Aashto 1998 Pavement Design Software Free Download

By Danny Gierhart, P.E.

How thick should I specify the asphalt on my projection, considering the number and types of traffic loads I look, and the support I think the subgrade will provide?" That is the basic question posed by engineers who want their pavement to last a long time, and in expert condition.

Pavement thickness designs are too ofttimes based on economics — how thick can the pavement be built with the dollars available for the project, regardless of the engineering realities. Or they are simply empirically-based — what has been observed to perform under similar conditions earlier.

In the late 1950s and early 1960s, a large-scale experiment was performed by the American Association of Highway Officials (AASHO). Vi pavement loops, consisting of several unlike pavement cantankerous sections, were continuously loaded to try to simulate a lifetime of fatigue in just a couple of years. The same level of traffic caused differing amounts of distress to the different sections. The analysis of the work resulted in a guide that has been used ever since, the AASHTO Guide for Blueprint of Pavement Structures (the "T" for "Transportation" was added in 1973).

One of the strengths of the design process outlined in the guide lies in the fact that fifty-fifty though it is empirically based, decades of feel have demonstrated that the method is adequately rigorous and typically provides reasonable thicknesses as long as the data used to pattern the pavement is reliable.

However, 1 of its weaknesses is that the equations used for pavement assay are very complicated. It took a certain level of training to properly use the nomographs and other tools necessary to brand the calculations. Mechanistically-based pavement thickness design methods are even more complicated to use and take, to appointment, required sophisticated calculator software and more than specialized training. Pavement design engineers in state and federal agencies have the necessary training and resource, merely often urban center, county and private consulting engineers and managers do non.

But what if there was a way to design and document cobblestone pavement thickness hands, that anyone could use? A way that used the accepted methodology of the AASHTO pavement design guide, a manner that was convenient?

Software as a solution

Pavia Systems, with sponsorship from the Asphalt Pavement Alliance (APA) and its constituent members, has developed gratis online pavement thickness design software called PaveXpress.

The software simplifies the process of using both the 1993 AASHTO pattern guide for asphalt pavements and 1998 AASHTO supplement for concrete pavements. The software is brimming with quick help buttons to assist the designer with obtaining and properly inputting the necessary data.

PaveXpress can do much more perform pavement thickness pattern. It contains a module which tin give a elementary cloth cost approximate for the pavement materials. The module is not detailed enough for employ by bidders for contract interpretation purposes, but tin be a tool for agencies and consultants to become a crude thought of pavement material costs.

It contains a module that can analyze a pavement structure using a more than mechanistic type of methodology, which considers the textile backdrop for a given pavement cross department, the predictable stresses induced by the traffic loading and the response locations on the pavement surface and at selected points inside the pavement structure. The user is allowed to select an analysis regarding the type of transfer functions to be used, which results in an estimate of the number of load cycles to failure.

The software developers are currently working on a module which can exist used to estimate life cycle costs. Lifecycle toll analysis (LCCA) is 1 of the tools by which dissimilar pavement structures are evaluated and somewhen selected by pavement owners. The life-bicycle toll of a road includes considerations such as the initial cost of construction of a road, anticipated maintenance costs over its lifetime and the costs to users for their delays during maintenance and reconstruction.

Anticipating traffic

PaveXpress has the ability to estimate a required pavement thickness to support anticipated traffic over a user-defined pattern period utilizing specified materials. The process is accomplished on a step-by-step footing. The designer must select the blazon of pattern to be performed: new full-depth cobblestone, new full-depth concrete, asphalt overlay over existing asphalt or an cobblestone overlay on concrete or composite pavement.

PaveXpress as well requires the designer to select the type of roadway the pavement is being designed for: interstate, regular highways or arterials, local roadways or residential streets. Default values in other areas of the programme are populated based on the type of roadway selected. Withal, whatsoever default value can be hands overridden by the designer when desired.

Next, the designer tin either go on the default blueprint period populated by the roadway type selection or override information technology with a dissimilar pattern flow. The default values for new structure range from 20 years for local and residential streets to 40 years for interstate highways.

The designer can either go along the default value or provide a different estimate of the expected ride quality immediately subsequently construction in the form of a nowadays serviceability index (PSI). The PSI is a subjective measure of ride quality using measurements of roughness and distress, e.m. cracking and patching and rut depth.

In the same way, the designer can either keep the default value or provide a different estimate of the terminal serviceability alphabetize, which is how far the designer will allow the pavement to deteriorate earlier it is considered to be at the cease of its useful service life.

The AASHTO Guide for Design of Pavement Structures requires some statistical values that are used to estimate the probability that the pavement will survive the design flow with a pavement serviceability level greater than the final serviceability level. PaveXpress once again provides reasonable default values for these statistical values, which may be overridden if the designer desires.

Another step requires the designer to provide estimates of the traffic predicted throughout the roadway's design life. Several dissimilar methodologies to estimate the traffic are provided in PaveXpress. These methodologies typically include the use of current traffic volumes, breakdowns of the type of traffic (cars, buses and diverse configurations of trucks) and projected traffic growth rates.

The designer so inputs the layer types (due east.thou. subgrade, aggregate base, asphalt mixture) and fabric layer coefficients. Once again, default values are provided based on the textile type. PaveXpress even provides a link to a National Eye for Asphalt Technology (NCAT) report on asphalt layer coefficients.

Finally, the designer inputs expected resilient modulus values for each layer in the sub-construction. The program provides reasonable defaults, but actual test information or historically-proven values for each layer type are preferable for the greatest accuracy. If the designer is uncertain regarding the numbers, in that location are many documents available which tin provide conviction that the values are "in the ballpark." For case, Cobblestone Institute's IS-91 provides reasonable values for poor, medium and good-to-excellent subgrades for R-values, California Bearing Ratio and resilient modulus.

The program and then calculates the layer thickness(es) for which the average number of expected traffic loads over the design life can exist carried, given the specific statistical, traffic and fabric inputs. The program runs very quickly, assuasive the designer to input a variety of scenarios for the same roadway, which can increase confidence in the final pattern.

In summary, PaveXpress is an unbiased tool for pavement thickness pattern which duplicates the assay of the AASHTO 1993 pavement design guide for asphalt and the 1998 supplement for concrete. It does not unfairly promote one type of material over another, or give unreasonable results for either cobblestone or concrete. The designer needs only to collect the all-time possible project, traffic and material data in order to provide the best accuracy. It is free and easy to employ, making it an ideal tool for those pavement designers without access to larger agency tools and expertise.