Building Loads

Introduction

The design of, selection of materials for and construction of Ag structures is based on the expected loads, use(s) of the building and the acceptable risk of

failure.

Design Decision

There is usually a higher acceptable risk of failure for an agricultural building because the cost of failure doesn’t usually include human life.

They are usually built to a lower standard, therefore they have a higher probability of failure.

Most Ag buildings are also usually designed with shorter life expectancy than residences and commercial buildings.

Should an agricultural building be designed to withstand the worse possible storm?

Agriculture buildings can be built to withstand the worst case scenario, but they would be very costly.

Ag structures are subject to complex loads

a) Forces from different directions

b) Different intensities of forces

c) Different frequencies

4 Common Types of Loads

Snow

Wind

Dead

Live

Dead LoadDead load is the weight of the building materials.

Dead loads will vary depending on the type of construction and materials used.

Is there any relationship between the dead load of a building and its ability to withstand wind?

Live Loads

Any load that will change during normal use of the building.

Vibration from equipment

Live loads are estimated on a pound per square foot basis for structural calculations.

EquipmentAnimals

Materials that are being moved.

Wind Loads

The effect of wind on a building is not consistent.

On the up wind side of a building, wall and roof panels experience a positive pressure, while on the down wind side there is a negative pressure or suction load.

The dashed line represents the “racking” forces caused by wind.

Wind Loads - cont.

Wind can have multiple effects on buildings.

How does the effect of wind influence building design and construction?

Wind--continued As the wind blows over and around the building, eddy currents are formed which exert varying negative pressures in those areas.

The destructive power of wind is dramatically increased when you include water and/or hail.

Snow Loads

1. Added load from sliding snow

2. Increased load for lower roof.

3. Drift load behind obstruction

4. Increased load in valleys

5. Unbalanced snow load6. Balanced snow load7. Increased load because of change in slope

Snow Loads - cont.

Results of excessive snow load

Results when snow load exceeds building designed load

The expected snow load varies by region.