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This paper presents a comparison of the acoustic emission (AE) energy and the plastic strain energy released by some reinforced concrete (RC) specimens subjected to cyclic or seismic loadings. AE energy is calculated, after proper filtering procedures, using the signals recorded by several AE low frequency sensors (25–100 kHz) attached on the specimens. Plastic strain energy is obtained by integrating the load displacement curves drawn from the measurements recorded during the test. Presented are the results obtained for: (i) two beams (with and without an artificial notch) and a beam-column connection subjected to several cycles of imposed flexural deformations; (ii) a reinforced concrete slab supported by four steel columns, and a reinforced concrete frame structure, both of the latter are subjected to seismic simulations with a uniaxial shaking table. The main contribution of this paper, which is a review of some papers previously published by the authors, is to highlight that, in all cases, a very good correlation is found between AE energy and plastic strain energy, until the onset of yielding in the reinforcing steel. After yielding, the AE energy is consistently lower than the plastic strain energy. The reason is that the plastic strain energy is the sum of the contribution of concrete and steel, while the AE energy acquired with thresholds higher than 35 dBAE captures only the contribution of the concrete cracking, not the steel plastic deformation. This good correlation between the two energies before the yielding point also lends credibility to the use of AE energy as a parameter for concrete damage evaluation in the context of structural health monitoring. ; This research received financial support from the local government of Spain, Consejería de Innovación, Ciencia y Tecnología, projects P07-TEP-02610 and PE12-TEP-02429, from the Spanish National Plan for Scientific Research, Development and Technological Innovation (projects BIA 2005-00591 and DPI 2006-02970), and from the Formación del Profesorado Universitario (FPU) Program of Spain's Ministry of Education, Culture and Sports (AP2010-2880).

This paper proposes a pulse-echo Ultrasonic Testing (UT) methodology to quantify the damage of hysteretic dampers subjected to cyclic loadings. Energy dissipation is known as an innovative strategy for the protection of buildings against earthquakes. It consists of installing special devices called dampers in the construction, which are entrusted to dissipate most of the energy input by the earthquake, thus keeping the main structure basically undamaged. In particular, the hysteretic dampers dissipate the input energy through plastic deformations in their metallic parts. Several moderate ground motions would not exhaust the capacity of the dampers, but they cause damage—plastic deformations in the device. Therefore, continuous or periodic inspections of the damper are required in order to decide upon its eventual replacement. In this particular work, several hysteretic dampers made of stainless steel were subjected to different patterns of low-frequency cyclic loads that caused diverse levels of damage. Each damper underwent pulse-echo UT before and after the cyclic loading. Spectral energy of the echo signals was properly calculated at each damage level in order to define a reliable damage index. The new index has been compared with a well-established mechanical damage index, ID, previously proposed by the authors. A successful correlation was observed, making the pulse-echo UT technique promising for this particular application. ; This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429.

The authors thank the PREDITEST Company, from the Czech Republic, and in particular Svoboda, for support in MMM equipment, measurements, and scientific discussions ; Inelastic deformation of metallic materials is one of the most effective mechanisms for the dissipation of energy input to a structure by an earthquake. Metallic dampers are special devices that resort to this source of energy dissipation, proving to be a cost-efficient solution for the seismic protection of structures. Two important issues arise when implementing metallic dampers in real structures: (1) Inelastic deformations cause damage that must be quantified after an earthquake to decide upon their eventual replacement; (2) dampers must possess an energy dissipation capacity large enough to endure severe earthquakes. This paper focuses on a particular type of metallic damper consisting of slit-plates made of stainless steel, applied to reinforced concrete frames with rocking columns at the first story. In particular, a new damage index based on the metallic magnetic memory (MMM) method is proposed and validated experimentally to quantify the damage of slit plate dampers subjected to cyclic loadings. Further, the seismic response of a frame with rocking columns that incorporate the damper is obtained to demonstrate that it can endure severe earthquakes without failing, and to emphasize the relevance of the proposed MMM damage index that would make its replacement after a severe earthquake unnecessary. ; This research was funded by Consejería de Economia, Innovación, Ciencia y Empleo, Junta de Andalucía, grant number TEP-02429, by Ministerio de Economía, Industria y Competitividad, Gobierno de España, grant number BIA2017 88814 R, and received funds from the European Union (Fonds Européen de Dévelopment Régional). The APC was funded by Ministerio de Economía, Industria y Competitividad, Gobierno de España, grant number BIA2017 88814 R.

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs. ; This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429, by the Spanish Ministry of Economy and Competitivity, research project reference MEC BIA2017 88814 R and received funds from the European Union (Fonds Européen de Dévelopment Régional).