# Special Issue on Advanced Technologies in Seismic Design, Assessment and Retrofitting
## 2 A Brief Overview of the Published Papers
### Advanced Techniques to Improve Seismic Response and Seismic Damage Control Using Dampers  
The effect of damping on the seismic response of structures is proven to be favourable in terms of damage reduction (displacement and stress control). For this reason, in addition to the inherent damping of a structure, it is often desired to artificially increase it by means of special devices, the dampers. Dampers are generally used in special engineering structures, such as bridges. Thus, damper technology is an advanced technique for improving the seismic response of structures. [PERSON] et al. [17] studied the seismic performance of bridges into which strengthened accelerated oscillator dampers had been built, enabling the control of the vibrations. Starting with the accelerated oscillator damper (AOD), which has been proven to be highly effective, they focused on the need for two upgrades. They proposed the innovative strengthened AOD with a linear spring (SAOD-LS), which can be installed and operated in traditional bridges. The proposed damper has a design that allows the installation of a secondary system and improved technical characteristics. In addition, the authors proposed the SAOD-NSD, an AOD additionally enhanced with a non-linear spring device (NSD) that provides protection against resonance during vibrations either due to earthquakes or wind. With these two upgrade proposals (SAOD-LS and SAOD-NSD), the drawbacks of the original AOD configuration are overcome. Finally, the proposed innovative upgrades/modifications of the AOD were also verified through finite element analyses. [PERSON] et al. [18] studied a solution to the problem of reducing seismic damage in steel structures through an innovative design based on the introduction of additional seismic energy dissipation mechanisms by friction dampers. More specifically, they dealt with the addition of friction devices (\"Free for Damage\" devices or FREEDAM devices) to steel beam-to-column joints. FREEDAM devices are designed to ensure the elastic behaviour of joints even in strong seismic events, thus ensuring the structural integrity of structures. Within the framework of the study, the calibration of advanced models of joints composed of solid finite elements using results obtained from experimental procedures was carried out. The analyses performed resulted in a number of useful conclusions for the correct configuration of joints with FREEDAM dampers and for the description of their seismic behaviour through the formulation of appropriate moment-rotation diagrams (discrimination of four phases during their seismic responses). Advanced Technologies That Increase the Effectiveness of Seismic Retrofitting or Rehabilitation Using New Special Materials and New Construction Techniques  
Research on the use of appropriate materials and structural configurations used for the retrofitting or the rehabilitation of existing structures is an important subject in earthquake engineering. The use of appropriate materials and devices can contribute substantially to increasing safety against strong seismic excitations while reducing the required construction cost. [PERSON] et al. [19] studied the problem of the seismic performance of underwater concrete piers strengthened using the precast concrete segment assembly method (PCSAM). Considering the fact that the PCSAM has some disadvantages, such as the considerable strength loss of filled concrete, poor accuracy and the poor connection performance of the segment sleeves, they developed and proposed the application of an innovative and improved strengthening method, IPCSAM. This method is efficient, economical and does not disturb the shipping traffic. To test and verify the proposed method, they investigated the seismic behaviour of reinforced piers through experiments. For this purpose, nine specimens were initially designed at a \(1/5\) scale with different characteristics and were tested under low reversed cyclic loading.