For a structural Engineer, the main purpose of structural design and analysis is to design safe structures, capable of withstanding all possible loads (applied and lateral loads) throughout its lifespan. It is common knowledge that structural failure, which can lead to losses of lives and property, can occur in the event of a poor structural design. Therefore, a structural engineer must take a lot of things into considerations during a structural design.
After the finalizing of architectural design and drawings, the room for a structural engineer to carry out structural design immediately opens. This article features six basic procedures of the structural design.
Design Code, Standards & Design Criteria
For a structural engineer, it is important to kick start structural design according to design codes and design criteria. Design codes are guidelines for designing a structure. Design codes differ for different locations. Considering local codes is also important where necessary.
Notably, international codes and standards like the US codes, the Euro codes, and British standards are the accepted standards in most countries. However, design codes are dependent on the structure’s location. Therefore, it is pertinent that the structural engineer knows the code and standards for the particular location of the structure.
Load Considerations and Calculations
The next thing for the structural engineer is to consider is all possible loads and their calculations. The possible loads that a structure can undergo throughout its lifespan are dependent on the type of structure, the use of the structure (that is the type of occupancy), and the structure’s location. When designing a building, a structural engineer considers three basic loads, which are;
- The dead load (DL) that usually composed of the self-weight of the member or a structure.
- The super-imposed dead load (SDL) that comprises of the floor finishes and the weight of the partitions.
- The live loads (LL) that constitute the movable loads that the structure may carry.
However, for a tall structure, seismic and wind loads will be added to its load consideration. One of the main purposes of a design code is to specify load considerations for a particular location and structure type. In the United States, ASCE 7 specifies appropriate load considerations.
The load combinations are also important. The Ultimate Limit State (ULS) and Working or service Limit State (SLS) gives the standard load combinations and these are available in the aforementioned design code.
Propose a Framing System
Afterload considerations, the next thing is to choose a framing system. The framing system is so vital that it constitutes the overall safety of a structure. This aspect requires that the structural engineer produces the best possible frame to support the building structurally. Notably, the engineer must be able to come up with a framework that will not compromise safety as well as the aesthetics of the building. In proposing a framework, the following should first be considered;
- The standard thicknesses of slabs, dimensions of beams and columns.
- Location and orientations of the Structure.
- Coordination of architectural and MEP drawings.
In the architectural drawing phase of the building, in order to avoid compromising the architectural aspect during the framing phase, a draft for the framing system is presented. Manual calculations or software aids the proposing of the framing.
Structural Modeling and Manual Design
Verifying how adequate a structure’s framing is, is possible through structural modeling. Structural modeling is possible using available structural software. The design of structural members, such as beams, slabs, and columns, require specific design forces, to extract these forces, the use of 3D modeling software like ETABS, SAP 2000 AND ROBOT STRUCTURE makes it convenient.
A manual design will suffice in the event of the unavailability of a structural software. However, manually designing a structure is worrisome, because, a manual design is only possible for small structures, not to mention the fact that it is time-consuming.
In this case, modeling a structure is best with structural software, and using manual calculations or spreadsheet containing member designs, to carry out individual checks on the structural members.
Designing of Structural Members
Structural modeling provides the design forces needed to design structural members. Hence, design forces are readily available whenever to need it. Structural modeling already provides the loads for member design, therefore, the structural engineer ought to design the reinforcement beams according to these loads.
Additionally, checking the slab design, punching reinforcement, as well as checking the design of vertical members such as shear walls and columns for buckling is imperative. More importantly, SLS load combinations should be considered when designing the extracted forces or column loads that the footing will carry.
Notably, verifying everything, structural member design is possible through manual calculations. So, it is always your prerogative.
Produce a Structural Drawing
After completing all the above procedures, it is necessary to represent the structure in structural drawings. The structural drawings are done by the structural draftsman. The draftsman receives a draft of the design and structural schedule of the framings and uses this draft to produce the structural drawings. Notably, it is necessary that the structural engineer supervises these drawings, this is to ensure the drawings account for every structural detail.
One last important thing is getting the building permit approval.