tee Ve

Traditional

cturstemhersn neivendeds latear

lding mof JeriChinarth asis estiuses bcountrre is a

also because of the necessity to construct new buildings in bothdeveloped and developing countries.

We must study the past; learn from the mistakes and imple-ment the positives so that new technologies and materials will al-low for a better existence in accordance with peoples needs and

sure is increased in areas of regular seismic activity.Failures that lead to the collapse of soil based constructions due

to external loads, in particular those made of adobe or rammedearth, usually occur as follows:

The rst failure is usually due to bending. The low tensile resis-tance of the soil causes the walls to detach from one another inthe corners. Starting from the top, the walls become indepen-dent of each other; they become separate elements with no lat-eral stability.

Corresponding author. Address: Departamento de Construcciones Arquitectn-icas, Universidad Politcnica de Valencia, Camino Vera s/n, 46022 Valencia, Spain.Tel.: +34 650 31 23 13; fax: +34 963 87 74 59.

E-mail addresses: quianib@csa.upv.es (Q. Angulo), amas@csa.upv.es (. Mas),

Construction and Building Materials 30 (2012) 389399

Contents lists available at

Construction and B

evvgalvan@csa.upv.es (V. Galva), josanmo2@arqt.upv.es (J.L. Santolaria).construction material, resulting in the self-construction of a livingspace using surrounding materials such as earth and wood. Devel-oped countries, under criteria of sustainability, are recovering an-cient construction systems which, thanks to being cost effective,efciently achieve the desired objectives.

This is why the understanding of how soil-based constructionswork and behave is so important. Above all for the conservationand rehabilitation of the many existing World Heritage Sites, but

acteristics and structural strength [1017].Another structural aspect of the construction design which is

concerning is that usually in earth construction, oor slabs androofs are not connected to walls with horizontal and vertical rein-forcements. Due to this, the oor slabs or roofs do not connect di-rectly to the framework and thus do not distribute pressure norreinforce the building. Walls become independent structures posi-tioned under external loads. This worrying issue of horizontal pres-StructureBracesReinforcementStiffen

1. Introduction

The natural soil, earth, etc. is a buiused for over 11,000 years. The cityZiggurats, Athens, the Great Wall ofare historic examples of the use of eathroughout the world. At present, itthe worlds population still live in ho50% of which represent third world

In many developing countries the0950-0618/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.11.024aterial which has beencho, the Mesopotamianand the Andean citiesa construction materialmated that over 30% ofuilt using soil systems,ies [19].lack of housing and of

the overall geo-environmental and development requirementssuch as safety and sustainability.

Structurally soil as a building material performs well againstcompression forces but has a low tensile strength. Therefore it isimportant to mold and condition the material towards compres-sion and avoiding tensile forces. Another problem is the poor join-ing of rammed earth wall sections, and adobes and mortar. Thismeans that any seismic activity could prove extremely dangerousfor users if appropriate security measures are not taken. Improvingsoil for either adobe or rammed earth walls, will improve its char-Rammed earthWall

2011 Elsevier Ltd. All rights reserved.Traditional braces of earth constructions

Quiteria Angulo-Ibez , ngeles Mas-Toms, VicenDepartment of Architectural Constructions, Polytechnic University of Valencia, Camino d

a r t i c l e i n f o

Article history:Received 2 September 2011Received in revised form 5 October 2011Accepted 24 November 2011Available online 30 December 2011

Keywords:EarthAdobe

a b s t r a c t

This paper studies the struconstruction comparing syocco, Mexico, Cuba and otcompared and later used iIt covers both the ineffectwith wooden beams embedring beams, ashlars or reedizontal forces of wind and

journal homepage: www.elsll rights reserved.Galva-LLopis, Jos Luis Sntolaria-Montesinosra s/n, 46022 Valencia, Spain

al performance of various traditional brace solutions for walls in soil baseds used in Spain with the most representative from Peru, Chile, Brazil, Mor-. A unique model for similar loads, seeing the differences to be analyzed,w construction (sustainable and low cost architecture) and rehabilitation.ess of certain braces (Buttresses and increased inside corners); incrementsand Tiranta aspada, and the signicant improvements of others, such astice to prevent the collapse of the soil based constructions against the hor-thquakes.

SciVerse ScienceDirect

uilding Materials

ier .com/locate /conbui ldmat

following the horizontal joints along the wall. Finally, failure due to overturning. Once the walls become inde-

nd Bpendent (bending failure) or once they begin to crack and break(shear failure), they behave as independent rigid structureswhich solely rely on their own weight and strength againstexternal pressures. If the acting momentum exceeds the resis-tant momentum, the wall or structure would collapse by fallingoff balance, and the roof on top of them could also fall down.

