With the photos and other details stated in previous messages, it appears that the failure was due to one of three possible modes:

1) One or more bar joist rafters buckled near the middle, and pulled the lower ends out of the masonry wall as a consequence of the buckling.

2) The masonry wall supporting the lower ends of the rafters failed in compression, allowing rafter ends to drop to the floor.

3) The loading of the rafters caused them to sag, thus causing them to assume a tensile loading lengthwise, and as this loading built up, it finally, and suddenly, plucked the lower ends of the rafters out of the masonry wall, allowing them to drop to the floor.

In the photos, there are buckled rafters with their lower ends pulled out of the masonry wall. While this precise effect would be the consequence of mode 1, it would also be the likely consequence of modes 2 and 3, as well, and yet, the three modes are entirely different. With mode 1, the buckled rafters would be the cause of the failure. With modes 2 and 3, the loss of support of the wall would be the cause, while buckled rafters would be part of the effect, occurring when the rafter ends hit the floor, after they were released from the support of the wall.

With the amount of engineering that must have gone into that structure, I cannot imagine that they would have anticipated a roof collapse with a few feet of snow. That would be an expected working load, and with a prudent safety factor, the actual collapse might not occur until the depth reaches several times more. So it seems improbable that the rafters would have buckled under the snow load as indicated by mode 1.

Equally improbable, for the same reasons, is mode 2. The greatest strength of the masonry wall is its compressive resistance to a vertical load, so a failure from such a load, in this case, would be unlikely. Of the three modes, number 3 is the most curious, most complex, least obvious, and I believe, the most probable. While mode 2 seems unlikely to be the direct cause, it is possible that it is combined with mode 3. If it is mode 3 that occurred, it raises some interesting questions about the design of that building.

The lower ends of the rafters are apparently solidly fixed to the masonry wall. I understand that the upper ends are hung on a steel ring that is the diameter of the upper section. If both ends of the rafters are fixed, it raises a question as to how the linear expansion and contraction from temperature variation could be accommodated. Perhaps there was little temperature variation when the building was originally in operation. Also, if the rafter ends are fixed, any tendency to sag will create a tensile load, lengthwise in the rafter, as the sagging tends to pull the ends points closer together.

With the iron hangers holding the upper end, and the lower end being held by the Hoover Dam-like structural advantage lent by the curvature of the masonry wall, the rafter might be prevented from sagging beyond a certain point simply because its end points are fixed. At this point, the rafter begins acting more like a rope bridge than a rigid beam. From this point, as the snow load increases, no further sagging is possible because the end points of the rafter are prevented from moving toward each other. However, the tensile pull on those end point anchors will increase dramatically due to the leverage advantage of the sagging condition. Add to this, the maximum thermal contraction of a winterÂ’s night. The weakest link in this contest is the anchoring of the lower rafter ends in the masonry wall. The wall itself will not tip because of its curved shape, but the pull of the rafters can locally fracture the masonry, allowing the lower ends to be released.

So when the tensile load reaches a certain point, its pull will break the attachment between the lower end of the rafter and the wall, fracturing the brickwork all around the rafter end, including the brickwork supporting the end. Adding to this fracture is the release of the stored energy in the tensile load of the rafter that has accumulated since the sagging was arrested by the anchored endpoints. This tensile release would literally cause the masonry work to explode out from around the lower ends of each rafter, instantly liberating the ends, leaving them in mid air, with many feet to fall.

Since the upper ends of the rafters are firmly anchored by the iron hangers, the bottom ends will not drop straight down, but rather, will drop at an inward angle about equal to the roof pitch. The lower end will actually travel in an arc with its center at the upper end. This will allow the bottom of the roof to abruptly fall without getting hung up on the wall. The angle of fall will also provide more free fall distance than a vertical fall. Because the roof is a cone shape, the dropping of the outer edge must also lead to compressive buckling in a circumferential direction. This force will quickly dislodge and break up the girts and sheathing.

If mode 3 is what occurred, it could have been avoided if the lower ends of the rafters were mounted in a manner that gave them vertical support, but allowed them to slide lengthwise. Then the rafter sagging could develop to its maximum, without developing any tensile load which might lead to premature failure by pulling the chunk out of the wall that supports the end of the rafter. Either end of the rafter being allowed to slide would be a remedy, but the lower end might be the more advantageous of the two. Any sagging will not move the bottom end very far, certainly not far enough to pull it off of its vertical support. But it will avoid the rafter assuming a tensile load, thus creating the localized stress in the anchor and support of the masonry. This juncture of the rafters with the masonry wall needs to be looked at very carefully.

