Masonry Arch & Bridge Strengthening Verification of Structural Analysis
VERIFICATION PROCESS
The process which has been undertaken to verify the analytical methods employed by Archtec includes a number of key stands as follows:
- Evaluation against conventional methods of arch assessment
- Evaluation against published data from full-scale tests of unstrengthened arches carried out by others, including the LINK funded programme.
- Evaluation against full-scale tests by TRL of bridges strengthened by the Archtec method which were specifically commissioned as part of the verification process.
These are covered in the following sections.
Additionally, a philosophy of freezing material parameters for whole series of tests where similar masonry construction has been employed (compressive strength of bricks, mortar type etc.) has been adopted. This makes it impossible to adjust an individual arch analysis within a series without influencing all others. Similarly the analysis of Archtec strengthening follows on from verified and frozen unstrengthened analyses.
EXECUTIVE SUMMARY
Archtec is an innovative system that has been developed for assessing and strengthening masonry arch bridges. In many circumstances it offers considerable advantages over other alternatives and since its creation in 1998 it has been used widely in the United Kingdom on Local Authority owned bridge stock and several projects have also been undertaken overseas. More than 120 bridges have now either been assessed or strengthened using the system.
At the heart of the strengthening system is the method of structural analysis used to assess arch bridge behaviour. This analysis is based on numerical simulation and the Finite/Discrete Element technique using the program ELFEN. The technique, never used before to model arch bridges, enables good prediction of strength and displacement and permits features such as rings in arches, multiple spans, slender piers, aspects of deterioration and strengthening to be fully quantified.
Extensive verification work has been undertaken to confirm the suitability and accuracy of the numerical methods employed, including evaluation against specifically commissioned full-scale tests and published data from tests by others, and against conventional methods of arch assessment.
Further to discussions with various client organisations through the offices of the Bridge Owners Forum (BOF)–Masonry Arch Sub-Group (United Kingdom), this report has been prepared to document the key aspects of the verification work that has been completed. It is intended to facilitate a better understanding of the basis of the system.
The verification undertaken demonstrates that the predictions of behaviour carried out using ELFEN correlate well with the broad range of test results considered and also with conventional methods of arch assessment, where they are directly comparable.
On the basis of this verification and subject to the use of the relevant material properties and parameters upon which the verification has been carried out, the use of ELFEN in the way described to determine the strength of both unstrengthened and Archtec strengthened masonry arch bridges (which are square or near square (up to the order of 20° skew)) is considered justified.
Finite/Discrete Element analysis of masonry structures also provides several significant new capabilities over conventional methods of assessment, namely;
* Explicit representation of defects such as ring separation, local distortion and mortar loss is possible and the verification process using ELFEN has established that these can also be reliably modelled.
* Deflections and serviceability behaviour can be predicted. This has not before been possible.
The verification process has established that deflections can be reliably predicted using ELFEN and this provides the basis for significant and exciting new capabilities for modelling arch behaviour at serviceability limit states.
INTRODUCTION
Archtec is an innovative system that has been developed for assessing and strengthening masonry arch bridges. In many circumstances it offers considerable advantages over other alternatives and since its creation in 1998 it has been used widely in the United Kingdom on Local Authority owned bridge stock. Several projects have also been undertaken overseas in the USA and Australia. More than 120 bridges have now either been assessed or strengthened using the system.
At the heart of the strengthening system is the method of structural analysis used to assess arch bridge behaviour. This analysis is based on numerical simulation and the Finite/Discrete Element technique using the program ELFEN. The technique, never used before to model arch bridges, enables good prediction of strength and displacement and permits features such as rings in arches, multiple spans, slender piers, aspects of deterioration and strengthening to be fully quantified.
Extensive verification work has been undertaken to confirm the suitability and accuracy of the numerical methods employed, including evaluation against specifically commissioned full-scale tests and published data from tests by others, and against conventional methods of arch assessment.
Further to discussions with various client organisations though the offices of the Bridge Owners Forum (BOF)–Masonry Arch Sub-Group (United Kingdom), this report has been prepared to document the key aspects of the verification work which has been undertaken. It is intended to facilitate a better understanding of the basis of the system and assist in its more widespread use.
It follows a report prepared for Railtrack/Network Rail in July 2002 (B1660A/W10/R01)(1) and provides greater detail with respect of the verification process.