Depending on available materials and various weights to beborne during construction, different techniques and bracings sys-tems have been developed all over the planet in an effort to solvethese problems. These construction systems have adapted to agreater or lesser extent to the characteristics and the requirementsof both the terrain and the users. Depending on success, power andcommunication they may have been globalized and exported toother locations or they may have remained local.

Currently, soil based constructions are being updated in areas ofhigh seismicity to improve resistance against earthquakes. In addi-tion to the improvement of earth characteristic and the traditionalguidelines and bracing systems [6,1829], other techniques andmodern elements (not being studied in this paper) are being incor-porated, even if this means extra cost and the acquisition of mate-rials that are not always available:

Columns and concrete beams as stiffeners reinforcementsattached both horizontally and vertically with earthwork inll.A main structure of reinforced concrete with walls of rammedearth or adobe with a sealing function. The connection betweenthe main structure and the earth walls to prevent walls collaps-ing, but not implicating the global collapse of the building, isvery important [30].

The integral masonry system, galvanized wire braided in theform of truss in walls and slabs [3136].

Plastering the walls with reinforced mortar or geogrid or wiremesh and cement mortar [3754].

The objectives of this study is to analyze various traditional sys-tems of bracing earth constructions and their inuence in the re-sponse to the stresses that occur throughout the life of a building.

There is no point in making an exhaustive calculation of differ-ent braces under specic loads, but an analysis of their perfor-mance in terms of the traditional design of a single model andwith the same loads is the appropriate option. This method allowsqualitative and quantitative comparison, therefore it is necessaryto perform some structural calculations.

In conclusion, it aims to assess the braces tested in accordancewith the structural benets they provide and make some construc-tive recommendations arising from its application.

2. Calculation methods: description of the model, materials and loads

The calculation uses a scalar damage model for frictional plastic materials, witha program developed by the Polytechnic University of Valencia (see Acknowledge-ments). In the CID, structural analysis program for CAD environments buildingstructures, an application has been implemented of the isotropic damage modeldeveloped in the last two decades. This application is based on damage mechanic,which is part of internal variables that introduce microstructural changes in the The following failure is usually due to shear. If you control thejoint between the walls and the possible failure of the corners,they better withstand horizontal pressures on the surface thatcould lead to failure by shear and in turn the appearance ofdiagonal cracks. In adobe walls, following the horizontal andvertical joints in a diagonal direction. In rammed earth walls,

390 Q. Angulo-Ibez et al. / Construction abehavior of materials, modeling the inuence of history of material behavior inthe evolution of stresses. With the proper denition of the damage function repre-senting the material response in compression and tension, you can model the non-linear behavior of the earth using the damage theory. The appearance of cracks andtheir evolution over time describe trajectories of several damaged spots, repre-sented as an effect of local damage in terms of material parameters and functionsthat control the progression of damage to the successive state of tension at eachpoint. This application has been calibrated with several works and studies as wellas existing physical elements [5561].

The typological model is a traditional house with two oors above ground of7.20 9.20 m (facade dividing wall) and load-bearing wall parallel to facade forsupporting oor slab and ridge beam. Load-bearing walls are rammed earth walland/or adobe 4060 cm thick depending on their slenderness and loads. Floor slabwith wooden struts 15 cm diameter every 50 cm with inll support of vault loam(adobe bricks and loam) or wattle and mortar on top of the beams. Pitched roofmade with logs, wattle and clay tiles supported on the load-bearing walls (facadeand intermediate wall). Ground height of 3.90 m and 6.00 m ridge. The height ofground oor is 2.5 m.

The structural model is discretized with nite hexahedral solid elements (volu-metric) for earth walls and nite bar elements (linear) in order to replace beamsand braces supported at the solid nodes and substituting oor inll for the appro-priate loads. Model has 1.972 hexahedron of 0.20 0.40 0.40 m per side with 8nodes each, 61 bars for roof and slab beams and 9 bars for lintels.

The soil based constructions to be analyzed are adobe and rammed earth walls.Both types of construction have the same building solutions and same struts are ap-plied, as they have the same physicalmechanical characteristics and suffer thesame type of pathology and collapse. Although they have perform slightly differ-ently because of their different systems (the rammed earth walls are constructionsmade with homogeneous material whereas adobe is composed of smaller piecesjoined together; they have been modeled as a single homogeneous material sincetheir overall performance is similar. Therefore, although models have been discret-ized as mud walls without joints, they can be compared to adobe walls.

