This is not a column predicting that the two cable-stayed bridges jointly called the Margaret McDermott Bridge over the Trinity River near downtown Dallas are going to collapse like the catastrophic bridge failure in Genoa, Italy, Tuesday. But it is a column noting disturbing parallels.
First is bridge design. A prominent civil engineer in Italy has been warning for two years that the Morandi Bridge, whose collapse Tuesday killed 39 people including three children, suffered from a fatally flawed design and would be better demolished and replaced than repaired.
This week in a briefing to a committee of the Dallas City Council, the city official who oversaw construction of the McDermott bridges said the city is considering suing the famous Spanish bridge designer, Santiago Calatrava, over defects in the McDermotts.
Sarah Standifer, the soon to be demoted director of the soon to be abolished Department of Trinity Watershed Management, singled out Calatrava as a litigation target while telling council members that the twin bridges completed a year ago may not be safe enough to open for another year and a half.
In the same briefing, Standifer, who is not an engineer, conveyed what she obviously intended to be a reassuring statement about whether or not the McDermotts are subject to collapse: “As Staff understands it,” she said in a memo, “the bridge is not anticipated to fall down or become unstable in the event that a cable breaks.”
I’m sorry. But look at Italy. Look at any bridge. Bridges are like airplanes. They carry people high up in the air.
Let me ask you something. Would you board a plane if the person at the check-in counter got on the public address system and said, “As staff understands it, the plane is not anticipated to fall down or become unstable in the event that something breaks”?
You would ask, “What staff? What something? Why are you telling us this? I want my luggage back.”
The stubborn reluctance of city staff to get right about this bridge, to come clean, to put it all out on the table right now is extremely unsettling.
I blame the council. They should hold investigative hearings. I am not saying there is any direct mechanical or engineering parallel between the bridge in Genoa and our bridges, but I am saying that the catastrophic loss of life in Genoa should awaken us to the gravity of the matter here.
By the way, after even more extensive examination, the problems with the McDermott bridges still seem rooted in decisions that were made by or under Standifer, the non-engineer, when she was trying to please the City Council by cutting costs. In particular, the problem still seems centered on the method by which steel cables are attached to the bridge deck, done with cheaper parts than Calatrava called for and without the stress testing he begged the city to perform.
Singling out Calatrava for implied blame while we still don’t appear to know what’s wrong seems political and sleazy rather than scientific or responsible, unless Standifer knows something she isn’t sharing publicly. If she does, that’s the kind of thing I’d like to know before anybody walks out there with their kids.
There are certain parallels between the Genoa bridge and the McDermott twins, but here we have to go very carefully, because those parallels may or may not have any bearing on our problems here. In both cases, the engineering problems have to do with stresses where steel cables meet concrete and what happens when one material moves differently from the other in high winds. In both cases, those issues seem to show up first as high maintenance costs.
In Italy, experts had been saying since 2016 that the government should consider demolishing and replacing the Morandi Bridge rather than patching it. In particular, one professor of civil engineering said both the method of construction and later patchwork maintenance had caused the Morandi Bridge to be “uneven” and “semi-horizontal.”
I have no idea what that means. I was an English and political science major. But I can tell you this. If I came to a bridge suddenly and there was a sign that said, “Warning, Bridge Semi-Horizontal,” I would put it in reverse and hope there were no school buses behind me. Likewise back at the ticket counter: “Warning, Plane Semi-Horizontal.” Not with me.
Three children died when 40 cars fell from the Morandi on Tuesday. We trust public infrastructure with our lives and with the lives most precious to us.
The McDermotts are designed to carry bicycle and foot traffic. These are massive steel arches intended to carry an egg-shell cargo of human souls through the sky. The safety of those bridges needs to be based on something a lot more than “as staff understands … .”
As Stephen Young has reported here already, Standifer made the following very unsettling concessions in her Monday briefing to the council:
“The Engineer of Record provided the City and TxDOT with drawings for two design alternatives in late July that may resolve the vibration and fatigue issues associated with the cable anchorage system.”
Key words: MAY resolve. Not will. May.
“The cable anchorage system has failed to perform as originally designed and intended for long-term maintenance.”
That is exactly what is being blamed in Genoa.
“The remedies to date including additional dampers have failed to address the vibrations.”
The fix they said a year ago would work, the dampers, didn’t work.
“Prior vibrations have subjected some of the elements to premature fatigue.”
Make that cracking.
“Because the anchor rods have been exposed to potential fatigue damage that is not quantifiable, it is not possible to assess if / when a particular cable anchor rod may fail.”
“In its currently constructed bridge configuration including the cable dampers, it is estimated the probability of failure for EB-C-E2-S (recent instrumented cable) is approximately 23 percent over the 40-year design service life.”
Slightly higher than one in five.
“Fracture of an anchor rod would be classified as a ‘brittle failure’ which means there in no appreciable plastic deformation prior to fracture. These types of failures typically occur without any prior evidence of a potential break, thus they are characterized by rapid crack propagation without significant plastic deformation.”
If you like this story, consider signing up for our email newsletters.
SHOW ME HOW
You have successfully signed up for your selected newsletter(s) - please keep an eye on your mailbox, we're movin' in!
No way to see it coming.
“As Staff understands it, there is a potential for the anchor rod that holds the cable to the bridge to break. If that happens, the loose cable could swing into the pedestrian path.”
As staff understands it, that would be really bad.
It would be a gesture of honor and respect to the dead in Italy for us to demand a complete and painstaking airing of all these issues with our own cable-stayed bridges. We would be fools not to demand it.