scholarly journals TENSILE, COMPRESSIVE AND FLEXURAL STRENGTH REDUCTION OF TIMBER IN FIRE

2009 ◽  
Vol 1 (3) ◽  
pp. 148-156 ◽  
Author(s):  
Zoja Bednarek ◽  
Mečislavas Griškevičius ◽  
Gintas Šaučiuvėnas
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Reduction Rate ◽  
Strength Reduction ◽  
Timber Structures ◽  
Static Tests ◽  
Reduction Coefficient ◽  
Temperature Ranges ◽  
In Fire ◽  
Linear Expression

The present research was dedicated to investigation into the strength of timber structures under fire conditions. Two kinds of timber specimens including oak and pine were used. The carried out investigation covered static tests on tensile strength, compressive strength along the grain, compressive strength perpendicular to the grain and flexural strength. The specimens were tested under the temperatures of 50°C, 100°C, 150°C, 200°C and 230°C. The obtained results show that pine specimens have better properties over the entire temperature range in case of tests on tensile and flexural strength. Also, as for these types of strength, oak specimens show a higher strength reduction rate than those of pine specimens, whereas oak specimens have better properties over the entire temperature ranges in case of compressive strength perpendicular to the grain. Based on statistical analysis, a linear expression of the strength reduction coefficient was proposed.

scholarly journals The Effect of Fire on the Strength of Concrete Material

2021 ◽  
Vol 12 (1) ◽  
pp. 63-68
Author(s):  
HM Iqbal Mahmud ◽  
Md Kawser Babu Raju ◽  
Md Lokman Hosen
Keyword(s):  
Experimental Investigation ◽  
Compressive Strength ◽  
Flexural Strength ◽  
Engineering Science ◽  
Structural Members ◽  
Concrete Material ◽  
Two Systems ◽  
Forced Cooling ◽  
In Fire

Structural members exposed to fire may damage considerably, lose their durability, and even collapse due to the failure of the members. This work presents the results of an experimental investigation of the effect of fire on the strength of concrete. Cylindrical and beam specimens were prepared and burnt in the fire for one hour. In both cases, two systems were followed for cooling the samples, (i) natural cooling in the air (ii) forced cooling in the water. Afterwards, the compressive and flexural strength of the specimens were determined. The result shows that the strength of concrete was considerably reduced due to burning in fire. The compressive strength of cylindrical specimens was decreased by 44% and 60%, respectively, for the natural and forced cooling of the specimens. In the case of beam samples, the flexural strength was decreased60% and 69%, respectively, for the natural and forced cooled specimens. This research also reveals that the specimen cooled in air showed better performance compared to that cooled in water. Journal of Engineering Science 12(1), 2021, 63-68

scholarly journals Analysis of the stress state at the double-step joint in heavy timber structures

2019 ◽  
Vol 69 (335) ◽  
pp. 196
Author(s):  
J. R. Villar-García ◽  
P. Vidal-López ◽  
J. Crespo ◽  
M. Guaita
Keyword(s):  
Shear Stress ◽  
Cross Sections ◽  
Shear Crack ◽  
Experimental Tests ◽  
Strength Reduction ◽  
Timber Structures ◽  
Double Step ◽  
Reduction Coefficient ◽  
Simplifying Assumptions ◽  
Shear Strength Reduction

The double-step joint is among the most frequently used layouts, within carpentry joints, for transmitting higher forces that would allow a single notch. They are especially effective in heavy timber structures. Nowadays, computer-aided manufacturing is being used more often, demanding further progress in its understanding. The conventional design of these joints is conducted by using simplifying assumptions, in particular regarding the shear stress distribution. This is overcome by the use of strength reduction coefficient, which is currently under study. Numerical simulation and experimental tests were carried out with heavy timber cross-sections for rafter to tie-beam truss joint. They were manufactured in glue-laminated timber owing to the large cross-sections tested. Experimental load-strain and load-displacement diagrams were compared with numerical results. This allowed observing the great shear stress concentration produced in the failure by shear crack, which suggests the application of conservative shear strength reduction coefficients.