Granted, this is all speculative, and I am sure that a thorough, professional investigation will ensue. I just wanted to throw this out prior to any investigation to make sure that mode 3 is not overlooked. Seemingly the most fundamental and apparent cause of this roof failure would be the buckling of one or more rafters (mode 1), and that might appear to be the obvious explanation since there are buckled rafters in the wreckage. If this happened to be the conclusion of an investigation, and I threw out some other possibility afterward, it might be overruled by the shear weight of a different conclusion, already officially arrived at.

Ron Keagle



KEAGLEDESIGN@VISI.COM

If the aerial shots are any indication you can see that there was definitely more snow on the roof of the remaining cupola towards the side that collapsed. I could not see from the photos if the roof was built to retain snow (snow eagles or built in gutter) or built to shed it. You always have to take into account the aging of the "iron" fittings (if they are really cast iron). This stuff has very little give and tends to fail as a brittle fracture. The internal microstructure of cast iron (unless treated) consists of three dimensional snowflakes of pure carbon surrounded by iron and air and slag impurities. Over the years constant flexing causes the carbon structure to fracture causing microcracks that gradually propagate reducing the strength of the casting. In compression, untreated cast iron almost never fails but in tension is a very brittle material subject to sudden failure.

lamontdc@adelphia.net

A gentle reminder to ponder if you must but not too ponderously - it is a fragile structure.

dave

> A gentle reminder to ponder if you must but
> not too ponderously - it is a fragile
> structure.

> dave

I go with Dave's opinion. I'm no engineer, having dropped math just as quickly as the law would allow, so I just sit and listen to the experts. But the present more-or-less informed speculation seems to center on some single roof truss shearing away from its upper connection -- that is, the point where it was fastened to the ring supporting the two cupolas. This single failure probably then caused a domino effect by stressing each neighboring connection. Further, the thinking seems to be that although the roof has borne similar loads in the past (remember that it collapsed some time before the record snowfall had accumulated), it was "just plain weary", from,perhaps, a combination of age and possibly lack of maintenance in a location that it difficult to reach.

But all this is just a collection of "perhapses" and "possiblys."

herbhar@yahoo.com

> With the amount of engineering that must
> have gone into that structure, I cannot
> imagine that they would have anticipated a
> roof collapse with a few feet of snow. That
> would be an expected working load, and with
> a prudent safety factor, the actual collapse
> might not occur until the depth reaches
> several times more. So it seems improbable
> that the rafters would have buckled under
> the snow load as indicated by mode 1.

I might point out that this was not the only roof in the area to collapse in this storm. Several other more modern, presumably well engineered commercial roofs were lost as well.

> Several other more modern, presumably well
> engineered commercial roofs were lost as
> well.

No kidding. I feel like this storm has been preferentially hunting my childhood memories. The Toys R Us in Maryland whose roof also came down supplied nearly everything I owned between 2 and 8 years of age...


eledbetter@rypn.org

The Toys R Us roof collapse was 6 days later during a major rain storm.

> No kidding. I feel like this storm has been
> preferentially hunting my childhood
> memories. The Toys R Us in Maryland whose
> roof also came down supplied nearly
> everything I owned between 2 and 8 years of
> age...


dcockey@tir.com

Greetings All! I am a professional, diagnostic roof consultant, early retired from Baltimore and loving life in the tropics.

A few of my friends told me about the roof collapse. If some of you can point me to some photos of the collapse I will be more than willing to render my two cents worth opinion.

A beautiful old building that I enjoyed to visit on many occasions.

Regards,

Dale Banks
Roof Consultant

crcroof@coqui.net

No P.E. here either, but I do have one handy in the room.
Two quick thoughts - one, is that unlike the Columbia, we have plenty of forensics to look at here, including destructive material analysis and calculated load. But, unlike steel, nobody can accurately forecast load/stresspoints on old wrought iron. Which is why iron bridges are so rare, by the way. But of more interest is the half of the roof that DIDN'T collapse, giving some credence to dead load as opposed to pure thermal stress contraction. I'm also marvelling at the wonderful stuff that didn't get crushed under the half that stood. I'm as curious about what kept the other half up, and if it dare be left there, no matter how historic the fabric. So the solution can't be just to repair the half that fell.

> With the photos and other details stated in
> previous messages, it appears that the
> failure was due to one of three possible
> modes:

> 1) One or more bar joist rafters buckled
> near the middle, and pulled the lower ends
> out of the masonry wall as a consequence of
> the buckling.

