Earthquake Engineering
Building collapse: Most important secondary effect of
earthquakes:
-- "Man-made hazards"
-- "Earthquakes don't kill people; buildings kill
people"
Compare effects of 1988
Armenia and 1989 Loma Prieta eqs
Armenia: 25,000
deaths, 15,000 injuries, 500,000 homeless, $14B damage
--near-total destruction of Spitak &
Leninakan
Loma Prieta: 67
deaths, 3700 injuries, $7-8B damage
Large ratio death/damage @
Armenia. Causes:
(1) proximity to city
(2) poor construction techniques
(3) poor disaster preparedness/response
Preparation/construction DOES
make a difference
Kobe
(1995) ==> extreme damage to city, primarily in older, non-engrd buildings
EQ
Engineering: design of structures to
resist earthquake-induced forces
integration of: eq seismology, 'strong-motion seismology',
geotechnical engineering,
structural engineering
Key
problem: bldgs designed for 'dead
loads' (=weight of bldg + contents) = static
Bldg collapse <== 'superimposed
loads'
unusual weights
snow on roof
wind pressure
impacts
eq loads
EQs
==> 'live loads' = dynamic
Irregular
movement of ground ==> horizontal loads on building
Forces
applied at base
Real
earth: complex motions in 3 dimensions
EQ
forces ==> 'drift' of building
Critical
factors controlling damage:
(1)
forces acting on building:
EQ magnitude, proximity, depth,
interaction w/ soil (amplification)
(2)
duration of shaking
(3)
frequency of shaking
interaction w/ natural period of
building ==> resonance
natural period (sec) = 0.1 x no. of
storeys
(4)
response of building:
Horizontal
forces ==> drift (max. deflection
of bldg)
how will building respond?
ductility of building: (flexibility--opp. brittleness)
brittle materials: concrete, brick, adobe ==> cracks
ductile materials: steel! ==> flexibility
concrete w/ rebar ==> flexibility +
strength
collapse of Cypress Freeway:
failure of concrete in
tension & rebar in compression
structural joints: connections
between columns & beams, slabs, walls
tie structure together by
strong/flexible joints
almost all structural failures <==
failure at joints
Risk factors
(1) unreinforced
masonry
(2) shape of bldg: right-rectangular = safer
irregular bldg ==> torsion
(3) more openings ==> higher risk
--soft first storey (houses
w/ 2nd story over garage)
(4) importance of fixing house to
foundation
--anchor bolts = homeowners
mitigation strategy
(5) avoid changes in structural
system: foundation --> roof
--interruption
of shear walls
(6) danger from heavy roof materials
(7) hazards from 'non-structural
collapse
(e.g., ornamentation,
facades, marquees, etc.)
New
technique: focus on transmission of
force --> bldge
= base
isolation: set building on
bearings, rubber dampers
Building codes = legal docs adopted by cities/states to control
construction practices
include risks from fire, flooding,
storms, eq, etc.
= minimum standards; good engineers
==> exceed standards
other
factors controlling damage
quality of engineering, workmanship
poor materials
no enforcement
Critical
structures: dams, power plants, fire/police
stations, hospitals, schools
==> higher standards
Lifelines:
Transportation system: roads, railways, bridges, tunnels, airports
Power system: transmission lines, generating systems,
substations
Communication system: transmission lines, poles, substations
Natural gas pipelines, pumping/control
systems
Water system: pipelines, canals, aqueducts, reservoirs
Sewage system: pipelines, disposal facilities
Dependence
on Lifelines: critical element in
survival
Lesson in eq preparedness: self-sufficiency!