Please note that the minimum score at your post graduate level should not be less than 55 percent in your case for being eligible for UGC NET examination in your case, since you hail from General Category. A concession to the extent of 5 percent is offered to female candidates, SC, ST and OBC.,
Now talking for the subject Structural Engineering, the same is not included in the syllabus and hence you need to opt for a subject included in the list in which the candidate has to appear apart from a common paper known as paper 1. For the paper2, you will have to see the list and choose a subject of your liking ranging from Humanities to Mathematical Science to Civil Engineering. Your preparation should continued according to your chosen paper.
A final list of eligibility of the candidates would be prepared depending upon your scoring in the test. They follow certain cut off points necessary to secure so as to qualify the test.
Apart from this, you need to clear the viva conducted by the faculty of experts assessing your potential. You will be selected for the post of lecturership as per scoring in both written and viva.