It is impossible to predict precisely the damage a building will experience in a future earthquake, because each earthquake is unique, and building simulations only model approximate responses to shaking. Losses due to earthquakes are even more unpredictable because they depend on the post-eartahquake actions of individual owners, insurers, design professionals, building officials, and contractors. Nevertheless, property investors need to understand the risk associated with property investments. Seismic risk assessment reports have become standard practice in financial due diligence.
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Author Archives : Ronald O. Hamburger, S.E. SECB
Ronald O. Hamburger (rohamburger@sgh.com) is a senior principal at Simpson Gumpertz & Heger in San Francisco.
Located at 301 Mission Street, the 650-foot-tall Millennium Tower was designed to be San Francisco’s premier residential address. The project geotechnical report predicted 4 to 6 inches of settlement over the project’s life; however, as construction neared completion in 2009, the settlement had already reached 10 inches. As development occurred on adjacent parcels, accompanied by continuous dewatering of the surrounding soils, settlement continued. By 2014, instrumentation installed to monitor the effect of adjacent construction recorded that the mat had dished, settled nearly 14 inches and that the roof had tilted to the northwest a similar amount. As the City of San Francisco threatened to red tag the building, counsel for the developer, Mission Street Development (MSD), retained Simpson Gumpertz & Heger (SGH) to determine if the settlement had damaged the structure and created a safety issue. Although SGH found that settlement had not appreciably affected the structure’s adequacy, in 2015, with settlement exceeding 16 inches, litigation ensued between the homeowners’ association, MSD, the City of San Francisco, and the development teams for adjacent projects. Under the terms of a negotiated settlement, SGH designed a foundation stabilization upgrade that formed the basis for dispute resolution and is currently under construction. This article focuses on the structural aspects of the problem and the upgrade.
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The Earthquake-Resisting System that Surprised the Profession
This is one of a series describing surprising lessons engineers have learned from earthquakes and, in particular, the January 17, 1994, Northridge earthquake. Engineers have been learning from earthquakes for more than 100 years by observing the patterns of damage earthquakes have caused in the built environment. Sometimes, things only partly true were part of the lesson, discovering the mistake only after a later earthquake causes unexpected damage. Such was indeed the case with steel moment frame structures and the 1994 Northridge earthquake. …
Most building codes worldwide have been developed to protect building occupant health and safety under likely loading, including earthquakes. Severe wind, snow, and live loads frequently occur during a building’s life. Therefore, in addition to protecting life safety, code requirements for these loads also result in a very low probability that buildings will be damaged by these loads. Earthquakes, however, occur rarely and most buildings never experience a significant earthquake. …
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ASCE 7-16 Now Available
After six years of intensive effort by nearly 350 volunteers, the 2016 edition of the ASCE 7 Standard on Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-16) is now complete and available for purchase through the ASCE bookstore (www.asce.org/asce-7). …
A Rebuttal
Jim DeStefano raises many good points as to the complexity of the building codes in general and the ASCE 7 standard in particular. I have made these same arguments many times over the years, in this same magazine and other venues. However, the challenges to adoption of ASCE 7-16 had nothing to do with code complexity or changes in design procedures. …
Please assist us in supporting the I-Code adoption of ASCE 7-16 and opposing the attempt to block the update to the 2016 edition of ASCE 7 Minimum Design Loads & Associated Criteria for Buildings and Other Structures for the International Building Code (IBC), International Residential Code (IRC), and International Existing Building Code (IEBC). …
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Past, Present and Future
Over the past twenty years, the seismic design value maps referenced by the building codes have undergone revolutionary changes, affecting the information they portray, the way they are developed and the design procedures that reference them. Many structural engineers, noting these constant changes and the effects on their designs, question why this happens and if it is necessary. This article presents a historic review of major developments in seismic design value mapping and a look forward to potential future changes. …
Rising to the Challenge of Coordination
Today’s building codes and the consensus standards they adopt – including ASCE-7, ACI-318, AISC-360, and others – are a complex web of inter-related documents. Each refers to, and in some cases, modifies or takes exceptions to materials contained in the others. Coordination of structural design standards among each other and with the building code takes proactive efforts from many groups. …
From Conceptual Design to Implementation
Over the past 15 years, and particularly following the events of September 11th 2001, there has been increasing demand to incorporate blast resistance in important government and commercial facilities. Exterior walls of such buildings are designed to withstand blast impulse loading without a failure that would endanger building occupants, either through penetration of harmful debris or pressure waves. Operators of petrochemical facilities are also concerned about similar explosive threats due to large accidental explosions. …