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2019 - 11 - 09
With the rapid development of the economy and the continuous improvement and innovation of the company's fatigue testing machine product research and development technology, our company is constantly expanding the international market and has been recognized by foreign customers.On November 3, foreign agents came to our company's workshop to visit and inspect. Our company Yang always warmly received Southeast Asian customers from afar. The Southeast Asian customers' trip was mainly to visit our company's dynamic fatigue testing machine. Accompanied by the technical director, the customer visit...
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2019 - 08 - 02
Our company has been studying and exchanging with Professor Huang Peiyan, School of Civil Engineering and Communications, South China University of Technology for a long time. Under the guidance of Professor Huang Peiyan, we have a deep understanding of the durability, fatigue fracture and corrosion resistance of bridge structures. With rich experience, strong technical force and good corporate reputation, Empoda successfully won the bid on July 30 for the project of Creep Load Long-term Performance Testing System, a large-scale environmental simulation cabin of Southeast University Urban Scie...
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2019 - 08 - 01
Distinguished users:Hello! First of all, thank you for your long-term concern and support for Empoda Industrial Systems Co., Ltd.  This revision includes computer website (www.szenpuda.com) and mobile website (m.szenpuda.com), aiming to further play the role of external publicity and communication of the website, and to provide customers with better service. At the same time, it also shows customers the new look of Enpda's continuous development.Compared with the old version of the website, the new page style is adopted and the whole structure is clearer. But we can't be perfect eith...
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2019 - 06 - 11
Recently, our company has successfully passed the ISO 9001:2008 quality management system certification of Shenzhen Bid Winning International Certification Center. It marks that our company has stepped into a standardized, standardized and scientific track of modern enterprise management.The certificate of ISO901:2008 quality management system certification is the standardized and standardized comprehensive inspection of the company's various management work, and an important guarantee for the company's sustained, stable and healthy development. We will further optimize and standardize various...
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2019 - 05 - 29
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2019 - 05 - 21
On May 18, Enpuda delivered another batch of hydraulic silent servo oil source system equipment to Taiwan's agents to help Empoda successfully gain access to the Taiwan market and lay a solid foundation.The key technology of hydraulic servo cylinder controls the minimum displacement loading of 1 micron/s, and the maximum noise of silent servo oil source is less than 62 decibels. Users come to our company for acceptance on the spot and use calibration instruments to measure all the indicators meet the requirements.This is the second cooperation after the success of the last project. It is a hig...
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2018 - 11 - 01
In October 2018, a teacher from Shijiazhuang Railway University came to our company to make a technical discussion on the 'Rail Rolling Contact Fatigue Test Bench'. After more than one year's exchange of theoretical and practical experience between the two sides, and consultation with relevant experts from Southwest Jiaotong University and China Academy of Railway Sciences, the project has been deeply understood and discussed; for dynamic fatigue test-bed, multi-channel coordinated loading test-bed, rail rolling contact fatigue test-bed. The technology of wheel-rail fatigue test-bed is deeply ...
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2018 - 06 - 14
On June 20, our company, together with Southwest Jiaotong University Railway Development Co., Ltd. and Hong Kong Polytechnic University, completed the most critical test in the project of 'High-speed Railway Turnout Safety Monitoring System'. Rail fracture signal acquisition and validation under natural frequency and load applied by dynamic fatigue test bench. In the course of two years'research in more than a dozen relevant experimental centers in China, they finally reached a cooperative relationship with our company.Dr. Wang of Hong Kong Polytechnic and Zhang Gong of Southwest Jiaotong Univ...
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2018 - 05 - 29
In this hot May, Empoda brought you good news. Successfully won the bid on May 18 - In 2017, the central government guided the local science and technology development special fund project 'Guizhou Highway Engineering Inspection and Inspection Technology Innovation and Service Platform Construction' inspection equipment procurement project.The leadership of the bidding company attaches great importance to the bidding documents, technical quality and other specific requirements. Due to the time constraints and heavy workload, under the leadership of the department, colleagues worked together to...
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2018 - 03 - 25
In March of spring blossom, after a month of basic information collation, various department managers organization and coordination, ushered in the Enpda ERP project officially successful online operation. It also marks a big step forward in the internal management of the company in the new year.Enpuda ERP system operation project is an important measure to improve company management and control, optimize resource allocation, enhance core competitiveness of enterprises, and promote enterprise management and development. The project has received the attention and support of company leaders and ...

