The closure, sparked when a 12ft strut sprang free from its metal connecting shoe, was confirmed by parliament presiding officer George Reid following a meeting with engineer Arup.
Mr Reid said temporary strengthening work could allow the chamber to be reoccupied between mid-April and mid-May but permanent additional stainless steel supports would need to be designed and procured, which “could take some time”.
Arup’s initial investigation into the beam incident has revealed that one metal bolt connecting the beam to its connecting shoe had failed and the other was missing. The thread of the failed bolt, which had its head missing, and socket were damaged, indicating difficulties during the original installation.
Arup said the bolt had suffered a torsional (twisting) failure which had probably been caused by the bolt becoming jammed and someone trying to remove it. Two further bolts from the strut’s top connection were found to be of differing lengths, casting doubt on the condition and adequacy of bolts elsewhere in the roof.
Engineers said there was a “very small risk” of further roof failure.
Parliament plenary sessions have been transferred to committee rooms.
