The design of a building involves many disciplines, and each of them contributes an important element to the process.
Architects give your building the appearance of your choice and make it function the way you want.
Mechanical, electrical, and plumbing engineers design the systems that let your occupants enjoy comfortable temperatures, fresh air, the convenience of electricity, potable water, and sanitation services.
Structural engineers make your building stand. They design structures to defy gravity, withstand heavy winds, and continue standing even as the ground beneath them starts to shake. Engineers support their design with structural calculations - a complex, little-known tool that lacks the glory of architectural design. If you are planning a construction project, you’ve likely heard of them. You may have wondered what they were, or whether they applied to your project.
So, what are structural calculations?
They are the math behind your building’s ability to stay upright. Engineers use them to determine the loads that a building must withstand and the properties of members that comprise its structure. These include piers, piles, footings, columns, joists, beams, slabs, trusses, and rafters, as well the various connection mechanisms that hold the structure together.
From a budget perspective, quality calculations can help you economize on your project. On average, the materials and labor involved in erecting a building’s structure can add up to 20% of the total construction costs. With such a large portion of your budget at stake, your structural calculations must afford the most efficient way of constructing a compliant, sturdy building. An experienced engineering team will pinpoint structural efficiencies through their calculations and help your project meet its intended budget.
In the permitting process, the accuracy of structural calculations plays a critical part. Building department officials examine them for compliance with all applicable local codes; non-compliant calculations are sent back for revisions to the engineering team, thus delaying the permit process and your scheduled construction date. Quality structural calculations, on the other hand, can streamline permitting and get you building faster.
How Structural Calculations Fit Into the Design Process
Architectural planning is the first stage of the design process. This phase gives you-the client-a chance to share your vision with the architect, and communicate your intentions regarding the building’s appearance, function, and cost. The architect then interpolates your conceptions into the design and lays them out in a set of drawings.
The next step is to design a structure that can support the building’s architectural features. The engineers in charge of this process will perform several calculations during this process.
First, engineers must predict what loads they expect to act on the building. Referred to as specified loads, these include:
- live loads, which are imposed by the occupants, furniture, vehicles, and equipment
- dead loads, caused by the weight of the building itself
- loads inflicted by the forces of nature, such as wind, earthquakes, and snow
Engineers can find most of these loads in local adaptations of the Building Code.
Next, engineers must work out the design loads - the loads they intend the structure to handle. These are higher than specified loads, as buildings are typically designed to withstand more loads than they are likely to bear.
With loads established, engineers can design the structure. At this stage, building code dimension tables will be used to find out the appropriate sizes of structural members. These tables allow the user to arrive at unknown variables, such as the depth of a beam or the width of a column, by looking up established values, such as dead and live loads.
Engineers will also calculate members’ stiffness and strength. Stiffness refers to a member’s ability to resist deformation when subjected to a force. Stiffness is expressed as a ratio of force to deformation, and is measured in pounds per inch when the force is tensile or compressive, or pounds per degree for rotational, shear, and torsional forces.
A material’s strength tells us the maximum load that it can withstand before deforming or failing. To arrive at a member’s strength, engineers would calculate its bending or shear stress, depending on what stresses are expected to act on the member.
Once the structural design is complete and sent for plan check review by your local building department, the correctness of structural calculations will become an important factor in streamlining the permit process.
Building Permit Requirements
A building permit is your local government’s authorization to perform the construction activities related to your project. Not to be confused with approvals, this compliance enforcement mechanism scrutinizes your project’s adherence to local codes. In every country, there are several codes that a project must comply with to get the permits associated with the work. Most buildings require at least the following permits before construction may commence:
- demolition permit
- grading permit
- building permit
- mechanical, electrical, and plumbing permits
Each permit application requires supporting documentation, typically consisting of plans and specifications for the relevant scope. Building permit applications normally include architectural and structural drawings, as well as the structural calculations upon which the drawings are based.
In assessing your building permit application, the building officials must make sure that your project has a structure that can withstand gravity and environmental loads specified in the building code.
The structural calculations submitted with the permit application justify the engineers’ choice of structural members and their configuration. By providing a clear set of accurate structural calculations to support the drawings, your engineers help the reviewing official understand how they arrived at their design. This, in turn, speeds up your permit application.