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Due to the vulnerability of the traditional adobe construction even in regions of low (intensity MSK VII) to moderate (intensity MSK VIII) seismicity the strengthening
of the existing house stock is critical to preserving life safety and minimising property loss. |
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| The discussion in this section of the guide is divided in two portions: |
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| Strengthening of adobe houses |
In the existing adobe housing not only different properties of adobe masonry are present but also
different types of construction systems and form. However their earthquake damage can be classified based on the three factors
discussed in
Improved Adobe document.
Since the planning and layout in the case of rehabilitation of adobe houses is not an option the technical measures are classified into:
- Measures for improving the strength of masonry walls
- Measures for providing seismic details for continous load path
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| Strengthening of adobe walls can be achived by reinforced cement jacket applied on both sides.
The reinforcing material can be ordinary reinforcing steel mesh as well as ferro-cement or carbon-fibres. In the case of steel wire mesh used first the surface of the adobe
wall is prepared by cleaning and moistening it and drilling holes for the cross ties. Then a base of cement:sand mortar, mixed in 1:4 proportion and thickness 10-15mm is applied
on both sides of wall. The steel meshes (diameter min 2mm @ 50x50 pitches) are then placed on both sides of wall connected together with steel anchors (6mm steel bars cemented
in the pre-drilled holes. The anchors should be at 300mm O/C. After fixing the reinforcing meshes onto the wall a second layer of mortar coating with thickness 15mm is applied.
Steel mesh lapping when required to be min 300mm.
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However strengthening of walls in itself doesn't equal strengthening of the house. To achieve the desired level of
strengthening the following criteria should be met:
- The walls for jacketing should be selected such that they are symmetrical in respect of the geometrical center of the house. This should be
observed in both plan directions.
- At least two walls should be jacketed in each direction. Strengthening the 4 exterior walls may be adequate in most situations.
- The steel mesh at wall intersections are to be lapped by 600mm angle shaped steel wire mesh on each side
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| An experimental project at PUCP,Lima in Peru was focused on developing simple techniques to reinforce existing adobe housing.
Particular objective of the project was developing methods for collapse prevention in the event of a severe earthquake. Numerous materials are tested including: timber boards,
1/2" rope, hexagonal wire mesh and ordinary reinforcing welded mesh. Seismic simulation tests were
performed on 'U'-shaped walls, with and without reinforcement, as shown in Figure 1. |
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Figure 1- Dynamic Testing of 'U' Shaped Walls (Zegarra et al, 1997) |
A highly effective solution is proposed delaying significantly the collapse of the building. The
main details are given below:
Reinforcement consists of welded wire mesh(1mm wires spaced at 3/4"(10mm)), nailed with mettalic bottle caps agains the wall surface Figure 2.
The reinforcing is placed between lintel and roof level as well as vertically at wall intersections. The attached wire mesh is after covered with cement-sand mortar. |
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Figure 2 – Placing reinforcement On traditional adobe wall (Zegarra et al,1997). |
| Existing adobe houses that have been externally reinforced according this detail remained undamaged
during the Arequipa earthquake in Peru (2001). In comparison unreinforced houses were damaged or collapsed. |
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| Post-earthquake strengthening of adobe houses |
| To beginning of document |
| The decision to retrofit (strengthen) or repair a structure is based on the building's seismic resistance. However assessment of
the degree of damage of a traditional adobe housing and whether the strength of structure is adequate can be very complicated and unreliable. Thus with the exception of historic adobe buildings retrofit of adobe houses is best avoided. Rebuilding of houses is recommended incorporating
Improved Adobe construction. |