> 2) The masonry wall supporting the lower
> ends of the rafters failed in compression,
> allowing rafter ends to drop to the floor.

> 3) The loading of the rafters caused them to
> sag, thus causing them to assume a tensile
> loading lengthwise, and as this loading
> built up, it finally, and suddenly, plucked
> the lower ends of the rafters out of the
> masonry wall, allowing them to drop to the
> floor.

> In the photos, there are buckled rafters
> with their lower ends pulled out of the
> masonry wall. While this precise effect
> would be the consequence of mode 1, it would
> also be the likely consequence of modes 2
> and 3, as well, and yet, the three modes are
> entirely different. With mode 1, the buckled
> rafters would be the cause of the failure.
> With modes 2 and 3, the loss of support of
> the wall would be the cause, while buckled
> rafters would be part of the effect,
> occurring when the rafter ends hit the
> floor, after they were released from the
> support of the wall.

> With the amount of engineering that must
> have gone into that structure, I cannot
> imagine that they would have anticipated a
> roof collapse with a few feet of snow. That
> would be an expected working load, and with
> a prudent safety factor, the actual collapse
> might not occur until the depth reaches
> several times more. So it seems improbable
> that the rafters would have buckled under
> the snow load as indicated by mode 1.

> Equally improbable, for the same reasons, is
> mode 2. The greatest strength of the masonry
> wall is its compressive resistance to a
> vertical load, so a failure from such a
> load, in this case, would be unlikely. Of
> the three modes, number 3 is the most
> curious, most complex, least obvious, and I
> believe, the most probable. While mode 2
> seems unlikely to be the direct cause, it is
> possible that it is combined with mode 3. If
> it is mode 3 that occurred, it raises some
> interesting questions about the design of
> that building.

> The lower ends of the rafters are apparently
> solidly fixed to the masonry wall. I
> understand that the upper ends are hung on a
> steel ring that is the diameter of the upper
> section. If both ends of the rafters are
> fixed, it raises a question as to how the
> linear expansion and contraction from
> temperature variation could be accommodated.
> Perhaps there was little temperature
> variation when the building was originally
> in operation. Also, if the rafter ends are
> fixed, any tendency to sag will create a
> tensile load, lengthwise in the rafter, as
> the sagging tends to pull the ends points
> closer together.

> With the iron hangers holding the upper end,
> and the lower end being held by the Hoover
> Dam-like structural advantage lent by the
> curvature of the masonry wall, the rafter
> might be prevented from sagging beyond a
> certain point simply because its end points
> are fixed. At this point, the rafter begins
> acting more like a rope bridge than a rigid
> beam. From this point, as the snow load
> increases, no further sagging is possible
> because the end points of the rafter are
> prevented from moving toward each other.
> However, the tensile pull on those end point
> anchors will increase dramatically due to
> the leverage advantage of the sagging
> condition. Add to this, the maximum thermal
> contraction of a winterÂ’s night. The weakest
> link in this contest is the anchoring of the
> lower rafter ends in the masonry wall. The
> wall itself will not tip because of its
> curved shape, but the pull of the rafters
> can locally fracture the masonry, allowing
> the lower ends to be released.

> So when the tensile load reaches a certain
> point, its pull will break the attachment
> between the lower end of the rafter and the
> wall, fracturing the brickwork all around
> the rafter end, including the brickwork
> supporting the end. Adding to this fracture
> is the release of the stored energy in the
> tensile load of the rafter that has
> accumulated since the sagging was arrested
> by the anchored endpoints. This tensile
> release would literally cause the masonry
> work to explode out from around the lower
> ends of each rafter, instantly liberating
> the ends, leaving them in mid air, with many
> feet to fall.

> Since the upper ends of the rafters are
> firmly anchored by the iron hangers, the
> bottom ends will not drop straight down, but
> rather, will drop at an inward angle about
> equal to the roof pitch. The lower end will
> actually travel in an arc with its center at
> the upper end. This will allow the bottom of
> the roof to abruptly fall without getting
> hung up on the wall. The angle of fall will
> also provide more free fall distance than a
> vertical fall. Because the roof is a cone
> shape, the dropping of the outer edge must
> also lead to compressive buckling in a
> circumferential direction. This force will
> quickly dislodge and break up the girts and
> sheathing.

