Department of Civil, Mining and Environmental Engineering

A test to failure has been carried out on a 50-year-old RC
railway trough bridge strengthened in flexure with nearsurface
mounted (NSM) Carbon Fibre Reinforced Polymers
(CFRP) bars. The failure occurred at 11.7 MN load, by a
flexural shear failure mechanism. At failure intermediate
crack (IC) debonding of the CFRP bars was noticed, and at
the same moment the major shear crack opened. The NSM
CFRP increased both the flexural and shear capacity of the
bridge. The present codes provided conservative estimates of
shear force capacity; more accurate models are required for
detailed capacity assessments of existing concrete through
bridges.

This paper presents experimental and numerical assessments of the effectiveness of strengthening dapped-
end reinforced concrete beams using externally bonded carbon fiber reinforced polymers (CFRPs).
The research was prompted by a real application, in which the dapped-ends of several precast/prestressed
concrete beams developed diagonal cracks due to errors during assembly. Hence, the dappedends
were strengthened on-site using CFRP plates to limit further crack opening. In the empirical phase
of the study, four similar specimens were tested: one unstrengthened reference specimen, two strengthened
with high-strength CFRP plates, and one with high-modulus CFRP sheets. The specimens strengthened
with plates had slightly higher load carrying capacity than the reference element, but failed by
debonding, while the specimens strengthened with sheets showed no increase of capacity and failed
by the fibers rupturing. Nonlinear finite element analysis of the specimens under the test conditions indicated
that: (a) debonding is more likely to occur at the inner end of dapped-ends and (b) the capacity
could have been increased by up to 20% if the plates had been mechanically anchored.

Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test
objects. This article reports the results of a ‘test-to-failure’ performed using a real bridge. The results obtained in such
tests are valuable for assessing analytical models, updating finite element models and investigating the real behaviour of
structures. The specific intention in these experiments was to study the shear failure of the bridge, which is a less wellunderstood
mode of failure than is bending. To this end, it was necessary to strengthen the bridge using near-surfacemounted
reinforcements made of carbon fibre–reinforced polymer bars in order to prevent bending failure. The bridge
was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable
differential transducers alongside new monitoring systems such as fibre-optic sensors, strain rosette linear variable differential
transducers and a novel photographic monitoring system. This article presents the photographic strain measurements
and describes the use of the photographic tools in monitoring and characterizing the behaviour of the failure zone
during the full-scale test. The strains measured using the photographic method were found to agree well with those
measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method
provided crucial insights into the strains within the bridge’s failure zone. This study was conducted under the remit of
the EU ‘Sustainable Bridges’ Project.

A reinforced concrete railway trough bridge in O¨ rnsko¨ldsvik, Sweden, was strengthened in bending with rods of carbonfibre-
reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European
Research Project ‘Sustainable Bridges’ regarding assessment and strengthening of existing bridges. A steel beam was placed
in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7 MN. It was
initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal
steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile
reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were
improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional
nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge.

This paper presents a parametric investigation, based on non-linear finite element modeling, to identify
the most effective configuration of carbon fiber-reinforced polymers (CFRP) for strengthening reinforced
concrete (RC) dapped-end beams. Following a field application and laboratory tests, it focuses on effects
of 24 externally bonded (EBR) and near surface mounted reinforcement (NSMR) configurations on yield
strain in steel and the capacity and failure mode of dapped-end beams. The investigated parameters were
the mechanical properties of the CFRP, the strengthening procedure and the inclination of the fibers with
respect to the longitudinal axis. Two failure scenarios were considered: rupture and debonding of the
FRP. The results indicate that high-strength NSM FRPs can considerably increase the capacity of dapped-
end beams and the yielding strains in reinforcement can be substantially reduced by using high
modulus fibers.

A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the load-carrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in-situ as the bridge had been closed following the construction of a new section of the railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European Research Project “Sustainable Bridges”. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion and bond failures at an applied load of 11.7 MN (= 2630 kips).
A computer model was developed using Brigade software (based on Abaqus), to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (= 74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over 6 times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe and the U.S.

The purpose of this paper is to review the advances that have been made in the design of monolithic and precast reinforced concrete walls, both with and without openings, subject to eccentrically applied axial loads. Using the results of previous experimental studies, a database was assembled to enable statistical assessment of the reliability of existing design models. Several design aspects are highlighted, including the size and position of openings, and the roles of boundary conditions and geometric characteristics. In addition, the performance of fiber-reinforced polymers in strengthening wall openings is discussed. Overall it is found that design codes provide more conservative results than alternative design models that have been proposed in recent studies. Research into the strengthening of walls with openings is still in its early stages, and further studies in this area are needed. The paper therefore concludes by highlighting some areas where new investigations could provide important insights into the structural behaviour of strengthened elements.

This document presents the work related to the assessment of the effectiveness of strengthening reinforced concrete (RC) dapped-end beams using carbon fiber reinforced polymers (CFRP). Several non-linear finite element analyses were performed using different strengthening configurations, from the simplest solutions to the more complex ones in which different application schemes were overlapped. The work is focused on evaluating the strengthening systems, considering the ultimate capacities they can lead to and the failure modes involved. There were modeled 17 different strengthening configurations. While some of them provided a marginal increase in the ultimate load that can be applied, several of them provided significant load bearing capacity increase. The observed failure modes ranged from a sudden failure of the whole strengthening system up to the desired progressive failure of the individual components of each strengthening system.