Salesforce Tower (rendering), San Francisco
We have an excellent view of the San Francisco skyline from our windows in the East Bay. The city is again on a building binge, especially with the disruptions of constructing the new Transbay Terminal in the downtown area. Over the past couple of months we’ve seen a new spire shooting up, the Salesforce Tower, which is part of the terminal complex. Even though it’s not yet completed, either the central concrete elevator core or the surrounding steelwork which lags it by a couple of floors, the tower already exceeds every other building in the city, and the construction cranes attached to its upper levels—beautiful at night with their white lights—push even higher. This 61-story office tower, at 1070 feet, is projected to be the tallest building in the Western U.S. and the seventh tallest in the country.
Having worked for a number of years as a technical writer in an engineering and construction company, I have some appreciation for the scheduling and logistics problems involved with such a project. Think about it. The site is in the middle of a busy city, without acres of empty land nearby for a laydown area where the construction crew can receive, sort, and stockpile incoming materials. The city has no working freight railroad anywhere nearby to deliver those materials, so everything must come in by truck, in relatively small loads. And the only access to the site is by two bridges and two freeway systems, both of them regularly jammed for hours at a time with commute traffic.
The receipt of all that concrete, steel, glass, and drywall—not to mention thousands of redundant fixtures like various grades of pipe, lighting ballasts, toilets, sinks, and doors—must represent a just-in-time scheduling ballet of mammoth proportions. And once all those fixtures are dumped at the curbside, another ballet involving the limited number of construction cranes—and later, elevator cars—must go on twenty-four hours a day to deliver everything to the right floor at the right time.
We imagine that Egypt’s pyramids were built by thousands of slaves chipping granite, hauling sledges, and greasing the rollers as in those old Cinemascope biblical epics. But thousands of workers are not building the Salesforce Tower—or not all at once or at the same time. On any one day, perhaps a few hundred are involved, and those are parceled out among the skilled trades: excavators, rebar stringers, and concrete masons; high-steel workers and crane riggers; glaziers; pipefitters and plumbers; electricians; heating, ventilating, and air conditioning (HVAC) technicians; communications and cable installers; and on and on. That work must be coordinated, too, so that plumbers are not putting water and drain pipes in spaces reserved for electrical and communications—now in fiber optics—conduits. And the glass outer shell must be made weather tight before anyone starts putting up interior walls and laying carpeting. Thousands of people do crawl all over the building in the course of its construction, but their activities are as carefully coordinated as the materials and systems they will install.
Think, also, about everything that must go right about planning, designing, and erecting such a building and its systems. In San Francisco we have an example, right down the street from the Salesforce Tower, of just one thing going disastrously wrong.
This part of San Francisco, between Telegraph Hill on the north and Rincon Hill—now the jumping-off place of the Bay Bridge—to the south, is the former cove around which the city originally sprung up during the Gold Rush. First Street is called such because it was the first street along the water. Everything east of there was a shallow harbor cut out of the Bay. The story is that sailors on vessels arriving in the 1850s were so eager to reach the goldfields that they would abandon ship. The earliest businesses were conducted aboard hulks sitting at the quayside and eventually collapsing into the mud. All of the buildings in this area—including the Federal Reserve Bank, which I watched from next door as it was being built—stand on a sea of bay mud above layers of sand and clay. Bedrock, a saddle of the same stone that lifts Telegraph and Rincon hills, lies fifty to a hundred feet down. For the Federal Reserve, I watched the crews auger out black muck in holes two feet wide on centers about five feet apart, then drive in reinforced concrete piles more than fifty feet long, until the site was a sea of square stumps. Imagine, if you will, trying to stabilize a cube of Jell-O by driving into it dozens of toothpicks until they touch the plate underneath.
Most of the piles under these buildings go down to bedrock, or we hope they do. For the Millennium Tower, a high-rise condominium for the super-rich, however, the builders used a more modern system. Or so the story goes—there are competing legal claims. But it seems that instead of driving the supporting piles to bedrock, they took them down to the layers of sand under the mud. The idea was that the pressure of the pilings would compact the sand, and the sand would grip the pilings, and the whole thing would stand on friction without having to touch rock. Apparently, it works elsewhere in the world. But no one planned for massive excavation right next door, part of construction for the Transbay Terminal. Dewatering that later site changed the soil composition under the Millennium Tower. The tower has already sunk 16 inches below the sidewalk level, continues to sink, and is also tilting a couple of degrees off vertical. Fixing this problem—if it even can be fixed, in a building that is already completed, with all its units either sold or rented out—will be not only an engineering but also a legal problem.
I know from my own experience, working alongside construction engineers, that every project has its underlying assumptions, like using friction piles in the foundation. Every project has its compromises with the planning commission and the building inspectors. And every project has its share of errors and oversights. The condominium complex where we live had three notable issues early in our occupation. Concrete roof layers were poured without a slope, so that water would not drain from the fiberglass roofing materials installed above them. Foam bearing strips were improperly shortened in constructing the garage, so that the floor pads came into direct contact with the underlying concrete and could not dissipate the shock of moving cars; the floor pads then began to crack and spall. And six-inch-wide vertical drain pipes were connected at the bottom to four-inch-wide horizontal pipes, on the theory that hydrostatic pressure—or something like it—would overcome the volume difference; the result was sewer backups into apartments on the lower floors. All of these issues had to be taken to court, remedies sought, and fixes installed. Litigation like this happens all the time.
New ideas, like using friction piles, are continuously developed, tested, and used in the construction business. In most cases they work well, save time and cost, increase efficiency, or add some other benefit. In almost all cases, the owners and occupants of the building never notice a difference. This is the way construction practices and standards are improved. It’s the way technology advances—until someone digs a three-story deep pit next door to a building supported by friction piles and begins drawing off groundwater.
It’s a wonder that, with all these risks, we don’t have more sinking buildings, more technical blowouts, more errors that cannot be fixed with any amount of money. But we don’t. Most of the construction taking place in the 20th and now the 21st century has been flawless. Elevators work. Interiors are heated and cooled behind curtain walls of glass. Water runs hot and cold on the 60th floor. Drains don’t back up when you flush. The lights come on when you flip the switch. This is the effect of engineers, soil experts, planning departments, contractors among all the different trades, and building inspectors—all of them doing their jobs. And lawyers and judges get to adjudicate the few cases where things actually go wrong.
Human imagination and ingenuity are powerful forces. Human planning, scheduling, logistics, and the cooperation to push an office tower a thousand feet into the air in a matter of months—those are even more powerful forces. The next time someone tells you that ancient structures like the pyramids must have been built by space aliens because poor old human beings simply don’t have the knowledge, the skill, or the organization to accomplish these marvels, well … just look around you.