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

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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
	Reverse	19.35	90.11	4.66
S2	Forward	28.1	72.03	2.56	2.37
	Reverse	32.92	71.94	2.06
S3	Forward	29.28	72.05	2.38	2.32
	Reverse	32.97	71.97	2.06
S4	Forward	27.65	67.87	2.45	2.20
	Reverse	34.91	68.12	1.95
S5	Forward	26.48	68.10	2.57	2.29
	Reverse	33.96	67.92	2.00
S6	Forward	26.66	75.03	2.81	2.63
	Reverse	30.73	74.90	2.44

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
	20	436	633	2.00 × 105
φS15.2 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
	Negative	73.24	82.62	1.13
S2	Positive	74.54	86.52	1.16	1.10
	Negative	77.98	80.66	1.03
S3	Positive	78.39	87.43	1.12	1.15
	Negative	76.84	90.75	1.18
S4	Positive	80.09	91.8	1.15	1.13
	Negative	83.01	29.53	1.12
S5	Positive	79.76	91.93	1.15	1.13
	Negative	93.85	103.04	1.10
S6	Positive	87.46	110.45	1.26	1.26
	Negative	76.65	97.09	1.27

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
	Forward	77.65	89.9	0.86
S2	Reverse	50.03	71.94	0.70	0.75
	Forward	58.06	72.03	0.81
S3	Reverse	49.58	72.17	0.69	0.73
	Forward	55.21	72.05	0.77
S4	Reverse	42.87	68.12	0.63	0.67
	Forward	48.79	67.87	0.72
S5	Reverse	47.66	67.92	0.70	0.76
	Forward	55.48	68.1	0.81
S6	Reverse	60.38	74.9	0.81	0.83
	Forward	64.14	75.03	0.85