2. THE ARCHTEC METHOD OF STRENGTHENING

Archtec has been described as ‘Key Hole Surgery’ for bridges and comprises retrofitting stainless steel reinforcement around the circumference of the arch barrel; a typical arrangement of reinforcement is illustrated in Figure 2.1. The reinforcement is grouted in to holes drilled in to the bridge with a coring rig from the road surface (refer to Figure 2.2) or, alternatively in the case of multi-span structures, from below.

Figure 2.1 Typical Arrangement of Reinforcement
Simplified diagram of a single span with from-above installation

Figure 2.2 Installation using Precisely Aligned Diamond Drilling Coring Equipment

Masonry arches, whilst being one of the oldest forms of bridge are in fact complex structures that are difficult to analyse. Accurate analysis is made more difficult by geometry and material variability. The tool at the heart of the Archtec design process is the computer program ELFEN. Using the Finite/Discrete Element (DE) technique to generically model masonry this software is used to represent the behaviour of arch barrels allowing accurate prediction of structural behaviour, as illustrated in Figure 2.3. Simply, each brick or block is modelled and the contact between them automatically calculated as load is applied.

Arches conventionally fail by the development of four hinges leading to a mechanism. The design basis for the strengthening is to locate the reinforcement so as to provide bending strength at the critical locations thereby resisting the development of the hinges. By providing bending resistance the arch barrel is able to resist the critical loading conditions more efficiently and the peak compressive stresses in the masonry are reduced. A similar procedure is applied to multi-span arches although failure mechanisms and anchor positioning is often more complex.

Figure 2.3 Typical Numerical Simulation of the Failure of Masonry Arch
Results shown are Von Mises equivalent stresses

Archtec has been developed by a partnership comprising Cintec International who are responsible for overall project management and also manufacture the anchoring system used, Rockfield Software who produce the ELFEN structural analysis software and Gifford who developed the strengthening concept and provide the engineering design on each individual project.

Although Archtec was originally conceived for efficient, economic and sympathetic strengthening of arches the method of structural analysis also provides accurate strength assessment of existing bridge stock.