Pad Size Calculations 塔吊理论：计算垫片尺寸

Determining the safe operation limits for a large structure such as a crane is a very important skill that all engineers would need to be able to do. The math needed to perform these calculations is not overly difficult; however, there are several steps that need to be calculated in order to complete the necessary calculations. This activity guide will walk you through each step while also explaining the purpose for each step.

确定大型结构（如塔吊）的安全操作极限是所有工程师都需要具备的一项非常重要的技能。执行这些计算所需的数学不是太难；但是其中几个步骤是有必要完成的。此活动将引导你完成每个步骤，同时解释每个步骤的目的。

Step 1: Determine the Weight of the Crane (Point Load) 步骤1：确定塔吊的重量（点荷载）

The weight of the crane will include the the combined weight of the “tower”, “jib” and the “counter weight”. These weights remain constant during operation and will create a downward “point force” at the centre of the tower.

塔吊的重量将包括“塔架”、“吊臂”和“配重”的组合重量。这些重量在运行期间保持不变，并将在风塔中心产生向下的“点力”。

Weight of Crane (Tower + Jib)   75t

Weight of Counter Weight   50t

Point Load 125t

Step 2: Determine the Weight of Irregular Loads (Irregular Loads) 步骤2：确定不规则荷载（不规则荷载）的重量

The second value that needs to be calculated is the combined total of any irregular weight that can change during operation. These weights include the “load”, “hook block”, and a “fly jib” if it has been installed. These weights are considered irregular because they can change during operation. This is because the size of the load can change. Moreover, the position of the hook block and load can also change as the hook block moves forwards and backwards along the “jib”.

需要计算的第二个值是运行期间可能发生变化的任何不规则重量的总和。这些重量包括“负载”、“钩块”和“起重臂”（如果已安装）。这些重量被认为是不规则的，因为它们在操作过程中可能会发生变化。这是因为负载的大小可以改变。此外，钩块的位置和负载也可以随着钩块沿“吊臂”前后移动而改变。

Weight of Load (variable) 12.5t

Hook Block / Tackle   1.0t

Fly Jib (if Fitted)   0.5t

13.0t

Step 3: Determine Ground Pressure 步骤3：确定地面压力

Once you have completed the calculations from steps 1 & 2 you can substitute values into the “Ground Pressure” (GP) equation. To calculate GP you Use the formula:

完成步骤1和2后，将数值代入“地面压力”（GP）方程。使用以下公式计算GP：

Ground Pressure = (Point Load  x 0.75 ) + (Irregular Loads)

GP = (PL x 0.75) + (IL)

GP = (125t x 0.75) + (13t)

GP = 93.75t + 13t

GP = 106.75t

(GBP) Ground Bearing Pressure Table 地面轴承压力表：

Non Cohesive Soils – Gavel, or Sand and Gravel Mixtures:
Dense gravel, or a mixture of both> 61.2 t/m2> 600 kN/m2
Medium dense gravel, or a mixture of both20.4 ~ 61.2 t/m2200 ~ 600 kN/m2
Loose gravel, or a mixture of both< 20.4 t/m2< 200 kN/m2
Non Cohesive Soils – Sand Only:
Compact sand> 30.6 t/m2> 30 kN/m2
Medium Dense Sand10.2 ~ 30.6 t/m2100 ~ 300 kN/m2
Lose sand< 10.2 t/m2< 100 kN/m2
Cohesive Soils – Clay:
Very Stiff Boulder Clays and Hard Clays> 61.2 t/m2> 600 kN/m2
Stiff Clays15.3 ~ 30.6 t/m2150 ~ 300 kN/m2
Firm Clay7.6 ~ 15.3 t/m275 ~ 150 kN/m2
Soft Clays and Silts< 7.6 t/m2< 75 kN/m2

Step 4: Determine the “Ground Bearing Pressure” Constant 步骤4：确定“地面轴承压力”常数

Ground Bearing Pressure (GBP) is a mathematical constant that can be looked up using the provided table. The value for GBP varies based on different types of surface conditions that your crane will be used. So make sure you lookup the most suitable GBP constant for each unique situation that your crane will be used. Lets’ assume the crane will be insulated on a layer of “soft clay or silts”. We will look up the constant for this type of ground surface and then use this value for our next calculation.

地面轴承压力（GBP）是一个数学常数，可使用提供的表格进行查找。GBP值根据塔吊将使用的不同类型的地面条件而变化。因此，请确保为塔吊将要使用的每个独特情况查找最合适的GBP常量。让我们假设塔吊将绝缘在一层“软粘土或淤泥”上。我们将查找此类型地面的常数，然后使用此值进行下一次计算。

GBP: Soft Clays and Silts < 7.6 t/m2 < 75 kN/m2

Step 5: Determine the Minimum Acceptable Pad Size 步骤5：确定可接受的最小焊盘尺寸

To determine the minimum acceptable pad size for your crane you simply divide the “Ground Pressure (GP)” from step 3 by the “Ground Bearing Pressure (GBP)” that you looked up in step 4. Then use the following equation to determine “Pad Size (PS)”.

