As the U.S. government shutdown drags on, President Trump has said that he’s willing to compromise with Congressional Democrats by building a steel wall instead of a concrete one along the country’s southern border.
In a recent interview with NBC, acting chief of staff Mick Mulvaney said, “If he has to give up a concrete wall, replace it with a steel fence in order to do that so that Democrats can say, ‘See? He’s not building a wall anymore,’ that should help us move in the right direction.”
But whether or not the Democrats would be more likely to agree on funding a steel wall, it’s unlikely that such a wall would be very useful for its stated function. To understand why, we need to know something about the prototype-testing process, the building properties of steel, and the recent increase in material costs.
See-Through, Saw-Through
According to the Department of Homeland Security (DHS), the plan is to build a “steel bollard-style wall” that’s made of hollow, vertical steel beams filled with concrete and rebar. The proposed wall sounds similar to the bollard fences that already populate parts of the border, with gaps between the bollards to allow for visibility through the border.
"The steel bollard construction is based on the operational requirements of the United States Border Patrol and is a design that has been honed over more than a decade of use,” DHS spokesperson Katie Waldman said in a recent statement.
While the new barrier design might be easier to see through, there’s one slight problem with it: the border wall prototype tests showed that steel bollards are relatively easy to cut through with a common circular saw.
In 2017, the DHS tested eight possible wall prototypes along the U.S.-Mexico border in San Diego, four made of concrete and four made of “other materials” (including two made of bollard-style metal columns). The department asked the U.S. military to try to scale the wall, as well as to breach it with common hardware tools. While a report wasn’t released to the public at the time, a heavily redacted version was released under a Freedom of Information Act to public broadcasting station KPBS in September 2018.
Despite the redactions, a careful reader can figure out that all of the prototypes were vulnerable to at least one breaching technique. In the section on breaching, the report says, “The (redacted) breaching technique was rescheduled to be last breaching technique on each mock-up, since the technique had the potential to impact the structural integrity of the entire mock-up.” Earlier in the section, it’s mentioned that the breaching technique compromised the “structural integrity” of the wall prototype it was used on.
“It wasn’t intended on their part, but when they ran this test, they must have realized it was causing some kind of major damage to the mock-ups,” Robert K. Dowell, associate professor of structural engineering, told KPBS. “And they put it at the end because of that. They thought it was going to collapse.”
It’s difficult to see what impact the tests might have had on the walls in the initial report, as almost all of the photos are redacted. Even though 13 of the redacted photos are labeled as “breached,” there’s no way of knowing to what extent those prototypes were actually breached. But one redacted photo recently leaked to NBC News gives us more information about how the bollard wall prototypes performed under stress.
The photo showed a steel bollard-style wall with four of its slats sawed through, leaving a substantial hole. While it is not clear from the picture what this wall was breached with, it’s possible to make some educated guesses.
It’s difficult to saw through steel with just a hand-powered hacksaw, but using electric tools and special blades would make the job far easier.
To saw through steel, you can use a circular saw, a reciprocating saw, or an angle grinder. A circular saw uses a circular blade that spins around an arbour (think of it as an “axel” for tools) to generate the circular force to cut. A reciprocating saw is a two-handed saw with a straight blade that uses a back and forth motion (otherwise known as “reciprocation”) to cut. An angle grinder uses an abrasive disc, essentially “sanding” its way through material. To cut through steel, these saws are equipped with a blade made from diamond or tungsten carbide, a tungsten-carbon compound with a 9 rating on the Mohs hardness scale.
All of these saws, and the steel-cutting blades, can be purchased legally at any hardware store.
Speaking to KPBS last fall, Customs and Border Patrol (CBP) spokesman Ralph DeSio said that the wall prototypes “were not and cannot be designed to be indestructible,” and that they’re meant to “impede or deny efforts to scale, breach, or dig under such a barrier, giving agents time to respond.”
