Tag Archives: AASHTO

Concrete Design Software Easier-to-Use, Capabilities Expand

MnDOT has upgraded its concrete pavement design software, MnPAVE-Rigid, to make it easier to use and allow more design inputs.

“In the original software, we only allowed one aggregate base thickness and one aggregate type. MnPAVE-Rigid 2.0 allows two base thicknesses and three base types,” said Tim Andersen, Pavement Design Engineer, MnDOT Office of Materials and Road Research.

MnDOT hired American Engineering Testing to update the design software as part of a research project advised by Andersen and funded by the state research program.

Background

MnDOT developed its own pavement design software, MnPAVE-Rigid, in 2014 that incorporated the methodology of the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic–Empirical Pavement Design Guide (MEPDG). Minnesota’s pavement designers use MnPAVE to apply AASHTO’s most sophisticated design principles for both rigid and flexible pavement, focusing on mechanical properties of the pavement and prevention of early cracking and other distress.

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AASHTO’s mechanistic–empirical (M–E) design methods entail hundreds of inputs, each a mechanical parameter, a measure of site-specific characteristics or a design goal. To simplify the input selection process, AASHTO’s M–E design software offers various input levels to reduce the data gathering and input burden. The most basic level uses default values for most of the inputs based on national averages, but still requires dozens of inputs for the number of pavement layers, traffic expectations, climate and other features.

MnPAVE-Rigid for concrete pavement design reduced that number of inputs to nine, operating like a module of AASHTO’s M–E software. MnPAVE-Rigid inputs work with a set of default values for jointed plain concrete selected by the MnDOT Office of Materials and Road Research in 2014, as described in the MnPAVE-Rigid 1.0 report.

“Many states ignored the challenge of adopting AASHTO M–E or they bought an AASHTO
software license. MnDOT used its accumulated knowledge of AASHTO M–E and Minnesota conditions to build MnPAVE-Rigid, and so can account for its M–E design results firsthand,” said Derek Tompkins, Principal Civil Engineer, American Engineering Testing, Inc.

Since implementing MnPAVE-Rigid 1.0, MnDOT has gathered feedback from users about their experience with the software. In the current project, MnDOT wanted to address this feedback, and expand and improve the original software by exploring additional options with some of the default parameters for concrete pavements.

What Was Our Goal?

The goal of this project was to update MnPAVE-Rigid 1.0 by expanding the range of inputs for traffic, subgrade type, base type and thickness, and to make the user interface more accessible.

What Did We Implement?

MnPAVE-Rigid 2.0 allows users to enter 11 inputs, including inputs related to specific traffic levels and aggregate base types; calculate the new design thickness; and print a project report that summarizes the inputs and the recommended thickness. The upgraded software is more user-friendly, and MnDOT can maintain or make future upgrades to the source code.

How Did We Do It?

Researchers met with the Technical Advisory Panel and reviewed the list of software improvements requested by pavement designers and the MnDOT Office of Materials and Road Research.

Because every change to an input affects a large number of default input variables, investigators ran over 21,000 simulations to analyze the impact of changes made to inputs for base type, base thickness, subgrade type and traffic level. The research team also modified the traffic input calculator to allow designers to enter traffic values from MnDOT’s weigh-in-motion and traffic counting data. The calculator runs input traffic data in software simulations and assigns the input an appropriate axle value for design.

MnPAVE-Rigid 1.0 ran designs based on Class 5 aggregate base over a subgrade like clay loam. Other aggregate types were added to simulations to determine how the software responds to these changes. Investigation also explored the addition of subgrade material options in design simulations.

The code developer modified elements of the advanced inputs tab and PDF report generation features to improve performance for software users, and rebuilt the software in JavaScript 2.0 code, including an installer for use with Windows software.

What Was the Impact?

MnPAVE-Rigid 2.0 is more user-friendly. Its tabs better match designer needs, and the software offers a design report PDF file for export. Instead of selecting from limited options for traffic volumes (default, normal and heavy), users can now input traffic data that the software will categorize. Designers can input Class 5 aggregate, Class 5Q (a higher quality aggregate with fewer fines) and open graded aggregate (no fines). Users can also choose 4-inch or 12-inch aggregate base thicknesses. An additional subgrade option was not included, as simulations indicated a sand subgrade input did not discernibly impact structural thickness outputs.

The AASHTO M–E software is expensive, and agencies that use it have to work closely with consultants to receive training and to explore or modify the code. MnDOT owns and manages the source code for MnPAVE-Rigid 2.0, can keep it secure, and can continue to change and upgrade it internally for Windows and Linux platforms.

What’s Next?

The updated MnPAVE-Rigid is now available online. Presentations about the software upgrades will be made at meetings for materials and soils engineers through the fall of 2018.

Still underway is an effort to further incorporate recycled material properties into MnPAVE Flexible, the design software for asphalt pavement.

This Implementation Summary pertains to Report 2018-17, “MnPAVE-Rigid 2.0,” published May 2018.

MnDOT Develops Best Practices Guide for Culvert Repair (Updated, with Video)

County engineers and MnDOT hydraulics engineers have to wear many hats. One of them is maintaining culverts — the channels beneath roadways that facilitate passage of water and wildlife.

But culvert maintenance is practically a field of knowledge unto itself. To help engineers identify and apply the best repair techniques for specific problems, MnDOT recently produced a best practices guide for culvert repair (links below).

“We wanted to develop a state-of-the practice and put it into one place so engineers could easily find the information they need,” said Lisa Sayler, MnDOT Assistant State Hydraulic Engineer.

It might not always be the most visible or exciting issue from the public’s perspective — although, as the video above illustrates, occasionally it can be very visible — but culvert repair is a critical issue for transportation professionals. In fact, MnDOT submitted the repair guidebook as one of its choices for the AASHTO-RAC’s 2014 high-value research publication.

“There are many different fixes and products available for failing or deteriorating  pipes,” explained District 4 Hydraulics Engineer Jane Butzer, who requested the guidebook. “This guide steps through the different products and practices, and further assists the hydraulics engineer by providing special provisions and standard detail drawings to include in project plans.”

Culvert repair practices have evolved significantly in recent years, so it can be difficult for individual engineers to keep abreast of new practices that come from a wide variety of sources. The guidebook draws from a wide range of sources, including the Federal Highway Administration, the National Cooperative Highway Research Program, AASHTO and numerous state DOTs.

“We synthesized previous work and expanded it from there to provide more details and more quantitative guidance for some specific repairs. We tried to provide more specific design procedures than what we found in previous documents,” said project manager Bruce Wagener of CNA Consulting Engineers.

In addition to providing detailed explanations of rehabilitation and repair methods, the guide includes a table that compares most methods of repair.

Researchers will next conduct a brief feasibility study to identify which culvert repair methods can be observed and tested to document the cost, longevity and effectiveness of repairs.

Sliplining, a common culvert rehabilitation method, involves inserting a fiberglass pipe liner (shown) or other material into a deteriorated culvert.
Sliplining, a common culvert rehabilitation method, involves inserting a fiberglass pipe liner (shown) or other material into a deteriorated culvert.
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