Experimental Verification of Analysis Model of Seismic Isolation With High-Static-Low-Dynamic Stiffness

This paper verifies the model of high-static-low-dynamic stiffness (HSLDS) for seismic isolation based on an experiment. Seismic isolation is widely used in several countries. Moreover, the number of seismically isolated buildings has rapidly increased in these few decades. Seismic isolation extends a natural period of a building and decreases the absolute acceleration to re-duce a seismic force. However, as there is a trade-off between displacement and absolute acceleration, it might result in the maximum displacement be-yond an allowable range. HSLDS is nonlinear, and its restoring force can be approximated cube of a displacement. Thus, HSLDS applies a large restoring force for significant displacement, and the force is small for small perturbation around an equilibrium position. To improve the control performance of seismic isolation for displacement, we apply HSLDS for seismic isolation. This paper conducts an experiment and compares the results with a time-history analysis to verify a numerical model of HSLDS

Estimation of Maximum Drift of MDOF Shear Structures Using Only One Accelerometer

This paper presents a new method to estimate maximum drifts, relative displacements between adjacent floors, of all stories of multi-degree-of-freedom (MDOF) shear structures using only one floor’s absolute acceleration time history response under the ground excitation. The absolute acceleration and relative displacement are formulated in modal coordinates and the state-space expression is derived. Then the numerical simulation for a three-story structure was conducted to verify the performance of the state-space equation. The comparison of the estimated state and input with actual values is made and shows the good agreement. In addition, the relative displacement time histories of all floors were obtained, and the errors of maximum displacements and inter-story drifts were analyzed. The robustness against environmental noise was also investigated by numerical simulations as well. The results of simulations indicate the estimation is satisfactory, and very robust against the environmental disturbance.

Performance of TMDI for Tall Building Damping

This study investigates the vibration reduction of tall wind-excited buildings using a tuned mass damper (TMD) with an inerter (TMDI). The performance of the TMDI is computed as a function of the floor to which the inerter is grounded as this parameter strongly influences the vibration reduction of the building and for the case when the inerter is grounded to the earth whereby the absolute acceleration of the corresponding inerter terminal is zero. Simulations are made for broadband and harmonic excitations of the first three bending modes, and the conventional TMD is used as a benchmark. It is found that the inerter performs best when grounded to the earth because, then, the inerter force is in proportion to the absolute acceleration of only the pendulum mass, but not to the relative acceleration of the two inerter terminals, which is demonstrated by the mass matrix. However, if the inerter is grounded to a floor below the pendulum mass, the TMDI only outperforms the TMD if the inerter is grounded to a floor within approximately the first third of the building’s height. For the most realistic case, where the inerter is grounded to a floor in the vicinity of the pendulum mass, the TMDI performs far worse than the classical TMD.

Seismic Acceleration and Displacement Demand Profiles of Non-Structural Elements in Hospital Buildings

The importance of non-structural elements in performance-based seismic design of buildings is presently widely recognized. These elements may significantly affect the functionality of buildings even for low seismic intensities, in particular for the case of critical facilities, such as hospital buildings. One of the most important issues to deal with in the seismic performance assessment of non-structural elements is the definition of the seismic demand. This paper investigates the seismic demand to which the non-structural elements of a case-study hospital building located in a medium–high seismicity region in Italy, are prone. The seismic demand is evaluated for two seismic intensities that correspond to the definition of serviceability limit states, according to Italian and European design and assessment guidelines. Peak floor accelerations, interstorey drifts, absolute acceleration, and relative displacement floor response spectra are estimated through nonlinear time–history analyses. The absolute acceleration floor response spectra are then compared with those obtained from simplified code formulations, highlighting the main shortcomings surrounding the practical application of performance-based seismic design of non-structural elements. The absolute acceleration floor response spectra are then compared with those obtained from simplified code formulations. The results, both in terms of absolute acceleration and relative displacement floor response spectra, highlighted the influence of the higher modes of the structure and the inaccuracy of the code provisions, pointing out the need for more accurate simplified methodologies for the practical application of performance-based seismic design of non-structural elements.

H∞ Optimization of Tuned Inerter Damper with Negative Stiffness Device Subjected to Support Excitation

In this study, H∞ optimization is conducted for a tuned inerter damper (TID) with negative stiffness device (denoted as TID_NSD) subjected to harmonic support excitation. The study shows that there are still two nonzero-frequency fixed points independent of the damping of the TID_NSD; therefore, the optimum tuning frequency and damping ratio for the TID_NSD are, respectively, derived based on the well-known fixed points theory. By imposing the zero-frequency fixed point having the same amplitude as the other two nonzero-frequency fixed points, the optimum negative stiffness ratio, which makes the primary system with a TID_NSD remain stable, is obtained. Moreover, the role of a negative stiffness device of a TID_NSD system in response control of a single degree-of-freedom (SDOF) structure is evaluated through parametric study. Also, a numerical analysis is conducted on both a SDOF and multiple DOFs structure to validate the feasibility of the derived formulas by simulations with real earthquake records. Numerical results demonstrate that the maximum displacement and the maximum absolute acceleration of the structure equipped with TID_NSD system are reduced by increasing the absolute value of negative stiffness ratio. The results also show that the optimally designed TID_NSD system outperforms the optimally designed TID system in terms of the displacement and absolute acceleration mitigation control. The closed-form solutions proposed in this study can be useful for the optimal design of the structure equipped with TID_NSD.

