It is very important for novice designers to thoroughly understand the design process, including the steps involved and the time allocated to and spent on performing each step.
Major steps in the design process are
Major steps in the design process are
- schematic (conceptual) design
- detailed (final) design
- development of contract documents
- services during construction
This step involves the identification of project constraints, including cost, building shape, and architectural form, and functional constraints, including column spacing, materials, and serviceability limits. Conceptual design is the most important part of the entire design process. At this stage, the structural engineer has the pivotal role of developing a practical structural concept that strikes the proper balance between the external constraints and the project objectives. To develop a good structural concept, the designer needs to have not only a sound background in reinforced concrete design but also a strong appreciation for the architectural aspects of the project, constructability issues, and the owner's overall design objectives. The final goal is to develop a structural concept that is simple to build, aesthetically pleasing, functionally effective, and affordable to the owner. Once all the design issues have been identified, the designer should be able to make a schematic drawing of the structural system and decide on the general arrangement of structural elements. Further on, the structural designer can estimate gravity and lateral loads and develop trial sizes of key structural members.
This process may require a few iterations before the optimal solution is found. Next, the preliminary concrete outlines to be used for both architectural and structural drawings are developed. Finally, a preliminary construction budget is determined. Depending on the complexity of the project, this phase could take I 0% to 20% of the total time on the project.
Detailed (final) Design
This step involves the detailed analysis, evaluation, and sizing of members and more refined calculation of gravity and lateral loads. At this stage, the designer needs to ensure the safety and serviceability of the structure by carefully following the requirements of pertinent building codes. However, the designer also needs to keep in mind that several external factors may have an adverse effect on the performance and safety of reinforced concrete structures. Whenever possible, the designer should take advantage of available opportunities to increase the structural capacity, that is, to provide a reserve capacity in the structure. In general, reserve capacity may be required to account for construction errors in the field, errors in load estimates, load increases due to design modifications by the owner or architect, change of building use leading to load increase, variations in soil capacities, etc.
The best design solutions involve good judgment based on experience and knowledge, consideration of the economy and construction issues, repetition, simplicity in rebar placements, reduction of potential field errors, etc. A detailed design takes approximately 20% of the total time spent on the project.
Development of Contract Documents
The main focus in this step is to transfer the concept and details from the mind of the designer to those involved in the construction. The contract documents include drawings and specifications. Drawings are a graphical representation of the design, whereas specifications are written descriptions of materials and construction procedures. A well-designed building will not perform in a satisfactory manner when poorly constructed. Therefore, preparation of clear and correct contract documents is an essential part of the design and may take up to 50% of the total time spent on the project.
The designer needs to keep in mind that structural design is only one component of the overall building design. Other disciplines include architectural, electrical, mechanical, geotechnical, and civil engineering. The structural designer needs to coordinate the design with other disciplines. This stage might be rather time-consuming and may take up to 10% of the total time spent on the project.
Services During Construction
Structural designers are routinely involved in the review of shop drawings, concrete mix designs, and laboratory testing reports. The designer must make regular visits to the construction site to observe the construction, answer questions, and clarify contract documents. The main objective of these visits is to verify that the work is progressing in the manner intended by the design. The involvement of a designer at this stage varies with design and construction complexity; however, it may take about 10% to 20% of the total time spent on the project.