Typhoon Wind Modeling and Flutter Fragility Analysis of Long-Span Bridges in Coastal Regions of China

Typhoon or hurricane or tropical cyclone, which is a large-scale air rotating system around a low atmospheric pressure center, frequently causing devastating economic loss and human casualties along coastal regions due to violent winds, heavy rainfall, massive storm surges, flash flooding or even landslides in mountainous areas. The coastal region of China, which is characterized by high population densities and well-developed cities, is always exposed to typhoon threats with 7~8 landfall typhoons every year since Western Pacific Basin is the most active typhoon basin on earth, accounting for almost one-third of global annual storms. With more long-span bridges are being constructed along this coastal area, it is of great importance to perform the risk assessments on these flexible or wind-sensitive structures subjected to typhoon winds. To reconstruct the mean typhoon wind speed field, a semi-analytical height-resolving typhoon boundary layer wind field model, including a parametric pressure model and an analytical wind model was first developed in Chapter 2 using a scale analysis technique. Some basic characteristics of the inner structure of typhoon wind field, such as the logarithmic vertical wind profile near the ground and super-gradient winds were reproduced. Then, Chapter 3 develops a dataset of two wind field parameters, i.e. the radius to maximum wind speed, R_(max,s) and the Holland pressure profile parameter, B_s in Western Pacific Ocean using the wind data information from best track dataset archived by the Japan Meteorological Agency (JMA) coupled with the present wind field model. The proposed dataset of R_(max,s) and B_s is able to reproduce the JMA wind observations as closely as possible, which allows performing more accurate typhoon wind hazard estimation. On this basis, the maximum wind hazard footprints for over-water, roughness only and roughness and topography combined conditions of 184 observed landed or offshore typhoon-scale storms are generated and archived for risk assessment. Moreover, this supplementary dataset of R_(max,s) and B_s enables the development of recursive models to facilitate both sub-region typhoon simulations and full track simulations. Since the present wind field model can only generate long-time-duration speed, say 10-min mean wind speed, Chapter 4 develops an algorithm to compute the gust factor curve by taking the non-stationary and non-Gaussian characteristics of typhoon winds into account. The real wind data of nine typhoons captured by the structural health monitoring system (SHMS) installed in Xihoumen Bridge were utilized to validate the proposed model. Then, the probability distributions of gust factor associated with any gust time duration of interest can be readily achieved after introducing the statistical models of skewness and kurtosis of typhoon winds. To predict the typhoon wind hazard along the coastal region of China, a geographically-weighted-regression (GWR) -based subregion model was proposed in Chapter 5. The storm genesis model was first applied to a circular boundary around the site of interest. Then, the typhoon forward model including the tracking model, intensity model, and wind field parameter model was developed utilizing the GWR method. A series of performance assessments were performed on the present subregion model before it was employed to predict the typhoon wind hazards around the coastal regions of China. Chapter 6 develops a framework to investigate the probabilistic solutions of flutter instability in terms of critical wind speed accounting for multiple resources of uncertainty to facilitate the development of the fragility curve of flutter issue of long-span bridges. The quantifications of structural uncertainties, as well as aerodynamic uncertainties or the randomness of flutter derivatives, were conducted using both literature survey and experimental methods. A number of probabilistic solutions of flutter critical wind speed for two bridges, say a simply supported beam bridge and the Jiangyin Suspension Bridge were achieved by introducing different sources of uncertainty utilizing both 2D step-by-step analysis and 3D multimode techniques. To examine the flutter failure probability of long-span bridge due to typhoon winds, a case study of a 1666-m-main-span suspension bridge located in the typhoon-prone region was performed. The fragility curves of this bridge in terms of critical wind speed and the typhoon wind hazards curves of the bridge site as the probability of occurrence with respect to any years of interest were developed, respectively by exploiting the techniques achieved in previous chapters. Then a limit state function accounting for the bridge-specific flutter capacity and the site-specific mean typhoon wind hazard as well as the gust factor effects was employed to determine the flutter failure probabilities utilizing Monte Carlo simulation approach

Theoretical Analysis of Ultimate Main Span Length for Arch Bridge

The advancement of construction techniques and high-performance sustainable materials enables the increase of span length for arch bridge. It is of great importance to study the theoretical ultimate span length of arch bridge. Based on the parabolic and catenary arch axes, the analytical solutions of ultimate span length of arch bridge are solved using theoretical derivation accounting for the strength, in-plane stability and out-plane stability conditions, respectively. Then, the use of high-performance concrete, reactive powder concrete and high-strength steel is considered to study the relationship between theoretical ultimate span length and rise-span ratio as well as material strength for concrete and steel arch bridges. The results show that the theoretical ultimate span length derived by catenary arch axis is smaller by about 2–6% than that obtained by parabolic arch axis, but the difference is insignificant. When the rise-span ratio is 1/5, the theoretical ultimate span length for concrete arch bridge using R200 reactive powder concrete can reach 2000 m (2161 m for catenary arch axis and 2099 m for parabolic arch axis) while the main span of steel arch bridge using Q690 high-strength steel can be longer than 2500 m (2948 m for catenary arch axis and 2865 m for parabolic arch axis)

A Novel Shape Finding Method for the Main Cable of Suspension Bridge Using Nonlinear Finite Element Approach

The determination of the final cable shape under the self-weight of the suspension bridge enables its safe construction and operation. Most existing studies solve the cable shape segment-by-segment in the Lagrangian coordinate system. This paper develops a novel shape finding method for the main cable of suspension bridge using nonlinear finite element approach with Eulerian description. The governing differential equations for a three-dimensional spatial main cable is developed before a one-dimensional linear shape function is introduced to solve the cable shape utilizing the Newton iteration method. The proposed method can be readily reduced to solve the two-dimensional parallel cable shape. Two iteration layers are required for the proposed method. The shape finding process has no need for the information of the cable material or cross section using the present technique. The commonly used segmental catenary method is compared with the present method using three cases study, i.e., a 1666-m-main-span earth-anchored suspension bridge with 2D parallel and 3D spatial main cables as well as a 300-m-main-span self-anchored suspension bridge with 3D spatial main cables. Numerical studies and iteration results show that the proposed shape finding technique is sufficiently accurate and operationally convenient to achieve the target configuration of the main cable

Typhoon Wind Field considering the Probabilistic Correlation among Field Parameters Modelling and Validation

This paper was reviewed and accepted by the APCWE-IX Programme Committee for Presentation at the 9th Asia-Pacific Conference on Wind Engineering, University of Auckland, Auckland, New Zealand, held from 3-7 December 2017