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The Holmes And Rahe Stress Scale is often used by doctors to find and answer to the question: Can the most stressful life events predict future illness or a failure? Two researchers in 1967 thought so. Combing through the medical records of over 5,000 patients, with an eye to seeing if there is a correlation between illness and the most stressful life events, they indeed found that a strong relationship does exist. The correlation was so strong that, with respect to causing future illnesses, the stressful situations could be ranked on a scale from most stressful to least stressful event; or, from most likely to least likely to cause illness.
Today, we can find the same correlation between engineering stress/strain and structural integrity and failure. Structural failure is initiated when the material in a structure is stressed to its strength limit, thus causing fracture or excessive deformations. The following link gives examples of structural failures and collapse: https://en.wikipedia.org/wiki/List_of_structural_failures_and_collapses
Everyone talks about feeling stressed out these days. But what’s the reality of stress in our infrastructure and structures? How many overloaded transfer trucks have crossed a particular bridge every day for decades? How many shockwaves has that building experienced from earthquakes (major) or small tremors (minor)?
We feel stressed when we feel that “things are out of control” but when overloaded trucks pass over the same bridge day after day, that structure gets tired and becomes closer to failure because of the excessive stresses. Buildings experiencing regular shockwaves from motions in the earth’s mantle will develop cracks at critical load bearing locations, setting up the real possibility of total collapse.
Along with our personal stress level, and what it can do to our health, we should also consider how the daily infrastructure we use responds to the effects of stress, and how those structures cope with stresses and what can be done to extend a healthy structural life. We should be aware of overloaded conditions and the possible negative impact it has on the structural health of bridges, buildings, roads, or just the chairs we sit in.
One result of stress on our personal health is to make us feel continuously tired. We all feel like joining in with Madeline Kahn on the chorus to, “I’m Tired”. But as dams, tunnels, and walls get older, they will also become tired from all the stresses accumulated over the years. Just as we feel fatigued, so can these structures. And when they experience a fatigue failure, it can mean toppling down into a pile of rubble.
But stress isn’t always an enemy. Sometimes a little stress helps us to develop better structures. A majority of the stress analysts who had felt highly stressed in the past month said that at some point their identified stress had been a good thing. And, there are the conditioning techniques which create compressive stresses in structural materials to develop a favorable state of stress that is more capable of surviving future stressful events. One such technique is “shot peening”. Humans do the same thing, and it’s called exercising. By doing so, we stress our muscles and immune systems, so these systems are more capable of surviving highly stressful events.
But there are a few stress analysts, believe it or not, who may be missing out on the positives and negatives of stress in their structures. Many of them said they hadn’t had any stress at all in the past month. How is that possible? Well, two-thirds of the unstressed said it was because of their personality structure. Other factors that helped their structures stay relaxed were steps they had taken in advance to reduce stress concentrations, like exercising and creating an environment free of stressful events. Regardless of their perception, it would be wise for them to test their structures regularly with tools available for determining stress levels, like bonded electrical resistance foil strain sensors.
Do we really understand the impact of long-term stress? Many failure theories exist to predict the end result of accumulated or single event stresses. Along with good engineering computations and measuring tools, these can help minimize the risk of future structural illnesses caused by routine stressful events.
What can you do about it? If you find that your structure is at a moderate or high level of risk, then an obvious first thing to do is avoid future life crises that produce dangerously high levels of stress. Carefully monitor truck weighs on the highways. Test plane wings thoroughly under all possible loading conditions and perform regular heath-monitoring. Don’t sign off on a new design until the stress results are carefully scrutinized and found within design specifications.
While this is clearly easier said than measured, you should normally avoid using only computer models to predict stress levels. While these tools are useful in the design stages of a project, only a small part of the stress story is written by them.
The Strain Gage Stress Scale is a well-known tool for measuring the amount of stress your structure is experiencing. Taking the test can help you see clearly if you’re at risk of losing your project due to stress.
We experience different incidents in our lives due to old and cracked infrastructures that turn our world upside down and cause us to feel stress. Most of these incidents we cannot control, others we can control to a certain degree when we measure the strain and identify the stress concentrations.
Who’s stressed more the bridge or the person that walks or drives on it? Seeing all the cracks in the road and feeling the vibrations certainly does cause us personal stress, but these blemishes also cause stresses in the structures which can led to future failures.
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