Tag Archives: Construction

New Project: Creating a Tool to Estimate Bridge Construction Time and Costs

MnDOT recently executed a contract with WSB & Associates Inc. to begin work on a research project titled “Bridge Construction Time and Costs.”

The research project will help the State of Minnesota’s Bridge Office develop a guidance document and a tool for bridge construction time estimation to be used by MnDOT District project managers and construction staff. The tool will provide a range of production rates based on specific design criteria, being more concise based on the level of information available and will aid in evaluating the potential benefit for accelerated bridge construction (ABC) techniques.

“This research will enable District project managers, who may not have bridge knowledge or background, to complete project planning and scoping more effectively,” said Paul Johns of MnDOT’s Office of Construction and Innovative Contracting.

Mike Rief of WSB & Associates will serve as the project’s principal investigator. Johns will serve as technical liaison.

According to the initial work plan, the project is scheduled to be completed by early March 2018, and WSB & Associates will complete the following tasks:

  1. Conduct an existing practices literature review of current departments of transportation processes around the United States for bridge time and cost estimation.
  2. Review and compile actual case study bridge construction production rates and cost data for major bridge components from state-provided diaries, schedules and bridge plans.
  3. Evaluate and select the best software format and style for a bridge construction time estimation tool. Load state case study production rate data into estimation tool and run validation using bridges currently under construction.
  4. Produce a research report summarizing the literature review on best practices. Produce a user guide for bridge time estimation tool and training presentation.
  5. An optional task, if the budget allows, will include the development of a cost estimating tool. Cost estimation data would be gathered from the literature review and case study analysis during the development of bridge construction time estimation tool for efficiency.

New work-zone warning app featured on KARE 11

A new app that sends warning messages to drivers as they approach work zones was featured on KARE 11 News on Thursday. The app was developed by U of M researchers in a project sponsored by MnDOT.

The story aired as part of KARE 11’s #eyesUP campaign to end distracted driving.

The app works by pairing with Bluetooth low-energy tags placed in work zones, triggering audio warnings in smartphones that are within their range. This allows drivers to get a warning message without having to look down at their phones—or at warning devices such as changeable message signs outside their vehicles. And if a driver is being distracted by their phone, the app will interrupt whatever they are doing to provide a warning that a work zone is up ahead.

U of M researchers Chen-Fu Liao and Nichole Morris, who worked on the project, are interviewed in the story, along with Ken Johnson, work-zone, pavement marking, and traffic devices engineer at MnDOT.

Work-zone warnings could soon be delivered to your smartphone

Imagine that you’re driving to work as usual when your smartphone announces, “Caution, you are approaching an active work zone.” You slow down and soon spot orange barrels and highway workers on the road shoulder. Thanks to a new app being developed by University of Minnesota researchers, this scenario is on its way to becoming reality.

“Drivers often rely on signs along the roadway to be cautious and slow down as they approach a work zone. However, most work-zone crashes are caused by drivers not paying attention,” says Chen-Fu Liao, senior systems engineer at the U’s Minnesota Traffic Observatory. “That’s why we are working to design and test an in-vehicle work-zone alert system that announces additional messages through the driver’s smartphone or the vehicle’s infotainment system.”

As part of the project, sponsored by MnDOT, Liao and his team investigated the use of inexpensive Bluetooth low-energy (BLE) tags to provide in-vehicle warning messages. The BLE tags were programmed to trigger spoken messages in smartphones within range of the tags, which were placed on construction barrels or lampposts ahead of a work zone.

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The researchers also developed two applications for the project. First, they designed a smartphone app to trigger the audio-visual messages in vehicle-mounted smartphones entering the range of the BLE work-zone tags. A second app allows work-zone contractors to update messages associated with the BLE tags remotely, in real time, to provide information on current conditions such as workers on site, changes in traffic, or hazards in the environment.

Field tests proved the system works. “We found that while traveling at 70 miles per hour, our app is able to successfully detect a long-range BLE tag placed more than 400 feet away on a traffic barrel on the roadway shoulder,” Liao says. “We also confirmed the system works under a variety of conditions, including heavy traffic and inclement weather.”

“This was a proof of concept that showed that smartphones can receive Bluetooth signals at highway speeds and deliver messages to drivers,” says Ken Johnson, work-zone, pavement marking, and traffic devices engineer at MnDOT. “Future research will look into how we should implement and maintain a driver alert system.”

This future work includes using the results of a human factors study currently under way at the U’s HumanFIRST Laboratory to create recommendations for the in-vehicle message phrasing and structure. Then, researchers plan to conduct a pilot implementation with multiple participants to further evaluate the system’s effectiveness.

According to MnDOT, another phase of the project may investigate how to effectively maintain the BLE tag database. This phase could also investigate implementation options, such as how MnDOT can encourage drivers to download and use the app.

Behind the bridge slide: dish soap and a lot of planning

Using Dawn dish soap to grease the rails, MnDOT crews inched the new Larpenteur Avenue Bridge into place two weeks ago using an innovative construction method.

As the bridge reopens to traffic tonight over I-35E, MnDOT celebrates the success of its first slide-in place bridge construction.

