March/April 2024 - 107

Saint Sebastian Bridge:
Reuse Requires Creative Thinking
FEATURE ARTICLE
The old bridge
The Sint Sebastiaansbrug (Saint Sebastian
Bridge) in Delft, the Netherlands,
was built in 1964. The bridge crosses
the Delftse Schie, or waterway, with a
fixed span of 12 m (39 ft) and a movable
span of 12 m (39 ft). In the middle of the
waterway, both the fixed and movable
bridge decks rest on a pier. The vertical
clearance of the fixed part is 4.5 m
(15 ft). On both banks there is an approximately
80 m (262 ft) long access
ramp, consisting of a concrete construction
on piles. Each section of the
access ramp has a span between
supporting structures of approximately
10 m (33 ft).
During the preparations for converting
the bridge to accommodate a
tram in 2006, a thorough inspection of
the bridge was executed. The inspection
conclusions were very unfavourable.
Several supporting structures had
settled considerably, causing structural
damage to the upper structure.
Adding bearing capacity to the
failed foundation, repairing the structural
damage and accommodating the
tram on a wider bridge was studied in
2010 and was found unfeasible and the
uncertainty profile associated with
this solution was also considered to
be too high.
Then, a conventional bridge replacement
(demolishing the old bridge
and building a new one) was evaluated.
The resulting design required an
estimated budget of €50 million
($54 million), which exceeded the
available budget by a high margin.
The design team tried to
reuse as much as possible
of the old structure to
optimize the design for
the budget
Cracks in the concrete
In 2016, the engineering department
of the city of Rotterdam was hired to
design a new bridge given an available
budget of €25 million ($27 million).
Design Constraints
The main design objective was to create
a design within the available budget.
Furthermore, the bridge had to accommodate
pedestrian, bicycle, car and
public transport traffic (tram and bus).
The design team tried to reuse as much
as possible of the old structure to optimize
the design for the budget. This
led to preservation of the bridge elements
most costly to replace.
Design Challenges
Demolishing and rebuilding the
counterweight basement and the
central pillar in the waterway were
very expensive. The concrete structure
ramps on both sides of the channel
were expensive to replace as well. One
of the reasons for these high costs was
the foundation pile type that was used
to build the original ramps. These
precast concrete piles had a toe with an
extended diameter to increase the pile
bearing capacity. These wide pile toes
had two disadvantages:
AUTHORS Rodriaan Spruit, Albert Allaart and Hans Pacejka, City of Rotterdam Engineering; and Suzanne J.M. van Eekelen, Deltares
DEEP FOUNDATIONS * MAR/APR 2024 * 107

March/April 2024

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TOC
March/April 2024 - Intro
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