Abstract
This paper presents an experimental investigation of the effect of helix pitch and helix diameter on beam be- haviour through testing 10 helically confined beams. Two groups of beams had exactly the same geometry and reinforce- ment; with the only differences being the helices diameter and pitch. 8 mm helix was used in the first group of beams and 12 mm bars in the second group. The helix pitches varied between 25 mm and 160 mm. Beams' cross section was 200 300 mm, with a length of 4 m subjected to four point loading. The main results indicate that the helical effectiveness is neglected when the helical pitch is 160 mm (helix diameter) and the displacement ductility index increases as the helical pitch decreases. Finally, there is a considerable release of strain energy responsible for spalling off the cover. efficiency of tie confinement is 50% of the helical confine- ment for the same lateral reinforcement ratio. The same ef- fectiveness of confinement is applicable in columns and beams. Helix confines the concrete more effectively than rectangular ties as the helix applies a uniform radial stress on the concrete along the concrete member, whereas a rectangu- lar tie tends to confine the concrete mainly at the corners. Thus the effective concrete area at the cross section is re- duced because the concrete pressure will tend to bend the tie sides outward due to their low stiffness compared to the four corners (3). As such a significant portion of the concrete in the cross section is considered as unconfined. On the other hand the arching of the concrete between the ties reduces the effective confined concrete at the cross section of the mem- ber. Thus using helical confinement in the compression zone of rectangular beams is more effective than using rectangular ties. Nevertheless, to prove experimentally that the helix is more effective than the rectangular ties, there is a need to compare beams helically confined with beams confined us- ing rectangular ties. A study by Whitehead and Ibell (4) proved that the use of helical confinement is more effective than rectangular ties in beams.
Highlights
The development of the construction industry has led to the continual improvement of construction materials, where high strength concrete of 100 a compressive strength and reinforcement of 500 a yield strength are being used in beams and other construction elements
The aim of the experimental program in this study is to investigate the behaviour of over-reinforced High strength concrete (HSC) helically confined beams and determine the effect of helix pitch on ductility
The experimental program in this study is to investigate and provide experimental evidence about the significant effect of helical pitch on the displacement ductility of helically confined HSC beam
Summary
The development of the construction industry has led to the continual improvement of construction materials, where high strength concrete of 100 a compressive strength and reinforcement of 500 a yield strength are being used in beams and other construction elements. High strength concrete (HSC) is used when the reduction in member cross section is required. The disadvantage of using HSC in over reinforced beams is its brittle failure. One option for changing the type of failure from brittle to ductile is through confining the compression region of the concrete. Helical reinforcement can be used to achieve the required ductility. It is generally accepted that helical confinement is more effective than the rectangular ties in increasing the strength and ductility of confined concrete. Helical reinforcement is effective for concrete under compression to increase the ductility as well as the compressive strength by resisting the lateral expansion due to Poisson’s effect upon loading. The helical reinforcement is used in the compression zone of the beams. This paper presents the experimental results of testing ten beams with 4000 mm length and a cross section of 200 mm in width and 300 mm in depth
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