Monday, November 29, 2010

ENGINEERS TEST EFFECTS OF FIRE ON STEEL STRUCTURES

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Researchers at Purdue University are studying the effects of fire on steel structures, such as buildings and bridges, using a one-of-a-kind heating system and a specialized laboratory for testing large beams and other components.

Building fires may reach temperatures of 1,000 degrees Celsius, or more than 1,800 degrees Fahrenheit, said Amit Varma, a Purdue associate professor of civil engineering who is leading the work.

"At that temperature, exposed steel would take about 25 minutes to lose about 60 percent of its strength and stiffness," he said. "As you keep increasing the temperature of the steel, it becomes softer and weaker."

One project focuses on how a building's steel-and-concrete floor and its connections to the building behave in a fire. Another project concentrates on how fire affects steel columns and a building's frame.

Such testing is customarily conducted inside large furnaces.

"However, in a furnace it is very difficult to heat a specimen while simultaneously applying loads onto the structure to simulate the forces exerted during a building's everyday use," Varma said.

To overcome this limitation, Purdue researchers designed a system made up of heating panels to simulate fire. The panels have electrical coils, like giant toaster ovens, and are placed close to the surface of the specimens. As the system is used to simulate fire, test structures are subjected to forces with hydraulic equipment.

In practice, beams and other steel components in buildings are covered with fireproofing materials to resist the effects of extreme heating.

"Because the steel in buildings is coated with a fireproofing material, the air might be at 1,000 degrees but the steel will be at 300 or 400 degrees," Varma said. "We conduct tests with and without fire protection."

The work is funded by the National Science Foundation and the U.S. Department of Commerce's National Institute of Standards and Technology.

The heating system is being used to test full-scale steel columns at Purdue's Robert L. and Terry L. Bowen Laboratory for Large-Scale Civil Engineering Research. It is believed to be the only such heating system in the world, Varma said.

Each panel is about 4 feet square, and the system contains 25 panels that cover 100 square feet. Having separate panels enables researchers to heat certain portions of specimens, recreating "the heating and cooling path of a fire event," Varma said.

The Bowen Lab is one of a handful of facilities where testing can be performed on full-scale structures to yield more accurate data. The 66,000-square-foot laboratory is equipped with special hydraulic testing equipment and powerful overhead cranes.

The research group also has tested 10-foot-by-10-foot "composite floor systems" - made of steel beams supporting a concrete slab - inside a furnace operated by Michigan State University. The composite design is the most common type of floor system used in steel structures.

Findings from that research will be compared with floor-system testing to be conducted at the Bowen Lab. Results from both experiments will be used to test and verify computational models used to design buildings.

"Most of these experiments are showing that we have good models, and we are using data to benchmark the models and make sure the theory and experiment agree with each other," Varma said.

Models are needed to design composite floor systems, which can be heavily damaged by fire.

"When you have a floor supporting weight, the floor starts sagging from the heat," Varma said. "It expands, but it's got nowhere to go so it starts bowing down, which produces pulling forces on the building's frame. It starts pulling on the columns and then it becomes longer and permanently deformed. After the fire, it starts cooling, and then it starts pulling on the columns even harder."

(Photo: Purdue University/Mark Simons)

Purdue University

THE LIFEBLOOD OF LEAVES: VEIN NETWORKS CONTROL PLANT PATTERNS

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New University of Arizona research indicates that leaf vein patterns correlate with functions such as carbon intake and water use – knowledge that could help scientists better understand the complex carbon cycle that is at the heart of global climate warming.

"Leaves have very different networks of veins. They have different shapes, different sizes, different thicknesses," said Benjamin Blonder, a doctoral student in the department of ecology and evolutionary biology. "The really interesting question is how a leaf with a certain form produces a certain function."

Blonder developed a mathematical model to predict the functions of leaves based on three properties of the vein network: density, distance between veins and number of loops, or enclosed regions of smaller veins much like capillaries in humans.

Vein density reflects how much energy and resources the leaf has invested in the network, while distance between veins shows how well the veins are supplying resources to the leaf. The number of loops is a measure of the leaf's resilience and plays a role in determining its lifespan. If the veins reconnect often and part of the leaf becomes damaged, resources can be circulated through different pathways.

"It's like in a city where there's a roadblock somewhere," said Blonder. "If the city was designed well, you can still take another road to get to where you want to be."

Blonder won the UA Graduate and Professional Student Showcase President's Award for his work, which was published this week online in the journal Ecology Letters.

The vein network inside of a leaf is like most of the important organ systems in a person, Blonder said.

