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#72138 - 09/05/18 10:52 PM Certainity of fatigue life due to vibration cyclic loading
sam Offline
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Registered: 02/25/04
Posts: 641
Loc: Maharastra, India
Certainity of fatigue life due to vibration cyclic loading ?

Recently a 50 year old bridge over railway track has fallen down in Kolkata of India.

People are raising doubt with what certainty we can predict fatigue life of any structure subjected to wear and tear, live load of vehicles over bridge and heavy vibration caused by a recently erected metro rail foundation structure.

For example, if we have piping subjected to vibration or cyclic thermal load, we can't predict the fatigue life with complete certainity. With some percentage of probability, we can produce a fatigue curve of a thick band instead of a line curve.

For a person of non STEM background, such justification can look strange.
But, what our forum members think - can we predict a timing of earthquake or a fatigue failure with complete certainity ?
reg,
Sam
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#72147 - 09/09/18 12:56 AM Re: Certainity of fatigue life due to vibration cyclic loading [Re: sam]
sam Offline
Member

Registered: 02/25/04
Posts: 641
Loc: Maharastra, India
None commented on falling of a bridge .. due to age, too much live load and end enhanced by piling vibration in the vicinity.

Has there been nothing in common with piping failure ... Steady load of pressure and weight, thermal load of temperature, cyclic pressure fluctuations faced in high pressure hydraulic piping with pulsating source within.

In gen Z people around, we expect more curiosity. We are not insects which do not feel pain .. just live to mate and eat. Our youth only aspire to concour others and promote themselves!

Both US and Hinduism became great not by winning others by force .. but by teaching others value of liberty, use of science and religion.
Great nation and religion need no promotion! Let us be human enough ..God wants only that much!
Reg, sam
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#73217 - 05/01/19 06:49 AM Re: Certainity of fatigue life due to vibration cyclic loading [Re: sam]
sam Offline
Member

Registered: 02/25/04
Posts: 641
Loc: Maharastra, India
Months passed when I wrote this post. Meanwhile, in Mumbai where I live has witnessed a road over bridge for railway passangers falling down because of corrosion and fatigue. Engineers responsible for engineering and audit/upkeep are behind bars ..Trying to prove that any bridge can fall due to human movement generated resonance.

Reality is we can predict fatigue damage by analysis .. both for design and upkeep! Have Caesar II, ANSYS as tools, but let us take responsibility of customers and people around! No AI will replace ethical souls! Long live Buddha/ Jesus within us!
Reg,
Sam



Edited by sam (05/01/19 06:57 AM)
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#73218 - 05/01/19 09:50 AM Re: Certainity of fatigue life due to vibration cyclic loading [Re: sam]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 709
Loc: Louisiana, US
Originally Posted By: sam
But, what our forum members think - can we predict a timing of earthquake or a fatigue failure with complete certainity ?


I won't comment on earthquake prediction, as that is not my field of expertise.

No on fatigue failure, because we'll never be afforded the unlimited budget and time constraints required to fully evaluate an existing structure. It would be cheaper to purchase a brand new one that's 10x more adequate, which I would say with perhaps 75% confidence.

But that only covers my input parameters. I cannot guarantee the bedrock under the structure. I cannot guarantee against items outside the scope of my imagination, or, if you're the one providing scope definition, your imagination.

Ultimately, as designers, we are limited in our ability to control what others use our designs for, or even track how it's used. I guarantee you that if those monorail trains have an occupancy / capacity maximum, it gets flagrantly disregarded, but the engineers "should have known better." Yet when we design for "knowing better," we're forced to redo the work, because it's stronger than the norm.

Originally Posted By: sam
In gen Z people around, we expect more curiosity. We are not insects which do not feel pain .. just live to mate and eat. Our youth only aspire to concour others and promote themselves!


I'll respond to this with another quote. Note the author.

Originally Posted By: Socrates
The children now love luxury; they have bad manners, contempt for authority; they show disrespect for elders and love chatter in place of exercise. Children are now tyrants, not the servants of their households. They no longer rise when elders enter the room.
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#73233 - 05/04/19 10:22 AM Re: Certainity of fatigue life due to vibration cyclic loading [Re: sam]
sam Offline
Member

Registered: 02/25/04
Posts: 641
Loc: Maharastra, India
Most of the times when we are called in an operating plant having vibration, we do not have luxury of hiding our inaccuracies of prediction of fatigue life with ample factor of safety. Plant needs shutdown or can wait for next shutdown .. we need to choose among the two. If we prove wrong, faith of people on us will be lost forever!

I do not want our youth to obey us; replace us not by just age count, but by replacing us with improved service to the customers through deep work of real value, creativity and productivity.
New India of our young enginners must be safe, cost effective in life cycle cost and environmental foot print! If 5G days become more unsafe than radio days of yester years, there must be somewhere something wrong in our development model. Youth in China or Germany can be responsible, why can't our own learn from them.
Reg,
Sam
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#73240 - 05/06/19 09:00 AM Re: Certainity of fatigue life due to vibration cyclic loading [Re: sam]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 709
Loc: Louisiana, US
This is why we must learn to choose our words carefully, write our assumptions, and convey what our errors in our assumptions may result in.
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