Yanhui Liu

Bio: Yanhui Liu is an academic researcher from Guangzhou University. The author has contributed to research in topics: Damper & Natural rubber. The author has an hindex of 1, co-authored 3 publications receiving 8 citations.

Experimental and numerical studies on the optimal design of tuned mass dampers for vibration control of high-rise structures

Abstract: The use of Tuned Mass Damper (TMD) is effective in reducing the vibration response of the high-rise structures and in improving the structural comfort and safety under wind and earthquake excitation. However, it is occasionally difficult to use TMD for a given vibration control project when the available structural space cannot meet the requirements for the stroke of the designed TMD. If the TMD could be designed with a reduced stroke requirement, not only it will make the resign design a feasible vibration control option but also a cost-effective one. This paper presents an optimal design method for the TMD design, where in frequency domain and using genetic algorithm under random excitation the control effect of TMD is treated as the optimization objective and the stroke of TMD is chosen as the constraint condition. A 168-meter high tower with TMD was used as an engineering example for a numerical study, where the optimization method was used to obtain the TMD design parameters. Additionally, a TMD with an eddy current damper was designed according to optimal design method and was introduced to a 7-story scaled down structural model. Shaking table tests were performed to evaluate the performance of the designed TMD using the optimization design method, and compared against the one designed by Den Hartog’s formula. The numerical simulations show that the TMD designed with the proposed method to achieve a limited TMD stroke has a similar control effectiveness in comparison to the Den Hartog’s solution. While achieving a good control performance, the proposed design method also effectively limits the TMD stroke where the peak TMD displacement of the proposed design method is 0.78 m, much smaller than that obtained by Den Hartog’s formula, 0.95 m. Similar results are observed in the experimental study. Therefore, the proposed optimal design method can improve the reliability of the TMD and it reduces the probability of failure.

Adaptive-passive tuned mass damper for structural aseismic protection including soil–structure interaction

Abstract: As one of the most traditional vibration mitigation devices, tuned mass dampers (TMDs) are applied widely in aseismic protection of building structures. The control effect of a passive TMD is depended on its parameters, especially the frequency ratio. Nevertheless, passive TMDs are high sensitive to the frequency detuning issue, and a mistuned TMD will lose its aseismic protection. Soil-structure interaction (SSI) will deviate the structural frequency and lead to a mistuned TMD. Besides, different soil conditions will lead to different frequency deviations of the primary structure. However, it may be difficult to obtain parameters of the soil exactly. To solve this problem, a recently developed adaptive-passive eddy current pendulum TMD (APEC-PTMD) is applied to a benchmark 40-story tall building including SSI in this study, and four different soil conditions are considered. The APEC-PTMD can identify the optimal TMD frequency in the building with different soil types, and then retune itself through adjusting the pendulum length, and also the air gap between the conduct plate and permanent magnets to reset its damping ratio. Therefore, no prior knowledge of the soil condition is needed for the APEC-PTMD. To verify the aseismic protection effect, 44 far-field earthquake excitations are chosen, and two passive TMDs are used for comparison, while one is optimized for the base-fixed structure and the other is optimized based on the dense-soil model. The passive TMD will become mistuned when SSI is considered or soil parameters are changed, while APEC-PTMD can adapt to the structural dominant frequency with different SSI. Therefore, it always works as a passive TMD with well-tuned parameters. Results show that the APEC-PTMD has a better aseismic protection than the passive TMD, especially in the soft-soil model, and it has an excellent control effect compared to the without TMD case at the same time. • An adaptive-passive eddy current tuned mass damper (APEC-TMD) with variable pendulum length and damping ratio is proposed. • The APEC-TMD is applied to a benchmark high-rise building considering soil-structure interaction (SSI). • The APEC-TMD can identify the dominant frequency of the building with different SSI condition. • The APEC-TMD has the best structural aseismic protection performance compared to passive TMDs.

