圆形截面直径(mm)

耐火极限(h)

保护层厚度di (mm)

λ = 20

λ = 40

λ = 60

λ = 80

1200

1.0

13

22

34

48

1.5

17

29

45

64

2.0

20

34

54

76

2.5

24

40

63

88

3.0

27

45

71

99