This document summarizes a study comparing concrete filled steel tube (CFST) diagrid structures to steel tube diagrid structures for high-rise buildings ranging from 50 to 80 stories tall. Key findings from structural analyses using ETABS software show that CFST diagrid structures have lower base shear, shorter period of vibration, and lower displacements at the top story under lateral loads compared to equivalent steel tube diagrid structures. The reductions in response range from 4-15% depending on the load case and building height. Tables of member sizes, forces, and response comparisons are provided to support the conclusions.

1. Concrete Filled Steel Tube Diagrid
Structural System for High Rise Buildings
Guided by:
Dr. Paresh V. Patel
Prepared by:
Urvesh R. Patel
1
For
2nd International Conference on Innovation in Structural Engineering (IC-ISE-2017)

2. Flow of Presentation
• Introduction
• Need of Study
• Objectives of Study
• Scope of Work
• Literature Review
• Comparison of Steel Tube and CFST Diagrid
• Conclusion
2

3. Introduction
• Design of tall building is governed by lateral load. Followings are various lateral load
resisting structural systems for tall building.
Vertical load
Lateral load
Wind load
Earthquake load
• Design of tall building is governed by lateral load. Followings are various lateral load
resisting structural systems for tall building.
Interior system
Exterior system
3

4. 4
Figure 1 - Exterior system

5. 5
Figure 2 - Interior system

6. • Diagrid is type of space truss structural system.
• It consists of peripheral inclined steel members which
forms diagonal grid on periphery. Diagonal grid forms
series of triangulated truss system by intersection of
diagonal grid and perimeter ring beam
• In conventional lateral load resisting system lateral
load is resisted by bending and shear. While in diagrid
lateral load is resisted by diagonal member by axial
force because of its truss configuration.
6

7. Examples of Diagrid Structures
Figure 1 -Hearst Tower ,
New York(USA)
Source: CTBUH
Figure 2 -Swiss Re,
London(UK)
Source: CTBUH 7

8. Figure 3 –Poly International plaza,
China
Source: CTBUH
Figure 4 – Guangzhou West
Tower, China
Source: CTBUH
8

9. Figure 5 - Dorobanti Tower,
Romania
Source: CTBUH
Figure 6 –CITIC financial
center, China
Source: CTBUH
9

10. Need of study
Among various structural system diagrid system has emerged as the most versatile
structure because of architectural elegancy, high redundancy and high lateral stiffness.
Apart from this it also offer following advantages.
• Diagrid system offers mostly column free exterior and interior space.
• Generous amounts of day lighting due to less number of interior columns and
structure.
• Perimeter diagrid system saves approximately 20 percent of a structural steel when
compared to a conventional moment-frame structure.
• Diagrid system has higher torsional rigidity than the other structural systems.
• Free and clear, unique floor plans are possible.
• Aesthetically dominated and expressive.
10

11. • The use of composite material in tall building has significantly increased. Apart from
the structural advantages of daigrid the advantage of use of composite material such
as concrete filled steel tube in diagrid structural system is also need to be studied.
11

12. Objectives of Study
• To understand the behavior of concrete filled steel tube diagrid structural system for
high rise building.
• To understand the design of concrete filled steel tube member and connection and
foundation system.
12
Scope of Work
• Comparison of behavior of concrete filled steel tube diagrid structure with steel tube
diagrid structure.
• Analysis and design of G+50, G+60, G+70, G+80 storey concrete filled steel tube
diagrid structure using ETABS software.

