Securing of reinforcing strips

An arrangement and method for reinforcing a structural component utilizes an elongated strip or lamina which is applied to the surface of the structural component and which has at least one end which submerges into a recess in the surface of the component and is anchored in that recess. This has been found to greatly increase the reinforcing effect of the strip on the structure.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to an arrangement for reinforcement at a 
longitudinally and/or areally extending structure or structural component 
by means of at least one lamina-like reinforcement disposed on the 
structure or structural component or masonry, slacked or prestressed, a 
structural component provided for support functions, as well as a method 
for reinforcing a structure or structural component. 
For many years research and practice has been engaged in the subsequent 
reinforcement of structures, such as in particular ferroconcrete 
structures and masonry by applying additional reinforcement. The 
beginnings of this technique are described in J. Bresson, "Nouvelles 
recherches et applications concernant l'utilisation des collages dans les 
structures. Beton plaque.", Annales ITBTP No. 278 (1971), Serie Beton, 
Beton arme No. 116, and go back to the 1960s. Bresson directed his efforts 
in particular to the research of the composite tension in the region of 
the anchorages of steel laminae affixed by adhesion. 
For approximately the past twenty years, existing structures, such as 
ferroconcrete structures, such as for example bridges, floor and ceiling 
plates, longitudinal girders and the like, but also nonreinforced masonry, 
can consequently be reinforced through subsequent affixing by adhesion of 
steel laminae. 
The reinforcing of concrete structures and masonry by affixing steel 
laminae with, for example, epoxy resin adhesives, can be considered to be 
standard technique at this time. There are a variety of reasons which make 
reinforcement necessary: 
increase of load capacity, 
change of static systems by removing, for example, bearing elements such as 
supports, or their support functions are reduced, 
reinforcement of structural components endangered by fatigue, 
increase of rigidity, 
damage of bearing systems or renovation of existing structures and of 
masonry, as well as 
faulty calculation or workmanship of the structures. 
Subsequent reinforcement with steel laminae affixed by adhesion have been 
found to be useful on numerous structures such as is described for example 
in the following literature citations: Ladner, M., Weder, Ch.: "Geklebte 
Bewehrung im Stahlbetonbau" {Adhered armouring in ferroconcrete 
construction}, EMPA Dubendorf, Bericht No. 206 (1981); "Verstarkung von 
Tragkonstruktionen mit geklebter Armierung" {Reinforcement of bearing 
structures with adhered armouring}, Schweiz. Bauzeitung, Sonderdruck aus 
dem 92. Jahrgang, No. 10 (1974); "Die Sanierung der Gizenenbrucke uber 
Muota" {Renovation of the Gizen bridge across the Muota}, Schweiz. 
Ingenieur & Architekt, Sonderdruck aus Heft 41 (1980). 
However, these reinforcement methods entail disadvantages. Steel laminae 
can only be supplied in short lengths which only allows application of 
relatively short laminae. Consequently, laminar stacks become necessary 
and thus potential weak points, cannot be avoided. The awkward handling of 
heavy steel laminae on the site can in addition lead to especially 
difficult problems in implementation techniques in the case of high 
structures or those difficult to access. Moreover, in the case of steel, 
even with careful corrosion protection treatment, the danger of lateral 
concealed rusting of the laminae, or the corrosion on the interface 
between steel and concrete exists which can lead to the detachment and 
thus the loss of reinforcement. 
Accordingly, it was suggested in the publication by U. Meier, 
"Bruckensanierungen mit Hochleistungs-Faserverbundwerkstoffen" {Bridge 
renovation with high-performance fiber composites}, Material+Technik, Vol. 
15, No. 4 (1987), and in the dissertation by H. P. Kaiser, Diss. ETH No. 
