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Pittsburgh bridge collapse
32

Pittsburgh bridge collapse

RE: Pittsburgh bridge collapse

Is one trillion enough?

RE: Pittsburgh bridge collapse

Here is the location:

https://www.google.com/maps/@40.4395116,-79.900510...

This is not a small, forgotten bridge on a back road somewhere.

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

2
https://bridgereports.com/1456104

Name: FORBES AVENUE over 9 MILE RUN & FERN HOLLOW
Structure number: 000000000002410
Old structure number: 027301000030330 (from 1992 edition)
Location: 301033 NEAR S BRADDOCK AV

Latest Available Inspection: September 2017
Good/Fair/Poor Condition: Poor
Status: Posted for load [P]
Average daily traffic: 14,500 [as of 2005]
Truck traffic: 7% of total traffic
Deck condition: Fair [5 out of 9]
Superstructure condition: Poor [4 out of 9]
Substructure condition: Satisfactory [6 out of 9]
Structural appraisal: Meets minimum tolerable limits to be left in place as is [4]
Deck geometry appraisal: Basically intolerable requiring high priority of corrrective action [3]
Water adequacy appraisal: Superior to present desirable criteria [9]
Roadway alignment appraisal: Better than present minimum criteria [7]
Channel protection: There are no noticeable or noteworthy deficiencies which affect the condition of the channel. [9]
Scour condition: Bridge foundations (including piles) on dry land well above flood water elevations. [9]
Sufficiency rating: 18.7
Recommended work: Bridge rehabilitation because of general structure deterioration or inadequate strength. [35]
Estimated cost of work: $1,522,000

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

Hard to see on Google, but it looks like a rigid K-frame.

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

Condition rated as poor since 2011.

[/sarc] Nothing to see here. [/end sarc]

RE: Pittsburgh bridge collapse

Gathering some data...

Story says there was an articulated city bus on the bridge and at least 4 vehicles.

There was at least some snow on the bridge.

As of the May 2019 street view photo, the bridge was posted at 26 TONS.

From Wikipedia, PAAC has New Flyer D60LFR buses, which have a 41,500-43,700 curb weight and New Flyer XD60 Xcelsiors which have a curb weight of 39,000-45,500 lb.

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

I grew up 5 or six miles from that bridge. I remember its predecessor, but I had to search to refresh my memory of the current structure, which agrees with the picture above.

Google street view shows it posted with a 26 ton weight limit.

Also, for what it's worth, from Wednesday night into yesterday morning it was awfully cold here. Minus 12 at 7:30 a.m. where I was.

RE: Pittsburgh bridge collapse

Pic from December 2018 from Twitter @gpk320

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

It looks like they tried a band aid fix for that. But not a large enough band aid if that member goes into compression.

With a few inches of snow and the bus, that was well over the posted weight limit. Interesting to see how this might affect public transportation policy if our vehicles are too large for our aging infrastructure.

RE: Pittsburgh bridge collapse

It looks like the east bent is missing the lower cross bracing compared to the west end. It's a bit blurry from the google street view but its still clearly missing. The resolution is too poor to see if the cables are still there. The images are from 2020, 2 years after the pic of the cables was posted.

RE: Pittsburgh bridge collapse

bradw1128

Thanks for the inspection report, I was just watching a video of Mayor Ed Gainy (sp) speaking to reporters as he was given false information on that inspection date, he was told September of 2021. First he said he thought it was about 2 yrs ago.

https://www.youtube.com/watch?v=Nl6LgfLEJCU - time stamp at around 15:00 in.

It's amazing timing that 3 days ago Biden planned this visit to Pittsburgh today.

RE: Pittsburgh bridge collapse

There was a snow event on Jan 16-17 that put down about 7" in that area, but this morning's snow was an inch, or less.

RE: Pittsburgh bridge collapse

Looks like maybe the city was considering repairs as of 2019:

From the 2019 capital budget
https://apps.pittsburghpa.gov/redtail/images/4499_...

Page 172:
Legislative & Contractual Committments [OMB] Maintenance and Improvements to Forbes Ave Bridge $ 3,000,000.00 $ - 4

I can't tell if it was ever actually funded.


And from a draft STIP project page, a longer term replacement plan:
https://www.spcregion.org/wp-content/uploads/2021/...

Page 45:

Allegheny Forbes Ave Bridge over Fern Hollow* $6,892,000 7301 Long‐Term (2033‐2045)
Bridge restoration/replacement on Forbes Avenue
Bridge over Fern Hollow in the City of Pittsburgh,
Allegheny County; Project sponsor is City of
Pittsburgh
Bridge Reconstruction 20192023

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

A more interesting question, "How much more of that stuff is out there?" I'm glad there were no fatalities.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

dik, as I drive around Ohio and surrounding states, I would have to say that it is extensive. The levels of corrosion and failing concrete is spooky. 90% of this issues in this area are a direct result of the application of de-icing materials, be it salt, calcium chloride, brine, etc. At some point, we need to wake up and stop the direct application of these chemicals to our bridge decks. Galvanizing and epoxy paint can only do so much. My state DOT uses and average of 600,000 tons of salt per year. This does not include all of the cities, counties, townships, etc. that also clear roads.

RE: Pittsburgh bridge collapse

I was thinking of that condo unit in Florida that collapsed, killing nearly 100. I suspect a lot of the problem was poor design and lack of maintenance. Things will not get better without 'fixing' things.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

The link to inventory data above is outdated. I downloaded the 2021 inventory data below.

