Interface Shear Behaviour between Precast and New Concrete in Composite Concrete Members: Effect of Grooved Surface Roughness

Erjun Wu,Olawale Olatunde Ayinde,Guangdong Zhou 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.6

A major condition for the quality performance of connected-concrete layers is enough shear strength at the interface. Research shows that the interface shear behaviour is highly dependent on the texture of its interface. Although, several research on the effect of surface roughness on the interface shear behaviour of concrete to concrete connection using different interface patterns exists; however, there is scant literature on studies using quantitatively controlled interface texture, especially studies considering the roughness tooth geometrical parameters. In this study, seven different interface roughness geometries were designed and utilised as the study parameters for the interface shear behaviour, as well as the initial confining pressure. The double-sided shear test was used to determine the shear behaviour, failure mode, shear transfer mechanism, alongside the friction and cohesion values for all the studied interface types. The test results showed that both the interface roughness geometry and the magnitude of the confining pressure have a significant effect on the interfacial shear behaviour. Using different formations of the interface geometry provided a 15.4% difference in interfacial shear strength. For most of the interface geometries, interface cracking load increases linearly with the increase of initial confining pressure, while for the shear strength, the increase in confining pressure is more effective at lower pressure values. The friction and cohesion coefficients are influenced by the roughness tooth angle and tooth distribution.

Experimental study on the mechanical performance of column underpinning joints with prestressed U-shaped steel bars

Kaijun Yuan,Erjun Wu,Ning Dong 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.5

To meet the requirements of highly efficient force transmission, easy operation and low damage in RC column underpinning engineering, a new underpinning joint with prestressed U-shaped steel bars was proposed. Static testing of seven specimens was carried out, and the number of the U-shaped steel bars, their arrangement and the pre-pressure acting on the joint were considered as the main parameters. The results demonstrated that the U-shaped steel bars might greatly increase the load-bearing capacity of the underpinning joint, and the more the number, the higher the capacity; the arrangement of the U-shaped steel bars also had a significant effect on the load-bearing capacity. Two pairs of the U-shaped steel bars arranged on the opposite sides of the column was better than that arranged on four sides. And the horizontal part of the UsSBs embedded in the column grooves was better than in the underpinning beams; the pre-pressure could effectively improve the sliding stiffness of the underpinning joint, while the effects on the load-bearing capacity was not obvious. Based on the curve of load-displacement, force process of the underpinning joint was divided into four phases: no slip, initial slip, interfacial slip expansion and punch slip, consequently a constitutive force-slip model was constructed. As a result, a simple mechanical model of the underpinning joint was established, and the calculation formula for the load-bearing capacity of the new joint was proposed. Finally, the engineering design expression was prepared according to the characteristics of the real underpinning project.

Repair of Pre-cracked Reinforced Concrete (RC) Beams with Openings Strengthened Using FRP Sheets Under Sustained Load

Bashir H. Osman,Erjun Wu,Bohai Ji,Suhaib S. Abdulhameed 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.1

Strengthening reinforced concrete (RC) beams with openings by using aramid fiber reinforcement polymers (AFRP) on the beams’ surfaces offers a useful solution for upgrading concrete structures to carry heavy loads. This paper presents a repairing technique of the AFRP sheets that effectively strengthens RC beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability (deflection produced under working loads be sufficiently small and cracking be controlled) of pre-cracked RC beams with openings. To investigate the possible damage that was caused by the service load and to simulate the structure behavior in the site, a comprehensive experimental study was performed. Two unstrengthened control beams, four beams that were pre-cracked before the application of the AFRP sheets and one beam that was strengthened without pre-cracking were tested. Cracking was first induced, followed by repair using various orientations of AFRP sheets, and then the beams were tested to failure. This load was kept constant during the strengthening process. The results show that both the preexisting damage level and the FRP orientation have a significant effect on strengthening effectiveness and failure mode. All of the strengthened specimens exhibited higher capacities with capacity enhancements ranging from 21.8 to 66.4%, and the crack width reduced by 25.6–82.7% at failure load compared to the control beam. Finally, the authors present a comparison between the experimental results and the predictions using the ACI 440.2R-08 guidelines.

