英文翻译2020届毕业设计14

1、Hybrid FRPconcretesteel tubular columns: Concept and behavior J.G. Teng a,*, T. Yua, Y.L. Wonga, S.L. Dongb a Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China b Department of Civil Engineering, Zhejiang University, Hangzhou 310027, China Received

2、 20 January 2005; received in revised form 24 May 2006; accepted 19 June 2006 Available online 28 August 2006 Abstract Hybrid FRPconcretesteel double-skin tubular columns are a new form of hybrid columns recently proposed by the fi rst author. The column consists of an outer tube made of fi ber rein

3、forced polymer (FRP) and an inner tube made of steel, with the space between fi lled with concrete. In this new hybrid column, the three constituent materials are optimally combined to achieve several advantages not avail- able with existing columns. In this paper, the rationale for the new column f

4、orm together with its expected advantages is fi rst explained. A series of axial compression tests on stub columns are then presented to demonstrate some of the expected advantages. These test results confi rm that the concrete in the new column is very eff ectively confi ned by the two tubes and th

5、e local buckling of the inner steel tube is either delayed or suppressed by the surrounding concrete, leading to a very ductile response. The application of the proposed hybrid section form in beams is also examined by presenting the results of a series of tests on beams with a hybrid section in whi

6、ch the inner steel tube is shifted towards the tension side. The test results also show that such beams have a very ductile response and that the GFRP tube in such beams enhances the structural behavior by providing both confi nement to the concrete and additional shear resistance. ? 2006 Elsevier L

7、td. All rights reserved. Keywords: Hybrid columns; Tubular columns; Concrete-fi lled tubes; FRP; Steel; Concrete 1. Introduction In recent years, fi bre reinforced polymer (FRP) compos- ites have found increasingly wide applications in civil engi- neering, both in the retrofi t of existing structure

8、s and in new construction. FRP composites possess several advan- tages over steel, including their high strength-to-weight ratio and good corrosion resistance. As a result, the use of FRP composites as externally bonded reinforcement for the retrofi t of structures has become very popular in recent

9、years 1,2. These same advantages can also be exploited in new construction, and indeed a large amount of research around the world is currently under way exam- ining the performance of various forms of structures made of FRP composites alone (i.e. all FRP structures) or FRP composites in combination

10、 with other materials (i.e. hybrid structures). Examples include FRP bridge decks, concrete fi lled FRP tubes as columns and piles, and FRP cables. Compared with the two primary traditional structural materials, namely steel and concrete, FRP composites also have some disadvantages. These include th

11、eir relatively high cost, linearelasticbrittle stressstrain behavior, low elastic modulus-to-strength ratio, and poor fi re resistance. In retrofi t applications, cost savings arise from a number of aspects that off set the higher material cost, but this is harder to achieve in new construction at t

12、he present. The low elastic modulus-to-strength ratio is not critical in retro- fi t applications as the FRP is generally used to resist ten- sion. The poor fi re performance is also not an acute problem in retrofi t applications either because the structure is in the open space (e.g. bridges) or be

13、cause the FRP is not required to make any contribution to structural resistance during a fi re. When FRP composites are deployed in new construction, the consequences of their weaknesses need 0950-0618/$ - see front matter ? 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.06.0

14、17 * Corresponding author. Tel.: +852 2766 6012; fax: +852 2334 6389. E-mail address: .hk (J.G. Teng). Construction and Building Materials 21 (2007) 846854 Construction and Building MATERIALS to be minimized as in retrofi t applications. Based on these considerations, it may be conc

15、luded that the successful applicationofFRPcompositesinnewconstruction requires the following three criteria to be met: (a) cost eff ec- tiveness at least in terms of a life-cycle cost assessment; (b) FRP to be used in areas subject to tension as much as pos- sible; (c) fi re resistance to be non-cri

16、tical. It should be noted that criterion (c) is easily met for bridge structures and other outdoor structures, while the fi rst two require- ments very often mean that FRP composites should be used in combination with other materials to form hybrid structures. Based on the above discussion, it is ap

