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?

Pedestrian bridges, often called foot bridges, have been both separate from and part of vehicular bridges. As separate structures they were often constructed in rural or wilderness areas tied to trails rather than roads and were designed with a rustic look.

However, pedestrian bridges associated with urban areas are in demand now and often include bicycle usage. As shown by the three bridges presented here, the reduced scale of urban bridges and their proximity to human beings and nature no longer call for a rustic design.

Despite the fact that these three bridges have gained praise and publicity, the present economic downturn has given them uncertain futures. Hence the title “Bridges to Nowhere—for now.”

THE ST. PATRICK’S ISLAND BRIDGE, CALGARY, CANADA

Rendering of the St. Patrick's Island Bridge, Calgary, Canada

The St. Patrick’s Island Bridge in Calgary was designed in 2009 by Endres Ware* and Ammann & Whitney**, as a gateway to the activities of the island’s Centenary Park. The two-part bridge will also frame views of Calgary and the Rocky Mountains.

The bridges connect to a central platform located where they meet on a mound of earth to be constructed on a site in Centenary Park. The rendering shows a curved path on a mound leading to a ramp lifted up and attached by some of the cables to another land form behind the main pier. The bridges’ low arches, also visible in the rendering, rise just high enough above the underlying flood plain to avoid possible flooding but will not block views of the surroundings.

The bridges’ structure allows the weight of the concrete decks to be carried by a series of main cables running up to the two masts from which backstay cables transfer the deck’s weight back to the ground.

Site plan for St. Patrick's Bridge, Calgary

The two separate cable-stayed bridges, one longer than the other, span the Bow River flowing by the city of Calgary.

Night rendering of St. Patrick's Bridge, Calgary

The masts are bent to reduce their height. The main cables are strung evenly along the length of the masts; the backstay cables, gathered near their tops, are “harped”, meaning that the cables have different lengths.  They cables splay from the top of the mast downward and extend to the adjacent bridge, which reduces the amount of force necessary for their anchorage and allows the bridges to brace each other horizontally.

The bridges appear to bow to their respective destinations, the city and the neighborhoods on the riverbanks. One hopes that users from both places will be able to respond with their feet to their salutes in the not too distant future.

THE LEWIS EATON PEDESTRIAN AND BICYCLE BRIDGE

The Lewis Eaton Bridge

The Lewis Eaton Bridge project began in 2007 and was designed to enable pedestrians and bicycles to cross the San Joaquin River at a location near Fresno west of Highway 41, which is known as “the Yosemite Freeway.” The bridge is part of the efforts of The San Joaquin River Parkway and Conservation Trust to conserve the river, rehabilitate the surrounding land in the 100-year flood plain, and connect the City of Fresno with Madera County. The commission for the project was awarded to landscape architects Patrick and Jane Miller of 2M Associates as the prime and architects and  Endres Ware for the bridge design.

Site plan for the Lewis Eaton Bridge

Visible from Highway 41 as well as from the Fresno and Madera County river bluffs, the bridge will be a landmark for the San Joaquin River Parkway. A multi-use trail located on or parallel to the existing vehicular access road parallel to the river will provide an entry to the bridge.

The soil characteristics of the site were a major challenge to the design process. Although the ground on the west bank is stable the landing is on an island that may wash out in heavy flooding. The dry riverbed is not suitable for a landing because of possible flooding and poor soil conditions.

Diagram of the cable-stayed structure of the Lewis Eaton Bridge

The cables surrounding the bridge deck will provide a sense of enclosure and increase the deck’s stability. They will also create a “gateway” to views of the river by splaying down from the mast to the approach deck which passes under the it.

A gathering place for pedestrians at the bridge access path.

As the ramps descend from the mast to the ground, they will create a small area for people to gather in the tower’s shade .

Although Endres Ware and 2M Associates were commissioned to design the bridge and its surrounding landscape in 2010, a lengthy permit process of five years or more must be concluded before its construction begins. Although the design may change during the time required to gain final approval, one hopes the vision depicted in these images endures.

THE WEST END BRIDGE ADDITION FOR PITTSBURGH, PENNSYLVANIA.

The international competition, sponsored by ALCOA, for the West End Bridge Addition over the Ohio River in Pittsburgh, Pennsylvania,  was held in 2006. Endres Ware’s winning design for a new pedestrian crossing to be connected to the historic Bridge over the Ohio River respected the existing bridge while

The West End Bridge and the proposed addition, Pittsburgh, Pennsylvania.

updating the structure with a dramatic suspended bridge that will improve access for pedestrians, cyclists, and boaters to new recreation and park facilities.

Site plan of the existing bridge framed by the new pedestrian addition.

There are two access points for the bridge. One is a ramp on the bridge addition that runs down to the park ground below. The other is from the historic bridge at its westernmost tower. Pedestrian and bike lanes run from there along the south side of the bridge until they reach the shore.

A Rendering of the new pedestrian addition to the West End Bridge.

For Riverlife, the organization that managed the competition, the West End Bridge project is a top priority, and although funding for the bridge during the slow economy has been tricky, 70% of the work on the surrounding park lands has been completed, and hope for the rest is growing.

Related Links

• Endres Ware, Architects and Engineers
• Ammann & Whitney, Bridge Engineers

Endres Ware provided architecture and engineering services for the site, including the design of a bridge with a 105-foot span for pedestrians and light vehicles that leads to newly restored wetland areas.

Bridge deck plan

The wood deck of the pedestrian bridge, which is cantilevered from a torsion pipe beam that  spans between concrete piers,  is set back from its support so that it gives the illusion that the bridge is floating above the natural landscape below. The sinuous railing provides areas for people to lean out over the creek without blocking the deck.

Along the trails through the park are a maintenance building, public restrooms, and picnic and shade shelters that Endres Ware also designed for Ryder Park. The structures contribute an open framework that allows visitors to pursue the activities of their choice from strolling, jogging and cycling to picnicking. The uniform palette of materials: Ipe wood, also called ironwood, decking, solid concrete bases, steel pipe, and the curvilinear forms shared by the structures promote a perception of the meandering park as a single entity.

References to nature are most obvious in the splayed forms of the two picnic shelters arcing away from each other that suggest wind-blown leaves. Wood slats recalling leaf veins are bound together by upper and lower steel cables that run through them to form the central vein like that of a real leaf.

Picnic shelters plan

The shade structure, shown here in structural drawings and a photograph continue the palette of materials used in the picnic shelters and their skeletal form.

As shown in the photograph above, the 70-acre park projects a festive feeling appropriate to a waterside recreation area.