“The slide-in worked very well,” said David Herzog, MnDOT’s project manager for the I-35E Corridor – MnPass Project. “I think the process has given us the confidence to possibly use it again in the future.”

Slide-in technology

The slide-in method has been used in the past for railroad bridges and large bridges with high traffic and limited construction options. Now, state agencies and the Federal Highway Administration are applying the method to smaller, more routine bridges to minimize impacts to the traveling public.

Whereas the typical phased construction of a bridge builds one-half of the structure at a time, slide-in bridge technology allows the entire superstructure to be built at once, requiring just a brief, temporary closure of the highway.

Crews constructed the 3.5-million-pound Larpenteur Bridge right next to the existing bridge and then slowly slid it into place during the course of two nights. This effectively sped up construction from 110 days to 47 and reduced traffic impacts to drivers. (Watch video of the slide.)

The quality of the bridge also improves with this method, since it eliminates the deck construction joints and girder camber problems associated with phased construction, according to the FHWA. The pressure to use faster concrete cure times is also reduced.

History

With a quarter of the nation’s bridges in need of repair or replacement, the FHWA is pushing the slide-in method as a cost-effective technique that can cut construction time in half. It has previously been used in Oregon, Utah, Missouri, Michigan, Colorado and Massachusetts.

The concept has been around for more than a century, but slide-in technology is relatively new for small or medium-sized bridges, and it’s the first time MnDOT has attempted it on a state bridge.

Although MnDOT staff had flown out to Utah to view a slide-in, it was Burnsville-based Ames Construction that proposed reconstructing the Larpenteur Avenue bridge that way when it made its successful bid for the corridor project.

The slide-in method is about 15 percent more expensive, Herzog said, but it allowed the bridge to re-open in 47 days, versus 110 days.

Earlier this summer, Ames replaced the Wheelock Parkway and Arlington Avenue bridges in conventional fashion, although they were only closed for 65 days because they were constructed on a very accelerated timetable.

“Larpenteur is more of a major thoroughfare and we thought shortening the duration of its closure would be more valuable to  MnDOT,” said Steve McPherson of Ames Construction, who was brought in from Utah to oversee the corridor project.

The fast reconstructions will allow the company to complete the bridge replacements and highway reconstruction in just 120 days. Next year it’ll finish the other half of the corridor.

All three bridges are being replaced to make room for the new MnPASS lane on I-35E.

One of the drawbacks to slide-in technology is that it requires ample room to build the bridge on-site. An alternative is to construct off-site.

The new Maryland Avenue/I-35E bridge was built off-site, as was the Hastings Hwy. 61 bridge. It was then loaded onto a barge, floated down the Mississippi River and lifted into place.

Related Resources

Video: 3D Technology Enhances Underwater Bridge Inspection

A new technology that uses 3D-imaging sonar will enable MnDOT engineers to visualize the substructure of a bridge in a way they never have before.

Until now, MnDOT has relied on human divers and depth finders to identify problems beneath the water.

Divers are limited by what they can see and feel in murky waters, however, and depth finders can only look down, not around.

“With this new technology, we will be able to provide high resolution three-dimensional images of underwater areas, structures and objects to show what is occurring, regardless of water clarity,” said MnDOT Bridge Waterway Engineer Petra DeWall, who has received funding from MnDOT’s Transportation Research Innovation Group to purchase the equipment.

Video imagery from a sonar inspection of Minneapolis’ Third Avenue bridge is above.

Currently, MnDOT hires engineer divers to physically inspect about 500 bridges every five years. They look for cracked concrete, exposed reinforcement and other detrimental conditions.

Although divers can spot issues, they can’t always thoroughly assess the scope of a problem, such as the amount of sediment being washed out around a bridge pier, a problem called bridge scour.

It can also be difficult — or dangerous — for divers to venture down for an inspection.

This was the situation last winter with the Third Avenue Bridge in downtown Minneapolis, where the streambed has degraded around a bridge pier, causing erosion to the pier.

“The Third Avenue inspection was not totally detailed. We knew there was a void under the bridge, but it was very hard to visualize,” DeWall said.

Early ice build-up halted further inspection in November, so MnDOT asked 3D sonar scanner manufacturer Teledyne BlueView to scan the area as a demonstration of its equipment.

A video of the inspection is below:

Multiple holes were cut in the ice sheet to deploy the sonar, which provided an image of the bridge scour by emitting sound-waves that created a point cloud.

“It gives you a large data set of where the sound reaches and comes back to the equipment,” DeWall explained.

The 3D image provides a level of detail that will enable repair and construction contractors to make more accurate bids, saving MnDOT money on projects.

Although dive inspectors are also beginning to invest in this new technology, MnDOT wants its own equipment to perform quick assessments of troublesome spots without going through the lengthy contracting process.

The Federal Highway Administration is conducting a pooled fund study to see if the technology eliminates the need for dive inspectors all-together.

MnDOT also plans to use its 3D scanning sonar to inspect repair projects and assess bridge construction.

One of DeWall’s first goals is to take a scan of the Hastings bridge after construction is complete, which will provide a baseline scan that can be compared against future inspections. The old bridge has had problems with the loss of rocks at its piers. It is unclear if the rock just sinks or is washed away downstream. Monitoring will let MnDOT see what is happening over time.

