A report recently released by the National Transportation Safety Board (NTSB), an independent Federal Government Agency in the USA, cites that ‘errors in bridge design, inadequate peer review and poor engineering judgment led to the collapse of the bridge’ and that ‘the consulting engineer failed to notice the designer’s design calculation errors that contributed to the collapse’. In addition, it states that ‘the cracks should have indicated to the project team that the bridge was failing’. The bridge collapsed only five days after it was put in place, leading to the death of six people.
A lot, including myself, would go many steps back to criticize the engineering education. Indeed we have to admit that nowadays engineering students spend more time typing in engineering software in PCs than calculating by hand using the old fashioned hand calculators. They trust the software (not called by chance black box!) more than their judgment rather than using the software to validate what should already be designed and roughly calculated in their ‘engineeringly’ educated brains. How many times have we not heard in the industry that ‘but this is what the software calculates!’. Of course, experience comes with time and this is where the experienced checker and peer review comes into play.
Others, again including my good self, would argue that stringent QA/QC procedures are nowadays more like a box ticking and paper gathering exercise to comply with ISO and contractually required procedures and requirements rather than a robust plan for checking, inspecting, verifying and validating the works on site.
Whatever the arguments may be, the notion ‘errors in design’ always brings to my mind the tunnel failure statistics, included in the Ruler Consult co-authored paper Tunnel losses: causes, impact, trends and risk management, presented in the ITA World Tunnel Congress in 2016 which can be found in our publications corner. As per the statistics presented by IMIA in 2011, 41% of the recorded tunnel losses were attributed to design errors. Tunnels are excavated inside ‘unknown territory’ with significant inherent uncertainties, albeit extensive geotechnical investigations which may be carried out, and errors in design would be expected (but maybe not accepted in a risk framework approach) to be higher compared to bridge design where design loads and material properties and resistances are better known and controlled.
Risk management deals with mitigating the risks, i.e. reducing the risks of any unforeseen events to ALARP. In unforeseeable circumstances, mitigating the risk to ALARP is the matter among others of a cost/benefit analysis, the risk appetite of the stakeholders and the accepted adverse probability the general public is exposed to, as it was very well presented by Prof. Kavvadas in the 8th Geotechnical Conference in Athens earlier this month in his key note lecture Safety of (geo)technical works: Myths and Reality.
In the case of the Florida bridge collapse, the cause was neither an unforeseen nor an unforeseeable event. The collapse occurred due to design errors and ineffective human intervention.
The NTSB report concludes that ‘The failure of all concerned parties, to recognize and take action on the threat to public safety presented by the significant observed bridge structure distress prior to the collapse, led to the tragic loss of life in this preventable accident.