The Effect of Changing Stirrup Spacing and Hook Angle on RC Cantilever Beams with Industrial Iron Chips Waste


 In this study, the usability of industrial iron chips waste was investigated in order to provide recycling in the production of reinforced concrete cantilever beams with different stirrup spacing and hook angle. In the concrete produced for cantilever beams, aggregates not larger than 4 mm in diameter were reduced by 20% and replaced with iron chips waste. Cantilever beams are manufactured with stirrup spaces of 50, 100 and 150 mm. The hook angles of the stirrups are differentiated to be 90 and 135 degrees. The experimental setup was prepared in such a way that one side of the samples was fixed, and the other side was free. The loading process was done from the end point of the released side. Load-Displacement curves of cantilever beams were obtained. In the research, it was observed that although 20% iron chips added cantilever beams experienced a decrease in their strength compared to the reference beams, they increased their ductility values at all three different stirrup spaces. As the stirrup spacing widened, the ductility values decreased. However, the effect of iron chips additive on ductility has increased. Samples with stirrup hook angle of 135 degrees increased both strength and ductility values compared to samples with 90 degrees.


Introduction
Technological developments in recent years have enabled the proliferation and development of industries. The rapid increase in the world population has increased consumerism in society. For this reason, the amount of waste material coming out of the industries has reached great proportions. A signi cant portion of industrial solid waste is generated through the iron and steel industry. Such solid wastes are generally formed in iron and steel production facilities, but they can also occur due to various workshops [3,4,6,8,12,14].
There are different ways to reduce the waste generated because of industrial processes. Some of these are the limitation of production by the places that produce waste material, the recovery of the wastes that can be recovered, and various recycling methods. Iron and steel waste are frequently used materials for recycling [1,3,9].
In many countries, the rapid decline of natural resources has restricted access to raw materials and caused raw material prices to increase. For this reason, the use of industrial waste materials as raw materials by recycling methods in the construction sector has been a logical way [4,5,9]. Reusing iron and steel waste as aggregate substitute in concrete production will reduce the need for raw materials from natural sources. Conservation of natural resources contributes to sustainable development for future generations [8,13].
In previous studies on this subject [8], iron wastes were investigated instead of sand in concrete.
Substitution rates were determined as 10%, 15% and 20%. Samples containing iron waste were prepared and subjected to various tests. As a result of the experiments, the highest exural strength and compressive strength were found in the samples with 20% iron waste additives.
In another study [10], the replacement rates of iron waste for sand in concrete were determined as 10%, 20%, and 30%. As a result of the experiments, 20% iron waste added samples increased their compressive strength by 13.5% and exural strength by 4.8%.
In another study [7], granite powder and iron powder replacement percentages were determined as 5%, 10%, 15% and 20%. Samples were tested after 7 days and 28 days. Samples with 20% iron powder added increased their compressive strength by 33.3% for 7 days and by 33.2% for 28 days. In exural strengths, these rates were 45.1% for 7 days and 44.9% for 28 days.
In the other study [2], lathe iron waste dusts were substituted for ne aggregate in concrete by 5%, 10%, 15% and 20%. As a result of the 20% substitution process, 38% increase in compressive strength and 19% increase in exural strength has been achieved.
Academic studies dealing with the use of iron waste in concrete for recycling show that 20% iron waste substitution can be more e cient than other rates. Studies have generally focused on compressive strength tests and exural strength tests. The fact that the additive directly affects the behavior of the building material should be known and its effect on the behavior of the building element should be examined indirectly. However, the reaction of the additive to the building elements with different properties should be considered.
In this study, iron chips waste, which is frequently created by the iron and steel industry, has been substituted for aggregate in concrete by 20%. The effect of this situation on the behavior of cantilever beams has been taken as a subject. It has been investigated whether the recycling of iron chips waste from industrial factories can be achieved. The spacing and hook angles of the stirrups used in the production of cantilever beams were changed and the effect of iron chips on various stirrup spacing and hook angles was investigated.