This represents the 2019 routine inspection and 2020 fracture critical and special inspection. All seemed to be on a September schedule. There likely was a +/- September 2021 inspection after this data was uploaded.

There were fracture critical and special inspections on a 12 month frequency.


STATE_CODE_001 PA
STRUCTURE_NUMBER_008 000000000002410
RECORD_TYPE_005A on
ROUTE_PREFIX_005B city street
SERVICE_LEVEL_005C mainline
ROUTE_NUMBER_005D n/a
DIRECTION_005E n/a
HIGHWAY_DISTRICT_002 11
COUNTY_CODE_003 Allegheny
PLACE_CODE_004 61000
FEATURES_DESC_006A
CRITICAL_FACILITY_006B
FACILITY_CARRIED_007 'FORBES AVENUE'
LOCATION_009 '301033 NEAR S BRADDOCK AV'
MIN_VERT_CLR_010 99.99
KILOPOINT_011 0
BASE_HWY_NETWORK_012 1
LRS_INV_ROUTE_013A
SUBROUTE_NO_013B
LAT_016 40262229
LONG_017 79540120
DETOUR_KILOS_019 5
TOLL_020
MAINTENANCE_021 City or Municipal Highway Agency
OWNER_022 City or Municipal Highway Agency

FUNCTIONAL_CLASS_026 other principal arterial
YEAR_BUILT_027 1970
TRAFFIC_LANES_ON_028A 4
TRAFFIC_LANES_UND_028B 0
ADT_029 14500
YEAR_ADT_030 2005
DESIGN_LOAD_031 H 20
APPR_WIDTH_MT_032 15.2
MEDIAN_CODE_033 0
DEGREES_SKEW_034 0
STRUCTURE_FLARED_035 0
RAILINGS_036A 0
TRANSITIONS_036B 0
APPR_RAIL_036C 0
APPR_RAIL_END_036D 0
HISTORY_037 Bridge is not eligible for the National Register of Historic Places
NAVIGATION_038 0
NAV_VERT_CLR_MT_039 0
NAV_HORR_CLR_MT_040 0
OPEN_CLOSED_POSTED_041 posted for load
SERVICE_ON_042A highway-pedestrian
SERVICE_UND_042B waterway
STRUCTURE_KIND_043A steel continuous
STRUCTURE_TYPE_043B frame
APPR_KIND_044A n/a
APPR_TYPE_044B n/a
MAIN_UNIT_SPANS_045 3
APPR_SPANS_046 0
HORR_CLR_MT_047 15.2
MAX_SPAN_LEN_MT_048 50.6
STRUCTURE_LEN_MT_049 136.2
LEFT_CURB_MT_050A 2.1
RIGHT_CURB_MT_050B 2.1
ROADWAY_WIDTH_MT_051 15.2
DECK_WIDTH_MT_052 19.5
VERT_CLR_OVER_MT_053 99.99
VERT_CLR_UND_REF_054A N
VERT_CLR_UND_054B 0
LAT_UND_REF_055A N
LAT_UND_MT_055B 0
LEFT_LAT_UND_MT_056 0
DECK_COND_058 poor
SUPERSTRUCTURE_COND_059 poor
SUBSTRUCTURE_COND_060 satisfactory
CHANNEL_COND_061 There are no noticeable or noteworthy deficiencies which affect the condition of the channel
CULVERT_COND_062 n/a
OPR_RATING_METH_063 load factor (LF)
OPERATING_RATING_064 29.9 metric tons
INV_RATING_METH_065 load factor (LF)
INVENTORY_RATING_066 17.2 metric tons
STRUCTURAL_EVAL_067 Meets minimum tolerable limits to be left in place as is
DECK_GEOMETRY_EVAL_068 Basically intolerable requiring high priority of corrective action
UNDCLRENCE_EVAL_069 n/a
POSTING_EVAL_070 10.0 - 19.9% below (relationship of operating rating to maximum legal load)
WATERWAY_EVAL_071 Superior to present desirable criteria
APPR_ROAD_EVAL_072 Meets minimum tolerable limits to be left in place as is
WORK_PROPOSED_075A Bridge rehabilitation because of general structure deterioration or inadequate strength.
WORK_DONE_BY_075B Work to be done by owner's forces
IMP_LEN_MT_076 136
DATE_OF_INSPECT_090 Sep-19
INSPECT_FREQ_MONTHS_091 24
FRACTURE_092A Yes - 12 months
UNDWATER_LOOK_SEE_092B N
SPEC_INSPECT_092C Yes - 12 months
FRACTURE_LAST_DATE_093A Sep-20
UNDWATER_LAST_DATE_093B
SPEC_LAST_DATE_093C Sep-20
BRIDGE_IMP_COST_094 113,000
ROADWAY_IMP_COST_095 332,000
TOTAL_IMP_COST_096 1,522,000
YEAR_OF_IMP_097
OTHER_STATE_CODE_098A
OTHER_STATE_PCNT_098B 0
OTHR_STATE_STRUC_NO_099
STRAHNET_HIGHWAY_100 0
PARALLEL_STRUCTURE_101 N
TRAFFIC_DIRECTION_102 2
TEMP_STRUCTURE_103
HIGHWAY_SYSTEM_104 Inventory Route is on the NHS
FEDERAL_LANDS_105 n/a
YEAR_RECONSTRUCTED_106 0
DECK_STRUCTURE_TYPE_107 Concrete Cast-in-Place
SURFACE_TYPE_108A Bituminous
MEMBRANE_TYPE_108B none
DECK_PROTECTION_108C none
PERCENT_ADT_TRUCK_109 7
NATIONAL_NETWORK_110 The inventory route is not part of the national network for trucks
PIER_PROTECTION_111
BRIDGE_LEN_IND_112 yes
SCOUR_CRITICAL_113 Bridge foundations determined to be stable for calculated scour conditions; scour within limits of footing or piles
FUTURE_ADT_114 18000
YEAR_OF_FUTURE_ADT_115 2030
MIN_NAV_CLR_MT_116 0
FED_AGENCY N
SUBMITTED_BY 42
BRIDGE_CONDITION P
LOWEST_RATING 4
DECK_AREA 2655.9

