The effect of creep on modular ratio is
A. To decrease it
B. To increase it
C. Either to decrease or to increase it
D. To keep it unchanged
Answer: Option B
Solution (By Examveda Team)
The modular ratio is defined as: m = Es / Ec Where: Es = Modulus of elasticity of steel (approximately constant) Ec = Modulus of elasticity of concreteWhat is Creep? Creep is the long-term deformation of concrete under a sustained load. Over time, concrete subjected to constant stress will slowly deform. This is a time-dependent increase in strain, even when the stress remains constant.
How Creep Affects Modulus of Elasticity: Due to creep, the concrete shows more strain for the same level of stress. This means its effective modulus of elasticity reduces over time. In other words, Ec becomes smaller than its short-term value.
Impact on Modular Ratio: Since modular ratio = Es / Ec, and Es remains constant, a reduction in Ec (due to creep) results in an increase in the modular ratio.
Why Some Get Confused: In some design approaches (e.g. working stress method), to indirectly account for creep and long-term deflection, a lower modular ratio is used empirically. This is a correction based on behavior, not a direct mathematical consequence of the creep effect on elasticity.
But theoretically and fundamentally, the effect of creep is to increase the modular ratio.
Therefore, the correct answer is: Option B — To increase it.
This Question Belongs to Civil Engineering >> Concrete Technology And Design Of Concrete Structures
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Comments (4)
In symmetrically reinforced sections, shrinkage stresses in concrete and steel are respectively
A. Compressive and tensile
B. Tensile and compressive
C. Both compressive
D. Both tensile
Critical section for shear in case of flat slabs is (adopting standard notations)
A. At a distance of effective depth of slab from periphery of column/drop panel
B. At a distance of $$\frac{{\text{d}}}{2}$$ from periphery of column/capital/drop panel
C. At the drop panel of slab
D. At the periphery of column
A. depends on as, only
B. depends on aCbC only
C. depends on both crst and acbc
D. is independant of both ast and acbc where d is the effective depth, ast is per-missible stress in steel in tension and ocbc is permissible stress in concrete in bending compression.
The diameter of ties in a column should be
A. More than or equal to one fourth of diameter of main bar
B. More than or equal to 5 mm
C. More than 5 mm but less than one-fourth of diameter of main bar
D. More than 5 mm and also more than one-fourth of diameter of main bar
The effect of creep on modular ratio is that it increases the modular ratio.
Explanation:
- Modular ratio (m) = Es / Ec, where:
- Es = Modulus of elasticity of steel
- Ec = Modulus of elasticity of concrete
- Creep reduces the effective stiffness of concrete over time.
- As concrete deforms more under sustained load, Ec effectively decreases.
- Hence, the modular ratio (m = Es / Ec) increases due to creep.
In Working Stress Design:
- A modified modular ratio is used to account for creep:
- m = 280 / (3 × σcbc)
where σcbc is permissible compressive stress in concrete.
This adjusted ratio reflects the long-term effects of creep on the structure.
Ec' = Ec/[1+theta(c)]> So, Ec will decrease with time. So m=Es/Ec will increase.
Due to lang turm creep load the values of Es reduce 2-3 times.
M=Es/Ec
So if Ec decrease than M will increase
Please explain.