{"335441":{"#nid":"335441","#data":{"type":"news","title":"Retrofitting old buildings to make them earthquake safe","body":[{"value":"\u003Cp\u003ENon-ductile reinforced concrete buildings are among the most common structures in the United States. They are also among the most deadly.\u003C\/p\u003E\u003Cp\u003EStructures built prior to the 1950s in California and prior to the 1980s in the central and southeastern United States were typically not designed with proper details to perform adequately during earthquakes.\u003C\/p\u003E\u003Cp\u003EThrough a grant provided by the National Science Foundation, researchers at the Georgia Institute of Technology \u2014 along with partners at Virginia Tech, Rice University, Howard University and the University of California, Los Angeles \u2014 are testing retrofits that potentially can make these buildings safer and more secure.\u003C\/p\u003E\u003Cp\u003E\u201cThese buildings are considered among the most deadly in the United States,\u201d said Reginald DesRoches, Karen and John Huff Chair and professor in Georgia Tech\u2019s School of Civil and Environmental Engineering. \u201cTheir reputation comes from the fact that there are so many of them and they are brittle, which means they will not have a lot of bend before they fail and collapse.\u201d\u003C\/p\u003E\u003Cp\u003EGeorgia Tech and its partners are studying how a full-scale reinforced concrete building reacts during large-scale testing. This testing shakes the structure, allowing researchers to assess different kinds of techniques to make similar buildings more durable so they don\u2019t collapse during an earthquake.\u003C\/p\u003E\u003Cp\u003E\u201cOur focus right now is trying to understand from a scientific perspective what works and what doesn\u2019t,\u201d DesRoches said. \u201cWe built this unique structure, which is split into different bays, that allows us to test three different retrofits as well as one bay without any added support.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EThe building\u003C\/strong\u003E\u003Cbr \/\u003EAccording to DesRoches, it is unusual for researchers to build such a massive structure allowing this type of testing.\u003C\/p\u003E\u003Cp\u003EOriginally, the research team tried to locate an existing building they could test, but they then realized there were benefits to building a new structure.\u003C\/p\u003E\u003Cp\u003E\u201cIt is a full-scale building that was constructed from plans of a building that was built in the 1950s in California,\u201d DesRoches said. \u201cWe know exactly what is in the columns and how it was designed.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EHow the structure is tested\u003C\/strong\u003E\u003Cbr \/\u003EThe building was constructed so that it was sliced up into bays, allowing researchers to actually test different portions of the building separately and evaluate different retrofit measures.\u003C\/p\u003E\u003Cp\u003EFour different bays, or different test structures, were tested.\u003C\/p\u003E\u003Cp\u003EResearchers mounted a shaker on top of each research bay, clamping it down to the building. This shaker produced more than 100,000 pounds of force, and researchers could control the sort of harmonic load or non-harmonic load needed.\u003C\/p\u003E\u003Cp\u003E\u201cNobody has really tested anything at this scale the way we are testing it with a large-scale shaker on top of the building,\u201d DesRoches said. \u201cFrom a technical perspective, this is very unique.\u201d\u003C\/p\u003E\u003Cp\u003EWith this equipment, researchers replicated the 1940 El Centro earthquake and the 1994 Northridge earthquake. By monitoring hundreds of instruments attached to the structure, researchers were able to get a detailed understanding of what exactly took place at different points in the building and essentially get a picture of the entire structure at any point during testing.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EThe retrofits\u003C\/strong\u003E\u003Cbr \/\u003EThe research involved testing three retrofits to strengthen the building\u2019s columns after an initial series of tests on the virgin structure or bare columns.\u003C\/p\u003E\u003Cp\u003EThe first retrofit is a black carbon-fiber wrap. The idea is when you wrap the columns with something very strong, you actually confine them.\u003C\/p\u003E\u003Cp\u003E\u201cOne of the biggest problems with these non-ductile columns is that they are not well confined,\u201d said DesRoches.\u0026nbsp; Confinement takes place by placing steel horizontally along the length of the column.\u0026nbsp; This is typically referred to as transverse reinforcement.\u003C\/p\u003E\u003Cp\u003EIn older reinforced concrete buildings, the transverse reinforced is spaced too far apart \u2013 typically around 12-16 inches apart.\u0026nbsp; In new building, the code limits the spacing to 4 inches in critical sections of the column.\u003C\/p\u003E\u003Cp\u003EIn the old buildings, there are not enough non-ductile columns and they are spaced too far apart \u2014 typically about 16 inches apart. In new buildings, by contrast, they are spaced just 3 to 4 inches apart. The wrapping confines the columns, making them stronger and more ductile. That means the structure can tolerate more movement.\u003C\/p\u003E\u003Cp\u003EThe second retrofit is similar to first. It is a round carbon-fiber tube that has been filled with concrete. The concrete is grouted in so it is confining or squeezing the column. According to DesRoches, when you squeeze the column in such a way, you increase the ductility and the strength of the column.\u003C\/p\u003E\u003Cp\u003EThe third and final retrofit uses a \u201csmart\u201d material known as a shape-memory alloy. It can deform significantly and then revert to its original shape.