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

While salt/chlorine is bad for bridges, I do think a part of the issue here is lack of maintenance over the year. Relatively speaking the bridge being 50 years old should not be in such a poor condition for so long (since 2011?). We use probably just as much salt here in Toronto and of all the road bridges I inspected past few year I do not recall seeing one with an entire bracing member corroded through.

RE: Pittsburgh bridge collapse

Dik - I'd wager every major city in a snowy climate has at least 1 similar situation. when i lived in pittsburgh, there was an old (80 years old) concrete bridge i remember that had such bad spalling problems they ended up building a deck over the road below to catch the falling debris. they finally replaced the concrete bridge a few years back but that catch deck was up for 10 or 15 years.

In our small town in Maine the DOT has been trying to replace an 80 year old truss bridge since 2017 but has been stymied by court efforts from historic preservation groups that want it preserved and rehabbed rather than replaced. a beautiful bridge for sure, but the prolonged court proceedings has meant that neither replacement nor repairs have been made at all and the bridge was posted to 10 tons a couple months ago.

https://bridgehunter.com/me/cumberland/2016/

I'll be reconsidering my driving routes the rest of winter.

RE: Pittsburgh bridge collapse

Quote (Post Gazette)

The bridge collapsed as the city prepared for a visit from President Joe Biden, who is scheduled to speak about infrastructure Friday afternoon at Mill 19 in Hazelwood. Multiple officials said the collapse illustrated the need for infrastructure investment.

Glad nobody was seriously hurt, but truly this bridge had a sense of humor.

RE: Pittsburgh bridge collapse

Karma...

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Pittsburgh bridge collapse

Here is the element level data.
https://infobridge.fhwa.dot.gov/Data/BridgeDetail/...

All 4 steel columns were at condition state 4 (severe)
2 of 4 movable bearings were at CS3 (poor)

I would expect that having a CS4 condition on a primary structural element like that would have triggered a more detailed structural review. I don't know the policies in PA though or how city-owned bridges might follow it.

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

Old timber truss bridges are neat...pipe

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

How are the reduced posted weight limits determined in these scenarios? Is 26 tons chosen through detailed structural analyses assuming certain failed members or is it a judgement call based on the types of vehicles that they want to prohibit?

RE: Pittsburgh bridge collapse

Quote (bradw1128 (Civil/Environmental)28 Jan 22 14:02)


It makes one wonder how they decided that the cross member required supplemental measures but the column didn't.

RE: Pittsburgh bridge collapse

Quote (timeforchili)

How are the reduced posted weight limits determined in these scenarios? Is 26 tons chosen through detailed structural analyses assuming certain failed members or is it a judgement call based on the types of vehicles that they want to prohibit?

Someone would have had to completed a structural evaluation (inspection and analysis) to determine the load posting. They would have modelled failed connections, section loss, verified material strengths, etc.

RE: Pittsburgh bridge collapse

I am not sure how we got to a point in the country were a bridge in a local municipality needs to be paid for by the federal government. I can see perhaps federal involvement on bridges in the interstate highway system. I think waiting for the benevolent hand of the feds to dole out money is never going to work. The local agency should be responsible. If they need to raise taxes or utilize tolls, so be it.

RE: Pittsburgh bridge collapse

Quote (timeforchili)

How are the reduced posted weight limits determined in these scenarios? Is 26 tons chosen through detailed structural analyses assuming certain failed members or is it a judgement call based on the types of vehicles that they want to prohibit?

It goes through a certain structural analysis program for the load rating of bridges, in accordance with the FHWA and state DOTs.

RE: Pittsburgh bridge collapse

3
Bill Watterson is the best!

RE: Pittsburgh bridge collapse

2
Well the feds aren't going to pay for it anyway because Congress can't get out of their own way, and the locals aren't going to raise taxes because then people might actually care about local elections and replace them.

So I think deficient bridges should simply be closed. Don't let people drive across them. Eventually people will be pleading the local government to take their money to make the repairs that are needed...or we'll all just wait in traffic for 2 hours to get to the grocery store. Either way, we get what we deserve.

RE: Pittsburgh bridge collapse

4
Without getting political, there's a real downside to Reaganomics; this is the beginning.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Quote (phamEng)

So I think deficient bridges should simply be closed. Don't let people drive across them.

Especially non-redundant ones.

RE: Pittsburgh bridge collapse

2

Quote:

So I think deficient bridges should simply be closed. Don't let people drive across them.

