Excessive Wind-induced Vibrations Research Articles

Wind-Induced Vibration Monitoring of High-Mast Illumination Poles Using Wireless Smart Sensors.

This paper describes the use of wireless smart sensors for examining the underlying mechanism for the wind-induced vibration of high-mast illumination pole (HMIP) structures. HMIPs are tall, slender structures with low inherent damping. Video recordings of multiple HMIPs showed considerable vibrations of these HMIPs under wind loading in the state of Kansas. The HMIPs experienced cyclic large-amplitude displacements at the top, which can produce high-stress demand and lead to fatigue cracking at the bottom of the pole. In this study, the natural frequencies of the HMIP were assessed using pluck tests and finite element modeling, and the recorded vibration frequencies were obtained through computer vision-based video analysis. Meanwhile, a 30.48 m tall HMIP with three LED luminaires made of galvanized steel located in Wakeeney, Kansas, was selected for long-term vibration monitoring using wireless smart sensors to investigate the underlying mechanism for the excessive wind-induced vibrations. Data analysis with the long-term monitoring data indicates that while vortex-induced vibration occurs frequently at relatively low amplitude, buffeting-induced vibration was the leading cause of the excessive vibrations of the monitored HMIP. The findings provide crucial information to guide the design of vibration mitigation strategies for these HMIP structures.

Improving aerodynamic performance of tall buildings using façade openings at service floors

Modern tall buildings demand innovative solutions for combatting excessive wind-induced vibrations and achieving occupant comfort criteria. The integration of building openings can help reduce wind-induced vibrations, but traditional implementation of this strategy places considerable constraints on architectural and structural design. This paper proposes the treatment of building openings as a minor modification where façade elements at service floors are removed while the underlying structure remains unchanged. A systematic investigation of 18 façade opening configurations is performed to assess the impact opening location and quantity on peak floor accelerations at wind speeds corresponding to comfort and structural design thresholds. A single wind azimuth perpendicular to the building surface is considered. Results indicate that both location and quantity of façade openings affect performance, with a larger number of openings achieving better performance. A single opening was most effective when located at 70% of building height, and compliance with ISO10137 comfort limits was achieved with three or more openings. Results were sensitive to geometric details at service floors, particularly at resonant wind speeds. The study provides valuable insight into the strategic placement of façade openings at services floors to reduce wind response in tall buildings while minimising impact on architectural and commercial considerations.

Performance-based design with life-cycle cost assessment for damping systems integrated in wind excited tall buildings

The application of performance-based design (PBD) is gaining increasing interest in the wind engineering community. A popular design approach to minimize wind induced vibrations in flexible civil structures is to size structural stiffness and supplemental damping systems in order to restrict the motion to a given threshold for providing safety and comfort, while ensuring that structural components meet strength requirements. In this paper the PBD paradigm is extended to wind excited tall buildings equipped with motion control systems. The objective is to improve the design of damping systems under different wind events while considering maximum acceleration as performance measure. In addition, since the installation of damping devices implies additional costs (e.g., installation and maintenance costs) while it helps decreasing the costs associated with performance failure, a life-cycle analysis (LCA) is integrated in the PBD. In the LCA framework, the percentage of building occupants affected by discomfort and motion sickness caused by excessive wind-induced vibrations is considered to account for the consequences of different target performance levels. The developed PBD is applied to a 39-story building that has documented issues with excessive vibrations under wind events. The wind load is simulated as a multivariate stochastic process, in the time domain. Two passive vibration mitigation strategies are investigated: viscous and friction dampers, both designed to meet the target performance levels. LCA are conducted for the building equipped with each damper type, and benchmarked against the one without dampers. Results show that the PBD leads to a rational and economically effective approach for the design of the damping systems in wind excited tall buildings.

