scholarly journals Post-Fire Behavior of Post-Tensioned Segmental Concrete Beams under Monotonic Static Loading

2020 ◽  
Vol 6 (5) ◽  
pp. 889-906
Author(s):  
Nazar Oukaili ◽  
Amer F. Izzet ◽  
Haider M. Hekmet
Keyword(s):  
High Temperature ◽  
Concrete Beams ◽  
Heating Temperature ◽  
Fire Behavior ◽  
Experimental Program ◽  
Time Interval ◽  
Internal Layers ◽  
Fire Event ◽  
Standard Fire ◽  
Post Tensioned

This paper presents a study to investigate the behavior of post-tensioned segmental concrete beams that exposed to high-temperature. The experimental program included fabricating and testing twelve simply supported beams that divided into three groups depending on the number of precasting concrete segments. All specimens were prepared with an identical length of 3150 mm and differed in the number of the incorporated segments of the beam (9, 7, or 5 segments). To simulate the genuine fire disasters, nine out of twelve beams were exposed to a high-temperature flame for one hour. Based on the standard fire curve (ASTM – E119), the temperatures of 300◦C (572◦F), 500◦C (932◦F), and 700◦C (1292◦F) were adopted. Consequently, the beams that exposed to be cool gradually under the ambient laboratory condition, after that, the beams were loaded till failure to investigate the influence of the heating temperature on the performance during the serviceability and the failure stage. It was observed that, as the temperature increased in the internal layers of concrete, the camber of tested beams increased significantly and attained its peak value at the end of the time interval of the stabilization of the heating temperature. This can be attributed to the extra time that was consumed for the heat energy to migrate across the cross-section and to travel along the span of the beam and deteriorate the texture of the concrete causing microcracking with a larger surface area. Experimental findings showed that the load-carrying capacity of the test specimen, with the same number of incorporated concrete segments, was significantly decreased as the heating temperature increased during the fire event.

scholarly journals Post-Fire Behavior of Non-Prismatic Beams with Multiple Rectangular Openings Monotonically Loaded

2021 ◽  
Vol 11 (6) ◽  
pp. 7763-7769
Author(s):  
B. F. Abdulkareem ◽  
A. F. Izzet ◽  
N. Oukaili
Keyword(s):  
Ultimate Strength ◽  
Heating Temperature ◽  
Fire Behavior ◽  
Exposure Period ◽  
Experimental Program ◽  
Residual Deflection ◽  
Exposure Temperature ◽  
Load Carrying ◽  
Influence Of Temperature On ◽  
Ultimate Load Carrying Capacity

The main objective of this paper is to study the behavior of Non-Prismatic Reinforced Concrete (NPRC) beams with and without rectangular openings either when exposed to fire or not. The experimental program involves casting and testing 9 NPRC beams divided into 3 main groups. These groups were categorized according to heating temperature (ambient temperature, 400°C, and 700°C), with each group containing 3 NPRC beams (solid beams and beams with 6 and 8 trapezoidal openings). For beams with similar geometry, increasing the burning temperature results in their deterioration as reflected in their increasing mid-span deflection throughout the fire exposure period and their residual deflection after cooling. Meanwhile, the existing openings situation was compounded. The burned NPRC beams were left to gradually cool down under ambient laboratory conditions, and afterward, they were loaded until failure. The influence of temperature on the residual ultimate load-carrying capacity of each beam was studied by comparing these beams with unburned reference beams. Increasing exposure temperature reduces the ultimate strength of solid NPRC beams exposed to temperatures of 400°C and 700°C by about 5.7% and 10.84% respectively. Meanwhile, NPRC beams with trapezoidal openings showed ultimate strength reductions of 21.13% and 32.8% (for beams with 8 openings) and 28% and 34.4% (for beams with 6 openings) under the same burning conditions. The excessive mid-span deflections for these three types of beams were 2%–30.8%, 1.33%–21.8%, and 1.5%–17.4% under the same burning conditions.

scholarly journals Influence of Alkali Treatment on the Microstructure and Mechanical Properties of Coir and Abaca Fibers

