Why reinforced masonry?

Systems for reinforcing earth block walls have been developed in order to improve the resistance of earth buildings to earthquakes. Most of the regions exposed to this risk have imposed norms which require the use of vertical and horizontal reinforcement (e.g. Peru, Turkey, USA). The building systems exploited use the principle of a wooden or steel ring-beam sunk into the walls, and also reinforcement of the corners of walls and opening frames. The existence of reinforcement considerably improves the tensile and bending strength of the masonry.

Special blocks

It is possible to reinforce masonry using ordinary compressed earth blocks but it is preferable to use special blocks which make it easier to incorporate reinforcing elements. Blocks with channels, hollows or holes allow for vertical and horizontal reinforcement.

Upper ring-beams

The ring-beam is the ultimate earthquake resistant building system. Indeed if there is no ring-beam, any other earthquake resistant building approach is rendered practically useless, particularly with thin, high walls. The ring-beam ensures good transmission of loads and allows a highly organized masonry structure to be formed.

Horizontal and vertical ring-beams are the reinforcement systems most used. They can sometimes consist in very localized reinforcement, located in the weakest parts of the masonry structure, either at the corners, or at the reveals of openings. Such localized reinforcement is most often sunk into mortar beds and is made of wood, steel, metal mesh or grids.

The part played by the reinforcement is particularly important to ensure the stability of compressed earth block masonry, as it is for all types of masonry using small building elements (e.g. fired bricks). It remains indispensable even in regions which are not exposed to seismic risk particularly for thin wall construction.

Reinforcement reduces the danger of cracking which is the effect notably of dlfferential settling, shrinkage; swelling, thermal expansion, rotation or shearing stress (at openings and walls junctions), stress caused by the pressure of flooring, the lateral force of the wind, sloping roofs, arches or vaults. Reinforcement enables the harmful effects of these stresses to be reduced by containing the wall in all directions, continuously.

FIGURE (FIG.115;116)

Fig. 115: Bonding pattern enabling vertical reinforcement to be incorporated.
Fig. 116: Special blocks for reinforced masonry and ring-beams.

FIGURE (FIG.117;118)

Fig. 117: Masonry using special blocks and reinforced with wood.
Fig. 118: Reinforced masonry using bamboo with special square blocks.

The main role of reinforcement is to bond the walls together, notably to absorb horizontal loads, as vertical loads are absorbed by the foundations. This bonding effect can be ensured only if the reinforcement is perfectly connected to the wall and if it is perfectly rigid and impossible to deform, particularly to ensure good tensile strength.

Reinforcement can also be used for other purposes to reduce deformations due to the risk of buckling (in which case it is preferable to locate it at an intermediate height in the masonry, under the lower edge of the openings or at the level of the lintel), to ensure that loads are evenly distributed, to provide a continuous lintel or to serve as a support and anchor-point for the floors and roof.

Fig. 119: Thin walls, buttresses and reinforcement.

Reinforcement materials

The main materials used are wood, steel and concrete. These materials must possess good adherence with the earth block masonry to ensure the efficiency of the reinforcement. Reinforcement made of wood (bamboo, eucalyptus) or of steel are generally laid in a bed of mortar within the thickness of the walls. Steel must be correctly tied, especially at the corners of walls and sufficiently well covered with concrete. Concrete reinforcement is either poured at the top of the thickness of the wall (leaving the problem of a thermal bridge to be resolved), or into special hollow blocks or used in a block bonding system of lost formwork.

Thin masonry

For thin walls (fig. 119) buttresses can be integrated into the facades, notably at the corners and in the vicinity of the reveals of large openings. The walls are also horizontally reinforced at the level of the floors and/or the roof and these upper and lower reinforcements are linked together by vertical elements at the corners and at adjacent walls.

For gable-end walls, integrating a pillar into the axis of the wall, taking care with precise bonding and toothing with the wall masonry ensures good reinforcement. This pillar makes the wall panel rigid and improves its resistance to wind pressure. Reinforcement at the base of the gable-end wall absorbs the wall loads.

Fig. 120: Ring-beams and reinforced comers using wood or steel embedded in the wall.

Fig. 122: Ring-beams of mesh embedded in the mortar or in reinforced concrete.