, Spencer; Marullo, Thomas (September 2024, Engineering Structures)

   Real-time hybrid simulation (RTHS) divides a structural system into analytical and experimental substructures that are coupled through their common degrees of freedom. This paper introduces a framework to enable RTHS to be performed on 3D nonlinear models of tall buildings with rate dependent nonlinear response modification devices, where the structure is subjected to multi-directional wind and earthquake natural hazards. A 40-story tall building prototype with damped outriggers is selected as a case study. The analytical substructure for the RTHS consists of a 3-D nonlinear model of the structure, where each member in the building is discretely modeled in conjunction with the use of a super element. The experimental substructure for the RTHS consists of a full-scale rate-dependent nonlinear viscous damper that is physically tested in the lab, with the remaining dampers in the outrigger system modeled analytically. The analytically modeled dampers use a stable explicit non-iterative element with an online model updating algorithm, by which the covariance matrix of the damper model’s state variables does not become ill-conditioned. The damper model parameters can thereby be updated in real-time using measured data from the experimental substructure. The explicit MKR-α method is optimized and used in conjunction with the super element to efficiently integrate the condensed equations of motion of a large complex model having more than 1000 nonlinear elements, thus enabling multi-axis earthquake and wind hybrid nonlinear simulations to be performed in real-time. An adaptive servo-hydraulic actuator control scheme is used to enable precise real-time actuator displacements in the experimental substructure to be achieved that match the target displacements during a RTHS. The IT real-time architecture for integrating the components of the framework is described. To assess the framework, 3D RTHS of the 40-story structure were performed involving multi-axis translational and torsional response to multi-directional earthquake and wind natural hazards. The RTHS technique was applied to perform half-power tests to experimentally determine the amount of supplemental damping provided by the damped outrigger system for translational and torsional modes of vibration of the building. The results from the study presented herein demonstrate that RTHS can be applied to large nonlinear large structural systems involving multi-axis response to multi-directional excitation. 

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