Project: The Development of Retrofitted Reinforcing Techniques for Masonry Arch Bridges

Reference: CSU 28/4/50

Last update: 04/08/2003 08:58:35

Objectives

To develop and test new repair methods to increase the strength of existing masonry arch structures.

Description

The installation of small diameter stainless steel reinforcing distributed throughout the arch ring will be investigated by means of constructing and testing three models on the masonry arch facility at TRL. Data from these tests will be used to calibrate finite element models to the examine the range of applicability of the systems to larger structures and a range of differing material strengths.

Contractor(s)

British Waterways Board
Wellington Park House, Thirsk Row, Leeds, LS1 4DD
0113 245 0711

Railtrack Civil Engineering
Room 17, Railway Terraces, Derby, DE1 2RY
01332 263786

Helifix Ltd
21 Warple Way, London, W3 0RX
020 8735 5200

London Underground Ltd
30 The South Colonnade, Canary Wharf, London, E14 5EU
0207 308 2697

Oxfordshire County Council
The County Surveyors Society, Speedwell House, Oxford, OX1 1NE
01865 815260

SSP Consulting Engineers
First Avenue, Queenborough, Isle of Sheppey, Kent, ME11 5JK
01795 665927

Contract details

Cost to the Department: £81,488.00

Actual start date: 01 October 1997

Actual completion date: 30 September 1999

Publication(s)

The Development of Retrofitted Reinforcing Techniques for Masonry Arch Bridges
Author: S K Sumon, Transport Research Laboratory
September 1999
Source: TRL, Old Wokingham Road, Crowthorne, Berkshire, RG45 6AU

Summary of results

  1. Two strengthening systems were assessed by testing 5 metre span segmental arches and the development of finite element (FE) models.
    As part of the LINK programme three masonry arches containing ring-separation have been strengthened and tested to failure. The 'Helibeam' System was used to strengthen and test two of them. One arch was strengthened using a prototype and the other arch used a modified version, developed as the result of the first test. The third arch was strengthened using a modified version of the Masonry Arch Repair and Strengthening ('MARS') System, which was developed following earlier tests under a separate programme at TR.L. Within the earlier programme an arch was tested twice; first unstrengthened and then reprofiled and strengthened using the prototype version of the MARS System. Both systems consist of a network of stainless steel wires (helical profile in the Helibeam System and standard ribbed in the MARS System), that are installed and bonded into rebates cut into the soffit of the arch. Radial pins are also used for tying together the separated arch rings. For comparison purposes test data from both programmes was utilised. Following modifications to the initial installation procedures, both systems have demonstrated a significant increase in load carrying capacity when compared to the prototypes and the unstrengthened 'control' model arch.
    Three arches, an unstrengthened and one strengthened by each system, were then represented using two-dimensional finite element (FE) models, which were developed and calibrated using the test data. The analyses were performed using the proprietary FE software LUSAS. Good correlation between the experimental and FE models was obtained. The purpose of the FE models was to be able to model the test behaviour of the arches tested. Further that in the future, the models could be extrapolated for use on different spans and with different strengthening techniques.

    The objectives of the project were to: 1) "establish that strengthening existing arches with distributed small diameter reinforcement is economic and effective both for strength and serviceability". It was not possible to establish the economics as costing was not covered as part of the project. Hence, the part of the objective that has been achieved is to "establish that strengthening existing arches with distributed reinforcement is effective both for strength and serviceability".
    2) "establish the parameters to be taken into account when designing strengthening using these methods and develop design guidelines". Design guidelines have not been developed as part of this project. This was because the design and design calculations are the responsibility of the 'contractor'. Each h of which has produced their own methodology as part of the project. The main purpose of the project was to test existing strengthening systems and provide information on the most effective way of installing of the systems. This has been established.

    3) "make recommendations as to the practical limitations with particular regard to the safety of the structure during installation of the strengthening". This has been established.
    Further, the test data was used to calibrate and develop finite element models as part of the project. It was initially anticipated that crude representation would be adequate but as the project progressed this became a large part of it. The FE models used were developed under the TRL Seedcorn programme. However, in order to develop the findings in the LINK project TRL has provided these in kind. Significant progress has been made in the FE work and this is reflected in the output. Hence, this work in its own right is an additional objective.

    Conclusions

    Five multi-ring masonry arch bridges containing built in ring- separation were tested under the worst case load condition. The tests showed that the load carrying capacity was significantly increased by the strengthening. Radial and circumferential reinforcement provided additional stiffness into the barrel and this limited the movement of the separated rings in both the radial and circumferential directions making them behave in a composite manner. Compared to sprayed concrete or saddling minimum reinforcement is required to achieve a significant increase in the strength of the structure. Hence using small diameter reinforcement is an effective method of strengthening masonry arch bridges.
    Three of the arches were analysed using two-dimensional FE models, which were developed and calibrated using the experimental data. The arches were first modelled using linear analyses, which provided some indication of the behaviour. However, due to the nature of the materials used it was necessary to use non-linear analyses. The FE models have shown that the material properties play an important part in the behaviour of the arch so both model definition and mesh accuracy are crucial. Good correlation between the experimental and FE models was obtained with calibration.
    Strengthening the soffit using stainless steel reinforcement gave a significant increase in the load carrying capacity. This type of strengthening would be most beneficial for an arch with mortar or masonry because it distributes the reinforcing effect evenly over a large area of the ring.
    The loading conditions in both the experiments and analyses were simple, involving self-weight and a single-line load. Further, only two-dimensional behaviour was considered in the FE analyses. Considering multi-line loading would give a better indication of how the other components of the bridge would behave under simulated traffic loading. The behaviour of the backfill could be investigated further, to consider the effect of water and different types of backfill material. The work could be extended to look in detail at the effect of the bond between the reinforcing steel and the brick in the strengthened arch. The FE models could be further refined and expanded to three-dimensions.
    The methods of testing and analysis developed in this project have the potential to be adapted and used in the assessment of other masonry arch strengthening systems.

Departmental Assessment Status: Project completed prior to implementation of Departmental Publication Scheme.