13. Literature Review
13

14. Diagrid Structural Systems for Tall buildings: Characteristics and Methodology for
Preliminary Design (2007)
By
Kyoung-sun Moon et al.
The Structural Design of Tall and Special Buildings , 16(3), 205-230
 Moon et al. developed simple methodology for preliminary member sizes for
diagrid and optimum angle for G+60 storey diagrid structure.
 They considered 60 storey building with plan dimension 36m × 36m with typical
floor height of 4m.
 They considered different diagrid angle for diagrid with column and diagrid without
column.
 For first scheme with corner column the optimum angle lies between 53 degree to
76 degree for 60 story building. For second scheme without corner column the
optimum angle lies between 63 degree to 76 degree for 60 story building.
14

15.  Kyoung Sun Moon discussed about the impact of variation of angle along the height
of building on the material consumption.
 He analyzed and diagrid structures with different aspect ratio.
 He considered two different cases in the first case diagrid structure is designed with
uniform angle throughout the height of building and in the second case building is
designed with varying angle of diagrid along the height of building in SAP 2000.
 He concluded that diagrid with varying angle is less economical compared to diagrid
with uniform angle up to aspect ratio of 7.
 He concluded that diagrid with varying angle with steeper angle toward base is more
economical compared to diagrid with uniform angle for building above aspect ratio
of 7.
15
Optimal Grid Geometry of Diagrid Structures for Tall Buildings (2008).
By
Kyoung Sun Moon.
Architectural Science Review, 51(3), 239 -251.

16. Three-dimensional Exterior Bracing Systems for Tall Building (2015)
By
Rupa Garai et al.
CTBUH Conference proceeding.
• Garai el at. They presented case study of poly International Plaza, Beijing, China.
That is 32 story height building. It has combination of perimeter diagrid and inner
concrete shear wall.
• They used CFST with 1300mm diameter at base while 800 mm at top. The shear
wall varies 1300mm thickness at base and 400mm at top.
• They carried out cyclic load test and FEM analysis of diagrid connection with
concrete fill steel tube and only steel tube.
16

17. • Both FEM analysis and test results showed that in concrete filled steel tube
connection failure takes place at the connection of node and diagrid member while in
steel tube failure takes place at the node itself.
• This shows that sound concrete within the node move the eventual failure location
beyond the node.
17

18. Comparative Study of 50, 60, 70,80 Storey Steel Tube and CFST
Diagrid
• Building configuration
 Plan dimension = 36m ×36m
 Story height = 3.6m
 Steel Grade for beam column= Fe 250
 Steel Grade for Tube = Yst310
 Grade of concrete = 40N/mm2
 Slab thickness = 150mm
 Floor Finish= 1kN/m2
 Live load = 2.5kN/m2
 Live load reduction factor = 0.25
18

19. • Earthquake load Parameters(IS-1893 :Part-1,2016)
 Response reduction factor =5
 Importance factor = 1
 Place = Ahmadabad
 Zone = 3
 Soil type = medium
• Wind load parameters(IS-875:Part-3,2015)
 Wind speed = 39m/s
 Terrain category = 3
 Probability factor k1 = 1
 Topography factor k3= 1
 Importance factor k4 = 1
19

20. 20
1. DL+FF 13.1.2DL+1.2FF+1.2LL+1.2WLX
2.DL+FF+LL 14.1.2DL+1.2FF+1.2LL-1.2WLX
3. 1.5DL+1.5FF 15.1.2DL+1.2FF+1.2LL+1.2WLY
4. 1.5DL+1.5FF+1.5LL 16.1.2DL+1.2FF+1.2LL-1.2WLY
5. 1.2DL+1.2FF+1.2LL+0.6WLX 17.1.2DL+1.2FF+1.2LL+1.2COMB WX
6. 1.2DL+1.2FF+1.2LL-0.6WLX 18.1.2DL+1.2FF+1.2LL-1.2COMB WX
7. 1.2DL+1.2FF+1.2LL+0.6WLY 19.1.2DL+1.2FF+1.2LL+1.2COMB WY
8. 1.2DL+1.2FF+1.2LL-0.6WLY 20.1.2DL+1.2FF+1.2LL-1.2COMB WY
9. 1.2DL+1.2FF+1.2LL+0.6COMB WX 21.1.5DL+1.5FF+1.5WLX
10.1.2DL+1.2FF+1.2LL-0.6COMB WX 22.1.5DL+1.5FF-1.5WLX
11.1.2DL+1.2FF+1.2LL+0.6COMB WY 23.1.5DL+1.5FF+1.5WLY
12.1.2DL+1.2FF+1.2LL-0.6COMB WY 24.1.5DL+1.5FF-1.5WLY
WLX: Static wind , COMB WX: dynamic along wind x+ dynamic across wind x
COMB WY: dynamic along wind y+ dynamic across wind y
Table 1 – Load combination

