What Is a Load Diagram?

Mary McMahon

A load diagram is a detailed representation of the loads on a structure, calculated for structural engineering purposes. Engineers and architects create such diagrams in the process of developing plans for a new building to make sure that the building is engineered to address the strain to which it will be subjected with the weight of the components and contents. In some regions, a copy of this diagram must be submitted along with other supporting details in permit applications and the documentation that accompanies the construction project. The copy demonstrates that the calculations were performed.

Scientist with beakers
Scientist with beakers

Many types of strain can occur along the height, width and breadth of a building, including bending and shearing forces. In the load diagram, the engineer should be able to show the distribution of loads in the building, using known information about the construction and how the building will be used. The engineer can point out what kinds of loads will be present and might map out their intensity.

If the load diagram reveals a hot spot where forces are particularly high, the building might need special engineering to address it, or it might be necessary to change the building design slightly to redistribute the loads more appropriately. With innovative new design, particularly projects that have large amounts of open space and interesting new materials, the load diagram is very important, because the engineer might not have a similar existing building to use as a model.

This is part of the structural analysis performed to make sure that a building will remain stable while in use. In addition to thinking about the loads that are intrinsic to the building, engineers might also have to consider earthquakes, storms and other factors that could add stress to a building. A load diagram should be able to show how the building will maintain its integrity in the event of a situation such as an earthquake, by absorbing and distributing the stress rather than crumpling or cracking under the strain.

Computer-aided design (CAD) programs can calculate a load diagram using known parameters that are inserted by an engineer. There also are engineering programs that can perform similar tasks. Using a computer might help ensure the accuracy and detail of the calculations, or an engineer can check manual math with the assistance of the computer program. Errors in a load diagram can be a significant issue, because they might lead to situations such as under-engineering in the belief that a building is perfectly stable and does not need additional supporting trusses and other structural elements.

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