Figure 1.
Fabrication of a square tube with stiffeners. (a) Lipped fabrication. (b) Plate-by-plate fabrication.
Figure 1.
Fabrication of a square tube with stiffeners. (a) Lipped fabrication. (b) Plate-by-plate fabrication.
Figure 2.
The effective cross-section area of the concrete in a stiffened CFDST column. (a) Square column. (b) Circular column.
Figure 2.
The effective cross-section area of the concrete in a stiffened CFDST column. (a) Square column. (b) Circular column.
Figure 3.
The cross-section of the CFDST columns. (a) Typical square CFDST with plate stiffeners. (b) Typical circular CFDST with plate stiffeners.
Figure 3.
The cross-section of the CFDST columns. (a) Typical square CFDST with plate stiffeners. (b) Typical circular CFDST with plate stiffeners.
Figure 4.
The side-view of the test specimens. (a) Typical square CFDST with plate stiffeners. (b) Typical circular CFDST with plate stiffeners.
Figure 4.
The side-view of the test specimens. (a) Typical square CFDST with plate stiffeners. (b) Typical circular CFDST with plate stiffeners.
Figure 5.
The flow process for fabricating the square specimens. (1). Drill the holes following the weld hole spacing. (2). Weld the plate stiffeners onto the inner surface of the outer tube. (3). Pour the concrete into the channel between the outer and inner steel and cover the top and bottom of the specimen with steel plates.
Figure 5.
The flow process for fabricating the square specimens. (1). Drill the holes following the weld hole spacing. (2). Weld the plate stiffeners onto the inner surface of the outer tube. (3). Pour the concrete into the channel between the outer and inner steel and cover the top and bottom of the specimen with steel plates.
Figure 6.
Side view of the column with a weld spacing of 20t.
Figure 6.
Side view of the column with a weld spacing of 20t.
Figure 7.
Experiment setup. (a) Typical loading for square column. (b) Typical loading for circular column.
Figure 7.
Experiment setup. (a) Typical loading for square column. (b) Typical loading for circular column.
Figure 8.
Failure modes of the square and circular specimens. (a) Square specimens. (b) Circular specimens.
Figure 8.
Failure modes of the square and circular specimens. (a) Square specimens. (b) Circular specimens.
Figure 9.
Effect of the weld spacing on the ultimate load of each specimens for two stiffeners’ size. (a) bs × ts = 18 mm × 2.3 mm. (b) bs × ts = 25 mm × 2.8 mm.
Figure 9.
Effect of the weld spacing on the ultimate load of each specimens for two stiffeners’ size. (a) bs × ts = 18 mm × 2.3 mm. (b) bs × ts = 25 mm × 2.8 mm.
Figure 10.
Load–displacement response for the square specimens from the experiment and the finite element model. (a) S100, (b) S100/32, (c) S100/32-18a-10t, (d) S100/32-18a-20t, (e) S100/32-18a-30t, (f) S100/32-18a-40t, (g) S100/32-25b-10t, (h) S100/32-25b-20t, (i) S100/32-25b-30t, (j) S100/32-25b-40t.
Figure 10.
Load–displacement response for the square specimens from the experiment and the finite element model. (a) S100, (b) S100/32, (c) S100/32-18a-10t, (d) S100/32-18a-20t, (e) S100/32-18a-30t, (f) S100/32-18a-40t, (g) S100/32-25b-10t, (h) S100/32-25b-20t, (i) S100/32-25b-30t, (j) S100/32-25b-40t.
Figure 11.
Load–displacement response for the circular specimens from the experiment and the finite element model. (a) C100, (b) C100/32, (c) C100/32-18a-10t, (d) C100/32-18a-20t, (e) C100/32-18a-30t, (f) C100/32-18a-40t, (g) C100/32-25b-10t, (h) C100/32-25b-20t, (i) C100/32-25b-30t, (j) C100/32-25b-40t.
Figure 11.
Load–displacement response for the circular specimens from the experiment and the finite element model. (a) C100, (b) C100/32, (c) C100/32-18a-10t, (d) C100/32-18a-20t, (e) C100/32-18a-30t, (f) C100/32-18a-40t, (g) C100/32-25b-10t, (h) C100/32-25b-20t, (i) C100/32-25b-30t, (j) C100/32-25b-40t.