"It's like the skeleton because it holds the whole leaf up and lets it capture sunlight and not get blown over in a windstorm. It's like the circulatory system because it's distributing water from the roots up to all the cells within the leaf, and it's also bringing resources from the leaf back to the rest of the plant after photosynthesis has happened. It's also like a nervous system because there are chemical signals that are transmitted to the leaves from other parts of the plant through the liquid in the veins," he said.

"This is important for the function of the leaf because when this one structure is implicated in so many different patterns, clearly there're going to be tradeoffs between being able to do all of these different functions well," said Blonder. For example, a leaf with a very loopy network of veins might live longer, but it will also cost a lot of carbon, which plants absorb from carbon dioxide in the atmosphere, to develop that vein network.

Blonder's model successfully predicted relationships among photosynthetic rate, lifespan, carbon cost and nitrogen cost for more than 2,500 species worldwide based on global data. But that doesn't mean it will work on a local scale.

To find out, the team tested leaves from 25 plant species on the UA campus. While initial results appear to show that the model will work, the team hasn't tested enough samples to know if it successfully predicts relationships in leaf function on a case-specific basis. More extensive studies will include leaves from species at the Rocky Mountain Biological Laboratory in Colorado.

"If it's successful, we hopefully have a really satisfying way of understanding why leaves look different in different environments – also a useful way of understanding how leaves are functioning in different environments that can be used for climate modeling or for reconstructing past climates from fossils of leaves," said Blonder.

So how do relationships among plant leaf functions impact global carbon levels?

"Carbon can only get into leaves through little pores on the leaf surface, and when carbon comes in, which is something good for the plant, water also comes out," said Blonder. "There's this incredibly tricky tradeoff for all plants where they need to gain carbon to make energy, but to gain that carbon they lose a lot of water in the process. So if you want to gain more carbon, you have to lose more water."

Plants with denser vein networks – veins that are closer together – are able to withstand higher levels of water loss and absorb more carbon. Unfortunately, that doesn't mean you should plant trees with dense leaf vein networks if you want to save the planet.

"It becomes a little bit more difficult to scale up beyond there because a plant is not only just its leaves: It's also the trunk and the roots and so on," said Blonder. "The important thing to think about is that other parts of the plant are going to be contributing to the carbon cycle also in terms of decomposition or other large-scale environmental effects."

"Carbon flux from plants is critical to understanding global change and the global carbon cycle," said Blonder. "What we're hoping to be able to do is understand the leaf side of the picture, but there's clearly a lot more to plants and the environment than that. So this is not the answer to every environmental question but it's a good start because leaves are the site of photosynthesis and carbon flux, and it's certainly necessary to understand those before you can understand plants in general."

Blonder hopes to use his model to develop more comprehensive climate models that take plants into account and to better understand past climates. Blonder's model could play an important role in understanding plant ecology, global carbon cycling and other environmental processes in the future.

(Photo: Tuan Cao)

University of Arizona

BODY CLOCK CONTROLS HOW BODY BURNS FAT

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UC Irvine researchers have discovered that circadian rhythms — the internal body clock — regulate fat metabolism. This helps explain why people burn fat more efficiently at certain times of day and could lead to new pharmaceuticals for obesity, diabetes and energy-related illnesses.

The study was headed by Paolo Sassone-Corsi, Donald Bren Professor and chair of pharmacology. A leading expert on circadian rhythms, he discovered many of the key molecular switches governing these biological processes. He and his colleagues found that one of these, a protein called PER2, directly controls PPAR-gamma, a protein essential for lipid metabolism. Since circadian proteins are activated by 24-hour, light-dark patterns, PER2 turns on and off PPAR-gamma’s metabolic capabilities at regular intervals.

“What surprised us most, though, is that PER2 targets one specific amino acid on the surface of the PPAR-gamma molecule,” Sassone-Corsi said. “This kind of specificity is very rare in cell biology, which makes it exciting, because it presents us with a singular target for drug development.”

Daniele Piomelli, Louise Turner Arnold Chair in Neurosciences at UCI, and Todd Leff, associate professor of pathology at Wayne State University in Detroit, collaborated on the study, which appears this month in Cell Metabolism.

Twenty-four-hour circadian rhythms regulate fundamental biological and physiological processes in almost all organisms. They anticipate environmental changes and adapt certain bodily functions to the appropriate time of day. Disruption of these cycles can profoundly influence human health and has been linked to obesity, diabetes, insomnia, depression, heart disease and cancer.

Last year, Sassone-Corsi helped discover that proteins involved with circadian rhythms and metabolism are intrinsically linked and dependent upon each other to ensure that cells operate properly and remain healthy.

(Photo: Daniel A. Anderson / University Communications)

University of California, Irvine

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