Influence Of Helical Confinement On Crack Development In RCC Beams

Structures made of reinforced concrete are susceptible to developing cracks when they are in the path of earthquakes, strong winds, or increased structural loading. It is therefore possible that it will be necessary to manage structural cracking in the Service Limit State to maximise the lifetime and strength of the structural components under any stress. Helical containment is superior to rectangular containment in terms of its ability to strengthen and ductile the Reinforced Concrete (RC) structural member. In the current work, six distinct beams were each subjected to a series of tests to see how they behaved in terms of cracking when subjected to bending loads. Each of these tests used a unique helical pitch space distance. The beams all measured 150 mm by 150 mm and 750 mm in length. They were designed in accordance with the criteria of Euro code 2, with the identical dimensions. Both 50 and 100 mm were used to take the measurement for the helical pitch. The findings indicate that the utilisation of helical elements does influence the cracking behaviour of the beams. The most important finding was that the measurement of the crack’s thickness was slightly reduced when the beams were restricted to a helical zone with a closer spacing between them. The fact that the theoretical crack is longer than the actual crack that was measured experimentally demonstrates that the Euro code 2 standard provides a more accurate forecast as well as a higher factor of safety. This is demonstrated by the fact that the theoretical crack is larger than the actual crack that was measured.


Introduction
The rapid rise of the world's population has led to an increase in the number of new building constructions that satisfy the people's demands.There are several basic features that must be met for a building to be considered for better serviceability conditions.The construction industry is facing day to day challenges that includes the design of sustainable materials [2].In building, this material is frequently utilized because of its cheapness and flexibility to be molded into various sizes and shapes.The material's strength can withstand significant compression stresses as well [1].Due to its brittleness, this material cannot be used as a stand-alone component in the building.To be able to bear tensile loads, this material needed to be strengthened.The use of "reinforced cement concrete" was introduced because of this perspective.Reinforced cement concrete, often known as reinforced concrete, is a combination of concrete and steel bars that is commonly used in the construction of buildings.Steel bars are used to counteract the tensile forces that are generated by the ductility of the 1282 (2023) 012008 IOP Publishing doi:10.1088/1757-899X/1282/1/012008 2 material [3].Reinforced concrete structures consist of slabs, beams, columns, frameworks, footings, and walls.As a focal point, the beam is featured in this article.Beams made of reinforced concrete resist vertical loads from the structure's walls, slabs, and their own weight.In earthquake-prone areas, it is also utilized to provide additional structural support to existing structures.Deflection in this structural component mostly occurs via bending.It deflects in a manner that compresses the top and tensions the bottom of the beam when it is subjected to large loads.However, the compression area where the concrete is effective, and the steel bars are tension resistant.Beams can be either a single or double reinforced depending on the strength of the weights being applied.
There are steel bars at the tension zone of the single-reinforced beam and Steel bars are placed in both tension and compression zones of the doubly reinforced beam [4].On the other hand, Reinforced structures are frequently plagued by cracks.According to Tammo, Kristian [5], structural elements acquire flexural cracks when their tensile strength deteriorates.It takes a lot of tension for secondary cracks to form since the primary ones aren't strong enough to resist the increasing tension.The corrosion of the reinforcement was caused by deep fissures in the structural part, which in turn led to failure [5].To lessen the width of cracks in reinforced concrete, helical confinement was tested in this paper.The main research highlights are: • To investigate the cracking behavior of Helical containment beams under bending loads.
• To demonstrate that helical containment influences beam cracking behavior, with the crack thickness measurement being significantly smaller when beams are constrained to a helical zone with a tighter spacing [19].

Methodology
Rebar size, shear connection, and nominal cover were all considered when designing six reinforced concrete beams in accordance with Eurocode 2 [6] regulations.The beams were 150 mm x 150 mm x 750 mm long, with the same dimensions.The pitch distances were 50mm and 100mm.The details of each beam's steel reinforcement are shown in the table below.Table 3 gives the dimensions and details of the six beams that have been used in the experiment.A particular code was assigned to each of the six beams depending on the design type, i.e., balanced type as U, over-reinforced type as O, and spacing of stirrup in mm.There are multiple shuttering areas depending on the distance between helical confinements.A cross-sectional view of the beams is seen in Figure 1-6.

