中国与美国规范混凝土基础设计对比
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Standard load combination:
,
Basic load combination:
;
According to the above combination principle of load and the standard value of force given in table 1, the standard value and design value when considering seismic action combination are respectively; , , and , , , .In the calculation, the larger value of the two groups of combinations is taken; , , and , , .
Design according to Chinese standard C35 concrete, (prismatic strength), HRB335, reinforcing bar,
According to the American manual C35 concrete, (cylinder strength), reinforcing bar, .
2.3.1According Chinese codes:
(1)Considering earthquake load combination
(a)Net plate reaction deBaidu Nhomakorabeaign value:
(b)Basic shearing resistance checking:
,satisfied
Thickness of protective layer :75 mm, Average bulk density of foundation and soil: 20 kN/m3,Characteristic value of foundation bearing capacity: 400 kPa; embedded depth of foundation: 5.00m, Force elevation: -0.500m;
,satisfied
,satisfied
(2)According American code.
,satisfied
2.3.Basic calculation
A Chinese and American code, the basic combination value of net reaction force of foundation floor corresponding to the basic combination of load effect isadopted.Foundationdesign, the Chinese standard mainly includes the shear, scouring and bending design, and the American Standard mainly includes the shear and bending design, in which the shear calculation includes two aspects: one way and two-waydirections.
The various forces on the basis are shown in table 1.
Table1Force standard
D, dead load
(kN)
L, live load
(kN)
E, earthquake load
Ydirection (kN)
W, wind load
Standardloadcombination:
Basic load combination:
According to the above combination principle of load and the standard value of force given in table 1, the standard value and design value when considering seismic action combination are respectively; , , and , , ;the standard value and design value when considering wind load combination are respectively; , , and , , .
(1)AccordingChinese code.
Consideringearthquakeload combination
,satisfied
,
,satisfied
Where, A is area of base, is soilweigh
Considering wind load combination
(2)There are differences in the test method, the guarantee rate and the design value of concrete strength between China and the United States. When designed according to the standard of China, the strength design value of steel and concrete is used. The yield strength is used in the design and calculation of the steel bar according to the American manual, and the experimental value of the concrete is adopted.
2.2.The foundation calculation
In the calculation of foundation, the ChineseandAmericancodes all adopt thestandardvalue of the total floor slabreactionforce corresponding tothe standard combination of load effect.However, the Chinese code will adjust the characteristic value of foundation bearing capacity for seismic combination conditions, while theUScode does not have such adjustment requirements.
(2)Considering wind load combination
(a)Net plate reaction design value:
(b)Basic shearing resistance checking:
,satisfied
(c)Basic punching check:
, satisfied
Calculation example
Concrete foundation design comparison between Chinese and American codes
1.Basic design parameters
In this comparison calculation, a large equipment foundation of a foreign project was selected as the design object. In order to make the comparison result more intuitive, a unified regulation was made:
(2)Americanstandard load combination.
Due to the specification relevant foundation calculation, combination condition, the earthquake is not to adjust the bearing capacity of foundation and component, so this example based calculation, only the maximum combination.According to“Theminimum design load code”,the following load combination is adopted.
(1)Both the Chinese and US standard calculation examples use the same upper load standard value, and consider only the horizontal load in the Y direction, but the load combination uses their respective coefficients.
2.Basic calculation example
2.1.Load combination
(1)China standard load combination.
As the earthquake action participates in the combination, the carrying capacity of the foundation must be adjusted according to the specifications. Therefore, this example uses the Chinese code to calculate the load combination and distinguishes them based on whether there is an earthquake or not, “Loading Codes for Building Structures” and “Codes for Seismic Design of Buildings”. The required load combinations are as follows:
(3)The same foundation size and characteristic value of foundation bearing capacity are adopted.
(4) The specific parameters are as follows: according to the estimation, the basic size is shown in figure 1 (unit mm).
Where, , , , ,
(c)Basic punching check:
, satisfied
Where, , , ,
(d)Base bending calculation:
Bending calculation:
Reinforcement calculation:
Where, : compute area of footwall length
Ydirection (kN)
P
1300 380
P
1500 220
P
1500 1100
P
700 450
Note: p is vertical load, downward to positive, isthe horizontal load along the X-axis, isthe horizontal load along theY-axis.