But unfortunately for anyone interested in knowing about the border wall’s response to scaling or digging, the redacted report doesn’t provide information on either factor. The entire section on the wall prototypes’ resistance to scaling is redacted, making it difficult to know whether or not the walls provide protection against climbers. And judging from the report, it doesn’t appear that CBP performed any tests to determine whether it’s possible to dig under the prototype, or whether digging might destabilize the border wall.
“While the design currently being constructed was informed by what we learned in the prototypes, it does not replicate those designs," DHS spokesperson Katie Waldman said, in a statement to NBC. "The steel bollard design is internally reinforced with materials that require time and multiple industrial tools to breach, thereby providing U.S. Border Patrol agents additional response time to affect a successful law enforcement resolution.”
The core material of the new steel wall is unknown—for obvious security reasons—and may indeed make it harder for people to breach the wall. But the wall will have more difficult opponents than a few people with power tools: the forces of wind, water and weather.
Steel vs. Concrete
Steel and concrete are the complementary opposites of building: while concrete is highly resistant to compression (“pushing”) forces, steel is highly resistant to tension (“pulling”) forces. After the president’s latest announcement about the wall, it’s worth considering how the two materials differ, both in properties and in price point.
One of the positive aspects of steel is that it's relatively "flexible" and easy to repair. “The steel systems are easier to repair and demount, reuse and recycle, as in the case for all steel structures," said Mark Lawson, a professor of construction systems, speaking to New Civil Engineer. “Because the steel systems are less bulky, they are easier to transport and construct on rough terrain. In the same way, the steel systems would be better adapted to uneven ground as they would require less ground preparation apart from drilling of the ground to 2m to 3m plus depth for the posts."
A steel wall would likely be easier to build than a concrete wall, and would allow for more customization after its construction. The main problems with this material would be maintenance costs, and expenses caused by recent tariff increases on imported steel.
"Concrete is a stronger material and more durable than steel,” engineer George Mendoza told CBS 4. "Steel, since it's exposed to the weather, it will over time exhibit rust or perhaps other problems that Mother Nature causes to it.” Mendoza concluded that a steel wall might be less expensive to build, but would require more expensive maintenance in the long run.
"Most of the boarder is in a low corrosion zone, being inland and with a dry climate, and I would expect a steel wall would work as well as a concrete wall," said Charles Clifton, an associate professor of civil engineering. But we know from CBP's own estimates that steel maintenance is still costly. In a 2017 report from the U.S. Government Accountability Office (GAO), CBP had not the GAO a current life-cycle cost estimate to maintain its steel bollard fences. But back in 2009, the agency estimated that it would cost over $1 billion to maintain its existing fencing over twenty years—a number that isn't factored into the $5.7 billion in funding that the President is requesting from Congress.
And the up-front expenses might be greater than anticipated, because of recent tariff increases on imported steel. Back in March 2018, the current administration put a 25 percent tariff on imported steel, in a bid to improve the fortunes of struggling American steel companies. While U.S. steel prices have dialed back from the 40 percent increase they were sitting at in mid-2018, they are still the highest they’ve been since 2011.
It’s difficult to know what impact the tariffs might have on the wall’s cost because there have been no official cost figures released—either for a concrete wall or a steel one. Estimates range from $12 billion (President Trump’s estimate) to $70 billion (the U.S. Senate Democrats’ report). It is also unclear what the $5.7 billion the Republicans are requesting for the wall would actually build.
State(s) of Emergency
President Trump has suggested that he could declare a state of national emergency if his wall doesn’t get funded, citing "higher” border crossing rates. There is a real national infrastructure emergency, but it has nothing to do with the southern border. Instead, it’s the country’s infrastructure repair backlog, which the American Society of Civil Engineers estimates will reach $4.5 trillion by 2025.
With limited testing, a vulnerable structure, and uncertain building and maintenance costs, a steel wall would become just another infrastructure burden on an already burdened country. If Trump really wants to make America great again, he should start by building roads, not walls.