As I often point out on disaster posts, this is how the existing process is supposed to work. Unfortunately nobody stateside seems interested in holding the muni engineers accountable for failing to close infrastructure before disasters like this, instead they spend hours blaming politics for lack of funding. Sorry not sorry but an engineer belongs in jail for this.

RE: Pittsburgh bridge collapse

The infrastructure bill, that has already been passed by Congress, has almost #2 billion earmarked to replace/repair bridges in Pennsylvania, in addition to $4 billion for general road repair and maintenance.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Pittsburgh bridge collapse

When a bridge has important structural items at "needs fixing" it should surely be closed and fixed (or removed, if it's redundant) kind of immediately? There's no point having inspection regimes and rating of safety levels (which actually seem to have been followed quite well in this case) if you don't actually do the repairs they flag up.

Also, it seems like it would be a good idea for gas mains to have periodic auto-shutoff valves, or at least where they're built into a bridge, so if something bad happens to sever the line it doesn't allow lots of gas to escape.

RE: Pittsburgh bridge collapse

Quote:

Especially non-redundant ones

Structurally non-redundant ones should be candidates for closure

But what we really need to do is shrink the system, as the Iowa DOT commissioner says some years ago. If we can't generate the revenue to maintain our roads and bridges, maybe we need to get rid of some

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

RE: Pittsburgh bridge collapse

...and wonder what the effect of carbon footprint reduction will have on transportation. ponder

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Well at least they could have closed a lane on each side. Damn. Also those columns are covered in rust. That break in the cross member should have been the moment you shut the bridge down and fixed it.

You know during COVID a bit of engineering work would be great. True? Stimulate the economy by building and fixing stuff.

RE: Pittsburgh bridge collapse

Bradley Wilder, P.E.
Construction P.E. (KY), MBA
Bridge Rehab, Coatings, Structural Repair

RE: Pittsburgh bridge collapse

The cables may have been an attempt to stabilize the structure after the bracing became unreliable. Not something I would consider, except for an out of service structure, while awaiting or during a rehabilitation.

Quote (https://www.wonkette.com/why-did-joe-biden-blow-up...)

Let's all take a few minutes to remind ourselves that government is what we do to make sure the roads don't fall apart under our buses, and that if a disaster like that does happen, there'll be rescue crews and ambulances and hospitals to help. Wonkette (a Pittsburgh paper) January 28, 2022 03:15 PM

RE: Pittsburgh bridge collapse


Quote (Also those columns are covered in rust.)

- looks like weathering steel from the photos, but that's not to say weathering can't corrode.

Anyway, this will give Pennsylvania another opportunity to be on "Engineering Catastrophes"

RE: Pittsburgh bridge collapse

2
There's an old saying, "There's never time (or money) to do it right, but there's always time to do it over." This is the exact opposite. Someone made a decision to build a road, a bridge, a sewage collection system, etc. and pay for it. But then no one expected to ever maintain it? I just don't get it.
In the 50's and 60's the US made a decision to build an interstate highway system. It's one of the engineering wonders of the world. Note that it had military undertones, but so what, it got done. In the dollars of the time, I'm sure it was a massive expense. It has been a driver of a massive economic boom. And now it's falling apart, because we're too cheap to take care of it.

I don't disagree with closing substandard bridges. But a little story is in order: In Arizona we have seasonal washes. They only flow after rainstorms. And rainstorms are not all that common. But sometimes we get a bad one. Well, one of these washes needed a bridge, but it's traffic would be low and Arizona only builds infrastructure for politically connected developers. So a couple of years ago a family tried to cross the wash when it flooded and three of their kids drowned. The parents are going to jail as it was 95% their fault. But closing bridges has cascading effects that must be recognized.

Another story: A farmer was bragging to his neighbor, "I've got a mule and I stopped feeding him. And guess what, he works just as hard." So a couple of weeks later, the neighbor saw the farmer, and asked him, "Where is your mule?" The farmer just grumbled, "I don't have him anymore." In the 80's we decided it was time to stop feeding our mules.

RE: Pittsburgh bridge collapse

3

Quote:

Note that it had military undertones, but so what, it got done.

Quote:

And now it's falling apart, because we're too cheap to take care of it.

It's the same dynamic now as it was back then. We aren't too cheap- we continue to spend all our hard-earned money on military expenditures. Just happens that roads and bridges aren't that strategically important to the military as they were back then. We probably spent more rebuilding infrastructure in Iraq and Afghanistan over the past 20 years than we did on our own infrastructure. The military industrial complex is a giant black hole sucking away society's resources. Sorry to get on a soapbox but it's such a frustrating situation. My son's future elementary school is a mess - cobbled together with temporary trailers - while we spend trillions on F-35 fighter jets. How many bridges could we have repaired for the cost of that single F-25 jet that's sitting at the bottom of the South China Sea right now?

RE: Pittsburgh bridge collapse

and they keep trying to land them in the water, it would seem.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Can't figure out how to reply to a post, so to @Milliontown: "With a few inches of snow and the bus, that was well over the posted weight limit. Interesting to see how this might affect public transportation policy if our vehicles are too large for our aging infrastructure."

26 tons would be the weight allowed for A vehicle on the bridge, not ALL vehicles on the bridge. It's indicated that the bus is 23 tons, which should be ok. Two inches of snow is not heavy, well less than 0.5 kPa (10 psf). The background lane loading that would be allowed with the 26 ton truck would be about 3 kPa. Essentially the load posting says a 26 ton truck can be on the bridge along with almost bumper to bumper car traffic. At least according to the Canadian Bridge Code.

