Posts tagged with "seismic design":

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Why doesn't the U.S. design buildings to survive earthquakes?

Earthquakes have been in the news lately with increasing regularity: Southern California recently experienced a July 4th quake registering 6.4 on the Richter scale followed by one just a day later at 7.1. It's predicted that within the week there's an 11 percent chance that a major quake could follow, and, of course, there's the looming specter of the so-called Big One. But despite the relative frequency of seismic activity on the West coast and in other parts of the United States, in general, the U.S. lags behind other earthquake-prone countries, especially Japan, in terms of earthquake readiness. A recent New York Times investigation asked why, when buildings can be designed to stand up to earthquakes, the United States has so few of them. Though there are notable exceptions—like older retrofits such as Los Angeles’s city hall, and luxurious new construction like Apple’s Foster + Partners-designed headquarters, a ring that floats on base isolators rather than being fixed to a traditional foundation—most buildings in the States feature concrete cores, relatively un-rigid construction, and no seismic shock absorbers or isolation systems. Even those that do, the Times reports, are of varying quality of construction, with many failing basic preparedness tests. Simply put, while Japanese buildings are, in general, designed to sway in an earthquake and minimize damage (and use a steel grid to make up their core), American buildings are designed primarily to fail and collapse in a way that will hopefully minimize loss of life. This can mostly be chalked up to not only weak regulations, but to economics. It’s more costly to build an earthquake-ready building, though obviously only in the short run. A federal study demonstrated that rebuilding after a quake in urban centers will cost billions of dollars, and is four times as expensive as simply building a structure that can stand up to an earthquake in the first place. However, with lax laws and a real estate and development market that prioritizes short term ownership and thinking, building owners and developers remain wary of spending the extra cash up front; estimated to only add approximately 13–15 percent in cost in a seven-story building, according to the Japanese construction company Nice Corporation. Though, per the Times, engineer Ian Aiken says that some systems “can cost as little as 5% more.” Tokyo, which experiences more than 1,000 seismic events each year, is also anticipating its own big quake in the next 30 years, a follow up to the devastating 1923 earthquake. while predictions of the potential damage remain calamitous, there is perhaps no city more ready to take the hit. Not only are high rises, skyscrapers, and smaller buildings all designed to withstand significant seismic activity, but, as The Guardian reports, “parks feature hidden emergency toilets and benches that turn into cooking stoves, and the city has the world’s largest fire brigade, specifically trained to prevent the kind of flash blazes that spread after earthquakes.” The city is not only a world population and business center, but also a major tourist destination, something that's likely to become only more true with events like the upcoming 2020 Summer Olympics and Paralympics. But even new construction for the Olympics is getting the high tech treatment. Seismic isolation bearings are being placed inside the new Tokyo Aquatics Center and the Ariake Arena, which will be home to Olympic volleyball and wheelchair basketball games. The aquatics center and arena are using Bridgestone Seismic Isolation Systems, an update to older methods that relied on increasing the rigidity of buildings or adding additional framing. Instead of adding greater rigidity, base isolation systems use rubber bearings ranging in size between approximately 23 inches and 70 inches to allow structures to sway slowly and cause only minor disturbances, if any at all, on the floors above, instead of allowing the whole structure to shake violently. Similar such bearings can be found in buildings like Tokyo Station and Los Angeles's City Hall. While the isolators are often placed in the foundations of buildings, for the new arenas, they’ve been located in the roofs, a common approach for buildings with large open spaces that helps decrease the stress on the roof’s support elements. Still, all the technology in the world only goes so far if the community isn’t prepared. As Tokyo-based disaster preparedness specialist Ronin Takashi Lewis told The Guardian, even all this tech, “If you look around the Tokyo skyscrapers it’s incredible how advanced a lot of technology here is, especially seismic resistance – but my concern is preparedness at the community and individual level.” As per usual, technology alone won’t save us. Still, hopefully the United States can learn from Tokyo and invest in resilient buildings for safer cities and communities.
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Flexible 3-D-printed cement stretches the possibilities of construction

Concrete is a ubiquitous building material, applied to the bulk of contemporary construction projects. While the sedimentary aggregate is commonly used due to its impressive compressive strength, it remains a brittle material subject to damage or failure during extreme environmental events such as earthquakes. In response to this inherent weakness, a team of researchers based out of Purdue University’s Lyles School of Civil Engineering comprising professors Jan Olek, Pablo Zavattieri, Jeffrey Youngblood, and Ph.D. candidate Mohamadreza Moini has developed a 3-D-printed cement paste that actually gains strength when placed under pressure. The project, initiated in August 2016 with funding from the National Science Foundation, looked towards the natural durability and flexibility of arthropod shells. “The exoskeletons of arthropods have crack propagation and toughening mechanisms,” said Pablo Zavattieri, both of which can be reproduced “in 3-D-printed cement paste.” For the prototype, the research team cycled through a number of geometric configurations, including compliant, honeycomb, auxetic, and Bouligand designs. Each of these formats responds to external pressures differently; a compliant design acts as a spring under stress while the Bouligand boosts crack resistance. To assess the structural qualities of each prototype during and following testing, the team relied on micro-CT scanners. Through the use of this tool, the team was able to identify weaknesses present within the 3-D-printed objects, improving upon them with successive prototypes. What are the implications of the Purdue team’s 3-D-printed cement paste? In boosting the flexibility of concrete construction, the cement paste could add an extra factor of safety for the brittle material within conditions of environmental extremes, dampening the impact of momentary shocks. Admittedly, Zavattieri noted that the “minimum amount of material was used to prove the hypothesis.” However, there is no significant engineering hurdle in scaling up the technology to a potentially full-scale prototype and its ultimate application in architectural design.
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This New Zealand library beams with luminous aluminum and indigenous motifs

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The 2011 Christchurch earthquake devastated much of New Zealand's capital city, knocking down or severely compromising civic buildings across the metropolitan area. Located within the cordoned off Central City Red Zone, the Christchurch Central Library was closed to the public for three years prior to its ultimate demolition in 2014. Completed in October 2018, the new Central Library, titled Turanga after the Māori word for base or foundation, designed by Schmidt Hammer Lassen Architects features a luminous perforated aluminum veil that cloaks a seismically engineered unitized curtain wall assembly.

