As part of a new University Campus development in the city of Northampton (UK), a new road access bridge was required. The aspirations and the planning requirements were set to keep the character of the existing landscape while creating an appropriate landmark structure for the new campus. The client's specimen design included a concrete flat arch bridge spanning 49 m with a shallow rise of 3.7 m above the navigable river. An alternative design was developed using a steel-concrete composite structure solution for the deck. The awarded tender solution includes 220 tons of welded steel plates to form a shallow and flat arch structure.
26
thema
18000 (Sq.)
Navigation channel
54600 Centre skew span
C
South Abutment
Clearance
envelope
Vehicle parapet Reinforced concret
e
pilecaps
Safety barrier Safety barrier
L C
North Abutment L
55.960(NWL)
57.300
58.200
58.960 17550
North span
17550
South span C
North Pier L C
South Pier L
55.300
55.300
Clearance envelope 33600 central between piers
Lighting column
Cables protected during construction
Cables diverted/protecte
d
as required and agreed with WPD
57.300
49000 Clear skew span between banks
Sheet pile wall to allo w
construction of pier foundation
59.710
Steel-concrete
composite flat
arch bridge
1
The bridge design had to address a number of site specific chal-
lenges as listed below:
- accommodate a road alignment that would tie-in with
Bedford Road Junction and the new campus;
- span without any support in the River Channel (48.5 m min)
and provide 18 m wide navigation channel with 3 m clearance
above normal water level; As part of a new University Campus development in
the city of Northampton (UK), a new road access
bridge was required (photo 1 and 2). The aspirations
and the planning requirements were set to keep the
character of the existing landscape while creating
an appropriate landmark structure for the new
campus. The client's specimen design included a
concrete flat arch bridge spanning 49 m with a
shallow rise of 3.7 m above the navigable river. An
alternative design was developed using a steel-con-
crete composite structure solution for the deck. The
awarded tender solution includes 220 tons of
welded steel plates to form a shallow and flat arch
structure.
thema
Steel-concrete composite fiat arch bridge 3 2017
27
18000 (Sq.)
Navigation channel
54600 Centre skew span
C
South Abutment
Clearance
envelope
Vehicle parapet
Reinforced concret e
pilecaps
Safety barrier
Safety barrier
L C
North Abutment L
55.960(NWL)
57.300
58.200
58.960
17550
North span 17550
South span C
North Pier L C
South Pier L
55.300
55.300
Clearance envelope 33600 central between piers
Lighting column
Cables protected during construction
Cables diverted/protecte d
as required and agreed with WPD
57.300
49000 Clear skew span between banks
Sheet pile wall to allo w
construction of pier foundation
59.710
- provide a clearance envelope beyond the navigation require-
ments to meet the flood risk design criteria with a 1 in 200
years return period;
- minimize disruption to the extensive number of buried
services (11kV cables across the river, 33kV and 132kV in the
North bank);
- maintain river navigation during construction period;
- minimal disruption to the river to maintain the ecology and
biodiversity;
- create a safe and pleasant pedestrian/cycle environment along
the river banks;
- address cost, statutory authority and build ability issues.
Reference design scheme
The client's engineer proposed an 89.7 m long structure
comprising a single 49.0 m skew span concrete shallow arch
structure supported at each river bank with 17.55 m approach
span on each side connecting to the bridge abutments (fig. 3).
Comparison of the shallow arch bridge in North ampton with
other, similar span arch bridge structures is given in table 1. The proposed structure included a concrete ladder deck with
deck beams supported on precast concrete arch ribs and
forming balanced cantilever frames spanning from piled foun-
dations on each bank (fig. 4).
Tender design
The constraints imposed by the planning documentation do not
allow any deviation from the very flat arch requirements with a span
to rise ratio of approximately 13. However, the geometry of the
Riccardo Stroscio
Tony Gee and Partners LLP 1
Steel-concrete composite flat arch bridge
2 Aerial view - November 2016
credtis: Commission Air3 Reference design - elevation
Table 1 Arch bridges ? comparison of similar spans (road bridges)
bridge TavanasaVessyNew Runnymede Northampton
Year constructed 190619361979 2016
Span (arch) [m] 51.056.054.6 50.3
Rise [m] 5.574.776.96 3.61
Span/Rise 9.211.77.8 13.9
Structural depth
1 [m] 0.83 0.831.80 1.19
1)Structural depth at mid-span
Waterside Campus
Bedford Road
2
3
Steel-concrete composite ?at arch bridge 3 2017
28
7300 2000 2000 500 500 East footwayCarriagewayWest footway
2.5% 2.5% 2.5% 2.5%
2820 2820 7100
1500 1500
300 Precast or cast in situ
reinforced and post-tensione
d
bridge deck
25061.010
Post-tensioned reinforced concrete arch rib
Vehicle parapet
Sub-surface
carriageway drainag e Lighting column mounted
on edge beam corbel with
ducting as required
deck structural depth of the side span is constraint by the road
alignment and the clearance to the river side walkway. The
bending moment, shear and axial force distribution is shared
between the deck and the arch in proportion to their relative
stiffness. The overall overturning moment to the abutments is
reduced by the stabilising effects from the granular backfill
material preventing any net tension in the piles.
