of control for each component. The total weight of the structure is 2,756 metric tons.
The coating system used for the painted elements consists
of a standard three-layer system defined by European codes.
Since the color would be of prime importance in the final appearance, gray was chosen to create a harmonious transition
between the concrete and the weathering steel. The coating
system is designed to last more than 15 years.
As mentioned above, the three side spans at either end
of the bridge are of cast-in-place concrete but have the same
outer shape as the steel portions. These side spans were built
of posttensioned concrete using a span-by-span erection sequence. The concrete deck has the same outer shape as the
steel portions. The internal posttensioning tendons each have
a tensile strength of 1,860 MPa. Each tendon is made up of
27 strands, each 140 mm² in cross section. To improve the
durability of the deck’s reinforcing steel, the top slab is protected with a waterproofing system that comprises two courses of an asphalt wearing surface.
The bridge substructure and
foundations were designed to minimize the environmental footprint.
Special attention was given to the
aesthetic design of the piers below
the deck. The pier shafts have curved
faces perpendicular to the bridge axis
and planar faces in the longitudinal
direction. The cross section of piers
1, 2, 4, 5, 7, and 8 (numbered west
to east) does not vary with height
and can be inscribed in a rectangle
6. 15 m long and 2. 12 m wide.
Piers 3 and 6, beneath the ends
of the suspended spans, each take
the form of a pair of inclined columns to achieve a more striking visual connection between the piers and the overhead steel diagonals. The cross section of each of the piers’ columns can be
inscribed in a rectangle 2. 4 m long and 1. 4 m wide. The surfaces have vertical grooves to impart aesthetic appeal.
All piers and abutments are founded on reinforced-concrete
drilled piles 1. 5 m in diameter that reach the sound rock below
the alluvial deposits in the river. Reaching depths of approximately 13 m, the piles were socketed into the sound marl rock
to attain bearing capacities in service of 4,500 to 10,000 kN.
The number of piles required beneath each pier varied. Piers 4
and 5 are each supported by nine piles, piers 4 and 5 are supported by three piles per column, and the rest of the piers are
each supported by four piles.
The superstructure rests on neoprene bearings at the abutments and at the piers supporting the approaches. At piers 3
through 6, however, it rests on pot bearings. The piers near
the main stream were built on a temporary peninsula that
also provided a platform from which the steel bridge deck
could easily be assembled over temporary supports.
The structural analysis of the bridge was conducted with
the aid of version 8i of RM Bridge, developed by Bentley
Systems, Inc., of Exton, Pennsylvania, and Robot Structural
Analysis Professional, developed by Autodesk, Inc., of San
Rafael, California. The model included both the substruc-
ture and the superstructure and accounted for soil-structure
interactions. A complete step-by-step analysis that modeled
the actual erection sequence was performed. In this way the
designers could take into account not only the actual dura-
tion of each of the construction stages but also the possibility
of cracking and other long-term effects on the concrete. The
parametric nature of the structural model made it possible to
rapidly respond to the various alternatives and changes that
are common on a project of this nature. The time-dependent
effects and the consequences of modifying erection phases
were calculated automatically.
To determine the transverse bending moments, the
stresses from shear lag, and other local effects, various finite-element models were constructed in the domain of linear
elasticity. These refined models were used to analyze the different construction phases, and they integrated all of the
elements—steel box girders, ribs,
diaphragms, and slab. Other analyses were conducted to determine the
distribution of stresses on the structural nodes and areas that would
be strongly stiffened. The analyses
used elastic three-dimensional shell
members and, in some cases, considered geometric imperfections.
This detailed and challenging
modeling produced a design that
made optimal use of the materials
and yielded considerable cost savings.
The construction of the piers,
abutments, and temporary supports
began in 2011. During the bridge
construction, Pedelta provided construction engineering services to the
contractor, adapting the design and approving the final erection and assembly procedures. In some cases it was necessary
to update the precambers and redesign certain structural
The approach spans were built using a traditional span-by-span procedure on falsework. The deck was built using
traditional falsework as well. The placing and posttensioning of the concrete were carried out in two phases. The first
involved the central core of one span of the deck, which was
60 percent posttensioned before the formwork was advanced
to the subsequent span. In the second phase, the remainder
of the concrete placement and tensioning was performed on
the initial span.
The steel box girder was assembled from 20 different segments, some of which were put together on-site in pairs and
lifted to their final positions on nine temporary supports. These
steel towers rested on pile caps above micropiles. The steel
girder and the cantilever ribs were welded in the field. Pedelta
was retained to review shop drawings and worked closely with
the steel fabricator and erector—URSSA, of Vitoria-Gasteiz,
Spain—to review critical details and facilitate both fabrication
and erection. The work required careful planning and analysis
were used to
analyze the different
and they integrated
all of the elements–
steel box girders,