A SELF-COMPACT CONCRETE-STEEL COMPOSITE STRUCTURE FOR ELECTRICAL TRANSMISSION TOWER

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Bartholomew Goodman
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1 A SELF-COMPACT CONCRETE-STEEL COMPOSITE STRUCTURE FOR ELECTRICAL TRANSMISSION TOWER Ju Chen (1), Yin Ye (2), Xiao-Hong Sheng (2), Da-Yu Huang (2) and Wei-Liang Jin(1) (1) Zhejiang University, Department of Civil Engineering, Structural Engineering Institute, China (2) Zhejiang Electric Power Design Institute, China Abstract A new electric transmission line lattice structure with the height of 370m has been developed to provide a connection between the electric net of Zhoushan and Ningbo. The primary feature of the lattice structure is that the four main columns are designed as self-compact concrete-filled steel tubes (CFST). This paper address the details of the CFST columns in the electrical transmission tower. The material properties of self-compact concrete in the CFST was carefully examined. Experimental investigation which aimed to provide reference information for the project was also conducted. 1. INTRODUCTION In 2007, a 220kV electrical net connection program between Zhoushan and Ningbo was identified over a four years period. Zhoushan is an island and the transmission line has to across the Luotou international waterway. The distance between the two ends of the connection (one in Zhoushan, the other in Ningbo) is 2756 m. The steel lattices structures are widely used in the transmission line towers which has the advantage of easy construction, light weight and good performance and was also used in this project. However the transmission tower will be very high for this extremely long, and the lateral resistant requirement results in very large diameter and thickness of the steel main columns. Therefore, pure steel structure may not suitable. The use of composite steel-concrete construction has spread throughout the world in recent decades. The range of applications varied widely encompassing buildings, bridges, foundations, and special structures. Popularity of this construction is attributed to the advantages it provides over reinforced concrete or steel structures. A few of the key advantage include increased flexural strength, stiffness, ductility, and fire resistance, as well as improved economics. It has been shown over years that the creative use of construction material and technology has led to advances in the structural field and has enabled the achievement of 697

stronger and taller structures. [1] In addition, the concrete inside the tube will provide lateral stability to the wall of the tube as well as added lateral resistance of whole column.

Although there is many CFST application in tall building, bridges, this project is the first application of self-compact concrete filled steel tubes in electric structures in China.

2 stronger and taller structures. [1] In addition, the concrete inside the tube will provide lateral stability to the wall of the tube as well as added lateral resistance of whole column. [2] By using the concrete-filled steel tube, the thickness of the main column could be relative thin and high strength steel could be used [3,4]. Although there is many CFST application in tall building, bridges, this project is the first application of self-compact concrete filled steel tubes in electric structures in China. Due to the difficulty in the concrete vibration in long steel tubes in electric transmission tower, the self-compact concrete was used. Self-compacting concrete (SCC) has been used for large office buildings and also for advanced types of extruded tunnels in combination with steel fibers [5,6]. Use of SCC could solve the problem of vibration and also lowered the noise level on the construction site and diminished the effect on the environment [7]. Although there is some research conducted on the self-compact concrete-filled steel tubes [8]. Experimental investigation of the self-compact concrete material and the concrete-filled steel tubes were carried out to provide reference for this project. 2. BACKGROUND The electric of Zhoushan island is independent of the whole electrical net of Zhejiang provision. The insufficient electric power supply limit the economic increasing of Zhoushan. It is necessary to transmit the electric power to Zhoushan island from Zhejiang provision electric net which require the connection between the two nets. Therefore, the Zhoushan Zhejiang electric net connection program was determined to be conducted. The total length of the transmission line built is 41 km. 3. ELECTRICAL TRANSMISSION TOWER There are two same electrical transmission tower located in Damao Hill and Liangmao Hill, respectively. The design height of the tower is 370 m. The weight of each single tower is expected to be 5999 ton. The whole tower is steel truss structures with the four main columns are CFST. The largest diameter of the main columns is 1400 mm with the maximum thickness of 20 mm. The design strength of the self-compact concrete is C50. The steel tubes of the tower are firstly construction in three stages. The three stages are 89 m, 263m and 370m. The concrete is cast from the top of the steel tubes during the construction stage, as shown in Fig. 2. Figure 1: Electrical tower in construction 698

4. MAIN COLUMNS AND CONNECTIONS The tubes were all manufactured from mild steel sheet, with the plate being cut from the sheet, cold-formed into a circular shape and then

Since the member of the tower has large dimensions, the steel stiffeners are welded on the wall of the steel tubes.

It is shown that there are small stiffeners at the two ends of each steel tubes.

Figure 2: Casting of SCC Figure 3: Steel tube with steel frame inside Figure 4: Side connection 5. CONCRETE MATERIAL TESTS The design grade of concrete is C50.