So I don't think the bridge was overloaded beyond what the sign allowed.

RE: Pittsburgh bridge collapse

That was when it was certified... maybe things had deteriorated in the last decade or two. Things don't usually get better on their own. pipe

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

My understanding of bridge weight limits is that vehicles over the limit will cause further deterioration--not immediate failure. You should be able to drive 26 ton vehicles over that bridge all day long without it falling down. Somebody please correct me if I'm wrong.

(Maybe I should phrase that differently--Vehicles *under* the limit will not hasten the deterioration. Obviously for any given bridge you could find something heavy enough to kill it.)

RE: Pittsburgh bridge collapse

the east side of the bridge appears to have ended up much further from its abutment than the west side. for reference, the 2018 twitter photo was of the west side, but you can the same similar cable remediation on the east side as well in the streetview from the trail below bridge, taken in 2020.

in this photo, the east side is on the left with the bus and the west side is on the right, using that gazebo at top right for reference. the broken section the bus is on appears to be the only section that ended up underneath another section of bridge. 35 mph zone so the bus is taking about 7 or 8 seconds to get that far across the bridge.



Could that be enough of a clue to indicate which side failed first?

are either of these plausible failure modes?

-East side (bus side) columns fail first as the bus load reaches them, deck breaks at the column and the bus section kinda pivots as it falls due to some resistance still there at the columns, then slides down the hill before stopped by other debris, everything else just falls mostly straight down as its way too much load for the columns to provide any resistance now.

-West side column fails first, falls more straight down and pulls rest of bridge down towards it as it fully collapses, causing east side to be so far away

lot of good photos at the trib
https://triblive.com/local/photos-bridge-collapse-...

RE: Pittsburgh bridge collapse

The Bridge Hunter website confirms that the bridge was constructed from weathering steel. There are also some notes speculating about the cause of failure. It's not clear if the person commenting is from PennDOT

Link

I noted on the Bridgeport site that the bridge was only 21 years (1991) old and rated in fair condition and in 1995 was rated in "Poor" condition. apparently some work was done between 1995 & 1997 to up the rating to "Fair".

I'd be interested in seeing the bearing details. bradw1128 wrote that the bearings were rated "Poor". Maybe thermal stress from frozen bearing at one of the piers is the cause? According to AccuWeather the Friday's temperature was between 15F & 30F with wind chills of -15F. perhaps it was something else: There could have been a fatigue failure or a brittle fracture. Poor detailing may have contributed to the failure. Weathering steel does corrode.

Forgot something: Could it be a geotechnical failure? On an episode of "Engineering Catastrophes" about a landslide in Pittsburgh someone mentioned the area has pockets of funky soils.

I'd like to the actual inspection reports, particularly from 2009 and 2011 when the bridge went from "Fair" to "Poor". Until PennDOT or the County releases this information, everything is just speculation.

RE: Pittsburgh bridge collapse

Quote (Maybe thermal stress from frozen bearing at one of the piers is the cause? According to AccuWeather the Friday's temperature was between 15F & 30F with wind chills of -15F. perhaps it was something else: There could have been a fatigue failure or a brittle fracture.)


I've been curious as to why it would have ultimately failed when so lightly loaded. (One bus and a handful of personal vehicles.)

Temperatures Wednesday night into Thursday morning were into the minus single digit range. Is it plausible to think that something could have fractured during that period, and not ultimately failed until a bus crossed it 24 or so hours later? The straw that broke the camel's back, so to speak.

Quote (the east side of the bridge appears to have ended up much further from its abutment than the west side.)


I think that's due to the fact that a good sized portion of the deck folded up into a vertical position. (The back of the bus is resting against it.) Had that eastern end of the deck landed flat on the ground beneath, that distance might look more similar to the other end.

Quote (It looks like the east bent is missing the lower cross bracing compared to the west end. It's a bit blurry from the google street view but its still clearly missing.)


Looks to me like it's the cross bracing on the west end that's missing. The gazebo, while hard to see, is discernable between the column and deck, at the left side.

RE: Pittsburgh bridge collapse


Quote (I've been curious as to why it would have ultimately failed when so lightly loaded. (One bus and a handful of personal vehicles.))


I was speculating about a thermal load, which can get pretty high even with a modest change of temperature.

RE: Pittsburgh bridge collapse

Quote (The Bridge Hunter website confirms that the bridge was constructed from weathering steel.)


There can be a problem with weathering steel, if the environment is aggressive... it can 'corrode' faster if the protective coating is removed. This is what happened to a local floodway with the S Beam guiderails.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

As add for weathering steel states

Quote (https://usbridge.com/what-is-weathering-steel/)

The Cons of Weathering
Although weathering steel may sound ideal, there are a few factors that should be considered before construction. Certain weather and climate conditions can lead to issues with durability and corrosive resistance.
If unpainted, weathering steel depends on a patina to provide corrosion protection. If the patina is compromised the resulting rust blisters will contain corrosion cells, defeating the steels corrosion resistance. Rust blisters appear to be present in some of the pictures above. Road salt is one of the potential drivers of weathering steel corrosion.
https://www.metalsupermarkets.com/what-is-weatheri...

Question - do the bridge inspections compare observed section loss to design section loss (corrosion allowance)?

