CR4® - The Engineer's Place for News and Discussion®


"An expert is a man who has made all the mistakes, which can be made, in a very narrow field." -Niels Bohr

These words frame the OH CR4P! blog, a place which encourages engineers to discuss, reminisce, and learn about mistakes, failures and mishaps made by those who have become "experts" the hard way.

The San Fran Skyscraper with a Six-Inch Slant

Posted September 28, 2016 9:05 AM by HUSH

Skyscrapers are a lot more to a city than just real estate. They represent financial prosperity and engineering acumen. They transform the identity of a city, emerging as a new shape that must be depicted in skyline silhouettes. When tourists arrive, they flock to the Empire State Building or Willis Tower for ten-mile views and selfies.

For the city of San Francisco, skyscrapers are being built quickly and steadily, with 14 over the last 14 years and another 10 expected by 2019. San Francisco has a complicated history with skyscraper development, seeing a spurt of buildings over 200 ft. between 1890 and 1930, another era of upward expansion between 1955 and 1972, and yet another that kicked off shortly after the turn of the Millennium.

There are several reasons for this boom-or-bust building cycle in the City by the Bay, ranging from a very low building height limit (areas in yellow on the map have a limit of just 40 ft.); overprotective laws against ‘Manhattanization;’ laws that ensure community areas such as parks and plazas aren’t oppressively shadowed; historical ordinances; and advances in seismic engineering that show tall buildings are safer than smaller buildings, as they are constructed to cope with some lateral deflection anyhow.

Millennium Tower, opened in 2009 in San Fran’s South of Market neighborhood, has been the source of some controversy lately. Millennium Tower has sunk 16 inches and now tilts 6 inches, and the sink could double before the building finally settles. In a city with major earthquake concerns, the poor structural integrity of the building is generating unease for its residents and neighbors.

Now people are trying to figure out who to blame.

Is it the tower developers? Millennium Tower includes a concrete mat-slab foundation and 950 friction piles, each 60 to 91 feet long, that are drilled into the underlying soil composed of mud and fill after the 1906 earthquake ruined much of the neighborhood. For friction-type foundation piles, the load capacity is solely based on the soil’s ability to provide friction against the shaft of the pile. Historically, buildings on friction piles have done quite well in San Francisco beforehand, although there has never been one as heavy on top of such squishy soil.

Is it the tower’s new neighbors? Across the street, four buildings are being erected by Transbay Joint Powers Authority, including what will become the city’s tallest tower. Each is being constructed with end-bearing piles, which are driven 200 ft. into the ground to the Franciscan Assemblage bedrock. Millennium Tower developers and engineers accused the new construction of dewatering the soil beneath the Millennium Tower, resulting in the soil compressing and destabilizing the tower’s foundation. The authority denies the dewatering accusation, and says Millennium is simply a case of poor engineering.

Is it the fault of the city? The city had previously rejected a similar tower in the area in 2004, under grounds that friction piles wouldn’t be enough to support the project. Apparently the same questions weren’t raised this time around, because the city didn’t have the engineering expertise to evaluate the soil integrity of the project, and didn’t have the ability to make Millennium’s builders do the evaluation. Instead the city relied on computer models provided by the developers.

Who is to blame is ultimately up to the courts to decide. Now engineers have some options for ‘fixing’ the tower.

· Remove the top 20 floors

· Reinforce soil underneath building

· Balancing the lean with a heavy building on the other side of Millennium Tower

· Doing nothing, as Millennium Tower promises the building is still structurally sound

· Do nothing, and move residents if/when the tower approaches a tipping point

Fun fact: Millennium Tower received nine awards for excellent design and engineering. Today, the project looks like it will eventually be condemned.

Who do you think is to blame? And how do you think Millennium Tower could be rescued?

20 comments; last comment on 01/25/2017
View/add comments

World's Most Dangerous Dam Threatens Up to 1.5 Million

Posted March 30, 2016 10:16 AM by HUSH
Pathfinder Tags: civil enginering dam flooding grout

There could be an unprecedented engineering disaster in the weeks or months ahead. Mosul Dam in north Iraq is dangerously close to collapsing, years after being identified as fundamentally flawed and in need of major overhaul.

(Edit: NO, this is the correct dam!)

Saddam Hussein constructed the dam during the Iran-Iraq war. It was needed to limit Tigris River flooding downstream in Mosul and Baghdad, Iraq's second- and first-largest cities, respectively.

Saddam constructed it in the middle of the Iran-Iran War to show how prosperous things remained despite the war, but in actuality the dam was built quickly and cheaply.

Before construction engineers suggested heavy foundation grouting and preparation before building the dam as it sat on soluble gypsum. But political pressure meant the dam would proceed without sufficient grouting. Instead a grouting curtain nearly 500 ft. below the dam would compensate for the limited 82 ft. of grouting in the foundation.

Grouting curtains are regularly used to pump a bentonite, cement, water and air slurry below the dam to prevent upward pressure on the underside of the dam from underground seepage. The heavily gypsum bedrock meant that water seepage under the dam was inevitable and considerable maintenance would be needed to keep the dam safe. Insufficient grouting caused the uplift that toppled the St. Francis Dam in California in 1928, which killed 431 people.

