Mingfeng Huang

Vibration Control of a Wind-Excited Benchmark Tall Building with Complex Lateral-Torsional Modes of Vibration

This paper describes a proposed wind-excited benchmark tall building incorporating three-dimensional lateral-torsional modes of vibration, which is typical of a significant number of modern tall buildings. A series of wind tunnel pressure tests were conducted on a 1:400 scale model to determine the translational and torsional wind forces acting on the benchmark building. A finite element model was also constructed and mass, damping, and stiffness matrices were subsequently formulated as an evaluation model for numerical analysis. The evaluation model was further simplified to a state reduced-order system (ROS) using the state order reduction method. A numerical vibration control example was conducted to demonstrate the suppression of the wind-induced three-dimensional lateral-torsional motions using a bi-directional tuned mass damper (TMD) incorporating two magnetorheological (MR) dampers, one in each orthogonal direction, to act as a semi-active control system, referred to as a smart tuned mass damper (STMD). The optimal control forces generated by the MR dampers were obtained through the linear quadratic regulator (LQR) to minimize the storey accelerations. The formulation details, methodology and numerical simulation results are outlined in this paper.

Stiffness Optimization for Wind-Induced Dynamic Serviceability Design of Tall Buildings

Contemporary tall buildings with increasing height and slenderness are highly sensitive to the actions of wind. The structural design of modern tall buildings is generally governed by the need to provide adequate strength and stiffness against dynamic movement induced by strong wind. In addition to the strength-based safety design considerations, the major design effort of a tall building is related to the assessment of the wind-induced serviceability design requirements in terms of lateral drift and motion perception criteria. With tall buildings of today continuing to increase in height, the mitigation of wind-induced vibrations in tall buildings becomes a more critical challenge in the design synthesis process. This paper presents an integrated dynamic analysis and computer-based design optimization method for minimizing the structural cost of tall buildings subject to wind-induced serviceability acceleration design criteria. Once the optimal dynamic serviceability design problem is explicitly formulat...

INTEGRATED STRUCTURAL OPTIMIZATION AND VIBRATION CONTROL FOR IMPROVING WIND-INDUCED DYNAMIC PERFORMANCE OF TALL BUILDINGS

Structural optimization and vibration control have long been recognized as effective approaches to obtain the optimal structural design and to mitigate excessive responses of tall building structures. However, the combined effects of both techniques in the structural design of wind-sensitive tall buildings with excessive responses have not been revealed. Therefore, this paper develops an integrated design technique making use of both the advantages of structural optimization and vibration control with an empirical cost model of the control devices. While the structural optimization is based on a very efficient optimality criteria (OC) method, a smart tuned mass damper (STMD) is used for the structural control purposes. Utilizing data obtained from synchronous pressure measurements in the wind tunnel, a 60-story building of mixed steel and concrete construction with three-dimensional (3D) mode shapes was employed as an illustrative example to demonstrate the effectiveness of the proposed optimal performance-based design framework integrating with structural vibration control.

Experimental and computational simulation for wind effects on the Zhoushan transmission towers

Long-span transmission tower and conductor line systems become important infrastructures in modern societies. The analysis of wind-induced dynamic responses of transmission towers is an essential task in the design of spatial lattice tower structures. Wind effects on the worlds tallest transmission tower are presented in this paper. The tower with a total height of 370 metres, part of the Zhoushan long-span transmission project, enables high voltage conductor lines to span as long as 2750 metres over the typhoon-prone sea strait. A multi-DOF aeroelastic model test with and without conductor lines was carried out to investigate the dynamic performances of Zhoushan tower during typhoon events. Using the response measurement results in the wind tunnel, the inertial force based gust loading factors (GLFs) are applied to represent dynamic wind load effects on the tower for structural design purposes. Time domain computational simulation approach is also employed to predict dynamic responses of the transmission tower and the displacement based gust response factors (GRFs). The fair comparison of GLFs or GRFs are made between the results of the experimental approach and the computational simulation approach, which is an effective alternative way for quickly assessing dynamic wind load effects on high-rise and complex tower structures.

Hermite Extreme Value Estimation of Non-Gaussian Wind Load Process on a Long-Span Roof Structure

AbstractThis paper presents a combined study of wind tunnel experiment and numerical simulation of the wind-induced pressures on the long-span roof of the Hangzhou East Railway Station Building. Wind tunnel tests were performed on a 1∶250-scale rigid model of the station building. Based on the measured pressure data, the third and fourth statistical moments of the pressure processes were evaluated to quantify the non-Gaussian nature of the wind-induced pressures on the station roof. Using the recently reported Hermite moment model, an analytical form of the non-Gaussian peak factor was proposed for a given hardening load process and was verified using numerical integration. The currently available simulation algorithm was revised to generate sample functions of skewed hardening load processes. The simulated pressure data samples provide a basis for the direct statistical analysis of extreme peaks. The peak factors for non-Gaussian wind load effects were estimated by employing various state-of-the-art meth...

Time-domain dynamic drift optimisation of tall buildings subject to stochastic wind excitation

Wind-resistant design of tall buildings has been traditionally treated using the equivalent static load approach. In order to account for the uncertainties in random wind excitation, it is necessary to develop a comprehensive and reliable dynamic optimisation technique in the time domain. The optimal lateral stiffness design problem of wind-excited tall buildings consists of (1) identifying the critical dynamic drift response in the time domain and (2) searching for the optimal distribution of element stiffness of the building subject to multiple drift design constraints. The critical time-history drift constraints of a wind-excited building are first treated by the worst-case formulation and then explicitly expressed in terms of element sizing variables using the principle of virtual work. The extreme value distribution and the Gaussian assumption are employed to formulate and simplify the probabilistic drift constraints, which are explicitly considered in the dynamic optimisation problem. The system reliability associated with the inter-story drift is estimated approximately by the bound approach to ensure that the most cost-efficient solution also attains an acceptable reliability level. A full-scale 45-story building example under wind tunnel derived time history wind loading is presented to illustrate the effectiveness and practicality of the reliability-based dynamic optimisation technique.

Two-Parameter Bifurcation and Stability Analysis for Nonlinear Galloping of Iced Transmission Lines

AbstractThis paper presents an analytical approach in the study of bifurcation and stability behavior for nonlinear galloping of iced transmission lines. Equations of motion are established to describe three-dimensional galloping behavior observed on iced transmission lines. Stability analysis of iced conductor galloping is carried out. The center manifold theory, together with the normal form theory, is used to derive the governing bifurcation equations. A new formula is also proposed to calculate the maximum dynamic tension of iced conductors. The technique developed in this paper is implemented using a symbolic analysis module for practical usage. A real transmission line with a span of 244 m, which was damaged by the galloping accidents, is presented to demonstrate the effectiveness and accuracy of the developed two-parameter bifurcation analysis technique for nonlinear galloping of iced conductors. The galloping amplitudes in three orthogonal directions are analytically obtained for a broad range of ...

Full-scale measurement and analysis of K11 building in Hong Kong during typhoon

The full-scale measurement of typhoon effects on K11 building in Hong Kong was studied.This paper presented the acceleration data of the building under Typhoon Kammuri in 2008.The acceleration data were analyzed in terms of the third and fourth moments,The occupant comfort of the building under wind-induced vibration was evaluated.The vibration frequencies of the building were identified by spectral analysis technique,and were compared with the finite element method results and empirical results.Both the traditional peak factor method and the improved Gumbel method were applied to estimating the peak factor of wind-induced acceleration response.The peak factor results show good agreement with the other two methods.The values in GB50009-2001 are low.

Dynamic Wind Load Combination for a Tall Building Based on Copula Functions

Dynamic wind loads on tall buildings can be decomposed into three components, i.e. two translational components and one torsional component. When one component reaches its maximum, the other two components have low probability to take their maximum values. It is common to use combination coefficients for estimating the mean extremes of linearly combined wind loads. The traditional design practice for determining wind load combinations relies partly on some approximate combination rules and lacks a systematic and reliable method. Based on the high frequency force balance (HFFB) testing results, wind loads can be acquired in terms of time history data, which provides necessary information for the more rigorous determination of combination coefficients by probabilistic methods. In this paper, a 3D copula-based approach is proposed for determining the combination coefficients for three stochastic wind loads associated with a specific exceedance probability and a set of 3D realizable equivalent static wind loads (ESWLs) on tall buildings. Using the measured base moment and torque data by the HFFB wind tunnel test, a case study is presented to illustrate the effectiveness of the proposed framework to determine the dynamic wind load combinations and associated 3D realizable ESWLs on a full-scale 60-story building.

Optimal Wind Resistant Performance-Based Design of Tall Buildings

The world is experiencing an upsurge of tall building construction. Recent trends toward developing increasingly taller and irregularly-shaped complex buildings imply that these structures are potentially more sensitive to wind excitation. Structural engineers are facing the challenge of striving for the most efficient and economical design solution while ensuring that the final design of a building must be serviceable for its intended function, habitable for its occupants and safe over its design life-time. Performance-based design (PBD) is a modern approach to the design of building structures. While PBD is still under active development primarily in seismic engineering, the concept of performance-based wind engineering should be extended to the design of wind sensitive tall buildings. This paper presents a computer based technique for optimal wind resistant performance-based design of tall buildings under various levels of wind hazards. Once the wind-induced loads and responses of a tall building structure under multiple levels of wind events are accurately determined, the optimal performance-based design problem can then be explicitly formulated. A rigorously derived Optimality Criteria (OC) method is to be developed to solve the optimal structural solution satisfying the strength (life-safety), drift (damage) and acceleration (occupant comfort) design performance constraints. The effectiveness and practicality of the optimal design technique are illustrated through an actual 40-story building with complex 3D mode shapes.