SOM

SOM

Structural Ingenuity: A New Type of Pedestrian Bridge

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Pushing the Boundaries

Since opening for commercial service in the 1940s, the Los Angeles International Airport (LAX) has served as the gateway to one of America's most storied cities. A sweeping, multibillion-dollar modernization project is now underway at the bustling transit hub. As part of this undertaking, SOM designed a prototype for a series of new, structurally ingenious pedestrian bridges within the Central Terminal Area (CTA). A multidisciplinary team developed a concept that embodies sophisticated simplicity while pushing the boundaries of engineering.

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Proposed Site

Measuring between 122 and 161 feet in length, the new bridges would replace seven existing bridges that connect parking garages to airline terminals.

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Lightweight, Modular Design

SOM proposed a modular design characterized by innovation, environmental responsibility, and visual minimalism. The bridge is composed of a walking deck suspended from a lightweight overhead structure. The prototype aligns with LAX’s newly defined design ethos, which calls for excellence that is both quantitative and qualitative.

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Ingenuity Meets Simplicity

The orthotropic bridge design represents a fusion of structural ingenuity and architectural simplicity. The team employed topology optimization, a numerical technique that redistributes material in an iterative fashion. Using this calculation method, structural stiffness is maximized while material volume is minimized. This concept reduces material waste, resulting in a reduced carbon footprint.

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Structural Optimization

In recent years, structural optimization techniques have been used in the aeronautical, automobile, and mechanical industries, where natural force flows are modeled and the least energy response is achieved. These fundamental principles of optimization have been used to develop SOM's novel response to the long-span pedestrian bridge.

During phase one of the prototype bridge study, SOM introduced the concept of a tapered orthotropic plate. During phase two, topology optimization was used to refine the structural member. Phase three resulted in the optimized orthotropic plate.

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Streamlined Aesthetic

By concealing the corbel inside the orthotropic plate, the bridge and columns come together to create a streamlined appearance.

1. Orthotropic Plate
2. Support Columns
3. Glass Enclosure
4. Hung Concrete Walking Surface
5. Terminal
6. Parking Structure

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Replicating the Prototype

In order for the prototype to be replicated throughout the CTA, structural and architectural components are designed as modules to accommodate differing bridge spans.

1. Orthotropic Plate
2. Steel Diaphram Plates
3. Glass Skylights 4. Concealed LED Lighting
5. Support Columns
6. Formed Acrylic Panels
7. Steel Rods
8. Glass Enclosure
9. Glass Attachment Hardware
10. In-Ground Linear LED Lighting
11. Lightweight Metal Decking
12. Aluminum Cladding
13. Natural Ventilation

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Optimized Steel Plates

Three-dimensional modeling leads to computer-controlled (CNC) cutting of thin steel plates. The plates are then assembled in areas where material is needed to resist imposed load. Material typically placed in areas of low or no stress is removed and reused for stiffening elements within the overall section.

1. Perforated Flat Plates
2. Perforated Conical Plates
3. Perforated Cylindrical Plates

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Looking Ahead

While SOM's design was a prototype study, it represents great potential for the future. Large bridge components or even entire bridge systems could be created using these optimizations techniques combined with three-dimensional printing.

1. Diaphragm Plates
2. Basic Structural Module
3. Adjustable Section Required by Bridge Span
4. Module Determined by Shortest Span
5. Deck Support
6. Composite Metal Deck
7. Steel Rods
8. Glass Enclosure
9. Attachment Hardware
10. Architectural Module