Dead load is the term structural and mechanical engineers use to describe the weight of all the permanent parts of any structure. Here, "weight" means the downward force the structure exerts on the Earth. Dead load is distinguished from live load by the fact that the live load will change depending on the environment around the structure. Live load can be affected by high winds, people or vehicles traversing the structure, or air pressure.
- Skill level:
Things you need
- Structure blueprints
- Engineering data book
Measure the areas of each component of the structure using the ruler on the blueprints. Make a note of these values.
Apply appropriate formulae to calculate the dimensions of the structure's components to work out their volumes. In the case of rectangular components, multiply the length by the width by the thickness. In the case of cylindrical components, multiply the square of the cross-sectional radius of the cylinder by pi, and then multiply the resultant value by the length of the cylinder. Make a note of each of these values.
Multiply the volumes of each of the components by the density of the material out of which the components are made. These data can be found in an engineering data book. This calculation determines the mass of each of the components. Make a note of each of these values.
Add the mass of each of the components. Make a note of this value.
Multiply the sum of the mass of all the components by the gravitational field strength of the Earth, g, which is approximately 9.81 meters per second squared or 32.2 feet per second squared. This final value is the dead load of the structure.
Tips and warnings
- Ensure that you use a consistent system of units throughout this process. If you use cubic feet to measure the volume, you must use the values of density quoted in pounds per cubic foot and the value of gravitational field strength of 32.2 feet per second squared. The final value will be in pounds-force.
- This procedure is fine for working out the dead load of an existing structure but should not be used in any attempt to alter a structure. Any such alterations should only be made under the supervision of qualified engineers and undertaken by trained professionals.
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