...are there laws in place that insulate the government from law suits if it is proven the bridge was structurally deficient?
Very hard to sue or even fire an individual government employee but cities are sued/settle millions every year.
Most cities are “self insured”, which means that the cities/government carries -no- insurance and the taxpayer pays when it is all over.
Milwaukee and Wisconsin has paid millions this year due to police beatings, police shootings and false convictions.