Single-storey precast reinforced concrete (RC) frame type buildings are mainly preferred in manufacturing plants and storehouses. The behaviour of semi-rigid beam-column connections of the buildings is one of the main sources of uncertainty. The common damages observed after credible earthquakes were falling off large-span beams and large plastic deformations at the column base. New generation Lead Extrusion Damper (LED) developed by the authors is utilized in the seismic retrofitting of these buildings in use. This paper discusses the seismic performances of pre- and post-behaviour of the retrofitted buildings and evaluates the efficiency of the applied retrofitting technique. It is exposed that seismic demands are diminished essentially. The relative storey drifts decrease by about 40-90% while the reduction in the strain at the column base section reaches to 70%.