,
Basic load combination:
;
According to the above combination principle of load and the standard value of force given in table 1, the standard value and design value when considering seismic action combination are respectively; , , and , , , .In the calculation, the larger value of the two groups of combinations is taken; , , and , , .
Design according to Chinese standard C35 concrete, (prismatic strength), HRB335, reinforcing bar,
According to the American manual C35 concrete, (cylinder strength), reinforcing bar, .
2.3.1According Chinese codes:
(1)Considering earthquake load combination
(a)Net plate reaction deBaidu Nhomakorabeaign value:
(b)Basic shearing resistance checking:
,satisfied
Thickness of protective layer :75 mm, Average bulk density of foundation and soil: 20 kN/m3,Characteristic value of foundation bearing capacity: 400 kPa; embedded depth of foundation: 5.00m, Force elevation: -0.500m;
,satisfied
,satisfied
(2)According American code.
,satisfied
2.3.Basic calculation
A Chinese and American code, the basic combination value of net reaction force of foundation floor corresponding to the basic combination of load effect isadopted.Foundationdesign, the Chinese standard mainly includes the shear, scouring and bending design, and the American Standard mainly includes the shear and bending design, in which the shear calculation includes two aspects: one way and two-waydirections.
The various forces on the basis are shown in table 1.
Table1Force standard
D, dead load
(kN)
L, live load
(kN)
E, earthquake load
Ydirection (kN)
W, wind load
Standardloadcombination:
Basic load combination:
According to the above combination principle of load and the standard value of force given in table 1, the standard value and design value when considering seismic action combination are respectively; , , and , , ;the standard value and design value when considering wind load combination are respectively; , , and , , .
(1)AccordingChinese code.
Consideringearthquakeload combination
,satisfied
,
,satisfied
Where, A is area of base, is soilweigh
Considering wind load combination
(2)There are differences in the test method, the guarantee rate and the design value of concrete strength between China and the United States. When designed according to the standard of China, the strength design value of steel and concrete is used. The yield strength is used in the design and calculation of the steel bar according to the American manual, and the experimental value of the concrete is adopted.
2.2.The foundation calculation
In the calculation of foundation, the ChineseandAmericancodes all adopt thestandardvalue of the total floor slabreactionforce corresponding tothe standard combination of load effect.However, the Chinese code will adjust the characteristic value of foundation bearing capacity for seismic combination conditions, while theUScode does not have such adjustment requirements.
(2)Considering wind load combination
(a)Net plate reaction design value:
(b)Basic shearing resistance checking:
,satisfied
(c)Basic punching check:
, satisfied
Calculation example
Concrete foundation design comparison between Chinese and American codes
1.Basic design parameters
In this comparison calculation, a large equipment foundation of a foreign project was selected as the design object. In order to make the comparison result more intuitive, a unified regulation was made:
(2)Americanstandard load combination.
Due to the specification relevant foundation calculation, combination condition, the earthquake is not to adjust the bearing capacity of foundation and component, so this example based calculation, only the maximum combination.According to“Theminimum design load code”,the following load combination is adopted.
(1)Both the Chinese and US standard calculation examples use the same upper load standard value, and consider only the horizontal load in the Y direction, but the load combination uses their respective coefficients.
2.Basic calculation example
2.1.Load combination
(1)China standard load combination.
As the earthquake action participates in the combination, the carrying capacity of the foundation must be adjusted according to the specifications. Therefore, this example uses the Chinese code to calculate the load combination and distinguishes them based on whether there is an earthquake or not, “Loading Codes for Building Structures” and “Codes for Seismic Design of Buildings”. The required load combinations are as follows:
(3)The same foundation size and characteristic value of foundation bearing capacity are adopted.
(4) The specific parameters are as follows: according to the estimation, the basic size is shown in figure 1 (unit mm).
Where, , , , ,
(c)Basic punching check:
, satisfied
Where, , , ,
(d)Base bending calculation:
Bending calculation:
Reinforcement calculation:
Where, : compute area of footwall length
Ydirection (kN)
P
1300 380
P
1500 220
P
1500 1100
P
700 450
Note: p is vertical load, downward to positive, isthe horizontal load along the X-axis, isthe horizontal load along theY-axis.