| Wind Load Factor Based on Wind Load Statistics for Reliability-Based Bridge Design Codes Ji Hyeon Kim
ABSTRACT This work presents a general approach for evaluating wind load factors based on measured wind data for reinforced concrete columns. The equivalent static wind pressure is adopted to approximate the aerodynamic wind pressure using the gust factor. The probabilistic model of wind velocity is established based on measured wind data, and that of wind pressure is constructed by Monte-Carlo simulations. For calibration of reliability-based wind load factors, the relationship between statistical parameters of wind velocity and pressure are required. In this study, the normalized wind pressure is defined to develop the relationships between statistical parameters of wind velocity and pressure. The P-M interaction diagrams of the pylons define the limit state function of the pylons subjected to unaixial bending. The load contour method is utilized to estimate the strength of a reinforced concrete column subjected to biaxial bending. Load and strength parameters are considered as random variables in the reliability analysis. The strength parameters of an RC column include the material properties and geometric properties of the cross section of an RC column. The HasoferLind Rackwitz-Fiessler algorithm with the gradient projection method is employed to calculate the most probable failure point and the reliability index. The continuous and differentiable P-M interaction diagram is constructed with discretely defined sampling points of the P-M interaction diagram using the cubic spline interpolation. The sensitivities of the P-M interaction diagram are calculated through the direct differentiation of the cubic spline and sampling points of the P-M interaction diagram. Detailed expressions of the sensitivities of the P-M interaction diagram with respect to the random variables are presented. Reliability analyses are carried out by the proposed method to investigate the wind load-governed limit state for the reinforced concrete pylons of five cable-supported bridges in Korea. energy filter. Dividing them in this manner simplifies a filtering process. Based on the results of the reliability analysis, dead load factors are set to the bias factors of dead load components, and a P-M interaction diagram drawn by the mean values of the strength parameters is used to define a design equation. The most probable failure point of the wind load is obtained by equating the probability of non-exceedance of wind load at the most probable failure point to the probability of safety corresponding to a given reliability index. An analytical form of the wind load factor is derived in terms of the statistical parameters of wind load and the target reliability index. Validity of the proposed load factors is verified through a reliability assessment of the pylon sections of the five bridges. It is shown that the proposed load factors secure the target reliability levels within a 2% error. The proposed wind load factor is adjusted to be used with the dead load factors and the resistance factor specified in several reliability-based design codes. The validity of the adjustment procedure is confirmed by calibrating the wind load factor for the AASHTO LRFD Bridge Design Specifications. The wind load factor adjusted for Korean Highway Bridge Design Code (Limit State Design) ? Cable- supported Bridges is presented in terms of the coefficient of variations of the wind velocity. To adapt the wind load factor as 1.0, the recurrence periods of the basic wind velocity are calculated to secure target reliability indexes. The analytical form of determining the basic wind velocity for Korean Highway Bridge Design Code (Limit State Design), which yields a uniform target reliability level, is proposed by using the statistical parameters of wind load and the adjusted wind load factors. The validity of the proposed wind load factor is also confirmed through the reliability assessment of the RC pylons with various sizes of cross-sections. The reliability indexes of the pylons subjected to biaxial bending are calculated to investigate the effects of biaxial loads on the reliability level for the wind load combinations. It is confirmed that the wind load combination allowing vehicular live loads does not govern the design of pylon sections.
Key Word Wind load factor; Calibration; Probability of failure; Target reliability index; Reinforced concrete column; Wind pressure; Reliability analysis; Wind Load Statistics; Biaxial Load; Reliability-based bridge design codes;
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