![]() ![]() Economics usually governs the choice between fewer long piles compared to more short ones, but both systems have proved to be reliable.ĭays after the Millennium Tower story broke, marketers of nearby buildings under construction were advertising the fact that their foundations were solidly supported on bedrock. Bedrock is stronger than sand/clay, and for a tall building in general, fewer piles are necessary when founded in bedrock rather than upper strata material. This geologic complexity is responsible for our stunning topography, and it calls for sophisticated engineering. There are all kinds of layers of various densities below the surface strata capable of bearing the weight of a building are sometimes near the surface and sometimes very deep. The problem here is geologic complexity our bedrock is technically called a mélange by geologists, because it is a jumble of metamorphic rocks. But the Franciscan Complex in the Bay Area can be removed with a pick-axe. The word itself suggests solid, reliable, and dependable attributes, and in many large cities, bedrock must be blasted out with dynamite. Sounds scary, especially when parroted by lawyers, but friction piles embedded in strata above bedrock have been used successfully to support massive buildings in San Francisco for years.īedrock, in San Francisco anyway, is over-rated. He pointed out that the foundation piles do not go down to bedrock, but instead, rely on support from upper stratum sands and clay. The story of the tower’s sinking was revealed by a suburban geologist retained by the homeowner’s association, a licensed practitioner, but one without any clear expertise in the design of tall building subsurface structures. The most famous tilting building in the world peeks out behind the Pisa Cathedral. The Leaning Tower of Pisa is only 183 feet tall if the Millennium Tower leaned 4.0 degrees, its top would be displaced 45 feet! London’s 315 foot Big Ben is also leaning, but merely 0.26 degrees, a little over twice the tilt of the Millennium Tower. Right now, its apex is displaced about 13 feet. How significant is this? At its most precarious, Pisa’s famous tower leaned about 5.5 degrees, but it has been stabilized in recent times to lean “only” 4.0 degrees. Settlement is normal, (more about that later), but what about the tilt? Let’s do a little math: at the top, the horizontal displacement is 15.2 inches (hypotenuse of a 14:6 triangle), and the building is 645 feet tall, so the Millennium Tower is leaning 0.11 degrees to the west-northwest. Most reports say the building has settled about 17 inches, and is leaning 14 inches westward and 6 inches northward at its crown. What actually did go wrong? The building has settled downwards, and is, in fact, tilting. In this age of over-stimulated media, the rabid coverage of this issue has sown doubt in the minds of ordinary citizens about the competence of those of us who develop, design, and build large things. ![]() Is it likely to fall over? In a word: NO.īased 5% on insider information and 95% on the laws of physics, San Francisco’s 58-story Millennium Tower is in no danger of tipping over. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |