On the morning of May 16, 1968, a minor gas explosion blew out the exterior walls of apartment 90 of the Ronan Point apartment tower (London). This triggered a progression of failures, resulting in the collapse of the southeast corner of the tower. This collapse revived the intellectual debate on structural collapse, and spurred a significant amount of research into disproportionate collapse and robustness of structures. As a result of this event, and the consequent report of the Commission of Inquiry, a number of countries implemented provisions to minimise the potential for disproportionate collapse. Following the recent terrorist attacks on the Murrah Federal Office Building, in 1995, and the World Trade Centre, in 2001, interest in this subject appears to have reached a peak. These events have highlighted the increased threat of terrorism worldwide and the need to consider hazards (explosions or detonations) that may not have been viewed as significant in the past.
Hopper is capable to assess structural robustness and disproportionate collapse by means of notional removal of key structural elements. The applied element method allows to easily estimate the percentage of collapse per floor in order to capture if the building remains stable and that the area of floor at any storey at risk of collapse does not exceed 15% of the floor area of that storey or 100m2.