> If mode 3 is what occurred, it could have
> been avoided if the lower ends of the
> rafters were mounted in a manner that gave
> them vertical support, but allowed them to
> slide lengthwise. Then the rafter sagging
> could develop to its maximum, without
> developing any tensile load which might lead
> to premature failure by pulling the chunk
> out of the wall that supports the end of the
> rafter. Either end of the rafter being
> allowed to slide would be a remedy, but the
> lower end might be the more advantageous of
> the two. Any sagging will not move the
> bottom end very far, certainly not far
> enough to pull it off of its vertical
> support. But it will avoid the rafter
> assuming a tensile load, thus creating the
> localized stress in the anchor and support
> of the masonry. This juncture of the rafters
> with the masonry wall needs to be looked at
> very carefully.

> Granted, this is all speculative, and I am
> sure that a thorough, professional
> investigation will ensue. I just wanted to
> throw this out prior to any investigation to
> make sure that mode 3 is not overlooked.
> Seemingly the most fundamental and apparent
> cause of this roof failure would be the
> buckling of one or more rafters (mode 1),
> and that might appear to be the obvious
> explanation since there are buckled rafters
> in the wreckage. If this happened to be the
> conclusion of an investigation, and I threw
> out some other possibility afterward, it
> might be overruled by the shear weight of a
> different conclusion, already officially
> arrived at.

> Ron Keagle


randy.gustafson@westpa.net

The neighbors of the Museum insist that what happened was that snow buildup slipped off the top cupola roof, and that sudden addition of extra weight caused the collapses (two different instances, remember). I have yet to find an actual WITNESS who will testify that s/he SAW it happen or heard it, but it's pretty much accepted as gospel around the Museum neighborhood.

lner4472@bcpl.net

There is also the possibility that the roof was not "engineered" as we now consider it. It may have been constructed to "common practice" and while it held snow for a century the weakness of design and age of the components caught up with it. How it failed and why will be important questions when it comes to rebuilding it but the better question for the rest of us is what shape are the rest of our historic structures really in?

pfdx@aol.com

I am wondering if anyone was inside the building immediately prior to the collapse. Roofs do not silently collapse into the building beneath. They complain loudly before they fail. They moan, creak, screech, snap, crackle and pop prior to giving into the force of gravity.

That is usually the case unless:
> "The neighbors of the Museum insist that what
> happened was that snow buildup slipped off
> the top cupola roof, and that sudden
> addition of extra weight caused the
> collapses"

There would be little to no warning noises with this mode of failure. Similar to the WTC sudden collapse. Tremendous new live load due to gravitational forces.

82* and sunny today here in the islands. Whatcha got up north?

je,je,je!

DB

crcroof@coqui.net

Hi Paul - I was also thinking about the combination of crystalization, temperature, fatigue and such as it relates to ancient wrought and cast iron components. Randy is right (as usual) - whatever else, the entire roof structure will probably have to be rebuilt in stress relieved modern steel.

Has anybody brought Matt Austin in for a forensic analysis?

Dave

The half of the roof that collapsed was mostly the southern side. The snow fell during light to moderate NE winds. That wind direction would cause the snow to settle more on the southern half of the roof than the northern. Unusual also was that the wind was not as gusty as typical during most snowstorms of this magnitude. As a result, the snow tended to accumulate rather than blow off.

The weight of snow is roughly 5 pounds / cubic foot. I did some quick estimates and came up with a snow load on the order of 50,000 pounds on that part of the roof. Due to the unusual nature of the storm, the roof may never have experienced that great a load before.

> No P.E. here either, but I do have one handy
> in the room.
> Two quick thoughts - one, is that unlike the
> Columbia, we have plenty of forensics to
> look at here, including destructive material
> analysis and calculated load. But, unlike
> steel, nobody can accurately forecast
> load/stresspoints on old wrought iron. Which
> is why iron bridges are so rare, by the way.
> But of more interest is the half of the roof
> that DIDN'T collapse, giving some credence
> to dead load as opposed to pure thermal
> stress contraction. I'm also marvelling at
> the wonderful stuff that didn't get crushed
> under the half that stood. I'm as curious
> about what kept the other half up, and if it
> dare be left there, no matter how historic
> the fabric. So the solution can't be just to
> repair the half that fell.


B&O Maryland Photo Tour
intersys@insystem.com

I have been resisting this so far, but in honor of West Virginia Pulp and Paper #1 (on the first track South in the roof collapse) and for your humble perusal; (Yes, I know he was actually writing about a horse buggy)

The Wonderful "One Hoss-Shay"
by Oliver Wendell Holmes(1809-1894)

Have you heard of the wonderful one-hoss shay,
That was built in such a logical way
It ran a hundred years to a day,
And then, of a sudden, it -- ah, but stay,
I'll tell you what happened without delay,
Scaring the parson into fits,
Frightening people out of their wits, --
Have you ever heard of that, I say?

