Seismic performance of precast prestressed concrete frame joints with buckle mechanical connection of reinforcing bars

Wang, Yi; Sushant, Subedi; Ge, Wen Jie; Sun, Chuanzhi; Cheng, Jinsheng; Tong, Lei

doi:10.2478/msp-2025-0027

Figures & Tables

Schematic diagram of the buckle-type mechanical connector. (a) Before connection, (b) after connection, (c) reinforced bar mechanical connection method, (d) internal structure of the connector.

Detailed diagrams of each specimen. (a) S1, (b) S2, (c) S3–S6, (d) column-end reinforcement (joint region), (e) column-end reinforcement (normal region), (f) beam-end reinforcement (dense zone), (g) beam-end reinforcement (normal zone), and (h) key grooves.

Specimen fabrication process. (a) Fabrication of column rebar cage, (b) fabrication of cast-in-place joint rebar cage, (c) attachment of strain gauges, (d) insertion of rebar cage into the mold, (e) concrete pouring, (f) second concrete pouring, (g) tensioning of steel strands, (h) strain gauge sensor, and (i) placement diagram of the strain gauge sensor.

Mechanical properties testing of steel reinforcements and mechanical connectors. (a) Tensile test of steel bar, (b) fracture of steel bar, (c) tensile test of mechanical connection steel reinforcement, (d) fracture of mechanical connection steel reinforcement, and (e) comparison of uniaxial tensile stress–strain curves for rebar and mechanical connector.

Experimental setup and loading schematic. (a) Schematic of the experimental setup and (b) on-site image of the experimental setup.

Layout of measuring points and measurement methods. (a) Reinforcement strain measurement points, (b) speckle pattern in the core region, (c) DIC instrument, and (d) crack width measuring instrument.

Crack distribution and failure features of cast-in-place specimen S1. (a) Cracks at the left beam of specimen S1, (b) cracks at the right beam of specimen S1, (c) cracks at the joint core of specimen S1, (d) failure at the left beam end of specimen S1, and (e) concrete crushing in the right beam of specimen S1.

Crack development and failure characteristics of precast non-prestressed specimen S2. (a) Overall failure mode of specimen S2, (b) cracks in the left beam of specimen S2, (c) cracks in the right beam of specimen S2, and (d) cracks in the joint core of specimen S2.

Crack development and failure characteristics of precast prestressed specimen S3. (a) Cracks in the left beam of specimen S3, (b) cracks in the core joint of specimen S3, (c) cracks in the right beam of specimen S3, (d) overall failure mode of specimen S3, (e) reinforcement exposure in the left beam of specimen S3, and (f) connector exposure in specimen S3.

Crack propagation and beam-end damage in precast prestressed specimen S4. (a) Cracks in the left beam of specimen S4, (b) cracks in the joint core of specimen S4, (c) cracks in the right beam of specimen S4, (d) concrete spalling at the bottom of the beam in specimen S4, and (e) reinforcement exposure in the right beam of specimen S4.

Cracking, connector exposure, and spalling in precast prestressed specimen S5. (a) Cracks in the left beam of specimen S5, (b) cracks in the joint core of specimen S5, (c) cracks in the right beam of specimen S5, (d) overall failure mode of specimen S5, (e) concrete spalling at the bottom of the beam in specimen S5, (f) connector exposure at the bottom of the beam in specimen S5, and (g) concrete crushing at the upper end of the beam in specimen S5.

Severe cracking and reinforcement exposure in precast prestressed specimen S6. (a) Cracks in the left beam of specimen S6, (b) cracks in the joint core of specimen S6, (c) cracks in the right beam of specimen S6, (d) overall failure mode of specimen S6, (e) concrete crushing at the upper part of the left beam in specimen S6, (f) reinforcement exposure in the right beam of specimen S6, and (g) exposure of connectors and stirrups at the bottom of the beam in specimen S6.

Comparison of the hysteresis curves. (a) S1, (b) S2, (c) S3, (d) S4, (e) S5, and (f) S6.

Comparison of the strength degradation. (a) Strength degradation of S1, (b) strength degradation of S2, (c) strength degradation of S3, (d) strength degradation of S4, (e) strength degradation of S5, and (f) strength degradation of S6.

Comparison of the stiffness degradation.

Equivalent elastic-plastic energy method.

Energy dissipation coefficient calculation diagram.

Comparison of energy dissipation coefficient.

Comparison of beam longitudinal reinforcement strains of specimens S2 and S6.

Comparison of column longitudinal reinforcement strain of specimens S2 and S6.

Comparison of the stirrup strain distribution of specimens S2 and S6.

DIC strain contour plots of specimen S2.

