New Pedestrian Bridge Collapses in Miami

[Peter Dow]

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Experts cite explosive joint failure as cause of Florida bridge collapse

“I think they probably were carrying out jacking works,” said Bourne. “You only have a jack connected to the bar on for the few minutes you’re stressing and it’s still on in the collapsed condition. If they weren’t stressing it, it wouldn’t be there.”

It is this additional force being put into the diagonal member during the jacking operation that Bourne thinks could have caused failure of the critical end joint.​

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Damage to the side of truss member #11 is spalling caused by the explosive release of elastic energy which was stored in the highly stressed post-tensioning bar within when it snapped.

This, along with the picture of the jack still attached to the P.T. bar, is the smoking gun.

Forensic engineering conclusion

There is no satisfactory way to "implement" a house of cards. It is an intrinsically precarious structure.

Maybe somewhere there is a house of cards which has stood the test of time, but it is generally understood that the metaphorical reference to a "house of cards" is to compare it with something that is precarious, unstable and prone to failure - in this case the FIU pedestrian bridge.

If, as it seems the evidence may be pointing to, the bridge failed because of what one worker did in a minute dangling from crane with a jack to a P.T Bar then that proves that the bridge was precarious and so it had a bad design.

A good design should exclude the possibility for one worker doing something inept, whether under orders to do that something inept or not, which causes the collapse of the whole structure.

A good design would build in redundancy so that if one component failed - like a P.T. bar or a truss member or a truss joint - then other P.T. bars or truss members or joints would save the bridge.

Or a good design would use a truss made from rigid metal-only members (tubes or girders) and metal-only joints and avoided the problems of trusses made from prestressed or post-tensioned concrete on such a critical component of a bridge.

Political questions

The FIU bridge collapse story was reported by the BBC in Britain and world-wide and that's how the story came to my attention. FIU claims to be an "International" university - an invitation (or at least an excuse) for discussion of FIU's affairs on the world wide web, maybe?

Public Safety

A pedestrian underpass would have been safer and cheaper than a bridge, right? So public safety and cost was not the top priority. Is that acceptable?

Management

The bridge project was mismanaged to the point of killing people. Are there wider problems which this tragedy highlights - problems with mismanagement of this university, other universities, civil engineering management at this site or elsewhere?

Legal

Florida Involuntary Manslaughter Laws
Overview of Florida Involuntary Manslaughter Laws

When a homicide, the killing of a human being, does not meet the legal definition of murder, Florida state laws allow a prosecutor to consider a manslaughter charge. The state establishes two types of manslaughter: voluntary and involuntary. While voluntary manslaughter describes an intentional act performed during a provocation or heat of passion, involuntary manslaughter does not require intent to kill or even intent to perform that act resulting in the victim's death.

To establish involuntary manslaughter, the prosecutor must show that the defendant acted with "culpable negligence." Florida statutes define culpable negligence as a disregard for human life while engaging in wanton or reckless behavior. The state may be able to prove involuntary manslaughter by showing the defendant's recklessness or lack of care when handling a dangerous instrument or weapon, or while engaging in a range of other activities that could lead to death if performed recklessly.​

Who are the individuals responsible for the loss of life and are they criminally culpable with regard to the decisions they made negligently or recklessly that disregarded the dangers to human life and contributed to the deaths?

Civil liability. Who should pay compensation and how much?

Political

Who is to blame politically, Obama or Trump or neither? Will anyone be held politically accountable for these deaths?

 

[Peter Dow]

The pedestrian bridge was being built next to a 4-way intersection or crossroads, with a pedestrian crossing, where the traffic has to stop for the lights anyway.

It seems that the cost of a pedestrian bridge (or pedestrian underpass) could not be justified.

The existing pedestrian crossing could be made safer by installing

• good quality cameras to video anyone jumping the lights or speeding, take their number plates and fine them
• good quality lighting so that the cameras work beautifully even at night
• the pedestrian crossing may even turn a profit

It seems that the pedestrian bridge plan was not really for functional reasons but was wanted by the Florida International University for advertising purposes.

I suppose if they had known what they were doing and built a safe bridge safely that would have been OK.

Possibly few would have used it because it would still have been easier to use the crossing at the traffic lights but hey, it wouldn't be the first architectural folly.

But they didn't know what they were doing and their recklessness got innocents killed and in my opinion that is a crime.

 

[Markle]

Thank you for the information.

