1. Development Of Alternative Composite Concrete Bridge
Systems For Short And Medium Span Bridges
By
Dinesha Kuruppuarachchi (B.S.)
COLLEGE OF ENGINEERING AND SCIENCE
LOUISIANA TECH UNIVERSITY
July 2016

2. ABSTRACT
• A total of four new bridge systems for short and medium span bridges are presented.
• These bridge systems are lightweight, efficient in flexure and shear and can be used in sites
with stringent vertical clearance requirements while being able to accelerate construction by
eliminating the need for site installed formwork.
• The proposed configurations are compared with traditional adjacent box beam
• and decked bulb tee systems for spans that range from 80 ft to 150 ft.
• Both normal weight and lightweight concrete options are investigated.
• The comparison is made in terms of span to depth ratios, weight, number of strands, live
load deflection and camber.
• It is demonstrated the two proposed systems (PS1 and PS2) that feature concrete
topping are lighter than the adjacent box beam system for all spans considered.
Additionally, PS2 requires fewer strands. Both proposed topped systems feature
lower camber when compared to the adjacent box beam system. PS2 provides
shallower superstructure depths for a given span compared to the adjacent box
beam system.

3. Topped system means that the bridge uses a deck.
Un-Topped system means that the bridge do not use a deck.
Proposed bridge systems
INTRODUCTION

4. Proposed bridge systems (Cross section of the bridge)

5. Traditional bridge systems

6. Traditional bridges
1. Box beams
• Positive - Strength, stiffness
• Negative - failure of connections leads to
reflective cracking
2. Decked bulb tees
• Positive – strength, stiffness
• Caution – Need to be properly braced
before the installation
Introduction Methodology Results Conclusion
Traditional bridge systems

7. Objective
The goal of this project is to develop alternative composite concrete
bridge systems for short to medium-span bridges, which are
lightweight, efficient in flexure and shear and can be used in sites
with stringent vertical clearance requirements while being able to
accelerate construction by eliminating the need for site installed
formwork

8. Methodology
• Description od the bridge systems
• Live load distribution factors
• Validation
• Longitudinal connections

9. Figure 2.1 Proposed Bridge Systems
Description of the bridge systems
Dimensions of the
traditional bridge
systems (box beams
and Decked bulb tees)
3D image of
proposed systems

10. Dimensions of
proposed bridge
systems

11. • 2 different unit weights
• 3 lanes
• 48ft width
• Different compressive strengths
General notes about the bridge
Description of the bridge systems

12. • Eg: Box bridge systems
– 80ft span length : 33in in depth
– 100ft span length : 39in in depth
– 120ft span length : 42 in depth
And so the PS1 and PS2 used the same depth as Box bridge system.
The superstructure depth for the proposed systems is kept the same
so that a comparison could be made in terms of weight, number of
strands, live load deflection and camber.
• Eg: Decked bulb tee bridge systems
– 80ft span length : 35in in depth
– 100ft span length : 42in in depth
– 120ft span length : 53 in depth
– 150ft span length : 65in in depth
And so the PS3 and PS4 used the same depth as Decked bulb tee bridge system.
Description of the bridge systems

13. • Eg: Box bridge systems
– 80ft span length : 33in in depth
– 100ft span length : 39in in depth
– 120ft span length : 42 in depth
And so the PS1 and PS2 used the same depth as Box bridge system.
The superstructure depth for the proposed systems is kept the same
so that a comparison could be made in terms of weight, number of
strands, live load deflection and camber.
• Eg: Decked bulb tee bridge systems
– 80ft span length : 35in in depth
– 100ft span length : 42in in depth
– 120ft span length : 53 in depth
– 150ft span length : 65in in depth
And so the PS3 and PS4 used the same depth as Decked bulb tee bridge system.
Description of the bridge systems

14. Live load Distribution factors
AASHTO (American Association of State Highway and Transportation Officials)code already
provide information on how to find live load distribution factors (LLDFs) for traditional
systems
Live load distribution factor is a quantitative value which indicates the percentage of live load that
each girder can carry due to a wheel load.
But for the proposed systems we do not know how to get the live load distribution factors. But we
can use an equation to find LLDFs.

