From the top of the structure, jump to the ledge at the bottom of the wooden ramp.

Turn around and notice the two handholds of the structure. You have to grab the bottom handhold, so ignore to the top one. As you can see, the bottom handhold goes halfway the structure (the other half is broken).

Go to the back of the ledge. From this spot, you cannot see the bottom handhold, so turn to face the direction of it (diagonally to the right). You have to make a "blind" standing jump and grab the handhold. If you take a running jump, Lara will grab the top handhold and you do not want that.

So, from the back of the ledge press Up and Jump at the same time. The jump is quite long and Lara usually grabs the handhold with one hand. Press the Interact button to save her. From there, jump to the alcove with the Artifact.