Date: July 1, 2014
Source: Purdue University
Summary: Researchers have developed a new design for the framework of columns and beams that support bridges, called ‘bents,’ to improve performance for better resistance to earthquakes, less damage and faster on-site construction.


Researchers have developed a new design for the framework of columns and beams that support bridges, called “bents,” to improve performance for better resistance to earthquakes, less damage and faster on-site construction.

The faster construction is achieved by pre-fabricating the columns and beams off-site and shipping them to the site, where they are erected and connected quickly.

“The design of reinforced concrete bridges in seismic regions has changed little since the mid-1970s,” said John Stanton, a professor in the Department of Civil and Environmental Engineering at the University of Washington, Seattle, who developed the concept underlying the new design. The team members include professor Marc Eberhard and graduate research assistants Travis Thonstad and Olafur Haraldsson from the University of Washington; and professor David Sanders and graduate research assistant Islam Mantawy from the University of Nevada, Reno.

Research findings are included in a paper being presented during Quake Summit 2014, the annual meeting for the National Science Foundation’s George E. Brown, Jr. Network for Earthquake Engineering Simulation, a shared network of laboratories based at Purdue University. This year’s summit is part of the 10th U.S. National Conference on Earthquake Engineering on July 21-25 in Anchorage, Alaska.

Until now the majority of bridge bents have been made using concrete that is cast in place, but that approach means time is needed for the concrete to gain strength before the next piece can be added. Pre-fabricating the pieces ahead of time eliminates this requirement, speeding on-site construction and reducing traffic delays.

“However, pre-fabricating means the pieces need to be connected on-site, and therein lies a major difficulty,” Stanton said. “It is hard enough to design connections that can survive earthquake shaking, or to design them so that they can be easily assembled, but to do both at once is a real challenge.”

Moreover, the researchers have achieved this goal using only common construction materials, which should smooth the way for owners and contractors to accept the new approach, he said.

An important feature of the new system is that the columns are pre-tensioned.

“A good analogy is to think of a series of a child’s wooden building blocks, each with a hole through it,” Stanton said. “Stack them on top of one another, put a rubber band through the central hole, stretch it tight and anchor it at each end. The rubber band keeps the blocks squeezed together. Now stand the assembly of blocks up on its end and you have a pre-tensioned column. If the bottom of the column is attached to a foundation block, you can push the top sideways, as would an earthquake, but the rubber band just snaps the column back upright when you let go.”

This “re-centering” action is important because it ensures that, directly after an earthquake, the bridge columns are vertical and not leaning over at an angle. This means that the bridge can be used by emergency vehicles in the critical moments immediately following the earthquake.

“Of course, the real bridge columns do not contain rubber bands, but very high-strength steel cables are used to achieve the same behavior,” Stanton said.

To keep the site operations as simple as possible, those cables are stressed and embedded in the concrete at the plant where the columns are fabricated. The columns also contain some conventional rebar, which is also installed in the fabrication plant.

The technology was pioneered in the building industry in the 1990s but is now being adapted for use with bridges.

When the columns rock during an earthquake, they experience high local stresses at the points of contact, and without special measures the concrete there would crush. To counteract this possibility, the researchers protected the ends of the columns with short steel tubes, or “jackets,” that confine the concrete, not unlike the hoops of a barrel, or the steel cap that ranchers use to protect the top of a fence-post while driving it into the ground.

“Cyclic tests of the critical connections have demonstrated that the system can deform during strong earthquakes and then bounce back to vertical with minimal damage,” Stanton said.

Those tests were conducted on individual connections by graduate assistants Olafur Haraldsson, Jeffrey Schaefer and Bryan Kennedy. In July, the team will test a complete bridge built with the system. The test will be conducted at 25 percent of full-scale on the earthquake-shaking tables at a facility at the University of Nevada, Reno. The facility is part of NEES.

Travis Thonstad led the design and built the components for that test. The column and cap beam components were then shipped to the University of Nevada, Reno, where Islam Mantawy is leading the construction of the bridge. The team from Washington and Nevada will be processing the data from this project, and it will be archived and made available to the public through NEES.

The Quake Summit paper was authored jointly by the team. The research was supported by the NSF, the Pacific Earthquake Engineering Research (PEER) Center and the Valle Foundation of the University of Washington.

Story Source:

The above story is based on materials provided by Purdue University. The original article was written by Emil Venere. Note: Materials may be edited for content and length.


Roy Fallon, chief operator of the wastewater treatment plant at the village of Tequesta in Palm Beach County, Fla., said that after the company installed two reverse osmosis (RO) systems in 2000, it was more than eight years before the membranes needed to be cleaned. Naturally, after using an RO system for eight years to desalinate a water supply — and never cleaning it even once — one might assume that the build-up of dirt and slime would be more than even a hazmat team could stomach.

But that’s not the case at Tequesta.

“From my experience, even with a relatively clean water source, when you hit six or seven years with one of these systems, you’ve typically gone through multiple cleanings and you’re even thinking about replacing the membranes,” said Fallon, who is responsible for managing all phases of water treatment at the plant, including maintenance, water quality control, and laboratory safety. “We’ve recently passed eight years since we installed the reverse osmosis systems, and we haven’t had to clean them once.”

Located at the very northern end of Palm Beach County, the water treatment plant in the village of Tequesta serves 5,000 water customers, including residents of Tequesta, Jupiter Village, and Jupiter Island, as well as a number of residents from unincorporated areas of Palm Beach and Martin counties. Based on the performance of the RO systems, which have increased the capacity of the plant to more than 5 million gallons per day (mgd) of potable water, Tequesta now enjoys complete water supply autonomy.

