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CONTENTS
Volume 31, Number 5, November 2020
 

Abstract
Despite that the failure of sign structure may not have disastrous consequence, its sheer number still ensures the need for rigorous safety standard to regulate their maintenance and construction. During its service life, a sign structure is subject to extensive wind load, sometimes well over its permissible design load. A fragility analysis of a sign structure offers a tool for rational decision making and safety evaluation by using a probabilistic framework to consider the various sources of uncertainty that affect its performance. Wind fragility analysis was used to determine the performance of sign structure based on the performance of its connection components. In this study, basic wind fragility concepts and data required to support the fragility analysis of the sign structure such as sign panel's parameters, connection component's parameters, as well as wind load parameters were presented. Fragility and compound fragility analysis showed disparity between connection component. Additionally, reinforcement of the connection system was introduced as an example of the utilization of wind fragility results in the retrofit decision making.

Key Words
compound fragility; mechanical and chemical anchor connection; protruding sign structure connection system; wind fragility assessment; sign structure reinforcement

Address
Viriyavudh Sim and WooYoung Jung:Department of Civil Engineering, Gangneung-Wonju National University, 7 Jukheon-gil, Gangneung 25457, Republic of Korea


Abstract
Long-span bridges with high flexibility and low structural damping are very susceptible to the vortex-induced vibration (VIV), which causes extremely negative impacts on the ride comfort of vehicles running on the bridges. To assess the ride comfort of vehicles running on the long-span bridges subjected to VIV, a coupled wind-vehicle-bridge system applicable to the VIV case is firstly developed in this paper. In this system, the equations of motion of the vehicles and the bridge subjected to VIV are established and coupled through the vehicle-bridge interaction. Based on the dynamic responses of the vehicles obtained by solving the coupled system, the ride comfort of the vehicles can be evaluated using the method given in ISO 2631-1. At last, the proposed framework is applied to several case studies, where a long-span suspension bridge and two types of vehicles are taken into account. The effects of vehicle speed, vehicle type, road roughness and vehicle number on the ride comfort are investigated.

Key Words
ride comfort assessment; wind-vehicle-bridge system; vortex-induced vibration; road vehicle; long-span bridge

Address
Helu Yu, Bin Wang, Guoqing Zhang, Yongle Li and Xingyu Chen:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China


Abstract
To investigate the effects of central buckles on the dynamic behavior and flutter stability of long-span suspension bridges, four different connection options between the main cable and the girder near the mid-span position of the Aizhai Bridge were studied. Based on the flutter derivatives obtained from wind tunnel tests, formulations of self-excited forces in the time domain were obtained using a nonlinear least square fitting method and a time-domain flutter analysis was realized. Subsequently, the influences of the central buckles on the critical flutter velocity, flutter frequency, and three-dimensional flutter states of the bridge were investigated. The results show that the central buckles can significantly increase the frequency of the longitudinal floating mode of the bridge and have greater influence on the frequencies of the asymmetric lateral bending mode and asymmetric torsion mode than on that of the symmetric ones. As such, the central buckles have small impact on the critical flutter velocity due to that the flutter mode of the Aizhai Bridge was essentially the symmetric torsion mode coupled with the symmetric vertical mode. However, the central buckles have certain impact on the flutter mode and the three-dimensional flutter states of the bridge. In addition, it is found that the phenomenon of complex beat vibrations (called intermittent flutter phenomenon) appeared in the flutter state of the bridge when the structural damping is 0 or very low.

Key Words
long-span suspension bridge; central buckle; flutter stability; time-domain; beat vibration

Address
Yan Han:School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China

Kai Li:School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China

C.S. Cai:Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge LA 70803, U.S.A.

Abstract
Weibull distribution is a conspicuous distribution known for its accuracy and its usage for wind energy analysis. The two and three parameter Weibull distributions are adopted in this study to fit wind speed data. The daily mean wind speed data of Ennore, Tamil Nadu, India has been used to validate the procedure. The parameters are estimated using maximum likelihood method, least square method and moment method. Four statistical tests namely Root mean square error, R2 test, KolmogorovSmirnov test and Anderson-Darling test are employed to inspect the fitness of Weibull probability density functions. The value of shape factor, scale factor, wind speed and wind power are determined at a height of 100m using extrapolation of numerical equations. Also, the value of capacity factor is calculated mathematically. This study provides a way to evaluate feasible locations for wind energy assessment, which can be used at any windy site throughout the world.

Key Words
three parameter Weibull distribution; estimation of Weibull parameters; statistical tests; capacity factor; extrapolation; wind power density

Address
K. Sukkiramathi:Department of Mathematics, Sri Ramakrishna Engineering College, Coimbatore, India

R. Rajkumar:Department of Mathematics, Kumaraguru college of Technology, Coimbatore, India

C.V. Seshaiah:Department of Basic Science and Humanities, GMR Institute of technology, Srikakulam, India

Abstract
The modern tall buildings are often constructed as an unconventional plan and as twin buildings. Wind load on the tall building is significantly influenced by the presence of another building in the near vicinity. So, it is imperative to study wind forces on an unconventional plan shaped tall building. Mean wind pressure coefficients of a square and 'H' plan shape tall buildings are investigated using wind tunnel experiments. The experiments were carried out for various wind directions from 00 to 900 at an interval of 300 and various locations of the identical interfering building. The experimental results are presented at the windward face from the viewpoint of effects on cladding design. To quantify the interference effects, interference factors (I.F) are calculated. Mean pressure coefficients of both models are compared for isolated and interference conditions. The results show that pressure reduces with an increase in wind angle till 600 wind direction. The interfering building at full blockage interference condition generates more suction than the other two conditions. The interference factor for both models is less than unity. H-plan building model is subjected to a higher pressure than the square model.

