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Foundation variations for Integral Bridges
Univ.-Prof. Dr.-Ing. habil. Dr.-Ing. E.h. K.
Zilch Technische Universität München, Munich,
Germany, massivbau_at_mb.bv.tum.de
Dipl.-Ing. R. Methner Technische Universität
München, Munich, Germany, methner_at_mb.bv.tum.de

• Introduction
• Integral bridges that means bridges without
  joints and bearings are standard for concrete
  bridges with short spans. For middle spans, they
  can be an interesting and economical alternative
  to conventional bearing bridges. The abdication
  from bearings and expansion joints should mainly
  reduce the maintenance costs and can furthermore
  advance the driving comfort and the appearance.
• Because of the structure-ground-interaction, the
  knowledge of the ground characteristics and the
  choice of the foundation (size, arrangement) is
  very important for the structural analysis.
• Structure-ground-interaction (ground
  characteristics)
• The determination of the ground characteristics
  is a important part for the safety level of an
  integral bridge. All possible effects, witch can
  be influence the load capacity of the foundation,
  must include by the determination, e. g.
• the natural variance (local and global) of the
  ground characteristics- type of foundation
  (shallow / deep foundation)- production method
  (e. g. initial setting) - interaction between
  different foundations- cyclic-dynamic effects
  (long-term influence)- non-linear (plastic)
  effects- temperature influence (e. g. frost)-
  ground / seepage water- etc.
• As a result of this effects the ground
  characteristics are normally given as upper and
  lower limit values. But, to be an overall
  economical alternative to a conventional bearing
  bridge the foundation of a integral bridge must
  have a small range of the foundation-stiffness,
  both in vertical and horizontal direction, during
  the service time. A safety choice of the ground
  characteristics does not exist. And of course,
  the lower the determination effort is the bigger
  the uncertainty of the ground characteristics.

FE-Analysis A other way to bring a minimum range
of the foundation-stiffness is a good choice of
the structural possibilities of the foundation,
witch was subject of the FE-Analysis. The
numerical FE-Analysis of different
column-foundations with cast-in-place piles
should determinate the minimum range of the
foundation-stiffness based on different
foundation variants (number, diameter,
arrangement) and different grounds. The analysis
includes the primary stress state of the ground,
which means the natural preload due to the dead
load of the ground itself. The description of the
ground takes place with the Hardening-Soil-Model,
which allows the consideration of the non-linear
material effects (loading, load relieving,
reloading). Results The following results shown
the comparison between a foundation with 3 piles,
diameter 1.20 m and 5 piles, diameter 0.90 m.
Both foundation variants have approximate the
same resistance in vertical direction. 3 piles
1.20 mPile ground area 3.40 m²Pile surface
area 13.3 m²/m 5 piles 0.90 m Pile ground area
3.15 m²Pile surface area 14.1 m²/m For
different ground characteristics in a cohesive
soil (g 20 kN/m³, c 10, j 22.5, n 0.3)
the horizontal deformations are shown. Thus, a
foundation with 5 piles tends to a smaller range
of horizontal deformations, based on the natural
range of ground characteristics. 3 piles 1.20
m 5 piles 0.90 m Outlook In a second
step the behavior of abutments variations should
be analyzed too.
e. g.
load test
single measurement and transfer of ground
characteristics
empirical values from literature / standards