Surveying Undergraduate Programmes

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Longitudinal schemes for bridges Introduction
Dr Ana M. Ruiz-Teran
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Longitudinal schemes for bridges. Bridge types
Beams
Trusses
Portal frames
Arch bridges
Cable-stayed bridges
Suspension bridges
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• There is a certain range of spans lengths for
  every single bridge type
• It is not possible to establish a limit for every
  particular bridge type
• The cost of a particular solution depends on many
  other parameters (materials, technical
  requirements, construction procedure, etc)
• The most economic solution depends on the
  specific conditions of every single case

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Longitudinal schemes for bridges. Part 1 Beams
Dr Ana M. Ruiz-Teran
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• Beam bridges are supported in two or more
  sections. They are able to resist the actions
  acting on them and transmit them to the
  foundations.
• The Bending and Torsion Responses due to vertical
  loading are not coupled in straight beams
• The span for bending response is determined as
  the spacing between support sections that are
  able to transmit vertical reactions (all of
  them). The span for torsion response is
  determined as the spacing between support
  sections that are able to transmit couples (two
  bearings per section deck and piers linked by a
  fixed connection, etc)
• The connection between piers and deck is pinned
  in the longitudinal direction. The longitudinal
  stiffness of the piers does not affect the
  response of the deck under vertical loading. The
  longitudinal stiffness of the piers affect the
  response under horizontal loading

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• In curved bridges, the bending and torsional
  resistance mechanisms are coupled

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• In skewed bridges, the bending and torsional
  resistance mechanisms are coupled

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• The deck has an axial response under imposed
  longitudinal deformations (due to prestressing,
  time-dependent effects, temperature, etc) due to
  the stiffness of the bearing-pier-foundation
  system

The stiffness K should be obtained at bearing
level
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Location of the neutral point
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• In bridges with variable depth the Resal effect
  (shear load resisted by normal stresses) must be
  taken into consideration
• Bridges with independent spans. Advantages (1)
  Easier analysis, (2) lack of internal forces in
  the case of a support settlement. Disadvantages
  (1) a single structural response mechanism
  available, (2) lack of continuity in rotations at
  the support sections, (3) larger bending moments,
  (4) larger deck depths
• Continuous bridges with balanced end-spans
• Location of joints. Compromise solution.
  Advantages (1) Eliminate global internal forces
  due to temperature changes, (2) Reduction on
  bearing movements when including several joints.
  Disadvantages (1) High cost, (2) Traffic
  disturbance, (3) maintenance, (4) durability

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Longitudinal schemes for bridges. Part 2
Trusses
Dr Ana M. Ruiz-Teran
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• Model with pin-jointed connections for
  preliminary analyses and with rigid- and
  semi-rigid- connections for detailed analyses
• The neutral axes of all members meeting at one
  joint should intersect at a single point in order
  to about induced bending moments

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Longitudinal schemes for bridges. Part 3
Portal frames
Dr Ana M. Ruiz-Teran
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• In portal frames, there is a link between the
  piers and the deck in order (1) to reduce the
  bending moments at mid-span (either to reduce the
  deck depth or to increase the span range for a
  certain depth/span ratio) and (2) to share the
  external bending moment due to permanent and live
  load between the support and mid-span sections
• Consequences (1) the piers are working also
  under bending, (2) an horizontal reaction is
  transmitted to the foundations
• How can this effect being promoted? (1) Designing
  a fix connection between the piers and the
  foundation, (2) Increasing the flexural stiffness
  of the piers, (3) reducing the height of the
  piers
• The deck shortening due to imposed longitudinal
  deformations (due to prestressing, time-dependent
  effects, temperature, etc) reduces the horizontal
  reaction and the portal-frame action

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Effect of the horizontal stiffness of the soil in
the bending moments in the deck
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Longitudinal schemes for bridges. Part 4 Arches
Dr Ana M. Ruiz-Teran
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• Arches are designed with their shape in order to
  work mainly under compression, avoiding most of
  the bending
• In permanent state, the bending moments can be
  almost cancelled. This is not the case under live
  load of imposed deformations (temperature,
  time-dependent effects, etc.)

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Anti-funicular shape of a certain loading
(neglecting axial deformations)
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The larger the axial deformation, the smaller the
horizontal thrust
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REFERENCES CHEN, W. F. AND DUAN L. 2003. Bridge
Engineering. CRC Press LLC HAMBLY, E.C. 1991.
Bridge Deck Behaviour. Spon Press. PARKE G,
HEWSON N. 2008. ICE manual of bridge engineering.
ICE. MANTEROLA, J. BRIDGES. (6 Volumes, in
Spanish). ETSICCP, Madrid