17、parent that the area of hybrid structures should be a major research focus in the use of FRP composites in new construction. Within the area of hybrid structures, the aim shall be to optimally combine FRP with traditional structural materials such as steel and concrete to create innovative structura

18、l forms that are cost-eff ective and of high-performance. To this end, simple duplications of existing structural systems are often inadequate. This paper presents the idea of a new form of columns, namely FRPconcretesteel hybrid double-skin tubular columns (DSTCs), proposed by the fi rst author of

19、the paper, as well as test results to evaluate their axial and fl exural behavior. 2. New hybrid column Concrete-fi lled steel tubes have been a common form of columns. The simplest form of concrete-fi lled steel tubes consists of a single hollow steel tube fi lled with concrete with or without inte

20、rnal steel reinforcing bars. A variation of this simple system is the double-skin tubular column, consisting of two generally concentric steel tubes with the space between fi lled with concrete. To the best of the authors knowledge, such double-skin tubes were fi rst reported in late 1980s 3. Since

21、then, much research has been conducted on these columns (e.g. 412). The inner void reduces the column weight without signifi cantly aff ect- ing the fl exural rigidity of the section and allows the easy passage of service ducts. More recently, hybrid FRP columns consisting of an FRP tube fi lled wit

22、h concrete with or without internal reinforcement have received a great deal of research 1319. Furthermore, double-skin hybrid FRP columns consisting of two FRP tubes and a concrete infi ll have been also been studied 15. The advantages of simple concrete-fi lled FRP tubes over simple concrete-fi ll

23、ed steel tubes include the lightweight and corrosion resistance of the FRP tube. Simple concrete-fi lled FRP tubes have been proposed for use as bridge columns and piles. Con- crete-fi lled FRP tubes have a number of disadvantages particularlywhenusedasbuildingcolumns.These include poor fi re resist

24、ance, diffi culty for connection to beams,inabilitytosupportsubstantialconstruction loads, brittle failure in bending, and high cost as the tube needs to be relatively thick in order to resist axial loads. As a bridge column, the fi re resistance and connection problems are not signifi cant. To over

25、come the existing disadvantages of concrete- fi lled FRP tubes, a new form of hybrid columns has recently been proposed by the fi rst author and is being investigated in an ongoing research project at The Hong Kong Polytechnic University. The new column consists of a steel tube inside, an FRP tube o

26、utside and concrete in between (Fig. 1). The inner void may be fi lled with con- crete if desired. The FRP tube is provided with fi bers which are predominantly oriented in the circumferential direction to provide confi nement to the concrete and additional shear resistance. The new column is an att

27、empt to combine the advantages of all three constituent materials and those of the structural form of DSTCs, so as to achieve a high- performance structural member. The novel feature of the new column form compared to the existing DSTCs is that the inner tube is made of steel but the outer tube is m

28、ade of FRP with fi bers oriented mainly in the hoop direction to provide confi nement to the concrete for enhanced ductility 20. This simple change to the existing DSTC forms off ers many advantages, lead- ing to a column which is easy to construct and highly resis- tant to corrosion and earthquakes

29、. Direct comparisons can be made with the steelconcrete DSTC or the FRPcon- crete DSTC. Compared to the steelconcrete DSTC, the advantages of the new column include: (a) a more ductile response of concrete as it is well confi ned by the FRP tube which does not buckle; (b) no need for fi re protectio

30、n of the outer tube as the outer tube is required only as a form dur- ing construction and as a confi ning device and additional shear reinforcement during earthquakes; (c) no need for corrosion protection as the steel tube inside is well pro- tected by the concrete and the FRP tube. Compared to the

31、 FRPconcrete DSTC, the advantages of the new col- umn include: (a) ability to support construction loading Fig. 1. Typical sections of double-skin tubular members. J.G. Teng et al. / Construction and Building Materials 21 (2007) 846854847 through the use of the inner steel tube; (b) ease for connec-

32、 tion to beams due to the presence of the inner steel tube; (c) savings in fi re protection cost as the outer tube is required only as a form during construction and as a confi ning device and additional shear reinforcement during earth- quakes; (d) better confi nement of concrete as a result of the

