Answer:
personification
Explanation:
A house does not have a backbone, but a person does. With this in mind, this quote is using personification.
"Lifting, fastening bulky beams, Building the backbone of a sturdy house..."
(alliteration could also be thought, <u>b</u>ulky <u>b</u>eams, <u>B</u>uilding the <u>b</u>ackbone, but as the question only asked for one I thought that personification was the biggest figurative language being used here!)
Have a nice day!
If this is not what you are looking for - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather