Civil EngineeringCivil EngineeringScience Concepts

ForcesForces

Static forces act on objects at rest.Compression forces shorten objects.

These forces push structures. Tension forces pull objects. These forces

lengthen objects. Torque is the rotational effect of a force.

ForcesForcesIf a spring rests on

a surface and weight is placed on top of the spring, it is compressed. This is an example of a compression force.

ForcesForcesIf the spring is

suspended in the air, like the spring of a grocery store produce scale, and weight is applied to the end of the spring, it is stretched.

This is a tension force.

ForcesForces

The forces acting on a structure should be balanced.

Torque is important in determining the strength of a material. Structures built in tornado or hurricane-prone areas need beams that are able to withstand a significant amount of torque before breaking.

Forces DemonstrationForces DemonstrationIf one person holds

the ends of a slinky in each hand and stretches the slinky, a small number of coils will be evenly spaced in the middle.

This section of stretched coils illustrates a beam.

Forces DemonstrationForces DemonstrationIf a second person

applies a small amount of force on top of the stretched section of the slinky with their hand, the tops of the coils move closer together while the bottoms of the coils move further apart.

Forces DemonstrationForces DemonstrationThe top is under

compression.The bottom is

under tension.Notice the

centerline of the coils. This area remains basically the same.

Properties of MaterialsProperties of Materials

Factors to Consider to Determine Materials to Use

StrengthDurabilityFlexibility

Properties of MaterialsProperties of Materials

Strength of a material must be strong enough to withstand the load put upon the structure.

Load is the overall force applied to a structure including the weight of a structure, the people and/or vehicles supported by the structure, and external forces (wind, snow, rain, and so forth) on the structure.

Two Types of StrengthTwo Types of Strength

Tensile Strength◦The amount of tension stress a material can

withstand before failing.Compressive Strength

◦The amount of compression a material can withstand before failing.

Properties of MaterialsProperties of Materials

Durability◦How long can a material last? Concrete and

steel are very durable.Flexibility

◦Can a material bend and flex with stress? In certain designs this property could be important.