15. Deflections in the mid-span of the bridge
Live load distribution factors for moment

16. Reactions at the edge of the bridge
One way to find deflections and a reaction forces of a bridge is by
using finite element analysis. So we used this method. We use abaqus
software for the analysis.
Live load distribution factors for shear

17. Live load distribution factors for moment

18. Finite element analysis
• Draw the model
• Partition (for the loads)
• Material properties (elastic modules, poison ratio)
• Boundary conditions (pin and roller )
• Loads (in terms of tire pressure)
• Tie connections
• Mesh (6in mesh)

19. Tie connections
6in Mesh

20. Loading positions
We used an AASHTO Truck and a tandem truck to explore the critical loading
condition
AASHTO truck
AASHTO tandem loading
1 2

21. 3 4
5
Loading positions

22. Light weight (0.12 kip/ft) , and normal weight (0.15 kip/ft) options were also
considered. With the unit weight change the elastic modules of the material will
change . So, that would impact for the model in abaqus.
6
7
Loading positions

23. Loads are placed at the edge of the bridge to get the maximum reaction
force. That will help to get the maximum shear force.

24. All proposed and traditional systems are designed based on AASHTO LFRD Specifications
using Mathcad.
The number of strands obtained from Mathcad calculations for the traditional bridge
systems are compared with that obtained from the PCI Bridge Design Manual and
Conspan software to validate the approach.
Validation

25. • Flexural stress at transfer at the mid span, at the edge
• Flexural stress at service at the mid span, at the edge
• Flexural stress at strength
• Shear Strength
• Deflection checks
Flexure is more critical in these kind of bridges than shear.
The next step is to determine how much shallower could the superstructure depth be for the
traditional systems if LLDFs for moment computed from FEA are used instead of those
calculated based on AASHTO LFRD Specifications
Once the shallowest superstructure depth for the traditional systems is obtained, the proposed
systems are designed to maintain the same depth and a comparison in terms of weight and
the number of strands required is performed.
Design Process

26. Perfectly bonded connections- due to the large contact surface between deck and
precast components.
12in deep shear keys for the box beams using the tie constraints.
The connection between the flanges of adjacent decked bulb tees is simulated using a
tie constraint for the full depth of the flange.
Longitudinal connections

27. Both are discrete connections spaced at 4 ft on center . The dimensions of this pocket are 6 in. in
the transverse direction, 3 in. deep and 12 in. in the longitudinal direction.
The tension force in the longitudinal connections is calculated by recording the transverse
normal stress in the 3D solid elements in the bottom precast flange and by multiplying it with
the area of the elements that are part of the transverse connection.
Longitudinal connections in PS 1 and PS2

28. The transverse bending moment per one foot of length is calculated by recording the
transverse compression and tensile forces in the top and bottom finite elements and
multiplying them with the moment arm
Longitudinal connections in PS 3 and PS4

29. Results
To be able to perform a consistent comparison between the proposed systems and
the traditional systems, live load distribution factors (LLDF) for moment for all systems
are computed using finite element analyses
The traditional adjacent box beam system featured the lowest computed LLDFs compared to PS1 and
PS2.The computed LLDFs for the decked bulb tee system are also lower than those calculated using
AASHTO provisions.
Live load distribution factors for moments
Live load distribution factors

30. The computed LLDFs for shear are less than half of those calculated based
on AASHTO provisions.
Therefore, if a more economical shear design is pursued, the computed
LLDFs for shear presented in the report may be used in lieu of those
calculated based on AASHTO provisions.
There is not a significant difference between the computed LLDFs for shear
in the proposed systems and traditional systems.
Live load distribution factors for shear
Live load distribution factors

31. LLDFs for the normal weight and lightweight concrete options are similar.
When lightweight concrete is used the beams deflected more compared to the
normal weight option, however this resulted in similar LLDFs for moment.
Superstructures with and without barriers are analyzed and it is found that when
the barrier is omitted LLDFs for moment are higher
From the investigated load positions the ones that featured edge loading resulted
in higher LLDFs.
It is determined that the case that featured a two truck loading configuration
controlled over the other cases.
Other observations about Live load distribution factors

32. Mesh size Validation
A mesh sensitivity analysis is performed to determine whether the computed
LLDFs are influenced by the size of the finite elements. This exercise is done for the 80 ft span
decked bulb tee system. Four different mesh sizes are considered, 3 in., 4.5 in., 6 in., and 7.5
in.
Figure demonstrates that the mesh size did not make a difference in terms of
LLDFs.