\u003C\/p\u003E\u003Cp\u003E\u201cYou can bend it, and it does not break,\u201d DesRoches said. \u201cThe idea behind seismic retrofit is that you want the structure to bend, but not break. So we have these braces and shape-memory alloy cables in this brace, and when it deforms, it puts the force right back on the structure to pull it back into position.\u201d\u003C\/p\u003E\u003Cp\u003EDesRoches continues, \u201cWhat we\u2019re trying to do in an earthquake is limit the deformation, particularly in an area where we know it is vulnerable. In this case, it is the base of the structure. We want to limit it to a level that we know is safe, and we believe this material can do that for us.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWhat researchers hope to find out\u003C\/strong\u003E\u003Cbr \/\u003EResearchers hope to give building owners a number of different options at a variety of price points to retrofit their buildings and make them safer. Some of these options, like the shape-memory alloy brace, have never been tested before. Others have been tested, but not at this scale or capacity.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EHow the tests performed\u003C\/strong\u003E\u003Cbr \/\u003EDuring the test, researchers want to see various amounts shaking. When testing the retrofits, researchers start with low levels of shaking and gradually build up to larger levels of shaking.\u0026nbsp;\u003C\/p\u003E\u003Cp\u003E\u201cYou may not see as much shaking as when we tested the virgin structure because in that case we went to the point where we had to stop because the structure was about to collapse,\u201d DesRoches said during the final test. \u201cYou do not see that amount of shaking because we\u2019re testing a retrofit that has been very successful and effective in limiting the deformation that you get in the structure.\u201d\u003C\/p\u003E\u003Cp\u003EOverall, DesRoches and his team were pleased with the testing.\u003C\/p\u003E\u003Cp\u003E\u201cI feel great about what I saw,\u201d he said. \u201cI was here for the first test, and the structure was classicly dangerous \u2014 what we call soft story \u2014 where the first story moved so much that if we hadn\u2019t had the safety ropes inside, it would likely have collapsed.\u201d\u003C\/p\u003E\u003Cp\u003EHe continued, \u201cYou can see in the last test, it moved very little and it performed well. In fact, we almost made it too strong in a sense. I wouldn\u2019t mind seeing a little more movement. We could have made it half as strong with half as much material and still received\u0026nbsp; good performance from it. We did not come anywhere close to pushing those devices on the last test. It performed very well.\u201d\u003C\/p\u003E\u003Cp\u003ENow researchers will spend the next three to six months combing through and analyzing all the data they\u2019ve gathered during six months of testing.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EFuture of structure\u003C\/strong\u003E\u003Cbr \/\u003EMeanwhile, researchers are looking at a number of ways to continue utilizing the structure.\u003C\/p\u003E\u003Cp\u003EThe first bay that they tested without any retrofit is significantly damaged, so they are looking at ways to repair it.\u003C\/p\u003E\u003Cp\u003E\u201cThis is the type of problem that we know we have after earthquakes,\u201d DesRoches said. \u201cWe have a structure damaged, and they typically tear down the building if they feel it is not safe to reoccupy.\u0026nbsp; However, we think there may be opportunities to develop rehabilitation methods to actually preserve and reoccupy the building without completely demolishing it.\u201d\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EThrough a grant provided by the National Science Foundation, researchers at the Georgia Institute of Technology \u2014 along with partners at Virginia Tech, Rice University, Howard University and the University of California, Los Angeles \u2014 are testing retrofits that potentially can make these buildings safer and more secure.\u003C\/p\u003E\u003Cp\u003E.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Through a grant provided by the National Science Foundation, researchers at the Georgia Institute of Technology \u2014 along with their partners, are are testing retrofits that potentially can make these buildings safer and more secure."}],"uid":"27304","created_gmt":"2014-10-20 13:49:13","changed_gmt":"2016-10-08 03:17:19","author":"Matthew Nagel","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2014-10-20T00:00:00-04:00","iso_date":"2014-10-20T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"335351":{"id":"335351","type":"image","title":"Shape-memory alloy brace","body":null,"created":"1449245150","gmt_created":"2015-12-04 16:05:50","changed":"1475895046","gmt_changed":"2016-10-08 02:50:46","alt":"Shape-memory alloy brace","file":{"fid":"200485","name":"15c10302-p6-028.jpg","image_path":"\/sites\/default\/files\/images\/15c10302-p6-028_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/15c10302-p6-028_0.jpg","mime":"image\/jpeg","size":7441027,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/15c10302-p6-028_0.jpg?itok=jFzdbwZE"}},"335401":{"id":"335401","type":"image","title":"Shape-memory brace","body":null,"created":"1449245150","gmt_created":"2015-12-04 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Sustainable Infrastructure"},{"id":"39471","name":"Materials"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Cstrong\u003EGeorgia Tech Media Relations\u003C\/strong\u003E\u003Cbr \/\u003ELaura Diamond\u003Cbr \/\u003E\u003Ca href=\u0022mailto:laura.diamond@comm.gatech.edu\u0022\u003Elaura.diamond@comm.gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-894-6016\u003Cbr \/\u003EJason Maderer\u003Cbr \/\u003E\u003Ca href=\u0022mailto:maderer@gatech.edu\u0022\u003Emaderer@gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-660-2926\u003C\/p\u003E","format":"limited_html"}],"email":["Nagel@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}