PET FRP约束矩形RC柱中纵筋屈曲行为

白玉磊; 孙鹏轩; 贾俊峰

doi:10.13801/j.cnki.fhclxb.20211019.002

PET FRP约束矩形RC柱中纵筋屈曲行为

doi: 10.13801/j.cnki.fhclxb.20211019.002

北京工业大学　城市与工程安全减灾教育部重点实验室，北京 100124

基金项目: 国家自然科学基金 (51778019；51978017)；北京市自然科学基金(8212003)；北京市教委青年拔尖人才培养计划项目(CIT&TCD201904018)

详细信息

通讯作者:
贾俊峰，博士，教授，博士生导师，研究方向为新材料与新型结构体系　E-mail: jiajunfeng@bjut.edu.cn

中图分类号: TB332
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出版历程
- 收稿日期: 2021-08-12
- 修回日期: 2021-09-18
- 录用日期: 2021-10-08
- 网络出版日期: 2021-10-20
- 刊出日期: 2022-08-22

Buckling behavior of steel rebars in PET FRP-confined rectangular RC columns

Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China

摘要

摘要: 大应变纤维增强聚合物复合材料(LRS FRP)具有大断裂应变(大于5%)的特性，可能带来较高的结构延性，为钢筋混凝土(RC)柱的抗震加固提供了一种新的选择。外包FRP通过混凝土保护层为纵筋提供侧向支撑，防止或减缓纵筋的屈曲。但当箍筋间距较大时纵筋仍可能发生屈曲，尤其是在FRP不均匀约束的矩形柱中，纵筋的提前屈曲降低了柱子的承载能力。为研究不均匀约束情况下，FRP加固柱中钢筋的屈曲行为，本文共设计了28个聚对苯二甲酸乙二醇酯(Polyethylene terephthalate，PET) FRP约束矩形试件，包括16个RC柱和12个素混凝土(PC)柱，对其进行单调轴压试验，研究FRP层数、箍筋间距和截面形状比对约束柱承载力和延性的影响；从试验结果中得到纵筋的平均应力-应变曲线，对FRP约束RC柱中纵筋的应力-应变关系进行定量分析。结果表明，PET FRP约束RC柱可提高其强度和延性，在一定范围内，当约束刚度越大、截面形状比越接近1时，约束效果越好；外包FRP的侧向支撑作用可将纵筋的屈曲推迟到较高的变形水平。
- 聚对苯二甲酸乙二醇酯纤维增强聚合物 /
- 纵筋屈曲 /
- 单调轴压 /
- 纤维增强聚合物约束柱 /
- 侧向支撑
Abstract: Large-rupture-strain fiber reinforced polymers (LRS FRPs) have the large tensile rupture strain value of more than 5%. This characteristic might enhance the load-bearing capacity and ductility and provide a new choice for seismic strengthening of reinforced concrete (RC) columns. The FRPs provide lateral support for the longitudinal bars through the cover concrete, which might prevent or delay the buckling of longitudinal steel bars. However, the buckling of the longitudinal reinforcement might still be observed when the stirrup spacing is relatively large. Especially, for the FRP-confined rectangular columns, the ununiform confinement provided by the external FRP for the specimen might result in the buckling of longitudinal bars and reduce the load-bearing capacity of the specimen. In order to study the buckling behavior of longitudinal bars in rectangular RC columns confined by FRP, a total of 28 polyethylene terephthalate (PET) FRP-confined rectangular columns, comprising 16 RC columns and 12 plain concrete (PC) columns, were prepared and tested under monotonic axial compression. The effects of the thickness of external FRP jackets, stirrup spacing and section aspect ratio on the load-bearing capacity of FRP-confined RC columns were studied. To carry out a quantitative study on the buckling behavior of longitudinal steel bars in FRP-confined RC columns, the average axial stress-strain curve of a single longitudinal bar was obtained from the test results. The experimental results show that the application of PET FRP jackets can effectively improve the load-bearing capacity and ductility of RC columns. A large confinement stiffness and a low section aspect ratio close to 1 lead to a high confinement level for RC columns. And the lateral support of FRP can delay the buckling of the steel bars to a higher deformation level.
- large-rupture-strain fiber reinforced polymer /
- bar buckling /
- axial compression /
- FRP-confined column /
- lateral support

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图 1 聚对苯二甲酸乙二醇酯纤维增强聚合物复合材料(PET FRP)约束矩形钢筋混凝土(RC)柱试件详细尺寸及其配筋

