It also provides modifications, retrofitting and refurbishment to existing vehicles. I improvements were focused on reducing the cost of retrofitting future systems. Existing structures can be modified by seismic retrofitting to improve their resistance to earthquakes. Because of the heavy use of retrofitting and refitting fictional navies also include the concept. The cathedral underwent repairs for earthquake retrofitting and subsidence prevention in 2012. Beam-column joint connections are a common structural weakness in dealing with seismic retrofitting. Building a supermax prison, or even retrofitting an old prison, is very expensive. Plastic linings are also used as a method of retrofitting damaged concrete linings. In December 2016, BART awarded a contract to perform further seismic retrofitting. The yard started retrofitting aircraft carriers to accommodate jet aircraft. Prohibitions relative to certain retrofitting of diesel-powered vehicles. In February 2013, the seismic retrofitting was completed. Instead, the resonance was controlled by retrofitting 37 viscous fluid dampers to dissipate energy. A program of retrofitting older rolling stock has been underway since 2013. However many are starting the process of retrofitting these lines with platform screen gates.