RE: Pittsburgh bridge collapse

Quote (Question - do the bridge inspections compare observed section loss to design section loss (corrosion allowance)?)


Maybe, depending on the state. In NY, the DOT requires an additional 1/16" (min.) on the design thicknesses for weathering steel plates. Typically, in the biennial inspections in NY, primary members are supposed to be re-rated if section loss is observed.

Forgot something, on the news this morning, there was a story that the NTSB is supposed to release its initial findings in about two weeks. The final report will be issued in the next 12 to 18 months.

RE: Pittsburgh bridge collapse

2
Early morning failure under modest traffic indicates that thermal self-straining load was a contributing factor. It could be that bridge was probably trying to contract with frozen bearings, and the bus finished it off. Cold temperatures also may have increased fracture susceptibility in existing fatigue cracks.

That doesn't account for the column issues, though. Maybe the ineffective bracing meant the columns weren't doing much to begin with? If the inadequately-braced columns were shedding load to the girders, maybe the failure initiated in the girders, causing them to fracture and result in two cantilever spans that immediately collapsed.

Quote (digger242j)


My understanding of bridge weight limits is that vehicles over the limit will cause further deterioration--not immediate failure. You should be able to drive 26 ton vehicles over that bridge all day long without it falling down. Somebody please correct me if I'm wrong.

(Maybe I should phrase that differently--Vehicles *under* the limit will not hasten the deterioration. Obviously for any given bridge you could find something heavy enough to kill it.)

Theoretically. And they DID run 26-ton vehicles over this bridge all day long. As we've established, these buses with regular routes across the bridge were up to 20+ tons, and probably reached 26 tons when full. Random trucks in excess of 26 tons was probably a daily or weekly occurrence. I'm also going to go out on a limb and say the reasoning behind the actual posting was probably imprecise at best and objectively incorrect at worst, so I wouldn't be surprised if fatigue due to a too-high posting was an issue.

Quote (ACtrafficengr)

Structurally non-redundant ones should be candidates for closure

But what we really need to do is shrink the system, as the Iowa DOT commissioner says some years ago. If we can't generate the revenue to maintain our roads and bridges, maybe we need to get rid of some

This is the position I take. I see so much infrastructure, especially car infrastructure, that is obviously overbuilt compared to the number of cars on the road, even without taking "induced demand" into account. Glad to hear similar opinions from a traffic engineer. I like to take it a step further and say we also just need to dial back the number of cars on the road. We need more transit, more public thoroughfares where pedestrians and cyclists don't get turned into little pink clouds, and stricter driver licensing requirements.

Even as we speak, this new infrastructure bill is going to pour money into projects we don't need but that we'll never be able to tear down once they're built. My favorite is lock and dam upgrades on the eastern end of the Ohio River. As far as I can tell, the financial justification for these projects is mainly that the coal industry needs them (an assertion which I actually find dubious to begin with). Sometimes it takes the feds 20 years to finish lock projects. Who says the coal industry will even still be around in 2042?

And, yeah, we spend to much on the military, too.

EDIT: Oh, shoot, speaking of infrastructure being maintained indefinitely with a forgotten purpose, I just read an article about how flood control dams "need" melting winter snow to fill their reservoirs for boaters and fishermen in the summer. No! That's backwards! We need the dams to protect us from the melting winter snow. Maybe. A lot of those were built basically as make-work for unemployed people during the Great Depression, so some of their benefit-to-cost ratios could probably also stand to be re-examined.

RE: Pittsburgh bridge collapse

Thanks CAR...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Does it seem reasonable that perhaps the governing authority reviewed the bus weights and decided to post the bridge limit high enough to allow the buses without having to do a detailed analysis of the actual limits that should have been imposed? I can see a bean counter providing a cost/benefit analysis that would "...keep the buses running..."

RE: Pittsburgh bridge collapse

3
For a minute, I thought this was an engineering forum.
"... Without getting political, there's a real downside to Reaganomics."
"... The military industrial complex is a giant black hole."
"... we spend to much on the military, too." (sic)

Most of us recognize infrastructure requires public funds. And civil structures require maintenance. No argument here. But when approx 1/3 or less of many federal spending "infrastructure bills" goes to actual civil construction, I don't think blaming the military is rational.

Anyway, thanks to the others (engineers?) for the engineering discussion. Thermal strains and secondary loads routinely get ignored in most civil structures.

RE: Pittsburgh bridge collapse

Quote (For a minute, I thought this was an engineering forum.)


It is... and the comments do not detract from it... I recall a first year engineering class titled, "Engineering and Society."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Quote (Does it seem reasonable that perhaps the governing authority reviewed the bus weights and decided to post the bridge limit high enough to allow the buses without having to do a detailed analysis of the actual limits that should have been imposed?)


As Dirty Harry said "...are you feeling lucky...?" It's possible but it shouldn't be done. I'm sure PennDOT is similar to NYSDOT, which prohibits postings without calculations.

I don't believe the city just pulled a number out of their @$$. According to the bridge data posted by bradw1128, the design live load is H20 (for the uninitiated, that's a 40K vehicle with two axles spaced at 14', from axle is 8k; rear axle is 32k). The Inventory Rating is 17.2 Metric Tons (slightly less than the weight of an H20 truck, which does indicate some deterioration.) and the Operating Rating is 29.9 MT. The posted load of 26 T is less than the Operating load, which is SOP.

