Irreparable damage to a building in Kobe by the 1990 earthquake

Saving people’s lives from the disastrous results of major earthquakes is the most important part of California’s building codes, as indeed it should be. But what about saving the lives of buildings?

We bring this subject up because an extreme seismic event is likely to damage buildings – even those constructed in compliance with the current codes – to such a degree that repairing them would be the equivalent of re-building them. Their destruction and re-building would involve a huge expenditure of energy and carbon emissions which, in effect, would cancel whatever energy-saving measures had been used in their construction and operation.

What is being done to ameliorate this crippling situation? Examples of structural components that could lessen the damage to the building frame and the consequent huge cost of repair are being developed. One such component, the Pin-Fuse Joint, was  patented in 2004 by Mark Sarkisian, structural engineer and director in the firm SOM.

A model of the Pin-Fuse Joint

The Pin-Fuse Joint operates in much the same way as some joints in the human frame; for example, the movement of the shoulder joint, as  shown in the drawing below.

Pin-Fuse Joint comparison.

As shown above, the horizontal steel beams end in a circular plate that connects to the steel of the associated columns within the moment-resisting frame. The  columns connect the curved steel end plates. A steel pin or hollow steel pipe in the center of the moment-frame beam provides a well-defined rotation point. Under typical conditions including wind and moderate seismic events, the joint remains fixed if the exterior forces do not overcome the friction resistance provided between the curved end plates. In an extreme event, the plate is designed to rotate around the pin joint, with the slip-critical bolts sliding in long-slotted holes in the curved end plates. With this slip, rotation is allowed, energy dissipated, and “fusing” occurs.

Pin-Fuse Joint comparison. All pictures and drawings appear courtesy of SOM.

The rotation of the Pin-Fuse Joint during extreme seismic events, depicted above, occurs sequentially in designated locations within the frame. As the slip occurs, the building frame is softened. The dynamic characteristics of the frame are altered so that smaller forces are attracted to the frame and deformations are reduced. After the seismic event, the elastic frame finds its pre-earthquake position. The brass shim located between the curved steel plates provides the predictable coefficient of friction (0.4) required to determine the onset of slip and enables the bolts to maintain their tension with Belleview washers from the original tightening. The joints re-establish their fixity after the earthquake.

Given the threat of catastrophic earthquakes in the Bay Area and other heavily populated centers of our state one would think that this and other such eminently useful structural components would be recognized by building codes. But this has not happened.

Surprisingly, the Leadership in Energy and Environmental Design organization, the LEED, which awards building designers by giving points for energy conservation and environmental responsibility, does not recognize environmental impacts related to the construction process. Points are given for using recycled products such as rebar, but there is no overall recognition of the environmental impact of buildings at the time of their construction and throughout their existence.

Furthermore, even though need for reducing the carbon footprint of buildings is something we hear about on a regular basis, the LEED does not address how the issue figures in the overall creation of the structure. What kind of leadership is this?

The Brower Center at Oxford and Allston Streets.

The recently completed David Brower Center in downtown Berkeley is a memorial to a major figure in this country’s environmental movement. Brower served as the first Executive Director of the Sierra Club from 1952 fo 1960 and later founded such environmental organizations as Friends of the Earth, the League of Conservation Voters, and Earth Island Institute. He inspired a generation of environmental activists, some of whom now work in the building at the intersection of Allston Way and Oxford Street that bears his name.

Thirty some national and international groups occupy 24,000 sq. ft. of office space on the building’s upper three floors. Their mission is to foster collaborations, engage new people in advocacy and facilitate cross-sector communication and partnerships.

Although the work of the building’s tenants is a story in itself, the subject of this article is the Center’s building design and its structural system, which were created to insure that the physical embodiment of Brower’s legacy would be a state-of-the-art expression of his life’s work. The building is on track to receive a LEED platinum rating—the highest possible—from the US Green Building Council.

