Why do buildings collapse in earthquakes? Building for safety in seismic areas. Robin Spence

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Why do buildings collapse in earthquakes? Building for safety in seismic areas - Robin Spence


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costliest disaster, and indirect losses from the nuclear reactor failure continue to rise. The total casualties resulting from the event have been estimated over 18000. The vast majority (>90%) of these were deaths by drowning, directly caused by the tsunami, but significant numbers of casualties (>4%) were crush injuries caused by the collapse of buildings over a wider area. As in Christchurch, the scale of the damage was largely because the buildings and the sea defences were not built to withstand the effects of an earthquake of that magnitude. At that time, the maximum magnitude envisaged in the Japan trench, on which building and coastal defence design was based, was Mw8.4.

Photo depicts typical damage in tsunami-affected region. Timber frame building in Kamaishi City at a location with a maximum of 7 m inundation.

      Source: EEFIT. Reproduced with permission.

Photo depicts typical damage in tsunami-affected region. Steel frame building in Yamamoto-cho, Miyagi Province which was struck by a tree trunk in the debris flow.

      Source: EEFIT. Reproduced with permission.

      Overall, data collected by the National Police Agency (NPA) in November 2011 (NPA 2011) showed that 120 157 buildings were totally destroyed and a further 830 000 buildings had been damaged.

      2.2.10 The 25.4.2015 Gorkha Nepal Earthquake: Mw7.8, 8831 Deaths

      Observations on building construction and damage are taken from the reports of the EEFIT and EERI reconnaissance missions (EEFIT 2015; EERI 2016). According to these reports, in both urban and rural areas of Nepal, masonry construction predominates. In the urban areas, many buildings are of three to four storeys in height, and built in close proximity to each other. Masonry is constructed using fired brick, which is laid in a lime or mud, sometimes cement, mortar. Floors and roof structures were traditionally of timber (floor planks on joists), and in better‐built houses these were connected by pegs to wall plates to prevent overturning (EEFIT 2015). More recent masonry buildings have RC floor and roof slabs. Urban areas also have a proportion of RC frame buildings, with masonry infills. Few are built according to the Nepalese code of practice or guidelines for concrete buildings, and there is no inspection (EEFIT 2015).

      In rural areas masonry construction is low‐rise, using local stone or brick, with a lime or mud mortar. As in urban areas, floors have timber beams and roofs use timber beams or trusses covered with a lightweight tiles or metallic sheet.

      Many important heritage buildings, including temples, were seriously damaged or destroyed by the earthquake. There was evidence though, that retrofitting of some traditional masonry buildings using wall ties had been effective. And the work of the National Society of Earthquake Technology, NSET, in strengthening school buildings, and in creating guidelines for improving earthquake safety of rural buildings, was considered by EEFIT (2015) to have protected many buildings from serious damage (see Chapter 7).

Photo depicts typical damage to masonry construction in urban areas of Nepal.

      Source: EEFIT. Reproduced with permission.

Photo depicts typical damage to masonry construction in urban areas of Nepal.