Expert calls for regular checks of elevated railway structure after concrete slab falls

[rooster59]

Expert calls for regular checks of elevated railway structure after concrete slab falls

By The Nation

 

 

The head of an engineering association has urged the operator of the Bangkok’s elevated railway to regularly check infrastructure after rusty parts reportedly led to a concrete slab falling recently.

 

Professor Amorn Phimarnmas, president of the Thai Structural Engineers Association, issued the call without taking names. The BTS Skytrain is the only elevated railway, whose structure is also old enough to get rusty.

 

Amorn said a concrete slab fell from a station of an elevated railway a few days ago, endangering the lives of people and motorists.

 

Amorn said according to reports the slab fell due to erosion caused by rust in a part of the station. He said it was yet to be studied whether the rust had occurred inside the structure or on the metal fasteners outside the structure of the railway.

 

Amorn said rust was becoming a major issue in reinforced concrete structures.

 

He said metal parts of buildings or infrastructure could rust because of several causes.

 

First, the city’s air has a lot of carbon dioxide released by vehicles. He said the carbon dioxide caused carbonation that reduced the alkalinity in the concrete structure, making metal parts vulnerable to rust.

 

He said if the concrete that covers the metal parts is too shallow, chemicals could easily seep in and cause rusting.

 

Amorn said it there was a need to inspect how metal parts are used to fasten concrete slabs of the elevated railway. If the fasteners are improperly installed, the concrete slabs could fall. Moisture from rainwater could also cause the fasteners to become rusty, he added.

 

Amorn said elevated railways should be regularly checked by experienced engineers using both observations and the half-cell potential technique.

 

Observations are used to check metal parts outside while the half-cell potential technique uses electric current to check whether metal parts inside the structure have become rusty or not.

 

Source: https://www.nationthailand.com/news/30372921

 

-- © Copyright The Nation Thailand  2019-07-13

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[keith101]

The others in that top photo don't look to secure either so maybe it would be a good idea to close that section and take them all down just to be safe .

[Crossy]

7 minutes ago, keith101 said:

The others in that top photo don't look to secure either so maybe it would be a good idea to close that section and take them all down just to be safe .

 

They're just deco panels so are not structural, no need to close anything other than the road whilst they are removed/inspected. That area does look a bit mangy from the photo.

 

[expatfromwyoming]

Not a word about ineptness in the whole diatribe

[bristolgeoff]

you would think the concrete would last longer and not fall off.but this is thailand

[overherebc]

53 minutes ago, Crossy said:

 

They're just deco panels so are not structural, no need to close anything other than the road whilst they are removed/inspected. That area does look a bit mangy from the photo.

 

True but that area looks like a major junction corner.

Properly mixed and cured concrete can handle many adverse conditions but the metal fastenings and rebar are a whole different ball game.

Any steel fastners expand and contract at a much different rate to the concrete and shoold really be set in the concrete using very high strength epoxy glue not just stuck in position while the concrete sets.

Just talking generally.

Edited July 13, 2019 by overherebc

[scorecard]

Obvious question, why are there not already regulations and reporting in place for many years in regard to all aspects of overhead railway, tollway, and bridge structures? 

 

Sorry.

[Justgrazing]

1 hour ago, rooster59 said:

 

Amorn said elevated railways should be regularly checked by experienced engineers using both observations and the half-cell potential technique

Brain , prison .? I dunno give us a clue on that one .. Fascinating to read about concrete , reedbar ( what is that ) curing etc .. I know nothing of these things but given Bangkok has a lot of elevated roadways made of concrete will this prove to be an ongoing issue in the future .. 

Edited July 13, 2019 by Justgrazing
Sp

[Emdog]

Checking is one thing, doing something about it......

[Chang_paarp]

3 hours ago, rooster59 said:

Amorn said elevated railways should be regularly checked by experienced engineers using both observations and the half-cell potential technique.

 

Observations are used to check metal parts outside while the half-cell potential technique uses electric current to check whether metal parts inside the structure have become rusty or not.

 

Given that the structures are over 29 years old, this would be part of the regular scheduled maintenance? ????????????

[Reigntax]

3 hours ago, overherebc said:

True but that area looks like a major junction corner.

Properly mixed and cured concrete can handle many adverse conditions but the metal fastenings and rebar are a whole different ball game.

Any steel fastners expand and contract at a much different rate to the concrete and shoold really be set in the concrete using very high strength epoxy glue not just stuck in position while the concrete sets.

Just talking generally.

The reason why steel and concrete are successfully used together is because the expansion coefficients are so closely matched. 

[Redline]

3 hours ago, scorecard said:

Obvious question, why are there not already regulations and reporting in place for many years in regard to all aspects of overhead railway, tollway, and bridge structures? 

 

Sorry.

