PSI - Issue 42

António Mourão et al. / Procedia Structural Integrity 42 (2022) 1744–1751 António Mourão/ Structural Integrity Procedia 00 (2019) 000 – 000

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2. Experimental data 2.1. Material

An accurate assessment of the material mechanical properties is paramount to the assessment of structural response and thus evaluation of structural integrity particularly when local phenomena such as fatigue are concerned. Given the wide range of existing bridges in both United States and Europe predating the first iteration of structural steel delivery standards, as well as the grueling effects that time under service along with environmental conditions undoubtedly play in the long-term material properties degradation, a case study dependent experimental campaign is a must to determine present material parameters and future maintenance and/or replacement or given structural members. For the work at hand, a set of laboratory experimental tests were conducted in material extracted from the Várzeas bridge, which can be seen below in Figure 1, were developed by Horas (2021) with aims to evaluate the metallographic, monotonic, cyclic and fatigue properties.

Fig. 1. Várzeas bridge overview, Souto et al. (2019).

Given the sensitivity of pre-standard materials, namely, puddle iron found in historic Portuguese bridges, material properties are highly direction dependent (Cremona (2013), Mohabeddine (2022)), as such, to achieve reasonable values, both location and direction of the specimens have been taken under consideration for creating the specimens, for the present work only metallographic samples and monotonic tensile strength tests are pertinent. A brief overview of some historic Portuguese bridges material chemical composition can be seen in Horas (2021). Purely from the carbon content it is possible to see an evolution of the control conditions in the manufacturing process, where bridges made purely from puddle iron before the beginning of the 20 th century have a carbon composition ranging from 0.81 to 0.09, the latter being for more recent constructions. On another hand, several similarities can be seen in bridges made using material from the 20 th cen tury until the 1950’ whereas the chemical composition of the base material, namely carbon content follows the same tendency, ranging from 0.02 0.15% of total mass. Even though carbon content in the base material is simply one of the added components during the manufacturing process it is possible to classify the two groups of parent material referencing the eutectic point in the iron-carbon phase diagram, thus leading to different crystalline structures, a representative metallographic diagram of the samples gathered for the Várzeas bridge material can be seen in Figure 2 which shows an isotropic grain distribution of the steel with an average size of 32 μm , along with the grain size distribution which was seen to follow a lognormal distribution.