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Article
Publication date: 20 June 2023

Kei Kimura, Takeshi Onogi and Fuminobu Ozaki

This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain…

Abstract

Purpose

This work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain rates, to propose appropriate reduction factors considering the strain rate effect.

Design/methodology/approach

The stress–strain relationships of 385 N/mm2, 440 N/mm2 and 630 N/mm2-class steel plates at elevated temperatures are examined at three strain rate values (0.3%/min, 3.0%/min and 7.5%/min), and the reduction factors for the effective yield strength at elevated temperatures are evaluated from the results. A differential evolution-based optimization is used to produce the reduction-factor curves.

Findings

The strain rate effect enhances with an increase in the standard design value of the yield point. The effective yield strength and standard design value of the yield point exhibit high linearity between 600 and 700 °C. In addition to effectively evaluating the test results, the proposed reduction-factor curves can also help determine the ultimate strength of a steel member at collapse.

Originality/value

The novelty of this study is the quantitative evaluation of the relationship between the standard design value of yield point at ambient temperature and the strain-rate effect at elevated temperatures. It has been observed that the effect of the strain rate at elevated temperatures increases with the increase in the standard design value of the yield point for various steel strength grades.

Details

Journal of Structural Fire Engineering, vol. 15 no. 1
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 6 April 2021

Kun Liu, Wei Chen, Jihong Ye, Jian Jiang, Wenwen Chen and Mingyue Zhao

Most previous thermal-mechanical modeling of cold-formed steel (CFS) walls did not consider the failure of screwed connections under fire conditions because of the limited data of…

Abstract

Purpose

Most previous thermal-mechanical modeling of cold-formed steel (CFS) walls did not consider the failure of screwed connections under fire conditions because of the limited data of such connections at elevated temperatures.

Design/methodology/approach

In this study, 285 steady-state tests are conducted on CFS screwed connections with single-layer gypsum plasterboard (GPB) and Bolivian magnesium board (BMB) sheathing at ambient and elevated temperatures. The failure of these connections is described as the breaking of the loaded sheathing edge.

Findings

For the BMB sheathing screwed connections, hydrochloric acid gas is generated and released above 300°C, and the shear strength becomes much less than that of the GPB sheathing screwed connection above 370°C. Hence, BMB may not be suitable for use as the face-layer sheathing of CFS walls but is still recommended to replace GPB as the base-layer sheathing. The major influencing parameters on the shear strength of screwed connections are identified as the type of sheathing material and the loaded sheathing edge distance.

Originality/value

Based on the previous and present test results, a unified expression for the residual shear strength of screwed connections with GPB and BMB is proposed at ambient and elevated temperatures with acceptable accuracy. It can be used as the basic input parameter of the numerical simulation of the CFS structures under fire conditions.

Details

Journal of Structural Fire Engineering, vol. 12 no. 2
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 7 December 2021

Sachin Vijaya Kumar and N. Suresh

The Reinforced Concrete(RC) elements are known to perform well during exposure to elevated temperatures. Hence, RC elements are widely used to resist the extreme heat developing…

Abstract

Purpose

The Reinforced Concrete(RC) elements are known to perform well during exposure to elevated temperatures. Hence, RC elements are widely used to resist the extreme heat developing from accidental fires and other industrial processes. In both of the scenarios, the RC element is exposed to elevated temperatures. However, the primary differences between the fire and processed temperatures are the rate of temperature increase, mode of exposure and exposure durations. In order to determine the effect of two heating modalities, RC beams were exposed to processed temperatures with slow heating rates and fire with fast heating rates.

Design/methodology/approach

In the present study, RC beam specimens were exposed to 200 °C, to 800 °C temperature at 200 °C intervals for 2 h' duration by adopting two heating modes; Fire and processed temperatures. An electrical furnace with low-temperature increment and a fire furnace with standard time-temperature increment is adapted to expose the RC elements to elevated temperatures.

Findings

It is observed from test results that, the reduction in load-carrying capacity, first crack load, and thermal crack widths of RC beams exposed to 200 °C, and 600 °C temperature at fire is significantly high from the RC beams exposed to the processed temperature having the same maximum temperature. As the exposure temperature increases to 800 °C, the performance of RC beams at all heating modes becomes approximately equal.

Originality/value

In this work, residual performance, and failure modes of RC beams exposed to elevated temperatures were achieved through two different heating modes are presented.

