Lead Research Organisation: University of Bath
Department Name: Architecture and Civil Engineering


The proposal aims to develop a practical generalised model for analysing realistically dimensioned and loaded rectangular columns strengthened using FRPs. Strengthening circular concrete columns can be achieved by wrapping with FRP (fibre reinforced polymer). This confines the concrete, and can result in increases in load and strain capacity of over 100%. However, most columns are square or rectangular in cross section. Tests, mainly on small-scale rectangular columns, have shown a lower increase in strength, but still up to 50%. A number of simple empirical models have been developed to predict the increase in strength, based upon these small-scale tests. However, , due to size effect, the limited size of columns used in the tests provide little justification for using these models for the larger size rectangular columns found in practice. Thus, a fundamental investigation is required in order to provide a reliable model of behaviour. In order to establish such a general behavioural model there are three fundamental issues which are not well understood, nor limits defined, and therefore need addressing; size effect, aspect ratio and load eccentricity. Confinement of rectangular columns occurs by generating forces at the corners of the column through strain in the FRP, resulting in an effectively confined cruciform region. When the bond between the FRP and the face of the column breaks down, the FRP is no longer effectively anchored to the sides of the column and, ultimately, must strain from corner-to-corner resulting in lower confinement forces for large columns than for small columns with a small side length. For similar reasons, aspect ratio must also be considered. Additionally, as aspect ratio increases, the effectiveness of confinement is known to reduce. Finally, most columns are loaded eccentrically or have combined bending and axial loads. This results in uneven strain distribution across the section and, therefore unequal confining forces at each corner, resulting in a non-cruciform confined area. The behaviour, considering these three issues, will be ascertained via a series of instrumented and monitored tests on large-scale rectangular columns (for comparison with existing small scale test results), together with qualitative finite element modelling to establish the evolution of the shape of the effectively confined area. This information, together with a suitable bond-stress-slip and concrete failure models, will be used to develop an analytical model for strengthening of rectangular columns based upon the mechanics of the behaviour rather than by fitting experimental results.


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Description Existing models of behhaviour are not appropriate for representing column heaviour when subject to bending combined with compression (as all columns are).
There is no size effect - small columns behave the same as large columns.
Columns with an aspect ratio larger than 1:1.5 do not benefit significantly from wrapping with carbon fibre in an attempt to increase thier capacity.
Debonding of carbon fibre jacket can occur when columns are subject to large amounts of bending an this needs to be accounted for in design otherwise capacity can be over estimated.
Exploitation Route Structural Engineerng consultants- now have teh ability to confidently design strengthening systems to large rectangular columns - something which was not possible before.
Building and bridge owners (e.g. the Highways Agency, Network Rail) have the ability to retrofit their structures rather than condeming them as unfit for use.
Eurocode committees have evidence of the effectiveness of the method as well as a straightforward procedure for design of rectangular column strengthneing. This will be incorporated into the next revision of the current concrete Eurocode 4, EN1994.
Other researchers will have valuable large scale test data on which to base further research.
Sectors Construction,Transport

Description The findings of this research have led to the development of robust methods for designing strengthneing schemes for rectangular concrete columns. The methodology developed from this research has been incorporated into the Concrete Society's Technical Report 55, which is the UK guidance document for strengthening concrete structures using advanced composite materials. This allows designers to strengthen columns of the type found in buildings and bridges using this method. The results of this work are now being fed into revisions to Eurocode 2, the european design standard for concrete structures.
First Year Of Impact 2012
Sector Construction,Transport
Impact Types Societal,Economic

Description CEN250/WG5/TG1 Task group for updating Eurocode 2 (concrete structures) to include strengthening and reinforcement using fibre reinforced composites
Geographic Reach Europe 
Policy Influence Type Membership of a guideline committee