The experimental investigation of the structural feasibility of adopting
CFRP cloth material as pre-stress slab¡¡Li Fangyuan, Li Guoping, Chen Airong
Bridgework
Engineering Department of Tongji University
Abstract
¡¡¡¡CFRP cloth
material's production techniques are quite mature. It is widely used in the concrete
structure's reinforcement.
¡¡¡¡Utilize the CFRP cloth material to exert pre-stress
can give fuller play to its high tension and corrosion prevention.
This thesis
gives a clear analysis and description of the feasibility of pre-stress exerted
by CFRP cloth material and introduces the test instance of adopting CFRP cloth
material as pre-stress slab
Keyword: CFRP cloth anchor, pre-stress slab,
pre-stress stretch
1 Summary
¡¡¡¡ Engineering practice shows that CFRP composite
can adapt to modern times engineering structure development trends towards big
span, soar, and heavy load, high intensity, light weight and it can meet the demands
of adverse condition.
It conforms with the industrialization requirements of
modern times engineering technique and is increasingly applied to many structures
such as bridge, different types of civilian construction, ocean, off sea O as
well as subterranean structures. There are two application methods: one is, directly
apply it to newly constructed structures; the other is, use it for the maintenance
and enforcement of old structures to achieve good economic efficiency.
Our
country started the formal research on the application of CFRP to civil construction
in 1996-1997 and launched the actual engineering practice in 1998. Up till now,
there have been nearly ten scientific research institutes, over ten institutions
of higher learning in our country. They do research on the technical performance
of CFRP and make substantive scientific research payoffs. However, domestic research
achievement and object show that our country's research basically gives priority
to structure reinforcement and restoration
¡¡¡¡Obviously, it lags behind the
overseas countries which have already adopted CFRP to substitute the reinforcing
steel bar and pre-stress bar or cable.
¡¡¡¡Although the high tensile strength
and the low elastic modulus make CFRP bar bundles suitable to exert pre-stress,
it has the drawbacks of high heterogeneity and friability. This heterogeneity
makes the CFRP bar bundles easy to destroy at the pressured anchor time, whereas
its friability makes it more hazardous than steel products at stressing time.
So far, there is no anchorage system which can guarantee the best conveyance of
pre-stress among the CFRP force bars. This thesis is also one of the architectural
researches on CFRP pressured anchor.
¡¡¡¡At present, the research on CFRP as
pre-stress stuff mainly focuses on exploitation correlation pre-stressed anchor
tool, at the same time, develop the high performance of CFRP stuff.
Whereas
the CFRP sheet has been applied to the constructional engineering earlier, its
application and exploitation are rather mature, and the application, quite prevalence.
The application of high performance concrete, in particular, that of self-leveling
concrete, by dint of the incorporation of mature CFRP cloth material and pre-stress
technology, will tender new application mode and clue to CFRP stuff and pre-stress
technology.
¡¡¡¡This thesis mainly introduces the CFRP stuff the writers are
developing and the writers' research on the performance and construction technique
of slab structure. The relevant report about research on adopting CFRP cloth as
pre-stress stuff is unavailable for the moment.
2¡¢ Merit and meaning of adopting
CFRP cloth material to exert pre-stress
Carbon fiber reinforcement plastics
have the merits of high strength, fine corrosion proof and durability, etc. People
both at home and abroad all have started the applied research of substituting
it for steel products, but many of the researches are limited to the use of CFRP
as extrinsic reinforcement material.
The maturity of the development technique
of CFPR stuff in recent years and the rapid fall of its price give people good
opportunity to proceed the structural application of CFRP. The conception of adopting
CFRP as pre-stress bar has existed for a long time, but its friability poses great
difficulty in its anchorage. Therefore, the writers' research is on exerting pre-stress
by CFRP cloth material, which enjoys mature technology, instead of by CFRP steel
bar, which requires pre-stressed anchor tool.
Exerting pre-stress by CFRP with
the form of cloth pattern has merits as follows:
(1) need no anchorage, or
develop correlative plumb stage equipment to substitute the anchorage required
by bar material, thus saving the anchorage expense.
£¨2£©exert pressure by flaky
material itself, thus avoiding rupture, which is the result of adopting conventional
anchor tool.
£¨3£© Cloth pattern of CFRP has bigger surface and can have sufficient
contract area with concrete, thus guaranteeing the complete and plenary felt between
CFRP and concrete.
£¨4£© The cloth pattern of the weft's interlace and stretching
can conveniently exert the pre-stress at the portrait and transverse direction.
£¨5£©Flexible arrangement and relatively skim room occupation of CFRP in cloth
pattern can avoid the construction inconvenience resulted from the superabundance
use of steel bar.
