Structural Forensic Analysis: The Hills of Rivermist, San Antonio, TX

Posted on 01/25/2010 by Jeff Lineberger, P. E.

When the forensic analysis of the earth movement and partial collapse of the retaining wall system in the Hills of Rivermist in Northwest San Antonio is complete, a clear picture of the cause and origin of what most residents of San Antonio rarely see:  An apparent slope failure and retaining wall collapse.  But did the retaining wall collapse cause the massive movement of soil downhill, or did the fill material on the slope overwhelm the retaining wall?

Slope failures are quite common throughout the United States, but they are a rare occurrence in the San Antonio area.  Robert Day in his book “Forensic Geotechnical and Foundation Engineering”,  notes that slope failures may be related to periods of prolonged moisture.  During the hot and dry summer period, the slope face (earth or fill) can dry and shrink.  During the rainy season or when excess water is introduced into the slope surface, the shear strength of the soil or fill diminishes downhill creep begins.   Slope failure occurs when the pull of gravity is greater than the soil’s  ability to resist it, and the earthen mass moves laterally or parallel to the slope of the hill.  Structural barriers such as retaining walls function to prevent the uncontrolled movement of earth or fill on slopes.  Gravity type retaining wall failure can occur when the weight of the earthen slope mass exceeds the resistance capacity of the retaining wall.

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Structural Update – Haiti Recovery Ensues

Posted on 01/21/2010 by Jeff Lineberger, P. E.

1.21.2010

The National Council of Structural Engineers Associations (NCSEA)

The National Council of Structural Engineers Associations (NCSEA) expresses its deep sorrow for the devastating losses suffered by the people of Haiti in the January 12th earthquake that struck Port-Au- Prince and the surrounding areas. It is our fervent hope that assistance of the United States and other countries around the world helps to alleviate the suffering to the greatest extent possible.

The Structural Engineering profession is committed to protecting the public safety; and a number of Structural Engineers are already participating in the rescue efforts in Haiti as members of search and rescue teams. The expertise of our members is vital to ensure the safe removal of debris and the design of temporary support shoring needed to extricate victims trapped in the rubble of collapsed structures.

NCSEA maintains a Structural Engineers Emergency Response (SEER) committee that consists of volunteer structural engineers across the country, trained in the structural engineering aspects of emergency response to earthquakes, hurricanes, and other natural or man-made disasters. The SEER Committee is currently communicating with the government and private sector to identify ways in which the structural engineering community can lend its talents, skills and experience. At the present time, however, public and private sector personnel are reminded that they should not self-deploy to affected areas. The United States Department of State is coordinating foreign disaster assistance, and U.S. assets should deploy only if tasked to do so by the State Department. The most urgent need at the present time is supporting ongoing disaster relief fundraising efforts. When requests for technical support are received through the proper authorities, NCSEA will look to its Member Organizations to provide trained volunteers.

The Haiti earthquake, as well as earthquakes in Turkey, India and China in the last decade, demonstrate the critical importance of designing structures in seismically vulnerable regions to meet the requirements of modern seismic codes, like the ones used by Structural Engineers in the United States for almost forty years. In addition to proper design, the process of construction and inspection must strictly enforce the design intent to ensure that the structures will protect the safety of the occupants in the event of a major earthquake. In the United States, even higher standards are set in our codes for critical buildings, such as hospitals, police and fire stations, and other structures needed for immediate post-earthquake response.

Vulnerable structures still exist in the U.S., similar to those that collapsed in Haiti. These structures are unreinforced masonry and non-ductile concrete frame buildings built before the mid-1970’s. Structural Engineers now have the tools, however, to evaluate and design retrofit schemes that can make these vulnerable structures safe from collapse. Some government agencies, major corporations and other building owners have taken steps to mitigate the hazard posed by vulnerable existing buildings; but more needs to be done if major cities and small towns in seismically vulnerable areas of the United States are going to be resilient enough to avoid the types of devastation suffered in Haiti and other countries when a violent earthquake strikes.

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In Haiti, Structural Engineers Begin to Survey Devastation

Posted on 01/21/2010 by Jeff Lineberger, P. E.

January 21, 2010

By Nadine M. Post
This article first appeared on Engineering News-Record

Damage from landslides is common in Haiti. In Port-au-Prince, there is widespread destruction of nonductile concrete structures. Many rubble or unreinforced masonry walls failed. The E-in-plan Presidential Palace in Port-au-Prince still has much of the first floor intact, with windows unbroken, but there is total collapse above the first floor. There is very light reinforcing evident in failed columns near the entry. At the port, there is a collapsed pier and cranes, and several buildings are under water. Extensive lateral spreading and liquefaction is evident.

These and numerous other on-site observations on damage from Haiti’s magnitude 7 earthqauke are from Eduardo Fierro, a principal of forensic and seismic engineer Bertero Fierro Perry Engineers Inc., Van Nuys, Calif.  Fierro is on the ground in Haiti surveying damage to bridges, industrial buildings, the port and more. His photos of structures with major and minor damage, along with his assessments, are available at http://www.eqclearinghouse.org/20100112-haiti/general-information/fierro-photos-part-2 (the Haiti Earthquake Clearinghouse). The Website is managed by the Earthquake Engineering Research Institute.

Fierro notes odd failures in buildings with minor damage. For example, in one building, there is a single broken window but the concrete and glass block appears undamaged. In another area, there is a concrete structure that collapsed but dilapidated wood structures adjacent show little sign of earthquake damage.

More engineers are leaving to do reconnaissance work. Seismic engineer, Kit Miyamoto, left Jan. 18 for Haiti with the nonprofit Pan American Development Foundation of the Organization of American States. Miyamoto will provide structural engineering expertise to support PADF disaster relief efforts. Miyamoto, CEO of Miyamoto International, will assess structural stability of damaged structures; identify safe access for PADF personnel; and assess the overall structural damage conditions and how these lessons may apply to other countries. Miyamoto’s reports from Haiti will be posted at www.miyamotointernational.com.

PADF, a natural disaster relief arm of the OAS, is sending emergency relief supplies including food, tools, telecommunications equipment and more. PADF will be working with civil protection authorities, the private sector and community organizations to provide immediate and long-term assistance.

The National Council of Structural Engineers Associations is reminding public and private-sector personnel that they should not self-deploy to affected areas. “The U. S. Dept. is coordinating foreign disaster assistance, and U.S. assets should deploy only if tasked to do so by the State Dept.,” says NCSEA, in a Jan. 18 press release. “The most urgent need at the present time is supporting ongoing disaster relief fundraising efforts. When requests for technical support are received through the proper authorities, NCSEA will look to its member organizations to provide trained volunteers,” says the release.

According to NCSEA, its structural engineers emergency response (SEER) committee, which consists of volunteer structural engineers  trained in the structural engineering aspects of emergency response to earthquakes, hurricanes, and other disasters, is currently communicating with the government and the private sector to identify ways in which the structural engineering community can lend its talents, skills and experience.

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