8918 of the ETH Zurich (1989) to replace the steel laminae by carbon-fiber 
reinforced epoxy resin laminae. Laminae comprising this material are 
distinguished by a low bulk density, very high strength, excellent fatigue 
properties and outstanding corrosion resistance. It is thus possible to 
use, instead of the heavy steel laminae, light, thin carbon-fiber 
reinforced synthetic material laminae which can be transported virtually 
continuously in the rolled-up state to the construction site. It was found 
in practical determinations that carbon-fiber laminae of 0.5 mm thickness 
are capable of absorbing a tension force which corresponds to the yield 
force of a 3 mm thick FE360 steel lamina. 
The stated carbon-fiber laminae have been found to be highly useful even 
when used for reinforcement of masonry in seismically hazardous zones. In 
Bericht {Report} 229 of the Eidgenossische Materialprufungs- und 
Forschungsanstalt (EMPA) {Swiss material testing and research 
institution}, Dubendorf, by G. Schwegler with the title "Verstarken von 
Mauerwerk mit Faservebundwerkstoffen in seismisch gefahrdeten Zonen" 
{Reinforcement of masonry with fiber composites in seismically hazardous 
zones} it is in particular suggested to reinforce existing masonry shear 
walls or walls in the facade region subsequently with fiber composite 
laminae. Therewith masonry can be decisively reinforced with respect to 
shearing and tension strength, compared to nonarmoured masonry. It is for 
example suggested therein to affix by adhesion! the reinforcement laminae 
diagonally and crosswise on a shear wall, such as a facade wall, and it 
was found that for increasing the shearing resistance the terminal lamina 
anchoring, for example in concrete plates, is critical. 
Particular attention must be paid in all described cases to the shearing 
fractures formation in the concrete or the masonry, respectively. Shearing 
fractures lead to an offset on the reinforced surface which, as a rule, 
leads to the peeling or detaching of the reinforcement laminae. The 
shearing fracture formation is thus also a significant assessment 
criterion with respect to the load capacity of the nonreinforced 
structural component as well as also a potential detachment danger of the 
subsequently applied reinforcement laminae. 
The International Patent Application WO93/20 296 describes a method by 
means of which structural components intended for bearing functions are 
reinforced against shearing forces thereby that the above cited 
reinforcement laminae are each pressed by means of clamping elements in 
the terminal region margin onto the structure in order to prevent their 
detachment. The laminae are disposed such that the distance from the 
lamina end to the support or the concrete plates disposed terminally at 
shearing walls is as small as possible. The anchoring zone must be 
dimensioned such that the lamina tension force can be anchored and the 
transfer of the force to a support or to the margin of concrete plates of 
a shearing wall is ensured. 
But it was found in practice that anchoring the reinforcement laminae in 
the region of the supports is not always possible due to concrete beam 
haunches and shoulders which leads to an increase of the distance. Even 
when reinforcing shearing walls it is most often difficult and expensive 
to anchor the reinforcement laminae in the concrete plates disposed on 
these walls above and below. Furthermore, for reasons of handling at the 
construction sites it is advantageous if reinforcement laminae do not need 
to be excessively long which results automatically if, for example, when 
reinforcing bridges reinforcement laminae must each extend from support to 
support. 
SUMMARY OF THE INVENTION 
It is therefore a task of the present invention to disclose how, with 
shortened anchoring lengths on reinforcement laminae, a largely constant 
reinforcement on structures can be achieved. 
What is suggested is an arrangement for reinforcement on a longitudinally 
extending and/or areal structure or structural component by means of at 
least one lamina-like reinforcement disposed slacked or under prestress on 
the structure or structural component, wherein according to the invention 
the at least one lamina serving for reinforcement is anchored at least on 
one end extending into the structure or structural component. 
It is therein suggested that at least the one lamina-end, preferably at 
least nearly continuously arched, is deflected for extending into the 
structure or masonry in order to be anchored in the structure or masonry. 
In this way it is possible to attain, even with short anchoring lengths, a 
similar or nearly identical reinforcement on a structure or masonry as 
with relatively long practically from support to support and an anchoring 
of the lamina ends is possible in the region of the supports without 
encountering difficulties. Studies which will be discussed in further 
detail in the following with reference to the enclosed figures have shown 
that reinforcement laminae which are only disposed over a relatively short 
anchoring length with regard to the load introduction on the structure to 
be reinforced and which, according to the invention, have been anchored by 
projecting into the structural component, yield a nearly identical 
reinforcement on the structure as when the corresponding lamina end is 
anchored up to the region of the support. 