Aceleraciones de alta intensidad en el fútbol. ¿Por qué es importante el método de evaluación? (High-intensity acceleration in soccer. Why is the evaluation method important?)

El objetivo del presente estudio fue analizar las posibles diferencias entre el uso de diferentes tipos de umbrales para evaluar los esfuerzos de alta intensidad, tanto en número como en distancia recorrida en jóvenes futbolistas de élite. Un total de 26 jóvenes jugadores fueron analizados durante 18 partidos oficiales (n = 108). Los esfuerzos de alta intensidad se evaluaron utilizando un umbral relativo individualizado basado en la capacidad de acelerar a diferentes velocidades iniciales, considerando la aceleración de alta intensidad cuando fue >75% de la capacidad máxima de acelerar (>75% amax). Se utilizó también un umbral >21 km·h-1 cuando la intensidad de la aceleración fue >75% amax, y umbrales absolutos >3 m·s-2 y >4 m·s-2, contabilizando tanto el número como la distancia (metros). El análisis post hoc mostró diferencias significativas por pares entre el uso de umbrales a alta intensidad (p < .05), en número y distancia. Los resultados mostraron que el uso de umbrales absolutos podría sobreestimar (>3 m·s-2) y subestimar (>4 m·s-2 y >21 km·h-1) esfuerzos de aceleración a alta intensidad (tanto en número como en distancia) en comparación con el uso de un umbral relativo individualizado (p < .05). Por lo tanto, concluimos que el uso de umbrales de aceleración absolutos (>3 m·s-2 y >4 m·s-2) puede no ser apropiado para analizar estos esfuerzos de alta intensidad en jóvenes futbolistas. Además, los umbrales de velocidad de carrera podrían subestimar las acciones de alta intensidad desarrolladas en una distancia corta, siendo más apropiados combinarlos con un umbral relativo individual para evaluar las acciones de alta intensidad en partidos de fútbol. Abstract. The aim of the current study was to analyze the possible differences between the use of different kinds of thresholds to assess high-intensity acceleration efforts, both in number and distance covered in young elite soccer players. A total of 26 young soccer players were analyzed during 18 competitive matches (n=108). High-intensity acceleration efforts were assessed using an individual relative threshold based on the capacity of acceleration from different initial speeds, considering high-intensity acceleration when it was >75% of the maximal acceleration (>75% amax). It was also used a threshold >21 km·h-1 when the acceleration intensity was >75% amax, and absolute thresholds of >3 m·s-2 and >4 m·s-2, both in number and distance (meters). Post hoc analysis showed pairwise significant differences between the use of high-intensity thresholds (p < .05), in number and distance. The results showed that the use of absolute thresholds could overestimate (>3 m·s-2) and underestimate (>4 m·s-2 and >21 km·h-1) high-intensity acceleration efforts (both in number and distance) in comparison with the use of an individual relative threshold (p < .05), whereas a threshold based on high-speed running could underestimate high-intensity acceleration efforts (p < .05). Therefore we conclude that the use of absolute acceleration thresholds (>3 m·s-2 and >4 m·s-2) may not be appropriate to analyze these efforts in young soccer players. In addition, speed running thresholds could underestimate high-intensity actions developed in short distance, being more appropriate to combine with an individual relative threshold to assess high-intensity action in soccer matches.

Dimensionless design approach to translating flat faced follower mechanism with two-circular-arc cam

In this study, a dimensionless design approach was presented for translating flat-faced follower mechanism with two-circular-arc cam. Instead of second arc radius (r2), maximum follower lift (smax) and angle of the cam rotation angle (2θmax) variables from the cam profile design parameters were made dimensionless using r2∕r (=λ), smax∕r (=ψ) and θmax∕π (=μ) respectively. Equations for cam profile and follower movement were derived and graphics were obtained depending on the dimensionless parameters. λ and ψ should be in the range [0.0, 1.0], but μ should be in the range [0.0, 0.5]. λ and ψ were changed in the range [0.10, 0.90] and μ in the [0.25, 0.45] range and λ, ψ and μ values were determined for the cam profile. Maximum velocity (vmax), maximum absolute acceleration (amax) and average follower lift (save) changes, which are one of the critical characteristics of follower, were examined for possible cam profiles according to the change of λ, ψ and μ. As a result, vmax and save decreased when μ was increased, vmax and save increased and amax decreased when ψ was increased, amax and save increased when λ was increased.

FUZZY SLIDING MODE CONTROL OF A STRUCTURE BASED ON HEDGE ALGEBRAS CONTAINING INPUT TIME DELAY

In this paper, the authors present the sliding mode control problem of a structure using hedge-algebras-based fuzzy controller considering the impact of time delay (de-sHAC). Controlled model is a structure subjected to earthquake excitations. Numerical simulations are implemented in order to show advantages of the proposed controller. Obtained results include: variation of maximum displacement and maximum absolute acceleration versus time delay; time responses of displacement, absolute acceleration and control force of the structure in the uncontrolled case, the controlled case using the hedge-algebras-based fuzzy controller with input time delay (de-HAC) and the de-sHAC.