Figure 12.
Boundary conditions and element mesh.
Figure 12.
Boundary conditions and element mesh.
Figure 13.
Concrete stress–strain curve.
Figure 13.
Concrete stress–strain curve.
Figure 14.
Steel stress–strain curve.
Figure 14.
Steel stress–strain curve.
Figure 15.
Comparison of the deformation shape of the square CFDST with plate stiffeners. (a) S100/32-18a-20t, (b) S100/32-18a-30t, (c) S100/32-18a-40t, (d) S100/32-25b-40t.
Figure 15.
Comparison of the deformation shape of the square CFDST with plate stiffeners. (a) S100/32-18a-20t, (b) S100/32-18a-30t, (c) S100/32-18a-40t, (d) S100/32-25b-40t.
Figure 16.
Comparison of the deformation of the circular CFDST with plate stiffeners. (a) C100/32-18a-10t, (b) C100/32-18a-40t, (c) C100/32-25b-10t, (d) C100/32-25b-40t.
Figure 16.
Comparison of the deformation of the circular CFDST with plate stiffeners. (a) C100/32-18a-10t, (b) C100/32-18a-40t, (c) C100/32-25b-10t, (d) C100/32-25b-40t.
Figure 17.
The effect of different stiffener widths on the performance of the square CFDST. (a) ts = 2.3 mm, (b) ts = 2.8 mm.
Figure 17.
The effect of different stiffener widths on the performance of the square CFDST. (a) ts = 2.3 mm, (b) ts = 2.8 mm.
Figure 18.
The effect of different stiffener widths on the performance of the circular CFDST. (a) ts = 2.3 mm, (b) ts = 2.8 mm.
Figure 18.
The effect of different stiffener widths on the performance of the circular CFDST. (a) ts = 2.3 mm, (b) ts = 2.8 mm.
Figure 19.
The effect of different stiffener thicknesses on the performance of the square CFDST. (a) bs = 12 mm, (b) bs = 18 mm, (c) bs = 25 mm.
Figure 19.
The effect of different stiffener thicknesses on the performance of the square CFDST. (a) bs = 12 mm, (b) bs = 18 mm, (c) bs = 25 mm.
Figure 20.
The effect of different stiffener thicknesses on the performance of the circular CFDST. (a) bs = 12 mm, (b) bs = 18 mm, (c) bs = 25 mm.
Figure 20.
The effect of different stiffener thicknesses on the performance of the circular CFDST. (a) bs = 12 mm, (b) bs = 18 mm, (c) bs = 25 mm.
Figure 21.
Comparison of the shape of the CFDST column with ts = 2.3 mm on the axial load response. (a) bs =12 mm, ts = 2.3 mm, (b) bs = 18 mm, ts = 2.3 mm, (c) bs = 25 mm, ts = 2.3 mm.
Figure 21.
Comparison of the shape of the CFDST column with ts = 2.3 mm on the axial load response. (a) bs =12 mm, ts = 2.3 mm, (b) bs = 18 mm, ts = 2.3 mm, (c) bs = 25 mm, ts = 2.3 mm.
Figure 22.
Comparison of the shape of the CFDST column with ts = 2.8 mm on the axial load response. (a) bs = 12 mm, ts = 2.8 mm, (b) bs = 18 mm, ts = 2.8 mm, (c) bs = 25 mm, ts = 2.8 mm.
Figure 22.
Comparison of the shape of the CFDST column with ts = 2.8 mm on the axial load response. (a) bs = 12 mm, ts = 2.8 mm, (b) bs = 18 mm, ts = 2.8 mm, (c) bs = 25 mm, ts = 2.8 mm.
Table 1.
Specifications for the square CFDST.
Table 1.
Specifications for the square CFDST.