Effects of Mix Proportion on the Strength and Elasticity of Concrete Subjected to High Temperatures up to 800C

2016 ◽  
Vol 711 ◽  
pp. 472-479 ◽  
Author(s):  
Hironobu Nishi ◽  
Hideo Kasami ◽  
Takafumi Tayama
Keyword(s):  
Weight Loss ◽  
Compressive Strength ◽  
High Temperatures ◽  
Temperature Rise ◽  
Poisson’S Ratio ◽  
Reduction Rate ◽  
Strength Reduction ◽  
Poisson's Ratio ◽  
Exposure Temperature ◽  
Moduli Of Elasticity

This paper presents the results of an experimental study on the strength and elasticity of concrete subjected to high temperatures up to 800C carried out to determine the effects of exposure temperature and the effects of mixture proportion of concrete. Cylinders made of 4 mixture of normal-weight concrete with the W/C of 50 and 60% and slump of 50 and 210mm were subjected to 13 phases of temperatures from 20 to 800C without seal at the age of 91 days. Exposure term was 91 days for exposure up to 300C, 60 days for 400C and 24 hours for higher temperatures above 500C. After temperature exposure, cylinders were tested for weight loss, compressive strength, dynamic and static moduli of elasticity and Poisson's ratio at room temperature.Weight loss increased with exposure temperature, indicating greater loss below 110C and smaller loss above 300C. Compressive strength did not decline monotonously with temperature rise between 20 and 110C, but showed 10 % reduction at 35 to 50C and recovery at 80 to 110C, indicating the minimal and maximum points. The minimal point was associated with intermediate weight loss of 4 to 5 %. At temperatures higher than 400C, residual compressive strength showed greater reduction with temperature rise for smaller weight loss.As for the effects of mixture proportion, concrete with higher W/C and higher water content showed greater weight loss and greater strength reduction below 300C, while those with higher cement content showed greater strength reduction above 500C.Both dynamic and static modulus of elasticity declined monotonously with temperature rise, indicating higher reduction rate than compressive strength. And the relationship between the two moduli of elasticity was in good correlation. Poisson's ratio did not show monotonous change with temperature, but showed discontinuity between elevated and high temperatures, indicating downward peaks at about 80C which associated with 2 to 5 % weight loss, and an upward peak at 200 to 300C, which was associated with about 7 % weight loss, and a rapid increase at higher temperature of 700 to 800C.

scholarly journals Comparison of Long-Term Strength Development of Steel Fiber Shotcrete with Cast Concrete Based on Accelerator Type

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5599
Author(s):  
Kyong Ku Yun ◽  
Seunghak Choi ◽  
Taeho Ha ◽  
Mohammad Shakhawat Hossain ◽  
Seungyeon Han
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Steel Fiber ◽  
Strength Reduction ◽  
Strength Development ◽  
Fiber Reinforced ◽  
Cast Concrete ◽  
Long Term Performance ◽  
Term Performance

This study analyzed the effect of accelerating agents, such as aluminate, cement mineral, and alkali-free accelerators, on the long-term performance of steel-fiber-reinforced shotcrete. The shotcrete performance was studied based on the type and amount of steel fiber added. Performance tests were performed to identify the accelerator providing better long-term performance to the steel-fiber-reinforced shotcrete. Changes in strength and flexural performance over time were investigated. The compressive strength and flexural strength tests on 1-, 3-, 6-, 12-, and 24-month-old test specimens were performed, wherein 37 kg of steel fiber was added to the cement mineral and aluminate mixes, and 40 kg of steel fiber was added to the alkali-free mix. The 1-month compressive strength result of all the test variables satisfied the Korea Expressway Corporation standard. The compressive strength of the cast concrete and shotcrete specimens increased with age, demonstrating a strength reduction, particularly in the 24-month-old shotcrete specimens. Thus, the shotcrete performance may deteriorate in the long-term. In the 24-month-old specimen, substantial flexural strength reduction was observed, particularly in the aluminate and alkali-free specimens. The relative strength of the specimens was compared with that of the cast concrete mold specimens. The results suggest the use of alkali-free accelerators, considering the long-term performance of tunnels and safety of workers. Moreover, increasing the steel fiber performance rather than the amount of low-performance steel fiber must be considered.