Creating Test Samples
Within the scope of the study, 12 samples were produced. The dimensions of the samples were designed to be 150 mm wide, 200 mm high and 700 mm long. 300 mm of the length of the samples was designed as a column for reinforcement placement and 400 mm as a cantilever beam. 6 of the cantilever beams are designed with 20% iron chips added, and 6 of them are designed without additives. While the stirrup hook angle of 3 of the samples without additives was 90 degrees, 3 of them were formed as 135 degrees. The same process was repeated for the samples with 20% iron chips added. S420 steel was used in all samples. Diameter of transverse reinforcement was determined as 8 mm and diameter of longitudinal reinforcement was determined as 12 mm. 4 tension rebar and 2 compression rebar are used. Fig. 1. shows the reinforcement layout of the samples. Table 1. shows the material and cross-section properties of the test samples. used. The image of the iron chips is given in Fig. 2. The iron chips material was subjected to sieve analysis. The results of sieve analysis of iron chips are given in Table 2. Within the scope of the study, the materials used while creating this concrete were 8 kg of cement, 17.5 kg of sand and 21.25 kg of stone chips. The stone chips to be used were chosen as the number 2 stone chips. While creating the samples with additives, the aggregates were subjected to sieve analysis and the aggregate amount in the range of 0-4 mm was determined. The determined amount was reduced by 20% and iron chips substitution was carried out. It was mixed with 4 liters of water in the concrete machine and concrete was obtained. In Fig. 3., the view of the concrete machine before and after operation is given.
Small cylindrical samples were taken from the concrete used in reinforced concrete cantilever beams and kept in the curing pool for 28 days. At the end of 28 days, the samples were broken, and the Stress-Strain graph was obtained. The modulus of elasticity of concrete was calculated from the graphs. The obtained elasticity modules are given in Table 3.  Table 4. Mechanics Laboratory. The experimental setup is based on bending the cantilever beam by applying a load from the end of the cantilever beam. The applied load was measured by the load cell and the displacement was measured by the potentiometer. The values in the potentiometer with the load cell were recorded using the Test Lab Basic program. The image of the experimental setup is given in Fig. 4. In Fig. 5., the pre-experiment and post-experiment view of one of the samples is given.

Results And Discussion
Load-Displacement graphs of the samples were obtained by using Test Lab Basic while breaking the test samples. The ductility coe cients and maximum load values of the cantilever beams are given in Table   5. The ductility coe cients of the cantilever beam samples were calculated as given in Eq. (1). In the calculation of the ductility coe cient, the displacements at the time of yield and the maximum displacements were calculated as given in Fig. 6. [11]. In Eq. (1), (µ) represents the ductility coe cient, (u max ) the maximum displacement and (u y ) the displacement at the time of yield.
Below are the comparative graphics of the samples separated from each other according to their no additive and 20% iron chips added status. The ductility values of the samples and the maximum loads they carry are given in Table 6. In addition, the percentage increases in the ductility values and maximum loads of the samples with additive compared to the samples without additive are given.
The ones with additives of the samples with a stirrup spacing of 50 mm and hook angle of 90 degrees increased their ductility coe cient by 1.84% compared to the ones without additives. However, their strength decreased by 1.23%.
The ones with additives of the samples with a stirrup spacing of 50 mm and hook angle of 135 degrees increased their ductility coe cient by 1.25% compared to the ones without additives. However, their strength decreased by 1.37%.
The ones with additives of the samples with a stirrup spacing of 100 mm and hook angle of 90 degrees increased their ductility coe cient by 2.34% compared to the ones without additives. However, their strength decreased by 1.53%.
The ones with additives of the samples with a stirrup spacing of 100 mm and hook angle of 135 degrees increased their ductility coe cient by 6.00% compared to the ones without additives. However, their strength decreased by 1.38%.
The ones with additives of the samples with a stirrup spacing of 150 mm and hook angle of 90 degree increased their ductility coe cient by 4.89% compared to the ones without additives. However, their strength decreased by 1.38%.
The ones with additives of the samples with a stirrup spacing of 150 mm and hook angle of 135 degree increased their ductility coe cient by 11.06% compared to the ones without additives. However, their strength decreased by 1.22%.
Comparative graphics of the samples separated from each other by the stirrup hook angles are given below.
The ductility values of the samples and the maximum loads they carry are given in Table 7. In addition, the percentage increases in the ductility values and maximum loads of the samples with stirrup hook angle 135 degrees compared to the samples with stirrup hook angle 90 degrees are given. For the samples with a 50 mm stirrup spacing and with additives, the samples with stirrup hook angle 135 degrees increased their ductility coe cient by 4.57% compared to the samples with stirrup hook angle 90 degrees. And their strength increased by 3.29%.
For the samples with a 100 mm stirrup spacing and with additives, the samples with stirrup hook angle 135 degrees increased their ductility coe cient by 6.85% compared to the samples with stirrup hook angle 90 degrees. And their strength increased by 5.10%.
For the samples with a 150 mm stirrup spacing and with additives, the samples with stirrup hook angle 135 degrees increased their ductility coe cient by 9.05% compared to the samples with stirrup hook angle 90 degrees. And their strength increased by 5.11%. Comparative graphics of the samples separated from each other by the stirrup spacing are given Fig. 19.
The ductility values of the samples and the maximum loads they carry are given in

Conclusions
The study focused on the behavior of the cantilever beam, which is a structural element, rather than compressive strength tests of concrete. Within the scope of the study, cantilever beams were produced by changing the stirrup spacing and hook angle. In addition, 20% iron chips was added instead of the aggregate used in the production of cantilever beams, and the effects of this additive on the behavior of the cantilever beam were discussed because of experimental data.
As a result of the experiments, the following conclusions can be drawn: 1. It has been observed that the 20% iron chips substitution in the concrete used in the production of cantilever beams with various stirrup spacing and hook angle reduces the strength at low rates but contributes to the ductile behavior.  The image of the iron chips.