Structural Basics

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Structural Basics
There are several methods to find shear strength found by many researchers. In this study the shear strength was found by setup suggested by [Bairagi, N. K. and Modhera, C. D., (2004)] those who designed a practical method to find shear force in the absence of the usual or standard methods of shear force. Researchers have experimented with their design in a practical way in the laboratory and their work has been compared with (JSCE) method, but it was found that the proposed method of their design gives a 10% higher than (JSCE) method.
In normal or high and ultra-high strength concrete, especially when concrete grade is increased, the shear failure is of a brittle failure type. Therefore, many researchers have introduced and used steel fiber to increase the shear force capacity and concrete ability and strength to obtain ductile type of failure [J. Zatloukal,et. al., (2012), C. Bywalski, et.al., (2004)]. There many additives to concrete that effects the concrete behavior such as steel fiber, fiber type and silica fume with different ratios. The definition of shear force as sliding surface on another surface or one layer on another layer. This method of slip on the joint surface of the contact gives a clear picture of shear force transmitted through concrete [Khaloo R. and Nakeseok kim., (1997), A. Khanlou, et. al., (2013), Y. Voo, et. al., (2006)].
Experimental study on the direct shear force of normal materials, high and ultra-strength concrete using a simplified and reliable testing test suggested by [Bairagi, N. K. and Modhera,
C. D., (2004)] were presented here. The effect and influence of steel fiber (vf) ratios of (0, 1.0 and 2.0%) on concrete shear strength were studied. This type of experimental test for direct shear calculation represented the most, efficient and the simplest test and also more convenient and accessible to indicate a realistic and effective sliding mechanism in shear.

Experimental laboratory work for this research study consists of casting, examining and testing of (normal, high and ultra-high concrete samples) tested in direct shearing load. Three
(3) samples for each concrete type are made for each separate mixture, and take the mean value. Details and organizations for every laboratory experimental work test are displayed in the subsequent:

Normal Portland cement (type I) was used and adopted throughout and during the experimental laboratory work of this study. This cement complies with [Iraqi Standard Specification No. 5/1984]. Figure (2) display and shows the sample of cement used.

Natural sand was used for normal concrete mixtures while for high and ultra-high silica sand known as glass sand are used as shown in Figures 3 and 4. Fine grades satisfy to B.S. specification No.882/1992 and Iraqi Specification No.45/1984]. Table (1) shows the classification of fine aggregates.

Crushed aggregate was used with maximum particle size of 10 mm for the normal and high strength concrete mixes. The coarse aggregate classification used is consistent with [Iraqi specifications No. 45/1984]
For high HSC and ultra-high UHSC strength concrete blending procedures adopted in this experimental study is proposed by [Wille et al. 2011]. The cement and silica fume were combined and mixed for the first time for 4 minutes, then fine sand was introduced and the dry ingredients were added and blended for 5 minutes. For HSC gravel then added and mixing continuous for about 3 minutes. In these mixes superplasticizer should be added to the water, then the combined water and superplasticizer have been added to the dry mixture and the mixing process has lasted for at least 3 minutes. Finally, steel fibers were inserted and added during mixing in two minutes. Pour the samples by placing the concrete set in the molds continuously into three layers including each layer being vibrated using a vibrator table to get a compact concrete. With each mix control samples arranged and prepared to determine and obtain the mechanical properties of the concrete. Control samples include 3 cylinders (100mmx200mm) and 3 cubes (100mmx100mmx100mm) for compressive strength. After the full casting process have been complete, all samples were covered with nylon layer for 24 hours to prevent moisture loss, figure (11) shows concrete curing treatment. After one day from casting, all prepared samples were removed, transported and placed in water containers tanks to be treated and cured.

The results of mechanical properties (compressive strength) for (normal, high and ultra-high strength concrete) were presented and displayed in Table (6) and Figures (13, 14 and 15). The table shows the increasing percentage of compressive strength f'c with increasing the fiber content of all types of concrete.
• For normal concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength f'c of about (0, 6 and 10%).
• For high strength (HSC) concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength f'c (0, 10 and 19%).
• For ultra-high (UHSC) strength concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength (0, 18 and 42%).