The horizontal pull-out forces from the deck and the integral
connections are anchored into reinforced concrete buttress
walls within the abutments and the loads are transferred into
the pilecap via strut-and-tie models in the combined reinforced
concrete counterfort-wing wall systems (fig. 6).
The resulting net effects at the base of rigid pilecaps are resisted
by the piles transferring the load effects into the ground. A
review of various deck cross sections alternatives concluded
that a ladder type deck option using steel main and secondary aesthetic window on the riverside walkways enable to shorten the
extent of the side spans and the overall deck length can be reduced
to 64 m. The reference design 'piers' are thus being replaced with
larger abutments and wing walls on each bank (fig. 5).
The setting-out of the foundation is derived from the layout of
existing buried utility cables to prevent the need for any diver -
sion. The North abutment is to be constructed in stages with
the use of precast concrete elements in order to span the exist-
ing cables. For maintenance benefits, a fully integral bridge was
chosen. The overall length of 64 m and the 20° skew remain in
line with the geometrical range recommended in the UK for
integral bridges. The depth of the arch is shaped with a curved
intrados to provide the required stiffness and meet the clear -
ance enveloped above the river. Deeper girders are provided at
the arch-deck intersection zones tapering down to a shallower
section at mid-span and also towards the springing levels. The
4 Reference design ? deck
cross section
5 Alternative tender -
structural arrangement
6 Alternative design ?
abutments load path
4
5
6
thema
Steel-concrete composite at arch bridge 3 2017
29
BRIDGE
SETTING OU T
LINE
MIN 2000
EAST FOOTWAY MIN 2000
WEST FOOTWAY
STREET LIGHTING SUPPORTEDON LOCAL DECK WIDENING
2.5% 2.5% 2.5% 2.5%
SUB-SURFACE
CARRIAGEWAY
DRAINAGE
1.0m HIGH PARAPETSN1 CONTAINMENT
W1 WORKING WIDTH INACCORDANCE WITH TD/19/06
3 No. 150 ° SERVICE DUCTS
125 KERB UPSTAND
3 No. 150Ø
SERVICE
DUCTS
125mm SURFACING OVER
SPRAY APPLIED
DECK WATERPROOFING
250
625
500 500
CROSS GIRDERS @
3m CENTRES
1600 6100 1600 1500 1500
7300 CARRIAGEWAY
SEE NOTE 14.
350
225SLAB
PERMANENT
FORMWORK
BRIDGE
SETTING OU T
LINE
MIN 2000
EAST FOOTWAY MIN 2000
WEST FOOTWAY
STREET LIGHTING SUPPORTED
ON LOCAL DECK WIDENING
2.5% 2.5% 2.5% 2.5%
SUB-SURFACE
CARRIAGEWAY
DRAINAGE
1.0m HIGH PARAPETS
N1 CONTAINMENT W1 WORKING WIDTH INACCORDANCE WITH TD/19/06
3 No. 150 ° SERVICE DUCTS
125 KERB UPSTAND
3 No. 150Ø
SERVICE
DUCTS
125mm SURFACING OVER
SPRAY APPLIED
DECK WATERPROOFING
250
625
500 500
CROSS GIRDERS @
3m CENTRES
1600 6100 1600 1500 1500
7300 CARRIAGEWAY
SEE NOTE 14.
350
225SLAB
PERMANENT
FORMWORK
BRIDGE
SETTING OU T
LINE
MIN 2000
EAST FOOTWAY MIN 2000
WEST FOOTWAY
STREET LIGHTING SUPPORTED
ON LOCAL DECK WIDENING
2.5% 2.5% 2.5% 2.5%
SUB-SURFACE
CARRIAGEWAY
DRAINAGE
1.0m HIGH PARAPETSN1 CONTAINMENT
W1 WORKING WIDTH INACCORDANCE WITH TD/19/06
3 No. 150 ° SERVICE DUCTS
125 KERB UPSTAND
3 No. 150Ø
SERVICE
DUCTS
125mm SURFACING OVER
SPRAY APPLIED
DECK WATERPROOFING
250
625
500 500
CROSS GIRDERS @
3m CENTRES
1600 6100 1600 1500 1500
7300 CARRIAGEWAY
SEE NOTE 14.
350
225SLAB
PERMANENT
FORMWORK
7 Alternative design ? deck cross section
8 Extracts from computer idealised FE model
9 First the steel arch installation
construction. They are set within the minimum clearance from
the centre line of any buried cable. Each abutment is supported
by 750 mm diameter continuous flight auger (CFA) piles to
provide the most efficient and economical solution for the given
ground conditions. One of the main advantages of the steel
bridge solution is the lighter weight, which means it can be
erected from cranes on both banks without the need for exten-
sive temporary works and associated costs.
