Expert Tip: Creep Analysis - Next Steps

midas Civil , Creep Analysis .
Creep analysis

1 min read

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

Publish Date: 14 Jul, 2023

Composite Section Analysis

Finally we came to the composite section analysis. One of the best examples is from Dr. Gilbert and Dr. Ranzi (Example 5.10, Time-dependent behavious of concrete structures, CRC Press, 2010.)

Next Steps

The proposed example is AS5100.5 Type 3 girder with 2400×150 CIP deck.

 

Composite Section Analysis AS5100.5 Type 3 girder

Composite Section Analysis table

Composite-Section-Analysis3

The Different Steps

Step 0)

At age 7, the girder is released with PT=1000 kN/tendon. DL moment at span center is M=550 kN-m. Ducts have not been grouted yet.

 

Ec(7)=25 GPa.

A duct = (1/4)π(60mm)2 = 0.00283 mm2

 

Composite Section Analysis Table 1

 

Due To DL  Moment

Composite Section Analysis Calculations

 

Due To Post Tensioning

N = -2000 kN

M = (-1000 kN)(1.03m+1.16m) = -2190 kN-m

 

Screen Shot 2023-07-14 at 9.58.16 AM

Summary

Screen Shot 2023-07-14 at 10.15.49 AM

Screen Shot 2023-07-14 at 10.16.32 AM

Composite Structure Analysis4

Part 9 

Step 1)

Calculate strain and stress at age 40. The structural system is the same as step 0) and the differences are only the time effects.

General equation for the time-dependent analysis is as follows.

 

General equation for the time-dependent analysis

 

For step 1), the equation can be simplified as below.

 

General equation for the time-dependent analysis simplified

Ec(40)=32 GPa

 

Section property

Creep analysis section property

 

Restraining force and strain

Due to creep

Φ(40,7)=0.8

creep analysis due to creep

creep analysis due to creep

Due to shrinkage

εsh(40)=-100×10-6

 

creep analysis due to shrinkage

Due to relaxation

creep analysis due to relaxation

creep analysis due to relaxation 1

 

Unrestrained strain summary

creep analysis Unrestrained strain summary


Stress caused by unrestrained strain summary (MPa)

creep analysis Stress caused by unrestrained strain summary (MPa)

 

Restrained strain summary 0

creep analysis Restrained strain summary 0 1

creep analysis Restrained strain summary 0 1

Restrained strain diagram

 

 

Stress caused by unstrained and restrained strain summary (MPa)

Stress caused by unstrained and restrained strain summary

 

Step 2)

At this step deck is poured and the moment is M40 = 620 kN-m. The structural system is the same as step 1).

 

Due to deck moment

Due to deck moment

Step 2) - Restrained strain summary and diagram

Restrained strain summary and diagram

Step 2) - Stress caused by restrained strain summary (MPa)

Stress caused by restrained strain summary (MPa)

Step 2) - Stress caused by unstrained and restrained strain summary (MPa)

Stress caused by unstrained and restrained strain summary (MPa)

 

Step 3)

Duct grouting and deck composite commencement at day of 40.

Ec deck = 18 GPa

Duct grouting and deck composite commencement at day of 40

 

Step 4)

Calculate strain and stress at age of 60.

Calculate strain and stress at age of 60.

Strain summary

Strain summary

Due to creep

Due to creep

Due to creep 2

Due to shrinkage

Girder

due to shrinkage Girder

Deck

due to shrinkage deck

Due to relaxation

Due to relaxation

 

Step 4) - Unrestrained strain summary

Unrestrained strain summary

Step 4) - Stress caused by unrestrained strain summary (MPa)

Stress caused by unrestrained strain summary (MPa)

Step 4) - Restrained strain summary with diagram

Restrained strain summary and diagram1

Step 4) - Stress caused by restrained strain summary (MPa)

Stress caused by restrained strain summary (MPa)1

Step 4) - Stress caused by unstrained and restrained strain summary (MPa)

Stress caused by unstrained and restrained strain summary (MPa)1

 


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