Again, for the uninitiated:
Inventory Rating Level - The inventory rating level generally corresponds to the customary
design level of stresses but reflects the existing bridge and material conditions with regard to
deterioration and loss of section. Load ratings based on the inventory level allow comparisons
with the capacity for new structures and, therefore, results in a live load which can safely utilize
an existing structure for an indefinite period of time.

Operating Rating Level - Load ratings based on the operating rating level generally describe the
maximum permissible live load to which the structure may be subjected. Allowing unlimited
numbers of vehicles to use the bridge at operating level may shorten the life of the bridge.


RE: Pittsburgh bridge collapse

There's no problem with invoking politics in this forum. Civil engineering and public policy are inseparable.
The problem lies with selective facts and selective outrage and the inference that if only (x) wasn't governor, or the cost of jet fighters, or whatever if right in front of you isn't the way you think it should be ... then the bridge would have been maintained, and these failures wouldn't be happening so often.
That thinking is plain silly.
There's probably two or three main culprits for this bridge failure, but 100+ reasons why there was lack of correct and appropriate funding to minimize the risk of collapse.

RE: Pittsburgh bridge collapse

My comment on spending wasn't specific to this bridge failure. More of a general observation of spending priorities on a macroeconomic level over the course of history. Obviously there are specific reasons for this particular bridge failing that have no direct link to the national budget. I just disagree with the premise that road infrastructure in-and-of-itself was a high priority in the past. I think the military wanted it so the military got it. I don't think that particular dynamic has changed much.

RE: Pittsburgh bridge collapse

There was no outrage... simply an observation.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse

Quote (There's probably two or three main culprits for this bridge failure, but 100+ reasons why there was lack of correct and appropriate funding to minimize the risk of collapse.)


Close to 30 years ago, I had to take over supervision of a street reconstruction project in NYC - a lot of problems political and technical. Before taking over, I had to go for an interview with the City's borough engineer. Initially, he was reluctant because my background was mainly bridge work. He said to me "...keep in mind, bridges don't have constituencies; nobody lives on a bridge; people live on streets."

No one cares about bridges until they can't use them. There's a limited pot of money; for decades politicians have been robbing Peter to pay Paul for programs that buy them votes. States rely heavily on Federal money. In the past, the Federal funding formula didn't cover maintenance. At least things are changing somewhat. FHWA does recognize the need for "preservation." IN NY for example, the number of preservation projects that have been let has increased noticeably. we're making progress.

Quote (I think the military wanted it so the military got it. I don't think that particular dynamic has changed much.)


Federal funding for transportation come from the gasoline tax. We're still robbing Peter to pay Paul on transportation funding through the gas tax. That money is also used for things like bikeways, greenways, trails, etc. These are worthy project - I enjoy biking - but they're not bridges. Nobody lives on a bridge

RE: Pittsburgh bridge collapse

The funding issues here may have more to do with local budgets. Pittsburgh population is about 1/2 of it's population in the steel hayday. The road network is still about the same or even larger.

Pittsburgh was reported in 2006 to have 446 bridges in its 55.38 sq mi, serving ~ 300,000 people.

RE: Pittsburgh bridge collapse

Ha...that's about 673 people per bridge. So just tax them when the bridge needs to be fixed: hello, citizen, if you don't pay your $3k share of the $2M repair and maintenance for this bridge in 2 weeks, your commute to work will quintuple when we close the bridge. Yikes.

RE: Pittsburgh bridge collapse

Some of the bridges are owned and maintained by "other owning entities": Railroads come to mind.



spsalso

RE: Pittsburgh bridge collapse

Quote (Ha...that's about 673 people per bridge. So just tax them when the bridge needs to be fixed: hello, citizen, if you don't pay your $3k share of the $2M repair and maintenance for this bridge in 2 weeks, your commute to work will quintuple when we close the bridge. Yikes.)


Corporations are people to (that's what I've been told), but they tend to get tax breaks to move into certain locals, individuals not so much.

RE: Pittsburgh bridge collapse

Quote:

Ha...that's about 673 people per bridge. So just tax them when the bridge needs to be fixed

That's essentially what happens under normal circumstances - local taxes cover infrastructure, failure to pay leads to failures which cost locals more later. Paying a federal employee to pay a state employee to pay a city employee to pay a contractor to fix this bridge makes no sense, yet that's how we shuffle money then wonder why it disappears. Its much like blaming the military for their budget after your local politicians created jobs by forcing the military to hire local-yokels at $100k+ to do the simplest support jobs that the military already did for $40k to a much higher standard.

RE: Pittsburgh bridge collapse

Quote (Cool Controls)



Corporations are people to (that's what I've been told), but they tend to get tax breaks to move into certain locals, individuals not so much.


My point was that bridges that are owned by railroads in Pittsburgh are not maintained at the expense of the City. If getting "...tax breaks to move into certain locals..." negates that statement, I would like to see the logic. Those bridges are repaired and maintained at the expense of the stockholders, not the City of Pittsburgh.

spsalso

RE: Pittsburgh bridge collapse

It's not always about you spsalso, I was responding to a prior post. No doubt privately owned bridges should be maintained by the parties to whom they belong.

RE: Pittsburgh bridge collapse

2
Well, govt finances are largely about robbing Peter and not paying Paul :)

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Pittsburgh bridge collapse

Cool Controls,

I reread your post and do now see what you are getting at: corporations in Pittsburgh are getting financial breaks from the city, and should not be.

