I performed the structural settlement stress analysis for six steel utility pipes affected by the Highway 1 Mainline East widening project (FVH1CIP) in Abbotsford, BC. The pipes, both existing and proposed, sit beneath the highway alignment and are subject to additional positive trenching effects from embankment fill. Each profile required 18 separate analysis cases to evaluate reserve capacity under corrosion and varying soil conditions, and I built the automation tooling to run them.

My role

I was the Structural Engineer responsible for the settlement stress analysis of all six utility pipe profiles, including model development, automation, results interpretation, and wall thickness recommendations.

What I did

SAP2000 pipe modeling:

  • Built beam-on-elastic-spring models in SAP2000 for six pipe profiles: an existing 1067 mm sanitary, an existing 762 mm watermain, and four proposed 610 mm watermains and sanitary lines.
  • All pipes are ASTM A252 Grade 2 steel (Fy = 240 MPa) with wall thicknesses ranging from 12.02 mm to 19.1 mm.
  • Applied settlement profiles provided by the civil team as imposed displacements along the pipe length, with maximum settlements reaching 45.85 mm.

18-case analysis matrix per profile:

  • Modeled three corrosion loss scenarios per pipe: 0%, 25%, and 50% section loss to account for long-term degradation.
  • Applied three soil spring stiffness profiles per scenario: upper bound, best estimate, and lower bound, derived from geotechnical data.
  • Analyzed both inner and outer pipes for each profile, producing 18 distinct analysis points per profile that each required iterative convergence.

Automated iterative convergence with Python:

  • Used my open-source SAP2000 API wrapper (ak_sap) to automate the full analysis workflow: model setup, settlement profile application, analysis execution, result extraction, and iterative re-analysis until convergence.
  • The iterative process was necessary because applied settlements produce stresses that change pipe stiffness, which in turn changes the deflection response. Each of the 18 cases per profile needed to converge independently.

Reserve capacity evaluation:

  • Compared elastic bending stresses against the 96 MPa allowable stress for each profile and corrosion scenario.
  • Calculated reserve capacity as the ratio of allowable stress to actual bending stress (factor of safety).
  • Original factors of safety ranged from 8.2 (Profile 1, 1067 mm sanitary) to 50.2 (Profile 2, 762 mm watermain). After applying settlement-induced moment amplification, factors of safety reduced to 2.6 (Profiles 7 and 9) through 41.8 (Profile 2).

Wall thickness recommendations:

  • Identified that Profile 7 (proposed 610 mm watermain) required a wall thickness increase from 12.7 mm to 19.1 mm to maintain adequate reserve capacity under the 50% corrosion loss scenario.
  • Recommended the same 19.1 mm wall thickness for Profile 12 (proposed 610 mm watermain) based on the settlement-induced moment demands.
  • Resolved non-convergence in the 50% section loss cases by identifying that the original 9.2-9.53 mm wall thicknesses produced unstable analysis behavior under the high-stiffness spring condition, and confirmed that the recommended 12.7 mm minimum thickness resolved this across all soil profiles.

Deliverables

  • Produced a stress analysis summary report with deflection and moment diagrams for all six profiles, documenting the full 18-case analysis matrix.
  • Delivered an Excel results summary comparing original and amplified moments, factors of safety, and allowable stresses across all profiles and corrosion scenarios.
  • Provided wall thickness increase recommendations for Profiles 7 and 12, which were adopted into the design.
  • The analysis supported the municipal utility design package for the Highway 1 Mainline East widening project.