The 102,000-square-foot library rests atop a rectangular stone-clad podium detailed with expansive representations of Māori artwork. Rising to a height of five stories, the facade fissures to orient itself toward local geographic landmarks, including the mountain ranges of Maungatere, Ka Tiritiri o te Moana, and Horomaka.

 
  • Facade Manufacturer & Installer Alutec (curtain wall), Metal Concept (veil), Southbase Construction
  • Architects Schmidt Hammer Lassen Architects, Architectus
  • Facade Consultants Mott Macdonald, Lewis Bradford Consulting Engineers
  • Location Christ Church, New Zealand
  • Date of Completion October 2018
  • System Unitized glass curtain wall with clip-on cassette metal veil
  • Products Metal Concepts perforated aluminum sheets, Alutec unitized thermally broken aluminum curtain wall

The principal facade element, a wedge-shaped aluminum perforated panel system, was designed as an oversized evocation of the native evergreen species used for traditional Māori textiles. Each panel is approximately a standard height of just under five feet, with widths varying between two, four, and six feet. Similar to the flexibility considerations of the concrete structural system, the design team placed an open joint between each story of perforated panels to allow for differential movement during a seismic event.

For the golden veil that courses across the facade, Schmidt Hammer Lassen Architects coordinated with local fabricator of architectural metalwork, Metal Concepts. The aluminum sheets were pre-anodized to ensure color consistency and were subsequently cut, perforated, and folded into their respective shapes. To connect the panels to the curtainwall assembly, each is outfitted with a slotted hole at the rear of the frame which is fastened to a series of hooks extending from the story-height mullions of the unitized curtain wall. 

The perforations of the aluminum panels follow an approximately 2.5-square-inch triangular grid, with an indentation located on the corners of each triangle. Measuring just under an inch in diameter, the perforations play two roles; accentuating the depth and texture of the facade–the luminosity of the aluminum panels intensifies at sunset–and filtering light through the glass curtain wall.

For the design team, which worked in collaboration with Lewis Bradford Consulting Engineers, one of the crucial considerations for the facade and structural systems was durability during a future seismic event. According to the architects, this seismic force-resisting system is composed of a series of flexible concrete walls that shift during earthquake accelerations. With a system of “high tensile, pre-tensioned steel cables that clamp the wall to the foundations with approximately 1,000 tons of force per wall,” the building is capable of returning to its original position following a sizable earthquake.

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Seismic hot spots and facade design: Experts explain the risks and rewards

Southern California's enviable climate and landscape—sunny skies, balmy temperatures, picturesque mountains, and surfer-friendly beaches—come at a geological cost: proximity to active earthquake faults. Local AEC industry professionals are adept at meeting detailed building code requirements for structural safety. But when it comes to cutting-edge facade systems, said KPFF principals Mark Hershberg and Nathan Ingraffea, designers and builders are left with little to go on. Hershberg and Ingraffea will dig into this and other challenges and opportunities associated with seismic design at this month's Facades+ LA conference in a panel on "Anchors & Approvals: Structure and Skin in Seismic Design." In addition to Ingraffea (Hershberg will moderate), panelists include Dana Nelson (Smith-Emery) and Diana Navarro (California OSHPD). "A tremendous amount of time has been spent to increase the safety of building structures in seismic events through continual updates of the code, but very little work has been done to understand the behavior of facade systems in seismic events," noted Ingraffea. "This is a shame since the value of the facade system could be just as high as the value of the structure itself, and failure of either one could be catastrophic. This is a great opportunity for someone who wants to invest the time to modernize the code." In the meantime, designers, engineers, fabricators, and builders are left without "a well thought out design standard for seismic design of facade systems," said Ingraffea. The ASCE 7 contains only half a page on the topic. Worse still, the relevant text is "on one hand, very basic (one equation to check) and on the other hand overly onerous (dynamic racking tests), and they really do not apply to many modern facade systems," he said. As a result, building envelope design teams must tackle the issue of seismic design on a case-by case basis. "'Industry standard' is a term you hear a lot when you do a lot of facade engineering but from what I've seen the [seismic design] 'standard' is all over the board,'" said Ingraffea. In practical terms, a lack of data or guidance on seismic activity and building skins can cost precious time and money. "Most of the challenges we see with facade design in seismic hot spots are due to the amount of movement that can occur in a building system during a seismic event," explained Hershberg. "We service many clients who want to use new facade concepts or products that may have been developed overseas, and many times the products haven't been tested to determine the range of seismic movement that they can accommodate." The design team is thus forced to perform a series of qualification tests. "This introduces an additional set of schedule risks that are sometimes overlooked," said Hershberg. Learn more about the ins and outs of seismic design at Facades+ LA. Check out a full conference agenda and register for lab or dialog workshops today on the conference website.