Details

Journal of Structural Fire Engineering, vol. 13 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 3 September 2019

Mariyana Aida Ab Kadir, Mohammad Iqbal Khiyon, Abdul Rahman Mohd. Sam, Ahmad Beng Hong Kueh, Nor Hasanah Abdul Shukor Lim, Muhammad Najmi Mohamad Ali Mastor, Nurizaty Zuhan and Roslli Noor Mohamed

The purpose of this paper is to examine the mechanical properties, material composition of spent garnet as a sand replacement in high-strength concrete at room and elevated

Abstract

Purpose

The purpose of this paper is to examine the mechanical properties, material composition of spent garnet as a sand replacement in high-strength concrete at room and elevated temperatures. Bonding of the concrete containing spent garnet and reinforcing rebar is investigated. Moreover, the optimum thickness of concrete cover subjected to elevated temperatures is investigated.

Design/methodology/approach

First, the plain spent garnet was physically, chemically and thermally studied. Then, a series of concrete specimens with 0, 20, 40, 60, 80 and 100 per cent of spent garnet were prepared to determine the optimum percentage of spent garnet. Finally, the physical and mechanical behaviours of concrete specimens and effects of cover thickness on steel rebar when subjected to elevated temperature of 200°C, 400°C, 600°C and 800°C for 1 h were studied. It was observed that spent garnet was thermally stable compared to river sand.

Findings

Mechanical properties were found to be optimal for concrete with 40% spent garnet replacement. Physically, spent garnet concrete changed colour to brown at 400°C, and to whitish grey at 600°C. The residual compressive strength of spent garnet concrete was also found slightly higher than that for control specimens. At various high temperatures, the reduction in ultimate tensile stress for steel bar inside concrete cover of 30 mm was the lowest compared to that of 20 mm.

Research limitations/implications

Spalling effect it not considered in this study.

Practical implications

The optimum concrete cover is important issues in reinforced concrete design. This can be used as a guideline by structural designers when using a different type of concrete material in the construction.

Social implications

Utilization of the waste spent garnet reduces usage of natural aggregates in concrete production and enhances its performance at elevated temperatures. Natural aggregates are normally taken from sand and rock. The new innovation in concrete perhaps can produce light concrete, reduce the cost of concrete production and at the same time also mitigates environmental problems affect from waste material such as minimizing disposal area.

Originality/value

Utilization of spent garnet in ordinary Portland cement (OPC) concrete at high temperature is a new innovation. It shows that the concrete cover of the concrete element reduced as compared to the OPC concrete. Reduce in weight concrete however the strength of concrete is similar to conventional concrete. This study at elevated temperature has never been performed by any previous researcher.

Details

Journal of Structural Fire Engineering, vol. 10 no. 4
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 23 August 2022

Naveen Revanna and Charles K.S. Moy

A study on the mechanical characteristics of cementitious mortar reinforced with basalt fibres at ambient and elevated temperatures was carried out. To investigate their effect…

Abstract

Purpose

A study on the mechanical characteristics of cementitious mortar reinforced with basalt fibres at ambient and elevated temperatures was carried out. To investigate their effect, chopped basalt fibres with varying percentages were added to the cement mortar.

Design/methodology/approach

All the specimens were heated using a muffle furnace. Flexural strength and Compressive strength tests were performed, while monitoring the moisture loss to evaluate the performance of basalt fibre reinforced cementitious mortars at elevated temperatures.

Findings

From the study, it is clear that basalt fibres can be used to reinforce mortar as the fibres remain unaffected up to 500 °C. Minimal increases in flexural strengths and compressive strengths were measured with the addition of basalt fibres at both ambient and elevated temperatures. SEM pictures revealed fibre matrix interaction/degradation at different temperatures.

Originality/value

The current study shows the potential of basalt fibre addition in mortar as a reinforcement mechanism at elevated temperatures and provides experimental quantifiable mechanical performances of different fibre percentage addition.

Details

Journal of Structural Fire Engineering, vol. 14 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 21 March 2022

Jason Martinez and Ann Jeffers

A methodology for producing an elevated-temperature tension stiffening model is presented.

Abstract

Purpose

A methodology for producing an elevated-temperature tension stiffening model is presented.

Design/methodology/approach

The energy-based stress–strain model of plain concrete developed by Bažant and Oh (1983) was extended to the elevated-temperature domain by developing an analytical formulation for the temperature-dependence of the fracture energy Gf. Then, an elevated-temperature tension stiffening model was developed based on the modification of the proposed elevated-temperature tension softening model.

