Earthquake Damage Reduction in Timber Frame Houses Using Small-Size Fluid Damper

Timber frame structures are common traditional methods of housing construction, which use squared-off timber beams, columns, and walls as lateral load-bearing members. The seismic performance of timber frame houses can be secured by the load-bearing capacity of erected braces and walls; however, past major earthquakes have caused severe damage to earthquake-resistant timber frame houses. This study investigates the effect of small-size fluid dampers on the earthquake damage reduction in a timber frame house through earthquake response analyses. A detailed analytical model was generated based on an actual two-story timber frame house, which was designed for the highest seismic grade using the latest Japanese standards. Time-history response analyses were carried out for the analytical model subjected to the 2016 Kumamoto earthquake with and without small-size fluid dampers. The small-size fluid damper is equipped with a relief mechanism for the damping force, and its damping property can be expressed using the Maxwell model. Four or seven fluid dampers were installed in the first story of the model to investigate their effect on the earthquake damage reduction. The results of the earthquake response analyses show that the four and seven fluid dampers can reduce the maximum first-story drift angle by approximately one-third and half, respectively. The dampers suppress the residual deformation, control the elongation of the fundamental period during the response, and restrain the amplitude growth. A small-size fluid damper has an equivalent quake resistance to a conventional structural wall with a wall ratio of 3 plus.

Reliability assessment and seismic control of irregular structures by magnetorheological fluid dampers

The catastrophic damages of past earthquakes show that irregular structures are more vulnerable to seismic excitation. On the other hand, dynamic responses depend on the severity of irregularity which is hard to be determined precisely. In this study, performance and reliability of magnetorheological (MR) fluid dampers in controlling torsional-lateral responses of irregular structures are evaluated. In this regard, plan-asymmetry is studied by considering mass eccentricity; whereas vertical-irregularity is investigated by creating mass difference in adjacent stories of the structure. The performance of MR dampers in seismic control of the structure is then evaluated for passive and semi-active control scenarios. The reliability of the structure-MR damper system is then studied by considering uncertainties in severity of irregularities using the Monte Carlo simulation method. Six types of limit state function are defined and the reliability of the system for controlling the desired responses are derived. The results show satisfactory performance of MR dampers in controlling coupled torsional-lateral responses of the structure in which semi-active control system outperforms the passive control system. The results also confirm that the performance of the control system highly depends on the structure irregularity which should be taken into account for design of a safe and reliable structure.

Effects of Dissipative Systems on the Seismic Behavior of Irregular Buildings—Two Case Studies

Conservation of heritage buildings has become a very important issue in many countries, as it is in Italy, where a great number of existing buildings of historical–artistic importance are seismically vulnerable. To improve existing building behavior, researchers focus on the design of retrofit interventions. This paper presents the application of energy dissipation devices in the retrofit of two existing Reinforced Concrete (RC) buildings, both irregular in plan and along their heights, designed for gravitational loads only. These buildings are representative of Italian public housing built in the 1960s and early 1970s. Technical information and mechanical properties of materials are presented, and non-linear analyses are carried out to evaluate the buildings’ behavior under earthquake loads. Many of their structural members do not satisfy the verifications required by the Italian Building Code. Retrofit interventions with buckling-restrained axial dampers in one building and viscous fluid dampers in the other are proposed. The verifications of the retrofitted buildings and the amount of the energy absorbed by the devices with respect to that absorbed by the unretrofitted buildings show the effectiveness of the proposed interventions. Moreover, it is demonstrated that adequate dispositions of the dissipative devices in plan and along the height increase the torsional stiffness of the buildings, improving their structural response under seismic action.

Design and Development of Smart Semi Active Suspension for Nonlinear Rail Vehicle Vibration Reduction

In this paper, the semi-active suspension in railway vehicles based on the controlled magnetorheological (MR) fluid dampers is examined, and compared with the semi-active low and semi-active high suspension systems to enhance the running safety and ride quality for a high-speed rail vehicle. Predictive model controllers are used as system controllers to determine the desired damping forces for front and rear bogie frame with force track-ability. A 28 degree of freedom (DoF) mathematical model of the rail vehicle is formulated using nonlinear vehicle suspension and nonlinear heuristic creep model. The MR model of Ali and Ramaswamy is formulated to characterize the behavior of the MR damper. The simulation result is validated using the experimental results. Four different suspension strategies are proposed with MR damper, i.e. passive, semi-active low, semi-active high and semi-active smart controller based on predictive model controller. A comparison indicates that the semi-active controller gives the optimum for comfort vibration actuation and improves the ride quality and it has little influence on derailment quotients, offload factors, as a result, it will not endanger the running safety of rail vehicle.

Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 9 — Investigation Regarding Damage Between Furnace and Cage

Boilers in coal-fired thermal power plants were often damaged by earthquakes such as the Great East Japan Earthquake in 2011. Since the coal-fired thermal power generation has been one of the main power generation methods after the Great East Japan Earthquake, mitigation of damage of boilers in thermal power plants by earthquakes is the very important subject in order to recover our daily life immediately after strong earthquakes. Meanwhile, a boiler in a coal-fired thermal power plant was damaged by Hokkaido Eastern Iburi Earthquake in 2018, and this damage was one of the causes of Hokkaido’s prefecture-wide blackout. According to a report by an electric power company, a damage occurred between a furnace and a cage of the boiler. In general, lengths, shapes, weights and so on of a furnace are different from a cage, so vibration characteristics and seismic response are different as well. Thus the connecting part between the furnace and the cage is a weak point in the boiler, and the damages often occurred there. Therefore this paper investigates seismic response of a boiler by a numerical analysis using a frame model from the viewpoint of the damage of the furnace and the cage. Various seismic waves were used as input waves in order to investigate the influence of the input wave. A result of a modal analysis was also provided in this paper.