Performance of carbon nanotubes in mortar using different surfactants

2017 ◽  
Vol 44 (8) ◽  
pp. 619-625 ◽  
Author(s):  
M. Elkashef ◽  
M.N. Abou-Zeid
Keyword(s):  
Carbon Nanotubes ◽  
Raman Spectroscopy ◽  
Compressive Strength ◽  
Sodium Dodecyl Sulfate ◽  
Flexural Strength ◽  
Sodium Dodecyl ◽  
Strength Reduction ◽  
Degree Of Dispersion ◽  
Ultrasonication Time ◽  
Triton X

The performance of carbon nanotubes (CNTs) in cement-based composites relies to a great extent on its degree of dispersion. In this work, the performance of two commonly used surfactants; sodium dodecyl sulfate (SDS) and Triton X-100, is being compared. The effect of surfactant-to-CNT ratio on dispersion efficiency is studied using ultraviolet-visible (UV-Vis) spectrometry, to determine the optimum surfactant dosage. For the optimum ultrasonication energy, Raman spectroscopy is used to assess the degree of imperfections on CNTs. CNTs-reinforced mortar specimens prepared using Triton X-100 and SDS are tested for compressive and flexural strength. Triton X-100 is shown to exhibit better dispersion efficiency than SDS, leading to greater improvement in flexural and compressive strength. An ultrasonication time of 60 min (19.4 kJ/mL) is shown to be sufficient to achieve proper dispersion, however notable degradation of CNTs was noted beyond 30 min (9.7 kJ/mL) of dispersion leading to a strength reduction.

scholarly journals The Influence of Concrete Strength on the Effect of Synthetic Fibres on Fire Resistance

2017 ◽  
Vol 62 (1) ◽  
pp. 136-142 ◽  
Author(s):  
Éva Lublóy
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Pore Structure ◽  
Fire Resistance ◽  
Concrete Strength ◽  
Small Diameter ◽  
Concrete Surface ◽  
Strength Reduction ◽  
Fibre Reinforcement ◽  
Polypropylene Fibres

Numerous studies have verified that increased concrete strength reduces its resistance to fire, leads to a higher degree of strength reduction and higher chances of spalling of concrete surfaces.The risks of spalling of concrete surfaces can be reduced by adding synthetic polypropylene fibres. Numerous experiments have shown that the risk of spalling of the concrete surface is significantly lower when using short, small diameter fibres of polypropylene synthetic, because the pore structure created by the burning of fibres reduces the risk of cracking.However, the question arises whether other types of fibres of greater diameter and length are still able to prevent spalling of concrete surfaces without drastically reducing the strength and if so, in what range of concrete strength it is true.The experiments are aimed to determine the effects of micro and macro synthetic fibres on the post-fire residual compressive strength, flexural strength and porosity of concrete.Nine kinds of mixture were prepared and tested. Three of them are without fibers (reference concretes) with diverse strength, three with synthetic micro-fibres with diverse strength and three with synthetic macro-fibres of diverse strength. The experiment was conducted with three concretes with different strength. Each type had a reference concrete without fibre reinforcement, one with micro- and one with macro-fibres.

scholarly journals Mechanical properties of concrete reinforced with hybrid polypropylene- PET waste fibers

