Created analysis model Validated analysis model Verified analysis model But do you really understand how your structure is behaving???

Sensitivity Analysis

Sensitivity Analysis Investigate the effects of different values for features/parameters. Why? Better understanding of the behaviour of system being modelled. How much is necessary? Depends on how certain you are of the model behaviour.

Reference model results Change 1 feature/ parameter New revised model New results Change a different feature/ parameter New revised model New results Change a different feature/ parameter New revised model New results Change variables one at a time, go back to the reference model after each change.

Consider the parameters most indicative of the model behaviour: Maximum deflection? Maximum bending moment/shear force/axial force? Lowest natural frequency? Compare and report results without dimensions. Use percentage difference +/- % %diff = (value – reference value)/reference value  100 Or ratios For more detail see: http://www.imacleod.com/UsingStructM/Sensitivity-Analysis.pdf

Example The Model Geometry: The model is created in 2D, in the x-y plane. 1.5m 1.3m 1.4m 1.4m 1.4m 1.4m 1.3m 100x100x3.6 SHS – for all top and bottom chord members and vertical members. 100x100x8 EA – for tension diagonals.

Model 1 – pin joints Axial load Displacement

Model 2 – fixed/rigid joints Axial load Bending moment

Model 3 – no bracing Axial load Bending moment

Structural system comparison Comparison of results Max Displacement at node 4 (mm) % difference ratio Max Bending (kNm) % difference Max Axial (kN) compression Reference - Model 1 Pinned truss -0.5920 -   -13.67 Model 2 Fixed truss -0.5840 -1.4% 1.0 -0.1163 -13.52 -1.1% Model 3 Vierendeel, no bracing -6.1200 933.8% 10.5 -2.294 1872.5% -10.62 -22.3% Structural system comparison

Consider truss chord depth v diagonal depth Reference model - Model 1 Pinned truss 100x100x3.6 SHS – for all top and bottom chord members and vertical members. 100x100x8 EA – for tension diagonals.

Model 4 – Equal sections Axial load Displacement 100x100x3.6 SHS – for all top and bottom chord members and vertical members. 100x100x3.6 SHS – for tension diagonals. Axial load Displacement

Model 5 – section d, Chords–Ties 2:1 100x100x3.6 SHS – for all top and bottom chord members and vertical members. 50x50x3.6 SHS – for tension diagonals. Axial load Displacement

Model 6 – section d, Chords–Ties 1:2 100x100x3.6 SHS – for all top and bottom chord members and vertical members. 200x200x5 SHS – for tension diagonals. Axial load Displacement

Truss chord depth v Diagonal depth Comparison of results Max Displacement at node 4 (mm) % difference ratio x Max Axial (kN) compression Reference Model 1 Pinned SHS & EA -0.5920 -   -13.67 Model 4 Equal sections -0.6072 +2.6% 1.02 0% Model 5 d, Chords–Ties 2:1 -0.7572 +27.9% 1.28 Model 6 d, Chords–Ties 1:2 -0.5193 -12.3% 0.88 Truss chord depth v Diagonal depth