Main design parameters of specimens_

Specimen	S1	S2	S3	S4	S5	S6
Axial compression ratio	0.2	0.2	0.2	0.2	0.3	0.4
Prestress	—	—	0.4f _ptk	0.6f _ptk	0.6f _ptk	0.6f _ptk
Concrete	C40	C40	C40	C40	C40	C40
Column reinforcement	8φ20	8φ20	8φ20	8φ20	8φ20	8φ20
Beam reinforcement	4φ16	4φ16	4φ16	4φ16	4φ16	4φ16
Stirrups	φ8	φ8	φ8	φ8	φ8	φ8
Remarks	Cast-in-place	Buckle-type connection	Buckle-type connection	Buckle-type connection	Buckle-type connection	Buckle-type connection

Comparison of the characteristic displacements_

Specimen	Loading direction	Δ _y (mm)	Δ _u (mm)	μ	Average coefficient
S1	Forward	37.64	89.90	2.39	3.52
S1	Reverse	19.35	90.11	4.66	3.52
S2	Forward	28.1	72.03	2.56	2.37
S2	Reverse	32.92	71.94	2.06	2.37
S3	Forward	29.28	72.05	2.38	2.32
S3	Reverse	32.97	71.97	2.06	2.32
S4	Forward	27.65	67.87	2.45	2.20
S4	Reverse	34.91	68.12	1.95	2.20
S5	Forward	26.48	68.10	2.57	2.29
S5	Reverse	33.96	67.92	2.00	2.29
S6	Forward	26.66	75.03	2.81	2.63
S6	Reverse	30.73	74.90	2.44	2.63

Mechanical properties of steel materials_

Material type	Diameter (mm)	Yield strength f _y (MPa)	Ultimate strength f _u (MPa)	Elastic modulus E _s (MPa)
HRB400	8	422	541	2.00 × 10⁵
	18	442	618	2.00 × 10⁵
	20	448	633	2.00 × 10⁵
Buckle connection HRB400	18	427	611	2.00 × 10⁵
Buckle connection HRB400	20	436	633	2.00 × 10⁵
φ_S15.2 steel strand	15.2	—	1,930	1.95 × 10⁵

Concrete material properties_

Batch	Cube strength f cu 0 {f}_{\text{cu}}^{0} (MPa)	Axial strength f c 0 {f}_{\text{c}}^{0} (MPa)	Tensile strength f t 0 {f}_{\text{t}}^{0} (MPa)	Elastic modulus E _c (MPa)
First	46.6	34.6	3.2	33,960
Second	41.7	31.5	3.1	32,980

Comparison of energy dissipation coefficient (E) and equivalent viscous damping coefficient (h e)_

Specimens	S1	S2	S3	S4	S5	S6
E	1.53	1.12	1.2	1.33	1.38	1.63
h _e	0.25	0.18	0.19	0.22	0.22	0.26

Comparison of the characteristic parameters_

Specimen number	Loading direction	Yield load P _y (kN)	Peak load P _max (kN)	P _max/P _y	Average ratio
S1	Positive	78	83.61	1.07	1.10
S1	Negative	73.24	82.62	1.13	1.10
S2	Positive	74.54	86.52	1.16	1.10
S2	Negative	77.98	80.66	1.03	1.10
S3	Positive	78.39	87.43	1.12	1.15
S3	Negative	76.84	90.75	1.18	1.15
S4	Positive	80.09	91.8	1.15	1.13
S4	Negative	83.01	29.53	1.12	1.13
S5	Positive	79.76	91.93	1.15	1.13
S5	Negative	93.85	103.04	1.10	1.13
S6	Positive	87.46	110.45	1.26	1.26
S6	Negative	76.65	97.09	1.27	1.26

Comparison of residual deformation rate_

Specimen	Loading direction	Δ _r (mm)	Δ _u (mm)	μ _r (%)	Average value (%)
S1	Reverse	78.08	90.11	0.87	0.87
S1	Forward	77.65	89.9	0.86	0.87
S2	Reverse	50.03	71.94	0.70	0.75
S2	Forward	58.06	72.03	0.81	0.75
S3	Reverse	49.58	72.17	0.69	0.73
S3	Forward	55.21	72.05	0.77	0.73
S4	Reverse	42.87	68.12	0.63	0.67
S4	Forward	48.79	67.87	0.72	0.67
S5	Reverse	47.66	67.92	0.70	0.76
S5	Forward	55.48	68.1	0.81	0.76
S6	Reverse	60.38	74.9	0.81	0.83
S6	Forward	64.14	75.03	0.85	0.83

Seismic performance of precast prestressed concrete frame joints with buckle mechanical connection of reinforcing bars

Figures & Tables

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Main design parameters of specimens_

Comparison of the characteristic displacements_

Mechanical properties of steel materials_

Concrete material properties_

Comparison of energy dissipation coefficient (E) and equivalent viscous damping coefficient (h e)_

Comparison of the characteristic parameters_

Comparison of residual deformation rate_

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