Figure 1. Detailed dimensions and reinforcement of the polyethylene terephthalate fiber reinforced polymer (PET FRP)-confined rectangular reinforced concrete (RC) column specimens

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图 2 模板(a)和PET FRP拉伸应力-应变曲线(b)

Figure 2. Template (a) and tensile stress-strain curves (b) of PET FRP

E_a and E_b—Elastic modulus of the first and the second straight line

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图 3 试验装置

Figure 3. Test setup

LVDTs—Linear variable displacement transducers

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图 4 PET FRP 约束矩形 RC 柱试件破坏模式及钢筋屈曲

Figure 4. Failure model of FRP rupture and buckling of steel in PET FRP-confined rectangular RC specimens

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图 5 一层PET FRP约束矩形混凝土柱试件的荷载-位移曲线

Figure 5. Load-displacement curves of one-ply PET FRP-confined rectangular concrete column specimens

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图 6 两层PET FRP约束矩形混凝土柱试件的荷载-位移曲线

Figure 6. Load-displacement curves of two-ply PET FRP-confined rectangular concrete column specimens

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图 7 一层PET FRP约束矩形混凝土柱试件峰后软化荷载 (a) 和极限荷载 (b) 与峰值荷载的比值

Figure 7. Ratio of load after softening (a) and ultimate axial load (b) to peak axial load of one-ply PET FRP-confined rectangular concrete column specimens

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图 8 两层PET FRP约束矩形混凝土柱试件峰后软化荷载 (a) 和极限荷载 (b) 与峰值荷载的比值

Figure 8. Ratio of load after softening (a) and ultimate axial load (b) to peak axial load of two-ply PET FRP-confined rectangular concrete column specimens

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图 9 一层PET FRP约束矩形RC柱中纵筋的应变路径

Figure 9. Evolution of strains in longitudinal steel bars of one-ply PET FRP-confined rectangular RC columns

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图 10 两层PET FRP约束矩形RC柱中纵筋的应变路径

Figure 10. Evolution of strains in longitudinal steel bars of two-ply PET FRP-confined rectangular RC columns

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图 11 一层PET FRP约束矩形RC柱中纵筋的平均应力-应变曲线

Figure 11. Average stress-strain curves of longitudinal rebars in one-ply PET FRP-confined rectangular RC columns

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图 12 两层PET FRP约束矩形RC柱中纵筋的平均应力-应变曲线

Figure 12. Average stress-strain curves of longitudinal rebars in two-ply PET FRP-confined rectangular RC columns

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表 1 PET FRP约束矩形混凝土柱试件参数及试验结果

Table 1. Key information of PET FRP-confined rectangular concrete column specimens and test results

Specimen name	Cross section/mm	Type of FRP	Number of plies FRP	Nominal thickness of FRP/mm	Peak axial load P_cc/kN	Load after softening P_dt/kN	Ultimate axial load P_cu/kN	Ultimate axial deformation Δ_cu/mm
1PET-200RC(R170)-a	170×130	PET	1	0.841	959.9	874.8	856.5	7.33
1PET-200RC(R170)-b	170×130	PET	1	0.841	1029.1	933.2	920.6	7.83
1PET-PC(R170)-a	170×130	PET	1	0.841	907.7	713.9	735.4	4.97
1PET-PC(R170)-b	170×130	PET	1	0.841	976.2	715.4	710.0	6.74
1PET-200RC(R180)-a	180×120	PET	1	0.841	1001.1	846.5	853.2	6.29
1PET-200RC(R180)-b	180×120	PET	1	0.841	1022.0	887.5	900.6	7.56
1PET-PC(R180)-a	180×120	PET	1	0.841	942.6	713.8	709.0	7.10
1PET-PC(R180)-b	180×120	PET	1	0.841	879.3	674.8	697.6	9.29
1PET-200RC(S150)-a	150×150	PET	1	0.841	1026.1	951.0	929.9	5.75
1PET-200RC(S150)-b	150×150	PET	1	0.841	1007.2	958.9	962.9	5.18
1PET-PC(S150)-a	150×150	PET	1	0.841	954.2	804.7	793.9	5.92
1PET-PC(S150)-b	150×150	PET	1	0.841	948.4	807.4	772.0	6.80
1PET-240RC(S150)-a	150×150	PET	1	0.841	−	−	−	−
1PET-240RC(S150)-b	150×150	PET	1	0.841	1035.2	998.6	998.2	5.08
1PET-PC(S150)-a	150×150	PET	1	0.841	956.5	808.1	799.9	5.94
1PET-PC(S150)-b	150×150	PET	1	0.841	948.4	785.1	772.0	6.80
2PET-200RC(R170)-a	170×130	PET	2	1.682	−	−	−	−
2PET-200RC(R170)-b	170×130	PET	2	1.682	1179.7	1142.0	1309.9	9.69
2PET-PC(R170)-a	170×130	PET	2	1.682	1083.1	982.8	1256.1	9.16
2PET-PC(R170)-b	170×130	PET	2	1.682	1059.9	921.9	1042.4	7.20
2PET-200RC(R180)-a	180×120	PET	2	1.682	1135.2	1096.2	1204.7	9.35
2PET-200RC(R180)-b	180×120	PET	2	1.682	1197.5	1129.1	1230.9	11.31
2PET-PC(R180)-a	180×120	PET	2	1.682	1004.4	878.1	1050.1	9.50
2PET-PC(R180)-b	180×120	PET	2	1.682	1045.8	854.0	1047.5	9.76
2PET-200RC(S150)-a	150×150	PET	2	1.682	1246.2	−	1387.1	8.63
2PET-200RC(S150)-b	150×150	PET	2	1.682	1277.9	1272.5	1466.9	9.74
2PET-PC(S150)-a	150×150	PET	2	1.682	1123.1	1080.6	1200.7	6.80
2PET-PC(S150)-b	150×150	PET	2	1.682	1110.2	1063.9	1421.9	9.40
2PET-240RC(S150)-a	150×150	PET	2	1.682	−	−	−	−
2PET-240RC(S150)-b	150×150	PET	2	1.682	1222.8	−	1428.1	9.71
2PET-PC(S150)-a	150×150	PET	2	1.682	1126.8	1080.9	1200.7	6.80
2PET-PC(S150)-b	150×150	PET	2	1.682	1110.7	1061.3	1413.1	9.40
Notes: PET—Polyethylene terephthalate; RC—Reinforced concrete; PC—Plain concrete; Specimen name VW-X(Y)-Z: V—Number of plies; W—Type of FRP; X—Type of columns and stirrup spacing for RC columns; Y—Section type and width; S—Square column; R—Rectangular column; Z—a and b represent two identical components.

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表 2 钢筋力学性能参数

Table 2. Mechanical parameters of steel

Bar type	f_y/MPa	f_u/MPa	E_s/GPa	ε_u/%
Φ12	428	579	202	24.6
Φ8	453	649	201	20.6
Notes: f_y and f_u—Yield stress and tensile strength of the bars, respectively; E_s—Elasticity modulus of the bars; ε_u—Ultimate strain.

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表 3 PET FRP约束矩形混凝土柱试件中钢筋应力-应变曲线上重要点的值

Table 3. Values of important points on the stress-strain curves of longitudinal rebars in PET FRP-confined rectangular concrete column specimens

Specimen name	f_cc/MPa	ε_cc/%	ε_fy/%	f_cm/MPa	ε_cm/%	f_cu/MPa	ε_cu/%
1PET-200RC(R170)-a	88.7	0.74	−	395.6	2.37	332.5	2.92
1PET-200RC(R170)-b	114.4	0.30	1.37	508.1	2.29	449.5	2.92
1PET-200RC(R180)-a	190.8	0.95	−	423.2	3.18	403.8	3.70
1PET-200RC(R180)-b	99.2	0.08	2.26	406.7	1.10	484.3	3.70
1PET-200RC(S150)-a	71.3	0.23	1.94	428.0	1.94	411.6	3.05
1PET-200RC(S150)-b	63.0	0.21	2.02	439.4	2.70	432.5	3.05
1PET-240RC(S150)-b	117.1	0.34	1.19	526.4	2.50	496.1	3.01
1PET-200RC(R170)-b	47.3	0.18	1.50	503.4	2.86	460.7	4.23
1PET-200RC(R180)-a	54.3	0.02	1.10	552.4	2.10	427.2	5.50
1PET-200RC(R180)-b	176.0	0.09	0.63	636.1	3.27	459.4	5.05
1PET-200RC(S150)-a	88.7	0.21	1.54	551.0	2.82	450.5	4.00
1PET-200RC(S150)-b	263.1	0.13	1.19	528.9	3.16	480.0	4.00
1PET-240RC(S150)-b	90.4	0.58	−	426.0	2.57	353.0	4.00
Notes：f_cc and ε_cc—Stress and strain at the beginning point; ε_fy—Strain when the stress reaches yield strength; f_cm and ε_cm—Peak stress and strain, respectively; f_cu and ε_cu—Yield stress and ultimate strain, respectively.

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