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2636
Author(s):  
Petr Valášek ◽  
Miroslav Müller ◽  
Vladimír Šleger ◽  
Viktor Kolář ◽  
Monika Hromasová ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Composite Materials ◽  
Alkali Treatment ◽  
Fiber Surface ◽  
Cellulose Fibers ◽  
Sem Analysis ◽  
Experimental Program ◽  
Time Interval ◽  
The European Union ◽  
Vegetable Fibers

Composite materials with natural fillers have been increasingly used as an alternative to synthetically produced materials. This trend is visible from a representation of polymeric composites with natural cellulose fibers in the automotive industry of the European Union. This trend is entirely logical, owing to a preference for renewable resources. The experimental program itself follows pronounced hypotheses and focuses on a description of the mechanical properties of untreated and alkali-treated natural vegetable fibers, coconut and abaca fibers. These fibers have great potential for use in composite materials. The results and discussion sections contribute to an introduction of an individual methodology for mechanical property assessment of cellulose fibers, and allows for a clear definition of an optimal process of alkalization dependent on the content of hemicellulose and lignin in vegetable fibers. The aim of this research was to investigate the influence of alkali treatment on the surface microstructure and tensile properties of coir and abaca fibers. These fibers were immersed into a 5% solution of NaOH at laboratory temperature for a time interval of 30 min, 1 h, 2 h, 3 h, 6 h, 12 h, 24 h, and 48 h, rinsed and dried. The fiber surface microstructures before and after the alkali treatment were evaluated by SEM (scanning electron microscopy). SEM analysis showed that the alkali treatment in the NaOH solution led to a gradual connective material removal from the fiber surface. The effect of the alkali is evident from the visible changes on the surface of the fibers.

scholarly journals Investigation of the kinetics of spontaneous combustion of the major coal seam in Dahuangshan mining area of the Southern Junggar coalfield, Xinjiang, China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Shen ◽  
Qiang Zeng
Keyword(s):  
Particle Size ◽  
High Temperature ◽  
Coal Seam ◽  
Spontaneous Combustion ◽  
Heating Temperature ◽  
Characteristic Temperature ◽  
Mining Area ◽  
Particle Sizes ◽  
Coal Oxidation ◽  
Increasing Temperature

AbstractIn the present paper, with using diverse methods (including the SEM, the XRD, the TPO, the FTIR, and the TGA) , the authors analysed samples of the major coal seam in Dahuangshan Mining area with different particle sizes and with different heated temperatures (from 50 to 800 °C at regular intervals of 50 °C). The results from SEM and XRD showed that high temperature and high number of pores, fissures, and hierarchical structures in the coal samples could facilitate oxidation reactions and spontaneous combustion. A higher degree of graphitization and much greater number of aromatic microcrystalline structures facilitated spontaneous combustion. The results from TPO showed that the oxygen consumption rate of the coal samples increased exponentially with increasing temperature. The generation rates of different gases indicated that temperatures of 90 °C or 130 °C could accelerate coal oxidation. With increasing temperature, the coal oxidation rate increased, and the release of gaseous products was accelerated. The FTIR results showed that the amount of hydroxide radicals and oxygen-containing functional groups increased with the decline in particle size, indicating that a smaller particle size may facilitate the oxidation reaction and spontaneous combustion of coal. The absorbance and the functional group areas at different particle sizes were consistent with those of the heated coal samples, which decreased as the temperature rose. The results from TGA showed that the characteristic temperature T3 declined with decreasing particle size. After the sample with 0.15–0.18 mm particle size was heated, its carbon content decreased, and its mineral content increased, inhibiting coal oxidation. This result also shows that the activation energy of the heated samples tended to increase at the stage of high-temperature combustion with increasing heating temperature.

scholarly journals Experimental Study on the Torsional Behaviour of Prestressed HSC Hollow Beams

