One of these days, designers will realize that hanging heavy panels to make tunnels pretty and provide air plenums might not be the best way to go. Some sort of fireproof partitioning or duct system is needed to get air flowing into and out of the tunnel, but, in hindsight, hanging precast from any kind of anchor seems like a poor choice. It's not strictly a matter of the kind of anchor or how well it is installed. The system requires 100% performance by all components. Anchors have to hold, anchor rods have to maintain integrity, anchorage to the panels has to stay intact (any any condensation or free water will likely accumulate in the connection at the bottom of the sag/anchor rods), etc. It is what safety engineers refer to lovingly as "single point failure". The critical path to failure requires one, or very few, failures, without any real redundancy. And one panel that falls, with or without additional failures, creates a catastrophic situation.
We need to be critical of our profession and the choices we collectively make so that we can improve how and what we do. I'm not suggesting that we hang the individuals on any one project, only that we fully vet the underlying ideas and engineering to decide if it is what we want as our standard of care. Too often in many areas of engineering, we look to incremental improvement to solve what we see as the proximate cause of a failure (adhesive selection and installation, for example) rather than backing away and examining the entire system. Maybe that is OK, and maybe it isn't.
"The operator was exploring the possibility that bolts holding a metal piece suspending the panels above the road had become aged, he said." From an AP article. So let that be a lesson to anyone using bolts, that they should not use bolts subject to aging.
I agree with TX..it is poor engineering judgement, IMO, requiring perfect installation and constant inspection and maintenance ,while, at the same time subject to all kinds of corrosive exhaust fumes, etc...I suspect that this aspect of tunnel design is often left to the "add-on" suppliers and not given the attention and design by the qualified main tunnel design engineers....does not make sense, since the consequences of failure is immediate and life-threatening........the players involved in this aspect of the design seem to be all perifial with no integrated overall evaluation of each suppliers involvement....
