The coastal communities of Oregon will be subject to the strongest shaking and a swiftly following tsunami. They will be leveled.
Portland is inland so there will be attenuated shaking, which makes our case harder to predict. There is a wide span that exists between Major Destruction and Minor Disruption. These are my prediction:
Lets start with the obvious: the many utility poles will topple or be taken out by falling trees, the power grid will be down... which means no cell phone service. There will be some water main breaks in areas of liquefaction and lots of breakages at the connections to individual buildings. Natural Gas supply lines will also suffer breaks, again most of them occurring where the feeder pipe reaches an individual building.
The combination of leaking natural gas and sparking electrical wires will undoubtably start fires across the city. The fire department's job will be complicated by the difficulty in moving through the debris-strewn streets, irregular water supply at hydrants, and the overwhelming nature of the disaster.
Structures:
Wooden Homes are statistically the safest in a quake, the wood can flex with the shaking and loading is usually low. As with all of these categories, outcomes will vary. Newer homes and those with only a single story will do best. Some wooden homes in Portland have been moved from where they were originally built, this was done frequently in the days before modern safety regulations made moves cost prohibitive. Many of these homes are simply sitting on a foundation created for them at the new site. Many will shake off of their foundations and fall into the basement or suffer partial collapse. Most wooden homes will remain at least partially inhabitable. Hardest hit will be wooden homes affected by ground subsidence, houses perched on the West Hills, Alameda Ridge and Mt. Tabor are particularly vulnerable. Some of the newer construction in Portland, such as Hawthorne Twenty-Six (All wood, 4 stories, hillside location) seems particularly likely to be uninhabitable after a major quake.
Steel/High Rise Construction Most of the residential buildings of this type are newer construction. Glass windows might shake from their frames and crash to the streets below. None will collapse. 100-year old 1st generation steel buildings, 10 to 15 stories each will suffer the worst. Soil liquefaction will be a big threat downtown, which is built on sandy wash from the Willamette River. Older buildings could tilt dramatically and sink into the ground. Buildings in Lloyd Center will be comparatively unaffected.
Reinforced Concrete Structures will suffer brittle failure of the concrete at key joints but should hold together due to their steel reinforcements. Given the widespread use of this building material it is easy to imagine some small collapses due to either improper steel reinforcement linking during construction or corrosion of steel reinforcements exposed to Portland's humid climate through unrepaired cracks. Most will be declared uninhabitable following the quake.
Unreinforced Masonry Structures These are the killers, the mortar simply cannot hold as the bricks or cinder blocks start shaking themselves apart. A few of these buildings have had expensive seismic retrofits. Most have not. Many are shops and warehouses. The SE Industrial District will suffer many collapses. Multi-story residential buildings present the greatest danger: The Ford Building at the corner of SE 11th and Division is chic, it will not be here after the quake
This cute apartment at 1405 SW Park is 3 stories, its right next to a modern building too, it could probably take advantage of this location in a seismic retrofit.
The beautiful 4-story Trinity Place Apartments in the Alphabet District have had a seismic-retrofit on the order of half a million dollars, for 36 units, thats ~$14,000 a unit for a dramatic safety improvement. Cheap insurance on a human life. The City has compiled a Listing of Unreinforced Masonry Buildings in Portland.
Bridges, this city isn't called bridgetown for nothing. Perhaps the signature Willamette crossings, the Steel Bridge and the Hawthorne Bridge have huge counterweights suspended in towers. These will try to remain stationary as the bridge shakes back and forth during the quake, when the weights bang against the steel towers they will produce tremendous forces that will destroy the towers.
The I-5 interstate bridge shares this vulnerability. The Burnside and Morrison Bridges have a chance at survival. The Freemont, Marquam and St. Johns bridges have the best chance for survival. The New Transit bridge designed with the most current seismic knowledge is likely to suffer the least.
However there is a weak link for all the bridges of the 20th century -- the approach spans are concrete/steel truss sections which will shake off of their supports and fall.
I wouldn't want to be under this approach span to the Hawthorne Bridge during the quake.
This approach to The Morrison Bridge looks to be just as dangerous.