33、 increased rigidity of the inner tube. Similarly, the new column also has signifi cant advantages over other compos- ite/hybrid columns including concrete-fi lled steel tubes, concrete fi lled FRP tubes and concrete-encased steel col- umns in many applications. The section form shown in Fig. 1a cons

34、ists of two circu- lar tubes, but many diff erent combinations of tubes are possible. Fig. 1b and c shows some of such variations. Needless to say, the section form can also be employed in a beam, in which case the inner steel tube may be shifted towards the tension side (Fig. 1d). It should be note

35、d that if the column section with two concentric tubes is deployed in situations where axial compression does not dominate under service loading, the column should be provided with some longitudinal reinforcement to avoid the development of large tensile cracks. 3. Axial compression tests on stub co

36、lumns 3.1. General Obviously, for the new hybrid column to be accepted in practical applications, a great deal of research is required to develop knowledge of its structural behavior and reliable design methods. As a fi rst step, a series of stub column tests on this new DSTC were conducted. In para

37、llel, tests were conductedoncorresponding FRP-confi nedconcrete (FCC) cylinders for comparison, so as to reach a better understanding of the axial compressive behavior of this new member. Details of the test specimens and the test results are presented in this section. 3.2. Specimens A total of six

38、DSTC stub column specimens of three dif- ferent confi gurations were prepared and tested; two identi- cal specimens were made for each confi guration. The stub column specimens all had an outer diameter of 152.5 mm and a height of 305 mm. The steel tube inside each speci- men was identical and was c

39、ut from the same long steel tube. The outer GFRP tube had three diff erent thicknesses. In parallel, six FCC specimens were prepared for compar- ison. They had the same size as the DSTC specimens and covered the variations in the thickness of the outer FRP tube. Table 1 provides a summary of both th

40、e DSTC and FCC specimens. 3.3. Materials Tensile tests on steel coupons cut from the same original steel tube were conducted. These tests showed that the steel had a yield stress of 352.7 MPa, a tensile strength of 380.4 MPa, a Youngs modulus of 207.3 GPa and a long plastic plateau after yielding. I

41、n addition, three hollow steel tubes also cut from the same long tube that provided the steel tubes for the DSTCs were tested under compression. The steel tubes showed large plastic deformation until local buckling in the elephant foot mode took place, as shown in Fig. 2. The average ultimate load o

42、f these tubes was 273.8 kN. The FRP used here had an average tensile strength of 1825.5 MPa and an average Youngs modulus of 80.1 GPa based on six tensile tests following the ASTM standard 21 and a nominal thickness of 0.17 mm per ply. All the specimens used concrete of the same batch. The elastic m

43、odulus, compressive strength and compressive strain at peak stress of the concrete averaged from three concretecylindertests(152.5 mm 305 mm)were 30.2 GPa, 39.6 MPa and 0.00263, respectively. 3.4. Preparation of specimens ThepreparationprocessoftheDSTCspecimens included the following steps: (1) fabr

44、ication of the form, which consisted of a PVC tube outside and a steel tube inside; strain gauges on the steel tube were installed before the casting of concrete (Fig. 3); (2) casting the concrete; (3) wet-layup formation of the FRP tube after the concrete had hardened and the PVC form removed (Fig.

45、 4). A Table 1 Specimens for the axial compression tests SpecimensFRP tubeSteel tube Do(t) (mm)Void size (mm) DS1A, DS1B1 ply76.1(3.2)69.7 DS2A, DS2B2 plies76.1(3.2)69.7 DS3A, DS3B3 plies76.1(3.2)69.7 FCC1A, FCC1B1 ply/ FCC2A, FCC2B2 plies/ FCC3A, FCC3B3 plies/ Fig. 2. Buckling of hollow steel tubes

46、 under pure axial compression. 848J.G. Teng et al. / Construction and Building Materials 21 (2007) 846854 similar preparation process was adopted for the FCC spec- imens except step (1). For the FCC specimens, standard 152.5 mm 305 mm steel moulds were used for casting concrete. It should be noted t