No. | Specimen Designation | Outer Tube | Inner Tube | Plate Stiffener | Weld Spacing | Weld Spacing (mm) | First Hole’s Distance from Bottom (mm) | No. of Holes |
---|
| | Do (mm) | Bo (mm) | to (mm) | Di (mm) | Bi (mm) | ti (mm) | bs (mm) | ts (mm) | | | | |
---|
1A | S100 | 100 | 100 | 2.3 | - | - | - | - | - | - | - | - | - |
2A | S100/32 | 32 | 32 | 2.0 | - | - | - | - | - | - |
3A | S100/32-18a-10t | 18 | 2.3 | 10t | 23 | 19 | 15 |
4A | S100/32-18a-20t | 18 | 2.3 | 20t | 46 | 19 | 8 |
5A | S100/32-18a-30t | 18 | 2.3 | 30t | 69 | 7.5 | 6 |
6A | S100/32-18a-40t | 18 | 2.3 | 40t | 92 | 42 | 4 |
7A | S100/32-25b-10t | 25 | 2.8 | 10t | 23 | 19 | 15 |
8A | S100/32-25b-20t | 25 | 2.8 | 20t | 46 | 19 | 8 |
9A | S100/32-25b-30t | 25 | 2.8 | 30t | 69 | 7.5 | 6 |
10A | S100/32-25b-40t | 25 | 2.8 | 40t | 92 | 42 | 4 |
Table 2.
Specifications for the circular CFDST.
Table 2.
Specifications for the circular CFDST.
No. | Specimen Designation | Outer Tube | Inner Tube | Plate Stiffener | Weld Spacing | Weld Spacing (mm) | First Hole’s Distance from Bottom (mm) | No. of Holes |
---|
| | Øo (mm) | to (mm) | Øi (mm) | ti (mm) | bs (mm) | ts (mm) | | | | |
---|
1N | C100 | 100 | 2.0 | - | - | - | - | - | - | - | - |
2N | C100/32 | 32 | 2.3 | - | - | - | - | - | - |
3N | C100/32-18a-10t | 18 | 2.3 | 10t | 20 | 40 | 15 |
4N | C100/32-18a-20t | 18 | 2.3 | 20t | 40 | 40 | 8 |
5N | C100/32-18a-30t | 18 | 2.3 | 30t | 60 | 30 | 6 |
6N | C100/32-18a-40t | 18 | 2.3 | 40t | 80 | 60 | 4 |
7N | C100/32-25b-10t | 25 | 2.8 | 10t | 20 | 40 | 15 |
8N | C100/32-25b-20t | 25 | 2.8 | 20t | 40 | 40 | 8 |
9N | C100/32-25b-30t | 25 | 2.8 | 30t | 60 | 30 | 6 |
10N | C100/32-25b-40t | 25 | 2.8 | 40t | 80 | 60 | 4 |
Table 3.
The mix proportion of the sandwiched concrete.
Table 3.
The mix proportion of the sandwiched concrete.
Material | Cement (kg/m3) | Water (kg/m3) | Fine Aggregate (kg/m3) | Coarse Aggregate (kg/m3) | Weight of Concrete (kg) |
---|
Quantity | 441 | 256 | 800 | 903 | 2400 |
Table 4.
Mechanical properties of the steel material.
Table 4.
Mechanical properties of the steel material.
Material | Young’s Modulus, E(avg) (GPa) | Yield Stress fy (avg) (MPa) | Ultimate Stress fu (avg) (MPa) |
---|
Inner steel | 208.8 | 275.1 | 398.8 |
Outer steel | 209.1 | 276.3 | 399.9 |
Plate stiffener | 208.3 | 274.7 | 398.5 |
Table 5.
Experimental result.
Table 5.
Experimental result.
No. | Specimen Designation | Pu,Exp (kN) | Strength Ratio (%) | Location of Buckle * |
---|
1A | S100 | 534 | - | A |
2A | S100/32 | 592 | 10.9 | A |
3A | S100/32-18a-10t | 841 | 57.5 | A |
4A | S100/32-18a-20t | 832 | 55.8 | C |
5A | S100/32-18a-30t | 816 | 52.8 | C |
6A | S100/32-18a-40t | 789 | 47.8 | B + C |
7A | S100/32-25b-10t | 822 | 53.9 | B |
8A | S100/32-25b-20t | 786 | 47.2 | C |
9A | S100/32-25b-30t | 778 | 45.7 | B |
10A | S100/32-25b-40t | 762 | 42.7 | C |
1N | C100 | 516 | - | A + B |
2N | C100/32 | 565 | 9.50 | A + B |
3N | C100/32-18a-10t | 779 | 51.0 | A + B |
4N | C100/32-18a-20t | 762 | 47.7 | A + B |
5N | C100/32-18a-30t | 745 | 44.4 | A + B |
6N | C100/32-18a-40t | 731 | 41.7 | A + B |
7N | C100/32-25b-10t | 748 | 45.0 | A + B |
8N | C100/32-25b-20t | 736 | 42.6 | A + B |
9N | C100/32-25b-30t | 704 | 36.4 | A + B |
10N | C100/32-25b-40t | 699 | 35.5 | A |
Table 6.