It is understood that the suggested arrangement or anchoring, respectively, 
according to the invention of a lamina end such that it projects into the 
structure or masonry, respectively, is, suitable for any known 
reinforcement laminae, such as for example steel laminae, laminae 
reinforced by fiber glass or carbon fibers, for example produced with 
epoxy resins or polyester resins, extruded reinforcement laminae 
comprising a thermoplast, etc. 
The at least one end of the reinforcement lamina or also both ends of the 
reinforcement lamina are preferably set into the structure extending at a 
constant arch wherein each of the set-in end can be covered by means of 
concrete and/or a polymer-reinforced material, such as in particular an 
adhesive agent. In the case of, for example, carbon-fiber reinforced epoxy 
resins, it is advantageous to use an epoxy mortar or an epoxy 
resin-reinforced concrete polymer, respectively, in order to anchor or 
cover, respectively, the end of the lamina set into the masonry or the 
concrete, respectively. 
It is understood that it is also possible to press the lamina end 
projecting into the masonry or concrete structure, respectively, as 
suggested in WO93/20296, with a plate, lamina or truss-chord-like element 
against the structure or the structural component, respectively, in order 
to attain in this way a further reinforcement against occurring shearing 
forces. For this purpose is also suitable, for example, a wedge covering 
the lamina end. 
Instead of these pressing means it is also possible to anchor the lamina 
end additionally by means of prestressed or non-prestressed mechanical 
fastening means, such as in particular bolts, rivets, pins, loops and the 
like in the structure or the structural component, respectively, or the 
masonry. 
The arrangement suggested according to the invention is suitable for a 
structure or a structural component, respectively, intended for bearing 
functions, which is reinforced with one or several reinforcement laminae 
against occurring shearing forces. But also for the reinforcement of any 
structure or a masonry by means of one or several reinforcement laminae it 
is advantageous to anchor the lamina ends, such as is suggested according 
to the invention, such that it extends into the structure or structural 
component, respectively, or the masonry. It is for example possible when 
reinforcing masonry in seismically hazardous zones by means of GFK laminae 
to anchor the lamina ends such that they extend into the masonry, which 
makes superfluous the necessity to end for the purpose of anchorage the 
laminae into the concrete plates or cover plates, respectively, disposed 
terminally with respect to the masonry, which represents a significant 
simplification when applying such reinforcement laminae.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1, illustrates, schematically and in longitudinal section a reinforced 
concrete or ferroconcrete bridge 1, comprising a concrete plate 3 which is 
supported or held, respectively, by two piers 5 at the particular supports 
7. Due to ageing this concrete bridge has been reinforced by means of a 
reinforcement lamina 10 disposed between the two supports 7. The 
reinforcement lamina 10 extends between the two supports 7 and is affixed 
by adhesion over its entire length, for example with an epoxy resin 
adhesive agent, wherein also in region A' the lamina, as is conventionally 
customary, is adhered terminally on the concrete plate 3. As suggested in 
WO 93/20296, it is possible additionally to anchor or press the lamina 
ends against the concrete plate 3 by means of additional truss-chords or 
steel plates. 
FIG. 2 depicts a shearing wall 11 of a building, which is located in a 
seismically hazardous area. The masonry 13 is reinforced with laterally 
affixed by adhesion! reinforcement laminae 20, wherein the laminae are in 
conventional manner anchored in the concrete plates or the bottom 15 and 
cover plate 17, disposed terminally below and above the shearing wall 13. 
The lamina end extends for example in the region A" into the concrete 
plate 17 in order to be anchored in it. The production of this anchoring 
is expensive and requires large work expenditures. 
