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EARTHQUAKE DAMAGED FOUNDATIONS
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FOOTING & FOUNDATION DRAINS
FOOTINGS EXPOSED, Repair Methods
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FOUNDATION CONSTRUCTION TYPES
FOUNDATION CONTRACTORS, ENGINEERS
FOUNDATION CRACKS & DAMAGE GUIDE
FRAMING DAMAGE, INSPECTION, REPAIR
GRADING, DRAINAGE & SITE WORK
GUTTERS & DOWNSPOUTS
INSECT INFESTATION / DAMAGE
MOBILE HOMES, DOUBLEWIDES, TRAILERS
MODULAR HOME CONSTRUCTION
MOISTURE CONTROL in BUILDINGS
RETAINING WALL DESIGNS, TYPES, DAMAGE
RETAINING WALL GUARD RAILINGS
STRAW BALE CONSTRUCTION
STRUCTURAL DAMAGE PROBING
STRUCTURAL WOOD ASSESSMENT
THERMAL EXPANSION of MATERIALS
TIMBER FRAMING, ROT
WATER BARRIERS, EXTERIOR BUILDING
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Foundation damage due to earthquake activity: this article describes how we recognize different types and causes of complex or combined building foundation movement & foundation damage. Earthquakes shake building structures in different patterns, sometimes unique to a particular quake. The basic earthquake-generated forces that operate on buildings are side to side, up and down, or a combination of these. But depending on which forces are exerted, buildings shift and structural components fail in different patterns. Here we describe different damage patterns observed in building foundations or structures due to several different types of earthquakes.
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The photographs of earthquake-damaged building foundations and structures shown here are rather dramatic (and terrible as there were certainly fatalities in these buildings). More subtle is the detection of small movements, not immediately obvious, that break gas mains or cause other dangerous building conditions following an earthquake.
Here we distinguish among vertical movement, horizontal movement, leaning, tipping, bending, differential and uniform settlement, earthquake and storm damage, and other foundation damage patterns.
This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
To be used properly, this information must be combined with specific on-site observations at the particular building in order to form a reliable opinion about the condition of that building's foundation.
Watch out: Anyone having concern regarding the structural stability, safety, or damage of a building, foundation or other components, should consult a qualified expert.
Types of building movement: Northridge Earthquake 1994
As we describe here, the effects on buildings and how they moved or collapsed. Some building sections collapsed straight down while others were levered sideways by their supporting columns, moving sideways for a distance about equal to the height of the failing columns. Types of building collapse or movement depended on both the combination of directions earthquake forces and construction details of individual buildings.
At the 1994 Northridge Earthquake in Los Angeles, a very strong lateral shift was visible on many buildings. Force was sufficient to shift some entire buildings sideways in distances ranging from just an inch or so (broken gas mains, gas explosions, fire, burst water mains) to distances up to eight feet (where buildings were leveraged sideways as supporting columns failed). We observed:
1. Vertical Building Collapses due to Earthquake
The Northridge Earthquake in Los Angeles, California in January 1994 caused extensive damage as well as fatalities when buildings were shifted off of their foundations, leading to catastrophic collapse in some cases.
These photographs taken by the author at Northridge Meadows, a site of some of the worst fatalities, shows a section of building that collapsed straight down, compressing the first floor (and some occupants) to just a few inches.
The left portion of the photo shows a third floor balcony aligned with the second floor balcony of a building segment that did not collapse. Earthquake resistant construction has as a primary objective to prevent just this sort of collapse, as an effort to reduce the number of injuries and fatalities from an earthquake.
Examination of construction details such as the sequence of original construction and the failure to continue staggered plywood sheathing and continuous floor joist framing appeared to explain why the right-hand portion of the building stood while an entire floor of the left-hand building section collapsed, killing occupants of the first floor.
2. Horizontal Building Movement due to Earthquake
But there were more subtle failures at work - hollow steel pipes that failed where concrete-filled steel Lally columns should have been installed. The bent steel column (photo at above left) illustrates how a failing structural column, supporting foundation wall, or supporting knee wall can also lever a building sideways for a distance approximately equal to the column height.
Our photo at below left shows one of the bent, failed Lally columns. The building wall in the background of the photo was previously supported on top of this column. This photograph was taken at the rear of the apartment building shown in the pair of photographs above.
At below right our photograph shows that the bent Lally column top shows that the column was hollow. Like other Lally columns that bent over completely leading to building collapse and sideways shift, this column had been wrapped in a fire-barrier coating. An external inspection of the column after construction could not, without more sophisticated testing, disclose that the builder had use hollow steel rather than a properly-constructed concrete-filled column.
Structural engineers and experts with more experience than the author have examined this catastrophe. But we thought it worth noticing that some of the Lally columns that failed were hollow steel posts while others that remained standing at the same building project were ones that had been filled with concrete to resist bending. We wondered if the schedule-pressure of original construction at Northridge Meadows contributed to use of columns that were not what was called for.
This photograph (above left) shows an easy-to-determine case of significant lateral movement of a wood frame structure.
Often an improperly secured crawl space cripple wall simply leaned over, levering the building to one side for a distance equal to the height of the collapsing (cripple wall).