 Because miracles rarely happen in real life 

[overherebc]

21 minutes ago, Reigntax said:

The reason why steel and concrete are successfully used together is because the expansion coefficients are so closely matched. 

Very true particularly with re-enforced concrete where the steel is well buried in the concrete.

With exposed fastners where the steel may be exposed to hot sunshine it will heat up much faster than the concrete and obviously expand more quickly than the concrete its embedded in. This causes initial cracking, call it micro-cracking in the beginning, in the concrete next to the fastner and cracks never get smaller with time.

Pretty quickly the fasteners get loose, water gets in easier and fast corrosion sets in.

[overherebc]

3 hours ago, Justgrazing said:

Brain , prison .? I dunno give us a clue on that one .. Fascinating to read about concrete , reedbar ( what is that ) curing etc .. I know nothing of these things but given Bangkok has a lot of elevated roadways made of concrete will this prove to be an ongoing issue in the future .. 

Easy start. Concrete is extremely strong in compression ( when being squeezed ) but very weak when in tension, think ( being stretched )

If you think about your concrete driveway when you park your car on it the weight of the car is trying to bend the concrete so the top is being squeezed ( compression ) and the bottom surface is being stretched ( tension ) and if your car is heavy enogh it will crack from the bottom up.

Rebar ( re-enforcing bar ) or mesh embedded in the concrete spreads the forces and helps it to stop cracking and breaking.

????????????

This what happens when salts and/or water get into rebar. ????

Edited July 13, 2019 by overherebc

[Reigntax]

Just now, overherebc said:

Very true particularly with re-enforced concrete where the steel is well buried in the concrete.

With exposed fastners where the steel may be exposed to hot sunshine it will heat up much faster than the concrete and obviously expand more quickly than the concrete its embedded in. This causes initial cracking, call it micro-cracking in the beginning, in the concrete next to the fastner and cracks never get smaller with time.

Pretty quickly the fasteners get loose, water gets in easier and fast corrosion sets in.

In the example you detail, failure still should only occur if the embedded depth of the fastener was insufficient. Yes, corrosion can occur through incorrect fastener material properties.

In 40 years of structural engineering,I  have never seen a correctly cast in place fastner having suitable material properties for the duty, work loose.

 

Granted, some of these panels are quiet thin and the the quality of both pre cast and In situ concrete of the older sections are in some cases, pretty rough.

But I also have to say that some of the later concrete structures are of better quality.

 

Why they continue to design with these facade panels/cover panels is unknown as they are unnecessary as a structural element and will always just be an ongoing maintenance issue.

 

[Bangkok Barry]

5 hours ago, rooster59 said:

The head of an engineering association has urged the operator of the Bangkok’s elevated railway to regularly check infrastructure after rusty parts reportedly led to a concrete slab falling recently.

 

They have to be told this? Really? Thailand - Hub of No Maintenance.

[Justgrazing]

1 hour ago, overherebc said:

Easy start. Concrete is extremely strong in compression ( when being squeezed ) but very weak when in tension, think ( being stretched )

If you think about your concrete driveway when you park your car on it the weight of the car is trying to bend the concrete so the top is being squeezed ( compression ) and the bottom surface is being stretched ( tension ) and if your car is heavy enogh it will crack from the bottom up.

Rebar ( re-enforcing bar ) or mesh embedded in the concrete spreads the forces and helps it to stop cracking and breaking.

????????????

This what happens when salts and/or water get into rebar. ????

Excellent thanks .. Learn something everyday on TVF .. 

[overherebc]

1 hour ago, Reigntax said:

In the example you detail, failure still should only occur if the embedded depth of the fastener was insufficient. Yes, corrosion can occur through incorrect fastener material properties.

In 40 years of structural engineering,I  have never seen a correctly cast in place fastner having suitable material properties for the duty, work loose.

 

Granted, some of these panels are quiet thin and the the quality of both pre cast and In situ concrete of the older sections are in some cases, pretty rough.

But I also have to say that some of the later concrete structures are of better quality.

 

Why they continue to design with these facade panels/cover panels is unknown as they are unnecessary as a structural element and will always just be an ongoing maintenance issue.

 

I'm not an expert on concrete but I worked with/alongside civil inspectors in a few places.

What I do like reading about is the Roman concrete structures that are in a lot of cases stronger now than when built.

They are doing a lot of analysis on some of them, especially the structures in salt water

( harbour walls ) to determine the mix that makes them get stronger as time goes on.

Edited July 13, 2019 by overherebc

[overherebc]

4 minutes ago, Justgrazing said:

Excellent thanks .. Learn something everyday on TVF .. 

PS

I can spell 'enough'.  Big fingers, small keyboard. ????

[Chazar]

It takes an "expert" to realise  this?