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

Date: 2019-07-26
Views: 8

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

STRENGTHENED WTTH BFRP AND CFRP COMPOSITES

                             Wu Gang Gu Dongsheng Wu Zhishen                                                                                                                                 Jiang Jianbiao

                    (Collge of Civil Eninering, Southeast University Nanjing 210096)                                                           ( Bejjing Texida Technology Group Beijing 1001)1

Hu Xianqi

(Shanghai Russia & Gold Basalt Fiber Co., Ltd. Hengdian Group Shanghai 200940)

Abstract : Basalt fiber is expected to be widely applied in civil engineering for is fine mechanic performance, good stabilityand comparatively low price. However, there is sill litle research in the aspect concerning with the application of basatfiber in eivil Engineering. Comparative test on the seismic performance of circular concrete column strengthened with basaltfiber reinforced polymer ( BFRP) and carbon fber reinforced polymer (CFRP) was conducted. The infuence of fiber typeand fber amount on the strengthening ffeet was discussed. Test results show that BFRP and CFRP can both obviouslyimprove the seismic performance of circular concrete colunns , and more, BFRP has higher raio of performance to price.

Keywords : circular concrete columns   continuous basalt fiber scismic   retroft ductility

0 Introduction


Fiber reinforced polymer (FRP) is widely used in civil engineering, especially in seismic strengthening. At present, carbon fiber (CFRP), glass fiber (CFRP) and aramid fiber (AFRP) are widely used in engineering, especially in the field of engineering, but the price is relatively high, and the carbon fiber precursor basically depends on imports. GFRP and AFRP are cheaper, their mechanical properties are worse than CFRP, and some physical properties are not ideal, which affects their application.


Continuous basaltic fiber (CBF) is a high-tech fiber developed by the Soviet Union after more than 30 years of research and development. It is a continuous fiber made of natural volcanic extrusive rock, crushed and added to the furnace, melted at 1450-1500c, and drawn by platinum rhodium alloy. Compared with carbon fiber, aramid fiber and other high-tech fibers, it has many unique advantages, such as good mechanical properties, high temperature resistance, continuous operation in the range of - 269 ~ 700C, acid and alkali resistance, strong UV resistance, low moisture absorption, and better environmental resistance. Therefore, it has a very promising future, especially in recent years, China has also had the batch production of CBF, and began to pay attention to BF. Wide application [1-31)

1. Comparison of carbon fiber and basalt fiber

Figure 1 shows the performance comparison between basalt fiber and carbon fiber, in which the standard value of tensile strength of carbon fiber sheet is about 3500MPa, the modulus of elasticity is about 235cpa, and the ultimate tensile strain is about 1.5%. Continuous basalt fiber 1 is the mechanical index 4 measured according to the material property test of basalt fiber Twistless roving fiber in the early stage of manufacturer. It is also the material used in this test. Its tensile strength is 1835mpa, elastic modulus is 92gpa, and ultimate tensile strain is 1.99%. Continuous basalt fiber 2 represents the mechanical properties of a batch of basalt fiber cloth after the recent stable production by the manufacturer. The tensile strength is 2332mpa, the elastic modulus is 06gpa, and the ultimate tensile strain is about 2.4%. It can be seen from Figure 1 that the strength and modulus of elasticity of carbon fiber are higher than that of basalt fiber, and carbon fiber is more advantageous in flexural and shear strengthening, but the tensile strain of basalt fiber is higher than that of carbon fiber, so it is more advantageous in improving the ductility and other seismic performance of concrete columns strengthened by winding. Therefore, the experimental study on seismic performance of concrete columns strengthened by basalt fiber is carried out first, and Carbon fiber reinforcement is compared.