¡¡¡¡The report of research on adopting CFRP cloth material
as pre-stress stuff is unavailable now both at home and abroad. This thesis uses
concrete slab as research object, and gives an introduction about slab stress
and section performance when adopting cloth materials to exert pre-stress. Besides,
this thesis supplies theory gist for adopting CFRP cloth material to exert pre-stress
in wider scope. In the slab structure of constructional engineering and bridgework,
including prefabrication and cash irrigate method, adopting pretension method
can achieve a more perfect effect as far as CFRP cloth material pre-stress technology
is concerned. This method can be used for reference when adopting CFRP cloth for
reinforcement of pre-stress tensile structure.
3 the effects of exerting pre-stress
by CFRP cloth materials.
This test adopts Tonggu CFRP cloth, CFC2-2 type, manufactured
by Shanghai Yichang carbon fiber material Co.Ltd. Material parameters are as follows:
Product thickness Type of carbon fiber Extensile strength
0.17mm T-700-12K
¡Ý3500MPa
Tensile elastic modulus Extension at break Weight per area
220
Gpa 1.8% 200g/m2
Cloth width
100mm
Different from CFRP bar material,
CFRP cloth is thin and wide. So exerting pre-stress on CFRP cloth, its stretching
offset must be overcome. The stretching test adopts the device designed by writers.
The device is proceeded by Liuzhou Ouweimu Mechanism Limited Liability Company.
Photos in Chart 1 and 2 respectively display the destroy instance of part of CFRP
cloth resulted from non-uniform tension. Photo in Chart 2 displays the effect
of overcoming non-uniform tension. Photo in Chart 3 displays the scene before
loading when three CFRP are stretched and imbedded in concrete slab.
Photo
1 ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Photo 2
Chart 1 destroy instance of VFRP due to non-uniform
stretching
Chart
2 Photo of CFRP thanks to uniform stretching
Chart 3 the effect when CFRP cloth
is stretched and imbedded in concrete.
According
to the performance parameters of material provided by CFRP manufacturer, after
two tests of stretching, CFRP cloth pre-stress can be imbedded into concrete slab.
The slab's size is 2040¡Á600¡Á80mm£¬and it adopts two strips of CFRP cloth as pre-stress
stuff. It has 4 constructional bars of ¦Õ6 in portrait direction. In the transverse
direction, it has constructional bars with a space of 190mm between.
Chart 4 Shop drawing
of imbedding CFRP cloth pre-stress into concrete slab.
The test shows that
the CFRP cloth's tension is 2117 Mpa, about 0.6 of tensile strength, and the final
effective tension is 1529 Mpa, about 0.45 of tensile strength. It has passed the
middle third point load beam test to effective span of 2000mm. Photo in Chart
5 displays the destroy scene when static loading CFRP cloth pre-stress into slab.
Chart 5 Photo
of CFRP cloth pre-stress slab's structure when loading.
4.Conclusion
and prospects
1£©The research concentrates on the prestressing of CFRP and
the properties of concrete structures. To achieve this aim, we have to find a
effective method to adopt CFRP to increase prestressing.
2£©After twice extension
trial and the third extension when the final construction of prestressing concrete
slab, it is proved viable to increase prestressing on CFRP.
3£©The regular CFRP
as a prestressing material is stick, which indicates the problem of anchor. With
the material, it's great news for the concrete component prefabricate industry
that they cn increase self friction without anchors.l
4£©In concern of the
problems of the single direction anti-drag and the difficulties in construction
of the whole piece CFRP, the interleaving of CFRP lists can implement the effect
of the traditional reinforcing steeling bar networks.
5£©To increase the prestressing
with the material, positive crossing of lists can add prestressing on two directions.
This method is not favor only to the construction of concrete but also to the
stick of CFRP and concrete, which assures the CFRP and concrete support together.
6£©With
CFRP as prestressing adder, there is no similar protection width requirement under
traditional steeling bar construction. Multi flat material is possible up to request.
But reasonable configure with regular reinforce concrete.
The combination
of CFRP and prestressing techniques used in flat structure can take full advantage
of the properties of CFRP, prestressing techniques and concrete slab. In concern
with the inconvenient introduced from integrate of piece and slab, high capable
concrete is necessary during the construction. CFRP is placed and extended after
the irrigation of concrete base; another concrete flag is irrigated then.
5
The way ahead
¡¡¡¡ To use the CFRP in the concrete structure, there's still much
to research, among which is the research of the calculation method of the CFRP
piece behavior on prestressing, the support properties and destroy mechanism.
It's necessary to extend the research on the followings.
£¨1£©The relate research
on CFRP prestressing including more reasonable prestressing method, the design
and machining of prestressing equipments, the calculation and monitor of prestressing
and relate calculation on steeling bars.
£¨2£© The experimental research on the
CFRP prestressing support power. The behavior properties and calculate method
on flat support.
£¨3£©Rational design and construction techniques research is
favor to the application of CFRP in material structure and feasibility of the
CFRP in other construction.
Thanks
¡¡¡¡Liuzhou Ohm Machinery
for their extension equipments.
¡¡ Shanghai Yichang Carbon Fabric for their
CFRP
Reference
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