[overherebc]

6 hours ago, Justgrazing said:

Brain , prison .? I dunno give us a clue on that one .. Fascinating to read about concrete , reedbar ( what is that ) curing etc .. I know nothing of these things but given Bangkok has a lot of elevated roadways made of concrete will this prove to be an ongoing issue in the future .. 

It's generally accepted that concrete bridges etc have a lifespan of around 70 years.

However, it means that monitoring is becoming more important. Normally that means close visual inspection every two years.

Latest go to method of NDE ( Non Destructive Examination ) is the acoustic emission system.

Probes are fixed to the bridge and 'listen' to the noises the bridge makes internally. All this noise is transmitted electronically to a monitoring lab' where they are deciphered by trained experts.

Cracks etc change frequency of sound as they grow etc and that can be 'read' and compared to previous recordings.

Strangely it has an interesting start.  

As Micheal  used to say 'not a lotta people knows this'.

Think of the wheel tappers who tapped the newly made loco' wheel, basically if it went ding with a nice ring like a bell all the way around it it was ok. If it went 'dong' that didn't have any length of ring to it it was cracked or had a weak section internally.

The ultrasonic system they use for seeing inside the womb of pregnant ladies is how far the way ultrasound systems have advanced.

[Justgrazing]

3 minutes ago, overherebc said:

It's generally accepted that concrete bridges etc have a lifespan of around 70 years.

However, it means that monitoring is becoming more important. Normally that means close visual inspection every two years.

Latest go to method of NDE ( Non Destructive Examination ) is the acoustic emission system.

Probes are fixed to the bridge and 'listen' to the noises the bridge makes internally. All this noise is transmitted electronically to a monitoring lab' where they are deciphered by trained experts.

Cracks etc change frequency of sound as they grow etc and that can be 'read' and compared to previous recordings.

Strangely it has an interesting start.  

As Micheal  used to say 'not a lotta people knows this'.

Think of the wheel tappers who tapped the newly made loco' wheel, basically if it went ding with a nice ring like a bell all the way around it it was ok. If it went 'dong' that didn't have any length of ring to it it was cracked or had a weak section internally.

The ultrasonic system they use for seeing inside the womb of pregnant ladies is how far the way ultrasound systems have advanced.

I should imagine then with a lot of Bangkok roadways being elevated this may prove to be something they have to keep an eye .. 

[overherebc]

42 minutes ago, Justgrazing said:

I should imagine then with a lot of Bangkok roadways being elevated this may prove to be something they have to keep an eye .. 

It's something that should be considered , yes.

 

It can be a long read, depending where google takes you, but google failure of concrete bridges in USA.

Concrete bridges really started being built there after 1945 and that puts some of them in the 'end of life phase'.

I don't think at that time cyclic loading was even considered, ie one side full of rush hour traffic in the morning and the other side full in the evening rush hour the other way.

Many other factors come into it but I'll leave that to the designers. ????????

 

[Reigntax]

2 hours ago, overherebc said:

I'm not an expert on concrete but I worked with/alongside civil inspectors in a few places.

What I do like reading about is the Roman concrete structures that are in a lot of cases stronger now than when built.

They are doing a lot of analysis on some of them, especially the structures in salt water

( harbour walls ) to determine the mix that makes them get stronger as time goes on.

All concrete, if of a suitable mixture for the duty, will be stronger in 500 years than it is after curing. It continues to cure forever and basically the slower it cures by retaining the original moisture, the more durable a particular element will be.

Information regarding what mixtures are suitable for any given application are already known and modern admixtures can add durability, waterproofness and even self repairing.

All concrete cracks although many are so small the cannot be seen with the naked eye. Understanding the material properties and designing around it's strengths and weaknesses is how you achieve durability.

Concrete does have some resistance to tensile failure but the actual yield point can be unpredictable which is undesirable as failure occurs almost immediately at the same point.

Steel reinforcement creates a predictable tensile yield where the stress to strain ratio is proportional and beyond that point the reinforcement will suffer permanent deformation, the concrete will crack but will not immediately fail or collapse.

 

[WorriedNoodle]

9 hours ago, rooster59 said:

Amorn said a concrete slab fell from a station of an elevated railway a few days ago, endangering the lives of people and motorists.

 

Should motorists and people who are having their lives endangered be entitled to know which freaking station this happened at?

[mok199]

With all the non inspected high rise concrete work ,I am surprised it is not raining chunks, 24/7

Edited July 13, 2019 by mok199

[hotchilli]

18 hours ago, rooster59 said:

Expert calls for regular checks of elevated railway structure after concrete slab falls

Something to add into the non-existent maintenance manual then !

[hotchilli]

Amorn said elevated railways should be regularly checked by experienced engineers using both observations and the half-brain-cell potential technique.