B757-200
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Object
Aircraft Aircraft Damaged; General Maintenance Action
Airport; Environment - Non Weather Related; Human Factors; Procedure
I was notified several hours after the termination of our flight; that the elevator on our airplane had received significant damage during pushback on our first leg departing.Sometime during our pushback on our initial leg; the aircraft made contact with an object/structure that caused damage to the elevator. I did not feel anything out of the ordinary that indicated some type of impact during pushback nor was the flight crew notified by the pushback crew that an impact had occurred. I did not feel any abnormalities through the flight controls or the airplane during all stages of flight on the first leg when I was the pilot flying. On the second leg (throughout the entire flight) I did not feel or notice any abnormalities with the aircraft while I was performing duties as the pilot monitoring. The FO did not mention that he noticed or felt anything abnormal with the aircraft during the entire trip. The FO performed preflights at both stations.The alarming thing about this situation is that an airplane unworthy to fly went unnoticed because the event occurred after the exterior inspection and was not felt/ seen by the flight crew or pushback crew.  Fortunately; the damage was not catastrophic enough to compromise the safe outcome of the initial leg. These type of events could probably be prevented by simply having extra ground personnel to monitor the pushback in critical spaces.
Aircraft damaged during pushback; neither pilot felt impact (structure and elevator region). Tug driver did not indicate/notice impact. Crew taxied out and departed and flew flight to our first destination. No flight degradation noticed. Deplaned in ZZZ1. Crew went inside to break room (no rest facilities present). Ramp workers in and out of break room. Since space was at a premium; First Officer immediately took suitcase back to aircraft. First Officer left building and approached aircraft from the rear: did not notice damage. First Officer walked back into break room and he and Captain spent a period of time eating and attempting to rest. Ramp Agent then recommended crew go back to aircraft to get better rest. Both Captain and First Officer then walked to aircraft; approaching from rear: neither noticed damage. Crew spent next several hours attempting to rest. First Officer subsequently performed walkaround. First Officer saw small amount of fluid on ground below right engine nacelle; looked and could not find any oil on nacelle. Did not see any damage to elevator region. Do not recall any other problems on walkaround...Maintenance Rep never mentioned seeing any damage during his inspection. Crew completed performance data and briefed the return leg. Uneventful flight. Notified by Safety of Incident.Causal Factor for pushback damage: Lack of attention.Causal Factor for not seeing damage prior to flying 2nd leg: Predominately a lack of attention by First Officer during walk around. Also a lack of attention by maintenance rep during his walkaround. An additional potential minor causal factor was insufficient rest during turn.
B757 flight crew and ground personnel reported the elevator unknowingly struck a building during pushback and flew two flights with the undetected damage.