“Inspection is just one part of it,” DeWall said of the sonar equipment. “The big interest in this project is coming from our construction folks.”

Post-Construction

Imagine building a new house and not being able to complete the final walk-through.

This is the situation that transportation departments face when they build a new bridge, due to the limitations of underwater inspections.

“With 3D technology, you can go back afterward and check to make sure things were done the way they were supposed to,” DeWall said.

DeWall wishes the state had the scanner many years ago when a bridge was built that required expensive correction.

A bridge construction crew left construction material behind under the water, which wasn’t discovered until the redirected water flow caused significant erosion to the bridge pier.

Divers picked up that something was going on during a routine inspection, but engineers still had to bring in depth finders to get a better look. Due to the water current, they were limited in how close they could get to the bridge pier, and turbulence crashed their boat against the pier, damaging the transducer.

Not only would this 3D technology have provided a more thorough assessment than the depth finder, it also could have captured the imagery from a safe distance away.

New LRRB videos focus on work zone safety

The Minnesota Local Road Research Board is a major source of funding for transportation research in the state. Occasionally, it also produces educational videos designed to raise public awareness of important transportation topics.

Two new video offerings from the LRRB (embedded above and below) are focused on save driving in work zones. While not directly research-related, they might prove a useful resource to transportation professionals. More importantly, they serve to remind us all of the very real and dramatic consequences of work zone crashes, of which there are approximately 2,000 per year in Minnesota.

You might want to also check out some of their other recent YouTube offerings, including explanations of why we need stop signs and speed limits, as well as a fascinating look at how potholes are patched.

What happens when you incentivize transit use during construction projects

In 2010, MnDOT began a three-year long, $67 million repair and upgrade project on I-35 in Duluth. Dubbed the “Mega Project,” it created a serious disruption for Duluth-area commuters. To help mitigate the impact, the Duluth Transit Authority stepped up its bus services, offering free rides in newly established bus-only express lanes as well as access to new park-and-ride lots and various other enticements. Perhaps not surprisingly, many area residents took advantage of their new transit options to avoid construction-related travel delays. But what’s really interesting is what happened after the construction ended.

As described in a recently published MnDOT/University of Minnesota study, commuters who started taking the bus to avoid traffic caused by the construction ended up continuing to ride the bus even after the construction ended. Researchers surveyed riders during and after the 2010 and 2011 construction seasons and found that, even after bus fares went back to normal levels, only 15 percent of the new bus users switched back to driving. Researchers concluded that once riders developed a habit of using transit, the habit tended to stick.

The report author sums up the phenomenon quite nicely in her executive summary:

Human beings are creatures of habit. Most of us travel the same route every day to the same destination. Sometimes, however, something comes along to push us to examine our habits and possibly change them. A major highway construction project can be such an event. (…) This provides a very good opportunity to examine our travel patterns and possibly change our habitual modes.

Of course, this change didn’t just happen on its own. As the technical summary notes, the DTA marketed its services aggressively during this period. (The above photo is just one example.) The study also noted that the elimination of expanded bus services in the winter had a negative impact on ridership.

Read more:

Geotextile research at MnROAD

Geotextiles are synthetic polymer materials used to improve the performance of roadways. As discussed in this 2011 technical summary, geotextiles facilitate filtration and water drainage, improve the integrity and functioning of base materials, and provide a stable construction platform over soft or wet soils. These improvements can benefit both the cost-efficiency and longevity of pavements.

Geosynthetic materials have been used throughout Minnesota, and can be found in both reconstructed and new roadway projects. The use of geotextiles as a separator layer under concrete overlays, however, has had limited documentation in Minnesota and other cold weather climates. MnROAD‘s recent dedication of several test cells to this purpose will determine the performance of this application of geotextiles, with the goal of improving its applications on other Minnesota roadways.

The new test sections, designated as Cells 140 and 240, consist of a very thin, 3-inch concrete overlay over an existing 7-inch concrete pavement constructed 20 years ago. Some unique features of the design include the use of a fiber-reinforced concrete mix, two different thicknesses of the nonwoven geotextile, and the use of a special type of glue, rather than nails, to fasten it to the existing concrete before paving.

The fabric and fiber used in the concrete mix were supplied through a public-private partnership with Propex Geotextile Systems. The results of this study, along with other unbonded overlays constructed at MnROAD and around the country, will be incorporated into a new national pooled fund project — TPF 5-(269) — led by MnDOT. This project will develop an improved mechanistic design procedure for unbonded overlays.

A second application being demonstrated at MnROAD is the use of a geosynthetic drainage system under several dowel bar baskets in new concrete pavement test section. Minnesota has historically used a dense-graded base layer under concrete pavements to provide a stable foundation and construction platform. However, this material drains very slowly, and traps moisture within the joints, leading eventually to significant distress (See Effect of Drainage on the Performance of Concrete Pavement Joints in Minnesota.) This application will compare the use of the geotextile drainage material placed under both sealed and unsealed joints, as well as a control joint without the drainage material.