The Slump test
The workability or consistency of a concrete mix can be evaluated using the slump cone test, which can be performed in a laboratory or directly on the construction site as the work advances.To guarantee that the quality of the concrete remains stable during the entirety of the construction process, a slump test is carried out on each new batch of concrete.[15].Figure 7 shows the slump test [7] that used to determine the workability of fresh concrete.

Test of compressive force
The strength of concrete determined by a compression test, which involves smashing cubical concrete in a compression testing machine is known as compressive strength.It assesses the ability of concrete to bear a load before failing [16] and twelve cubes [8] were cast with 150 mm dimensions, and the concrete's compressive strength was measured.As shown in figure 8, compression test of cubes after water curing for 7, 14 and 28 days.

Flexural Test
Flexural strength is the amount of stress and strain that an unreinforced concrete slab, beam, or other structure can withstand without bending [17].Flexural strength is sometimes referred to as flexural bearing capacity.After 28 days of curing, flexural 4-pin loading was applied to each of the six reinforced concrete beams to perform an evaluation, as shown in figure 9.The purpose of this experiment was to determine the maximum amount of force necessary to bend the beam and to determine its fracture length.

2.5.
Measurement of breadth of crack Crack width measurements were made to examine the cracking pattern because of the beam being loaded.In the tension or shear zones, a crack is formed, and a failure pattern was forecasted.The microscope is used to measure the crack's breadth [22].

2.6.
Tests for tomography Using a CT scan, any concrete flaws were found in the beams.When concrete pieces are subjected to extreme loads or are frequently used, microcracks could occur.As an active measurement device, tomography [9], demonstrates that a bob is placed on the surface of the members and sensors are used to collect data.The Tomography gadget is depicted in Figure 10.

3.1.
Test of compressive force Compressive strength tests were performed on 12 concrete cubes at cure times of seven, fourteen and twenty-eight days.Table 4 displays the average concrete cube strength.The average strength of cubes grew as the curing period progressed, according to a study.At 28 days of cure, the average concrete strength was greater.The results in the table 4 showed that the strength of cubes has been increased with the age of curing.The strength of cubes at 7days has been increased by 20% at 14 days and 21% at 18 days.

3.2.
Flexural Test Average crack widths for the six beams are shown on Table 5. it can be seen from these results that the beams 4, 5, and 6 are more capable of resisting the weight than beams 1, 2, and 3. Beams 4 and 6 were where the cracks first appeared at a force of 60 kN.Beams 4, 5, and 6 each had a crack width of 7 x 10 -2 mm, 5 x 10 -2 mm, and of 6 x 10 -2 mm at 200 KN, respectively.In contrast, the crack widths of beams 1, 2, and 3 at 200 KN were 0.10 mm, 0.05 mm, and 0.07 mm in diameter.As a further detail, Beam 1 cracked at 40 kN, whereas beams 2 and 3 cracked at 60 kN.It appears that the helical 50 mm spacing is effective in lowering the crack breadth in Beam 2, which is having the narrowest average crack breadth among Beams 1 and 3. Due to lack of zero-shear blocking, beam 1 shows a larger average crack width than beams 2 and 3.

