TECHNICAL
INVESTIGATIONS
EXPERIMENTAL
General
There is no one-to-one correspondence between the mechanical
resistance of a column shoe as delivered and the mechanical resistance
of a column shoe connection. A connection is subjected to various action
effects like axial force, shear force, and bending moment in different
combinations, and the stiffness of the connection also has an impact on
the behavior and the design of the column. It is impossible to determine
the mechanical resistance or stiffness of a column shoe connection as a
set of values determined according to different standards and guidelines.
Therefore, these properties must be determined experimentally.
The EAD 1 summarizes the required tests and the related test setup,
and gives guidance on the evaluation of the test results. The values
determined in this way can then be used with the design method specified
in TR 068 2.
The following tests are mandatory according to EAD:
a) Bending Resistance Tests
b) Bending Stiffness Tests
c) Shear Resistance Tests
d) Fire Resistance investigations
a) Bending Resistance (BR) Tests
The target of the Bending Resistance (BR) tests is to show that the
resistance of the BOLDA® column shoe connection is at least equal to the
bending resistance of a monolithic cast-in-situ column.
b) Bending Stiffness (BS) Tests
In general, design of column-to-column or column-to-foundation
connections with column shoes should follow the design principles given
in EN 1992-1-1 for monolithic columns with continuous reinforcement. The
stiffness of columns and the moment-deflection-behavior respectively
is considered in EN 1992-1-1 by different buckling factors or buckling
lengths. Therefore, within these tests it is verified whether for column
shoe connections the same assumptions as for cast-in-situ columns apply.
With column shoe connections (column A in Figure 7), different zones
along the column length compared to cast-in-situ columns (column B in
Figure 7) must be considered. Within Zone 1, columns with column shoe
connections do not differ from cast-in-situ columns since the existing
reinforcement is identical. In Zone 2, the flexural stiffness of column A
with column shoes is much higher compared to column B. This is caused
by the overlapping of the anchor rebars of the column shoe with the
existing reinforcement of the column. In contrary, column B is designed
Zone 2 Zone 1
Column shoe zone
Zone 3
Column A Column B
Column
foundation
FIGURE 7: DIFFERENT STIFFNESS ZONES OF CANTILEVER COLUMNS
with continuous reinforcement in Zone 2 according to EN 1992-1-1 4,
even though in practice spliced reinforcement would be more common.
In Zone 3, the flexural stiffness of column A is lower compared to column
B, mostly due to the reduced effective concrete section at the bottom of
the column. Further reduction of the stiffness is caused by the eccentric
tension forces in the column shoes (compare Figure 7). The schematic
location of the measuring points along the length of the column is shown
in Figure 8.
With cantilevered columns, the stiffness of the column shoe connection
plays the most important role compared to other statical systems. The
behavior of cantilevered columns is extremely sensitive to geometrical
nonlinearity and therefore considerably influenced by the stiffness. Any
negative effect caused by a flexible connection will be amplified within
such system.
17 15 13 11 9 7 5 3
7
Column A
6 5 4 3 2 1
18 16 14 12
i Subzones i Measuring points
1
10 8 6 4 2
FIGURE 8: LOCATION AND NUMBERING OF THE SUBZONES AND MEASURING POINTS (TRANSDUCERS), SCHEMATIC
50 PEIKKO CONNECTIONS 1/2021