A salty situation
In the early 1980s, the local water management district discovered a significant amount of salt water intrusion occurring in the shallow aquifer (100 feet deep) from which the Tequesta water treatment plant was extracting its water supply. This salt water intrusion subsequently entered the village’s wells.

Because of the unwanted movement of the saltwater/freshwater interface, and to prevent more intrusion, the water management district implemented restrictions on the amount of water the plant could extract from the upper aquifer. Consequently, Tequesta officials developed a plan to draw water from a much deeper aquifer (2,000 feet deep). Because there were no restrictions on the deeper water supply — a supply that was far more abundant — the amount of water the plant needed to take from the upper aquifer was greatly reduced, alleviating the saltwater intrusion dilemma.

Unfortunately, this seemingly perfect solution had a downside: The water in the deeper aquifer was far more brackish, with a much higher salt content. This meant that while the aquifer itself would not be subject to salt water intrusion, water would require desalination before it was suitable for consumer use. Water from the upper aquifer had been treated using a standard aeration filtration system to remove iron and was then subsequently chlorinated. However, since the water from the upper aquifer was much purer, it did not require the level of treatment that deeper water would. Thus, the existing system had not been designed to provide the desalination that the deeper aquifer demanded.

Selecting a solution
Eager to identify a suitable solution, Tequesta officials solicited bids from a variety of engineering firms. The winning bid was ultimately submitted by Arcadis Engineering and the firm was contracted to design a new plant and recommend all of the requisite equipment.

“We were certainly aware of the kinds of processes available for a project of this type, such as electrodialysis reversal and ion exchange,” said William D. Reese, now vice president of Arcadis, a multi-disciplinary, international engineering firm headquartered in Denver. “But we didn’t try to go against the grain in terms of where the industry was headed. We were confident that a membrane-type process, specifically reverse osmosis, would be the optimal approach.”

For Reese, choosing Koch Membrane Systems (KMS) was relatively simple. About 10 years before the Tequesta job was initiated, he had worked with KMS on a membrane project for the village of Wellington, also in Palm Beach County.

“The Wellington project really demonstrated what Koch Membrane Systems was capable of,” Reese said. “It showed me the scope of what the company could do, not only with the membranes that they manufactured, but with the company’s overall expertise in water treatment and desalination.”

In late 1997, design of the facility that would include the RO systems commenced. A concrete block structure was conceived that would blend in with the architectural landscape of the village. And since there is a fair amount of noise associated with the pumps that feed the membrane process, they are housed in a different room, creating a far more comfortable operating environment when maintenance on the membranes is required.

How it works
The facility was built to house a maximum of three, 1.2-mgd RO trains, for a total capacity of 3.6 mgd. Currently there are two installed trains — the second one was commissioned in 2007. Both trains use the KMS MAGNUM 8060-HR-575 elements. After the water is pumped from the newer, deeper water source, booster pumps increase the pressure to provide the proper operating pressure for pre-treatment with sulphuric acid to keep the pH low. The lower pH helps keep the hydrogen sulfide gas in the well-water throughout the process. An anti-scalant is then added to prevent the formation of carbonates, after which the water travels through a pre-filter (one micron), before going to the high-pressure pump that increases the pressure to the RO membranes.

Once at high pressure, about 276 pounds per square inch (psi), the water is forced through the semi-permeable membranes to separate the impurities; the filtered water, or permeate, passes through the membrane and the concentrate is sent to waste and discharged. The permeate from the RO is pumped to the clearwell, or finished water tank, where it’s mixed with the 2.74 mgd of water still being drawn from the upper aquifer and going through a filtered system. The entire mix is then treated via the older filtration process, then goes into a clearwell.

The entire water treatment system is fully treated with chlorine and computer-driven; any out-of-range conditions are immediately communicated to plant operators for remediation or shutdown. This RO permeate is a very high-quality water, more like a distilled water, which makes it an excellent complement to the older water source.

“Combining the two water sources produces a perfect blend,” Reese said. “The older source comes out with a couple hundred parts per million of calcium hardness, which helps improve the taste. By blending it with the newer source, we still have enough calcium for taste concerns, but overall it’s a purer end product. And with [more than] 5.1 mgd of total capacity, we’re more than satisfying the needs of our customers, even in times of peak demand.”

Exceptional results
“There are a lot of factors that enter into how the system performs, not the least of which is the design of the wells and all the ancillary equipment,” Fallon explained. “But there’s no doubt that the RO system has done everything we had hoped it would. They’ve been almost maintenance free, which has saved us substantial dollars in labor costs. And of course, we’re now producing a higher-quality product than we were before the system was built.”

And how about the fact that the membranes remained so clean for so long?

“It’s time to clean membranes when either the feed pressure increases 10 percent or more from its original set point, or if when you hold the pressure constant, the production drops by 10 percent,” Reese said. “After eight years, we were just hitting the point where the feed pressures were bouncing slightly above 10 percent higher than they were at the original start of the plant. Maintaining your production within 10 percent for this long is not what I’ve experienced at other facilities.”

In the final analysis, the KMS RO systems used by the village of Tequesta have performed almost flawlessly, requiring little maintenance, and needing no cleaning until they passed their eighth birthday.

The village of Tequesta water treatment facility was built to house a maximum of three, 1.2-million gallon per day (mgd) reverse osmosis trains, for a total capacity of 3.6 mgd.

This article was provided by Koch Membrane Systems.