Everything You Must Know About Structural Loads on Your Metal Buildings

July 3rd, 2020

Structural loads are deformations, accelerations, and other external forces that are asserted onto structural steel buildings and their components. If not accounted for, such forces can cause deformations and displacements of the components, and excessive loads can even cause complete structural failure.

When designing and constructing a steel building, you have to consider the structural loads that your building may face throughout its lifespan. Since these structural loads are unlike those asserted on traditional building structures, additional considerations need to be addressed. This is because steel buildings have different minimum and maximum load values as opposed to wood or concrete.

The design of your structural steel building must meet the provincial codes and requirements so that such structural loads are accounted for. Thus, the design of your project is also driven by the accounted-for structural loads, depending on the category and intended use of your project.

Classification of Structural Loads

Structural loads that are exerted on your steel building vary a lot, depending on the location, elevation, environmental and seismic factors, and the intended use of the building itself. To make the process easier, the structural loads are classified into three major categories, as mentioned below.

1) Dead Loads

Also known as permanent or static loads, dead loads consist of the entire weight of the building itself, including the frame, roof, and other permanent non-structural items such as the HVAC system, plumbing grid, and built-in cabinets.

Since the dead loads assert static forces, the assumed pressure can be easily calculated based on the weights and volumes of the specific materials indicated in the blueprint.

However, it may not always be possible to predict the exact weight and volume of some materials. To counter this uncertainty, the design engineers are required to be conservative with their estimates. They consider the potential deflections, including the various margins of errors, and altercations over time, while designing the building. As a result, the presumed loads in the design exceed the actual experienced loads in reality. 

2) Live Loads

Unlike the static loads, there are live loads, also known as imposed loads. These are the uniform forces applied by all the temporary and transient forces that act on the structural steel building. Live loads include people, vehicles, furniture, and machinery.

Since such loads vary significantly, the estimates are based on the expected use and occupancy of the structure. It is calculated as if they were uniform across the structure even though the loads, in reality, may differ according to the time of the day.

Here, abiding by the provincial codes is crucial as they state how conservative the estimates have to be so that it leaves much room for the varying degrees of loads throughout the structure's lifespan.

3) Environmental Loads

The third major category of loads is the environmental loads. They are an extension of live loads that are caused by environmental or external factors. The most common environmental loads experienced in the Edmonton region are the following:

- Wind loads, applied by the movement of air relative to the structure

- Snow loads, imposed by the accumulation of snow upon the structure

- Seismic loads, asserted by the seismic activities near the structure

- Settlement loads, occurring when one part of the structure settles more than the other due to soil conditions under it

The design engineers must take into account all the environmental loads that may be experienced by the structural steel building, and that the provincial construction codes of Alberta are met. Failing to do so may lead to severe damage to both property and life.

4) Miscellaneous Loads

Apart from the major load categories, your steel building may also encounter other forms of loads that are not as common as the three mentioned above. Such loads include fire, corrosion, explosions, creep or shrinkage of the components, vibration, construction loads, and much more. 

The design engineer can safeguard the structure against these loads by meeting the provincial codes and leaving a margin for potential deflections.

Load Combinations

During certain times, the structural steel building may experience multiple loads or combinations of loads. The combination of loads may put additional stress on the building components that can damage the structure.

For example, during the winter months, the structure may experience snow load from the top along with soil movement under the foundation. The structure itself may experience some shrinkage due to the cold temperatures.

Thus, the design engineer must refer to the local construction codes as they specify the most common load conditions that your buildings may potentially face in the future.

Factors Influencing the Load Response

While calculating the load and the appropriate load response, several factors need to be taken into account. These factors enable you to determine the correct way to safeguard the building against the loads.

As mentioned earlier, the uniformity of load distribution is the first factor that needs to be considered. Additionally, the depth of the structural components, as well as the duration of the load should be accounted for, too.

The E-value, or modulus of elasticity, of the individual elements must be calculated. It is the ratio of the given load that causes the structural material to deform. A higher E-value indicates increased material stiffness.

Additionally, the Fb value has to be calculated for the materials. The higher the Fb value of the steel beams and girders, the higher their resistance to bending or buckling under extreme pressures.

Strength and Deflection

Lastly, there are the calculations made for the strength and deflection of the structure. 

The deflection is calculated exclusively on live loads to indicate the stiffness of the materials. It is limited by the maximum deflection that can be allowed before it compromises the material's structural integrity. The provincial building codes usually set the maximum deflections values for steel structures.

On the other hand, the minimum value for strength is calculated using both dead and live loads.

While designing and constructing structural steel buildings, structural loads are a critical aspect of the designing and planning process to ensure that the structure will be capable of withstanding such loads. Hire professional engineering contractors to ensure that your steel structure meets the code requirements and load conditions for the intended use. Northern Weldarc's 40 years of expertise can help you with that. Contact us now for more information.

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