21. 21
25.1.5DL+1.5FF+1.5COMB WX 37.1.2DL+1.2FF+1.2LL+1.2EQX
26.1.5DL+1.5FF-1.5COMB WX 38.1.2DL+1.2FF+1.2LL-1.2EQX
27.1.5DL+1.5FF+1.5COMB WY 39.1.2DL+1.2FF+1.2LL+1.2EQY
28.1.5DL+1.5FF-1.5COMB WY 40.1.2DL+1.2FF+1.2LL-1.2EQY
29.0.9DL+0.9FF+1.5WLX 41.1.5DL+1.5FF+1.5EQX
30.0.9DL+0.9FF-1.5WLX 42.1.5DL+1.5FF-1.5EQX
31.0.9DL+0.9FF+1.5WLY 43.1.5DL+1.5FF+1.5EQY
32.0.9DL+0.9FF-1.5WLY 44.1.5DL+1.5FF-1.5EQY
33.0.9DL+0.9FF+1.5COMB WX 45.0.9DL+0.9FF+1.5EQX
34.0.9DL+0.9FF-1.5COMB WX 46.0.9DL+0.9FF-1.5EQX
35.0.9DL+0.9FF+1.5COMB WY 47.0.9DL+0.9FF+1.5EQY
36.0.9DL+0.9FF-1.5COMB WY 48.0.9DL+0.9FF-1.5EQY
WLX: Static wind , COMB WX: dynamic along wind x+ dynamic across wind x
COMB WY: dynamic along wind y+ dynamic across wind y
Table 1 Continue..

22. Figure 7 – Diagrid Building Plan
22

23. Figure 8 – Elevation of Diagrid Building
23

24. 24
Figure 9 – 3D model of diagrid

25. Table 2 – Member Sizes
Sr. No. Element of
Diagrid
structure
Section Size
1 B1 ISMB 600
2 B2
ISWB 600 with top and bottom cover plate of
220× 50 mm
3 B3 ISWB 600
4 C1 1650 × 1650 for 50 storey
1800 × 800 for 60 storey
2000× 2000 for 70 storey
2200× 2200 for 80 storey
25

26. 26
Module Steel Tube CFST
F(kN) D(mm) t(mm) F(kN) D(mm) t(mm)
1 to 12 17330 750 30 18941 570 30
13to24 12191 640 25 13324 490 25
25to36 7750 520 20 8475 390 20
37to50 3750 370 15 4167 280 15
Table 3 – Axial forces and member sizes for 50 storey steel tube and CFST diagrid

27. 27
Module Steel Tube CFST
F(kN) D(mm) t(mm) F(kN) D(mm) t(mm)
1 to 12 23520 850 35 25706 670 35
13to24 17199 730 30 18797 570 30
25to36 11973 620 25 13086 480 25
37to48 7300 500 20 7997 380 20
49to60 3330 330 15 3640 280 12
Table 4 –Axial forces and member sizes for 60 storey steel tube and CFST diagrid

28. 28
Module Steel Tube CFST
F(kN) D(mm) t(mm) F(kN) D(mm) t(mm)
1 to 12 30929 970 40 33840 800 35
13to24 23272 850 35 25462 700 30
25to36 17117 730 30 18728 615 25
37to48 11595 610 25 12686 470 25
49to60 6762 460 20 7399 360 20
61to70 2785 290 15 3048 250 12
Table 5 – Axial forces and member sizes for 70storey steel tube and CFST diagrid

29. 29
Module Steel Tube CFST
F(kN) D(mm) t(mm) F(kN) D(mm) t(mm)
1 to 12 40337 1230 40 44133 910 40
13to24 30874 1090 35 33779 800 35
25to36 23536 970 30 25751 710 30
37to48 16933 850 25 18527 610 25
49to60 11131 590 25 12179 460 25
61to72 6151 430 20 6730 340 20
73to 80 2231 290 12 2442 225 12
Table 6 –Axial forces and member sizes for 80 storey steel tube and CFST diagrid

