Damage to concrete structures due to the 1994 Northridge earthquake

Abstract

Observations on damage to concrete structures, due to the 1994 Northridge earthquake, are reported from a Canadian code perspective. Most of the damaged structures were older, nonductile, structures that do not conform to current design and detailing requirements. Concern is expressed about the seismic hazard of older Canadian structures having similar deficiencies. A significant number of parking structures suffered extensive damage and a number of precast concrete parking structures collapsed. Deficiencies in these structures include lack of proper diaphragm connections, a mix of gravity load columns with ductile framing, inappropriate number and distribution of shear walls, torsional effects caused by ramps, and the creation of short columns due to geometric features. This earthquake also demonstrated the deficiencies in connections of pre-1973 tilt-up structures. Key words: seismic design, earthquake, Northridge, structures, codes, concrete, precast concrete.

Performance of steel structures during the 1994 Northridge earthquake

“…The east end wall was constructed of a double wythe of solid masonry brick with nominal reinforcing in the cavity between the wythes. This end wall was very similar to the one in the Kaiser Medical Building which suffered a complete second storey collapse on Balboa Avenue (Mitchell et al 1995).…”

Existing prefab R/C industrial buildings: Seismic assessment and supplemental damping-based retrofit

“…Prefab reinforced concrete (R/C) buildings designed with older Technical Standards have shown poor response capacities during lowto-moderate earthquakes in the past two decades [1][2][3][4][5][6][7]. The main causes of the damage surveyed in these structures -sometimes involving partial or complete collapse -are the failure of roof purlins-to-roof girders, roof tiles-to-roof girders, girders-to-columns, floor slabs-to-beams, beams-to-columns, columns-to-foundation and cladding panels-to-columns connections; the low ductility of columns; the insufficient in-plan stiffness of the roof and floor systems; and the unfavourable interactions between cladding panels and connected columns or beams.…”

Development of the CanRisk earthquake injury model

“…For example, during the 1994 M6.7 Northridge earthquake, OFCs were responsible for approximately five fatalities and over 7000 injuries (McKevitt et al 1995). Therefore, the primary factor of injury prevention is the development of superior building codes that are strictly enforced (Lomnitz 1970;Coburn and Spence 2002) as well as active and timely implementation of structural and non-structural retrofits (Bruneau 1990;Mitchell et al 1995).…”