What’s a structural load?

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Structural load is the total weight of a building, bridge or other object. This value includes the weight of the object, any equipment installed inside it, and the potential effects of weather and people. Loads created by the weight of the structure are usually called static loads and loads from occupants or atmospheric effects are called dynamic loads. Architects and engineers must include all possible loads and appropriate safety factors in the structural design to prevent load failures.

Using a building as an example, the static load of the building can include the steel structure, floors and interior walls. Any equipment installed to support building operations, such as heating and air conditioning, lighting, and plumbing, must be added to the static load calculations. These factors only equal the structural load of an empty building and are far below the minimum safety design requirements.

Additional loads occur from furniture, portable office equipment and personal effects brought into the building. The people who work in the building and any visitors are an ever-changing live load that must be structurally supported by the building. Winds, snow, or heavy rain can add significant weight to the building structure and should be included in structural load calculations.

Many governments set minimum load requirements for different types of building operations. An office building may have different loading requirements than a manufacturing operation with large equipment located on floors. Another consideration for industrial buildings is the effect of vibration on the building and structural vibration load calculations must be done with additional strengthening of the building and foundation.

Moving equipment also has structural loading considerations due to the effects of vibration and shock. Aircraft have large loads created by the effects of air on the wings and external surface. Passengers and baggage add additional loads that must be supported by the fuselage or aircraft body and wings that lift the entire structure. Turbulence, takeoffs and landings are live shock loads that can add significant stresses over short periods and must be considered in aircraft design. Similar shock loading occurs on trucks and cars when they travel on rough roads, and the vehicle’s frame and suspension must absorb these stresses.

Bridges have different structural loading considerations, because they are often supported only at each end or with regular support piers or columns. Moving traffic creates bending stresses in unsupported road sections and can cause vibratory stresses called harmonics that can damage the structure. Bridges that require longer unsupported sections often use cables or other supports to transfer loads to the main deck’s foundation piers or support columns. Cable supports help reduce the weight of the bridge structure, as the structure itself does not have to support the entire bridge and all moving loads.

Weather can create significant loads on structures and can be a major design consideration in parts of the world where winds are high or snowfall is heavy. Wind speed increases with height above the ground, which in hurricane-prone areas can create a significant load against a building’s exterior and internal structure. The heavy rains that often occur during tropical storms can add even more load that must be absorbed by the building. Since the early 20th century, many governments have structural load design requirements for hurricane prone areas and are revised from time to time as storm damage testing and investigations allow for a better understanding of wind stress.

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