To carry out the vulnerability analysis of an existing steel structure, the first phase is the planning of the investigation campaign to reach an adequate Knowledge Level of the structure. In today’s article I talk about the levels of knowledge required by the NTC 2018 for existing steel structures and the on-site tests and investigations to be performed for each level of knowledge. At the end of the you will be able to download a PDF handbook containing all the regulatory requirements relating to the investigations to be performed. If you happen to analyze existing steel structures, don’t miss out on today’s post.
Knowledge levels and confidence factors
As with existing masonry and reinforced concrete structures , even for existing steel structures, the Technical Standard defines three levels of knowledge:
As the level of knowledge grows (from LC1 to LC3), the information available on the structure will increase, regarding the properties of the materials and the construction details . Each Knowledge Level is associated with a Confidence Factor FC that will be used to reduce the strength of the steel. As the level of knowledge increases, the reduction in mechanical parameters will decrease by applying the corresponding Confidence Factors shown below:
- LC1 ⇒ FC = 1.35
- LC2 ⇒ FC = 1.20
- LC3 ⇒ FC = 1.00
- Rd = R / FC
Rd = design resistance to be used in verifications;
R = resistance obtained from on-site tests or from the original project specifications;
FC = Confidence factor.
Reduced material strength for the FC confidence factor
Preliminary analysis of the structure
One of the novelties of the NTC2018 concerning the existing structures is the introduction of the preliminary analysis of static safety and seismic vulnerability following the geometric survey of the structure. This analysis is preliminary to the correct planning of the number and location of on-site investigations and the tests to be performed. From the results obtained from the preliminary analysis we will be able to evaluate the level of static commitment of the individual structural elements and decide for which type of element to increase the number of necessary investigations and where to locate them.