I need help modelling horizontal BNWF with axial, transverse, and vertical (bearing & uplift) springs and spring damper at the ends to simulate connectivity.
I want to know how I can model these on to the beam and assuming the pipeline segment is 1 kilometer in length, at what intervals should the soil springs be applied? Can we assign line springs in OpenSees?
Thank you
P.S I would like to validate my results through this paper "Seismic risk assessment of buried steel gas pipelines under seismic wave propagation based on fragility analysis - Vahid Jahangiri, Hamzeh Shakib" - DOI 10.1007/s10518-017-0260-1
Hi
Here is one approach to model a horizontal beam on nonlinear Winkler foundation (BNWF) with axial, transverse, and vertical springs in OpenSees:
1. Discretize the 1 km long beam into elements (say 100 10m long elements).
2. Use an ElasticBeamColumn element for each beam segment.
3. Attach zeroLength elements to each node:
- zeroLength in local x-direction for axial soil springs
- zeroLength in local y-direction for transverse soil springs
- zeroLength in local z-direction for vertical springs
4. Use a Parallel material to combine the elastic behavior with a Bilin/Quad nonlinearity for each spring.
5. Apply spring properties like stiffness, yield strength, post-yield stiffness.
6. For damping, attach zeroLength elements with a ViscousDamper material at the ends.
7. Apply restraints and prescribed displacement to beam ends to simulate boundary conditions.
8. For load, apply point loads, prescribed displacements, or ground motion acceleration to the model.
The spacing of the soil springs depends on the desired discretization accuracy. A spacing of 5-10m would likely be reasonable for this length of beam.
This assembles a beam on springs system with nonlinear material models and damping to capture soil-pipeline interaction effects under dynamic loading. The zeroLength elements conveniently allow applying 1D spring-damper behavior between nodes.
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