This paper does not take into account different variants of rammed earth wallsdepending on their material and composition as it seeks to analyze the inuence ofdifferent bracing solutions in soil based construction. For the same reasons, this pa-per does not study other traditional systems such as wattle and daub, textile wallelements lled with earth, and direct forming with wet loam. Wattle and daub,thanks to their lightness and exibility of materials (rods and branches) prove tobe a good solution in areas of high seismicity risk.

The analysis adopts media and general physicalmechanical characteristics forearth material, without material implements neither composition. A unique modelwith same characteristics and loads for all braces for having an appropriatecomparison.

Earth characteristics of the corners elements were dened with less mechanicalresistance because of the difculty of creating the corners inside the frameworksand/or poor joints with vertical recess solution. Middle and conservative physico-mechanical properties has been adopted for materials from the results of tests(from La Manchuela, Albacete, Spain) and literature [6,18,6271] (Table 1).

For the hypothesis of loads and load combinations we have adopted the valuesof ofcial documents and regulations:

Selfweights loads: values from the tests results. Live loads: based on current Spanish law [72]. Earthquakes: according to the Spanish law [73]. Values have been taken to ana-lyze worst possible result, although this legislation would prevent the construc-tion of soil based buildings under such conditions.

In the process of calculation three methods were employed:

Linear static calculation: based on the assumption of linear elastic performanceof materials and taking into account the balance of the structure withoutbecoming deformed. Loads and load combinations are considered for the twomain directions.

Nonlinear static calculation: this takes into account the stressstrain perfor-mance of nonlinear material and geometric nonlinearity, i.e. achieving balanceof the structure in its deformed state. We analyzed four independent load com-binations for the two main directions, introducing proportional increases in 20loads, taking into account geometric variations and materials:

Gravitational loads (selfweights and live loads) without majority. Gravitational loads (selfweights and live loads) and horizontal (wind) withoutmajority.

Gravitational loads (selfweights and live loads) to collapse. Gravitational loads (selfweights and live loads) and horizontal (wind) tocollapse.

Dynamicseismic calculation, we have analyzed two equivalent static loadcombinations for earthquakes for the two main directions of the model.

3. Traditional analyzed braces

uilding Materials 30 (2012) 389399Before description of analyzed braces for earth construction, weshould highlight some basics concepts about the design, construc-tion and maintenance of earth buildings. Although not the objec-

Wooden beams embedded inside the wall as a reinforcement ofthe corners. While joining the corners of the walls together, woo-den struts are inserted in the longitudinal direction of the wallsthat are interconnected for reinforcing the corners.

In this solution it is important to ensure the partnership be-tween bracing wood and earth walls for is aided by a proper tiedcorner. We must also control the composition, density and thick-ness of the walls to prevent moisture, insects and fungi rottingthe wood.

Model 3. Earth walls 40 cm thick with reeled braces in the cor-ners on the top oor (wooden beams 15 cm diameter at 1 mfrom the inside corner). Tiranta aspada (3. Tiranta aspada)(Fig. 3).

Compressiveresistance Fc(N/mm2)

Shear resistanceFt (N/mm2)

Fracture energyGf (N/mm/mm2)

Shearretentionfactor

Reductionfactor d

1 0025 0.06 1 10.5 0.0125 0.06 1 120 2 0.06 1 11.5 1 0.06 1 140 60 0.06 1 1

nd Building Materials 30 (2012) 389399 391tive of this paper, they have major implications on the structuralperformance:

Appropriate design elements will prevent water absorption andleaks. The preservation and maintenance of the roof and wallsplasters, protect the soil from rain and humidity, avoidingwashing and weakening the walls.

Water presence in the walls. It is important to control moisturecontent in walls in contact with the wood or reed. Woodembedded inside the wall are protected by surrounding earthif density is more than 600 kg/m3. In the case of walls with athickness exceeding 25 cm reinforced with straw, wood chips,etc. whose density is less than 600 kg/m3, the high capillarityof the straw will extend the exposure to moisture and dryingof the walls. This increase of moisture in terms of humidityand time may attract insects and fungi that affect the strawand wood causing it to rot [6].

Connection between different materials and elements to ensurea better collaboration. Placing tie-beams such as wood or reedsinside walls or at the top may not be efcient if they do notwork together. If the earth slides over the reinforcing element,it will not be effective and it will be just like any soil based con-struction without braces.

