Puente de La Unidad Monterrey

PUENTE DE LA UNIDAD

INTERNATIONAL BRIDGE TECHNOLOGIES, INC.

Monterrey, Mexico

©2009 Copyright International Bridge Technologies, Inc.

Project Description

CABLE STAYED BRIDGE Overview

The signature structure of Puente de la Unidad project is a 304m (997ft) long asymmetrical cable-

stayed bridge, with a main clear span of 185.6m (609ft). The main pylon is inclined 30° to the vertical

and reaches a total height of 152.1m (499ft) from the top of foundation. Nearly all the main structural

components are made of 50MPa (7.25ksi) strength concrete. Thirteen pairs of harped stay cables support

the main span and are anchored on the outside of the roadway. One pair of vertical stays is anchored

into the back of the pylon. Main span carries 2 lanes of traffi c in each direction with pedestrian walkway

provided in middle. Pictures of the bridge are shown below.

International Bridge Technologies (IBT) was the lead designer for the bridge. The specifi c design tasks included:

• Main Span: Conceptual, Preliminary, and Final Design• Stay-Cables: Conceptual, Preliminary, and Final Design• Construction Methods: Conceptual, Preliminary, Final Design, and on-site support• Pylon: Conceptual, Preliminary, and Oversight of Final Design• Foundation: Conceptual, Preliminary, and Oversight of Final Design

The design of the bridge included detailed, 3-D FEM, non-linear, and time-dependent analysis. In addition, detailed studies were performed to ensure compatibility of the extensive network of post-tensioning tendons and non-orthogonal reinforcement.

Sistemas Optimos Constructivos S.A. (SOCSA) served as the prime consultant for the full viaduct project. SOCSA performed preliminary analysis and fi nal design for the pylon and foundation. West Wind Inc. provided wind studies and cable damping requirements.

PUENTE DE LA UNIDAD


Monterrey, Mexico


• Original or Innovative Applications of New or Existing Techniques: The fundamental behavior of a cable-stayed structure

is well understood. Typically the bridges are

symmetric by span and pier layout, and the balancing

of forces is accounted for in the basic concept. In

the case of this bridge, the asymmetry required the

design to go back to a more basic level to ensure

the structural load paths were well-established and

adequate capacities provided. Because the main span

is reliant on the counter-

balance of the pylon, a

delicate balance exists. The

structural capacity of the

pylon must be considered

in parallel with the ballast it

provides, and these two goals

did not always work in the

same direction. The Puente

de la Unidad project is a good example of an existing

bridge concept (cable-stay) used in an alternate way

to provide a striking visual appearance, and achieve

the goal of providing a single support outside of the

main riverbed.

• Future Value to the Engineering Profes-sion: As indicated above, this project presents a

good example how a complex project can be solved

by understanding the basic behavior and providing

reliable load paths. The value of dedicating time

at the conceptual phase is refl ected in this project.

Three locations on the bridge illustrate this. The fi rst

is the transition from the force in the edge beams to

the pylon, the second is the resolution of axial loads

between the pylon and main span, and third the

specially shaped spread footing to accommodate the

monotonic loads. These solutions are shown on the

following pages.

• Social and Economic Considerations: The bridge project includes a long viaduct to provide

congestion relief to the crowded streets of Monterrey.

Also, the Santa Catarina riverbed can crest at a level

where most other adjacent bridges are under water.

This bridge will provide a critical escape route for

the citizens on the South side of the river. In addi-

tion to these benefi ts, the design was performed with

consideration of local materials and construction skill

level. The bridge details were all considered in such

a away to promote ease of

construction.

• Complexity: The Puente

de la Unidad project pre-

sented many challenges due

to its complexity. Typically

the roadway geometry is

adjusted to accommodate

the bridge, but the opposite

was done for this project. The complexities included

large openings in the pylon at grade to allow traf-

fi c fl ow, the introduction of a vertical curve to the

alignment of the bridge deck, variable cross-fall at the

span along the pylon, and allowing for ramp connec-

tions on either side of the bridge. All challenges were

successfully incorporated into the fi nal design.

• Meeting and Exceeding Owner/Client Needs: The primary achievement for the Puente de

la Unidad project was the delivery of a design under

a very tight schedule. The design schedule was 9

months, and the contractor selection was selected in

advance of the fi nal design completion. The bridge

construction was completed in 15 months, a time

frame rarely achieved for this complex of structure.

The bridge was completed for $16.8 million, and was

within 3% of estimated costs.

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STRUCTURAL SYSTEMS

PUENTE DE LA UNIDAD


Monterrey, Mexico


Excavation of Foundation Foundation Reinforcement Cage

Starter Bars for Pylon Foundation Post-TensioningFoFoF ununddadatititionon PP Pososttt-TTeTensnsiioio ininingngg

Transition Span FrameTrTrT anan isisitititionon SS Spapap nn FFrFramamee

Flow of Forces FlFlFlowow o offff FFoForcrceses

FOUNDATION, PYLON BASE, AND TRANSITION SPAN

Key Features• Soil was injection grouted for added strength.

• Foundation was a spread footing and post-

tensioned in primary directions.

• Spread footing dimensions were optimized

for the monotonic loading. A trapezoidal

plan area was designed with a wider toe at the

front of the footing.

• 8000m3 (10500yd3) of concrete used for

foundation. Mass concrete casting procedures

implemented.

• Large axial forces at edge beams need to be

transferred to central pylon. Well-defi ned

load path provided by central and diagonal

beams.

PUENTE DE LA UNIDAD


Monterrey, Mexico


MAIN PYLON

Pylon Section Pylon Back Wall Post-Tensioning

Climbing Form Pylon Elevation Completed Pylon

Key Features

• Pylon is hollow with a typical width of 5m (16.4ft), which tapers to 15m (49.2ft)

from deck to foundation. The back wall of the pylon is post-tensioned.

• Pylon inclination provides signifi cant balance to main span forces.

• Pylon and deck forces resolved at one location and distributed to the foundation

by twin legs.

• Pedestrian access permitted through pylon.

• Pylon and span designed to allow for loss of back stays (i.e. terrorist attack.)

PUENTE DE LA UNIDAD


Monterrey, Mexico


Key Features • Main Span cast in 12m (39.3ft) sections.

Edge beams and steel beams cast in place,

followed by pre-cast panels with CIP stitch.

• In place of standard cantilever construction,

a moving casting table was used. The table

would launch to cast each segment and

be supported on the river bed. The bridge

geometry was evaluated on a real-time

basis and adjusted for each new casting.

• New in-line stay damper used to suppress

cable vibrations.

MAIN SPAN

Main Span Section Main Span Section Construction

Pre-cast Panel Placement Completed Bridge, Stay Anchors

Completed Bridge, Elevation

Documents

Puente de La Unidad Monterrey