EARTHQUAKE PREPAREDENESS: HOW DOES YOUR OFFICE STACK UP?

EARTHQUAKE PREPAREDENESS: HOW DOES YOUR OFFICE STACK UP?

By Craig Olson, PE and Greg Varney, PE
KPFF Consulting Engineers

Over the past ten years, seismic activity on the west coast has caused over $17 billion in property damage. The Northridge earthquake in 1994 was a wake up call for many business owners and developers. The lessons from this and other disasters has forced many to re-examine the performance criteria for their buildings. Building performance during an earthquake can change how a business or government agency functions. The economic implications for some businesses can be devastating.

While the current Building Code focuses on occupant safety, performance design targets a building's ability to function after an earthquake. Poor building performance increases the costs for business closure, damaged goods, lost data, repair and relocation. Owners are encouraged to focus on building performance to reduce the cost of an earthquake and increase the probability of continuing operations. Today's engineers work with a business or agency to establish the appropriate earthquake performance criteria. This criteria is incorporated into the design of new structures, renovation of existing buildings, preservation of historical structures, and the anchorage of a building's contents and mechanical and electrical systems.

The goals for building performance are determined by the owner's expectations for the building. This may include having a fully operational building, providing immediate occupancy, or simply maintaining a safe facility. In conjunction with these goals, the level of acceptable structural and non-structural damage can be determined. The design team must consider these issues to meet the expected performance when selecting the structural materials, simplifying the building layout, and incorporating redundancy into the building system.

New Construction

Traditionally and legally, new building construction conforms with the minimum earthquake provisions of the Uniform Building Code (UBC). Briefly, these are: 1) There should be no damage to buildings in a small earthquake; 2) There may be minor architectural damage, but no structural damage in a moderate earthquake; 3) There may be structural damage, but no collapse in a large earthquake. The code does not address building operations or damage to contents after an earthquake. Building owners who are concerned with the survivability of their property find that the building design must go beyond the Code. An appropriate building performance criteria can act as an added insurance for continued operations after an earthquake.

Building Renovation

Building renovations introduce more issues not relevant to those found in new construction. Working together with property owners, engineers can determine the desired level of performance for the renovated building. Sometimes they may decide to conform to the Code, at other times they may decide to conform to the less stringent provisions of the National Earthquake Hazards Reduction Program (NEHRP) Handbook for the Seismic Evaluation of Existing Buildings (FEMA-178). This handbook is designed to help engineers minimize the life safety risks to building occupants during an earthquake. It does not ensure that the business or agency will be operational after an earthquake, or even that the building will be salvageable.

Renovation of buildings with special historical significance, such as those buildings which are strongly tied to the community identity, may deserve a different structural solution; one that will preserve the historic fabric of the building as well as maintain life-safety conditions for the occupants. The 1992 renovation of the Old Federal Office Building in Seattle incorporated concrete walls to brace the existing frame while maintaining the building aesthetics. In some circumstances, sophisticated structural systems, such as base isolation or viscoelastic dampers can be combined with standard systems such as shear walls or braced frames to provide this higher level of performance for a historical building. The Pioneer Courthouse in Portland, Oregon, will be the first base-isolation of an existing building in Portland.

Contents Anchorage

In many circumstances, injury and loss of operation is caused by the movement of seemingly harmless items such as bookshelves, filing cabinets, light fixtures, personal computers and other incidental equipment. These items cause injuries when they are not properly braced to the building structure. Although the Building Code requires bracing some of these elements, savvy designers and owners are bracing more elements than required by code in new facilities. Unfortunately, these items are often not properly restrained in existing buildings. Because structural engineers are familiar with the forces involved in earthquakes, they can provide valuable services to owners who wish to survey and retrofit their facilities to minimize furnishing and office equipment damage, personnel injuries and the associated loss of operations. Many owners consider post earthquake operations essential. Agencies such as the Federal Emergency Management Agency (FEMA) and Safeco Insurance Company have retained our services to survey their facilities and assist them with retrofit designs for nonstructural items.

Mechanical and Electrical Equipment Anchorage

Loss of operations after an earthquake can also be attributed to the movement of unrestrained piping, ductwork, equipment, etc. These issues are addressed by structural engineers by the assessment of existing systems and the design of seismic anchors for all manner of equipment and distribution systems. While this restraint goes beyond the requirements of the Building Code, owners such as the Boeing Company have included these anchors in many of their new and existing buildings to improve the performance of their facilities in the event of an earthquake.

Special Facilities

In today's fast-paced business world, we rely more and more on technology-based facilities. The users and operators of emergency response centers, data storage centers, and medical facilities must have structures that are operational during and immediately after an earthquake. Structural engineers have several methods to achieve this higher level of performance. One solution uses base isolation to dramatically reduce the damage to these facilities. This innovative system uses rubber, steel or lead bearings, known as base isolators, to separate the building structure from the earthquake ground motions by acting as "shock absorbers". The University of Southern California Teaching Hospital, the first base-isolated hospital in the world, was operational immediately after the Northridge earthquake, while portions of St. John's Hospital in Santa Monica were closed for six months after the earthquake. Although base isolation can add up to 10% to the initial construction cost, this cost is quickly recovered through reduced earthquake damage, continued post-earthquake operations and preserving valuable contents.

Structural engineers learn more about building performance after every earthquake. Building owners and agency leaders are also learning that a building designed to conform with the Building Code may not be functional after an earthquake. By working together, engineers and owners can determine an appropriate criteria to drastically reduce the impact of the next earthquake.

Craig Olson, P.E. and Greg Varney, P.E. are both structural engineers with KPFF Consulting Engineers in Seattle.

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