Plans show the shape of the site and the Brower Center's rounded facade derived from the street corner it faces. Plans of the Oxford Plaza housing are shown on the right.

The building’s site is unusual in that the corner it faces has a rounded edge. This feature prompted the architects, WRT/Solomon E.T.C., to design a rounded façade that enables a more natural flow of space than the typical right-angled street corner. Pedestrian traffic flows from the building’s entrance on Allston Street past the Center’s ground-floor restaurant, Gather, to a gated open space between the Center and the apartment complex, Oxford Plaza.

The building’s façade suggests a temple form with engaged columns set on a raised base, a slightly projecting attic story above, and a cornice, which departs from the classical type by continuing the solid array of photovoltaic panels on the south side with a slatted trellis that follows the roof line and rises as it curves around the eave from south to north like an upturned hat brim.

View of the Brower Center from a building across Oxford Street.
Both photographs on this page are by Tim Griffith.

The panels’ downward slant on the south side moderates the greater amount of daylight entering the building from that direction and reduce heat gain in the summer; their upward tilt on the north side increase the admission of light to meet the seasonal greater need. Measures like these have made the interior nearly 100% daylit.

In respect to materials, the metal used for the façade is zinc, which requires less energy to mine and work into forms than aluminum or steel. Its matt surface avoids glare. The window glass redirects sunlight and thereby reduces heat gain. Operable window sections allow changes in ventilation.

The concrete used in the building is 70% blast furnace slag in the foundation and 50% slag in the super structure. The use of this by-product of manufacturing steel reduces the building’s energy content and its “carbon footprint” by 40%. The Brower Center is the first Bay Area Project to use high-slag concrete on such a scale.

OUTSIDE THE MUSEUM

The building’s long gently mounded form recalls the park’s original topography of sand dunes. The dunes are long gone and, given the park’s lush vegetation, it is even hard to imagine them. Still, it is sand, not dirt, that exists beneath the park’s man-made surface; tons of it were hauled away during excavation for the new building.

At the museum’s southwest end the downward sloping roof ends in a cantilever that overhangs the terrace outside the cafe. The terrace merges with the Barbro Osher Sculpture Garden, which shades into the Japanese Tea Garden beyond. A tower at the northeast corner commemorates the one that rose above the former building. The two structures link the museum to its narrow site between the Music Concourse and the John F. Kennedy Memorial Drive to the larger park.

The architects’ desire to have the building blend into the park led to their wrapping it in a skin of textured copper based on photos of the park’s tree canopies. The photos were converted into abstract patterns embossed in the form of “dimples and pimples” with different degrees of depth, which were stamped on the copper panels that camouflage the structure.

The perforated panels, used where the intake or exhaust of air was needed, have punched holes of different sizes that follow orthogonal patterns.

This effect was not achieved effortlessly because the building’s surface requirements and its geometry varied with the panels’ location. A special team assumed the task of attaching the 7,200 panels–no two alike–to the structure. Although the perforated skin does not give the building a gauzy transparency, sunlight creates a continuous rippling effect over the walls that conveys movement.

At this writing the copper skin has darkened to an unappealing cinnamon color that makes the building go dead on foggy days and has prompted comparison to a rusted aircraft carrier. But when oxidation has turned the copper green the building will merge more harmoniously with its leafy surroundings. The designers saw the gradual greening as a natural cycle in keeping with that of the park. Yet, even they may not have realized that, in the opinion of some metallurgists, San Francisco ’s mild climate may cause this process, if unaided, to take a half century or so to occur.

The landscaping that Walter Hood designed for the museum’s front yard addresses subtle issues of maintenance and use. The palms, some of which already existed, provide tree presence without requiring trimming to prevent hiding the building. From the drive between the Music Concourse and the museum’s facade the viewer sees the palm trees rising from an unbroken carpet of grass. But as the entry path is approached, a series of narrow stone paths appears to connect the areas on either side of the walkway. Benches are set intermittently on the paths.