Question

Problem 3- Concrete Stress-Strain (Everyone) A normal density concrete has a compressive strength (fc) of 14,000 psi. Strain corresponding to peak stress (Eo) is 0.0025. A compressive stress is applied to the concrete. (a) This stress is increased in value from zero to 10,000 psi over a short period of time and is then reduced to 6,000 psi. Calculate the compressive strain in concrete at this point in (b) The stress is then increased to 12,000 psi. Calculate the compressive strain at this point (c) Finally, the stress is reduced to zero. Calculate the residual compressive strain that time in time remains in the concrete after the compressive stress has been removed.

Answer 1

(a) Use Thorenfeldt, Tomasqewicz, and Jensen equations to sole given problem: n is curve fitting factor given by: n=0.8 + Foto = 0.8+ 14000 = 0.145 =97.4 97.46.002591 97.4-1+ 6000 97.46%) 14000 0.0025 & = 0.00106 Hence strain in concrete at the time of 6000 psi stress is 0.00106 (b) When the stress is increased to 12000 psi the corresponding strain is calculated as: 12000 - 97.4_*_ 0.0025 14000 9 7.41 97.4- 1 974-1+ 0.0025) E = 0.00212 Hence the strain corresponding to the stress of 12000psi is 0.00212 Since the concrete is not stressed beyond the peak compressive strength there is no residual strain left.