INFLUENCE OF (COATED) STIRRUPS ON OVERLAPPED SPLICE STRENGTH OF EPOXY COATED DEFORMED BARS.
INFLUENCE OF (COATED) STIRRUPS ON OVERLAPPED SPLICE STRENGTH OF EPOXY COATED DEFORMED BARS.
2.1: This section contains various literature studies on lap splice, bond strength and pull-out test respectively.
2.1.1: D. Christophe (2009), Investigated the performance of reinforcement lap splices in concrete masonry panels. Reinforcement lap splices in twelve concrete masonry panels were constructed and subjected to direct tension loading. The effects of reduced masonry cover, reinforcement distribution in the cells, and positioning of the transverse reinforcement inside or outside the spliced region were investigated. Results from the tests of the lap splices indicated that transverse reinforcement restrains tension cracking in the masonry and improves splice performance and also that the distribution of the spliced reinforcement has a significant effect on performance. For the same amount of reinforcement, the splices performed better when distributed in adjacent masonry cells rather than being concentrated in one cell.
2.1.2: H. Tarek, M. Ahmed, S. Judy, S. Ali and R. Sami (2011), evaluates the bond behavior of high strength (HS), steel reinforcing bars and highlights the effect of various key parameters believed to affect the bond characteristics. Nine reinforced concrete spliced beams were constructed and tested. The beams had different splice lengths and levels of confinements. The applicability of different hypotheses for development of conventional steel bars was examined for the high strength bars. The study is extended to examine the behavior of the reinforcing bars as shear reinforcement for concrete beams by testing twelve concrete beams reinforced with high strength steel stirrups under static loading conditions. The main variables in the study included steel type, concrete compressive strength, web reinforcement ratio and shear span-to-depth ratio. The applicability of various building codes and standards for concrete beams with high strength shear reinforcement was also evaluated.
2.1.3: E. Villalobos and S. Pujol (2014), investigates the seismic response of reinforced concrete walls with lap splices. Six large-scale reinforced concrete structural walls were subjected to increasing displacement reversals up to failure. The effects of the presence of lap splices, splice length (60 bar diameters and 40 bar diameters), and boundary-element confinement were studied. The aspect ratio of the test walls was 2.2.The measured drift capacity ranged from 2.5% to 3% for the walls without lap splices and from 1.5% to 2.5% for the walls with lap splices. The increase in drift capacity caused by the boundary-element confining reinforcement ranged between 20% and 67%. Concrete surface unit strains were measured using an optical tracking system. Tensile unit strain concentration was observed at the base of walls with lap splices. The relative increment in tensile unit strains was approximately 100%. Compressive unit strains were not observed to be sensitive to the presence of the lap splices.
2.1.4: E. Mahmoud, M. Hatem and F. Ahmed (2014), study the bond between high strength self-compacted concrete (HSSCC) and spliced tension bars in beams. It was focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups was considered. All beams are of 1800mm span and200× 400 mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure was recorded. Test results were compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.
2.1.5: S. Hatem, A. Hosny, S. Rizkalla, P. Zia, M. Briggs, S. Miller, D. Darwin, J. Browning, G. Glass, K. Hoyt, K. Donnelly and J. Jisra (2009), investigated the bond Characteristics of ASTM A1035 Steel Reinforcing Bars. Sixty nine large-scale beam-splice specimens were tested. Maximum bar stresses are compared with predictions obtained using the bond equations in the ACI 318-05 code provisions and those proposed by ACI Committee 408. Maximum stress levels of 120, 110, and 96 ksi (830, 760, and 660 MPa) were developed in No. 5, No. 8, and No. 11(No. 16, No. 25, and No. 36) bars, respectively, not confined by transverse reinforcement. Providing confinement for No. 8 and No. 11 (No. 25 and No. 36) spliced bars using transverse reinforcement allowed stresses of up to 150 ksi (1035 MPa) to be developed. The ACI Committee 408 equation provides a reasonable estimate of the strength for both unconfined and confined splices using a strength reduction factor (φ-factor) of 0.82 and design parameters (cover, spacing, and concrete strengths) comparable to those used in this test program.
2.1.6: E. Ahmed and M. Hatem (2014), presents an experimental study on the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. It reports the influence of several parameters on bond in splices. The parameters covered are casting position, splice length as a factor of bar diameter, bar diameter and reinforcement ratio. The research involved tests on sixteen simply-supported beams of 1800 mm span, 200 mm width and 400 mm thickness made of HSC. In each beam, the total tensile steel bars were spliced in the constant moment zone. Crack pattern, crack propagation, cracking load, failure load and mid span deflection were recorded and analyzed to study the mentioned parameters effect.
2.1.7: A. Abdel-Kareem, H. Abousafa and O. El-Ladidi (2015), investigated the behavior of a confined tension lap splice in high-strength reinforced concrete beams. Seventeen simply supported concrete beams to study the effect of transverse reinforcement on the behavior of the lap splice of a steel reinforcement in tension zones in high-strength concrete beams are presented. The parameters included in the experimental program were the concrete compressive strength, the lap splice length, the amount of transverse reinforcement provided within the splice region, and the shape of the transverse reinforcement around the spliced bars. The experimental results showed that the displacement ductility increased and the mode of failure changed from a splitting bond failure to a flexural failure when the amount of the transverse reinforcement in the splice region increased, and the compressive strength increased up to 100 MPa. The presence of the transverse reinforcement around the spliced bars had a pronounced effect on increasing the ultimate load, the ultimate deflection, and the displacement ductility. The prediction of maximum steel stresses for spliced bars using the ACI 318-05 building code was compared with the experimental results. The comparison showed that the effect of the transverse reinforcement around spliced bars has to be considered into the design equations for lap splice length in high strength concrete beams.