Bond behaviour at concrete-concrete interface with quantitative roughness tooth

Ayinde, Olawale O.,Wu, Erjun,Zhou, Guangdong Techno-Press 2022 Advances in concrete construction Vol.13 No.3

The roughness of substrate concrete interfaces before new concrete placement has a major effect on the interface bond behaviour. However, there are challenges associated with the consistency of the final roughness interface prepared using conventional roughness preparation methods which influences the interface bond performance. In this study, five quantitative interface roughness textures with different roughness tooth angles, depths, and tooth distribution were created to ensure consistency of interface roughness and to evaluate the bond behaviour at a precast and new concrete interface using the splitting tensile test, slant shear test, and double-shear test. In addition, smooth interface specimens and two separate the pitting interface roughness were also utilized. Obtained results indicate that the quantitative roughness has a very limited effect on the interface tensile bond strength if no extra micro-roughness or bonding agent is added at the interface. The roughness method however causes enhanced shear bond strength at the interface. Increased tooth depth improved both the tensile and shear bond strength of the interfaces, while the tooth distribution mainly influenced the shear bond strength. Major failure modes of the test specimens include interface failure, splitting cracks, and sliding failure, and are influenced by the tooth depth and tooth distribution. Furthermore, the interface properties were obtained and presented while a comparison between the different testing methods, in terms of bond strength, was performed.

Shear Behavior of Reinforced Concrete (RC) Beams with Circular Web Openings without Additional Shear Reinforcement

Bashir H. Osman,Erjun Wu,Bohai Ji,Suhaib S. Abdulhameed 대한토목학회 2017 KSCE Journal of Civil Engineering Vol.21 No.1

The introduction of an opening into a Reinforced Concrete (RC) beam leads to a reduction to both the beam’s stiffness and its overall structural capacity due to stress concentrations and local cracking around the opening. This paper uses both the experimental and finite element (FE) method to analyze the shear behavior of RC beams with opening. The shear span-to-depth ratios ( ), opening size, and opening location were considered as the main parameters. The beams were divided into three series according to the shear span-to-depth ratios. Three reinforced concrete beams without openings and one beam with openings were tested experimentally under two-point loading. These beams were considered as control beams so as to validate the FE model using ANSYS14.5 software. A total of 31 specimens were analyzed using ANSYS14.5 while considering the above mentioned parameters. Results showed that the openings located in a high shear region (the line connecting the load and support points) led to the early collapse of the beam. In addition, by comparing the experimental results with those of the non-linear FE analysis, it was concluded that both results were in accordance. An analytical equation for predicting the shear strength of RC beams with circular openings was then proposed, and the obtained results later compared with those from FE model. Furthermore, the developed FE models can serve as a numerical platform for performance predictions of RC beams with different web opening geometries.

Repair of Pre-cracked Reinforced Concrete (RC) Beams with Openings Strengthened Using FRP Sheets Under Sustained Load

Osman, Bashir H.,Wu, Erjun,Ji, Bohai,Abdulhameed, Suhaib S. Korea Concrete Institute 2017 International Journal of Concrete Structures and M Vol.11 No.1

Strengthening reinforced concrete (RC) beams with openings by using aramid fiber reinforcement polymers (AFRP) on the beams' surfaces offers a useful solution for upgrading concrete structures to carry heavy loads. This paper presents a repairing technique of the AFRP sheets that effectively strengthens RC beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability (deflection produced under working loads be sufficiently small and cracking be controlled) of pre-cracked RC beams with openings. To investigate the possible damage that was caused by the service load and to simulate the structure behavior in the site, a comprehensive experimental study was performed. Two unstrengthened control beams, four beams that were pre-cracked before the application of the AFRP sheets and one beam that was strengthened without pre-cracking were tested. Cracking was first induced, followed by repair using various orientations of AFRP sheets, and then the beams were tested to failure. This load was kept constant during the strengthening process. The results show that both the preexisting damage level and the FRP orientation have a significant effect on strengthening effectiveness and failure mode. All of the strengthened specimens exhibited higher capacities with capacity enhancements ranging from 21.8 to 66.4%, and the crack width reduced by 25.6-82.7% at failure load compared to the control beam. Finally, the authors present a comparison between the experimental results and the predictions using the ACI 440.2R-08 guidelines.