When we set out to write this blog, the intent was not to make it another "CAD" blog, but to create a blog that will help teach or reinforce civil engineering principles that have been taught. This being said when we look at Civil Engineering we can see it is grouped into seven major divisions of engineering: Structural; Environmental; Geotechnical; Water Resources; Transportation; Construction; and Urban Planning. In practice, these are not always hard and fixed categories.
Seven engineering disciplines
A civil engineer working on a land development project could very well make use of all of the above mentioned divisions. Conversely an engineer working on a DOT (Department of transportation) project could also make use of all of these divisions. The question then is what separates the two? How are the projects different?
The difference lies in the breakdown of these divisions. A land development project may spend a greater amount of time in planning than a road project. While certainly the road project will receive its share of planning it will be subject to different constraints when compared to the Land development project.
Because the DOT or road project requires that a road be designed to move traffic as quickly and efficiently as possible from one point to another. Constraints on the project have to have some limits. Planning for these projects will usually be done at a higher level of government. While input from more local levels is given the need to maintain and develop this infrastructure is vital and local objections can be addressed with design features that do not alter the planned road layout.
An example of design features that we would consider secondary to the road way may be wall structures to limit noise from the road to adjoining communities. Access ramps or intersection development along the corridor could be added or removed. Retaining walls, storm water controls, lighting and landscaping are all part of the design that can be altered without gross changes to the planned road alignment.
Land Development
Before we begin comparing our Land development project we may want to decide what type of project we are looking at.
One local Ordinance defines land development as:
From the definition above we could be describing a residential subdivision or a New School.
When we compare our Land development project, we will see the planning is quite different. While the planning is not entirely done at a local level, it is the local government agency that ultimately gives the final approval. This approval will usually require all other approvals such as DEP (Department of Environment Protection) permits and approvals first be obtained.
In addition to local Ordinances most local governments have planning comities to oversee all proposed development in the community.
As a civil designer on these projects the needs of the client or land owner take precedence in the design. Where our DOT project focused on getting people from point A to point B as quickly and efficiently as possible our site design will serve a purpose or invoke an emotion.
Typical Highway design will focus on moving people from point A to point B as quickly and efficiently as possible
The road traveling through a subdivision will often look entirely different from the highway or arterial road leading to the proposed development. Instead our site design road will be constrained by the topography, number of lots or parcels, Ordinance constraints such as prohibitive slopes, wetlands, riparian buffers, planning commissions and the designer's intent.
Once completed the road makes up a minor portion of the site design. Site grading and storm water control are major influences in site design. In the case of commercial site design we have different features or objects that we need to design for.
Parking lot design in itself requires the designer to be aware of the same storm water and grading as above but also the grading of the lot may be constrained by additional requirements such as ADA (Americans Disability Act) requirements, Local regulations governing slope of the lot or entrances onto the site, travel and turning requirements for the vehicles inside the parking lot, and more.
Because of these different requirements we need to ask ourselves if the design tools we use for Transportation and those for site design can be the same and effectively work in either scenario.
Low Impact commercial parking lot design is shown using Islands and plantings. Additional constraints in the form of accessibility, traffic flow, drainage and turning paths factor into the design
Because site design relies so heavily on relationships, the software we use should therefore also be able to create and maintain these relationships. The way we designed in the past did not allow for this "intelligent design".
PowerCivil breaks away from the previous mindset of CAD design into relationship modeling. The software had its beginnings eight years ago as "Site Modeler" developed by Jay Vose of Bentley Systems.
I believe Jay summed it up best in the quote below.
Here are my thoughts - they might be a little random but the seeds of site modeler were sown in the late eighties when I was a frustrated site designer. One thing to realize that since my first engineering job as a engineering tech while still in college I would write programs to help with tedious design concepts - detention ponds, water quality ponds, channels, culverts. The companies never approved of this since it wasn't billable time but I will be damned if I was going sit around and waste time redesigning all these things by hand. Anyway when I was doing one of my last site designs - a small grading, drainage and utility project the architect saw fit to move the buildings 18 times - reposition them, rotate them and changed the footprints. Each time it required me to re grade the site - redo the drainage and move the utilities around to follow the new layout. While doing this I said to myself that one day I would have to fix this - a few primary issues seemed most troublesome:
•1. I spend all this time and applying my engineering expertise to this design and all of its interrelationships and once input into the design packages it was all lost. Any change required reevaluation and recall of the design intent to insure I didn't violate some other required engineering constraint. Most everything was a series of relationships - horizontal and vertical and these are where my engineering experience was useful - not in redoing the design 18 times this was absurd!!!
•2. The plan content had to always be redone or at least checked every time I made a change - one forgotten elevation update and my boss would be buying the asphalt (this actually occurred - I had one old elevation in a pond detail once and it happened to be the one they staked it from so we had to rip the pond and adjacent parking lot out).
•3. Once could tell even back then we were building a 3 model - represented in more archaic fashion back then but it is what was going on. As I watched 3d design packages evolve there seem to be often more focus on the 3d aspect than the actual workflow. In reality site design is a series of horizontal and vertical relationships between features. The process is primarily done in this fashion - we horizontally locate features and then establish vertical relationships - we don't make the horizontal and vertical decisions at the same time so forcing me into a more 3d workflow was less intuitive. I want 3d when I want it. These thoughts led to the easily supported 2d workflow in site modeler and the when needed 3d. I didn't want to have a system that imposed a 3d workflow when it didn't fit my situation.
•4. The other aspect of available design packages, even now, is their reliance or primary focus on the linear and parallel aspect of design. Road products don't make good site products because in the site design world very few things are straight and parallel. Doing the math is easy when things are straight and parallel - that didn't help me as my stuff curves around is irregularly shaped and things like mathematical projections are in many cases impossible. Knots - projection errors and poor planar geometric considerations were the norm in packages that targeted road design - nobody attempted the hard solutions. While I didn't want to do the impossible - you ought to do a better job at solving these situations than the linear solutions provide. Almost nothing in site modeler depends on features be more linear and parallel - it was all targeted to provide the best reasonable solutions between very irregular feature paths.
•5. Design precedence - as I worked on these different design features I could see that some portions were more fixed than others (pavement sections versus slope tie downs) and that certainly the interfaces between them needed to almost float freely to as the backbones changed the interfaces would redo themselves automatically. This is where FIFO came from - determining the design precedence of object and allowing the interfaces to float and update in between them.
How do I add Blogs to a central location for later use? It seems I have to continuously search out Barkasi to find your specific Blogs?