The magnitude of the pretensioning forces that can be introduced into the lashing material is dependent on the tensioning forces used, the leverage on the tensioning element and the elasticity of the lashing material. Experience shows that the following lashing materials are able to attain the following pre-tensioning forces in the lashing material when tensioned with normal physical effort:

These values are not definitive; they are based on practical experience gained in a sea port. Practitioners should calculate the appropriate values for their field depending on the materials used. The use of special tensioning aids may make it possible to apply greater pretensioning force. The use of pretension indicators is recommended. These allow both accurate measurement of the pretensioning force during lashing, as well as allowing the residual pretensioning force to be checked during transportation. However, it must be said that this is of little use if the containers cannot be checked during the transportation process.
 
For reasons that will not be explained here, the pretensioning force is only permitted to be, at the most, half of the MSL or the permitted lashing force of a single lashing.
 
The vertical component of the pretensioning forces decreases as the lashing angle of the tie-down decreases. From a mathematical point of view, the rate of decrease is by the sine of the lashing angle. The following values can be used as guidelines:
 

The table below shows examples of the magnitude of the overall securing forces of tie-downs with a total pretensioning force of 600 daN when used with various lashing angles and coefficients of friction.

 

The table shows that with a total pretensioning force of 600 daN, a lashing angle of 90° and a coefficient of friction of 30% it is possible to achieve a securing force of 180 daN per tie-down. Thus, in order to secure a load with a mass of 9 t, 50 (fifty !) tie-downs will be required. This shows that tie-downs have only limited use as securing aids. In addition to this, tie-downs require an equal distribution of the pretensioning force on both sides. This can be achieved by using tensioning elements in pairs, centrally or alternately.
 
The effective securing forces can be very accurately calculated on site with very little effort and some basic mathematics, as long as the pretensioning and frictional forces are known or can be estimated with some accuracy.
 

 
The effective length of the lashing aid in the example is measured at 1.00 m (dark-green line). The vertical component of the lashing in the example is 0.80 m (light-green line). The vertical component of the pretensioning force is thus 80% or 0.8 (always divide the smaller value by the larger value). Multiplying the value with the pretensioning force of the lashing aid and the coefficient of friction between the package and the surface will give the securing force. With a pretensioning force of 500 daN and coefficient of friction of μ = 0.3, the lashing applies a securing force of 0.8 x 500 daN x 0.3 = 120 daN.

 

We translated the file about Securing forces depending on pretensioning force from English into Chinese.

 

 

能够引至栓系材料的预拉伸力的量级取决于作用的拉力、拉力组件的杠杆作用及栓系材料的弹性。经验表明下列栓系材料在正常体力作用下能够达到以下预拉伸力：

这些值并不是确定的；其取决于在海港获得的实践经验。操作员应按照所用材料计算其适当的值。使用特殊拉力工具能够施加更大的预拉伸力。推荐使用预拉伸指示器。这给予栓系过程中预拉伸力的精确测量，以及在运输过程中检查剩余预拉伸力。然而，因此可以说如果集装箱在运输过程中不能检查，这也用处不大。
 
出于这里不能解释的原因，预拉伸力最多允许为MSL的一半或单个栓系的允许栓系力。

预拉伸力的垂直分量随着栓系角度的减小而减小。从数学观点来看，下降率与栓系角度为正弦关系。下列数值可用作指导：
 
 栓系角度对垂直分量的影响

下表显示栓系的整体紧固力量级的例子，总预拉伸力为600daN，不同栓系角度和摩擦系数。
 

 紧固力取决于预拉伸力、栓系角度和摩擦系数
 

表中显示，总预拉伸力为600daN，栓系角度为90°，摩擦系数为30%时，能够获得每个栓系的紧固力为180daN。因此，为了紧固9t的荷载，需要50点栓系。这表明栓系只有限地用作紧固工具。除此之外，栓系需要预拉伸力在两侧的平均分布。这可以通过成对、中央或轮流使用拉紧组件获得。
 
只要预拉伸力和摩擦力已知或能够准确估计，有效的紧固力可以通过一些基本数学非常简单、准确地在现场计算出来。
 

在该例中，栓系工具的有效长度测量为1.00m（墨绿线）。栓系的垂直分量为0.80m（浅绿线）。因此，预拉伸力的垂直分量为80%或0.8（通常是较小值除以较大值）。乘上栓系工具的预拉伸力值和包装物与表面之间的摩擦系数，将得出紧固力。预拉伸力为500daN，摩擦系数为μ=0.3，栓系作用的紧固力为0.8 x 500daN x 0.3 = 120daN。

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