This example analyzes a specific concrete T-beam section to determine its moment capacity in accordance with ACI 318-08. This example specifically explores the condition when the depth of the Whitney stress block is greater than the thickness of the T-beam flange.

This example analyzes a specific concrete T-beam section to determine its moment capacity in accordance with ACI 318-08. This example specifically explores the condition when the depth of the Whitney stress block is less than the thickness of the T-beam flange.

This example analyzes a beam that is over-reinforced by ACI standards (it cannot be considered a tension controlled section). Typically, a beam is considered over-reinforced if the steel does not yield prior to failure, but this is not allowed by ACI for flexural members. In this example, the strain in the extreme layer of tensile steel is less than 0.005, and the section cannot be considered tension controlled. The phi factor when calculating the nominal moment capacity must be adjusted accordingly.

This example illustrates the ACI provisions for minimum steel in a concrete beam section. Specifically, the designed section has less still than the minimum allowed under ACI section 10.5.1, and uses the provisions of section 10.5.3 to satisfy minimum steel requirements.

This series of videos will walk you through the design of a simple rectangular concrete beam in accordance with ACI 318-08. These videos were created for those about to take the Civil Professional Engineering exam, and for those taking the Structural Engineering exam.

The first video discusses the assumptions required for the calculation, and walks you through stress and strain diagrams for a given reinforced concrete beam section. By the end of this video, you’ll be able draw the stress and strain diagram, calculate the depth from the extreme compression fiber to the center of the reinforcing steel, and calculate the depth of the compression region, a, using the Whitney stress block approximation.

The second video shows you how to calculate the depth from the extreme compression fiber to the neutral axis, c, in accordance with ACI 318-08. You’ll then determine the strain in the reinforcing steel at failure, and use it to determine if the steel yields, and if the section can be deemed a tension controlled section per ACI. Finally, you’ll calculate the minimum required steel for the given section per ACI.

Finally, you’ll calculate the nominal moment capacity and shear capacity for the given rectangular concrete beam.