2020 ◽  
Vol 10 (2) ◽  
pp. 642 ◽  
Author(s):  
Luís Bernardo ◽  
Sérgio Lopes ◽  
Mafalda Teixeira
Keyword(s):  
Experimental Study ◽  
High Strength Concrete ◽  
Concrete Beams ◽  
Concrete Strength ◽  
High Strength ◽  
Experimental Program ◽  
Pure Torsion ◽  
Strength Concrete ◽  
Hollow Beams

This article describes an experimental program developed to study the influence of longitudinal prestress on the behaviour of high-strength concrete hollow beams under pure torsion. The pre-cracking, the post-cracking and the ultimate behaviour are analysed. Three tests were carried out on large hollow high-strength concrete beams with similar concrete strength. The variable studied was the level of longitudinal uniform prestress. Some important conclusions on different aspects of the beams’ behaviour are presented. These conclusions, considered important for the design of box bridges, include the influence of the level of prestress in the cracking and ultimate behaviour.

In Situ XRD Study of Zirconia Phase Transformation Produced from Chemical and Mineral Processes

2016 ◽  
Vol 840 ◽  
pp. 375-380
Author(s):  
Meor Yusoff Meor Sulaiman ◽  
Khaironie Mohamed Takip ◽  
Ahmad Khairulikram Zahari
Keyword(s):  
High Temperature ◽  
Heating Temperature ◽  
Tetragonal Zirconia ◽  
Amorphous Structure ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Zirconyl Chloride ◽  
High Temperature Xrd ◽  
Temperature Phase Transition

The high temperature phase transition of zirconia produced from commercial zirconyl chloride chemical was compared with that produced from a Malaysian zircon mineral. Zirconyl chloride was produced from zircon by using the hydrothermal fusion method. Initial XRD diffractogram of these samples at room temperature show that they are of amorphous structure. High temperature XRD studies was then performed on these samples; heated up to 1500°C. The XRD diffractograms shows that the crystalline structure of tetragonal zirconia was first observed and the monoclinic zirconia becomes more visible at higher heating temperature.

Potential of a Novel Thermotolerant Lipase Bacillus stearothermophilus nr22 (Lip.nr-22) as Additive in High Temperature Operated-Neutral pH Liquid Detergent

2017 ◽  
Vol 735 ◽  
pp. 136-142 ◽  
Author(s):  
Nik Raikhan Nik Him ◽  
Nurul Shafika Azmi
Keyword(s):  
High Temperature ◽  
Bacillus Stearothermophilus ◽  
Laundry Detergent ◽  
Detergent Formulation ◽  
Time Interval ◽  
Oil Removal ◽  
Optimum Conditions ◽  
Detergent Concentration ◽  
Neutral Ph ◽  
Commercial Detergents

Enzyme-added detergent must have the capability to operate at high temperature to support the enzyme proteins to clean soiled-fabrics at optimum conditions. Lipase from Bacillus stearothermophilus nr22 (Lip.nr-22) has improved the oil removal from soiled-cotton fabric by 38.8-51.4% in 4 types of local commercial detergents. The later was the oil removal from an unrevealed detergent. The optimum conditions were 108U/ml Lip.nr-22 in 0.1M, pH 7.0, washing temperature and washing time interval as 80°C and 40 min, respectively; shaking wash at 300 rpm and percentage of detergent concentration as 0.5. Lip.nr-22 is a very potential enzyme in high temperature-neutral pH operated laundry detergent formulations. It has exhibited a very excellent thermostability at 80°C, was very stable with surfactants, commercial detergents as well as with oxidizing agents (H2O2, NaBO3H2O and NaClO). Lip.nr-22 as additive in detergent formulation is a promise for better detergent formulation.