Comparison of the 18 mm and 25 mm plate stiffeners.
Table 6.
Comparison of the 18 mm and 25 mm plate stiffeners.
Group * | Specimen | Pu (kN) | Strength Reduction Every 10t (%) | Cumulative Strength Reduction (%) |
---|
G1 | C100/32-18a-10t | 779 | - | - |
C100/32-18a-20t | 762 | 2.18 | 2.18 |
C100/32-18a-30t | 745 | 2.23 | 4.36 |
C100/32-18a-40t | 731 | 1.88 | 6.16 |
Average | | 2.10 | |
S100/32-18a-10t | 841 | - | - |
S100/32-18a-20t | 832 | 1.07 | 1.07 |
S100/32-18a-30t | 816 | 1.92 | 2.97 |
S100/32-18a-40t | 789 | 3.31 | 6.18 |
Average | | 2.10 | |
G2 | C100/32-25b-10t | 748 | - | - |
C100/32-25b-20t | 736 | 1.60 | 1.60 |
C100/32-25b-30t | 704 | 4.35 | 5.88 |
C100/32-25b-40t | 699 | 0.71 | 6.55 |
Average | | 2.22 | |
S100/32-25b-10t | 822 | - | - |
S100/32-25b-20t | 786 | 4.38 | 4.38 |
S100/32-25b-30t | 778 | 1.02 | 5.35 |
S100/32-25b-40t | 762 | 2.06 | 7.30 |
Average | | 2.48 | |
Table 7.
Details of the finite element modelling.
Table 7.
Details of the finite element modelling.
Parts | Concrete | Outer Steel Tube | Inner Steel Tube | Stiffener |
---|
Element type | C3D8R | S4R | S4R | C3D8R |
Mesh size (mm) | 12 | 12 | 12 | 12 |
Material behaviour | Drucker Prager | Deformation Plasticity | Deformation Plasticity | Deformation Plasticity |
Interaction surface | Slave | Master | Master | Slave |
Constraint | - | Tie—Master | - | Tie—Slave |
Steps | Static, General with Nlgeom stabilization |
Iteration | Newton-Raphson with increment size of minimum 0.01 to maximum 1 |
Interaction type | Surface-to-surface contact |
Contact property | Friction Coefficient of 0.6 with “Hard Contact” |
Boundary condition | Loading surface—Displacement/Rotation on Z-direction Bottom surface—pinned support |
Table 8.
Comparison of the finite element model with the experimental results.
Table 8.
Comparison of the finite element model with the experimental results.
Authors | Specimen | Pu,Exp (kN) | Pu,FEM (kN) | |
---|
Present study | S100 | 534 | 527 | 1.01 |
S100/32 | 592 | 580 | 1.02 |
S100/32-18a-10t | 841 | 841 | 1.00 |
S100/32-18a-20t | 832 | 801 | 1.04 |
S100/32-18a-30t | 816 | 778 | 1.05 |
S100/32-18a-40t | 789 | 767 | 1.03 |
S100/32-25b-10t | 822 | 834 | 0.99 |
S100/32-25b-20t | 786 | 812 | 0.97 |
S100/32-25b-30t | 778 | 769 | 1.01 |
S100/32-25b-40t | 762 | 758 | 1.01 |
C100 | 516 | 483 | 1.07 |
C100/32 | 565 | 541 | 1.04 |
C100/32-18a-10t | 779 | 732 | 1.07 |
C100/32-18a-20t | 762 | 724 | 1.05 |
C100/32-18a-30t | 745 | 723 | 1.03 |
C100/32-18a-40t | 731 | 720 | 1.02 |
C100/32-25b-10t | 748 | 718 | 1.04 |
C100/32-25b-20t | 736 | 716 | 1.03 |
C100/32-25b-30t | 704 | 702 | 1.00 |
C100/32-25b-40t | 699 | 697 | 1.00 |
[22] | C90-3S-10 | 461 | 482 | 0.96 |
C117-4S-50 | 653 | 701 | 0.93 |
C90-5S-35 | 476 | 510 | 0.93 |
Mean | | | | 1.01 |
Std. deviation | | | | 0.04 |
Table 9.