I'm still wondering if the type of concrete used had anything to do with the collapse. It is supposed to be some sort of new, self-cleaning, concrete. I don't remember which article it was in but I don't think it had been used in this sort of construction previously.

This will still be in litigation 20 years from now. The attorneys will end up "owning" both companies.

 

[Peter Dow]

Thank you for the information.

Hey no problem.

I'm still wondering if the type of concrete used had anything to do with the collapse. It is supposed to be some sort of new, self-cleaning, concrete. I don't remember which article it was in but I don't think it had been used in this sort of construction previously.

I doubt it. There is so much wrong with the way they used the concrete that even if it was the world's finest concrete ever, with the bad design of the bridge they used, it was never going to stand the test of time.

For example, the concrete truss member which failed - number 11 - they size they built it had a maximum allowable design load - I estimate - of at best of about 1112 kips but the weight of the bridge alone put a load of 1615 kips on that truss member #11.

So even before they started adding even more load from the post-tensioning cables, truss member #11 was already struggling to bear 145% of its allowable load.

It was a very poor design - the truss was the wrong material - concrete is not as good as metal - and it was too short (not high enough) for the length of span it needed to cross - and the truss members were too thin and weak for the load they were trying to carry.

This bridge was a house of cards - doomed to fall down.

 

[Peter Dow]

Thank you for the information.

I'm still wondering if the type of concrete used had anything to do with the collapse. It is supposed to be some sort of new, self-cleaning, concrete. I don't remember which article it was in but I don't think it had been used in this sort of construction previously.

This will still be in litigation 20 years from now. The attorneys will end up "owning" both companies.

Thank you for the information.

Hey no problem.

I'm still wondering if the type of concrete used had anything to do with the collapse. It is supposed to be some sort of new, self-cleaning, concrete. I don't remember which article it was in but I don't think it had been used in this sort of construction previously.

I doubt it. There is so much wrong with the way they used the concrete that even if it was the world's finest concrete ever, with the bad design of the bridge they used, it was never going to stand the test of time.

For example, the concrete truss member which failed - number 11 - they size they built it had a maximum allowable design load - I estimate - of at best of about 1112 kips but the weight of the bridge alone put a load of 1615 kips on that truss member #11.

So even before they started adding even more load from the post-tensioning cables, truss member #11 was already struggling to bear 145% of its allowable load.

It was a very poor design - the truss was the wrong material - concrete is not as good as metal - and it was too short (not high enough) for the length of span it needed to cross - and the truss members were too thin and weak for the load they were trying to carry.

This bridge was a house of cards - doomed to fall down.

More on concrete.
My estimate in my previous post was based on average concrete but I have since discovered that the the FIU FIGG-MCM proposal specifies a higher (the highest) grade of concrete - grade VI - 8.5 ksi.

So with this fairer assumption and considering the possibility that the concrete used wasn't up to specification, I have made detailed calculations which I can present graphically as follows.

This tells us that the concrete has to be fully up to the grade VI specification just barely to hold the bridge up with no additional load from post-tensioning bars or from any pedestrians on the bridge. Anything less than top notch concrete and that bridge is coming down.

Even for those calculations I had to assume a risky safety load factor of only 1.2 and the estimates using more cautious safety factors also warn that the bridge is too heavy for the design of member #11.

This tells us that only calculating with a risky safety factor of only 1.2 can we assess that the truss member #11 is just barely strong enough to hold the bridge up with no additional load from post-tensioning bars or from any pedestrians on the bridge. Using anything more cautious for a design safety factor would warn that the bridge is at an unacceptable risk of coming down.

So we can see that the bridge designers were gambling with people's lives even before a single bar was post-tensioned - which was what was being done at the time the bridge collapsed.

The "dead load of the bridge on member #11", if you are interested in this kind of thing, is calculated as follows.

 

[Peter Dow]

Thanks to the use of an online truss calculator, I have now been able to make a more accurate calculation of the likely forces which the bridge was subjected to when it failed.

Video evidence shows that the bottom northern end joint of the bridge failed first and so suspicion has fallen upon the elements of the bridge at the north end and so it was helpful to calculate the likely axial forces along member #11 (marked "M11" in the diagrams above).

The compression force from the dead weight of the bridge I calculated as - 1367 kip or 1,367 thousand pounds of force.