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS


2. The diameter of the reinforced concrete cylinder is 360mm, the total height of the test piece is 1600mm, I-shape, the bottom pier is fixed, the length of the column section is 800mm, the average compressive strength of the concrete cube is 4.3mpa, the longitudinal reinforcement is 12mm, the yield strength is 382.4mpa, the stirrup is 6 @ 150, and the yield strength of the stirrup is 319.8mpa; the axial pressure during the test is 1200kN. In order to prevent premature failure and concentrated deformation at the abrupt change of stiffness between the column root and the base during the test, the configuration of longitudinal reinforcement and stirrup is specially strengthened within 100 mm of the column root (this section is not regarded as the test section), so the effective length of the test column is 700 mm. In addition, three layers of CFRP are added for special reinforcement. Before pasting the fiber, polish the surface of the test piece, remove the scum and dust, brush the primer and leveling layer uniformly in turn, paste and wind the reinforcing fiber. Figure 2 shows the operation process of the basalt tow winding reinforcement. During the winding, strictly control the quality to ensure the uniform distribution and uniform penetration of the fiber and the resin colloid. After the colloid is completely solidified, carry out the test. See Table 1 for the basic test parameters and reinforcement of each test piece. The test pieces listed in this paper are part of a series of experimental studies on FRP seismic strengthening of the research group. For more details of the test pieces, please refer to


In this paper, four specimens are tested. One unreinforced specimen is used as the standard column, and one is wrapped with 1 and 4.5 layers of CFRP. According to the tensile test of the same batch of products, the strength of CFRP is 3945mpa, the modulus of elasticity is 249.6gpa, and the ultimate elongation is 1.52%. One reinforced column wrapped with basalt tow. This paper mainly studies the influence of different mechanical properties of fiber on the seismic performance of reinforced concrete columns, and discusses the influence of fiber content and type on the failure form, energy dissipation capacity, displacement ductility of reinforced columns. See Figure 3 for the test device.


COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

3 test results and analysis 3.1 failure mode of the test piece is shown in Figure 4, and the unreinforced pier column is a typical brittle shear failure (Figure 4a). When the amount of reinforcement is small (cl1-1.0c of the column strengthened with one layer of CFRP), during the loading process, the column body first appears oblique shear crack, and the local fiber of the column body breaks. With the increasing of the lateral displacement, the CFRP breaks in a large range, and the test piece loses the bearing capacity, which is the bending shear failure (Fig. 4b). When the amount of FRP reinforcement is large, the FRP of the column body directly bears the shear, and provides effective restraint to the concrete, avoiding the shear. In addition, the shear failure is avoided. Finally, the bending failure of plastic hinge zone restraint failure occurs in all the strengthened specimens. The failure of column ci2 strengthened by 4.5-storey CFRP and column Ci3 strengthened by BFRP belong to this situation (Fig. 4C, 4D).

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

3.2 load displacement curve

See Table 2 for peak load, ultimate displacement and lateral displacement angle of each test piece. Among them, the peak load is the maximum horizontal load in the whole loading process, and the limit displacement is defined as the lateral displacement corresponding to the failure of the test piece or when the horizontal load drops to 0.85 times the peak load. The lateral displacement angle is defined as the ratio of the limit displacement and the effective height of the column, and the test result is the average value in the positive and negative directions.

