Untitled Quiz

Earthquake Structural Damage

• A soft story is a story in a building with less resistance to earthquake-induced stresses than the stories above or below it.

• Soft stories often occur on the ground floor due to open public areas.

• Earthquake-induced building movement stresses the soft story on the ground floor more than other stories.

• Earthquake ground motion in buildings searches for structural weaknesses.

• Weaknesses are caused by changes in stiffness, strength, or ductility.

• Poor reactive mass distribution compounds these effects.

• Severe structural damage in modern buildings highlights the need to avoid sudden changes in lateral stiffness and strength.

• Sof stories often cause serious problems during earthquakes.

• Avoiding soft stories requires even distribution of flexibility, strength, and mass.

• Historical examples of soft story damage are seen in buildings in Turkey, Nepal, etc.

Inspection of Earthquake Damage

• Earthquake damage inspection and analytical studies show that structural systems with soft stories can lead to significant problems during severe earthquake ground shaking.

• Examples highlight the need to use consistent distribution of these factors.

Soft Story

• In shaking a building, an earthquake ground motion will search for every structural weakness.

• These weaknesses are usually created by sharp changes in stiffness, strength and/or ductility, and the effects of these weaknesses are accentuated by poor distribution of reactive masses.

Severe Structural Damage

• Severe structural damage suffered by several modern buildings during recent earthquakes illustrates the importance of avoiding sudden changes in lateral stiffness and strength.

• A typical example of building damage due to a "soft story" is cited.

Inspection of Earthquake Damage

• Inspection of earthquake damage, as well as analytical studies, demonstrates that structural systems with a soft story can lead to significant problems during severe earthquake ground shaking.

• Examples emphasize the need to avoid soft stories by using an even distribution of flexibility, strength, and mass.

Pancaking

• Pancaking occurs when earthquake shaking causes a soft story to collapse, leading to the complete failure of the overlying floors.

• The resulting crushed floors form a stack-like structure from one floor to another, similar to a stack of pancakes.

• Pancaking of reinforced concrete multistory buildings was common throughout the earthquake-stricken region of Turkey due to the Izmit earthquake on August 17, 1999.

• Examples of this type of damage are documented in specific figures.

• The damage caused by pancaking is attributed to the presence of soft lower stories and insufficiently reinforced connections at column-beam joints.

• Most buildings with this type of damage had soft stories with open spaces and shallow foundations which offered limited lateral resistance to seismic activity.

Pounding Damage

• Pounding damage occurs when two closely constructed buildings collide during earthquake shaking.

• Even if the buildings have different constructions or heights, pounding can still occur if they are close enough.

• Pounding damage is often more impactful in cases where one floor of a building hits the supporting column of an adjacent building, at different elevations.

• An example of pounding damage is the Anchorage-Westward Hotel in Alaska, damaged during the Prince William Sound earthquake in 1964.

• Figure 4.17 illustrates a case in Mexico, where the restaurant building next to the parking garage prevented collapse of the lower floors.

• In a case featuring a taller and/or squat building, the buildings will vibrate at different frequencies and amplitudes causing collisions.

Impact Damage from Collapse of Adjacent Structures

• The collapse of one structure can lead to damage to nearby structures.

• An example from the Izmit earthquake of 1999 shows a building that lost a corner column due to neighbouring buildings collapsing.

• Note that the roof of the collapsed building now rests at the third-story corner of the adjacent standing structure.

• Geotechnical engineers and earthquake geologists need to analyze and evaluate potential collapse of adjacent buildings based on poor soils or geological hazards.

Asymmetry

• Asymmetric buildings (T-shaped or L-shaped) can experience greater damage during an earthquake.

• The different segments of asymmetric buildings are usually stiffer and more resistant along their longitudinal axes rather than across the segments.

• The damage often occurs at the junction of segments.

Shear Walls

• Shear walls are structural components that hold adjacent columns or vertical supports and transfer lateral forces to the foundation.

• Forces on shear walls are predominantly shear forces, but for slender walls bending is also an issue.

• Examples of shear wall failures are documented for the West Anchorage High School (during a 1964 earthquake)

• Several common problems associated with shear walls include inadequate strength and inadequate attachment to the foundation.

• Discontinuities between floors can create a soft story condition.

• Even properly designed shear walls may not prevent collapse if severe building settlement occurs due to seismic activity.

• Shear wall failure modes have been observed in recent earthquakes.

Wood Frame Structures

• While generally resistant to earthquakes, poorly constructed, aged wood-frame structures are especially vulnerable.

• The 1995 Kobe earthquake saw significant damage to wood frame structures.

• Age-related deterioration, open first-floor areas, weak foundation connections, inadequate foundations, poor soil conditions, heavy roofs have all been identified as factors leading to wood-frame collapse.

Additional Earthquake Damage

• Many different types of structural systems can be used to resist inertia forces in a structure, which are produced by earthquake ground motion, including braced frames, moment-resisting frames, and shear walls.