The I-5 approaches to the Marquam Bridge have been retrofit with steel cables. They are designed to keep the steel road sections from collapsing even if they separate from their mounts.
Other I-5 connectors such as these flyovers where The Banfield Expressway meets I-5 appear not to have been retrofit and look like collapses waiting to happen.
Only the elevated sections of 99E appear safe. This newer construction has steel reinforcing ties between the deck and the support pylons that are surrounded by concrete.
Regardless of the extent of the actual damage all the bridges will be closed immediately following the quake so that engineers can assess their safety prior to reopening. Thus if you happen to be on the opposite side of the river from where you live, expect to be stuck... or swim for it... or wait to get on a boat. Impromptu ferry service is guaranteed to pop-up.
Lets start with the obvious: the many utility poles will topple or be taken out by falling trees, the power grid will be down... which means no cell phone service. There will be some water main breaks in areas of liquefaction and lots of breakages at the connections to individual buildings. Natural Gas supply lines will also suffer breaks, again most of them occurring where the feeder pipe reaches an individual building.
The combination of leaking natural gas and sparking electrical wires will undoubtably start fires across the city. The fire department's job will be complicated by the difficulty in moving through the debris-strewn streets, irregular water supply at hydrants, and the overwhelming nature of the disaster.
Structures:
Wooden Homes are statistically the safest in a quake, the wood can flex with the shaking and loading is usually low. As with all of these categories, outcomes will vary. Newer homes and those with only a single story will do best. Some wooden homes in Portland have been moved from where they were originally built, this was done frequently in the days before modern safety regulations made moves cost prohibitive. Many of these homes are simply sitting on a foundation created for them at the new site. Many will shake off of their foundations and fall into the basement or suffer partial collapse. Most wooden homes will remain at least partially inhabitable. Hardest hit will be wooden homes affected by ground subsidence, houses perched on the West Hills, Alameda Ridge and Mt. Tabor are particularly vulnerable. Some of the newer construction in Portland, such as Hawthorne Twenty-Six (All wood, 4 stories, hillside location) seems particularly likely to be uninhabitable after a major quake.
Steel/High Rise Construction Most of the residential buildings of this type are newer construction. Glass windows might shake from their frames and crash to the streets below. None will collapse. 100-year old 1st generation steel buildings, 10 to 15 stories each will suffer the worst. Soil liquefaction will be a big threat downtown, which is built on sandy wash from the Willamette River. Older buildings could tilt dramatically and sink into the ground. Buildings in Lloyd Center will be comparatively unaffected.
Reinforced Concrete Structures will suffer brittle failure of the concrete at key joints but should hold together due to their steel reinforcements. Given the widespread use of this building material it is easy to imagine some small collapses due to either improper steel reinforcement linking during construction or corrosion of steel reinforcements exposed to Portland's humid climate through unrepaired cracks. Most will be declared uninhabitable following the quake.
Unreinforced Masonry Structures These are the killers, the mortar simply cannot hold as the bricks or cinder blocks start shaking themselves apart. A few of these buildings have had expensive seismic retrofits. Most have not. Many are shops and warehouses. The SE Industrial District will suffer many collapses. Multi-story residential buildings present the greatest danger: The Ford Building at the corner of SE 11th and Division is chic, it will not be here after the quake
Bridges, this city isn't called bridgetown for nothing. Perhaps the signature Willamette crossings, the Steel Bridge and the Hawthorne Bridge have huge counterweights suspended in towers. These will try to remain stationary as the bridge shakes back and forth during the quake, when the weights bang against the steel towers they will produce tremendous forces that will destroy the towers.
However there is a weak link for all the bridges of the 20th century -- the approach spans are concrete/steel truss sections which will shake off of their supports and fall.
I wouldn't want to be under this approach span to the Hawthorne Bridge during the quake.
This approach to The Morrison Bridge looks to be just as dangerous.
Regardless of the extent of the actual damage all the bridges will be closed immediately following the quake so that engineers can assess their safety prior to reopening. Thus if you happen to be on the opposite side of the river from where you live, expect to be stuck... or swim for it... or wait to get on a boat. Impromptu ferry service is guaranteed to pop-up.
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