Advanced Creep Coefficient Analysis in Structural Design

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.

Download File [Click]

About the Editor

Seungwoo Lee, Ph.D., P.E., S.E.

Senior Supervising Engineer at WSP USAs (Tampa, FL)

He is a Senior Supervising Engineer with a high level of expertise in the design and analysis of suspension bridges. He has a solid fundamental understanding of structures and can apply his knowledge exceptionally well to the design and analysis of highly complex structures. He is also a strong communicator, able to identify and distill the key information that is relevant to the task at hand and present it in a clear and quickly understandable manner.