226 / 2022-06-11 16:45:39

Seismic behavior of engineered cementitious composites coupling beams with low aspect ratio

Engineered Cementitious Composite,coupling beam,low aspect ratio,seismic performance,shear strength

Diagonally reinforced concrete coupling beams have good ductility due to the shear resistance of diagonal bars, however, substantial reinforcement detailing is required in the beam, which may lead to bars congestion problems and construction difficulties. In order to improve the seismic performance of coupling beam with small span-to-depth ratio, engineered cementitious composites (ECC), which is a high toughness composite material with pseudo strain hardening behavior and multiple cracking characteristics, can be used to replace conventional concrete. Compared with ordinary concrete, ECC has a higher shear capacity, which can reduce the amount of diagonal bars. The end of the diagonal bars can be bent horizontally and extended into the wall pier, which is beneficial to assembly construction.



The pseudo-static tests of diagonally reinforced ECC beams, one ordinary reinforced ECC beams and one diagonal reinforced concrete coupling beams were carried out. The variable parameters were stirrup ratio, diagonal reinforcement ratio, types of layout of reinforcement, material of matrix, types of fibers and connection mode between the coupling beam and the wall pier. The seismic performance of the coupling beam, such as failure mode, hysteresis curve, displacement ductility, stiffness degradation and energy dissipation capacity were analyzed. Results showed that with the increase of stirrup ratio and diagonal reinforcement ratio, the shear capacity and ductility of the coupling beam increase gradually. Compared with the concrete coupling beam, the use of ECC in the matrix can improve the shear capacity and ductility of the beam, reduce the damage to the beam, which is easy to repair after earthquake. Compared with PVA fibers, using PE fibers as matrix materials can improve the strength, stiffness, ductility and energy dissipation capacity of coupling beam, reduce the amount of diagonal bars, and facilitate assembly construction. Diagonally reinforced ECC beams have higher shear capacity, ductility and energy dissipation capacity compared with conventionally reinforced ECC beams. The seismic performance of the coupling beam, which is connected to the wall piers with grouting sleeves, is excellent. It should be pointed out that the U-shaped reinforcement is needed to be added at the interface of the beam and the wall pier to improve the connection performance.



The averaged principal stress-strain relationships in the MCFT and local stress conditions at crack locations for ECC were modified based on the characteristics of ECC. When the coupling beam cracks, the fiber bridging action on the crack plane is considered. Considering the arch effect and the compatibility deformation between the truss model and the arch model, the formula for calculating the shear capacity of conventionally reinforced ECC coupling beam is proposed. Then, a formula for calculating the shear capacity of the diagonally reinforced ECC coupling beam was proposed. Based on the calculation results, the variation of the shear forces of diagonal ECC strut-and-tie, diagonal reinforcement and sub-struts with the span-to-depth ratio of the coupling beeam is given.