FEA model : comparing Warren and Vierendeel trusses

These Warren and Vierendeel truss Finite Element Analysis models have as much in common as possible

• length = 16m
• heights similar : Warren Truss 3.46m, Vierendeel Truss 4m
• material = rectangular (square) box section of 0.2m (200mm) width and height, and 0.005m (5mm) thickness, of steel
• load is in the centre, of 100,000N downwards (10 Tonnes force)

(Previous simulations, Warren-truss and Vierendeel-truss, were not "otherwise identical" - so could never be compared. This Vierendeel Truss here is the same as previously presented. The Warren Truss here now matches in its material - 200mm square 5mm thick steel box-section)

Presentation of the models and simulation results

• Presentation order in each section is
  • Warren Truss
  • Vierendeel Truss
  • (where present:) Observations I offer in comparing the two models
• Exaggerated deformation / displacement is always
  • 10X for Vierendeel Truss
  • 200X for Warren Truss

Note therefore that for similar as-displayed deflections, in reality the Vierendeel Truss is much more deflected than the Warren Truss.

FEA Model

Tensile force

The tensile forces are probably slightly lower for the Vierendeel Truss than for the Warren Truss because the Vierendeel Truss has a slightly greater height, therefore separation of the tension and compression chords, than the Warren Truss.

Bending moment

The bending moments are small in the Warren Truss - about a 100th part - compared to the Vierendeel Truss, which uses resisted bending moments in its load-bearing design strategy.

Displacement in vertical direction ("y")

Deflection of the Warren Truss at about 3.2mm is much less than the deflection of the Vierendeel Truss at about 90mm.

(R. Smith, 15Jun2016, 15Nov2016)