Detail design
During late spring 2015, the contract was awarded to Volker -
Fitzpatrick based on this alternative proposal. The detail design
phase started in early summer 2015 by setting an idealised 3D
finite element model to include the steel-concrete composite
superstructure (arch ribs, deck girders and slab) and the rein-
forced concrete abutments. A series of computer models with
shell and beams elements were produced to extract the stress
build up within the composite sections model considering long
term, short term and staged construction effects from arch ribs
erection, deck girder installation, backfilling behind abutments
and the concrete deck castings sequence (fig. 8).
The concrete deck slab connecting to the integral abutments
was also designed as a concrete tension member with consider -
ation of tension stiffening effects in line with EN1992-2 in
order to control crack widths at serviceability limit state.
beams offered the optimum solution (fig. 7).
The cross girders are set at 3 m centres orthogonal to the main
beams to simplify the connections, the seating details for the
concrete permanent formwork panels and the fixing of the deck
reinforcement. The 1500 mm deck cantilever allows the adop-
tion of a 250 mm reinforced concrete slab and the girders can be
set back to remain relatively in the shadow of the deck slab.
Furthermore, it allows the use of modular proprietary cantilever
falsework system that facilitates the construction of edge projec-
tion of deck slabs. The cross girders are shaped to provide a 225
mm constant concrete slab thickness with transverse cross fall in
line with the carriageway requirements. The main design
constraints for the foundations are the proximity of a significant
number of buried cables and the requirement to keep a 48.5 m
minimum clear span between the banks. Sheet pile walls form
the river side of the pilecaps and provide a scour protection to
the foundations as well as offering a temporary cofferdam during
7
8
9
Steel-concrete composite ?at arch bridge 3 2017
30
10 Steel arches and tie beams completed
into the predefined concrete pocket within each pilecap allow-
ing the central bolted splice connection to be completed using
tension control bolts and accessed using a mobile elevating
work platform on a floating pontoon (photo 9).
The same operation was repeated for the adjacent arch girder
and then followed with erection of the lighter tie beams (13.5 t
each) and cross girders.
The concreting phase could follow with completion of the
abutments and the parapet edge beams allowing installation of
the road restraint systems. With the main structure finalized,
the road pavement, footway verges and expansion joints could
be installed and the bridge construction was completed by the
end of 2016.
?
?
PROJECT DETAILS
client University of Northampton
design and build contractor VolkerFitzpatrick
civil and structural designer Tony Gee and Partners
highway designer Peter Brett Associates
independent checker Ramboll
client's Engineer CH2M
project manager MACE
bridge architect MCW
landscape architect LUC
steel Fabricator Briton Fabricators
piling contractor Van Elle
temporary works designer Tony Gee and Partners
? REFERENCES
1 Lewerer, J.-P., Peçon, Y. (1993). La Souplesse d'un ressort tendu: le
pont de Robert Maillart à Vessy. Faces-Genève, No 30 (1993/94),
pp. 50-55.
2 Smyth, W.J.R., Benaim, R., Philipott, D.H., (1980). The new Runnymede
Bridge. The Structural Engineer, Volume 58A/No. 1, pp. 5-11.
3 Solca, J. (1914). Die Rheinbrücken bei Tavanasa und Waltensburg.
Schweizerische Bauzeitung, No 63/64, pp. 343-346.
The soil-structure interaction analysis and pile load derivation
was computed by close calibrations between structural/global
models and separate geotechnical analyses. Upper and lower
bound pile stiffness were used for the global analyses of the
bridge. Combined with a pile test on site, the detail analysis
confirmed the tender design solution and offered a ten percent
reduction in pile length for the 63 CFA piles.
The main steel girders are shaped with a variable depth and a
constant width of 1600 mm. A stiffened steel box section was
generally adopted except for the tie beams where a pair of 560
mm deep plate girders was designed to respect the pedestrian
clearance on each banks. The combined arch-deck section is an
open top steel box section keeping steel continuity of the web
and the bottom flange. At its deepest, the girder is 2150 mm.
The lower part of the arch is 600 mm deep at springing levels
and it tapers up to 1400 mm before the arch meet the deck. It
was decided to infill them with self-compacting concrete (SCC)
grade C32/40 with slump-flow class SF2. Similarly, the 15 m
long central portion of the span where the depth of the steel is
shallower than 1200 mm, a 150mm thick concrete lining was
specified to the inside faces of the steel box with lightweight
expanded polystyrene void former in order to protect the steel
against corrosion. The benefit of concrete lining in midspan
and SCC infill within the lower part of the arch is that it
provides additional robustness against accidental vessel impact
actions. Stability of the arch girders and resistance to buckling
was analysed using a 3D finite element analysis model and
reviewed with hand calculation methods. As individual arches
where assembled on site, a temporary bracing arrangement was
required until the tie beams could be connected to the abut-
ments and cross girders installed.
Construction
Piling started on the North side in December 2015 and the
reinforced concrete pilecaps and abutments were completed by
July 2016. With the backfill completed, the construction site
could start preparing for the main steel lift with one 500 t
capacity mobile crane set behind each abutment. In August, the
main girders were delivered to site in 25 m long, 37 t sections.
Each half arch could then be lifted individually and lowered
10
thema
Steel-concrete composite fiat arch bridge 3 2017
Reacties