Analysis of Tomography
Non-destructive test software [10] and piezoelectric sensors [23] were used to determine the recorded wavelengths to produce technical images of the contained concrete.During the experiment [11], sensors measured the amplitude (A), which was recorded for each picture.The cracks in the following beams can be seen before and after loading, as shown in the figure 12.1 and 12.2: Using a CT examination [24], beam 1's concrete appears to be in good condition; however, a large side portion of the beam's concrete was damaged prior to loading.Poor compaction may lead to this damage.Despite this, the quality of the concrete is excellent, the flaws are confined to cover-point of the correct side and the design of beam inside is adequate.Following loading, the fracture spreads outward from the beam side, and the concrete's exterior surface fails first.Images in figure 13 are showing medium attenuation of critical concrete areas in beam 2 tomographic analysis because of sensor noise induced by the sensitivity [20].on the other hand, Interior confinements adequate, such that before loading very minor cracks observed in the concrete cover.When loading applied, the image reveals deterioration of the internal concrete and a crack pattern on the beam right side that extends into the beam.It's possible to simply see a minor change before and after loading.It's clear from testing that this beam's failure section only extends to the right side of the beam's centerline, owing to helical confinement explaining why the spreader's load is right side distributed.An experimental study conducted by Whitehead and Ibell [12] also proved that in beams that helical confinement is more effective than a rectangular tie.The topographical scan reveals that the inner cement of beam No. 3 seems to be in excellent condition, with just a few areas exhibiting symptoms of degradation prior to loading.Attenuation in concrete could be attributing to poor compaction and shrinkage microcracks.After loading, the failure of concrete beam on the tension side can be seen because of yielding the steel bar.Due to the high attenuation ratio, the concrete on the outside of Beam No. 3 is still in good condition, but the concrete on the inside of the beam is crumbling.Since the beam collapse is situated on the proper location, spreader bears a greater strain on the correct hand [18].Using the pre-loading picture of Beam 4, the inner bulk of cement is in excellent condition and that there are just a few areas of possible concrete shrinkage on the side of the beam.The constant attenuation implies quality concrete, which is passable in strength.Failure on the beam's correct side indicates the spread of load cracks after loading [21].
Owing to absence of helical confinement, Beam No. 4 has a substantial diminution rate, which directs a crack.If the beam fails on the proper side, this might indicate that the spreader is distributing its weight more evenly on the correct side than the left.Elbasha and Hadi [13] also tested experimentally tested helically confined high strength concrete beams and found similar results which clearly establishes present analysis is in coherence with literature with updated technology used in present experimental work.Images of beam number 5 before loading reveal that the concrete has a medium coefficient of attenuation, indicating that the concrete is properly contained to an inner area without injuring any areas.If a shrinkage crack appears on the beam's correct side, it can reveal the curing method.As seen, concrete structures have microcracks due to load, creep, and shrinkage [14].As a result of this, the beam's inner concrete remains unaffected by this point in time.Failure of the right-hand wall upon loading reveals exposed reinforcement bars.Owing to the concrete element of Beam No. 5 is in excellent shape, it is a brittle collapse.As a result of the high attenuation factor in the inner concrete failure, this is the case.Spreader load is concentrated on the right-hand side of beam, indicating that it was not evenly distributed on both sides.The tomographic examination of beam 6 that was performed prior to loading showed that the medium attenuation coefficient was applied to the concrete, which implies that the inner region is correctly restricted without damage.Additionally, the research confirms that there are no critical areas on the beam side, which indicates that there is no initial creep.After loading, the shot illustrates how the reinforcing bars have spread out across the cover, which finally results in the concrete splitting apart.Due to the unusually low attenuation coefficient of Beam No. 6, some of the concrete in the beam is still in great condition, and the inner confining concrete has not been weakened.This makes Beam No. 6's failure a remarkable achievement.Failure occurred on the proper side of the beam, and the weight from the spreader is distributed more uniformly on the correct side than it is on the left side of the beam.

Conclusion
Contained Helical Beam Cracking Behavior in Context is the primary objective of this article.Beams bound to a helical region that was closer in distance lowered the assessment of crack thickness marginally, according to presented work.When the tensile area of the beam is contained by helical containment, the ductility increases, and the shear disruption occurs.
Because of its high split width, the beam with no helical containment is over-reinforced and balanced section.It is because the helix delivers a consistent radial stress along the concrete part, while the rectangle confines the concrete, especially at the corners, that it is more effective than the tie.Due to their lower stiffness than the four corners, the tie's sides will tend to flex outwards, reducing the effective concrete surface area in the cross section.

Table 1 .
Details of the Steel Reinforcement.

Table 2 .
Concrete mix designs Specifications for the Beam case configurations, characteristics, and detailed descriptionTable 3. Specifications for the Beam case Sr. No. Beam Width

Table 4 .
Results of the compressive investigation

Table 5 .
The average width of the cracks in the beam