要确定塔吊的最小可接受垫尺寸，只需将步骤3中的“地面压力（GP）”除以步骤4中查找的“地面轴承压力（GBP）”。然后使用以下方程式确定“焊盘尺寸（PS）”。

Pad Size = Ground Pressure / Ground Bearing Pressure

PS = GP / GBP

PS = 106.75t / 7.6 t/m2

PS = 13.95 m2

Step 6: Determine the Dimensions of the Pad (Side Length or Radius)步骤6：确定衬垫的尺寸（边长或半径）

Depending on the design of your crane you may have either a square or circular base. Different calculations are needed to determine the dimensions of a pad since the formulas for the area of a square and circle are different.

根据塔吊的设计，可以使用方形或圆形底座。由于正方形和圆形的面积公式不同，因此需要进行不同的计算来确定衬垫的尺寸。

Since the “Pad Size” has already been pre-determined in step 5 the equations for finding the area of a square or circle need to rewritten to isolate “S” for side length, or
“r” for radius. Once you rewrite the equation you can substitute the value for “Pad Size” and then solve the equation. This will give you the necessary values. This will be the side length for a square pad or the radius if the pad is circular.

由于“焊盘尺寸”已在步骤5中预先确定，因此需要重新编写求正方形或圆形面积的方程式，以隔离边长的“S”，或“r”表示半径。重写方程式后，可以将该值替换为“焊盘尺寸”，然后求解方程式。这将是方形衬垫的边长，或者是圆形衬垫的半径。

Step 7: Rounding Final Pad Size (Always Round Up) 步骤7：四舍五入最终焊盘尺寸（始终记住要四舍五入）

Since the design of a crane and its pad will normally not be made using irregular measurement intervals it is important to round all values to the nearest meter.

由于塔吊及其衬垫的设计通常不会采用不规则的测量间隔，因此重要的是将所有值四舍五入到最近的米。

NOTE:Since rounding down could result in a “Pad Size” that would be below the minimum safe requirements it is important that all values are rounded UP.

注：由于四舍五入可能导致“焊盘尺寸”低于最低安全要求，因此所有值必须四舍五入。

Square Pad: Circular Pad:

Side = 3.73m  Radius = 2.11m

Side = 4m Radius = 3m

Step 8: Determine the Outrigger Point Load 步骤8：确定支腿点荷载

The final step is to determine the “Outrigger Point Load” (OPL) for the final design of the crane. The

The final step is to determine the “Outrigger Point Load” (OPL) for the final design of the crane. The OPL value takes into consideration the weight of the crane, the load, pad size, and the stability of ground that the crane has been placed on. The equation is:

最后一步是确定塔吊最终设计的“支腿点荷载”（OPL）。OPL值考虑了起重机的重量、荷载、垫块尺寸和起重机所在地面的稳定性。方程式为

Outrigger Point Load = Ground Pressure / Final Pad Size

OPL = GP / FPS

OPL = 106.75t / (4m x 4m)

OPL = 106.75t / 16m2

OPL = 6.67t/m2

In conclusion, if the final “outrigger point load” for the crane based on the specified value is 6.67t/m2. As long as the “Outrigger Point Load” OPL value is less than “ground bearing pressure” GBP the crane can safely be used.

综上所述，如果基于规定值的塔吊最终“支腿点荷载”为6.67t/m2。只要“支腿点荷载”OPL值小于“地面支承压力”GBP，塔吊就可以安全使用。

Extension Activity 拓展活动

  1. Calculate the Pad Size (PS) that would be needed if:
    计算以下情况下所需的焊盘尺寸（PS）：
    • The crane has a Point Load (PL) of 125t, an Irregular Load (IL) of 50t, and the crane will be installed on dense gravel.
      塔吊的点荷载（PL）为125t，不规则荷载（IL）为50t，将安装在密实砾石上。
    • The crane has a Point Load (PL) of 125t , an Irregular Load (IL) of 50t, and the crane will be installed on soft clay or silts.
      塔吊的点荷载(PL)为125t，不规则荷载(IL)为50t，将安装在软粘土或淤泥上。
    • Determine the Outrigger Point Load (OPL) for both scenarios.
      确定两种情况下的支腿点荷载（OPL）。
  1. Determine if the Pad Size (PS) of your crane is large enough. 
    确定塔吊的垫片尺寸（PS）是否足够大。
    • Can you operate your crane under a wide variety of scenarios? Why?
      你能在多种情况下操作塔吊吗？为什么？
      • What is the required Pad Size (PS) that is needed for your crane to operation under all situations? NOTE: this will the the largest pad size that you calculated which will allow the crane to be use on unstable ground.
        塔吊在所有情况下运行所需的焊盘尺寸（PS）是多少？注：这将是计算的最大垫片尺寸，允许塔吊在不稳定地面上使用。
      • What would the necessary pad size be for your model (scale is 1:500)?
        你的型号所需的垫片尺寸是多少（比例为1:500）？
    • Think about what you could do if the Pad Size in your proposed crane design is not large enough. What modifications could make your crane safer?
      如果你提议的塔吊设计中的垫片尺寸不够大怎么办？有哪些改进可以使塔吊更安全？

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