Masonry Magazine February 2005 Page. 32
Retrofitted Reinforced Masonry
Retrofitted reinforced masonry is stronger than unreinforced and is capable of resisting relatively high out-of-plane loads - loads that act perpendicularly to the surface of the wall depending on the level of reinforcement. Retrofitted reinforced masonry uses techniques developed in the building restoration industry, where existing structural masonry is diamond core drilled from the roof to the foundation and specially designed grout inflated masonry anchors are installed and allowed to cure. The system has been tested to 125psi and 284psi-ms and can be used to secure blast-proof windows within masonry walls, combining window security with masonry strengthening.
Research has shown that masonry walls with high levels of internal vertical loads (e.g., multi-story buildings) resist spalling better than those that are not loadbearing (e.g., infill panels or single-story construction). Retrofitted reinforced masonry can also be post-tensioned after installation to increase the internal vertical stress and maximize spalling protection in low-level masonry structures. The anchors are easily installed, even in occupied buildings, within the plane of the wall, and are not visible once installation is complete. Further, retrofitted reinforced masonry can also be used in areas of high seismic risk where dynamic loads due to ground movement have to be resisted.
Internal Concrete Skin
There are certain situations where the blast load is so large that it is not possible to provide the required level of protection using the conventional retrofitted techniques described above. In such cases, the only solution is to retrofit the building with an internal concrete skin. This is an effective but expensive solution. A full structural analysis is required to determine whether it is necessary to underpin the foundations to resist the additional dead loads. Also, additional structural reinforcement may be required to strengthen the building frame in order to resist the huge dynamic loads likely to arise and prevent building collapse. Further, there will be loss of space inside the building equivalent to the thickness of the concrete skin and the necessary "air gap" behind the existing wall. In such designs, the existing outer wall is assumed to fail under blast load and, in doing so, it will deflect inwards significantly. The remains of the masonry wall and the blast wave then impact on and are resisted by the internal concrete wall.
Durisol Block
A proprietary product known in the U.S. as Durisol Block provides a variation on the internal concrete skin.