Seventeen hundred and fifty-five.
Georgius Secundus was then alive, --

Snuffy old drone from the German hive.
That was the year when Lisbon-town
Saw the earth open and gulp her down,
And Braddock's army was done so brown,
Left without a scalp to its crown.
It was on the terrible Earthquake-day
That the Deacon finished the one-hoss shay.

Now in building of chaises, I tell you what,
There is always somewhere a weakest spot, --
In hub, tire, felloe, in spring or thill,
In panel, or crossbar, or floor, or sill,
In screw, bolt, thoroughbrace, -- lurking still,
Find it somewhere you must and will, --
Above or below, or within or without, --
And that's the reason, beyond a doubt,
A chaise breaks down, but doesn't wear out.

But the Deacon swore (as Deacons do,
With an "I dew vum," or an "I tell yeou")
He would build one shay to beat the taown
'N' the keounty 'n' all the kentry raoun';
It should be so built that it could n' break daown:
"Fur," said the Deacon, "'t 's mighty plain
Thut the weakes' place mus' stan' the strain;
'N' the way t' fix it, uz I maintain,
Is only jest
T' make that place uz strong uz the rest."

So the Deacon inquired of the village folk
Where he could find the strongest oak,
That couldn't be split nor bent nor broke, --
That was for spokes and floor and sills;
He sent for lancewood to make the thills;
The crossbars were ash, from the straightest trees,
The panels of white-wood, that cuts like cheese,
But lasts like iron for things like these;
The hubs of logs from the "Settler's ellum," --
Last of its timber, -- they couldn't sell 'em,
Never an axe had seen their chips,
And the wedges flew from between their lips,
Their blunt ends frizzled like celery-tips;
Step and prop-iron, bolt and screw,
Spring, tire, axle, and linchpin too,
Steel of the finest, bright and blue;
Thoroughbrace bison-skin, thick and wide;
Boot, top, dasher, from tough old hide
Found in the pit when the tanner died.
That was the way he "put her through."
"There!" said the Deacon, "naow she'll dew!"

Do! I tell you, I rather guess
She was a wonder, and nothing less!
Colts grew horses, beards turned gray,
Deacon and deaconess dropped away,
Children and grandchildren -- where were they?
But there stood the stout old one-hoss shay
As fresh as on Lisbon-earthquake-day!

EIGHTEEN HUNDRED; -- it came and found
The Deacon's masterpiece strong and sound.
Eighteen hundred increased by ten; --
"Hahnsum kerridge" they called it then.
Eighteen hundred and twenty came; --
Running as usual; much the same.
Thirty and forty at last arrive,
And then come fifty, and FIFTY-FIVE.

Little of all we value here
Wakes on the morn of its hundreth year
Without both feeling and looking queer.
In fact, there's nothing that keeps its youth,
So far as I know, but a tree and truth.
(This is a moral that runs at large;
Take it. -- You're welcome. -- No extra charge.)

FIRST OF NOVEMBER, -- the Earthquake-day, --
There are traces of age in the one-hoss shay,
A general flavor of mild decay,
But nothing local, as one may say.
There couldn't be, -- for the Deacon's art
Had made it so like in every part
That there wasn't a chance for one to start.
For the wheels were just as strong as the thills,
And the floor was just as strong as the sills,
And the panels just as strong as the floor,
And the whipple-tree neither less nor more,
And the back crossbar as strong as the fore,
And spring and axle and hub encore.
And yet, as a whole, it is past a doubt
In another hour it will be worn out!

First of November, 'Fifty-five!
This morning the parson takes a drive.
Now, small boys, get out of the way!
Here comes the wonderful one-horse shay,
Drawn by a rat-tailed, ewe-necked bay.
"Huddup!" said the parson. -- Off went they.
The parson was working his Sunday's text, --
Had got to fifthly, and stopped perplexed
At what the -- Moses -- was coming next.
All at once the horse stood still,
Close by the meet'n'-house on the hill.
First a shiver, and then a thrill,
Then something decidedly like a spill, --
And the parson was sitting upon a rock,
At half past nine by the meet'n-house clock, --
Just the hour of the Earthquake shock!
What do you think the parson found,
When he got up and stared around?
The poor old chaise in a heap or mound,
As if it had been to the mill and ground!
You see, of course, if you're not a dunce,
How it went to pieces all at once, --
All at once, and nothing first, --
Just as bubbles do when they burst.

End of the wonderful one-hoss shay.
Logic is logic. That's all I say.



SZuidervee@aol.com