Deterioration of Local Mechanical Properties of HVOF-Sprayed Stellite 6 after Exposure to High-Temperature Corrosion

2015 ◽  
Vol 662 ◽  
pp. 115-118 ◽  
Author(s):  
Zdeněk Česánek ◽  
Jan Schubert ◽  
Šárka Houdková ◽  
Olga Bláhová ◽  
Michaela Prantnerová
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
High Temperature Corrosion ◽  
Corrosion Testing ◽  
Time Interval ◽  
Coating Properties ◽  
Operational Conditions ◽  
Stellite 6 ◽  
Coating Surface ◽  
Before And After

Coating properties determine its behavior in operation. The simulation of future operational conditions is therefore the best quality test. The evaluation during operation is usually not possible to perform, and the coatings are therefore frequently characterized by their physical or mechanical properties. This text deals with the high temperature corrosion of HVOF sprayed Stellite 6 coating and with changes of its local mechanical properties before and after the corrosion testing. High temperature corrosion is defined as a corrosion in the presence of molten salts. In this case, the mixture of salts in composition of 59% Na2(SO)4 with 34.5% KCl and 6.5% NaCl was used. Two exposure temperatures 525 °C and 575 °C were selected and the tests for both temperatures were performed in the time interval of 168h in the autoclave. The coating with salt mixture layer was analyzed using scanning electron microscopy and nanoindentation. The high temperature resistance of Stellite 6 coating was evaluated according to the changes in the coating surface and by the occurrence of individual phases formed on the coating surface during the test. Generally, it can be said that the Stellite 6 alloys deposited by HVOF technology show selective oxidation under the salt film. This fact was also proved in this study. Furthermore, the nanoindentation measurements of Stellite 6 coating were performed before and after the corrosion testing. These measurements were used to evaluate the change of local mechanical coating properties.

Effect of High Temperature on Concrete: A Literature Review

2006 ◽  
Vol 302-303 ◽  
pp. 138-149 ◽  
Author(s):  
Gai Fei Peng ◽  
Sammy Yin Nin Chan ◽  
Qi Ming Song ◽  
Quan Xin Yi
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
High Temperature ◽  
Elevated Temperature ◽  
Literature Review ◽  
High Strength Concrete ◽  
High Strength ◽  
Research Needs ◽  
Standard Fire ◽  
Fire Condition

This paper presents a review on the effect of fire on concrete, citing 43 references. It was found that most of them are on the behavior of concrete under high temperature conditions more or less different from the standard fire condition. The problem of spalling, which high-strength concrete encounters when exposed to fire, is especially urgent to solve. Since the literature on the behavior of concrete under fire conditions is very limited, the literature even under elevated temperature has to be used as a part of the base of further research. The further research needs urgently to be carried out under the standard fire condition. Residual mechanical properties reported in most previous literature might be overestimated, where natural cooling was usually employed. Proper evaluation of fire resistance of concrete needs more experimental data obtained under various cooling regimes such as water spraying or water quenching.

Shear Failure Analysis of Concrete Beams Reinforced with Newly Developed GFRP Stirrups

2006 ◽  
Vol 324-325 ◽  
pp. 995-998
Author(s):  
Cheol Woo Park ◽  
Jong Sung Sim
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Concrete Beams ◽  
Fiber Reinforced Polymer ◽  
Experimental Program ◽  
Shear Stresses ◽  
Fiber Reinforced ◽  
Shear Span ◽  
Reinforced Polymer ◽  
A New Technique

Even though the application of fiber reinforced polymer (FRP) as a concrete reinforcement becomes more common with various advantages, one of the inherent shortcomings may include its brittleness and on-site fabrication and handling. Therefore, the shape of FRP products has been limited only to a straight bar or sheet type. This study suggests a new technique to use glass fiber reinforced polymer (GFRP) bars for the shear reinforcement in concrete beams, and investigates its applicability. The developed GFRP stirrup was used in the concrete instead of ordinary steel stirrups. The experimental program herein evaluates the effectiveness of the GFRP stirrups with respect to different shear reinforcing ratios under three different shear span-to-depth testing schemes. At the same shear reinforcing ratio, the ultimate loads of the beams were similar regardless the shear reinforcing materials. Once a major crack occurs in concrete, however, the failure modes seemed to be relatively brittle with GFRP stirrups. From the measured strains on the surface of concrete, the shear stresses sustained by the stirrups were calculated and the efficiency of the GFRP stirrups was shown to be 91% to 106% depending on the shear span-to-depth ratio.

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