Geometric and material properties of the stiffened square CFDST stub column for the parametric study.
Table 9.
Geometric and material properties of the stiffened square CFDST stub column for the parametric study.
Specimen Designation | Outer Tube (mm) | Inner Tube (mm) | Plate Stiffener (mm) | Weld Spacing | Weld Spacing (mm) | First Hole’s Distance from Bottom (mm) | No. of Holes | Pu (kN) |
---|
| Do | Bo | to | Di | Bi | ti | bs | ts | | | | | |
---|
S100/32-18b-10t | 100 | 100 | 2.3 | 32 | 32 | 2.0 | 18 | 2.8 | 10t | 23 | 19 | 15 | 863 |
S100/32-18b-20t | 18 | 2.8 | 20t | 46 | 19 | 8 | 815 |
S100/32-18b-30t | 18 | 2.8 | 30t | 69 | 7.5 | 6 | 792 |
S100/32-18b-40t | 18 | 2.8 | 40t | 92 | 42 | 4 | 789 |
S100/32-25a-10t | 25 | 2.3 | 10t | 23 | 19 | 15 | 808 |
S100/32-25a-20t | 25 | 2.3 | 20t | 46 | 19 | 8 | 799 |
S100/32-25a-30t | 25 | 2.3 | 30t | 69 | 7.5 | 6 | 759 |
S100/32-25a-40t | 25 | 2.3 | 40t | 92 | 42 | 4 | 749 |
S100/32-12a-10t | 12 | 2.3 | 10t | 23 | 19 | 15 | 786 |
S100/32-12a-20t | 12 | 2.3 | 20t | 46 | 19 | 8 | 760 |
S100/32-12a-30t | 12 | 2.3 | 30t | 69 | 7.5 | 6 | 753 |
S100/32-12a-40t | 12 | 2.3 | 40t | 92 | 42 | 4 | 742 |
S100/32-12b-10t | 12 | 2.8 | 10t | 23 | 19 | 15 | 812 |
S100/32-12b-20t | 12 | 2.8 | 20t | 46 | 19 | 8 | 775 |
S100/32-12b-30t | 12 | 2.8 | 30t | 69 | 7.5 | 6 | 761 |
S100/32-12b-40t | 12 | 2.8 | 40t | 92 | 42 | 4 | 752 |
S100/32-12a-60t | 12 | 2.3 | 60t | 138 | 42 | 3 | 721 |
S100/32-18a-60t | 18 | 2.3 | 60t | 138 | 42 | 3 | 755 |
S100/32-25a-60t | 25 | 2.3 | 60t | 138 | 42 | 3 | 733 |
S100/32-12b-60t | 12 | 2.8 | 60t | 138 | 42 | 3 | 730 |
S100/32-18b-60t | 18 | 2.8 | 60t | 138 | 42 | 3 | 777 |
S100/32-25b-60t | 25 | 2.8 | 60t | 138 | 42 | 3 | 746 |
S100/32-12a-90t | 12 | 2.3 | 90t | 207 | 76.5 | 2 | 697 |
S100/32-18a-90t | 18 | 2.3 | 90t | 207 | 76.5 | 2 | 749 |
S100/32-25a-90t | 25 | 2.3 | 90t | 207 | 76.5 | 2 | 717 |
S100/32-12b-90t | 12 | 2.8 | 90t | 207 | 76.5 | 2 | 707 |
S100/32-18b-90t | 18 | 2.8 | 90t | 207 | 76.5 | 2 | 759 |
S100/32-25b-90t | 25 | 2.8 | 90t | 207 | 76.5 | 2 | 725 |
Table 10.