I hope I've got that right.

I do hope the citizens and the government of the city will take heed. I would have thought the city government explored the profit/loss numbers before approving of these tax breaks, and decided that more income to the city would be generated than the breaks cost. Perhaps they were in error.



spsalso

RE: Pittsburgh bridge collapse

Quote (Well, govt finances are largely about robbing Peter and not paying Paul :))


lol

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

RE: Pittsburgh bridge collapse


Quote (It looks like Pennsylvania has a history of diverting bridge funds away from bridges.)


Nothing new. In PA, our gas tax is almost $0.59/gallon; 3rd highest in the US. When the legislature passed the infrastructure bill about 10 years ago, doubling the tax, the money was supposed to go into a lock box (shades of Al Gore?). Just like legalized gambling was supposed to lower the school tax.


Quote (bridges that are owned by railroads in Pittsburgh are not maintained at the expense of the City.)


I would venture to say that today railroads only maintain bridges carrying their tracks. In NYC, there are a fair amount of bridges - rail and vehicular - that were constructed by the railroads in the 19th & early part of the 20th Centuries. As the railroads starting going bankrupt after the war the ownership of the vehicular bridges was transferred to the city and state, mostly in the 50's/60's. Even in the 80's to get plans for these bridges we had to go to the railroad for them. A bit of history.

RE: Pittsburgh bridge collapse

I doubt there were many railroads that included vehicular pathways on their railroad bridges. Safety comes to mind. Plus: why would they do that?

Not saying it didn't happen, but I see it as quite rare.

However.

Transit rail is another thing. I do not view that as "railroad". For example, they are generally not common carrier. There was, for example, transit rail on the San Francisco Bay Bridge. I do wonder what, if anything, that carrier paid the "authority" for usage.

By now, most/all transit rail has been rolled into government ownership/support. So they wouldn't appear to be sources of more funding for bridge maintenance.

However.

In this case, we're talking about Pittsburgh, and its 400+ bridges. Separating transit rail from common-carrier rail, I wonder which bridges handling the latter do also support vehicular traffic.


spsalso

RE: Pittsburgh bridge collapse

PA also has their famous turnpike. About ten years ago my wife wandered onto the NE extension on a trip from DC to NY. I remember marveling from the passenger seat at the nice new road and a sign that must've been 10' tall bragging about ~$100M in construction, we thought PA was pretty ok until she had to pay $70 in tolls for her commuter car.

RE: Pittsburgh bridge collapse

Quote (I doubt there were many railroads that included vehicular pathways on their railroad bridges. Safety comes to mind. Plus: why would they do that?)


Let me clarify: I wasn't talking about a bridge with tracks and vehicles side by side on the same structure. If a grade separation was required, the railroad was responsible for the bridge.

Quote ($70 in tolls)


That's two round trips on the extension, without the EZ-Pass discount.

RE: Pittsburgh bridge collapse

Quote (bridgebuster)



Let me clarify: I wasn't talking about a bridge with tracks and vehicles side by side on the same structure. If a grade separation was required, the railroad was responsible for the bridge


Oh. If there was an existing railroad, and there was to be constructed a road with a grade separation over the railroad, the railroad was responsible for the bridge?

I would have thought whoever arrived at the location second pays for the crossing. And that if one party wanted an improvement in that crossing (changing an at-grade crossing to a separation), that party would pay for it.

spsalso

RE: Pittsburgh bridge collapse

Perhaps, but the railroad operators receives benefits as well, if nothing else than not having to maintain a grade crossing including gates and lights to say nothing of the infrastructure along the tracks required because of the crossing. And then there's the fact that the trains no longer have to slow down nor sound their horn (to the discomfort of the nearby residents) as they approach and pass the grade-level crossing. In our city, they've constructed three underpasses, replacing all but one grade-level crossing, on the mainline track (a double track shared by Amtrak, Metrolink and the freight operators).

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Pittsburgh bridge collapse

Here is an interesting discussion of funding for Riverside County grade separations:

Link

A quick read shows little railroad money included. The various physical structures (bridges, piers, abutments) involved would appear to be government owned and maintained.


spsalso

RE: Pittsburgh bridge collapse

Quote (Optical98)

It's amazing timing that 3 days ago Biden planned this visit to Pittsburgh today.

I am amazed that none of the very smart engineers around here have not made that cause and effect linkage yet.

(That collapsed section is in a deeper state than previously you could even say.)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Pittsburgh bridge collapse

yeah...and if you squint really hard, turn your monitor upside down, and then look out of the window 6 times, the bridge even forms the shape of a Q on the ground...

RE: Pittsburgh bridge collapse

Thanks!

Bridges look much bigger when they're on the ground.


spsalso

RE: Pittsburgh bridge collapse

NTSB release.

Link

This space intentionally left blank.

RE: Pittsburgh bridge collapse

Quote (Nukeman948)

NTSB release.

Link

Time for the news agencies to start incorrectly defining "fracture critical" to the public.

RE: Pittsburgh bridge collapse

Design is moving along; construction to begin in April. There was an article in Roads and Bridges today.

Link

RE: Pittsburgh bridge collapse

If I may summarise, as the bus is approaching the east end of the bridge (just prior to the east ends imminant collapse), the west end has already collapsed (behind the bus).

RE: Pittsburgh bridge collapse

Lawsuits ... make it official that this incident did indeed happen in the USA.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

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