Safety factors for bridge falsework by risk management

• Published in: Structural safety 2003-01, Vol.25 (2), p.227-243
• Main Authors: Sexsmith, R.G, Reid, S.G
• Format: Article
• Language: English
• Subjects: Applied sciences; Bridges; Buildings. Public works; Construction; Exact sciences and technology; Geotechnics; Risk management; Safety factors; Stabilization. Consolidation; Stresses. Safety; Structural analysis. Stresses; Temporary structures
• ISSN: 0167-4730; 1879-3355
• DOI: 10.1016/S0167-4730(02)00058-9

Determination of safety factors logically depends upon the cost of providing safety, the consequences of failure, the failure probability or rate, and the time of exposure to load. In the case of conventional structures these are indirectly accounted with safety factors prescribed by codes, and based on probabilistic studies and calibration. Bridge falsework may consist of structural systems that support relatively costly construction (with high consequences of failure) for very short time periods. Structural design codes generally do not prescribe safety factors for such temporary works. In the absence of prescriptive codes, contractors are left with decisions about safety factors. Some common policies are: to use factors or stresses and loads the same as for permanent construction; to use increased allowable stresses; or to use reduced return periods for environmental loads. This investigation applies basic principles of decision analysis and risk management to determine safety factors for several common bridge falsework or erection situations. The results indicate that substantial differences in the appropriate safety factors can be found, especially when low cost falsework supports costly permanent structure. In particular, the common practice of using increased allowable stresses or reduced load return periods can be seriously unconservative.