Proof-Loading of Scaffolding

When a scaffold system that is free to sway is tested to demonstrate its strength and stiffness, serious errors can occur if the load is applied by jacks with tiebars or cables. Experiments with techniques permitted by some specifications showed that strength was overestimated by amounts up to 63 percent, and second-order elastic analyses were consistent with that result. The current practice of using recovery of deflection as an indication of distress in a test scaffold is criticized because it has been shown to be inappropriate when the test structure is relatively stiff. This is so because it is likely that a higher proportion of its deflection consists of nonsystematic components. It is also misleading when the response of the structure comprises competing nonlinear modes.