Probabilistic serviceability-performance assessment of tall mass-timber buildings subjected to stochastic wind loads: Part I - structural design and wind tunnel testing

Tall mass-timber buildings utilize engineered wood panels to form their main gravity and lateral load resisting systems, which makes them lighter and very flexible. As a result, frequent exposure to excessive wind-induced vibrations can cause occupant discomfort and unserviceability due to horizontal floor acceleration and excessive deflection. Therefore, the objective of this and the companion paper is to assess the serviceability performance of tall mass-timber buildings probabilistically. For this purpose, the Alan G. Davenport Wind Loading Chain is adapted as a probabilistic Performance-Based Wind Engineering framework. The framework is applied to quantify the serviceability performance of a 102-m tall mass-timber building. In this paper, a complete tall-mass timber building structural design process is outlined. Wind loads are obtained from aerodynamic wind tunnel tests conducted at the Boundary Layer Wind Tunnel Laboratory at Western University. The design process involves preliminary strength design using the provisions of building codes, design revisions using wind load from wind tunnel tests, and serviceability checks. The structural design of the case study tall mass-timber building considers the axial compression, in-plane-shear, and in-plane and out-of-plane bending moment demands, along with their interactions due to gravity and wind loads. Dynamic analysis is carried out to assess the drift performance of the case study mass-timber building. The results show that the building satisfies the drift requirements prescribed by the building codes with a small safety margin. For the designed tall mass-timber building, an in-depth probabilistic serviceability-performance assessment and vulnerability estimations are presented in the companion paper.

WIND-INDUCED RESPONSE CONTROL MODEL FOR HIGH-RISE BUILDINGS BASED ON RESIZING METHOD

A variety of methods have been applied to reduce the effect of the wind-induced vibration of a high-rise building as the excessive wind-induced vibration at the top of a high-rise building can cause physical and psychological discomfort to the user or the residents. For structural engineers, the most effective approach to control the wind-induced responses of high-rise buildings would be to control the stiffness or natural frequency of the building. This paper presents a practical design model to control the wind-induced responses of a high-rise building. In the model, the stiffness of a high-rise building is maximized to increase the natural frequency of the building by the resizing algorithm. The proposed design model is applied to control the wind-induced vibration of an actual 37-storey building during the initial stage of its structural design.

Across and along-wind responses of tall building

Most modern tall buildings using lighter construction materials are more flexible, which can lead to excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. It is necessary to predict and mitigate such wind-induced vibration at the preliminary design stage. Fluctuating across and along-wind loads acting on a tall building that could not be formulated theoretically were simulated numerically in the time domain using known across and along-wind load spectra. These simulated wind loads were used to estimate the across and along-wind responses of a tall building, which are less narrow-banded processes, based on the state space variable approach. The simulated across-wind response of root-mean-square value (0.0047) and that of KAREEM’s (0.0040) and the simulated along-wind response of root-mean-square value (0.021) and that of SOLARI’s (0.027) were compared. It is found that these are good approximations of closed form responses. Therefore, these numerically simulated across and along-wind loads can be used for across and along-wind responses estimation for the wind-resistant design of a tall building at the preliminary design stage.

Passive control of along-wind response of tall building

Most of modern tall buildings using lighter construction materials with high strength and less stiffness are more flexible, which occurs excessive wind-induced vibration, resulting in occupant discomfort and structural unsafety. It is necessary to predict wind-induced vibration response and find out a method to mitigate such an excessive wind-induced vibration at the preliminary design stage. Recently, many studies have been conducted in using actuator control force based on the linear quadratic optimum control algorithm. It was accepted as a common knowledge that the performance of passive tuned mass damper (TMD) could increase by incorporating a feedback active control force in the design of TMD, which is called active tuned mass damper (ATMD). However, the fact that ATMD is superior to TMD to reduce wind-induced vibration of a tall building is still a question. The effectiveness of TMD for mitigating the along-wind vibration of a tall building was investigated. Optimum parameters of tuning frequency and damping ratio for TMD under a random load which has a white noise spectra were used. Fluctuating along-wind load acting on a tall building treated as a stationary Gaussian random process was simulated numerically using the along-wind load spectra. And using this simulated along-wind load, along-wind responses of a tall building with and without TMD were calculated and the effectiveness of TMD in mitigating the along-wind response of a tall building was found out.

