Mechanical properties of prestressing steel in and after fire

Zhang, Li; Wei, Ya; Au, Ftk; Li, Jingyuan

doi:10.1680/jmacr.15.00267

Cited by 28 publications

(8 citation statements)

References 9 publications

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“…Each specimen of prestressing steel has a total length of 800 mm and a clear length of 650 mm between grips after being mounted in the testing machine. The basic mechanical properties of both types of prestressing steel at ambient and elevated temperatures obtained from tests are shown in Table 2 [22]. Note: Yield strength is taken as the stress at 0.2% offset strain.…”

Section: Methodsmentioning

confidence: 99%

Thermal creep and relaxation of prestressing steel

Wei

Zhang

et al. 2016

Construction and Building Materials

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The thermal creep and relaxation of prestressing steel are crucial to the permanent loss of prestress in post-tensioned concrete structures after fire. Harmathy's creep model is widely used to account for the irrecoverable thermal creep strain. In view of advances in steel manufacture, it is desirable to determine the relevant parameters of Harmathy's creep model for common prestressing steel being used. Recently, Gales et al. found that the creep parameters obtained by Harmathy and Stanzak in the 1970s were out of date as the use of these parameters could not give accurate numerical results. They further identified the parameters through testing of prestressing steel to ASTM A417. This study further extended the work of Gales et al. Based on the steady state thermal creep and relaxation tests of prestressing steel to GB/T 5224 (Grade 1860) and BS 5896 (Grade 1860) over wide stress ranges, the parameters of Harmathy's thermal creep model were identified and calibrated. Using the approach of Maljaars et al., the lower limit of tertiary creep was estimated and the creep model was further fine-tuned to incorporate tertiary creep. Numerical

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Section: Methodsmentioning

confidence: 99%

Thermal creep and relaxation of prestressing steel

Wei

Zhang

et al. 2016

Construction and Building Materials

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“…Figure 3 shows a comparison of the residual yield strengths of various types of steel after cooling based on the maximum temperature reached (13,(15)(16)(17)(18)(19). In general, hot rolled structural and reinforcing steel have similar residual yield strengths for certain temperatures reached.…”

Section: Residual Strength Of Steelmentioning

confidence: 99%

“…Figure 4 shows a comparison of the residual ultimate strengths of various types of steel after cooling based on the maximum temperature reached ( 13 , 15–17 , 19 ). Comparing these with the residual yield strengths shown in Figure 3, it is found that the residual ultimate strengths of the different types of steel are generally less affected for a given temperature, with the exception of prestressing steel, whose ultimate strength is affected similarly to its yield strength.…”

Section: Residual Condition Of Tunnel Structural Materials After Firementioning

confidence: 99%

Review of Post-Fire Inspection Procedures for Concrete Tunnels

Menz

Gerasimidis

Civjan

et al. 2021

Transportation Research Record: Journal of the Transportation R

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It is well known that concrete structures can lose strength and long-term durability after a fire. The literature on the remaining capacity of tunnel structures after fire is quite scattered, however, and few published post-fire inspection guides exist. This paper reviews the available literature on the post-fire inspection and evaluation of concrete tunnels. The effects of fire on concrete and steel are discussed, including loss of strength, thermal spalling of concrete, and loss of strength in the bond between concrete and steel. In addition, studies on the residual strength of concrete members are presented. Available post-fire inspection strategies and methods are also discussed. Finally, the results of a survey of post-fire tunnel inspection practices at state Departments of Transportation and transit organizations across the United States are presented. Several models available in both structural building codes and experimental studies allow for the estimation of residual concrete compressive and steel tensile strength after heating and cooling from a given temperature. Furthermore, a variety of post-fire assessment methods are available, which include methods to assess the general post-fire condition of concrete tunnels, as well as methods to more directly assess the residual condition of concrete. Lastly, the review of literature and the survey of United States transit organizations revealed a lack of existing post-fire inspection procedures for concrete tunnels, and a need for further research on the subject.

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“…However, if the transient creep strain was overestimated, the slab deflection and tendon stress would be reduced, indicating that the transient creep strain has a positive effect on structural fire resistance. Thus it was concluded that the transient creep strain should be considered in the analysis by either an implicit or an explicit approach for its positive contribution to the fire resistance of post-tensioned concrete slabs.The paper contributed by Zhang et al (2017) was on the mechanical properties of pre-stressing steel both in and after the fire. Empirical formulae were proposed based on experimentally obtained results for the degradation of Young's modulus, yield strength and ultimate strength of pre-stressing steel both at elevated temperatures and after cooling to ambient temperature.…”

mentioning

confidence: 99%

“…The paper contributed by Zhang et al (2017) was on the mechanical properties of pre-stressing steel both in and after the fire. Empirical formulae were proposed based on experimentally obtained results for the degradation of Young's modulus, yield strength and ultimate strength of pre-stressing steel both at elevated temperatures and after cooling to ambient temperature.…”

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confidence: 99%

Editorial: Fire safety engineering design of concrete structures

2017

Magazine of Concrete Research

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Reducing deaths in fires and the impact of fire damage on buildings requires a comprehensive approach to fire safety. The structural fire safety capacity of concrete is very complicated because concrete is a heterogeneous material with considerable variations. When concrete is subject to sufficient heat such as from a fire the free water that fills the concrete pores and water chemically bound to the cement will evaporate. If the evaporation rate is greater than the vapour migration rate, pore pressure will build up. This built-up pore pressure, combined with the reduction in strength caused by elevated temperatures and the increase in stresses due to thermal effect, can cause concrete spalling and damage to structures. In addition, developments in concrete mix design have led to new types of concrete -including high-strength, ultra-high-strength and self-compacting concrete -which, besides having an increased structural performance at ambient temperature, have also shown a different performance when exposed to fire. The importance of understanding the behaviour of concrete materials in fire is very certain. This special themed issue of Magazine of Concrete Research contributes to our understanding of what has been achieved and what remains to be done in order to provide the fire safety engineering design and improved fire performance of concrete structures.This themed issue contains seven papers and presents results from both experimental and numerical studies on the fire behaviour of various concrete structures, ranging from the mechanical properties of concrete and steel reinforcement at elevated temperatures to the overall performance of concrete structures in fire.In the paper presented by Wei et al. (2017) the authors investigated the effects of transient creep strain of concrete on post-tensioned concrete slabs with unbonded tendons by using three-dimensional nonlinear finite-element analysis models. In their study, three concrete constitutive models were employed, one without transient creep strain and the other two with either explicit or implicit consideration of transient creep strain. The results showed that, the model without transient creep strain is too conservative in fire scenarios by giving much larger deflection and higher tendon stress although the model is sufficiently accurate at ambient temperature. In contrast, the models with transient creep strain were found accurate in fire scenarios. However, if the transient creep strain was overestimated, the slab deflection and tendon stress would be reduced, indicating that the transient creep strain has a positive effect on structural fire resistance. Thus it was concluded that the transient creep strain should be considered in the analysis by either an implicit or an explicit approach for its positive contribution to the fire resistance of post-tensioned concrete slabs.The paper contributed by Zhang et al. (2017) was on the mechanical properties of pre-stressing steel both in and after the fire. Empirical formulae were proposed based on experime...

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Mechanical properties of prestressing steel in and after fire

Cited by 28 publications

References 9 publications

Thermal creep and relaxation of prestressing steel

Thermal creep and relaxation of prestressing steel

Review of Post-Fire Inspection Procedures for Concrete Tunnels

Editorial: Fire safety engineering design of concrete structures

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