FIG. 3 depicts the way in which, according to the invention, in regions A' 
or A", respectively, the lamina ends can be anchored simpler and more 
effectively. In this way, in region A' the lamina end does not need to 
extend into the proximity of support 7 and in region A" it is not 
absolutely necessary that the lamina end must extend into the concrete 
plate 17. As is evident in FIG. 3, the lamina end 22 of the reinforcement 
lamina 10 or 20, respectively, curves and extends into a recess in the 
surface of the concrete plate 3 or the masonry 13, respectively, and it is 
correspondingly covered in this region by concrete or cement mortar, 
respectively. It is understood that it is also possible to implement the 
coverage 23 by means of a polymer adhesive agent, such as for example an 
epoxy resin mortar or a polyurethane or silicon formation. The optimum 
selection of the material to be used is a function, for example, of the 
material of which the reinforcement lamina is fabricated. The end of the 
strip-like elongated lamina terminates at the end of the recess and is 
thus braced against the recess as shown in FIG. 3. 
In conjunction with the following figures, it will be shown in the 
following that by inserting, shown schematically in FIG. 3, the lamina end 
into the structure or into the masonry, respectively, a decisive shearing 
reinforcement on the structure can be achieved even if the lamina length, 
not as usually required, is selected such that it extends from support to 
support or from concrete plate to concrete plate. With the experimental 
arrangement described in the following will in particular be shown that 
with identical lamina length an increase of the reinforcement can be 
attained if the lamina end(s) are anchored such that it (they) extend(s) 
into the structure or the structural component, respectively, or the 
masonry. 
FIG. 4a shows in longitudinal section a concrete girder 3 analogous to that 
of FIG. 1, which is used for the following experimental arrangements. 
Concrete girder 3 rests on supports 7 and comprises a steel armouring 4. 
The concrete girder 3 has additionally been reinforced on its under side 8 
by means of a CFK lamina 10 wherein the one end 11 of the lamina extends 
practically up to the corresponding support 7', while the opposing lamina 
end 13 is spaced apart from the other support 7". FIG. 4b shows the 
concrete girder from FIG. 4a in cross section. 
The concrete girders shown schematically in FIGS. 4a and 4b were subjected 
to bending tests in conjunction with different experimental arrangements, 
wherein at the two sites 15 indicated by an arrow, a force F was 
introduced. 
The experimental arrangement, shown in FIG. 5a, depicts the reinforcement 
lamina in plan view from below onto the concrete girder 3 to be 
reinforced, wherein the one lamina end 11 extends up to support 7' while 
the opposing lamina end 13' extends by a distance beyond the corresponding 
point of force introduction 15". The dimensioning of the experimental 
arrangement is shown in the representation of FIG. 5a, wherein the lamina 
end 13' extends correspondingly by 20 cm beyond the point of force 
introduction 15". In FIG. 5b are depicted schematically the measuring 
points 29 which are to be provided at the lamina end 13' for determining 
the forces occurring or the extension occurring, respectively. Site 24 in 
FIG. 5a marks the center of the concrete girder 3 at which also a 
measuring site is disposed. 
In order to prevent failure of the lamina 10 in the region of end 11, 
further a (not shown) pressing plate is provided. The lamina end 13' is 
anchored affixed by adhesion! in conventional manner on the underside of 
the concrete girder. 
FIGS. 6a and 6b show an analogous experimental arrangement wherein, 
however, the lamina end 13" extends by 30 cm beyond the corresponding 
point of force introduction 15", and thus extends closer to the 
corresponding support 7". Again, in the region of end 13" several 
measuring sites are provided, as well as also centrally at site 24 on the 
concrete girder 3. 