LQG Control of Across-Wind Response of a Tall Building with AMD

Modern tall buildings are more flexible so occur excessive wind-induced vibration resulting in occupant discomfort and structural safety. Many studies to reduce such a wind-induced vibration using a feedback controller and auxiliary devices have been conducted .The optimal control law of linear quadratic Gaussian (LQG) controller is used for reducing the across-wind vibration response of a tall building with an active mass damper (AMD). Fluctuating across-wind load treated as a Gaussian white noise process is simulated numerically in time domain. And using this simulated across-wind load estimated across-wind vibration responses of tall building with AMD using LQG controller.

Active Control of Along-Wind Response of a Tall Building with AMD Using LQR Controller

Most of modern tall buildings using lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. The optimal control technique for reducing along-wind vibration of a tall building based on the linear quadratic regulator (LQR) is presented in this work. Actively controlled reduced along-wind vibration response is obtained from the tall building installed in an active mass damper (AMD) with a LQR controller. Fluctuating along-wind load is generated using numerical simulation method, which can formulate a stationary Gaussian white noise process. Simulating wind load in the time domain using known spectra data of fluctuating along-wind load is particularly useful for estimation of windinduced vibration which is more or less narrow banded process such as a along-wind response of a tall building. In this work, fluctuating along-wind load acting on a tall building treated as a stationary Gaussian white noise process is simulated numerically using the along-wind load spectra proposed by G. Solari in1992. And using this simulated along-wind load estimated the reduced along-wind vibration response of a tall building installed in an AMD with a LQR controller.

LQG Control of Across-Wind Response of a Tall Building

Modern tall buildings using high strength and lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety . Recently, many studies have been advanced in using actuator force as an active control force based on the linear quadratic optimum control theory. It needs to predict the wind-induced response and the optimum control force to reduce the excessive wind-induced vibration. It takes a lot of time and cost to do wind tunnel test needed it, so numerical simulation approach instead of that is recommended sometimes. Simulating wind load in the time domain using known spectra data of fluctuating wind load is particularly useful for some prediction of windinduced vibration which is more or less narrow banded process such as across-wind response of a tall building. The simulation procedure is taken from Deodatis. In this study, fluctuating across-wind load acting on a tall building was simulated numerically in the time domain using the across-wind load spectra proposed by A.Kareem in1982. And using this simulated across-wind load estimated the reduced across-wind vibration response of a tall building using the linear quadratic Gaussian (LQG) control method.

LQR Control of Along-Wind Response of a Tall Building

Modern tall buildings using high strength and lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. Recently, many studies have been advanced in using actuator force as an active control force based on the linear quadratic optimum control theory .It needs to predict the wind-induced response and the optimum control force to reduce the excessive wind-induced vibration. It takes a lot of time and cost to do wind tunnel test needed it, so numerical simulation approach instead of that is recommended sometimes. Simulating wind load in the time domain using known spectra data of fluctuating wind load is particularly useful for some prediction of windinduced vibration which is more or less narrow banded process such as a along-wind response of a tall building. In this study, fluctuating along-wind load acting on a tall building treated as a stationary Gaussian white noise process was simulated numerically in the time domain using the along-wind load spectra proposed by G.Solari in1992. And using this simulated along-wind load estimated the reduced along-wind vibration response of a tall building which has an active tuned mass damper (ATMD) installed based on the linear quadratic regulator (LQR) control method.

