Critical Infrastructure

It's a mouthful. What does it mean? Well, that depends partly on your political view point. Now that the economy is at least in recession and governmental taxing authorities eye their next targets to make up for declining tax revenues, so-called conservatives use "critical infrastructure" to call attention to what they believe is government's duty and obligation to keep roads and bridges in good repair in lieu of maintaining entitlement programs (social engineering), which does not contribute directly to real wealth creation, only consumes it. The so-called progressives or liberals think that critical infrastructure has more to do with accommodating the people's need to comingle en masse through construction of light rail transportation, bike paths, etc. It has less to do with commerce and more with personal conveyance and convenience.

"Critical," A Telling Word
In all cases, whatever your political outlook, CRITICAL infrastructure must include largely civil engineering projects that are targeted for public commercial use like roads and bridges, rail lines, pipelines, waterways, electrical distribution networks, etc. Without these bulk access resources, our commonwealth would collapse. Who grows their own food, raises their own chickens and cattle, sows their own cotton, and drills for their own oil, fills in their own potholes? We are dependent on infrastructure.

These structures and systems require large capital expenditures to erect; neither Rome nor the USA were built in a day. Rapid economic growth over the last few decades permitted the rapid expansion of existing systems fueled by an expanding revenue stream and an inflationary fiat money system, which has accumulated into an unpayable mountain of debt (US debt will soon exceed GDP - used to be GNP, but the new terminology is more politically convenient as it masks the true enormity of US debt and shrinking US manufacturing capacity to foreign sourcing). In some cases, those technologies were not up to today's standards. In some cases, specific infrastructure builds were under-designed and over-utilized, which now requires very large capital expenditures to maintain or replace.

I35W Bridge Collapse

This Minneapolis bridge over the Mississippi river was built in the 60s. It was not designed to handle 21st Century traffic. It went down after many years of cyclic overloading. The State’s response to this infrastructure need was to accelerate inspections from once every two years to once a year based on the recommendations of infrastructure consultants under contract with the State. The consultants were reluctant to say that the bridge needed replacement because the State would most likely find another consultant. In many cases like this, sound economic or safety judgment is not based on sound engineering, but on passable politics. The science of building is best understood by engineers. The science of wear and tear should be as well. In the case of the I35W bridge collapse, the inspection cycle was based on neither.

It should be obvious that the bridge failure was due to fatigue. The inspection cycle should have changed from two years to one year. After that year, to six months, then every week, day, hour, then minute. That is the nature of fatigue failure: crack initiation, to accelerating propagation, to catastrophic failure. The State, nor its consultants, could know exactly when and where the probable failure would occur during the bridge’s useful life based on industry practise, but they could have qualified the likely critical failure mode, the weakest link(s) in the chain, then provide a remedy by employing "what if" FEA fatigue methodologies to study design enhancements and extend useful life, or perform a controlled tear-down and rebuild.

As it turns out, the State and Federal governments paid a very hansome premium for completion of the new bridge prior to the target date. Controlled demolition and a less aggressive rebuild of the bridge would have been less expensive years prior to the accident notwithstanding the loss of lives that are priceless.

FEA and Infrastructure
FEA would have indicated exactly where stress concentrations would have occurred leading to fatigue crack initiation and propagation speed. This would have been based on the dynamic cycling, or vibration, imparted by years of traffic. It would have been easy to gather empirically the vibration magnitude and cycle frequencies and apply them to the bridge structure. Bridge vibration harmonics assessed in the FEA virtual world would have very quickly identified which riveted gusset plates were subject to early failure and what remedy could be applied to prevent failure. It would have predicted how the bridge would collapse given the failure of any one gusset plate and clearly show the weakness of the 40 year old design and what could have been done to prevent collapse in the event a plate did fail.

FEA is not new. But, approval bodies have been slow to adopt standards based on FEA capabilities largely because analysis simulation set ups are as varied as analysts. The expert must be adept at designing the virtual model to mimic well the real to obtain the essential information. As good as FEA software is today, and as fast today's computers, compared to even four years ago, they are still not powerful enough or inexpensive enough to mimic every physical detail, even bridge structures. Compromises must be made that tax most analysts' ability to obtain the best result, or critical result, against obtainment of a merely good result. Unfortunately, most FEA analysts still do not demonstrate the skills necessary to simulate critical systems. Applycon, however, does. Want to learn more? Contact us. A conversation costs nothing. Ask the hard questions. We’re here to answer them.