Findings

The proposed tension stiffening model can be used to predict the response of composite floor slabs exposed to fire with great accuracy, provided that the global parameters TS and Kres are adequately calibrated against global structural response data.

Originality/value

In a finite element analysis of reinforced concrete, a tension stiffening model is required as input for concrete to account for actions such as bond slip and tension stiffening. However, an elevated-temperature tension stiffening model does not exist in the research literature. An approach for developing an elevated-temperature tension stiffening model is presented.

Article
Publication date: 14 July 2021

Sachin B.P. and N. Suresh

The purpose of the paper is to study the effect of elevated temperature on load carrying capacity of reinforced self compacting concrete beams and the performance of deteriorated…

Abstract

Purpose

The purpose of the paper is to study the effect of elevated temperature on load carrying capacity of reinforced self compacting concrete beams and the performance of deteriorated beams after retrofitting by GFRP sheets. The reinforced beams which were exposed to sustained elevated temperature and tested for flexural load-carrying capacity. Further deteriorated beams (exposed from 500°C to 800°C) were re-strengthened by adopting retrofitting with GFRP sheets.

Design/methodology/approach

The investigation includes the concrete specimens, i.e. cubes of 150 mm, cylinders of size 150 mm dia with 300 mm height and beams of 150 × 150 × 1,100 mm, reinforced with minimum tension reinforcement according to IS 456–2000. The specimens were subjected to elevated temperature from 300°C to 800°C with an interval of 100°C for 2 h. The residual compressive strength, modulus of elasticity, load at first crack of beams and load-carrying capacity of beams for 5-mm deflection were measured before and after retrofitting.

Findings

The result shows that there is a gain in residual compressive strength at 300°C and beyond which it decreases. The modulus of elasticity, load at first crack and load-carrying capacity of beams reduces continuously with an increase in temperature. The decrease in load-carrying capacity of beams is observed from 27.55% and up to 38.77% between the temperature range of 500°C–800°C and after the retrofitting of distressed beams, the load carrying capacity increases up to 24.48%.

Originality/value

Better performance was observed with retrofitting by GFRP sheets when the specimens were distressed due to elevated temperatures.

Details

Journal of Structural Fire Engineering, vol. 12 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 20 September 2019

Subhash Yaragal, Chethan Kumar B. and Manoj Uddavolu Abhinav

To reduce environmental impact caused by excessive use of ordinary Portland cement (OPC) and to mitigate scarcity of base materials such as natural coarse aggregate (NCA)…

Abstract

Purpose

To reduce environmental impact caused by excessive use of ordinary Portland cement (OPC) and to mitigate scarcity of base materials such as natural coarse aggregate (NCA), industrial by-products can be carefully used as alternatives to OPC and NCA, in production of concrete. This paper aims to describe the performance of using ground granulated blast furnace slag (GGBS), fly ash (FA) as a complete replacement to OPC and ferrochrome slag (FCS) as replacement to NCA in production of novel FCS based alkali activated slag/fly ash concretes (AASFC) and evaluate their performance at elevated temperatures.

Design/methodology/approach

Two control factors with three levels each i.e. FA (0, 25 and 50 per cent by weight) and FCS (0, 50 and 100 per cent by volume) as a GGBS and NCA replacement, respectively, were adopted in AASFC mixtures. Further, AASFC mixture specimens were subjected to different levels of elevated temperature, i.e. 200°C, 400°C, 600°C and 800°C. Compressive strength and residual compressive strength were considered as responses. Three different optimization techniques i.e. gray relational analysis, technique for order preference by similarity to ideal solution and Desirability function approach were used to optimize AASFC mixtures subjected to elevated temperatures.

Findings

As FA replacement increases in FCS based AASFC mixtures, workability increases and compressive strength decreases. The introduction of FCS as replacement to NCA in AASFC mixture did not show any significant change in compressive strength under ambient condition. AASFC produced with 75 per cent GGBS, 25 per cent FA and 100 per cent FCS was found to have excellent elevated temperature enduring properties among all other AASFC mixtures studied.

Originality/value

Although several studies are available on using GGBS, FA and FCS in production of OPC-based concretes, present study reports the performance of novel FCS based AASFC mixtures subjected to elevated temperatures. Further, GGBS, FA and FCS used in the present investigation significantly reduces CO2 emission and environmental degradation associated with OPC production and NCA extraction, respectively.

