Pullout behaviour of bars in concrete confined with post-tensioned steel straps

This paper presents the experimental results of bond and anchorage behaviours under Steel Strap Tensioning Technique (SSTT) confined high-strength concrete (HSC). The experimental tests consisted of pull-out test with short bond length and pull-out test with long bond length were performed to determine the bonding and anchorage capacity of SSTT-confined HSC. A total 36 specimens with short bond length and 16 specimens with long bond length were tested in this study. Three batches of concrete with compressive strength of 30 MPa, 60 MPa and 90 MPa were tested. Other parameter in this study was rebar diameter of 12 mm and 16 mm and different SSTT confinement ratios ranging from 0 to 0.2. To determine the effects of confinement on development bond and anchorage, an analytical expression was developed based on the parameters tested in this study. The equation is then verified with the bond strength proposed by the existing bond equations. The results from conducted tests indicated that the application of SSTT as an external confinement can increase the bond strength of confined concrete by up to 50%

Effects of palm oil clinker as coarse aggregates replacement in self curing concrete

Concrete, if properly design, can be one of the most durable material and widely used in construction due to its availability and good compressive strength. A good quality concrete can be produced not only through good design of concrete mix proportions but also good and proper curing process that ensure a complete hydration process of the cement. However, sometimes proper curing process was not provided during concreting on site due to various reasons. This study investigates the effects of 10 mm crushed Palm Oil Clinker (POC) as partial aggregates replacement to act as internal reservoirs in concrete to provide internal curing process of cement. This process or technique is also popularly known as self-curing process for concrete. The POC which has the density of 780 kg/m3 was used to replace 20% of the coarse aggregates. A water/cement ratio of 0.53 was used in the concrete mix design. Three different curing conditions were employed, namely, normal water curing, air curing and 7 days in water plus outside curing conditions. The workability of the POC and control concretes was determined through slump test. The concrete samples were tested for compression at the age of 3, 7 and 28 days while concrete prisms and cylindrical samples were tested at the age of 7 and 28 days. The experimental results show that the inclusion of POC was found to increase the workability of concrete by 27% but reduced the concrete compressive strength by about 6% compared with the control concrete. In addition, the flexural and tensile strengths of POC concrete were found to be less than the control concrete due to the properties of the POC which was lightweight and porous. The experimental results show that the porous structure of the POC aggregates can be utilised as water reservoir for the process of internal curing for the self-curing concrete

Bond between SSTT confined concrete and ribbed steel reinforcement bar

A study about bond strength of normal strength concrete (NSC) and Steel Strap Confining Technique (SSTT) confined NSC was presented. A series of 8 specimens pull-out test were carried out to investigate the bond strength of short embedment (5Db) in SSTT confined NSC. The concrete compressive strength was about 45 MPa meanwhile the 12mm diameter reinforcement tensile strength was about 500 MPa were used in the pull-out specimens. In order to determine the effects of lateral confinement pressure of steel strapping, three groups of different steel strap gap distance pull-out test were conducted and compared with control specimens and previous theoretical bond stress equation. It was found that SS-B pull-out specimen exhibited highest bond strength and about 40 percent higher compared with Cont-B specimen as lowest bond strength pull-out specimen in this study

Ductility and stiffness of slender confined reinforced high-strength concrete columns under monotonic axial load

This paper presents an investigation based on tests results of high-strength concrete (HSC) columns externally confined with post-tensioned steel straps, subjected to monotonic axial load. The parameters of the tests were eccentricity ratio (ei/es = 0, 1), load eccentricity (e = 25 mm, 50 mm), slenderness ratio (λ = 16, 24, 32) and confining volumetric ratio (ρv = 0.09, 0.25, 0.50). This paper is served as a continuation of a previous paper conducted by Ma et al. (2014b), which focuses on the ductility and stiffness analysis. The results show that the confinement of post-tensioned steel straps is beneficial to HSC columns but confining efficiency reduced drastically with the increase of column slenderness. Two ductility models were proposed to predict the ultimate ductility for slender confined HSC columns with the consideration of important parameters. The proposed models are simple and easy to apply but adequately accurate estimation is guaranteed. It is believed that the proposed ductility models can aid structural engineers in the designing a ductile structure especially in the seismic region. The confinement has no significant effect on the flexural stiffness of HSC columns

Design of steel-strapped, high-strength concrete columns subject to unequal end moments

A new equation is proposed for practical flexural design of high-strength concrete columns confined externally with tensioned steel straps. The proposed equation is based on the simplified approach of the equivalent moment factor adopted by existing design codes. It also accounts for non-linear behaviour of the materials, which is usually neglected in the codes. The equation was derived using results from rigorous theoretical analyses of 120 simulated strap-confined columns subjected to short-term ultimate loads and unequal flexural moments at the column ends. The theoretical simulations accounted for parameters shown to influence the design of strap-confined columns, such as load eccentricity, longitudinal reinforcement ratio, free concrete cover and volumetric confinement ratio. The proposed equation was found to predict the strength of strap-confined columns with sufficient accuracy, making it suitable for practical design and rapid assessment of such structures