In reinforced concrete structures, human-induced vibration can cause major serviceability issues. A number of recent significant projects, such as the Millennium Bridge in London, have encountered this issue. The bridge was subjected to synchronised lateral excitation. To eliminate the problem, the bridge had to be closed and mitigated. From this example, it is evident that human-induced excitement must be regarded seriously and dealt with appropriately. Several human caused excitation mitigation solutions will be covered in this paper. Vibration in the Structure of the London Millennium Bridge: Human footsteps caused lateral excitation on the London Millennium Bridge.
Passive Vibration Control Methods
How Can Vibrations Caused by Humans Be Controlled in Reinforced Concrete Structures?Human-induced vibration mitigation techniques include: Vibration control approaches that are passive Methods of active vibration control Semi active vibration control methods (or regulated passive approaches) (or controlled passive methods)The ways of vibration mitigation listed above can be utilised singly or in combination to get the desired outcome. The following sections will go over the major vibration mitigation systems: Passive approaches reduce energy dissipation demand in the primary structure by consuming the majority of the energy put on it. Isolation systems not only enable energy absorption, but they also allow the structure to be more flexible. As a result, the amount of energy that might be transferred to the structure would be significantly reduced.
Furthermore, passive dampening additional tools use the majority of the energy that the structure encounters. As a result, such a device protects structures from the potentially harmful effects of inputted energy. Supplemental passive damping devices generate forces that oppose the movement of the structure to which they are attached. The most significant benefit of such devices is that their dynamic characteristics will not alter over time. They also do not require an external source of energy to assist them in managing vibrations. As a result, these devices are unable to cope with changes in external loads such as excitation frequencies. Finally, there are a variety of passive damping supplementary devices that can be employed to address vibration serviceability issues in reinforced concrete structures caused by human produced excitation.
Stock Bridge Type Damper
Friction dampers, viscous dampers, viscoelastic treatments, tuned mass dampers or vibration absorbers, tuned liquid dampers, pendulum tuned mass dampers, unbonded braces, impact dampers, confined layer damping, and yield plates are only a few examples. show how passive approaches were used to control the imposed vibration that the structure was subjected to. Damper for Bridges in Stock Damper of the Stock Bridge Type The Millennium Footbridge in London has a pier damper. A pier damper is used to control lateral excitation in the London Millennium footbridge (tuned mass damper) Methods of Active Vibration Control The fact that active vibration control is linked to an external source of energy is the most noticeable feature. This energy is utilised to control the power of actuators, which govern the force applied to a structure.
Active vibration control techniques are capable of adapting to a variety of loading circumstances and controlling various vibration modes in the structure.The design methodologies for active vibration control systems are somewhat varied, and the choice of each method is based on a number of parameters such as preferred performance objectives, the nature of the active control device, and the characteristics of the controlled target.Finally, there are active tendon control systems, active mass drivers, active gyro stabilisers, active pulse control systems, active aerodynamic appendages, and active limited layer dampers, among others. Depicts an active vibration control system that detects vibration using sensors before effectively controlling it.
Controlled Passive Methods
Semi active vibration is a technique that combines active and passive vibration control systems, as the name suggests. The stiffness and damping characteristics of semi active vibration control devices can be modified in real time, but energy cannot be supplied into the regulated system. Semi active vibration control devices include electrorheological dampers netorheological dampers semi active tuned liquid dampers semi active pendulum tuned mass dampers and semi active tuned vibration absorbers Typical electrorheological fluid damper configuration shows a typical electrorheological fluid damper configuration. Liquid-tuned semi-active damper setup: Liquid-tuned semi-active damper arrangement.
You can request a copy of the full text of this study directly from the authors. Bibliography The mitigation of earthquake and wind-induced vibrations in civil engineering structures has been the subject of previous civil engineering vibration mitigation research. This paper examines a variety of solutions that can be used to mitigate much lower-level human-induced vibrations in civil engineering structures. It shows technologies (or combinations of technologies) that have been used in real-world civil engineering structures, as well as some structural response reduction levels (velocity, acceleration) that have been achieved. This is the first time a survey of vibration mitigation approaches with this specific focus has been given. A brief overview of human-induced vibration serviceability is offered, with a focus on floors, foot bridges, grandstands, and staircases.
Resonant and transient vibration responses
Buildings along transportation corridors frequently experience floor vibrations caused by passing trains or cars, which is a source of anxiety for property owners. A mathematical, impedance-based (wave propagation) model for forecasting train-induced floor vibrations in structures is described in this work. The model predicts velocities, velocity ratios, and impedances analytically. The model’s analytical predictions were compared to and confirmed against measured floor vibrations in a four-story scale model building built by the authors. These forecasts were very close to the actual results. The results of the approach show that the vibrations on the upper floors can be reduced by increasing the thickness of a floor on a lower level of the building. A blocking floor is a lower-level floor with a thicker thickness.
The key UK design recommendations for single human walking excitation of high-frequency floors, issued by the Concrete Society and Concrete Centre, were released more than ten years ago. The corresponding walking force model is derived from a set of single footfalls recorded on a force plate, and it employs a deterministic technique that counters the stochastic character of human-induced loading, including intra- and inter-subject variability. This study proposes an updated version of this force model for high-frequency flooring, which includes statistically specified parameters generated from a large database of walking force time histories, which includes numerous consecutive footfalls continually measured on an instrumented treadmill. The revised model provides for probability-based vibration level prediction for any likelihood of non-exceedance, whereas the present model only allows for a single chance of non-exceedance.
Acceptance Criteria for Human Comfort
Furthermore, the updated model increases the suggested cut-off frequency between low and high-frequency floors from 10 to 14 Hz. This is to account for higher force harmonics that can still cause the resonant vibration response to occur, as well as to avoid excessive amplification of the vibration response due to the near-resonance effect. A damping factor is used to account for minor near-resonance effects. Numerical simulations employing a finite element model of a structure and treadmill forces are used to compare the performance of the existing and upgraded models. The findings reveal that, whereas the previous model overestimates or underestimates vibration levels depending on the pacing rate, the new model yields statistically valid vibration response estimated.
For instance, machinery-induced vibrations can be minimised by using isolating mounts or motion-arresting pads.
Structural vibration control is to control the vibration of the structure under earthquake.
Abstract. It is generally perceived that vibration is not an issue for reinforced concrete floor systems.
Also Check
Operations in Embankment Dam Construction