e-mosty March 2019 Long Span and Multiple Span Bridges | Page 23

DESIGN REQUIREMENTS
Subsequent geotechnical exploration conducted by
CPC, the Contractor, confirmed the feasibility of a
suspension bridge with two main spans and a
center pylon founded on Roca Remolinos.
MOP developed the Instructions to Builders (ITB)
which contained the contract administrative and
technical basis, as well as project specific
requirements. In addition, the ITB referenced
standard codes, including the Manual de
Carreterras, the Chilean roads design manual; the
AASHTO LRFD Bridge Design Specifications, the
highway bridge design code for the United States;
and the AASHTO Guide Specifications for Seismic
Bridge Design.
As a result of all of these studies, CPC's final design
arrangement includes two spans suspended by
continuous cables. Few continuous, multi-span
suspension bridges exist in the world and Puente
Chacao will be the first in the Western
Hemisphere.
The contract permitted application of other design
standards in cases where the identified standards
did not address a specific design issue, provided
that the design build contractor proposed and
received acceptance for use of portions of these
standards.
In addition, the Puente Chacao's suspended span
lengths will be the longest in Latin America.
Another unique feature of the Puente Chacao is
the Central Pylon arrangement. While the North
and South Pylons have relatively conventional
arrangements of straight, vertical columns, the
Central Pylon has an inverted wishbone frame
arrangement with two longitudinally inclined lower
columns intersecting above the deck elevation.
The ITB also contained requirements for the design
build contractor to conduct surveys, tests and
studies related to site conditions and loadings
necessary for the project design. These included
Bathymetry
and
Topographic
Surveys;
Geotechnical
Field
Investigation
Program;
Geological Studies; Scour and Erosion Studies;
Maritime Studies (including currents and wave
heights); Seismic Studies including a Seismic Risk
Study Assessment and a Seismic Monitoring
Program; Wind Measurement Studies and a Wind
Tunnel Testing Program; Temperature Studies;
Vessel Traffic; and studies of other specific risks.
CPC summarized the project design requirements
in a Design Manual. Additionally the ITB mandated
the structure to be designed considering access,
ease of inspection & maintenance and with a 100
year durability requirement under normal
maintenance practices.
The intersecting lower columns are topped by
variable-width pylon columns extending upward to
the cable saddles. This arrangement is required by
unbalanced loadings on the Central Pylon, as well
as seismic and wind loads, which must be
transferred to the foundations.
A notable feature of the Puente Chacao results
from the site topography. Steep banks between 30
and 50 meters tall allow the bridge abutments to
be located close to the tops of both banks.
Grade adjustments at either end of the bridge are
accommodated by use of cuts and embankments,
eliminating the need to construct long approach
viaducts to connect with the approach roadways.
Figure 2:
General Bathymetry
1/2019