10th International Conference on Short and Medium Span
Bridges
Quebec City, Quebec, Canada,
July 31 – August 3, 2018
ROAD BRIDGE CROSSING THE HUANGYAN HIGHWAY: A RECTANGULAR
CONCRETE-FILLED STEEL TUBULAR TRUSS BRIDGE WITH PERFOBOND LEISTER
RIBS
Jiang, Lei1, Liu, Yongjian2,6, Fam, Amir3, Liu, Bin4 and Xiong,
Zhihua5
1 Chang’an University, China, and Queen’s University, Canada
2 Chang’an University, China
3 Queen’s University, Canada
4 Chang’an University, China
5 Tongji University, China
6 [email protected]
Abstract: The road bridge crossing the Huangyan Highway, north
of Huangling county, is the first rectangular concrete-filled steel
tubular truss girder bridge in China. The total length of the
bridge is 84 m including three spans with the longest span being 40
m and the truss depth is 2.5 m. The first structural innovation is
using a rectangular steel tube in the lower chords with concrete
filling at the hogging regions in compression, making use of the
concrete confinement effect. Similarly, concrete-filled steel box
sections were used for aesthetically pleasing Y-shaped piers.
Another technical innovation is the use of longitudinally welded
Perfobond Leister Ribs (PBLs) inside the inner faces of the chord
and pier box sections. The static and fatigue designs of the joints
of the welded steel truss are key considerations in design.
Numerical analysis is performed for the innovative rectangular
concrete-filled tubular joints stiffened with PBLs in the chords.
This analysis demonstrated the much enhanced performance of this
design compared to conventional rectangular hollow section joints.
Construction of the road bridge has been completed in October 2015.
The construction duration was only two months and an economic
analysis comparing this design with conventional prestressed
concrete girder system is also completed.
1. INTRODUCTION
Composite tubular truss bridges have been widely used in design
because of their high efficiency and aesthetics. The steel tubular
truss and concrete deck are combined in an efficient composite
system, where the deck slab bears compression along with the
compressive chord in the positive bending moment regions. On the
other hand, for continuous girder bridges, the deck slab is under
tension and no composite action can be considered in the negative
bending moment regions, and as such some measurements have been
proposed to optimize the structure at the internal supports of
continuous girder bridges.
One of the major design optimizations is the tubular truss
bridge with a concrete lower flange as adopted for the Nantenbach
bridge in Germay, and the viaduct over Ulla River in Spain. Both
bridges use a rectangular hollow steel tubular truss with a
variable depth. The double composite action concept, the top deck
slab and the concrete lower flange with their corresponding tubular
chord could bear compression in the positive bending moment regions
and negative bending moment regions, respectively, which is better
suited for meeting strict clearance requirements. Another design
optimization is to fill the lower chord with concrete, making full
use of the confinement effect of concrete to improve its
compressive strength. A typical application is Ganhaizi bridge in
China. When circular hollow steel tubes are used, welding at the
joints and connections between the steel truss and deck slab pauses
some challenges and a cast-in-place concrete deck system is used.
For this reason, the road bridge over Huangyan Highway in China
using concrete filled steel tubes only in the negative bending
regions was designed. The manufacture quality of the rectangular
section truss is more easily guarantied and the precast concrete
deck can be cast with arrangements to accommodate the prefabricated
shear connectors on the top of truss, which make the cost more
competitive compared to circular sections. Additionally, in order
to compensate for the lower confinement efficiency of rectangular
sections as opposed to circular sections, the longitudinally welded
PBLs inside the chord faces were proposed to enhance the bonding
behavior of the chords and the mechanical behavior of the
joints.
1. LAYOUT OF THE BRDIGE
Huangyan Highway, connecting the cities of Huangling and Yanan,
in Shaanxi province, China, is part of the Baomao Highway which
runs from Baotou in Inner Mongolia to Maoming in Guangdong
province. The pilot project, Road Bridge Crossing the Huangyan
Highway, is the first rectangular concrete-filled steel tubular
truss bridge in China. The total length of the bridge is 88 m that
covers three spans (24+40+24 m) (Figure 1). The bridge has a
straight alignment in plan with a 0.84% slope in elevation. To add
an aesthetically pleasing effect and ensure that the bridge would
blend into the surroundings, a Y-shaped rectangular concrete-filled
steel tubular pier design was adopted.