The effect of steel fiber variation on shear strength (normal, high and ultra-high strength concrete) were studied. Three different ratios of steel fibers (0, 1.0 and 2.0%) were added to the mixture and the shear strength was compared for all samples. Differences and Variations in shear strength gained from steel fiber variation. The experimental test results in Table (7) show and display that the ultimate shear strength of the concrete with the inclusion and addition of the fibers increases significantly over the plain concrete. With the addition of fiber, the samples do not suddenly fail and the failure load is higher than the plain concrete load. The amount of fiber used in plain concrete samples does not significantly influence the first cracking load but has a significant and important impact on the crack propagation rate and a load of failure. The tests indicated that samples specimens without fiber have a brittle failure compared to ductile failure for specimens with fiber. The brittle failure has one major crack while the presence of fiber leads to multiple small cracks and shear failure in a brittle mode does not notice. Steel fiber works inside the concrete as a cracks restrainer and confiner which arrested the concrete cracks and pulling-out the fibers from the matrix is observed at the final load step. Figure 16 shows the test procedure and the shape pattern of the failure of concrete samples. Typical variation of shear strength was made with respect and regard to the fiber volume fraction has been planned and plotted in Figure (17 to Fig 28). It should be noted that the maximum and the highest increase in shear strength was found for 2% fiber volume fraction adding in the plain concrete samples.
• For normal concrete, when steel fiber increases from (0, 1 and 2%) an increase in shear strength of about (0, 51.8 and 117.2%).
• For high strength (HSC) concrete, when steel fiber increases from (0, 1 and 2%) an increase in shear strength of about (0, 60.4 and 124.0%).






1. The test results and conclusions show that the setting of the proposed test by [Bairagi, N. K. and Modhera, C. D., (2004)] is very simple to find shear strength.
2. The experimental test work on inverted “L” samples shows that the samples specimens without fibers failed and fractured into a brittle behavior manner type. While the presence and occupation of fiber in the specimen’s samples indicates multiple visible cracks and the failure turn to ductile failure.
3. Due to and because of fibers presence, shear failure in a brittle mode does not notice and the cracks restrained and confined by fibers and this lead to appear of multiple cracks in concrete. In fact, fiber arrested the cracks and finally at the ultimate load, pulling-out the fibers from the matrix is observed
4. When concrete strength changes to high and ultra-high strength and with regard to the fiber presence; ductile failure was observed. Changing in concrete properties with the inclusions of material additives all these components leads to optimal packing density.
5. For normal concrete, when steel fibers increase from (0, 1 and 2%), the average compressive strength f'c increases by (0, 6 and 10%), while for high (HSC) strength concrete an increase in average compressive strength f'c of (0, 10 and 19%) and for ultra-high (UHSC) strength concrete, an increase in average compressive strength f'c (0, 18 and 42%) is achieved.
6. The presence and insertions of fibers increased shear strength of about (0, 51.8 and 117.2%) for normal concrete and about (0, 60.4 and 124.0%) for high strength (HSC) concrete and about (0, 71.5 and 136.3%) for Ultra high strength (UHSC) concrete, when the steel fibers (vf) increases from (0, 1 and 2%).

Submitted: October 04, 2018

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Submitted: October 04, 2018

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Structural Basics

There are several methods to find shear strength found by many researchers. In this study the shear strength was found by setup suggested by [Bairagi, N. K. and Modhera, C. D., (2004)] those who designed a practical method to find shear force in the absence of the usual or standard methods of shear force. Researchers have experimented with their design in a practical way in the laboratory and their work has been compared with (JSCE) method, but it was found that the proposed method of their design gives a 10% higher than (JSCE) method.

In normal or high and ultra-high strength concrete, especially when concrete grade is increased, the shear failure is of a brittle failure type. Therefore, many researchers have introduced and used steel fiber to increase the shear force capacity and concrete ability and strength to obtain ductile type of failure [J. Zatloukal,et. al., (2012), C. Bywalski, et.al., (2004)]. There many additives to concrete that effects the concrete behavior such as steel fiber, fiber type and silica fume with different ratios. The definition of shear force as sliding surface on another surface or one layer on another layer. This method of slip on the joint surface of the contact gives a clear picture of shear force transmitted through  concrete [Khaloo R. and Nakeseok kim., (1997), A. Khanlou, et. al., (2013), Y. Voo, et. al., (2006)].

Experimental study on the direct shear force of normal materials, high and ultra-strength concrete using a simplified and reliable testing test suggested by [Bairagi, N. K. and Modhera,

C. D., (2004)] were presented here. The effect and influence of steel fiber (vf) ratios of (0, 1.0 and 2.0%) on concrete shear strength were studied. This type of experimental test for direct shear calculation represented the most, efficient and the simplest test and also more convenient and accessible to indicate a realistic and effective sliding mechanism in shear.

 

Experimental laboratory work for this research study consists of casting, examining and testing of (normal, high and ultra-high concrete samples) tested in direct shearing load. Three

  1. samples for each concrete type are made for each separate mixture, and take the mean value. Details and organizations for every laboratory experimental work test are displayed in the subsequent:

 

Normal Portland cement (type I) was used and adopted throughout and during the experimental laboratory work of this study. This cement complies with [Iraqi Standard Specification No. 5/1984]. Figure (2) display and shows the sample of cement used.

 

Natural sand was used for normal concrete mixtures while for high and ultra-high silica sand known as glass sand are used as shown in Figures 3 and 4. Fine grades satisfy to B.S. specification No.882/1992 and Iraqi Specification No.45/1984]. Table (1) shows the classification of fine aggregates.