3 4. MAIN COLUMNS AND CONNECTIONS The tubes were all manufactured from mild steel sheet, with the plate being cut from the sheet, cold-formed into a circular shape and then welded with a single bevel butt weld. There is a steel frame built-up using steel angles by bolt connection and welding inside each main columns, as shown in Fig. 3. Since the member of the tower has large dimensions, the steel stiffeners are welded on the wall of the steel tubes. The side connection which connects the main columns and the side truss members are shown in Fig. 4. It is shown that there are small stiffeners at the two ends of each steel tubes. Four short steel tubes are weld on the main tube which are used to connect the side truss members, as shown in Fig. 4. However, there is no concrete in the side truss members. Figure 2: Casting of SCC Figure 3: Steel tube with steel frame inside Figure 4: Side connection 5. CONCRETE MATERIAL TESTS The design grade of concrete is C50. Table 1 shows the mix proportions of SCC used in this project. The aggregate size is 5-25 mm with the appearance density of 2640 kg/m 3. The grade of aggregate is shown in Table 2. The river sand having the appearance density of 2550 kg/m 3 is used. Table 3 presents the grade of the sand. SCC contains small quantities of superplasticizer. Furthermore, in order to avoid separation of large particles in SCC, additives 699

4 to increase the viscosity or fillers are used [9-11]. To increase the viscosity in SCC, the fillers of flash ash was used in this project. The flash ash used is CⅡ grade according to GB/T standard. The cement used is product P of Anhui Conch Cement Company Limited. Water used in the concrete satisfied the requirement of JGJ standard. The water reduced additive could reduced the water in cement of 24.5%. The test results of cement is presented in Table 4. The compressive strength was obtained on 150-mm cubes at 28 days and the average strength is 56.0 MPa. Table 1: Mix proportions of SCC used in this project Material Content (kg/m 3 ) Sand (%) 45.5 Cement 210 Water 522 Water 180 Sand 683 Aggregate 889 Expansive additive 58 Superplasticizer 9.57 Flash ash 58 Table 2: Grade of the aggregate Mesh size (mm) Residual (%) Table 3: Grade of the sand Mesh size (mm) Residual (%) Table 4: Cement strength test results Fracture strength (MPa) Compressive strength (MPa) 3d 28d 3d 28d MEMBER TESTS A series experimental program was carried out to provide reference to the project. CFST having relative small dimensions were tested. These tested specimens are cast in the construction site of the electrical tower and the same batch of self-compact concrete was used. 700

5 Fig 5 shows the stub column tests carried out in Zhejiang Univeristy structural laboratory. The test program includes short and long specimens to investigate both strength and stiffness of the self-compact concrete-filled steel tubes. The tests results could provide reference information for this project and will be reported in near future. Figure 5: Stub column compression tests 7. CONCLUSIONS A electric transmission line lattice steel structure having concrete filled-steel tubes as main columns was developed. Due to the difficulty in the concrete vibration in long steel tubes in electric transmission tower, the self-compact concrete was used. The detailed of the developed electrical tower were presented in this paper. Material tests of the self-compact concrete was conducted and test results were presented. Experimental investigation of self-compact concrete-filled steel tubes was carried out to provide reference information for the project. ACKNOWLEDGEMENTS The authors were appreciate the finial support from the Zhejiang Electric Power Design Institute-Zhejiang Univerisity cooperation project and China post doctor special funding. REFERENCES [1] Fouad, F.H., Foust, E.R., and Oliphant, A composite steel-concrete monopole for electrical transmission lines, Electrical Transmission Line, ASCE, 2006, pp [2] Uy, B., Local and postlocal buckling of fabricated steel and composite cross sections, Journal of Structural Engineering, ASCE, 2001, vol.127(6), pp [3] Chen, J., Jin, W.L., and Fu, J., Experimental investigation of thin-walled centrifugal concrete-filled steel tubes under torsion, Thin-Walled Structures, 2008, vol. 46(10), pp [4] Chen J., Chen J., and Jin W.L., Design of thin-walled centrifugal concrete-filled steel tubes under torsion, Thin-walled Structures, 2009, vol. 47(3), pp [5] Persson, B., Technical report, Japan Society for the Promotion of Science, Report 9803:12, Division of Building Materials, Lund Institute of Technology, Lund, 1998, 1. [6] Persson, B., Travel report from Workshop on Autogenous Shrinkage in Hiroshima, Japan, Report 9806:07, Lund Institute of Technology, Lund, [7] Persson, B., A comparison between mechanical properties of self-compacting concrete and the 701

6 corresponding properties of normal concrete, Cement and Concrete Research, vol. 31(2), [8] Han, L.H.,, Yao, G. H., and Zhao, X.L., Tests and calculations for hollow structural steel (HSS) stub columns filled with self-consolidating concrete (SCC), Journal of Constructional Steel Research, 2005, vol. 61(9), pp [9] Tazawa, E., Personal information, Hiroshima University, Hiroshima,1998. [10] Sakata, K., Personal information, Okayama University, Okayama, [11] Nishio, A., Tamura, H., and Ohashi, M., Self-compacting concrete with high-volume crushed rock fines, in: V.M. Malhotra (Ed.), Fourth CANMET/ACI/JCI International Symposium on Advances in Concrete Technology, Tokushima. ACI, 1998,. pp

Concrete-filled Double-skin Tubular Columns with External Steel Rings

Concrete-filled Double-skin Tubular Columns with External Steel Rings C.X. Dong 1 and J.C.M. Ho 2 ABSTRACT Concrete-filled-steel-tube columns have been adopted widely for column construction of tall buildings