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Factors influence to concrete creep

September , 15th 2023 | Author: Prontubeam (@Prontubeam_en) Read: 1204 times

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When concrete is acted upon by constant sustained stress, the creep strain of concrete develops over time. There are a variety of reasons, which are discussed in the paper, that cause an increase in the creep coefficient (φ) and creep factor (φ+1). The study is based on AS 3600:2018 ("Australian Standard for the Design of Reinforced Concrete Structures").

Keywords: Creep, Time-dependent, RCStructre, Concrete

 

1. Calculation of creep coefficient

Refer to provision 3.1.8 of AS 3600: 2018, design creep coefficient is calculated by formula below:

Creep coefficient factors

In which:

k2: time factor at t days

k3: factor of loaded time at τ days

k4: environmental factor

k5: modification factor for high strength concrete

k6: factor accounts for non-linear creep

φcc,b : basic creep coefficient

2. Factors affect to concrete creep

Many factors influence creep magnitude and creep development:

  • Time
  • Loading conditions: first loaded time, sustained stress
  • Concrete strength, water-cement ratio
  • Environmental conditions
  • Hypothetical thickness of member

 

The typical time t (days) is considered to research creep coefficient, the input data is shown as below:

Input data for creep coefficient

 

Regarding the initial loading time τ = 28 (days), Figure 1 shows that creep significantly increases in the first year (from 0.18 to 2.54). This growth continues from year 1 to year 10 (from 365 days to 3650 days) and remains constant after 30 years (10950 days) at 3.16.

Creep coefficient of concrete during time t, first loaded time τ = 28 (days)

Figure 1 Creep coefficient of concrete during time t, first loaded time τ = 28 (days) with input data above

As input data for concrete above, in comparison to the initial loading time τ, if the member is loaded early, the creep coefficient shall be greater, and vice versa. Figure 2 shows the comparison of first loaded time between 3 days, 7 days, 14 days, 28 days.

The comparison of first loaded time τ influence to creep coefficient of concrete during time t

Figure 2 The comparison of first loaded time τ influence to creep coefficient of concrete during time t with input data above

According to the table 3.1.8.3 of AS 3600:2018, the following table shows that the creep coefficient of high-strength concrete is less than that of low-strength concrete. Related to environment factor, the comparison between arid, interior, temperate inland, tropical is studied. Creep coefficient of arid environment is the greatest, but that of tropical environment is the smallest. Regarding the factor of hypothetical thickness, a comparison between 100mm, 200mm, and 400mm is researched. The comparison shows that if hypothetical thickness is thin, the creep coefficient is great and vice versa.

Table 1 Final creep coefficients for concrete after 30 years, first loaded at 28 days [1]

Creep coefficients results

3. Conclusion

As discussed above, the creep coefficient is summarized:

Creep coefficient increases significantly in 1 year. This growth continues increasing from 1 years to 10 years (from 365 days to 3650 days) and flat since time of 30 years.

If the member is loaded early, creep coefficient shall be greater and vice versa.

Creep coefficient of high-strength concrete is less than creep coefficient of low-strength concrete.

Related to environment factor, the comparison between arid, interior, temperate inland, tropical is studied. Creep coefficient of arid environment is the greatest, but that of tropical environment is the smallest.

Related to factor of hypothetical thickness, the comparison between 100mm, 200m, 400mm is researched. The comparison shows that if hypothetical thickness is thin, the creep coefficient is great and vice versa.

 

References

[1] Standards Australia , AS 3600-2018 Concrete structures.

[2] Raymond Ian Gilbert, Neil Colin Mickleborough, Gianluca Ranzi, Design of Prestressed Concrete to AS 3600-2009 (Second Edition), Taylor & Francis, 2015.

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Huy (Henry) Trương . Structural Engineer at Aurecon.
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