Reducing Fatigue in Wind-Excited Support Structures of Traffic Signals with Innovative Vibration Absorber

Support structures of traffic signals are flexible, lightly damped structures that are highly susceptible to wind-induced vibration. The sustained large-amplitude deflections caused by these dynamic vibrations can result in fatigue cracking and failure. The proposed innovative vibration absorber reduces fatigue in support structures of traffic signals with the use of the mass of the signal head as a damped-vibration absorber. This novel concept, referred to as a signal head vibration absorber (SHVA), provides energy absorption in the form of increased damping to the lightly damped signal support structure. A prototype smart vibration absorber, envisioned as an inexpensive retrofit to signal support structures that were experiencing excessive wind-induced vibration, was tested in a full-scale laboratory experiment at the University of Connecticut. The SHVA was experimentally shown to have increased the damping in the signal support structure from 0.2% of the critical damping ratio to 10.1%. For steady state vibration, this difference is equivalent to a 98.3% reduction in the response and virtually eliminates any deflections. A single SHVA can be applied to a wide range of signal support structures while still achieving reasonable performance. The SHVA can change the way vibration in traffic signal support structures is mitigated.

Nondestructive Evaluation of Tuned-Mass-Damper-Type Vibration Absorbers Using Vibration Signatures

Nondestructive evaluation methods are often essential in order to objectively assess the condition of structural and ancillary systems for bridges, particularly in cases where visual methods provide only limited or subjective data and the function of the systems being evaluated may not be disturbed using destructive evaluation techniques. This paper describes a nondestructive evaluation procedure that was developed to objectively assess the current condition of a system of 920 aged vibration absorbers installed on a long span cantilever truss bridge. The vibration absorbers, which are essentially tuned mass dampers consisting of a steel weight attached to the end of a viscoelastic rubber stem, were installed soon after the bridge was opened to mitigate the effects of excessive wind-induced vibrations that had occurred in many of the truss members. A nondestructive evaluation procedure was developed because the vibration absorbers had to remain in service during the evaluation process, and there were only a limited number of spare absorbers that could be used to replace any that might be destructively tested. The complete evaluation program included nondestructive vibration testing in the laboratory using impact methods to determine the current dynamic properties of the absorbers, and field testing to evaluate the energy dissipation characteristics of the installed vibration absorbers as they were actually operating. In addition, a limited number of destructive material tests were conducted in order to corroborate the results of the nondestructive tests. This evaluation program revealed that the current performance characteristics of the aged vibration absorbers were within the limits of the original design specifications, and that the synthetic rubber material used for the vibration absorbers had experienced no appreciable deterioration after nearly 25 years of continuous service.

Wind vibration mitigation of long-span bridges in hurricanes

Despite the massive population growth in the south and southeast along the hurricane coast of the United States, the transportation infrastructure has not increased its capacity accordingly. Long-span bridges are usually the backbones of transportation lines along the coastal areas. When a hurricane is approaching, these long-span bridges sometimes have to be closed in order to ensure the safety of the bridge as well as the transportation on them due to excessive wind-induced vibrations, which however greatly reduces the capability of hurricane evacuation through the bridges. To date, bridge vibration controls in high wind speeds have not been adequately addressed. Most previous control work dealt with the bridge buffeting under moderate wind speeds, along with some cases of flutter controls in high wind speeds. While active control devices may provide satisfactory multi-objective control performance in a full range of wind speeds, their dependence on external energy supply has hindered their applications to the disaster evacuations. Recently, some aerodynamic controls using flaps were proposed to control flutter instability. However, their applicability to buffeting control has not been reported and established. Vehicles on bridges act as a sort of Spring-Damper-Subsystems (SDSs) to the bridge. The SDS is used here as a general terminology to differentiate with Tuned Mass Dampers (TMDs). The former may or may not be pre-tuned, while the latter is pre-tuned to the optimal value (usually the fundamental frequency of the structural system) for efficient vibration control. The objective of the present study is to investigate the effects of different SDSs (with different vibration frequencies) on the bridge performance during hurricane evacuations and develop a truck-type of movable passive SDS. The passive nature makes the control approach more reliable than the active one, considering the reality that power may not be available during the hurricane disasters. The temporary/movable SDS can be conveniently driven on the existing bridges when necessary, and be removed when it is not needed. It has been reported that the gust wind speed during hurricanes could be up to 60-80 m/s or more in the United States and other areas. Though the duration may be short, the consequence of such strong winds may be catastrophic for both the safety of the bridge and the safety of traffic on the bridge.