The compression force from the post-tensioning (P.T.) bars within member #11 - I calculated had to be at least 304 kip but in practice would have been more, perhaps significantly more so we should have treated the P.T. bar force as a live load (LL), not a dead load (DL) for design purposes.

So the unfactored load on member #11 was at least 1367 + 304 = 1671 kip.

As recommended,

factoring the load as 1.2 x DL + 1.6 x LL suggests they should have designed for a
Maximum allowable design factored load of 1367 x 1.2 + 304 x 1.6 = 2127 kip

I estimated from this NTSB video



that member #11 used 10 x #7 bars which would suggest it was suitable for a factored load of only 2006 kip. which corresponds to a ratio of factored to unfactored load of 2006/1671 = 1.2 (only).

To get to a factored load of at least 2127 kip, as my table suggests, member #11 would have needed 14 x #8 or 12 x #9 or 10 x #10 rebars.

Even if member #11 was not designed or constructed within code we cannot conclude that the failure of the bridge's bottom northern end joint was caused by a failure of member #11 per se.

The remains of the bottom northern end joint of the bridge

The failure which the evidence of the video and photographs suggests is more likely to be with the design of the joint itself, an insufficiency of reinforcement in anchoring member #11 to the deck, leading to, I might suggest, shear fractures along the 2 planes either side of member #11 where they intersect with the deck which I have illustrated by annotating sheet B-8 from the design engineer's drawings as follows.

I may not know with 100% certainty what the cause of this bridge collapse is but I can offer my expert opinion on the basis of the available evidence so far.

 

[OldLady]

Thanks to the use of an online truss calculator, I have now been able to make a more accurate calculation of the likely forces which the bridge was subjected to when it failed.

Video evidence shows that the bottom northern end joint of the bridge failed first and so suspicion has fallen upon the elements of the bridge at the north end and so it was helpful to calculate the likely axial forces along member #11 (marked "M11" in the diagrams above).

The compression force from the dead weight of the bridge I calculated as - 1367 kip or 1,367 thousand pounds of force.

The compression force from the post-tensioning (P.T.) bars within member #11 - I calculated had to be at least 304 kip but in practice would have been more, perhaps significantly more so we should have treated the P.T. bar force as a live load (LL), not a dead load (DL) for design purposes.

So the unfactored load on member #11 was at least 1367 + 304 = 1671 kip.

As recommended,

factoring the load as 1.2 x DL + 1.6 x LL suggests they should have designed for a
Maximum allowable design factored load of 1367 x 1.2 + 304 x 1.6 = 2127 kip

I estimated from this NTSB video



that member #11 used 10 x #7 bars which would suggest it was suitable for a factored load of only 2006 kip. which corresponds to a ratio of factored to unfactored load of 2006/1671 = 1.2 (only).

To get to a factored load of at least 2127 kip, as my table suggests, member #11 would have needed 14 x #8 or 12 x #9 or 10 x #10 rebars.

Even if member #11 was not designed or constructed within code we cannot conclude that the failure of the bridge's bottom northern end joint was caused by a failure of member #11 per se.

The remains of the bottom northern end joint of the bridge

The failure which the evidence of the video and photographs suggests is more likely to be with the design of the joint itself, an insufficiency of reinforcement in anchoring member #11 to the deck, leading to, I might suggest, shear fractures along the 2 planes either side of member #11 where they intersect with the deck which I have illustrated by annotating sheet B-8 from the design engineer's drawings as follows.

I may not know with 100% certainty what the cause of this bridge collapse is but I can offer my expert opinion on the basis of the available evidence so far.

Any possibility you can say that in English? Like a couple sentences?
What caused it to fail?

 

[Peter Dow]

Any possibility you can say that in English? Like a couple sentences?

I could try but a picture paints a thousand words so I'll rather add a few sentences in red ink to this picture which I have extracted from the FIGG - MCM design-build team's own document pdf proposing to FIU that they get the contract to build the bridge.

What caused it to fail?

The bridge designers innovated (incompetently) a new I-beam design of bridge but where the I-beam's upright-supports (called an "open truss") join the deck of the bridge, the designers should have specified the necessary reinforcement to stop the severely stressed joints breaking apart - "should have" but negligently didn't and so the weakest link - the northern bottom end joint - failed first and it caused a catastrophic collapse of the whole bridge.

 

[Peter Dow]

The Florida Department of Transport has released the engineering design and construction plans for the FIU pedestrian bridge, which can be downloaded from this link.

