Big Dig Hearing Underway in Washington

My question is: why hasn't anyone questioned the wisdom of suspending 3 inch thick, multi-ton slabs of concrete over the heads of the motorists traveling through the tunnel, in order to form ductwork for airflow? Would the bolts have pulled out of their holes if the panels had been fabricated of a lighter material? Would the failure of the bolts have been as catastrophic if they failed while holding lightweight paneling? Was the decision to use bolts glued into place the first decision in the chain of bad decisions? Or was there an executive decision regarding the design, such as including the grossly oversized concrete panels, constituting the fundamental design flaw for which someone should be held accountable? Given the cravenness of modern executives and bureaucrats, I would suspect that the ultimate responsibility and proximate cause for the accident was a bad executive decision to use a flawed design, which was merely exacerbated by the use of the wrong epoxy. But of course, the engineers, workmen, and suppliers will get blamed, while the executives and bureaucrats absolve themselves of guilt.