CONCRETE DESIGN CONCEPTUAL
QUESTIONS & SOLUTIONS(RATED
A+)
Name several of the admixtures use in concrete and the purpose - ANSWERAir-
Entraining: Helps with freeze/thaw cycles; Accelerating Admix: Reduces curing time;
Retarding Admix: Slows curing time; Superplasticizers: Maintains workability with
reduced water/cement ratio
What factors influence creep of concrete? - ANSWERHigh water to cement ratio; High
cement content; Low aggregate content; Long term sustained loading; High air-
entrainment
What can be done to reduce creep? - ANSWERIncreasing the thickness of a member
because members with smaller thicknesses experience large amounts of creep
Why do surfaces of reinforcing bars have rolled-on deformations? - ANSWERTo provide
a space for concrete to adhere with the bars and make a strong bond with the bar
What are 3 factors that influence the magnitude of the earthquake load on a structure? -
ANSWERMass of the structure, Stiffness of the member, Natural frequency
Why does the ACI Code specifiy that a certain minimum percentage of reinforcing be
used in beams? - ANSWERBy providing a minimum reinforcement it will give sufficient
warning before failure due to cracking and deflection and sudden failure won't occur
Distinguish between tension-controlled and compression-controlled beams. -
ANSWERTension: Steel fails before concrete reaches its max strength; Failure is
because of yielding of steel in which tensile strain is equal to or greater than 0.005;
Deflections are larger and will give warning of failure; Members are ductile
Why are epoxy-coated bars sometimes used in the construction of reinforced concrete?
- ANSWERThey provide corrosion resistance.
What are the advantages of the strength design method as compared to the allowable-
stress or alternate design method? - ANSWERA more realistic factor of safety is used in
strength design; The strength method permits more flexible designs;
What is the purpose of strength reduction factors? Why are they smaller for columns
than beams? - ANSWERTo overcome analysis approximation, To allow variations in the
design equations of understrength methods; Columns primarily take compressive loads
and beams incur bending, which means they experience tension, compression, and
shear.
QUESTIONS & SOLUTIONS(RATED
A+)
Name several of the admixtures use in concrete and the purpose - ANSWERAir-
Entraining: Helps with freeze/thaw cycles; Accelerating Admix: Reduces curing time;
Retarding Admix: Slows curing time; Superplasticizers: Maintains workability with
reduced water/cement ratio
What factors influence creep of concrete? - ANSWERHigh water to cement ratio; High
cement content; Low aggregate content; Long term sustained loading; High air-
entrainment
What can be done to reduce creep? - ANSWERIncreasing the thickness of a member
because members with smaller thicknesses experience large amounts of creep
Why do surfaces of reinforcing bars have rolled-on deformations? - ANSWERTo provide
a space for concrete to adhere with the bars and make a strong bond with the bar
What are 3 factors that influence the magnitude of the earthquake load on a structure? -
ANSWERMass of the structure, Stiffness of the member, Natural frequency
Why does the ACI Code specifiy that a certain minimum percentage of reinforcing be
used in beams? - ANSWERBy providing a minimum reinforcement it will give sufficient
warning before failure due to cracking and deflection and sudden failure won't occur
Distinguish between tension-controlled and compression-controlled beams. -
ANSWERTension: Steel fails before concrete reaches its max strength; Failure is
because of yielding of steel in which tensile strain is equal to or greater than 0.005;
Deflections are larger and will give warning of failure; Members are ductile
Why are epoxy-coated bars sometimes used in the construction of reinforced concrete?
- ANSWERThey provide corrosion resistance.
What are the advantages of the strength design method as compared to the allowable-
stress or alternate design method? - ANSWERA more realistic factor of safety is used in
strength design; The strength method permits more flexible designs;
What is the purpose of strength reduction factors? Why are they smaller for columns
than beams? - ANSWERTo overcome analysis approximation, To allow variations in the
design equations of understrength methods; Columns primarily take compressive loads
and beams incur bending, which means they experience tension, compression, and
shear.
