An internal investigation into last month's collapse of a concrete floor at the new Louisville arena construction site blames the incident on human error.Executives from the arena's construction manager, M.A. Mortenson Company, told the Louisville Arena Authority that the concrete subcontractor failed to properly shore up the floor. The collapse injured three workers.Arena Authority Chairman Jim Host says he's satisfied with Mortensen's assessment of the mishap."We did not have what can be considered as pleasant conversations. they were very direct, very, very...we asked a lot of questions and we engaged our own counsel to check and recheck things," Host said.Host says the authority's lawyers also thoroughly investigated a construction worker's comments to a TV station that complaints about safety at the site had been ignored, but found no corroborating evidence.Mortensen executives say safety procecures at the site have been bolstered in the wake of the mishap, which will not affect the project's budget or schedule.A state OSHA investigation continues.More information about the investigation is available here.