Florida Department of TRANSPORTATION - Denney Pate signed and sealed FIU bridge construction plans - 2016 & 2017
https://cdn2.fdot.gov/fiu/13-Denney-Pate-signed-and-sealed-FIU-bridge-construction-plans.pdf

My analysis of these engineer's plans have revealed that my earlier suspicion that member 11 was dangerously under-reinforced has been confirmed, to such a degree that the collapse of member 11 (and consequently the whole bridge) under the compression load after the bridge was placed on the piers but before destressing was to be expected.

The engineering plans, signed off by the "Engineer of Record", W. Denney Pate of FIGG, were at dangerously at fault and so the construction team by simply following the plans faithfully would have guaranteed the collapse of the bridge.

The first point of concern to note from the engineering plans is that the plan's P.T. bar tensioning begins once the concrete reaches a strength of only 6,000 psi or more, as this quote shows -

"CONSTRUCTION SEQUENCE - STAGE 2 - SUPERSTRUCTURE PRE-CASTING
2. AFTER CONCRETE COMPRESSIVE STRENGTH HAS REACHED 6000 PSI, STRESS POST-TENSIONING OF THE MAIN SPAN IN THE FOLLOWING SEQUENCE ..."​

6,000 psi is less than the final full strength of the concrete was expected to be (at least 8,500 psi) when it has fully set and in this case proceeding with the construction while the concrete was not fully hard was a contributing factor to the collapse.

The next point of concern to note is that the engineer's plans recommend a P.T. bar setting for the 2 P.T. bars in member 11 which together total a P.T. bar tension of 560 KIP.

The results of my truss calculations show that the dead weight of the bridge exerts on member 11
* a tension force of 304 KIP while the bridge is being transported and
* a compression force of 1367 KIP when the bridge is placed on the piers, which is a point of concern to note.

The P.T. bar tension of 560 KIP on member 11 is somewhat higher than it needs to be - I have suggested that a P.T. bar tension of 390 KIP would have been plenty.

Now let us consider what all those forces together in the sequence they were applied mean for the compression force on the reinforced concrete of member 11.


I have considered 5 different stages, A, B, C, D and E. The bridge collapsed as a result of damage to the concrete member 11 sustained in stage D, so the bridge never got to stage E in good order, sadly, but inevitably given the plans followed.

Stage A
The concrete has hardened to at least 6,000 PSI and so post-tensioning is about to begin but at this stage the mainspan is still resting on the ground, so there are no troublesome forces on member 11, no P.T. bar tension, no bridge dead weight and so the reinforced concrete is not being compressed very much at all except under its own weight and that of the canopy immediately above it, but we will ignore that for now.

Stage B
The P.T. bars of member 11 have been tensioned to the recommended amount - a total of 560 KIP and that tension force on the P.T. bars is being provided by an equal and opposite compressive force of 560 KIP on the reinforced concrete. But the mainspan is still on the ground so not much in the way of dead weight of the bridge to worry about yet.

Stage C
The mainspan has been lifted onto the transporters and now the dead weight of the bridge is exerting an external tension force of 304 KIP on member 11. This has the effect of reducing the compressive force on the reinforced concrete of member 11 by 304 KIP down to 256 KIP.

Stage D
In this case, "D" for danger and for "Doom".
This is when things take a turn for the worse. The bridge gets placed on the piers and now the dead weight of the bridge is applying a compression force of 1367 KIP on to member 11.

So now the reinforced concrete has to take the full compression force of 560 KIP from the P.T. bars under tension plus the 1367 KIP dead weight of the bridge to suffer a whopping 1927 KIP of compression force, which is more than member 11 is able to cope with, especially so if the concrete has not reached is full strength of at least 8500 PSI, as is shown in this table from my concrete column calculator and this bar chart.





Therefore the collapse of member 11 must be expected if the strength of the concrete was only 8,000 psi or less and the plans only require that the strength of the concrete at this stage be at least "6,000 psi".

A point of concern to note is that the plans only call for 8 number 7 (diameter 7/8" inch, area 0.6 square inches each, axially orientated reinforcing bars), just barely 1% of a reinforcement ratio for that size of concrete member. The compression strength of member 11 was 99% concrete by areal cross-section.