Article
Publication date: 27 February 2023

Irindu Upasiri, Chaminda Konthesingha, Anura Nanayakkara and Keerthan Poologanathan

Elevated temperature material properties are essential in predicting structural member's behavior in high-temperature exposures such as fire. Even though experimental…

Abstract

Purpose

Elevated temperature material properties are essential in predicting structural member's behavior in high-temperature exposures such as fire. Even though experimental methodologies are available to determine these properties, advanced equipment with high costs is required to perform those tests. Therefore, performing those experiments frequently is not feasible, and the development of numerical techniques is beneficial. A numerical technique is proposed in this study to determine the temperature-dependent thermal properties of the material using the fire test results based on the Artificial Neural Network (ANN)-based Finite Element (FE) model.

Design/methodology/approach

An ANN-based FE model was developed in the Matlab program to determine the elevated temperature thermal diffusivity, thermal conductivity and the product of specific heat and density of a material. The temperature distribution obtained from fire tests is fed to the ANN-based FE model and material properties are predicted to match the temperature distribution.

Findings

Elevated temperature thermal properties of normal-weight concrete (NWC), gypsum plasterboard and lightweight concrete were predicted using the developed model, and good agreement was observed with the actual material properties measured experimentally. The developed method could be utilized to determine any materials' elevated temperature material properties numerically with the adequate temperature distribution data obtained during a fire or heat transfer test.

Originality/value

Temperature-dependent material properties are important in predicting the behavior of structural elements exposed to fire. This research study developed a numerical technique utilizing ANN theories to determine elevated temperature thermal diffusivity, thermal conductivity and product of specific heat and density. Experimental methods are available to evaluate the material properties at high temperatures. However, these testing equipment are expensive and sophisticated; therefore, these equipment are not popular in laboratories causing a lack of high-temperature material properties for novel materials. However conducting a fire test to evaluate fire performance of any novel material is the common practice in the industry. ANN-based FE model developed in this study could utilize those fire testing results of the structural member (temperature distribution of the member throughout the fire tests) to predict the material's thermal properties.

Details

Journal of Structural Fire Engineering, vol. 14 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 28 February 2019

Hala Mohamed Elkady, Ahmed M. Yasien, Mohamed S. Elfeky and Mohamed E. Serag

This paper aims to inspect the effect of indirect elevated temperature on the mechanical performance of nano silica concrete (NSC). The effect on both compressive and bond…

Abstract

Purpose

This paper aims to inspect the effect of indirect elevated temperature on the mechanical performance of nano silica concrete (NSC). The effect on both compressive and bond strengths is studied. Pre- and post-exposure to elevated temperature ranges of 200 to 600°C is examined. A range covered by three percentages of 1.5, 3 and 4.5 per cent nano silica (NS) in concrete mixes is tested.

Design/methodology/approach

Pre-exposure mechanical tests (normal conditions – room temperature), using 3 per cent NS in the concrete mix, led to the highest increase in both compressive and bond strengths (43 per cent and 38.5 per cent, respectively), compared to the control mix without NS (based on 28-day results). It is worth noticing that adding NS to the concrete mixes does not have a significant effect on improving early-age strength. Besides, permeability tests are performed on NSC with different NS ratios. NS improved the concrete permeability for all tested percentages of NS. The maximum reduction is accompanied by the maximum percentage used (4.5 per cent NS in the NSC mix), reducing permeability to half the value of the concrete mix without NS. As for post-exposure to elevated-temperature mechanical tests, NSC with 1.5 per cent NS exhibited the lowest loss in strength owing to indirect heat exposure of 600°C; the residual compressive and bond strengths are 73 per cent and 35 per cent, respectively.

Findings

The dispersion technique of NS has a key role in NSC-distinguished mechanical performance with NSC having lower NS percentages. NS significantly improved bond strength. NS has a remarkable effect on elevated temperature endurance. The bond strength of NSC exposed to elevated temperatures suffered faster deterioration than compressive strength of the exposed NSC.

Research limitations/implications

A special scale factor needs to be investigated for the NSC.

Originality/value

Although a lot of effort is placed in evaluating the benefits of using nano materials in structural concrete, this paper presents one of the first outcomes of the thermal effects on concrete mixes with NS as a partial cement replacement.

Details

Journal of Structural Fire Engineering, vol. 10 no. 1
Type: Research Article
ISSN: 2040-2317

Keywords

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