On Aug 24, 2011, at 10:16 AM, P. J. Alling wrote: > Tall buildings always sway a bit, if they were perfectly rigid something > would knock them over.
Last week's earthquake lecture here was about reinforced concrete buildings and some of the new technologies that have been developed to make them more earthquake-resistant. It's absolutely amazing stuff. What it comes down to is making the buildings rigid... to a point. You don't want them to swing around and make you seasick whenever the wind blows. But once they start getting shaken they are able to flex in a controlled fashion which prevents them from cracking up and falling to bits. The key is placing the flexibility in the right places. The down side is that they'll move about more which puts you at greater risk of injury from stuff falling over within the building. That can be mitigated at the building level by using base isolation (developed by an NZer but used more overseas than here for some crazy reason). Some of the new technology involves steel components designed to damp the shaking and be easily replaced afterwards. It's a lot easier to bolt on a new widget than it is to repair a concrete component. Having said that, the standards are fairly complicated in that what you build to depends on what the building will be used for. Something critical such as a hospital needs to be able to remain functional immediately, where an office block just needs to remain standing so its occupants can get out safely. I'm also not sure how the standards deal with multiple earthquakes. Tonight's lecture is about timber and unreinforced masonry. Timber buildings performed very well because of their inherent flexibility. Masonry is another matter... Dave -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