The hysteretic curves of each test piece are shown in Figure 5. It can be seen that: the unreinforced column has shear failure prematurely, the ultimate displacement is very small, the ductility is very poor, and the energy consumption capacity is low; the column strengthened with 1.0-storey CFRP has flexural shear failure, and the ductility is enhanced compared with the unreinforced column, but the brittle shear failure finally occurs; for the columns cl2-4.5c and cl3-bf with flexural failure, the ductility is very good, the hysteretic ring is full, and the energy consumption is very low. Compared with cl2-4.5c and CL3 BF, the hysteretic curves of the two are close, which shows that CBF filament winding is very effective for seismic strengthening of columns and CFRP wrapping is very effective for seismic performance improvement.


COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

3.3 strain characteristics and development law of FRP under different parameters

During the test, strain gauges shall be uniformly arranged on four symmetrical surfaces of each test piece's column body from 150 mm at the bottom of the column with an interval of 50 mm along the height to monitor the FRP strain characteristics and development law. See Figure 6 for the arrangement of strain gauges. Fig. 7 shows the relationship between strain and displacement ductility coefficient of f13 ~ F16 in the south of the specimen strengthened by CFRP in the 4.5-storey column. It can be seen that the strain from the bottom of the column to the top gradually decreases, which is basically linear distribution. When the displacement ductility coefficient is 10 times, the lateral bearing capacity declines seriously, and the law of column strain also changes. Figure 8 shows the relationship between the strain and the lateral displacement of F16 in the south of cl3-bf strengthened by BFRP. It can be seen that the strain increases with the increase of displacement, and the residual strain also increases when the displacement returns to zero. Fig. 9 shows the strain distribution of the South measuring point when the lateral displacement of cl1-1.0c and cl2-4.5c columns is 18mm. It can be seen that the FRP strain in the middle of cl1-1.0c column is larger than that in the bottom of the column, while the FRP strain in the bottom of cl2-4.5c column is larger than that in the bottom of the column, and the fiber at the bottom of the column is damaged first when the last failure occurs.

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS


COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

When the amount of CFRP is small, the constraint of CFRP on concrete and crack is not significant, so the concrete crack develops rapidly, correspondingly, the CFRP strain increases rapidly, as shown in the curve of average strain and displacement of column cl1-1.0c in Figure 10. When the amount of CFRP is large, the shear capacity of the columns strengthened with CFRP is improved, and the concrete in the core area is restrained. On the whole, the strain development of CFRP is relatively slow, and it is basically stable at a fixed value. For CL3 BF strengthened by BFRP, the strain development rule of fiber is basically the same as that of cl2-4.5c.

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS



3.4 analysis of hysteretic energy consumption

The hysteretic curve of each test piece is shown in Fig. 5. It can be seen that the unreinforced column has shear failure, small ultimate displacement, poor ductility and very low energy consumption capacity; the seismic performance of the 1.0-storey CFRP strengthened column has been improved, but the final failure mode is shear failure; the test pieces ci2-4.5c and CL3 BF have bending failure, good ductility, full hysteresis loop and strong energy consumption capacity. The seismic energy dissipation performance of the specimen can be evaluated by calculating the surrounding area under the load displacement curve. In this paper, the area of the first hysteretic loop of 4.5-storey CFRP and BFRP specimens under each displacement load is calculated to compare their hysteretic energy dissipation performance. It can be seen from Figure 11 that the energy dissipation performance of the two specimens is basically the same, but the curve is slightly different when the lateral displacement reaches 48mm. It can be seen from the hysteretic curve that when the lateral displacement reaches 48mm, the lateral bearing capacity of the two specimens decreases obviously. The attenuation of the lateral bearing capacity of the specimen strengthened by BFRP is slightly better than that of the specimen strengthened by 4.5-storey CFRP, which shows that BFRP can also have good seismic energy dissipation performance in the seismic reinforcement of concrete columns under the same lateral restraint stiffness.

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

Fig. 12 shows the comparison of effective viscous damping coefficient β between cl2-4.5c and ci3-bf, and the calculation method of β is shown in reference [4]. It can be seen that the effective viscous damping coefficient of basalt fiber reinforced specimen is slightly better than that of 4.5-layer CFRP restrained specimen at the same displacement level after about 2 times of yield displacement.

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS



4 Calculation of bearing capacity of concrete columns strengthened with FRP


4.1 calculation of flexural capacity

The calculation method of flexural capacity of strengthened columns is relatively mature 5). The key is to select the appropriate FRP confined concrete stress-strain relationship model (6,), and then use the strip method for nonlinear analysis 8, or select some current non-linear analysis software, such as openses (9). Figure 13 shows the bending moment curvature curve of cl2-4.5c and cl3-bf. It can be seen that the calculated bending bearing capacity is in good agreement with the test value, and the bending moment curvature curve of cl3-bf and ci2-4.5c is relatively close, which is also consistent with the test result. Based on the bending moment curvature curve, the influence of various parameters on the reinforcement effect can be systematically analyzed.

4.2 calculation of shear bearing capacity

The formula for calculating the shear capacity V of reinforced concrete columns strengthened with FRP is generally in the form of simple superposition, that is, on the basis of the shear capacity VEC of reinforced concrete columns, the contribution of FRP to the shear capacity V of reinforced columns is expressed as follows:

V = VRC + VF (1)

When the column body is reinforced with FRP, V; can be calculated by formula (2):

COMPARATTVE STUDY ON SEISMIC PERFORMANCE OF CIRCULAR CONCRETE COLUMNS

Among them, PR is the FRP fiber ratio. When the column body is reinforced with full wrapped FRP, ρ: = 2nrtid, NT is the number of FRP layers, 1 is the thickness of single FRP layer, D is the diameter of the column, e is the elastic modulus of FRP, θ is the angle between the diagonal crack and the column axis, generally taken conservatively as 45 °, ε P is the effective tensile strain of FRP.

The key to calculate the shear capacity is to determine the effective tensile strain, which is related to many factors, such as section form, FRP type, failure mode, etc. However, in the case of few test data of BFRP seismic strengthening, 10 can be determined temporarily by referring to the code.

5 Conclusion

According to the test comparison between CFRP and BF wire bundle, it can be seen that BFRP can significantly improve the seismic performance of concrete columns, especially its price is much cheaper than CFRP, so it has advantages over CFRP in seismic reinforcement and is worth popularizing.


Reference

1 Hu Xianqi, Shen Tu Nian. Application of continuous basalt fiber in military industry and civil leading cities. High tech fiber and application, 2005 (12)

2 Wu Gang, Hu Xianqi, Jiang Jianbiao, et al. Study on Application of continuous basalt fiber in seismic reinforcement of pier columns / / Proceedings of national FRP conference in 2005. Xi'an: 2005

3 Gu Dongsheng, Wu Gang, Wu Zhishen, et al. Experimental study on seismic behavior of reinforced concrete short columns with high axial compression ratio of CFRP. Engineering earthquake resistance and reinforcement, 2006 (12)

4 Wu Gang, Wei Yang, Jiang Jianbiao, et al. Comparative study on seismic behavior of concrete rectangular columns strengthened with basalt fiber and carbon fiber. Industrial architecture, 2007, 37 (6); 14-18

5 Seible F. scientific retrofit of RC columns with continuous carbon fiberjackets. ASCE, Journal of composites for construction, 1997 (3): 52 - 62

6 Wu Gang, LV Zhitao. Study on the stress-strain relationship of FRP confined concrete cylinder without softening section. Journal of building structures, 2003,24 (5); 1-8

7 Wu Gang, LV Zhitao, Wu Zhishen. Study on the stress-strain relationship of FRP concrete columns with softened section. Journal of civil engineering 2006,39 (11); 7-14

8 Guo Zhenhai. Strength and constitutive relation of concrete - principle and application, Beijing: China Construction Industry Press, 2004

9 open system for earthquake engineering simulation user manual, University of California, Berkeley, version 1.72006

10 technical code for engineering application of fiber reinforced composite (Draft for comments). 2006

 


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