Exploring Stiffness Methods in Creep Analysis of Girders

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Creep Analysis 3

We have gone through two different approaches by Dr. El-Badry so far. You can find the previous articles via these two links: Creep Analysis 1, Creep Analysis 2.

For creep analysis, the most common problem in the real-world design is continuous girders built as span by span. This example is very well explained by Dr. Ghali et al. (Concrete structures, Stresses, and deformations, 4th ed., CRC press, Example 4-2). Dr. Ghali et al. explained this problem by flexibility methods. The author will solve this same problem by stiffness methods. The programs do the matrix formulation and equation solve, and only the load matrix formulation and post-processing are our concern in the stiffness methods. Two MIDAS files are attached.

First, the author wants to define the sign convention for member forces clearly.

Expert Tips Creep Analysis 3

Sign Convention

Fixed end forces are the same for members 1 and 2.

At time t1, the member end forces due to uniform load at span two can be calculated below. Note that Ec(60)/Ec(7) = 1.26. (MIDAS file ex.2A)

the member end forces due to uniform load at span two

the member end forces due to uniform load at span two can be calculated

Analyze two-span continuous beam for these member end loadings. Note that the section properties are shown below, and the loading directions may not be identical for each program. (MIDAS file ex.2B)

Loading Diagram (ft, kips)

The results are shown below.

Moment (ft-kips)

Shear (kips)

Results (ft, kips)

Finally, the member end forces are

Span AB

Span BC Span BC

Download File [Click]

#Creep Analysis
#Continuous Girders
#Stiffness Methods

About the Editor

Seungwoo Lee PhD, P.E., S.E.

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.