In FIG. 7 is depicted an experimental arrangement, wherein now the lamina 
end 13'" is anchored such that it extends into the structural component 
which is shown schematically in longitudinal section of FIG. 7c. The 
lamina end 13'" extends therein again only by 20 cm beyond the 
corresponding point of force introduction 15", thus is spaced apart by 
more than 10 cm from the corresponding support 7", compared to the 
experimental arrangement according to FIG. 6a and 6b. The anchorage of the 
lamina end 13'" extends along a distance of 10 cm, wherein the FIG. 7c the 
continuously bent end piece 13a'" extending into the concrete girder 3 is 
shown schematically in longitudinal section. Over the lamina in region 23 
in the anchoring zone of the end segment 13a'" an epoxy resin mortar was 
applied. Again in FIG. 7b schematically several measuring sites 29 are 
depicted, which have been disposed on lamina 10. Also at site 24 in the 
center of the concrete girder 3 a measuring site was disposed on the 
reinforcement lamina 10. 
FIG. 8 shows in the form of a diagram the load deflection of the 
experimental girders measured in the center of the girder with the 
experimental arrangement used according to FIGS. 5, 6 and 7. The 
deflection .delta. (mm) is shown as a function of the force (KN) 
introduced at sites 15, wherein segregated by extension it is shown for 
the three experimental arrangements of FIGS. 5, 6 and 7. 
In each of the Figures a of FIGS. 9, 10 and 11 are shown the laminae 
extensions at the lamina end at different force stages for the three 
experimental arrangements of FIGS. 5, 6 and 7 as well as in the particular 
Figures b the extensions in the girder center. 
In the following Table 1 for the three experimental arrangements the 
measured girder resistances the mean lamina tension in the girder center, 
as well as the type of failure of the girder are listed. 
______________________________________ 
Girder FmaxkNm! .sigma.L (F) N/mm.sup.2 ! *) 
Failure 
______________________________________ 
FIG. 5 65 456 (60) lamina start 
FIG. 6 65 628 (65) lamina start 
FIG. 7 75 1'063 (75) lamina start 
______________________________________ 
*) mean lamina tension in girder center 
Discussion of the results or of the diagrams, respectively, according to 
FIGS. 8 to 11 as well as of Table 1: 
The maximum load, and in particular the maximum lamina extension, in the 
experimental arrangement according to the invention according to FIG. 7 
could be increased significantly relative to the girders of the 
experimental arrangements 5 and 6. In spite of different anchoring lengths 
in the region of ends 13' and 13", the girders according to FIGS. 5 and 6 
exhibit similar behavior. In the central girder region the same extensions 
are registered. {Each of} The laminae shear off the lamina end when they 
reach yield load. 
The lamina of the girder according to the arrangement suggested according 
to the invention in FIG. 7 is set at one end 13'" into the concrete girder 
3 and covered with adhesive agent 23. The maximum lamina extensions could 
be markedly increased relative to the experiments described above in 
connection with the arrangements according to FIGS. 5 and 6. This behavior 
can presumably be explained as follows: 
Deflection of the resulting tension components perpendicularly to the 
affixed lamina. Therewith the lamina is pressed on generating compression 
tensions in the concrete. With corresponding ideal and optimized geometry 
of the end segment 13a'" extending into girder 3 pressing of the lamina 
onto the girder can be achieved, which is comparable to the effect of the 
transverse tension described in the International Patent Application WO 
93/20296. 
The adhesive agent on the lamina or a pressing wedge according to FIG. 3 or 
the subsequent FIGS. 13a and b prevents the untimely detachment of the 
lamina end caused by the perpendicular tension component directed away 
from the girder. 
By means of the experimental arrangements in FIGS. 5 to 7 thus it can 
emphatically be shown that through the terminal anchoring according to the 
invention extending into the structure, of the reinforcement laminae a 
significantly increased reinforcement on the structure can be attained 
compared to a reinforcement lamina of equal or greater length, whose 
corresponding end is not anchored according to the invention so as to 
extend into the structure but rather, as known from prior art, is affixed 
by adhesion! along a significantly longer anchoring path onto the 
structure or is anchored in contact on the latter, respectively. 