 

Crushed aggregate was used with maximum particle size of 10 mm for the normal and high strength concrete mixes. The coarse aggregate classification used is consistent with [Iraqi specifications No. 45/1984]

For high HSC and ultra-high UHSC strength concrete blending procedures adopted in this experimental study is proposed by [Wille et al. 2011]. The cement and silica fume were combined and mixed for the first time for 4 minutes, then fine sand was introduced and the dry ingredients were added and blended for 5 minutes. For HSC gravel then added and mixing continuous for about 3 minutes. In these mixes superplasticizer should be added to the water, then the combined water and superplasticizer have been added to the dry mixture and the mixing process has lasted for at least 3 minutes. Finally, steel fibers were inserted and added during mixing in two minutes. Pour the samples by placing the concrete set in the molds continuously into three layers including each layer being vibrated using a vibrator table to get a compact concrete. With each mix control samples arranged and prepared to determine and obtain the mechanical properties of the concrete. Control samples include 3 cylinders (100mmx200mm) and 3 cubes (100mmx100mmx100mm) for compressive strength. After the full casting process have been complete, all samples were covered with nylon layer for 24 hours to prevent moisture loss, figure (11) shows concrete curing treatment. After one day from casting, all prepared samples were removed, transported and placed in water containers tanks to be treated and cured.

 

The results of mechanical properties (compressive strength) for (normal, high and ultra-high strength concrete) were presented and displayed in Table (6) and Figures (13, 14 and 15). The table shows the increasing percentage of compressive strength f'c with increasing the fiber content of all types of concrete.

  • For normal concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength f'c of about (0, 6 and 10%).
  • For high strength (HSC) concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength f'c (0, 10 and 19%).
  • For ultra-high (UHSC) strength concrete (when steel fiber increases from (0, 1 and 2%) an increase in average compressive strength (0, 18 and 42%).

 

The effect of steel fiber variation on shear strength (normal, high and ultra-high strength concrete) were studied. Three different ratios of steel fibers (0, 1.0 and 2.0%) were added to the mixture and the shear strength was compared for all samples. Differences and Variations in shear strength gained from steel fiber variation. The experimental test results in Table (7) show and display that the ultimate shear strength of the concrete with the inclusion and addition of the fibers increases significantly over the plain concrete. With the addition of fiber, the samples do not suddenly fail and the failure load is higher than the plain concrete load. The amount of fiber used in plain concrete samples does not significantly influence the first cracking load but has a significant and important impact on the crack propagation rate and a load of failure. The tests indicated that samples specimens without fiber have a brittle failure compared to ductile failure for specimens with fiber. The brittle failure has one major crack while the presence of fiber leads to multiple small cracks and shear failure in a brittle mode does not notice. Steel fiber works inside the concrete as a cracks restrainer and confiner which arrested the concrete cracks and pulling-out the fibers from the matrix is observed at the final load step. Figure 16 shows the test procedure and the shape pattern of the failure of concrete samples. Typical variation of shear strength was made with respect and regard to the fiber volume fraction has been planned and plotted in Figure (17 to Fig 28). It should be noted that the maximum and the highest increase in shear strength was found for 2% fiber volume fraction adding in the plain concrete samples.

  • For normal concrete, when steel fiber increases from (0, 1 and 2%) an increase in shear strength of about (0, 51.8 and 117.2%).
  • For high strength (HSC) concrete, when steel fiber increases from (0, 1 and 2%) an increase in shear strength of about (0, 60.4 and 124.0%).

 

 

 

 

 

 

  1. The test results and conclusions show that the setting of the proposed test by [Bairagi, N. K. and Modhera, C. D., (2004)] is very simple to find shear strength.
  2. The experimental test work on inverted “L” samples shows that the samples  specimens without fibers failed and fractured into a brittle behavior manner type. While the presence and occupation of fiber in the specimen’s samples indicates multiple visible cracks and the failure turn to ductile failure.
  3. Due to and because of fibers presence, shear failure in a brittle mode does not notice and the cracks restrained and confined by fibers and this lead to appear of multiple cracks in concrete. In fact, fiber arrested the cracks and finally at the ultimate load, pulling-out the fibers from the matrix is observed
  4. When concrete strength changes to high and ultra-high strength and with regard to the fiber presence; ductile failure was observed. Changing in concrete properties with the inclusions of material additives all these components leads to optimal packing density.
  5. For normal concrete, when steel fibers increase from (0, 1 and 2%), the average compressive strength f'c increases by (0, 6 and 10%), while for high (HSC) strength concrete an increase in average compressive strength f'c of (0, 10 and 19%) and for ultra-high (UHSC) strength concrete, an increase in average compressive strength f'c (0, 18 and 42%) is achieved.
  6. The presence and insertions of fibers increased shear strength of about (0, 51.8 and 117.2%) for normal concrete and about (0, 60.4 and 124.0%) for high strength (HSC) concrete and about (0, 71.5 and 136.3%) for Ultra high strength (UHSC) concrete, when the steel fibers (vf) increases from (0, 1 and 2%).


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