Linda M. Hanagan

Controlling Floor Vibration with Active and Passive Devices

This paper reviews research, conducted by the authors over the last decade, pertaining to the control of ex- cessive floor vibration using active and passive devices. The active device studied uses a proof-mass actuator to deliver the control force to the floor system. Effectiveness and stabil- ity characteristics for a single-input/single-output (SISO) con- trol scheme, using velocity feedback, are explored. The SISO system is shown to increase damping to 40% of critical on an experimental floor when amplitudes remain in the linear range. When implemented on two in-place floors, at least a 70% reduction in vibration amplitudes due to walking was ob- served. Next, the benefits of expanding to a practical single- input/multi-output (SIMO) control system are identified. Ad- ditionally, techniques to optimize the SIMO scheme are presented. Because of the stability characteristics of the controlled system, the improvement noted for the SIMO scheme is most dramatic for floors with fundamental frequen- cies near the natural frequency of the actuator. I na2H zfloor example, a SIMO control scheme provided seven times more reduction than that of the SISO system. The passive device research focuses on the experimental implementation of tuned mass dampers (TMDs) to control floor vibration. Two different configurations are explored. The uniqueness of the first device is that liquid filled bladders are used to provide an economical damping mechanism. When implemented on an office floor, a significant improvement of walking vibration lev- els was observed. Satisfaction with the repair was noted from the occupants. The second device utilizes a configuration that has great flexibility in the field, thus allowing for more eco- nomical mass production. Using two TMDs, a significant re- duction of response was noted for the 5 and 6 Hz modes. Research to improve these active and passive strategies continues and will be reported as significant results are achieved.

Semi-active TMD with piezoelectric friction dampers in floor vibration control

This paper analyzes the application of semi-active variable damping TMD (SAVDTMD) with piezoelectric friction dampers as an alternative to existing methods to control floor vibrations, especially walking-induced vibrations. The use of a MDOF floor model in the analysis provides some insight on the effect of modes not targeted in the design of the controller. An optimal semi-active control law originally developed for vehicle suspension control was incorporated into the analytical models. Two floor system examples, typical of those that would have a floor vibration problem, are evaluated and shown to be controlled successfully by the SAVDTMD at both the targeted and untargeted modes. Problems of spillover of the control force to untargeted modes was analyzed and determined to be stabilizing.

Active control of floor vibration: implementation case studies

Progress has been made toward controlling excessive floor vibration by means of active structural control. In this control scheme an electro-magnetic shaker is used to impart control forces on a floor system, thus, reducing the floor vibration levels. This paper presents an overview of the control system setup and describes two case studies where active control was implemented to improve floor vibration characteristics.

Evaluation of Vibration Assessment Criteria and Their Application to Stadium Serviceability

This paper explores the current recommended measures for assessing vibration serviceability in building structures and the recommendations for relating these vibration measures to levels of perception and expected occupant reactions. Two of these assessment measures, the maximum transient vibration value and vibration dose value, are discussed with respect to serviceability in stadium structures. The results of the monitoring and assessment of three stadium structures during several events are presented and these results indicate that the current recommendations are overly conservative in assessing occupant perception. Recommendations for vibration dose levels that are more consistent with the evaluation of events monitored in stadium structures are proposed.

MIMO floor vibration controller design

The MIMO controller proposed in the paper simultaneously determines optimal placements for multiple actuators, sensors and appropriate output feedback gains. The controller design is carried out in the digital domain hence typically lower sampling rates can be used at the implementation stage. A method of exponentially penalizing the persistent states of the system is used to obtain faster settling times in the presence of external disturbances. The nonlinearities associated with actuator saturation due to force/stroke limitation is considered explicitly in the optimization. The algorithm does not require closed form expressions for modal shapes. Hence it is applicable to a wider class of 2D structures that do not readily fall into any regular geometric shape.

Practical Implications of Optimizing an Active Floor Vibration Controller

Lightweight steel floor systems, utilizing typical bay sizes while supporting few non-structural elements, are prone to disturbing levels of floor vibration due to walking excitation. Even though design criteria exist to assess and avoid this problem, decisions based on cost are often made to construct a floor that is prone to excessive vibration. These floors are very difficult to fix by conventional means without great disruption to the occupants. Active control, using a velocity feedback loop and a proof mass actuator to deliver the force, has proven to be a very effective repair with little disruption to the occupants. Perhaps the greatest barrier to wider implementation of this repair technique is cost. To keep costs down while obtaining the best performance possible, it is important to understand the dynamic behavior and interaction of all the elements. This paper explains the important parameters in designing an active control system. Then specific hardware is described and utilized in implementing an active control system in an occupied building.

A Unique Vibration Serviceability Case Study of a Complex Structure

When several occupants of a newly constructed academic building raised a concern of disturbing vibrations in several of the third floor offices, an investigation ensued that aimed to capture and characterize this disturbing vibration. A remote monitoring system was utilized to monitor the offices of interest and the offending vibration was finally recorded. The recorded data indicated that this vibration was not a typical serviceability issue due to walking. The study that followed examined the dynamic characteristics of the floor structure through dynamic testing and consequently several unusual vibration sources were explored ranging from wind or traffic to mechanical equipment to an often overlooked human excitation best described as leg jiggling. Some of the findings related to this unusual and interesting case study are described in this paper.

A Whole Building Cost Perspective to Floor Vibration Serviceability

When selecting between lightweight steel joist floor systems and heavier composite or non-composite systems using rolled steel beams, two issues are generally considered to be in competition. These two considerations are cost and vibration serviceability. In general, it is thought that even though the joist floor is more prone to disturbing vibration levels, it is sometimes a better choice based on economy. This paper explores a whole building cost approach to assessing the economy of the lighter joist system relative to its rolled beam competitor. It is illustrated that other building systems, such as fire protection, are affected by the selection of the floor system, thus affecting total building cost. The end result is a closing of the cost gap between heavier rolled beam floors and lighter joist floors.

Mitigating Existing Floor Vibration Issues in a School Renovation

For over 40 years, students, faculty, and staff have been living with an often disturbing level of floor vibration caused by pedestrian traffic in an open plan library area of a suburban middle school. The library extends just beyond a 47 × 52 ft bay framed with a 3 in. slab on metal deck supported by 28 in deep steel joists spanning the short direction and W36 rolled girders in the long direction. As part of an upcoming major renovation, there is interest in exploring cost effective alternatives to reducing the impact of the current conditions. To quantify and understand the existing behavior and make suggestions to alter the behavior, a research study was undertaken. This paper describes the vibration measurements taken, assesses the behavior found including the surprising impact of higher order modes, and explores possible options to mitigate the impact of vibration on the occupants.

Isolating a Scanning Electron Microscope from Chiller Unit Vibrations

Although a scanning electron microscope (SEM) has very low tolerance to being disturbed by vibration, it requires a chiller for operation. Isolating the SEM from its associated chiller vibration takes careful consideration. This paper presents a case study of the performance of several slab-on-grade configurations. These configurations were specifically constructed to support various water chiller units and other service equipment as well as various vibration sensitive microscopes in a high performance research facility. In this study, the slabs are subjected to shaker-induced harmonic loading similar to that of a water chiller unit used to cool a SEM. The actual performance will be discussed in the context of generic design criteria for sensitive equipment and the SEM manufacturer-specified design criteria.