Nonlinear Dynamic Analysis and Fragility Development of Electrical Transmission Towers under Hurricanes

Electrical transmission towers are usually made of slender single angle members, which are prone to have flexural and flexural-torsional buckling behaviors under large deformations. In this research, both displacement-based and mixed beam-column elements are developed and implemented in the OpenSees software for simulating elastic and inelastic buckling of members with asymmetric sections such as steel angles and tees. Geometric nonlinearity is captured using a corotational total Lagrangian approach, while material nonlinearity is modeled using the fiber section method with uniaxial constitutive laws. The formulations try to minimize the number of elements needed through remedying membrane locking, representing nonlinear curvature within an element, and utilizing a kinematic model in the basic system that decouples axial, flexural, and torsional deformations for the first order effect. This research then proposes a procedure for developing collapse fragility curves of transmission towers subjected to hurricanes. The storm maximum gust speed is selected as the intensity measure and incremental dynamic analysis (IDA) is adopted to model collapse with the use of the newly developed beam-column element. Uncertainties in wind speeds, directions and durations are considered by running IDAs on transmission towers with a suite of hurricane wind records. The fragility curve is assumed to be the cumulative distribution function of the intensity measure at the onset of collapse. The parameters of the fragility curve are estimated by employing the method of moments with a premise that the intensity measure at the onset of collapse follows a lognormal distribution.

Learning Objectives:
Understand a new beam element formulation for nonlinear dynamic analysis of tee and angle sections

View content