Over the years 50,000 tonnes of grout material have been pumped continuously below the Mosul Dam by 300 workers on 24/7 shifts. When American military reached the dam in 2003, engineers found that the dam was dangerously close to failing from underground seepage. Due to the invasion, resources were routed away from the dam's maintenance and workers began quitting after not getting paid. The dam deteriorated to the point where the U.S. Army Corps of Engineers spent $27 million in 2007 for an emergency short-term solution.

Then in 2014, terrorist group ISIS/ISIL captured the dam for several days, but was pushed back. Had the radicals captured the dam for a longer period, it's entirely likely the dam would have already collapsed. Nonetheless, machinery that ISIS captured and workers it drove away have yet to return, meaning that for more than year and a half the dam has not had the equipment and just a 1/10 of the workforce needed to keep it stable..

Instead, millions of individuals live with the worry that the dam burst is imminent, right as spring runoff begins to occur. Estimates believe Mosul would be submerged in 65 ft. of water within four hours, and Baghdad in 15 ft. of water within 48 hours, if the dam were to break. Death toll estimates range from 500,000 to 1.5 million.

The situation is so dire that the U.S. Government issued a second advisory against traveling in the Tigris valley, on top of the general "you probably don't want to go Iraq" blanket advisory.

This blog might be posted in the Oh CR4p! section, but it doesn't have to be. The Iraqi government recently reached an agreement with an Italian firm to fix the dam, hopefully before it's too late.

12 comments; last comment on 03/31/2016
View/add comments

Why We Need Others To Catch Our Typos

Posted September 04, 2015 7:00 AM by cheme_wordsmithy

If yvo'ue raed something aoubt how the brian wrkos you may konw why you can raed tihs snetecne whiuott mcuh tbruloe.

I remember the first time I saw something like the mess you see above, and how amazed I was that I could read it so easily. What intrigued me more though was the concept that our brains can make the necessary assumptions to read words in bulk rather than through individual letter order. As long as all the letters are there and the first and last letters are in the right spot, our brains usually have no trouble piecing things together. This is because the brain is allowing itself to take shortcuts in order to complete the more complex goal in reading --> extracting meaning.

The brain actually does a lot of simplifying to help manage all that it does. Consider the fact that even when you are doing a brainless activity that requires no real thinking (e.g. fishing) your brain is busy processing everything you receive from your five senses, and simultaneously managing both passive and active motor functions in your body. When we add thinking to the mix, the brain looks for ways to simplify and generalize easy/component tasks in order to free up brain power. Taking the example above, the mind takes shortcuts on how we read individual words in order to focus on the harder task of pulling meaning out of a sentence or paragraph (aka "reading comprehension").

There is another shortcut our brains take when we read, and it actually inhibits our ability to proofread. When we read, our brains are pulling sensory information from our eyes (the words) and combining that with our prior knowledge to extract meaning and understanding. When we read our own work, we already know the meaning we want to convey, and we expect it to be there. This expectation makes it easy for us to miss things that would be obvious to others, because our brains are filling in the gaps for us. It's typically also this reason why we make typos in the first place. There have been many times where (in a draft) I've completely left out entire words or sentences about certain points, and not seen them during my review. In my head I read them, but I had not written them on the page.

Studies on "change blindness" show another way that our brains make compromises in order to focus. In this experiment at Harvard University, test subjects are asked by a man behind a desk to fill out a consent form for an experiment. When they complete the form, the man behind the desk ducks down to file it, and a completely different person stands up to tell them to go into the next room. About 75% of the people in the test don't notice this change, presumably because the brain is making assumptions for the things that it is not focusing on. Pretty amazing and yet pretty scary - it makes me wonder what kinds of changes I've missed this way in the past.

Even as we continue to push the envelope on human understanding and knowledge, it's important to remember that our minds are limited and that we will sometimes miss things and make obvious mistakes. Most of the time, though we would rather go it alone, there is no substitute for having someone else review and check our work.


19 comments; last comment on 07/18/2016
View/add comments

Big Bets Lost on Vegas Hotel

Posted April 23, 2015 11:12 AM by HUSH

If you're in Las Vegas, you're probably going to gamble. The city is well known for its attractions, from the resorts to the shopping to the shows to The Mint 400, but the town undoubtedly thrives by lost bets and 'misplaced' paychecks. When I visited several years ago, I only left about $200 under, and I'm one of the fortunate ones.

Yet the gambling environment extends beyond the casino floors. Virtually all stakes are raised in Las Vegas, especially those in the development game. Even classic hotels eventually need to be closed or renovated as yesterday's chic becomes today's retro. It was this cyclic resurgence that gave birth to the Harmon Hotel, a non-gaming boutique hotel that would reside in the MGM CityCenter development, which would replace The Boardwalk Hotel's faux Coney Island landscape.

To say the Harmon was opulent was an understatement. Forty-nine floors with 200 luxury condos, 400 hotel rooms, a rooftop pool, spa, salon, gourmet restaurant. In 2006, developers boasted that it would be the most expensive privately-funded construction project in U.S. history. In late 2014, MGM won a lawsuit that settled with plaintiffs who already purchased condos, as the demolition of the Harmon is scheduled to be finished this year.

