Engineering analysis and design software
Bridge design and engineering

Case Study

Namdo Bridge

  • Nielsen arch road bridge
  • local analysis of arch / girder connection
  • linear static analysis to optimise stiffener design

LUSAS Bridge has been used by Sambo Engineering Co Ltd to investigate localised stress distribution in a steel arch rib and girder connection for the Namdo Bridge in Whagae-Myun , Junlanam-Do, South Korea.

Overview

Namdo Bridge is a 160m span, 32m high Nielsen arch bridge that carries a 2 lane highway across the Seomjin river. It comprises a pair of 1.8m deep inclined steel connecting arches that support the 2.2m deep longitudinal steel box girders via cables inclined at 60 degrees. The angled cables help to transmit some of the internal forces in the stiffening girders back into the arch giving a stiffer structure with reduced deck deflections than for similar bridges with a vertical cable arrangement. At the junction where a longitudinal girder meets an arch rib large stresses are involved and careful detailed design of the web stiffeners is required in order to avoid high stress concentrations and potential fatigue problems.

Joonsang Son, an engineer on the project explains: "If the web thickness is increased excessively it can cause high residual stresses in the welds, and increase the possibilities of brittle fracture. Alternatively, if an excessive number of stiffeners is used then the structure becomes more awkward to fabricate. Therefore it is very important to accurately predict the stresses involved either by laboratory testing or by structural analysis using LUSAS Bridge".

A local model of the connection was built in LUSAS Bridge using thick shell elements. Dead load, surfacing load, live and wind loading was applied prior to a 3D static analysis being carried out. Results plots showing tensile and compressive principal stresses and shear stresses in the webs and plates helped Sambo Engineering Co Ltd to optimise and prove their design.

Arch and Girder Connection

Joonsang Son says: "We examined the flow and amount of stress near the end of the stiffening girders very thoroughly using LUSAS and showed that the stresses near the end of stiffening girder were less than the allowable stress". He continues, "LUSAS is good at modelling this kind of problem. Its shell and solid elements are easy to use, and the ability to plot results on selected parts of the model allows us to check the stress levels in a very straightforward manner. This is one of the many benefits in using LUSAS on this and other projects".

The bridge is scheduled for completion in late 2002 for clients the Administration hall of Junlanam-Do / Administration hall of Kyungsangnam - Do

Compressive and Tensile Stress in Web

"LUSAS is good at modelling this kind of problem. Its shell and solid elements are easy to use, and the ability to plot results on selected parts of the model allows us to check the stress levels in a very straightforward manner. This is one of the many benefits in using LUSAS on this and other projects".

Joonsang Son, Engineer, Sambo Engineering


 

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