1886 Charleston Earthquake - Citadelmacs.citadel.edu/chenm/sigma_xi/Abs_Mays_slides.pdf · The...

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The GREAT 1886 Charleston Earthquake!

Timothy Mays, Ph.D., PEAssistant ProfessorDepartment of CEEThe Citadel

March 6, 2009

IntroductionPictorial Summary of DamageCitadel StudyMiles Brewton House ResultsCharleston City Hall ResultsConclusionsModern ConstructionAcknowledgments

1886 Charleston Earthquake

Slides Developed by Tim

othy Wayne M

ays, Ph.D., P.E.

The Citadel – Department of Civil & Environmental Engineering

Introduction

• Date: August 31, 1886

• Estimated Magnitude: 7.3

• Effect: damaged or destroyed more than 2,000 buildings

• Casualties: 60

• The earthquake caused structural damage as far away as Ohio, and was felt in Boston and Chicago

• 300 aftershocks were reported over the next 35 years



othy Wayne M

ays, Ph.D., P.E.


Introduction

• Intraplate earthquake: quake occurred away from tectonic plate boundaries

• Cape Ann, MA and New Madrid, MO

• Not very well understood seismology

• Most scientists believe that the faults are hidden (i.e., in the underlying rock)

• Faults do not extend to the surface so they are difficult to map



othy Wayne M

ays, Ph.D., P.E.


Introduction

• Several sand craterlet sites were reported parallel to streams in areas near the epicenter

1886 Charleston EarthquakeSlides D

eveloped by Timothy W

ayne Mays, Ph.D

., P.E.


Introduction

• Previous research shows liquefaction capable events every 500 years or so (Talwani and others)

PaleoliquefactionEvent (ybp)

11354617

100133168370

354886650381665800500



othy Wayne M

ays, Ph.D., P.E.


Pictorial Summary of Damage

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othy Wayne M

ays, Ph.D., P.E.


Pictorial Summary of Damage1886 Charleston Earthquake


othy Wayne M

ays, Ph.D., P.E.



People encamped in the city park public square after the earthquake



othy Wayne M

ays, Ph.D., P.E.



Gable and out-of-plane wall failures



othy Wayne M

ays, Ph.D., P.E.





ayne Mays, Ph.D

., P.E.



• Stockton [1986] provides a historical summary of the earthquake’s impact on the city of Charleston.

• Robinson and Talwani [1983] provide a more technical summary of building damage based on insurance reports.

• [Parkins and Stewart, 1886], [Freeman, 1932] describe the damage to over 7,000 buildings in Charleston.

• Earthquake study performed by Dutton [1889].



othy Wayne M

ays, Ph.D., P.E.



Robinson and Talwani [1983] conclude that:

• Construction material was the single most important factor affecting earthquake damage distribution.

• Over 80% of the buildings damaged were of brick construction.

• 65% of all brick buildings and only 7% of all wood framed buildings suffered some type of damage.

• Since approximately the same percentage of brick buildings on fill were damaged as those on existing ground, the authors conclude that made vs. existing ground is a secondary factor for masonry construction.

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othy Wayne M

ays, Ph.D., P.E.



• Many buildings in Charleston survived the 1886 Earthquake with little or no damage.

• Typical buildings suffered less than 10% of their sound property value [Freeman, 1932].

• Most pictures show collapsed buildings.

• How large was the 1886 Earthquake?



othy Wayne M

ays, Ph.D., P.E.


Citadel Study

• Luft and Whitman [1981] considers the structural analysis of the Old State House near Boston that survived the 1755 Cape Ann Earthquake.

• Since pictures capturing structural damage from the 1886 Charleston Earthquake are available, the approach is viewed as even more applicable to this seismic event.

• Miles Brewton House and Charleston City Hall are both multistory structures and unreinforced masonry shear wall buildings on existing soil (i.e., not fill).

• Both are located in the historic district of Charleston, SC.



othy Wayne M

ays, Ph.D., P.E.


Citadel Study

Miles Brewton House:

• Constructed in 1769 and altered in the 1820s and 1840s [Poston, 1997].

• Basement and perimeter walls are constructed of 30 inch thick masonry while the first and second story masonry walls are of 24 and 19 inch thickness, respectively.

• All interior walls above the first floor level are wood framed.

• Floor and roof diaphragms are constructed with 1-inch thick pine flooring attached perpendicular to the floor joists and roof trusses and the structure has a slate roof.



othy Wayne M

ays, Ph.D., P.E.


Citadel Study

Miles Brewton House:

• It is known that this structure survived the 1886 Charleston Earthquake with only minor damage.

• Insurance report states that the east wall was slightly cracked, but it does not recommend repairs or assign any dollar value to the damage.

• Although no pictures of the structure in its damaged state are known to exist, there is an account of a former resident stating that there was damage to the roof and the chimneys fell, but the walls were not cracked [Cote, 2003].

• Help from local contractor.



ayne Mays, Ph.D

., P.E.


Citadel Study

Charleston City Hall:

• Constructed in 1804 and altered in the 1839 and 1882 [Poston, 1997].

• Basement and perimeter walls are constructed of 46 inch thick masonry while the first and second story masonry walls are of 38 inch thickness.

• All interior walls above the first floor level are wood framed.

• Floor and roof diaphragm are assumed to be constructed with 1-inch thick pine flooring attached perpendicular to the floor joists and roof trusses.

• Previously had a metal roof that was added in the 1882 renovation.



othy Wayne M

ays, Ph.D., P.E.


Citadel Study

Charleston City Hall:

• A good picture [Cook, Date Unknown] of the damage to the building from the 1886 Charleston Earthquake exists.

• The cracking pattern manifests a multistory pier rocking mechanism that was preceded by spandrel failure.

• The insurance report details are consistent with the cracking shown.

• Field measurements from a previous project were provided by the Historic Charleston Foundation and a local architect who worked on the project.

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othy Wayne M

ays, Ph.D., P.E.


Citadel Study1886 Charleston Earthquake


othy Wayne M

ays, Ph.D., P.E.


Miles Brewton House Results

First Mode: T=0.228 s East Wall (2519 nodes, 2260 elements)



othy Wayne M

ays, Ph.D., P.E.


Miles Brewton House Results

Maximum Normal Stresses for First Mode (ksi)



othy Wayne M

ays, Ph.D., P.E.


Charleston City Hall Results

First Mode: T=0.267 s East Wall (3070 nodes, 2896 elements)



ayne Mays, Ph.D

., P.E.


Charleston City Hall Results

Maximum Normal Stresses for First Mode (ksi)



othy Wayne M

ays, Ph.D., P.E.


Conclusions

• Based on the structural analysis of the Miles Brewton House and Charleston City Hall using known damage assessments from the 1886 Charleston Earthquake, spectral accelerations from the 1886 Earthquake appear to be a fraction of those used by the 2003 International Building Code [2002] for the design of structures in Charleston, SC.

• It appears that unless material properties, crack patterns, and crack sizes are known, crack initiation is not a good damage level for predicting the magnitude of seismic events. The levels of uncertainty associated with assumptions results in bounds with too great a range.

• On the other hand, buildings known to respond with certain mechanisms that exhibit ductility can be excellent structures for estimating seismicity levels.

• The primary assumption associated with such structures appears to be the amount of ductility exhibited by the structure during the response.

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othy Wayne M

ays, Ph.D., P.E.


Current Research

• Senator Leatherman

• $50,000 project to study International Residential Code and to propose changes to seismic provisions

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