An experimental and analytical study on the application of Steel Strapping Tensioning Technique (SSTT) confinement on twelve high-strength concrete cylinder specimens with dimension of 100 mm and 200 mm in diameter and height respectively has been studied and presented throughout this paper. The specimens were volumetric-identically confined with two different confining materials of different mechanical properties and lateral pre-tensioning stresses, namely SSTT(HC) and SSTT(SS). All concrete specimens were tested under uniaxial compression load. The performance of SSTT-type confined specimens were studied through their stress-strain relationship upon the longitudinal and transverse deformation, mode of failure, level of lateral pre-tensioning stress, and dilatancy behaviour. The results show that high-strength concretes confined with SSTT would significantly reduce the brittleness problem and at the same time, enhancing both ultimate compressive strength and ductility up to 65% and 344%, 36% and 269% for both SSTT(HC) and SSTT(SS), respectively. Those specimens confined with higher lateral pre-tensioning stress exhibits smaller radial expansion and higher rate of axial strain, able to slow down the dilation of confined specimens under loading and thus, helps in enhancing the compressive capacity and ductility. In addition, an analytical comparison between SSTT-type confinement and conventional confinement models have been presented and the results show a linear relationship between the compressive strength enhancement and confinement ratio. Current experimental results were also validated by comparing the observed stress-strain relationship proposed by Mander.
This research study is to introduce and investigate an effective technique of external pre-tensioning using steel strapping (SSTT) to reduce the brittleness and enhance the ductility of high-strength concrete cylinders. Fifteen cylinders with dimension of 150 mm and 300 mm in diameter and height respectively were casted, pre-tensioned with two and four layers of steel strapping and tested to failure under uniaxial monotonic and cyclic compression. The behaviour of SSTT confined cylinders was studied through their stress-strain relationship upon the longitudinal deflection, transverse strain, mode of failure, confinement ratio, and existence of an envelope curve. It is experimentally proved that SSTT confinement do helps in controlling the brittleness problem of high-strength concrete and at the same time, enhancing both the concrete ductility and compressive strength up to 46.2 % and 112.5 % respectively. The envelope curve of uniaxial cyclic loading also coincides with the corresponding monotonic loading curve, regardless of any loading activity. The observed stress-strain relationship of confined cylinders with different confining ratios are compared with existing strength and strain models and a stress-strain prediction model, the result showed a linear relationship between the compressive strength and strain enhancement and confining ratio, with acceptable agreement between the prediction model.
Steel strapping tensioning technique (SSTT) confinement has been proven as a type of external confinement to retrofit and upgrade concrete structures. Their remarkable enhancement to concrete mechanical properties, practicing active lateral confinement, low cost, easy to operate, time saving and no structure interruption during application have brought this technique as of the most affordable technique for column confinement, especially for high strength concrete (HSC) which naturally behaves insufficient in ductility. Although a great number of previous studies have demonstrated the performance of SSTT confinement, there are several anxieties related to the long term behaviour of SSTT confined columns which have yet been implemented especially in real hostile condition. Environmental effects, such as ultraviolet radiation exposure and saline solution (sea water) may affect the confining material properties, and therefore decrease the performance of the confined columns. In this study a total of twenty HSC specimens with dimension of 100 mm and 200 mm in diameter and height respectively were prepared, volumetric-identically pre-tensioned with steel strap and exposed to three conditions: indoor, outdoor and saline water for three months. The exposed specimens were monotonically tested and their performance was studied through the stress-strain relationship, mode of failure and degree of corrosion. The results show that none of the forenamed environmental conditions have exaggerating influence on the performance of the SSTT confined concrete specimens even some material has been severely corroded. It is then parallel compared with existing FRP confinement studies and the result proves that SSTT confinement able to possess the highest strength performance under similar environmental exposure.
The remarkable advantages and promising increment in concrete ultimate capacity as well as ductility by using steel straps as lateral confinement has brought the steel strapping tensioning technique (SSTT) as one of the most affordable confining technique in market. A number of studies have been reported the behaviour of SSTT-confined concrete under uniaxial monotonic compression loading but none of any study addressed the uniaxial cyclic response of such confinement. In this paper, twenty-one high-strength concrete cylinder specimens with diameter of 150 mm and 300 mm in height were cast, laterally pre-tensioned with steel strap in different confining layers and tested to failure under uniaxial cyclic and monotonic compression loading. A number of conclusions to be drawn from experimental results including the tangential validation of stress-strain curve for uniaxial monotonic and cyclic loading, independency of plastic strain to the amount of confining layers, the disagreement of uniqueness concept on the repeated uniaxial unloading and reloading cycles, and the promising effect of confining layers and loading patterns to the ultimate capacity of SSTT confinement. A plastic strain model is proposed and compared with existing plastic strain models. The result proved that SSTT confinement able to secure the lowest plastic strain among the others existing confinement method.
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