30. Comparison of Results
Table 7 -Comparison of Base Shear Results
30
Storey DWXA
(kN)
DWXC
(kN)
Static
(kN)
EQX (kN)
Steel
Tube
CFST
50 12490 711 3816 2276 2503
60 15761 1448 6446 2583 2752
70 19870 3284 10116 3095 3360
80 23758 5947 15009 3680 4022

31. Table 8 – Comparison of First Mode Time Period
31
Time period
Storey
Steel
Tube(sec) CFST (sec) % Reduction
50 3.71 3.54 4.40
60 4.41 4.15 5.87
70 5.07 4.76 6.04
80 5.75 5.41 5.92

32. 32
Table 9 – Comparison of Top Storey Displacement DWXA
DWXA
Storey
Steel
Tube(mm) CFST(mm) %Reduction
50 201 179 10.99
60 307 264 13.98
70 432 371 14.18
80 576 493 14.47

33. 33
Table 10 – Comparison of Top Storey Displacement DWXC
DWXC
Storey
Steel
Tube(mm) CFST(mm) %Reduction
50 36 32 10.89
60 66 57 13.86
70 134 115 14.03
80 218 187 14.38

34. 34
Table 11 – Comparison of Top Storey Displacement wind static
STATIC
Storey
Steel
Tube(mm) CFST(mm) %Reduction
50 185 165 11.04
60 282 242 14.03
70 395 339 14.25
80 528 452 14.50

35. 35
Table 12 – Comparison of Top Storey Displacement EQX
EQX
Storey
Steel
Tube(mm) CFST(mm) %Reduction
50 51 50 2.46
60 70 64 8.87
70 96 89 7.72
80 127 118 7.72

36. 36
Storey Steel Tube(%) CFST(%) % Increase
50 75 80 5.88
60 77 82 6.22
70 75 80 6.22
80 76 81 7.38
Table 13 – Comparison of percentage of lateral load resistance by diagrid

37. 37
Storey
Steel
Tube(%) CFST(%) %Increase
50 49 51 4.66
60 50 53 5.68
70 51 55 6.84
80 52 56 7.11
Table 14 – Comparison of percentage of gravity load resistance by diagrid

38. 38
Table 15 – Comparison of axial deformation(D.L.+L.L.+F.F.)
Storey
Steel
Tube(%) CFST(%) % Reduction
50 111 104 6.91
60 136 124 8.58
70 155 143 7.40
80 173 160 7.74

39. 39
Table 16 – Comparison of weight
Storey
Steel Tube CFST
% Increase
in weight
W (×107 kN) W (× 107 kN)
50 2.76 4.65 68.22
60 4.09 7.04 72.23
70 5.87 10.49 78.74
80 8.2 14.92 81.76

40. 40
Table 17 – Comparison of cost
Storey
CFST Steel Tube % Reduction in
cost
Rs (in lacs.) Rs (in lacs.)
50 994.43 1268.37 21.59
60 1502.54 1877.35 19.96
70 2049.08 2692.81 23.9
80 2907.94 3765.81 22.78

41. Conclusion
• The time period of concrete filled steel tube diagrid structure is lower than that of
steel tube diagrid structure.
• The reduction in top storey displacement of CFST diagrid due to earthquake varies in
the range of 3 to 9 percentages and for wind it varies in the range of 11 to 15
percentages. But percentage reduction in displacement due to earthquake is lower
than that of wind because of increase in weight of structure due to concrete infill.
• The percentage of gravity load and lateral load resistance by CFST diagrid structure
is more than steel tube diagrid structure.
• The axial deformation of the concrete filled steel tube diagrid structure is less as
compare to steel tube diagrid structure and it varies in the range of 7 to 9 percentage.
• The reduction in the cost of diagrid structure by using CFST varies in the range of 20
to 25 percentages.
41

42. References
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44

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45

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46

47. THANK YOU
47