All in all, MGM bet $279 million on hotel construction, $11.5 million in demolition, and $173 million in litigation. So what was the cause of this huge loss?

Improper construction techniques that made the structure virtually unusable, and falsified inspections that allowed the techniques to continue. Construction on the Harmon began in 2006 and Perini Building had been enlisted as the general contractor. Two years into the project it was discovered that Perini's subcontractor Pacific Coast Steel had been improperly installing rebar in floors 6 through 20. They claimed that there were errors in the blueprints, but Perini, as the general contractor, had authorized design modifications. Perini officials say that MGM executives never made a decision, and approved changes acting as MGM's agent. Rebar is critical to structure strength, as concrete excels at compressed loads but fails easily under tension without reinforcement.

It should also be noted that the steelwork in question was reviewed and approved by a private inspection firm on 62 consecutive days. It would later be revealed that these inspections were falsified. It wasn't until county inspectors arrived that the defects were identified. Not only was the structure at immense risk of collapse due to earthquake or other structural trauma, but remediation efforts would essential mean a rebuild. At first the Harmon was halved to 28 stories, before finally being shelved altogether in 2010.

It's probably for the better, as at least one architecture blog criticized the blue-glass elliptical tower as too bland for the Las Vegas Strip. The city offers a unique blend architectural marvels, so the Harmon would likely end up being rebuilt after 40 years or so. The Harmon might also appear as a huge loss for MGM, but they won the public-relations side of this issue by paying subcontractors who would have to wait for litigation, and are getting rid of the Harmon hotel relatively quietly.

It reinforces a pretty simple principle when gambling: mind your bets.

2 comments; last comment on 04/25/2015
View/add comments

Safety Concerns of Oil by Rail

Posted October 30, 2014 7:00 AM by cheme_wordsmithy

Historically, most oil in the U.S. has been transported via pipeline. In 2008, the U.S. saw the rise of a new alternative for crude oil shipment - railroad. While "crude by rail" was initially seen as a temporary solution until construction of pipeline infrastructure, it has become a staple part of the U.S. energy industry. Today, no small number (~939,000 barrels a day) of oil in the U.S. is shipped by rail, about a tenth of the quantity carried in pipelines.

Unfortunately, there have been a large number of accidents and spills related to shipping oil by rail, and that has raised concerns for Americans across the country. The biggest incident was in Lac-Megantic, where a 74-car train derailed, causing the fire and explosion of multiple tank cars that destroyed 30 buildings and killed 42 people. Other accidents, such as the accidents in Cassleton, North Dakota, and Lynchburg, Virginia, did not kill or injure anyone but did create massive explosions and oil spills. These, along with other accidents, have generated a lot of discussion about what can be done to make transporting oil by rail safer.

It seems that the culprit in the majority of these accidents is "Bakken crude," crude oil product obtained from the Bakken formation located in North Dakota and nearby states. Some 65-70% of Bakken crude (roughly 670,000 barrels per day) is transported by rail. The biggest issue with Bakken crude (and other forms of light crude oil) is its volatility and explosive potential. Heavy crude is less dangerous to transport because it is harder to ignite due to being largely devoid of combustible "light" components.

There is a way to decrease volatility in crude oil: a process called stabilization. Stabilization is the process of removing the more volatile components of the oil (residual gases, natural gas liquids and "light" liquid components). Stabilizing Bakken oil can effectively decrease its Reid Vapor Pressure (RVP, a common measure of volatility) from 8-16 psi to between 1.5-6 psi, which is a substantial change in explosive potential.

Unfortunately, like all things, stabilization costs money. In fact, mandating stabilization would require companies to spend potentially billions on stabilizers to recover natural gas liquids (NGLs) and pipelines to transport the NGLs to a suitable market. But to address this issue of railcar safety, it may be a necessary price.

There are other factors in the equation, including the traveling speeds of trains and the condition and maintenance of the railcars. Derailing and accidents often occur because a train is moving too fast, and old and poor-condition cars and connections can also cause problems. All of these items need to be addressed at the source because once a train is on the rail it is largely free from regulation by other states it passes through. North Dakota, where most of the Bakken crude is loaded and shipped from, is thus in a unique position to make safety improvements. Other states (including New York) have recognized this and have been petitioning North Dakota to increase its oversight of the oil train industry.

Interestingly enough, this issue literally hits close to home for me, since the office building I work in sits practically right across the road from a rail line that carries North Dakota crude cars through it every day. And while the likelihood of an accident is very small (the cars travel at <10mph in this area), it's a bit unnerving knowing that the potential for a major disaster is very real, and the costs would be much higher than the price of oversight to make things safer. These are things that I hope we consider as the use of rail for crude transport continues to grow.

WSJ - Dangers Aside, Railways Reshape Crude Market

Reuters - Safety Debate Eyes Taming Bakken Crude Before It Hits Rails

19 comments; last comment on 02/23/2015
View/add comments

Previous in Blog: Dangerous Drilling - Oil & Gas Rig Safety  
Show all Blog Entries in this Blog