(b)
(a)
Figure 1: Elevation drawing of the road bridge crossing the
Huangyan Highway, China: (a) Schematic of finished bridge (Unit:
m); (b) Photograph of the finished bridge
1. OPTIMIZATION OF TRUSS CHORDS AND PIER COLUMNS
Rectangular tube sections are more convenient to fabricate and
weld than circular steel sections. This made the rectangular
sections ideal for welding shear connectors to the inner surfaces.
Because of its ease of constructability, Liu et al. 2014 proposed
an innovative rectangular concrete-filled steel tube (RCFST) system
stiffened with PBL (Figure 2), and applied it to both the lower
chord of the truss girder and the pier. Extensive research related
to the compressive behavior, flexural behavior, bond behavior, and
buckling performance of this system have been conducted (Liu et al.
2015, Liu et al. 2017, Gao et al. 2017). The results indicate that
welding PBLs inside the steel tube walls offers the following
functions:
(a)
(b)
Figure 2: RCFST stiffened with PBL: (a) Diagram; (b)
Photograph
a) PBL is used as shear connector to enable the shear transfer
between the steel profile and concrete core. The interaction
between the concrete and PBL connectors with holes in them is
effective to prevent slip and debonding failure. b) PBL has the
function of a stiffener, which improves the local stability of the
steel tube. Figure 3 shows the buckling mode of a steel plate
stiffened with PBL and other without it. Under uniform axial load,
the behavior of the plate changes from a single wave buckling to a
double wave buckling. This enables a larger width-to-thickness
ratio for the steel plate in design. c) Comparing with
circular-concrete filled steel tubes, the confinement effect in
RCFST without PBL is lower. However, providing PBL can directly
bear additional axial load as part of the steel tube. Additionally,
it restrains the out of plain movement of the flat wall by having
it anchored to the concrete core. This enables the wall to be
better engaged in confinement. Figure 4 illustrates this point by
showing that the confined region of RCFST stiffened with PBL is
larger than conventional RCFST.
(a)
(b)
Figure 3: Buckling modes under uniform load: (a) RCFST wall; (b)
RCFST wall stiffened with PBL
(a)
(b)
Figure 4: Effective confinement area of: (a) RCFST; (b) RCFST
stiffened with PBL
1. DESCRIPTION OF THE SUPERSTRUCTURE
3. Main Truss Girder
The elevation arrangement of the main truss girder is Warren
type. The height of the truss from the upper edge of the deck slab
to the lower edge of the lower chord tube is 2.5 m, and is constant
along the span. Figure 5 shows a cross-section of the bridge,
including the road and the two truss girders. The total width of
the cross-section is 5.5 m and the width between the outer edges of
the two truss girders is 3.08 m. The slenderness (L/H) ratio of
this lightweight superstructure is 16, where L is the longest span
and H is the height. Compared to the triangular arrangement of the
bridge cross-section, the stresses in the lower chords are smaller
and the lateral stability is better in the rectangular arrangement
(Figure 5).
Figure 5: Cross section (Unit: mm)
The truss consists of 300 mm × 300 mm rectangular tube sections
for the lower chords and 300 mm × 200 mm for the diagonals. The
upper chord consists of three PBL steel plates to form a 300 mm ×
360 mm closed section embedded into the concrete slab (Figure
6(a)). Lower lateral bracings are placed at 4 m spacing using H
shape sections (Figure 6(b)). The steel plates are up to 16 mm
thick in the upper chords.
(a)
(b)
Figure 6: Detail of upper chord: (a) Simulation of upper chord;
(b) Photograph of upper chord
Another new innovation in this bridge is filling the steel tubes
with concrete at the hogging sections. Also, the deck slab was
prestressed for crack control. The concrete fill in the lower chord
was provided only within a 2.5 m length at end supports and a 13 m
length at pier supports. Figure 7 shows the calculated compressive
stress in the steel tube of the lower chord for the cases of hollow
tube and concrete-filling at hogging regions. It can be seen that
the maximum compressive stress in the RCFST system is 188 MPa,
which is 26% lower than that of the hollow section (253 MPa).
