In recent years the railroads in this country have been placing a fabric pad between the tie plates and the ties in their track systems. These pads were initially installed to keep moisture away from that underplate portion of the tie surface where it can cause progressive destruction of the tie. A properly designed and constructed tie pad will be so securely stuck to the tie that it will become integral with it. Moisture and abrasive materials cannot penetrate the seal between the tie pad and the tie. It has also been reported that these pads reduce rail joint wear and roadbed raveling. Under the sponsorship of Bird and Son, Inc. the Engineering Mechanics Section investigated the actual motion of rail and ties in the field and determined to what extent various pads affect track and tie vibration.
This work consisted of two vibration surveys conducted on the New York, New Haven, Hartford Railroad at Old Lyme and at Westbrook, Conn. These surveys were performed on padded and unpadded tracks. Comparative vibration data were obtained for several different types of pads.
The instrumentation consisted of vibration pickups attached to the bottom flange of the rails and to the ties. Displacement pickups