CE 441 - The Design Process

The design process is substantially different from the strictly analytical process most students have been exposed to up to this point - enough so that it merits some discussion on its own. Some of the key aspects of the design process include:

Who are you working for?

There are a variety of situations that arise. In most situations, you as a structural engineer will be working for an architect, i.e., the architect has hired you to make sure his/her building will not collapse. This is an interesting relationship, usually fraught with some tension because both of you are professionals, and both of you think you know what is best. It is useful to examine what you both really know and how to communicate that to your "partner."

Engineer

- The engineer knows (or should know)

These are all technical questions that rely on mathematical calculations for answers.

Architect

- The architect should know:

Many of these are "people needs" and are often not quantifiable. However, don't discount their importance, even though they can't be calculated. Paint color may not seem important, but if the client isn't satisfied, the architect's reputation can suffer just as it would if the beams sag.

Because of their emphasis "on people needs" most architects, by training, focus on intuitive processes rather than calculations. In order to work smoothly with them, you will often need to

  1. Educate them about the structural function are requirements.
  2. Use intuitive, physical arguements to persuade them rather than calculations.

Where do you start on a design?

The design process generally proceeds from the general to the specific. There are a variety of reasons for this. First of all, the client doesn't really know what he/she needs except in a general sense, e.g., "I need an office building," or, "I need a warehouse." Secondly, the design of a building is a very complex operation, and many of the specifics cannot be determined until the generalities have been addressed.

Defining the client's needs

As indicated above, one of the first steps is simply defining more clearly the client's needs. These needs might include:

Most of these determinations are made by the architect - often before the structural engineer is brought into the process. For example, questionnaires were circulated around the College of Engineering to determine our needs before the Engineering Physics building was designed.

Conceptual development of project

The next step is still fairly general. Once the architect has determined the client's needs as much as possible, they must prepare conceptual design. These are preliminary - not detailed - designs. They might be simple floor plans, sketches of exterior elevations, and estimates of cost. They provide the client a chance to determine if the architect's plans will meet his/her needs. This may go through several iterations as the client gets a better idea of what the architect plans to do, and what is possible within the budget and time con- straints.

A structural engineer typically becomes involved at this point because the choice of building materials, the layout of floor spans, and the choice of lateral force resisting system all affect the conceptual plans and the cost estimates. Since this involves a good deal of "seat of the pants," and "rule of thumb" information, this phase is typically handled by a partner in the structural engineering firm working as a member of the architect's design team.

This is the point at which you will begin your design projects and like the architect and engineer, you will have to go through several iterations to define the project and determine if your solution really satisfies the "client's" needs. As with the architect or engineer, you will need to bring your preliminary designs to "the client" (me) to determine if they will met the client's needs, and possibly refine your preliminary design through several iterations to arrive at an appropriate solution. Keep a brief journal recording my instructions; I may not provide the same scenario to all groups.

Detailed structural design

Once the basic parameters are determined, construction material, floor plan, lateral force resisting system, the detailed design can begin. This course should provide you with the basic tools for determining material strengths and member sizes, along with many other details required to produce a reasonable economical design.

Evaluation of acceptability

The architect and owner are putting an enormous amount of faith in your abilities as an engineer, because only another engineer is qualified to determine the strutural adequacy of your design in the short term. (Assuming it doesn't fail immediately). On the other hand, some factors are immediately obvious, including:

Appropriateness

Does the structure provide the required floor layout, provide clear spans and sight lines, blend with the aesthetics required by the architect or owner?

Economy

Can the structure be built economically? The architect will have some idea when he/she prepares an estimate. The final measure is the bid price provided by the contractors.

Structural adequacy

Not immediately obvious, and as mentioned, fairly difficult to evaluate. More discussion is provided below.

Maintainability

Some aspects of maintainability may be obvious during the design phase, but some may not. For example, concrete doesn't need to be painted which is obvious from the start. However if cracking is not properly controlled, exterior concrete may experience water infiltration, and corrosion of the reinforce- ment which may not be apparent for years.

Structural adequacy

Structural adequacy involves a variety of criteria, all of which the engineer must consider. The criteria can be divided into two general categories, strength and serviceability. The strength criteria affect the safety of the structure; the serviceabili- ty criteria affect the ability to use the structure efficiently and comfortably.