In this case the collapse was of a wood-framed supporting wall, not a masonry foundation.
The cripple-wall height of single family homes in the area was typically less than four feet. As a result both sideways and vertical collapse distances were less severe than those endured by sections of Northridge Meadows apartments that had been supported on eight-foot Lally columns designed to give parking space below the building's first occupied floor.
Combination of movements due to earthquake damage is demonstrated by the photograph above of an un reinforced stone masonry foundation and wall home in California. Un reinforced concrete structures are no longer permitted by California building codes for construction in areas of earthquake risk.
Continue reading at EARTHQUAKES, MAN-MADE
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Frequently Asked Questions (FAQs)
Is there anyway to prove earthquake damage to a foundation? I have a single story ranch house built in the 1930’s that has recently been subjected to a mild earthquake in 2009 and 2011 (Midwest) both of which I felt the house shaking and was awaken from a sound sleep.
I have glass block windows that have started to splinter in one of the sections of my basement. Started first sometime after March 2011 when I notice the blocks were cracked.
A couple of weeks later I found glass fragments splintering from blocks. Been watching it periodically then forgot until yesterday I found several larger pieces of glass block…corner pieces on two of them. The mortar that holds the blocks in window area show cracking as well. This would indicate to me that there is still ongoing stress to my frame house which is causing continual splintering from the glass blocks.
I contacted a structural engineer who said it was not possible by looking at it to tell whether it was earthquake damage or not. He indicated soil testing would have to be done which would be very expensive.
I am concerned that my home or at least parts of it will collapse. I have contacted my insurance agent but they do not provide any services of which to tell if it is earthquake related or not.
If you have any referrals or helpful information, I would appreciate it. - Thank you,- B.O. in Missouri
Reply: Expert, experienced inspectors should be able to form a reasonably confident opinion about building damage, extent, and cause
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with the structure, its history, probable cause, and extent of impact on the building and its safety.
I'm in no position by mere email to argue with your engineer, but having inspected a very large number of earthquake damaged buildings (while serving the Red Cross) it is my OPINION that an inspector, contractor, home inspector, or engineer who has familiarity with earthquake damage in general as well as with specific earthquake activity in a particular area can recognize the presence of damage to the building structure and form an opinion about its general safety.
If inspected by an experienced diagnostician, typical causes of building structural movement can almost always be traced to a probable cause. In all cases of building foundation or other structural damage, understanding the cause of the damage is an essential part in planning for the necessary repairs.
For example, lateral or horizontal "shaking" by an earthquake is likely to damage all sides of a building while differential settlement due to soil problems tends to cause focused cracking, bending, leaning etc. If the cause of foundation damage is inadequate footings the repair requirements may be quite different from earthquake damage.
I am unclear why soil testing is a high priority step in evaluating the building;
The first order of priority, which should not be delayed, is an inspection of the property for safety and safe occupancy. Unless your property actually has no significant damage of any kind (regardless of origin), that inspection needs to be performed for your own safety regardless of arguments about the root cause.
Watch out - some safety defects that may be present following an earthquake as well as following other structural movements or damage can be subtle such as gas leaks and unsafe electrical wiring - even if the visible structural damage is minimal. At Northridge following the LA earthquake some buildings were very extensively damaged by the side to side movement of the earth during that event. But other buildings looked just about perfect, still sitting square on their foundations. Yet some of those "perfect-looking" structures were unsafe due to gas leaks that risked (and in some cases occurred) explosions and fires caused when subtle building movements damaged the utility lines.
Question: our newly built townhouse vibrates and shudders and we hear banging
Just moved in to a new build town house which vibrates constantly and suffers with shuddering (top/3rd floor more noticeable with windows also shaking). On ground floor can sometimes hear banging, like someone has jumped or dropped heavy object from above. On a main road but this does not always happen when heavy vehicle drives past. Also suffering noise from pipes/ventilation outlets. - Lesley Anne 12/29/2011
If the building movement and noises you describe were due to an earthquake or ongoing temblers or tremors, you could quickly confirm that condition with your local emergency services departments and building department, or perhaps even neighbors, as other buildings would be experiencing symptoms as well.
If that is not the case, then what you describe sounds specific to your individual building. Because some building movements, vibrations, and sounds can be symptoms of a pending catastrophic collapse, it makes sense to ask for expert advice promptly. An expert will listen to your concerns and will make his/her own thorough inspection of the structure both outdoors and inside, looking for
Indications of actual building movement and related damage, such as cracks, separation of framing, sticking windows or doors, floors or ceilings out of level, walls out of plumb.
Indications of foundation movement or damage such as cracks, leans, bulges, bows.
The purpose of the initial assessment of building condition will focus on the discovery of signs of an immediate life safety hazard. If that sort of hazard is comfortably ruled out, what remains may be construction methods and materials issues to review with the building owner, contractor, or an independent professional structural or civil engineer who is familiar with the type of construction used for your building.
Keep us posted, what you learn may assist other readers.
Questions & answers or comments about how to recognize, diagnose, evaluate, and repair building foundation damage due to earthquake activity.
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