(a)
(b)
Figure 7: Comparison of compressive stresses in the steel tube
of lower chords (Unit: MPa) when: (a) concrete fill was provided at
hogging regions; (b) no concrete fill was provided
3. Truss Joints
The joints design is important for truss bridges due to the
complex state of stress in these regions where members meet. The
spatial fully welded RCFST joints stiffened with PBL are adopted at
the hogging cross-section. Both the chords and braces have the same
width of the members. Welded rectangular section joints are favored
by engineers because of their simple configuration and regular
shape compared to the circular hollow section joints and bolted
joints. The RCFST joints stiffened with PBL offer several
advantages as will be discussed next.
1. Static Behavior
For traditional hollow section joints, the typical failure modes
are chord face (top flange) plastification for width ratio (β) less
than 1 (Figure 8 (a)) and chord side wall failure for β=1, where β
is brace width-to-chord width ratio. Filling concrete in chord is
expected, as a rigid base, to limit the inward deflection on the
chord face. The failure mode is governed by the tension brace
transforming from the chord face plastification to the punching
shear failure of the chord. In addition, the shear action between
concrete and PBL limits the outward deflection on the chord face.
The design concept of joints having β=1 enables the transfer of the
load to the chord web. Therefore, the innovative joints are more
likely to exhibit the shear yielding of chord at the gap (Figure 8
(b)).
(a)
(b)
Figure 8: Failure mode comparison of different joints: (a) Chord
face plastification for rectangular hollow section joints (β<1);
(b) Shear yielding of chord in the gap of RCFST joints stiffened
with PBL (β=1)
1. Fatigue Behavior
The fatigue behavior of welded joints is a well-recognised
problem in the design of tubular truss bridge. The hot spot stress
method is a common practice in design codes. In this method, stress
concentration factor (SCF) is a dimensionless factor that is used
to quantify how concentrated the stress is in a material. The high
stress concentrations at the weld toes in the chord are mostly
caused by local bending, a result of chord face deformation for
rectangular hollow section joints. A review of current literature
shows that concrete-filling of the chord is an effective way to
reduce the stress concentrations. Furthermore, PBL welded inside
the chord also can reduce the local bending of chord. Two finite
element models are established to compare the SCF between
rectangular hollow section joints and RCFST joints stiffened with
PBL (Figure 9). A 1 MPa tensile stress is applied on the brace and
a quadratic extrapolation method is used for the rectangular
section (Figure 10).
Figure 9: Finite element model of the joint
Figure 10: Boundary condition and quadratic extrapolation
As shown in Figure 11, the maximum SCFs in the chord for the
RCFST joint stiffened with PBL and the hollow section joint are
1.95 and 2.71, respectively. The maximum SCFs in the brace for the
RCFST joint stiffened with PBL and the hollow section joint are
2.65 and 3.52, respectively. The results reveal that PBL limit the
outward deformation of top plate, reducing the bending stress and
making the stress distribution more uniform at the weld toe.
Therefore, the maximum SCFs on the chord and brace for stiffened
RCFST joints reduce by 25% compared with the maximum SCFs in hollow
section joint. Overall, the fatigue behavior of RCFST joint
stiffened with PBL is improved.
(a)
(b)
Figure 11: Maximum SCFs comparison of different joints with and
without a concrete fill: (a) in the chord; (b) in the brace
1. SUBSTRUCTURE
The substructure was essentially a RCFST Y-shaped pier stiffened
with PBL. This design has been inspired by the branches of tress
(Figure 12). Each pier consists of two Y-shaped columns connected
by three horizontal braces. The cross-section of each column is 400
mm × 300 mm × 16 mm. The tubes in the pier were manufactured using
structural steel of grade Q345 that conforms to the Chinese
Standard GB/T 700, in which grade Q345 steel has a minimum nominal
yield stress of 345 MPa. According to the finite element analysis
of the pier, the maximum compressive stress in the tube at service
is 155 MPa which is equivalent to only 56% of the allowable stress
in Q345 steel. The concrete core and inner PBL stiffener also help
resisting compression. At the top of the pier, the tube member is
directly welded to the bottom of the lower chord (Figure 13). As
for the connection between pier and the pile cap, several PBL
plates are embedded in the pile cap to achieve a rigid connection
(Figure 14).
