# Concrete civil engineering Assignment

Concrete civil engineering

• True or false: In a simply supported beam, the neutral axis moves upward in the cross section when the beam moves from the uncracked stage to the elastic cracked stage.

• True or false: In a simply supported beam, the neutral axis is at the same point in the ultimate strength stage as in the elastic cracked stage.

• What is the definition of failure?

• What is the assumption that must be checked about failure?

• True or false: The strain distribution is linear at all stages of beam behavior.

• True or false: The stress distribution is linear at all stages of beam behavior.

• Why do we use the Whitney stress block in place of the actual concrete compression stress distribution?

• Name three assumptions we use to calculate the ultimate moment.

• How large is the uniform stress in the Whitney stress block?

• How far does the Whitney stress block extend into the cross section?

• What value do we use for β1 if we are using 3500 psi concrete?

• What value do we use for β1 if we are using 6000 psi concrete?

• Which statics equation do we use to calculate the depth of the equivalent rectangular (i.e. Whitney) stress block a?

• How do we find the moment arm of the couple formed by the steel’s tension force and the concrete’s compressive force?

• What is the equation for the moment of the couple formed by the steel’s tension force and the concrete’s compressive force?

• True or false: The moment arm of the couple formed by the steel force T and the concrete compressive force C is always d-a/2.

• What is the steel reinforcement ratio ρ?

• What equation(s) are used to find the nominal strength of a beam cross section?

• What equation(s) are used to find the design strength of a beam cross section?

• True or false: The design strength of a beam cross section must be at least as big as the factored moment Mu.

• Where does the factored moment Mu come from?

• What is the equation for coefficient of resistance Rn?

• What is the yield strain for Grade 60 reinforcement?

• How is the steel’s yield strain calculated?

• How do we find the depth of the neutral axis c if the depth of the stress block a is known?

• What does the symbol εt stand for?

• What is the difference between dt and d?

• How do we find the value of the strain in the steel when the concrete reaches its crushing strain?

• What is a balanced section or balanced failure?

• If you have a cross section that is reinforced with a steel ratio ρ > ρb would you expect a ductile or a brittle failure?

• How does the steel reinforcement have to be adjusted (i.e. do you add more steel or remove steel) to change the failure mode from a brittle compression-controlled failure to a ductile tension-controlled failure mode?

• How does ACI 318 Code define a tension-controlled member?

• True or false: For beams that have a transition failure mode, steel yields before the concrete crushes.

• What value is used for φ in a tension-controlled member?

• Is the φ factor for a member in the transition zone greater or less than the φ factor for a tension-controlled member?

• What is the smallest value for εt that can be used for a beam according to ACI 318 Code?

• What is the largest amount of factored axial compressive load that can act on a cross section and still be classified as a “beam” or bending member, rather than a column member?

• What types of members can be designed as compression-controlled?

• True or false: The equation for φ for bending moment and axial load is the same for all grades of steel.

• True or false: The nominal strength Mn increases for increasing steel ratio ρ.

• How do we find the steel ratio ρ that corresponds to a particular value of steel strain εt (i.e. what do we use to find ρ0.005 when εt equals 0.005 or ρ0.004 when εt equals 0.004?

• If you wanted to design a cross section with εt greater than 0.005, would you need to use a steel ratio that was larger or smaller than ρ0.005?

• What assumption do we make to use T = Asfy in Example 1?

• Why is the compression force C = 0.85f’cab and why is the compression force located at a/2 down from the top of the cross section in Example 1?

• How is the assumption that T = Asfy checked in Example 1?

• How is the φ factor determined to be 0.9 in Example 1?

• Why is Mn calculated as T(d-a/2) in Example 1?

• Why is the compression force’s size and location in Example 2 found differently than was used in Example 1?

• Why didn’t we calculate a design strength φMn for the cross section in Example 2?

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