In order to assess the safety of old timber structures and eventually to select
appropriate strengthening strategies, the evaluation of mechanical properties
of the material is of key importance. Visual strength-grading coupled with the
use of nondestructive in situ testing allows these properties to be determined.
Nowadays, the defi nition of both nondestructive testing (NDT) procedures and
criteria for the results interpretation are almost exclusively in charge of the
producer. In Italy, effort has been made to develop codes for grading timber
on-site, and also by means of NDT. The aim of this paper is to highlight the
diffi culties and shortcomings that still occur in the assessment of traditional
timber members following the criteria established by the legislation in force
in Italy. The presented results can be helpful for the building surveyor who is
in charge of the inspection of existing timber structures. Indeed, the paper
gives some indications on the effectiveness of the grading criteria applied on
historical timbers, as well as on the level of accuracy of some nondestructive
methods.

• Visual strength-grading and NDT of timber in traditional structures