Key Words
Tall buildings; wind pressure; interference factor; mean pressure coefficients (Cp), blockage, wind tunnel

Address
Suresh K Nagar:Delhi Technological University, Delhi, India

Ritu Raj:Faculty of Civil Engineering, Delhi Technological University, Delhi, India

Nirendra Dev:Faculty of Civil Engineering, Delhi Technological University, Delhi, India

Abstract
The buffeting response is a vital consideration for long-span bridges in typhoon-prone areas. In the conventional analysis, the turbulence and structural vibrations are assumed as stationary processes, which are, however, inconsistent with the non-stationary features observed in typhoon winds. This poses a question on how the stationary assumption would affect the evaluation of buffeting responses under non-stationary wind actions in nature. To figure out this problem, this paper presents a comparative study on buffeting responses of a long-span cable-stayed bridge based on stationary and non-stationary perspectives. The stationary and non-stationary buffeting analysis frameworks are firstly reviewed. Then, a modal analysis of the example bridge, Sutong Cable-stayed Bridge (SCB), is conducted, and stationary and non-stationary spectral models are derived based on measured typhoon winds. On this condition, the buffeting responses of SCB are finally analyzed by following stationary and non-stationary approaches. Although the stationary results are almost identical with the non-stationary results in the mean sense, the root-mean-square value of buffeting responses are underestimated by the stationary assumption as the timevarying features existing in the spectra of turbulence are neglected. The analytical results highlights a transition from stationarity to non-stationarity in the buffeting analysis of long-span bridges.

Key Words
buffeting analysis; cable-stayed bridge; typhoon winds; stationary; non-stationary

Address
Tianyou Tao and Hao Wang: Key Laboratory of C&PC Structures of Ministry of Education, Southeast University, Nanjing 211189, China/ School of Civil Engineering, Southeast University, Nanjing 211189, China

Peng Shi and Hang Li:School of Civil Engineering, Southeast University, Nanjing 211189, China

Abstract
This study focused on the non-synoptic, tornado-like wind-induced effects on flexible horizontal structures that are extremely sensitive to winds. More specifically, the nonuniform, intensive vertical wind-velocity and transient natures of tornado events and their effects on the global behavior of a long-span bridge were investigated. In addition to the static part in the modeling of tornado-like wind-induced loads, the motion-induced effects were modeled using the semi-empirical model with a two-dimensional (2-D) indicial response function. Both nonlinear wind-induced static analysis and linear aeroelastic analysis in the time domain were conducted based on a 3-D finite-element model to investigate the bridge performance under the most unfavorable tornado pattern considering wind-structure interactions. The results from the present study highlighted the important effects due to abovementioned tornado natures (i.e., nonuniform, intensive vertical wind-velocity and transient features) on the long-span bridge, and hence may facilitate more appropriate wind design of flexible horizontal structures in the tornado-prone areas.

Key Words
tornado-like winds; long-span bridge; wind-induced static loads; motion-induced loads; two-dimensional indicial response function; aeroelastic analysis

Address
Jianming Hao:School of Highway, Chang'an University, Xi'an, Shaanxi, 710064, China/ Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, NY, 14260, U.S.A.

Teng Wu:Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, NY, 14260, U.S.A.

Abstract
The first-order method for estimating the extreme wind pressure on building envelopes with consideration of the directionality of wind speed and wind pressure is improved to enhance its computational efficiency. In this improved method, the result is obtained directly from the empirical distribution of a random selection of annual maximum wind pressure samples generated by a Monte Carlo method, rather than from the previously utilized extreme wind pressure probability distribution. A discussion of the relationship between the first- and full-order methods indicates that when extreme wind pressures in a nontyphoon climate with a high return period are estimated with consideration of directionality, using the relatively simple firstorder method instead of the computationally intensive full-order method is reasonable. The validation of this reasonableness is equivalent to validating two assumptions to improve its computational efficiency: 1) The result obtained by the full-order method is conservative when the extreme wind pressure events among different sectors are independent. 2) The result obtained by the first-order method for a high return period is not significantly affected when the extreme wind speeds among the different sectors are assumed to be independent. These two assumptions are validated by examples in different regions and theoretical derivation.

Key Words
wind load; extreme wind pressure; directionality; first-order method; full-order method; probability; Gaussian copula; return period; building envelopes

Address
Jingcheng Wang:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
/State Grid Shanghai Cable Company, Shanghai 200072, China

Yong Quan:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Ming Gu:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China


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