Another point of concern to note is that plans only call for member 11 to be of size 24 inches by 21 inches in cross section. Whereas the equivalent member at the south side of the bridge, member 2 was 150% wider, 36 inches by 21 inches and although it was carrying a higher dead weight from the bridge, member 2 survived intact.

Member 11 was not thick enough, it wasn't reinforced with steel bar enough, it was not strong enough to survive the forces it was subjected to during stage D.

The P.T. bars, 1.75" diameter steel bars, didn't contribute to the long term compression strength of member 11, but actually contributed to ruining the long term compression strength in stage D.



As I have noted there, W Denney Pate's drawings don't draw a section through member 11 with only 2 P.T. bars, only section B-B "(TYP. FOR ALL MEMBERS WITH P.T. BARS)" which draws 8 reinforcement bars. Bars marked here "7S11" are 8 size 7 (7/8" diameter) bars confirmed by the table on page 98, SHEET B-98, SUPERSTRUCTURE REINFORCEMENT BAR LIST AND NTSB images.

The plans specify an inadequate reinforcement and inadequate compression strength of the reinforced concrete of member 11 to withstanding the compression load of 1927 KIP before destressing the P.T. bars, which would have cracked, crumbled and weakened the member 11 during Stage D. This was catastrophic damage which would sooner or later cause the member 11 to fail.

Possibly at Stage D the cracked and crumbled concrete of member 11 was temporarily still being precariously held together by static friction increased by the additional compression on the concrete provided by the tense P.T. bars. (Sort of like if you crush a biscuit between your hands, the crumbs don't fall out until you release your grip.)

This would explain why the bridge did not collapse immediately when placed on the piers but only when destressing of member 11 began and the already cracked concrete lost some of its static friction cohesion by the reduction in compression and only then did the member 11 shatter, collapsing the bridge.

Member 11 was carrying the full weight of the structure. There is no redundancy in the FIU bridge design whereby other concrete columns can take the load if truss member 11 fails. It was all on member 11. When member 11 goes, the whole bridge goes down.

This picture shows "the smoking gun" - far too small and far too few reinforcement bars, marked "<-B->".


The picture also shows the broken stirrup reinforcement bars, which too, were inadequate to the task expected of them.

Stage E.
After destressing is complete. We don't know for sure if this stage was actually completely entirely but even if it had been, by that time the damage which had been done in Stage D was revealing itself and the member 11 was failing and bridge had begun the process of collapsing.

There was no way to complete stage E successfully because member 11 was on a hair trigger to collapse because of the severe damage to the concrete sustained in stage D.

The inadequate strength of member 11, alone, could be entirely responsible for the collapse of the bridge.

Additionally, I have concerns about the failure of the bottom joint under shear fracture where member 11 connects to the deck and member 12.

To my mind the responsibility for the collapse of the bridge lies with he who wrote those plans - W. Denney Pate.

Nevertheless, I believe that others too had a responsibility not to allow citizens to pass or drive under any bridge under construction, before it has been completed and certified as safe.

A collapsed bridge is a pity. A collapsed bridge falling onto citizens is a crime.

Peter Dow's 'Truss Forces - The weak points of the bridge and the forces they failed under' picture album on Flickr

Peter Dow's 'Mug Shots - FIU Bridge Collapse - Key personnel responsible' album on Flickr

 

[flacaltenn]

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Experts cite explosive joint failure as cause of Florida bridge collapse

“I think they probably were carrying out jacking works,” said Bourne. “You only have a jack connected to the bar on for the few minutes you’re stressing and it’s still on in the collapsed condition. If they weren’t stressing it, it wouldn’t be there.”

It is this additional force being put into the diagonal member during the jacking operation that Bourne thinks could have caused failure of the critical end joint.​

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Damage to the side of truss member #11 is spalling caused by the explosive release of elastic energy which was stored in the highly stressed post-tensioning bar within when it snapped.

This, along with the picture of the jack still attached to the P.T. bar, is the smoking gun.

Forensic engineering conclusion

There is no satisfactory way to "implement" a house of cards. It is an intrinsically precarious structure.

Maybe somewhere there is a house of cards which has stood the test of time, but it is generally understood that the metaphorical reference to a "house of cards" is to compare it with something that is precarious, unstable and prone to failure - in this case the FIU pedestrian bridge.

If, as it seems the evidence may be pointing to, the bridge failed because of what one worker did in a minute dangling from crane with a jack to a P.T Bar then that proves that the bridge was precarious and so it had a bad design.

