This tension member is the subject of our concern.

这个紧张成员是我们关注的对象。

So why would a tension member like this crack?

那么为什么像这样的受拉杆件会出现裂纹呢？

Of course, these ties aren't purely tension members holding the two sides of the arch together.

当然，这些系带并不是将拱门两侧固定在一起的纯粹的张力构件。

And the primary reason that a crack would initiate in a steel tension member of a bridge is fatigue.

桥梁钢受拉构件出现裂纹的主要原因是疲劳。