2.1.8: K. Iwaki, O. Makishima, H. Tanaka, T. Shiotani and K. Ozawa (2003), investigated the bond behavior between concrete and reinforcement due to compaction of concrete, concrete walls made of two different conditions of compaction and a wall made of SQC (super quality concrete; high strength and self-compacting concrete) were subjected to pull-out tests of steel bars. In evaluating temporal and spatial evolution of cracking during the pull-out tests, (Acoustic emission) AE measurements are conducted. Attention is paid to mechanical engagement between ribs of steel bars and concrete. Visual observation is also made for the sections of cored samples from the walls, and rifts between steel bars and concrete are measured. The results indicate that lower AE activities around steel bars show the locations of insufficient bond area, where it is also difficult to distribute stress of steel bars to concrete. The bond behavior of a conventional concrete is directly influenced by means of compaction, whereas stable bond behavior irrespective of the compaction is observed in the SQC.
2.1.9: A. Foroughi, S. Dilmaghani and H. Famili (2008), investigated the bond between self compacting concrete and steel reinforcement. The bonding strengths of reinforcing bars were measured using cubic specimens of SCC and of normal concrete. The SCC specimens were cast without applying compaction, whereas the specimens of normal concrete were cast by conventional practice with substantial compaction and vibration. The results showed that SCC specimens generated higher bond to reinforcing bars than normal concrete specimens and the correlation between bond strength and compressive strength of NC is more consistent.
2.1.10: W. Randy, Z. Jingna and M. Jason (2005), The primary objective of this project was to develop a test for measuring the bond strength between pavement layers and also to evaluate tack coat materials and application rates for the Alabama Department of Transportation (ALDOT).The project is of two phase, laboratory and field phase. For the laboratory work, the experiment included two types of emulsion (CRS-2 and CSS-1) and a PG 64-22 asphalt binder that are allowed by ALDOT’s specifications. Bond strengths were measured with a shear type device at three temperatures and three normal pressure levels. Three application rates that encompassed the specification range were investigated for each tack coat. Laboratory prepared mixture samples included a coarse-graded blend and a fine-graded blend to represent two different surface textures. The effects of tack coat type, application rate, mixture type, testing temperature and normal pressure on the bond strength were evaluated. In the laboratory phase, it was found that all of the main factors used in the test plan affected bond strength. Testing temperature had the most significant impact on bond strength. As the temperature increases, bond strength decreases significantly.
2.1.11: E. Raafat, E. Agroudy and S. Rizkalja (2006), investigated the bond characteristics of high-strength steel reinforcement bars commercially known as micro composite, multistructural, fonnable steel (MMFX). The objective was to examine the applicability of the ACI 318-02 equation and a current proposed equation by Zuo and Darwin on bond behavior of steel reinforcement to the concrete member. The experimental program included two phases. The first phase of the experimental program consisted of testing four beam-end specimens reinforced with MMFX steel bars, whereas the second phase included testing eight beam-splice specimens reinforced with MMFX steel bars. The selected four factors considered in this study were bar size, level of confinement, bonded length, and bar cast position. The bond behavior of the MMFX steel bars was found to be similar to that of conventional Grade 420 MPa (60 ksi) steel up to the proportional limit of 550 MPa (80 ksi). The bond strength of the MMFX significantly changes as the tensile stresses developed in the bar exceed the proportional limit. The test results indicated that both the ACI 318-02 equation and the current proposed equation by Zuo and Darwin on bond are adequate and resulted in conservative prediction at low stress levels up to 550 MPa (80 ksi).
2.1.12: G. Chen, C. Wu (2014), carried out experimental study of vitreous enamel coating effects on the bond strength between deformed rebar and normal strength concrete. A total of 24 beam splice specimens were tested under four-point loading with four parameters investigated: bar size, lap splice length, coating, and confinement conditions. As the splice length increases, the ratio of bond strength between coated rebar and black rebar first increases from 1.0 to a maximum value of 1.44, and then decreases to 1.0. The maximum bond strength ratio corresponds to the near initial yielding of coated rebar. On the average, enamel coating can increase the bond strength of steel rebar in concrete by approximately 15%. A coating factor of 0.85 is thus recommended to take into account the enamel coating effect in lap splice designs, according to ACI and AASHTO bond strength equations.
2.1.13: A. Munikrishna, A. Hosny, S. Rizkalla and P. Zia (2011), Investigated the behavior of concrete beams reinforced with ASTM A1035 Grade 100 Stirrups under Shear. Nine large-sized RC beams were tested under static loading up to failure. All beams were 22 ft (6.7 m) long and were designed using a nominal concrete compressive strength of 4000 psi (28 MPa). The beam length was chosen such that each beam could be tested twice, thus doubling the amount of collected data. The shear span-depth ratio (a/d) of all specimens was kept constant. The nine beams were classified into three groups based on their shear resistance. The spacing of the shear reinforcement was varied to reflect a minimum and maximum level of shear resistance allowed by ACI 318-08. The performance of these beams is compared to that of similar beams reinforced with ASTM A615 Grade 60 bars. The results indicate that by using the higher yield strength of ASTM A1035 bars with a reduced reinforcement ratio, the beams can achieve similar shear strengths as the beams reinforced with Grade 60 bars. The results also show that cracking and deflection under service load of the beams with a reduced reinforcement ratio are within acceptable limits.