A good design should exclude the possibility for one worker doing something inept, whether under orders to do that something inept or not, which causes the collapse of the whole structure.

A good design would build in redundancy so that if one component failed - like a P.T. bar or a truss member or a truss joint - then other P.T. bars or truss members or joints would save the bridge.

Or a good design would use a truss made from rigid metal-only members (tubes or girders) and metal-only joints and avoided the problems of trusses made from prestressed or post-tensioned concrete on such a critical component of a bridge.

Political questions

The FIU bridge collapse story was reported by the BBC in Britain and world-wide and that's how the story came to my attention. FIU claims to be an "International" university - an invitation (or at least an excuse) for discussion of FIU's affairs on the world wide web, maybe?

Public Safety

A pedestrian underpass would have been safer and cheaper than a bridge, right? So public safety and cost was not the top priority. Is that acceptable?

Management

The bridge project was mismanaged to the point of killing people. Are there wider problems which this tragedy highlights - problems with mismanagement of this university, other universities, civil engineering management at this site or elsewhere?

Legal

Florida Involuntary Manslaughter Laws
Overview of Florida Involuntary Manslaughter Laws

When a homicide, the killing of a human being, does not meet the legal definition of murder, Florida state laws allow a prosecutor to consider a manslaughter charge. The state establishes two types of manslaughter: voluntary and involuntary. While voluntary manslaughter describes an intentional act performed during a provocation or heat of passion, involuntary manslaughter does not require intent to kill or even intent to perform that act resulting in the victim's death.

To establish involuntary manslaughter, the prosecutor must show that the defendant acted with "culpable negligence." Florida statutes define culpable negligence as a disregard for human life while engaging in wanton or reckless behavior. The state may be able to prove involuntary manslaughter by showing the defendant's recklessness or lack of care when handling a dangerous instrument or weapon, or while engaging in a range of other activities that could lead to death if performed recklessly.​

Who are the individuals responsible for the loss of life and are they criminally culpable with regard to the decisions they made negligently or recklessly that disregarded the dangers to human life and contributed to the deaths?

Civil liability. Who should pay compensation and how much?

Political

Who is to blame politically, Obama or Trump or neither? Will anyone be held politically accountable for these deaths?

Thanks for insight. I'll read more of your notes. Since I'm from Florida and graduated from Univ of Florida in the same state school system -- I can tell you that FIU has the INTERNATIONAL in it because of it's research labs and programs that DO reach around the world. For instance, it has an international lab for hurricane studies and many others that I don't remember. It also has at least 3 official campuses in different countries. I know there was Spain and Italy and I think they added at least one other in China recently.

The other thing is --- Florida soil is NOT real amenable to tunneling for subterranean projects. Particularly in Miami where the water table is almost at street level before it rains. And it's very loose and sandy on top of spongy limestone thats prone to sink holes. So there arent many long tunnels anywhere in the state.

 

[Peter Dow]

Now considering member 2, which survived intact,

member 2's "SECTION C-C" -

- has 12 x size 8 (diameter 1", area 0.785 sq-in) reinforcing bars and member 2's P.T. bar force setting is

560 kip (same as member 11).
My truss calculation results were -
in transit tension of 458 kip
in situ compression of 1920 kip

Now let us consider what all those forces together in the sequence they were applied mean for the compression force on the reinforced concrete of member 2.

At the critical "Stage D", when the bridge is placed on the piers but before the P.T. bars can be destressed, the reinforced concrete of member 2 has to take the full compression force of 560 KIP from the P.T. bars under tension plus the 1920 KIP dead weight of the bridge to suffer a total of 2480 KIP of compression force, but member 2 was able to cope with that load of 2480 kip, so I calculated the maximum allowable design factored load to find out how strong the concrete must have been, in this table from my concrete column calculator and this bar chart.

Therefore the survival of member 2 may be expected, during Stage D anyway, if the strength of the concrete was 7,000 psi or more, albeit a reasonably safe load factor (at least 1.2) is not to be enjoyed until the concrete hardens to at least 8,285 psi.

Simply applying commonly used engineering design equations for concrete columns suggests clearly why member 2 survived but member 11 failed. Pate's under-design of member 11 was significantly further out of code than was his design of member 2.

 

[Ame®icano]

View attachment 182817

All women engineering team in action.

 

[WheelieAddict]

View attachment 182817

All women engineering team in action.

More like Florida in action.