33. All bridge systems are designed using AASHTO provisions using Mathcad . The results
obtained from Mathcad in terms of number of strands for the traditional systems
are compared with those obtained from the PCI Bridge Design Manual and Conspan.
During this comparison the LLDFs are based on AASHTO provisions.
This results suggests that the design calculations used in Mathcad lead to reliable results
Validation

34. Topped systems
• Strand configurations for both light weight and normal weight box beams,
• The strands in the box beam and PS2 are harped due to their natural shape. PS1,
however, cannot used harped strands because of its tapered web. It is more
economical when the strands can be harped because they can control both mid-
span stresses and other stresses at the end.
• Almost always, the controlling parameters are tensile stress at service, at mid-span.
• Light weight bridges always used less strands than normal weight bridges.

35. Light weight bridges uses less strands
Strand configurations for both light weight and normal weight box beams
Topped systems

36. PS1 cannot use harped strands. So the strand pattern in the
mid-span is also same as the strand pattern at the edge
Strand configurations for both light weight and normal weight PS1 beams
Topped systems

37. Strand configurations for both light weight and normal weight PS2 beams
Light weight bridges uses less strands
PS2 can use harped strands. So the strand pattern in mid-span is not
same as the strand pattern at the edge
Topped systems

38. Almost always, the controlling parameters are tensile stress at service, at mid-span.
Topped systems

39. Box beams, PS1 and PS2 use a deck.
Without the deck it is called as non-
composite section.
With the deck it is a composite
section.
Both normal and light weight options
considered in here.
Weight wise PS1 and PS2 are better
than Box beams.
Box beams are originally has a width
of 4ft but all the proposed systems
has a beam width of 6 ft. So the box
beams 4ft was converted to 6ft
width.
Material use - weight
Topped systems

40. Material use - strands
Strands wise PS2 is better than box beams
Topped systems

41. This slide shows a summary
of the material use in box
beam , PS1 and PS2 bridges
in both normal and light
weight options
Topped systems

42. Live load deflections and Camber
Live load deflections are lower
for BOX beams, which is a plus
point to box beams.
But the camber is lower in PS2
beams which is a plus point for
PS2 beams.
Topped systems

43. Shallowest depth
Topped systems

44. Un-topped systems

45. Un-topped systems
Strand configurations for both light weight and normal weight PS3 beams

46. Un-topped systems
Strand configurations for both light weight and normal weight PS4 beams

47. Un-topped systems
Almost always, the controlling parameters are tensile stress at service, at mid-span.

48. Un-topped systems
Material use - weight
Material use - strands

49. Un-topped systems
This slide shows a summary
of the material use in DBT
beam , PS3 and PS4 bridges
in both normal and light
weight options

50. Un-topped systems
Live load deflections and Camber
Ps4 has less live load
deflections and camber,
which means it is stiffer
compared to DBT.

51. Un-topped systems
Shallowest DBT can
get for 80ft is 32in
and it uses 22
strands. PS4 can
obtain that using 19
strands.

52. Transverse bending moments

53. Conclusion
A total of four composite concrete bridge systems are developed for short
and medium span bridges with spans ranging from 80 ft to 150 ft.
These bridge systems are lightweight, efficient in flexure and shear and can
be used in sites with stringent vertical clearance requirements while being
able to accelerate construction.
The developed systems consist of adjacent hollow precast concrete beams
with and without concrete topping.
The comparison is made in terms of span to depth ratios, weight, number of
strands, live load deflection and camber
PS2 and PS4 appear to be more competitive than Box, DBT, PS1 and PS3.
DBT needs more strong transverse connections

54. Questions

55. Thank you