No abstract

No abstract

Sensitivity and identifiability problems of the modal parameters in the presence of corrosion damage are studied. The first concerns the rate of change of the modal parameters against the damage increase. The second concerns the uncertainty intervals overlapping of the modal parameters between the sound and damaged states. To this end, different testing methods, different identification methods (time, frequency and time-frequency methods), different corrosion levels and different thermal condition (summer-winter) are considered. Prestressed concrete beams of identical geometry endowed with low to high reinforcement ratios are dynamically tested. The free decaying vibrations are used to identify the modal parameters: frequency, modal shapes and damping. The prestressing force is found to be not a variable of the problem. The damage levels range from very low to moderate. It is found that reliable damage identification is possible only for moderate damage. In spite of higher scatter, damping reveals a more stable and sensitive indicator than frequency. Modal shapes shows regular changes, but within the range of the uncertainty intervals.

This paper deals with research related to repair and strengthening of weak and brittle masonry infills in R.C. or steel frame structures. Masonry infills are commonly used in 20th century architectural heritage residential and office buildings. In case of earthquake damage to the weak and brittle masonry infills the commercial buildings go out of service and residents of residential buildings are prohibited from living in their homes although the main frame structure is not damaged. The new retrofitting method proposed in this paper may be either a preventive seismic improvement or a quick emergency intervention before seismic aftershocks: it is proposed to use a polymer PM to fill new horizontal and vertical joints between infilling masonry and frame or to fill cracks generated by the earthquake. The test results presented in the paper confirmed ability of polymer PM to fulfil requirements of quick repair material for seismic area.

An experimental campaign named the Pescara benchmark and devoted to study the dynamic behaviour of corroded p.c. joists has been conducted. The steel corrosion reduces the area of the reinforcement and causes cracking of concrete so that r/c members are subjected to loss of strength and stiffness. It is of interest to evaluate the corrosion level at which the damage can be detected through signal processing procedures and how close such level is to the r/c member safety limits. Joists of current industrial production having different steel to concrete ratios are tested in different laboratory conditions. Dynamic tests involve either free vibrations and forced vibrations due to a moving mass simulating actual traffic loads in railway bridges. The paper discusses the rationale of the tests including the set up of the artificial corrosion, the static characterization of the joist and the dynamic tests in the different stages of corrosion experienced.