Geometric and material properties of the stiffened circular CFDST stub column for the parametric study.
Table 10.
Geometric and material properties of the stiffened circular CFDST stub column for the parametric study.
Specimen Designation | Outer Tube (mm) | Inner Tube (mm) | Plate Stiffener (mm) | Weld Spacing | Weld Spacing (mm) | First Hole’s Distance from Bottom (mm) | No. of Holes | Pu (kN) |
---|
| Øo | to | Øi | ti | bs | ts | | | | | |
---|
C100/32-18b-10t | 100 | 2.0 | 32 | 2.3 | 18 | 2.8 | 10t | 20 | 40 | 15 | 753 |
C100/32-18b-20t | 18 | 2.8 | 20t | 40 | 40 | 8 | 749 |
C100/32-18b-30t | 18 | 2.8 | 30t | 60 | 30 | 6 | 736 |
C100/32-18b-40t | 18 | 2.8 | 40t | 80 | 60 | 4 | 724 |
C100/32-25a-10t | 25 | 2.3 | 10t | 20 | 40 | 15 | 694 |
C100/32-25a-20t | 25 | 2.3 | 20t | 40 | 40 | 8 | 692 |
C100/32-25a-30t | 25 | 2.3 | 30t | 60 | 30 | 6 | 690 |
C100/32-25a-40t | 25 | 2.3 | 40t | 80 | 60 | 4 | 686 |
C100/32-12a-10t | 12 | 2.3 | 10t | 20 | 40 | 15 | 670 |
C100/32-12a-20t | 12 | 2.3 | 20t | 40 | 40 | 8 | 667 |
C100/32-12a-30t | 12 | 2.3 | 30t | 60 | 30 | 6 | 660 |
C100/32-12a-40t | 12 | 2.3 | 40t | 80 | 60 | 4 | 657 |
C100/32-12b-10t | 12 | 2.8 | 10t | 20 | 40 | 15 | 696 |
C100/32-12b-20t | 12 | 2.8 | 20t | 40 | 40 | 8 | 693 |
C100/32-12b-30t | 12 | 2.8 | 30t | 60 | 30 | 6 | 689 |
C100/32-12b-40t | 12 | 2.8 | 40t | 80 | 60 | 4 | 681 |
C100/32-12a-60t | 12 | 2.3 | 60t | 120 | 60 | 3 | 638 |
C100/32-18a-60t | 18 | 2.3 | 60t | 120 | 60 | 3 | 708 |
C100/32-25a-60t | 25 | 2.3 | 60t | 120 | 60 | 3 | 669 |
C100/32-12b-60t | 12 | 2.8 | 60t | 120 | 60 | 3 | 670 |
C100/32-18b-60t | 18 | 2.8 | 60t | 120 | 60 | 3 | 724 |
C100/32-25b-60t | 25 | 2.8 | 60t | 120 | 60 | 3 | 687 |
C100/32-12a-90t | 12 | 2.3 | 90t | 180 | 90 | 2 | 629 |
C100/32-18a-90t | 18 | 2.3 | 90t | 180 | 90 | 2 | 704 |
C100/32-25a-90t | 25 | 2.3 | 90t | 180 | 90 | 2 | 667 |
C100/32-12b-90t | 12 | 2.8 | 90t | 180 | 90 | 2 | 666 |
C100/32-18b-90t | 15 | 2.8 | 90t | 180 | 90 | 2 | 719 |
C100/32-25b-90t | 25 | 2.8 | 90t | 180 | 90 | 2 | 682 |
Table 11.
The difference in the strength of stiffened square CFDST and stiffened circular CFDST.
Table 11.
The difference in the strength of stiffened square CFDST and stiffened circular CFDST.
Dimension of Stiffeners | Square to Circular Strength (%) |
---|
ts (mm) | bs (mm) | |
---|
2.3 | 12 | 13.7 |
2.3 | 18 | 8.78 |
2.3 | 25 | 11.3 |
Average | | 11.3 |
2.8 | 12 | 10.8 |
2.8 | 18 | 8.83 |
2.8 | 25 | 10.5 |
Average | | 10.0 |