In FIGS. 12a and 12b a method is depicted schematically of the way in which 
the terminal anchoring according to the invention of a reinforcement 
lamina 10 is possible relatively simply. As a rule, grinding-in, 
milling-in or grinding-off into the structure is not possible so that, as 
shown in FIGS. 12a and 12b, it is suggested to accomplish the terminal 
extension into the structure of the reinforcement lamina end 22 by means 
of so-called stepped-off core bores. Thus in the terminal region so-called 
core bores 31 are stepped-off by means of for example a conventional 
drilling machine into the concrete 3 to be reinforced, wherein the first 
bore removed from the lamina end has only a low depth while the last core 
bore 31 in the region of the lamina end has a great depth. Such core bores 
can have, for example, a hole diameter of 10 or more cm, depending on the 
width of the reinforcement lamina 10 to be anchored. After the disposition 
of the lamina end 22 such that it extends into the structure, an anchoring 
wedge 23 can again be placed, as described in FIG. 3. 
Such anchoring wedge is also depicted in FIGS. 13a and 13b, wherein now 
additional fastening means 33 are disposed, which can be, for example, 
screws, bolts, loops etc. By means of these securing means 33 the 
anchoring effect of the wedge 23 onto the lamina end 22 is additionally 
augmented. FIG. 13a shows the wedge 23 in longitudinal section while FIG. 
13b represents a top view onto wedge 23. 
In FIGS. 14a and 14b a concrete structure 32 is shown such as for example a 
bearing structure in galleries or tooling halls, in which structure the 
ceiling plate 35 and the side wall 37 are connected with one another in 
the corner region across a so-called haunch 39. If the underside of the 
ceiling 35 is to be reinforced by means of a reinforcement lamina 10, it 
is clearly evident in FIG. 14a that the anchoring of the lamina end 13 in 
the region of the haunch is unfavorable since upon the occurrence of 
tension forces acting! onto the reinforcement lamina 10 the latter 
becomes detached in the corner region 36. 
As shown in FIG. 14b, for this reason it is suggested according to the 
invention to anchor the reinforcement lamina 34 or its end 22, 
respectively, in the comer region 36 in such a way that it extends into 
the concrete ceiling 35. When the concrete ceiling 35 is under load, the 
tensile stress component due to the bending moment onto the lamina in the 
end region of the lamina is deflected into the ceiling which prevents the 
lamina end 22 from becoming detached. 
Lastly, FIG. 15 depicts a further structural arrangement, for example again 
a bearing structure, comprising a concrete ceiling 41 as well as a 
partition wall or a longitudinal pier 43, wherein again the ceiling 41 is 
reinforced by means of a reinforcement lamina 10. In the comer region 45, 
between ceiling 41 and pier 43, is anchored according to the invention the 
lamina end 22 such that it extends into the ceiling. 
In conjunction with the auxiliary line 53 drawn in FIG. 15 the course of 
the bending moment with respect to the structural component or to the 
system center plane 47 extending through the ceiling is shown. Therein is 
clearly evident the passage through a zero point at distance x from the 
pier 43 near the corner region 45 and a subsequent strong increase. 
Through the anchoring according to the invention of the lamina end 22 at 
interval range x where no tension force occurs, it is already possible 
starting at the zero point to absorb fully the subsequently generated 
tension stress through the reinforcement lamina 10. In the event that the 
reinforcement lamina 10, affixed by adhesion! as usual, were anchored in 
the corner region 45, an absorption of the generated tension stress would 
only be possible at a distance greater than! x from the corner region 45, 
whereby the danger of shearing-off of the lamina 10 from the concrete 
ceiling 41 is given. 
FIGS. 1 to 15 serve only for the further explanation and illustration of 
the concept according to the invention and it is understood that the 
terminal anchoring suggested according to the invention, of reinforcement 
laminae can be selected to be any desired one. The material used for the 
reinforcement laminae can also be any desired material, thus a lamina can 
be comprised for example of sheet iron, steel, aluminum, a reinforced 
polymer, such as in particular a GFK-reinforced epoxy resin, etc. 
Essential to the invention is the fact that a reinforcement lamina applied 
or affixed on a structure or masonry is anchored so as to extend at least 
with one end into the structure or masonry, respectively; whether or not 
therein a reinforcement wedge is used is not of primary significance and 
depends on the requirements and the locality.