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From CAD User AEC Magazine Vol 20 No 05 - MAY/JUNE 2007
Do you need 3D for Civil Design? Mike Barkasi of Bentley Europe puts the case forward for civil engineers to move up to 3D
Recent talk of 3D civil design has left many site designers and engineers scrambling to implement new technology. A quick look at discussion groups focusing on these topics may leave us wondering if this "new" way of designing can carry benefits to outweigh the cost of execution.
Before we begin to look ahead any further, we would do well to look at where we have come from. Several years ago, while working as a small municipal consultant, I came across a set of land development plans from the early 1980s. The plans were typical of a submittal for review from that era. The plan set was completed entirely by hand. It included the contours hand drafted at 5' intervals. The notations showed signs of a skilled draftsman whose style beautifully depicted a unique font, one developed over years of applying his skills at a drafting table. Also of note was the simplicity of the plan set. A similar site today would require 4 to 5 times the detail to satisfy current requirements.
While CAD (Computer Aided Drafting) had its beginnings on mainframe computers and dates back prior to 1970, CAD for PC was just making its presence felt around the same time the plan mentioned above was being drafted. Two of the major players in the civil design market were getting their start in the early 1980s. AutoCAD shipped its first releases in December of 1982 and Microstation introduced Dgn in 1985. While Bentley has been widely accepted as the standard for transportation, AutoCAD has won acceptance within the site design arena.
Civil transportation designers have been successfully working with true engineering software for years with Bentleys Inroads and GEOPAK. Designers accepted these solutions because they were able to continue to work in plan view just as they had when drafting by hand. However the ability to have a 3D tin, store geometry in COGO (coordinate geometry), and then reference this Z component gave the designers powerful tools. This same ability was also a benefit to civil site designers using LDT.
Since the early 80’s, regulations placed on land development have become
more restrictive. Topics such as storm water control, BMP (Best Management Practices),
wetlands regulations, DEP controls and restrictive planning commissions as Municipalities
expand beyond their earlier boundaries, have placed more demand on what we need
from our civil design tools.
At a time when interoperability in this area (land development, site design) should be at a premium, some CAD companies continue to force retirement and continue to change file formats at will, causing discontinuity, not only within add on applications, but also within their own format.
Sharing of this data requires software to be compatible with multiple CAD formats and other standards such as PDF. 3D can reap benefits, but being forced to design complex site elements a vertice at a time can become a frustrating experience.
Successfully modeling site objects such as intersections, cul-de-sacs, ponds, channels roads, etc. requires powerful element manipulation tools such as the tool sets in PowerCivil. With storm water regulations at a premium, retention pond design requires a tool that can create a pond to a specified volume or water elevation.
Additionally, because of the ever-changing nature of site plans, the pond (and other objects) may need to be relocated or reshaped and interact with other site objects in order to address client and municipal change requests.
Hydraulic design and analysis, with the ability to reference a dynamic model, such as the solutions offered in PowerCivil, give a designer the ability to create interactive models. The software can further save time by allowing parameters for design such as minimum and maximum depth of pipe. The ability to size the pipe according to the drainage area, creating reports and showing the HGL (Hydraulic Grade Line) can further save time in design.
Another example that illustrates how you can leverage the model is shown in parking lot design, providing the ability to hold a constant slope in relation to a building pad. If the pad is elevated, the parking lot also adjusts to hold ADA requirements for access. Storm water component preferences such as time of concentration, slope, drainage areas and rim elevations, referenced from the same model, would also automatically update.
With the implementation of a Site Model we can also address BMP by modelling out grading to divert water overland prior to storing. The ability to create islands or wetlands within ponds, or create roadside swales to collect water as an alternative to catch basins can also be, effectively, introduced into a model.
This gives designers the ability to view their grading objects as they are created and review the site for potential conflicts that may not have otherwise appeared until the construction process. 3D objects provide immediate visual feedback to the designer over the complete area of the design - unlike cross sections that only show the interaction between the design surface and the existing surface at specific locations.
Finally, the site designer needs the ability to quantify the proposed improvements. Most packages have the ability to balance cut and fill on a site. The ability of the software to track quantities of pavement, pipe, trenches, structures, and landscape items can save countless hours and should be a must. While land development and site design will continue to challenge civil engineers and designers, these tools should not only add productivity but also quality to their work. But don't get rid of your drafting table yet - you still need a workspace for your notebook computer. When you get tired of staring at the screen you can change your focus to the table and reminisce about where you came from.
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