Lead-rubber-bearing with negative stiffness springs (LRB-NS) for base-isolation seismic design of resilient bridges: A theoretical feasibility study

Abstract: • A novel LRB-NS system is developed to improve the base-isolation efficiency of LRB for bridges. • Theoretical deduction of NS-LRB system behavior is performed. • Mechanics, dynamic properties, and design procedure of LRB-NS system are provided. • NS springs show dual functionalities under slight and severe excitations. • LRB-NS can improve the system-level performance of base-isolated bridges. Advanced seismic isolation devices and systems have been recognized as promising measures toward resilient design of bridge structures. This paper proposes a base isolation system using lead rubber bearing with negative stiffness springs (LRB-NS), which is composed of traditional lead rubber bearing (LRB) and pre-compressed springs, installed at the bottom of bridge columns. These springs contain dual functionalities: (1) provide negative stiffness (NS) and negative restoring force during slight shakings and elongate the structural period that is determined by LRB products; and (2) offer significant restoring forces to prohibit excessive peak deformation and protect bearings from failure when subjected to strong earthquakes. Theoretical and analytical studies are first conducted to illustrate fundamental mechanics of the proposed LRB-NS device, followed by a series of parametric analyses to understand the influential factors of this device on structural behavior. Moreover, fragility analyses of typical highway bridges are conducted to demonstrate the feasibility of LRB-NS device via comparisons with non-isolated and traditional LRB systems. The results show that the LRB-NS device can be well designed to mitigate seismic demands of bridge columns, as well as highly effective to suppress the excessive deformation in bearings that often occurs in the traditional LRB system under strong excitations. The LRB-NS device can be used to facilitate the resilient seismic design of bridge structures.

Seismic Vulnerability of Cabinet Facility with Tuned Mass Dampers Subjected to High- and Low-Frequency Earthquakes

Abstract: The study investigates the collapse probability of a cabinet facility with a tuned mass damper (TMD) subjected to high- and low-frequency earthquakes. For this aim, a prototype of the cabinet in Korea is utilized for the numeric simulation. The accuracy of the finite element model is evaluated via the impact hammer tests. To mitigate the seismic response of the structure, a TMD system is developed whose properties are designed based on the outcomes from the modal analysis (i.e., modal frequencies and mode shapes). Furthermore, the influences of earthquake frequency contents on the seismic response are evaluated. The numeric analyses are conducted using a series of eighty earthquakes that are classified into two groups corresponding to low- and high-frequency motions. Finally, fragility curves are developed for the cabinet subjected to different ground motion sets. The results quantify the seismic vulnerability of the structure and demonstrate the influences of earthquake frequency contents and the vibration control system on the seismic response of the cabinet.

Investigation on the efficiency of deep liquid tanks in controlling dynamic response of high-rise buildings: A computational framework

Abstract: High-rise buildings are subjected to large deflection when exposed to environmental loading due to cyclones or earthquakes. Different methodologies are available to control such excessive deflections. The present work explores the utilization of liquid storage service tanks placed at the roof of the high-rise buildings in the form of passive damping devices in controlling unwanted vibration. These deep liquid tanks (DLTs) have a higher depth ratio than the conventional tuned liquid dampers (TLDs). A 10-storeyed reinforced concrete (RC) building model, square shaped, symmetric in plan, is considered for the numerical assessment. A multiple TLD (MTLD) system is designed to control the roof displacement of the building. This MTLD system is then replaced by a single DLT, which provides slightly better control efficiency under resonant harmonic loading. The system coupling facility of ANSYS Workbench provides fluid structure interaction (FSI) platform to solve structure-fluid coupled dynamics. ANSYS Transient Structural module is used to solve the structure part using the finite element analysis (FEA), whereas, ANSYS (FLUENT) for the fluid part using the computational fluid dynamics (CFD). The focus of the work is to develop a practical framework to demonstrate the efficacy of such liquid storage tanks considering the FSI effect using coupled FEA-CFD analysis. The aim is to arrive at an appropriate damper efficiency considering the position and size of the DLT with different liquid filling level. The selected DLT, along with the position is replaced by distributed deep liquid tanks (DDLTs), conserving the overall mass of the damper (liquid). It is observed that the DDLT may not be an effective alternative to the single DLT device. In specific cases, properly designed DLTs can be recommended over MTLD system as effective damping devices for vibration mitigation purposes in high-rise buildings.