Design of Bridges-Some Questions

QUESTIONS
1. Using simple sketch, explain the basic components of a bridge.

2. Bridge structures are normally made of concrete, steel and wood materials, briefly highlight
distinctive features of concrete and steel type of bridges.
3. Explain causes of collapse in bridges.
4. Using well labeled /appropriate sketches, discuss distinctive features and components of the
following types of bridges.
(i). Suspension and Cable stayed bridges
(ii). Arch and Truss bridges
5. Briefly explain two types of prestressing system for bridge beams.
6. Describe the distinctive features of cable stay bridge and arch bridges.
7. Clearly explain the permanent and transient loads in a bridge.
8. Clearly state functions of abutment wall in bridges
9. Give three (3) basic assumptions in analysis of prestressed members
10. Using simple sketch, describe features and components of suspension and truss bridges.
11. Explain how the following four (4) factors are affect the decision of bridge type, planning and the
location of a bridge.
(i). Geometric conditions of the site
(ii). Subsurface conditions of the site
(iii). Aesthetics
(iv). Economics and ease of maintenance
12. Give advantages and disadvantages of Prestressed Concrete as used for bridge beams.
13. Briefly explain two types of prestressing system for bridge beams.
14. The figure below illustrates a single barrel precast box culvert along Namanga Road. The culvert
carries a 1800mm depth of imposed soil material, together with vehicular live loading. Given the
following parameters; reinforced concrete density γconc. = 24kN/m3, saturated soil density γs. =
1800kg/m3, and effective angle of internal friction (φ). = 300, determine moments and shear
forces acting on the culvert. Sketch the bending moment and shear force diagram. Hence, design
the critical slab and wall of the culvert. Take carriage way width as 8.4m. All dimensions in
millimetres.
15. Determine the maximum moment and shear force on the box culvert. Draw the bending moment
and shear force diagram. Hence design and sketch the reinforced section of slab and wall of the
culvert. The culvert carries a 1000mm depth of imposed soil material, together with vehicular live
loading. The culvert should be designed to carry either HA loading udl ~30kN/m2 and KEL
~120kN/m and 30 units of HB loading. Take lane width as 3m, γconc. = 24kN/m3, active earth
pressure Ka ~ 1/3, saturated soil density ~1850kg/m3, C32/30 concrete mix. All dimensions in
milimetres.
16. A rectangular concrete beam, 100 mm wide by 250 mm deep, spanning over 8 m is prestressed
by a straight cable carrying an effective prestressing force of 250 kN located at an eccentricity of
40 mm. the beam supports a live load of 1.2 kN/m.
i). Calculate the resultant stress distribution for the central cross section of the beam. The
density of concrete is 24 kN/m3
ii). Find the magnitude of the prestressing force with an eccentricity of 40 mm which can
balance the stresses due to dead and live loads at the bottom fibre of the central section
of the beam.
17. The figure below show pier details for a bridge is located along Kitengela to Namanga Road. Given
the following parameters, thickness of pavement layers above deck 75mm, deck thickness
200mm, overall depth and breadth of supporting beams 800mm & 400mm respectively, carriage
width of 9000mm, γconc. = 24kN/m3, asphalt density γ. = 20kN/m3.
The bridge fully loaded and operational, work out the following;
(i). Design the cap beam
(ii). Check the stability & design the pier
18. The bridge below is made asphalt deck overlaying series of precast concrete beams spanning 20m
end to end. The beams are supported on free and fixed abutments as shown. Check the stability
and bearing pressure at the foot of the fixed end abutment. Hence, design the fixed end
abutment wall and base to support the traffic loading on the road. The bridge site is located at
across Chania river on Thika-Nyeri Road.
The ground investigation report shows suitable founding strata about 9.5m below the proposed road
level. The results also show the founding strata to be a cohesionless soil having an angle of shearing
resistance (ø)=300 and a safe bearing capacity of 400kN/m2. Backfill material will be class 6N with an
effective angle of internal friction (ø)=350 and density of 18kN/m2. Unit weight of asphalt 20kN/m2
The proposed deck consists of 11Nos. Y4 prestessed concrete beams and concrete deck slab as
shown.
19. The figure below, shows a simply supported reinforced concrete deck slab. The deck carries a
100mm depth of asphalt surfacing, together with a nominal HA live load udl of 17.5 kN/m2 and
knife edge load of 33kN/m. The deck should also be designed to carry 30 units of HB load. The
span of the deck is 12.0m c/c of bearings, γconc. = 24kN/m3, asphalt density γ. = 20kN/m3. Use
C32/40 concrete.
Work out the following;

(i). Loading using combination 1 of BS 5400
(ii). Design the deck using strip method
(iii). Check the serviceability when the bridge has just open
(iv). Crack control check
(v). Design for shear
The figure below shows a simply supported reinforced concrete deck slab. The deck carries a 100mm
depth of asphalt surfacing; the dead loads, together with vehicular highway loadings. The span of the
deck is 12.0m c/c of bearings, γconc. = 24kN/m3, asphalt density γ. = 20kN/m3. Take carriage way width
as 7200mm. All dimensions in millimetres.
20. The figure below shows longitudinal section of beam girders in a two-span bridge along highway
road class A. The loads ultimate loads (self-weights, HA and HB loadings) are as given in Table 1.1
below. Given that the overall depth and breadth of supporting beams 1400mm & 500mm γconc.
= 24kN/m3. Analyze and design for ultimate bending reinforcement, check for shear force and
cracking serviceability for the beam.
Table 1.1: Beam Ultimate loads
Transferred HA (UDL) load 75 kN/m
Transferred HA (KEL) load 152.4 kN
Self-weight alone (inclusive girder weight) 42.5 kN/m
Transferred HB load 285.05 kN
20 m 20 m
21. The figure below show pier details for a bridge is located along Ruiru Bypass to Embakasi. Given
the following parameters, thickness of pavement layers above deck 100mm, deck thickness
200mm, overall depth and breadth of supporting beams 1400mm & 400mm resp., carriage width
of 7500mm, γconc. = 24kN/m3, asphalt density γ. = 20kN/m3.
The bridge fully loaded and operational, work out the following;
(iii). Design the cap beam
(iv). Check the stability & design the pier
(v). Pressure distribution on the base & hence design the base

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QUESTIONS

1. Using simple sketch, explain the basic components of a bridge.

Work out the following;

Transferred HA (UDL) load 75 kN/m

Transferred HA (KEL) load 152.4 kN

Self-weight alone (inclusive girder weight) 42.5 kN/m

Transferred HB load 285.05 kN

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