47、hat the FRP tube was formed by the wrapping and resin impregnation of fi ber sheets on con- crete as is done in retrofi t applications, instead of the use of a prefabricated FRP tube into which concrete is cast. The wrapping process was used as prefabricated FRP tubes with fi bers oriented mainly in

48、 the hoop direction were not readily available to the authors. It is believed that there is little diff erence between the two ways of forming the FRP tube in terms of the performance of the hybrid column, based on previous research by Shahawy et al. 22. In the present specimens, all fi bers were or

49、iented in the hoop direction; that is, no longitudinal fi bers were present in these FRP tubes. 3.5. Test set-up and instrumentation For each hybrid DSTC column specimen, two bi-direc- tional strain rosettes (gauge length = 10 mm) were installed at the mid-height of the outer surface of the steel tu

50、be and four bi-directional strain rosettes (gauge length = 20 mm) were installed at the mid-height of the outer surface of the FRP tube. For each FCC specimen, four bi-directional 20 mm strain rosettes were installed at the mid-height of the FRP tube. The circumferential layout of the strain gauges

51、is shown in Fig. 5, in which the overlapping zone spans a circumferential distance of 150 mm. Fig. 4. Formation of the FRP tube. Steel tube SG3 SG5 Overlapping zone SG4SG2 SG6 SG1 FRP Fig. 5. Layout of the strain gauges. Fig. 3. Form for casting concrete. Fig. 6. DSTC specimen (a) before and (b) aft

52、er test. J.G. Teng et al. / Construction and Building Materials 21 (2007) 846854849 In addition, two linear variable displacement transduc- ers (LVDTs) were used to obtain the axial deformation of the middle region of 120 mm (Fig. 6a) for each speci- men. All compression tests were carried out using

53、 an MTS machine with displacement control at a loading rate of 0.003 mm/s. All test data, including the strains, loads, and displacements, were recorded simultaneously by a data logger. 3.6. Test results and discussions 3.6.1. Overall observations All specimens (FCCs and DSTCs) displayed continuous

54、loaddisplacement behavior until ultimate failure, which occurred by the rupture of the FRP tube as a result of hoop tension. The load kept increasing for the two- and three-ply specimens,butfortheone-plyspecimens,theload remained nearly constant in the second stage of deforma- tion. Specimen DS2A be

55、fore and after test is shown in Fig. 6. In the one- and two-ply DSTC specimens, no buck- ling was found in the inner steel tube after the test. How- ever, in the three-ply DSTC specimens, some ripples were found on the steel tube wall after the test, as shown in Fig. 7. 3.6.2. Axial loadaxial strain

56、 behavior of DSTCs The test results of all six DSTC specimens are summa- rized in Table 2. In this table, Pco is equal to the unconfi ned concrete strength times the area of the annular concrete section (=543.5 kN), while Psis equal to the average ulti- mate load of the three hollow steel tubes (=27

57、3.8 kN). Therefore, the ultimate load of the hybrid column is found to be 817.3 kN if the constituent parts do not interact and the confi nement eff ect of the FRP tube is negligible. The ultimate load of the hybrid column from the test is denoted by Pc, the ultimate strain is denoted by eu, while t

58、he FRP hoop rupture strain averaged from the three strain rosettes outside the overlapping zone is denoted by eh. As expected, the hoop rupture strains reached in the column tests are signifi cantly lower than those from the coupon tensile tests (2.3% on average) due to factors such as the non-unifo

59、rm deformation of concrete and curvature 23. For these spec- imens, the ultimate strain is the strain at the ultimate load. The strain of unconfi ned concrete at peak stress ecowas found from tests on three 152.5 mm 305 mm concrete cyl- inders to be 0.00263 and is used to normalize the test ulti- mate strain. The axial loadaxial strain curves of the six DSTCs are shown in Fig. 8, where the strains were found from the dis- placement transducer readings. Fig. 8 shows that the 2-ply DSTCs and the 3-ply DSTCs have a bilinear lo