Photograph of building damage near Los Angeles 1994  © Daniel FriedmanHow to Detect, Diagnose, & Evaluate Earthquake Damage
Earthquake-Damaged Foundations, Structures, Chimneys, Mechanical Systems

  • EARTHQUAKE DAMAGED FOUNDATIONS -CONTENTS: How to Evaluate and Diagnose Complex Combinations of Foundation Movement Cracks, Bends, Leans, or Shifts in Foundation Walls. Different causes of foundation leaning, bulging, cracking, creeping, tilting, sliding, or other movements, what they look like, how to fix them.
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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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Combinations of Building Foundation Movement due to Earthquake, Flood, or Storm Damage

Earthquake damaged bulding (C)  Daniel FriedmanThe 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
  2. Horizontal building shifts, leans, tilts.
  3. Combined horizontal shift followed by vertical collapse of buildings. A lateral or horizontal movement that damaged building supports then led to both straight-down vertical collapses as well as combined horizontal movement followed by vertical collapse

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.

Photograph of building damage near Los Angeles 1994  © Daniel Friedman Earthquake damaged bulding (C) Daniel Friedman

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.

Earthquake damage (C) Daniel Friedman Earthquake damaged bulding (C) Daniel Friedman

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.

Photograph of building damage near Los Angeles 1994  © Daniel Friedman

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.

Photograph of building damagenear Los Angeles 1994  © Daniel Friedman

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.


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