Civil Engineering Reference
In-Depth Information
In contrast to near-surface-mounted reinforcement, no minimum spacing rules apply
when using externally bonded reinforcement because the bond forces are transferred
directly into the surface underneath the adhesive and there is no significant spreading of
the bond stress over the width of the member.
3.7.2 Provision of shear straps
The provision of shear straps for the adhesively bonded reinforcement can be necessary
for any of the reasons explained in the preceding sections. Generally, it is necessary to
distinguish between three cases for externally bonded shear straps:
Case 1:
The externally bonded shear strap is required for the shear design. Straps for
case 1 can also serve as end straps to prevent a concrete cover separation failure. With
such a strap, it is also possible to take into account an increase in the bond force due to
the provision of shear wrapping. The effects due to the shear force, the provision of
shear wrapping and the crack opening force
F
u
(
α
b
) should be superposed in this
situation.
Case 2:
The externally bonded shear strap serves as an end strap or is required because of
the shear wrapping according to Section 3.4.1. An increase in the bond force may be
taken into account with this strap. In this situation the effects due to the provision of
shear wrapping are to be superposed on the effect due to the crack opening force
F
u
(
α
b
).
Case 3:
The externally bonded shear strap is provided because of an increase in the bond
force. This strap may be positioned anywhere and is to be designed for the crack
opening force
F
u
(
α
b
) according to Section 3.3.4.4.
3.7.3 Steel shear straps
Shear straps made from steel plates are normally made up of two L-plates to make them
easier to install. To ensure that deformation of the member does not lead to large forces/
stress normal to the adhesive surface at the lap joint, [86] requires that a closing
L-section (see Figure 3.14) be included to prevent the plates from coming apart. When
using the shear strap to increase the bond force at the end anchorage of
flexural
strengthening according to Section 3.3.4.4, the DAfStb guideline speci
es additional
geometrical requirements to be met by the individual L-plates due to the de
nition of the
values
l
1
to
l
4
according to [82].
Fig. 3.14
Function of the closing L-section
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