Expert Tips: Creep Analysis 1
Author: Seungwoo Lee, Ph.D., P.E., S.E.
Publish Date: 28 Dec, 2021
Creep Analysis 1
One of the best examples to understand creep behavior was developed by Dr. El-Badry. This example is from Dr. El-Badry’s paper with some modifications.
At time t0 = 7 days, the cantilever is subjected to a uniform load q = 0.225 klf (section is 12”×18”). At time t1 = 30 days, simple support is introduced at B, thus preventing the increase in deﬂection at B due to creep. Determine the end reaction RB at t2 = ∞. Ignore the diﬀerence between Ec(t0) and Ec(t1). RH (percent) is relative humidity and assumed 70%. f’c = 5 ksi (=34.47 MPa). L = 5ft.
First, calculate the creep coefficients based on CEB/FIP 90.
h0 = 100mm
In the same way,
Creep coefficient (t0 = 7 days)
Calculate modulus of elasticity.
Modulus of Elasticity
Deflections and rotations are
The restrained deflections/rotations for fixed end beam are
Apply this loading to the end supported cantilever, and we can get the following secondary reaction.
The MIDAS output is
The differences are around 2%. The complete theory for creep calculation in MIDAS is not opened, and we do not know where these differences come from. However, considering the uncertainty of creep itself, the two outputs are close enough for practical design problems. Please download the MIDAS file below.