2021 ◽  
Vol 8 (1) ◽  
pp. 10-22
Author(s):  
Sary Hussein ◽  
◽  
Azad Mohammed
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Fiber Length ◽  
Laboratory Experiments ◽  
Polypropylene Fiber ◽  
Strength Reduction ◽  
Hybrid Fiber ◽  
Good Opportunity ◽  
Pet Waste ◽  
Compressive Strength Of Concrete

In this article, flexural strength and compressive strength of concrete containing polypropylene fiber (PP), polyethylene terephthalate (PET) waste fiber and a combination between them were experimentally investigated. For this reason, laboratory experiments were performed on a total of 40 mixes. Results show that compressive strength property of concrete reinforced with PET waste fiber is not comparable to that of concrete reinforced with PP fiber, in which there is a compressive strength reduction, and the effect of PET fiber length on the strength is not important. Behavior of concrete contained PET waste fiber in flexure was found better. There is a good opportunity to use a hybrid fiber (25% PET and 75% PP) to enhance flexural strength of concrete.

scholarly journals Compressive Strength Gain Behavior and Prediction of Cement-Stabilized Macadam at Low Temperature Curing

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yongli Xu ◽  
Guang Yang ◽  
Hongyuan Zhao
Keyword(s):  
Compressive Strength ◽  
Low Temperature ◽  
Curing Temperature ◽  
Strength Development ◽  
Construction Process ◽  
Strength Gain ◽  
Estimation Model ◽  
Maturity Method ◽  
Temperature Ranges ◽  
Natural Temperature

For cement-based materials, the curing temperature determines the strength gain rate and the value of compressive strength. In this paper, the 5% cement-stabilized macadam mixture is used. Three indoor controlled temperature curing and one outdoor natural curing scenarios are designed and implemented to study the strength development scenario law of compressive strength, and they are standard temperature curing (20°C), constant low temperature curing (10°C), day interaction temperature curing (varying from 6°C to 16°C), and one outdoor natural temperature curing (in which the air temperature ranges from 4°C to 20°C). Finally, based on the maturity method, the maturity-strength estimation model is obtained by using and analyzing the data collected from the indoor tests. The model is proved with high accuracy based on the validated results obtained from the data of outdoor tests. This research provides technical support for the construction of cement-stabilized macadam in regions with low temperature, which is beneficial in the construction process and quality control.

scholarly journals Preparation of Electric- and Magnetic-Activated Water and Its Influence on the Workability and Mechanical Properties of Cement Mortar

2021 ◽  
Vol 13 (8) ◽  
pp. 4546
Author(s):  
Kaiyue Zhao ◽  
Peng Zhang ◽  
Bing Wang ◽  
Yupeng Tian ◽  
Shanbin Xue ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Compressive Strength ◽  
Flexural Strength ◽  
Cement Paste ◽  
Cement Mortar ◽  
Environmental Issues ◽  
Chemical Admixtures ◽  
Untreated Water ◽  
Alternating Voltage

Cement-based materials prepared with activated water induced by a magnetic field or electric field represent a possible solution to environmental issues caused by the worldwide utilization of chemical admixtures. In this contribution, electric- and magnetic-activated water have been produced. The workability and mechanical properties of cement mortar prepared with this activated water have been investigated. The results indicate that the pH and absorbance (Abs) values of the water varied as the electric and magnetic field changed, and their values increased significantly, exhibiting improved activity compared with that of the untreated water. In addition, activated water still retains activity within 30 min of the resting time. The fluidity of the cement paste prepared with electric-activated water was significantly larger than that of the untreated paste. However, the level of improvement differed with the worst performance resulting from cement paste prepared with alternating voltage activated water. In terms of mechanical properties, both compressive strength and flexural strength obtained its maximum values at 280 mT with two processing cycles. The compressive strength increased 26% as the curing time increased from 7 days to 28 days and flexural strength increased by 31%. In addition, through the introduction of magnetic-activated water into cement mortar, the mechanical strength can be maintained without losing its workability when the amount of cement is reduced.

Sign in / Sign up

Export Citation Format

Share Document