Figure 12: Design concept of pier
Figure 13: Connection between main truss and pier
Figure 14: Connection between pier and pile cap
1. MANUFACTURING AND CONSTRUCTION OF BRIDGE COMPONENTS
Steel structures enable accelerated construction. This bridge
took only two months to construct. As for the manufacturing, the
main truss is divided into several prefabricated portions with
lengths of about 10 to 12 meters. The pier is divided into the
irregular Y-shape segment and the tube straight segment. After
manufacturing, the steel segments are then transported to the
bridge site. The construction sequences are described as follows:
a) erecting the tube segment of pier to pile cap, establishing the
scaffolding system, erecting and assembling the Y-shape segment
(Figure 15), b) assembling the truss girder, hositing the span on
the left end support and then the span on the left pier support, c)
hositing the span on the right end support and then the span on the
right pier support, d) hositing the closing span, casting the
concrete in the lower chords (Figure 16 shows the construction
progress of truss girder), and e) the completed truss girder serve
as a scaffolding system to cast the deck slab, the framework is
established and reinforcement is assembled, concrete deck slab is
then cast-in-place (Figure 17 shows the construction progress of
deck slab).
Figure 15: Construction progress of pier
Figure 16: Construction progress of truss girder
Figure 17: Construction progress of deck slab
1. ECONOMIC ANALYSIS
In order to understand the economic advantages of this
innovative bridge, the frequently used bridge design in China,
namely prestressed concrete box girder bridge, was selected to make
comparison for the same span arrangement (Table 1) in terms of
quantities. In terms of superstructure, the steel quantity ratio
between scheme 1 (proposed design) and scheme 2 (conventional
design) is (1.3:1). Counting the substructure and foundation
quantities, the economic advantage of scheme 1 is obvious because
of the transparent and lightweight pier. The total steel and total
concrete quantity ratios between scheme 1 and scheme 2 are 0.85:1
and 0.70:1, respectively.
Table 1: Cost analysis of quantities comparing proposed new
design with prestressed box girder bridge
Scheme
Spans
(m)
Superstructure
Substructure and foundation
Total
Concrete
(m3/ m2)
Steel
(kg/ m2)
Concrete
(m3/ m2)
Steel
(kg/ m2)
Concrete
(m3/ m2)
Steel
(kg/ m2)
Scheme1: RCFST truss girder
24+40+24
0.528
308.9
1.135
78.5
1.663
387.5
Scheme2: PC box girder
24+40+24
0.929
238.2
1.433
219.7
2.361
457.9
1. CONCLUSIONS
The application of RCFST with PBL is a new innovation in road
bridge engineering in China. It has been demonstrated that this
design improves the interfacial composite action and bond
properties, buckling behavior and confinement effect. Numerical
analysis of RCFST joint stiffened with PBL has shown that, failure
mode of the joint is changed and stress concentration factor is
approximately 25% lower compared with conventional rectangular
hollow section joint. Accelerated bridge construction is easier to
achieve using RCFST truss bridges and the economic advantage
compared to conventional prestressed concrete box girder bridges
has been demonstrated.
1. ACKNOWLEDGEMENTS
This project was funded by National Key R&D Program of China
(Grant 2016YFC0701202), the National Natural Science Foundation of
China (Grant 51378068) and the Fundamental Research Funds for the
Central Universities (Grant 310821175015). The authors are grateful
to Dustin Brennan at Queen’s University, for his editing of the
manuscript.
1. REFERENCES
Gao, Y.M., Liu, Y.J., Jiang, L., Liu, J.P., Liu, X.H. 2017.
Experimental Research on Flexural Behaviour of Rectangular Concrete
Filled Steel Tubular Truss Stiffened with PBL. Journal of
Architecture and Civil Engineering, 34(5): 171-180. (in
Chinese)
Liu, Y.J., Cheng, G., Zhang, N., Zhang, J.G. 2014. Experimental
Research on Concrete-filled Square Steel Tubular Columns Stiffened
with PBL. Journal of Building Structures, 35(10): 39-46. (in
Chinese)
Liu, Y.J., Xiong, Z.H., Luo, Y.L., Cheng, G., Liu, G., Yang, J.
2015. Double-composite Rectangular Truss Bridge and Its Joint
Analysis. Journal of Traffic and Transportation Engineering
(English Edition), 2(4): 249-257.
Liu, Y.J., Xiong, Z.H., Feng, Y.C., Jiang, L. 2017.
Concrete-filled Rectangular Hollow Section X Joint with Perfobond
Leister Rib Structural Performance Study: Ultimate and Fatigue
Experimental Investigation. Steel and Composite Structures, 24(4):
455-465.
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