Description of the traditional analyzed bracing models withsketches of earth structures joints at the top part of the wallswhere braces are found:

Model 1. Earth walls without braces (Fig. 1).

Adobe walls with connecting bond. Rammed earth walls withcorner framework join perfectly to create a homogeneous and con-tinuous structure. Alternatively rammed earth walls making a ver-tical recess in the nished wall so that when the two walls are puttogether they join perfectly [74].

The nite hexahedral solid elements of the corners were de-ned with less mechanical resistance because of the difculty ofcreating the corners inside the frameworks and/or poor joints with

Table 1Physico-mechanical characteristics of materials.

DeformationE (N/mm2)

Poisson TransversalG (N/mm2)

Density(kg/m3)

Earth 500 0.2 208.3333 2000Earth of the corners 100 0.2 41.6667 2000Ashlars 20.000 0.2 8333.3335 2500Wood 11.200 0.25 4480 450Reeds 20.390 0.3 7842.3075 750

Q. Angulo-Ibez et al. / Construction avertical recess solution.

Model 1A. Earth walls 40 cm thick without braces.

This is the basemodel for implementing the analyzed braces andcomparing performances and results. It is used as the reference.

Model 1B. Earth walls 60 cm thick without braces.

This model tests the inuence of the thickness on the structureperformance against the loads.

Model 2. Earth walls 40 cm thick with wooden beams of 15 cmdiameter and 2 m long, embedded in the corners on top oor (2.Wooden beams embedded) (Fig. 2).Fig. 1. Model 1. Earth walls 40 and 60 cm thick without braces.Fig. 2. Model 2. Earth walls 40 cm thick with wooden beams 15 cm diameter and2 m long, embedded in the corners on the top oor. Wooden beams embedded.

nd BThis solution involves reinforcing the walls through woodenstruts and wedges that attach other struts to walls in order to limittheir movement.

Accessing the wedges at the facades allows the adjustment thetension of the log with the wall, having a good maintenance of thebrace and adjusting the working tension for dimensional variationsdue to temperature and moisture of the walls and wood.

It is easy to monitor the condition of the wood as they are usedfor outside walls.

Esthetic issues can dissuade the use of this brace because theedge of the strut and the wedge can be clearly seen on the facadeat the top corner of the wall.

Model 4. Earth walls 40 cm thick with wooden beams 15 cm indiameter at the top of the walls. Ring beams (4. Ring beams)(Fig. 4).

Wooden beams placed on the top of the walls reinforcing all thewalls together and distributing the roof loads. Ring beams, bondbeams, tie beams or perimeter beams.

Like the model 2. Wooden beams embedded, it is important thatthe ring beam and the walls work together to ensure the properbracing in the walls and the load sharing.

We must also control the composition, density and thickness ofthe walls to prevent moisture, insects and fungi rotting the woods.

Model 5. Earth walls 40 cm thick with wooden beams 15 cm indiameter at the top of the walls with reinforced corners. Ringbeams with reinforced corners (5. Reinforced ring beams) (Fig. 5).

Evolution of the model 4. Ring beams, by reinforcing cornerswith diagonal wooden struts that are attached to the beamsincreasing their lateral stability.

Model 6. Earth walls 40 cm thick with buttresses 80 cm long (6.Buttresses) (Fig. 6).

Walls extension by buttress.The buttress would only be possible in detached buildings lim-

iting their use.When using rammed earth, as Juan de Villanueva suggests [74]

a recess is made in the wall. If you use adobe, it would have to berigged. This solution, as already mentioned, would generate aweaker joint which the buttress would have to support.

Model 7. Earth walls 40 cm thick with built-up inside corners(7. Increased inside corners) (Fig. 7).

Reinforcing joint walls made by increasing a section of the in-side corner.

The rst aspect to study would be the construction process ofthe increased section and how it joins to the walls.

If the increased section is next to a wall but not connected, theywill not work together and we will not achieve a sound structure.Therefore the typical bending failure in the upper corners of thewalls will occur as in model 1A. Earth walls 40 cm thick withoutbraces.

If the increased section is constructed at the same time as thewalls, they will work together. Therefore the increase in resistantmaterial (see model 1B. Earth wall without bracing 60 cm), will in-crease the resistance at those points where the bending failureusually occurs.

392 Q. Angulo-Ibez et al. / Construction aModel 8. Earth walls 40 cm thick with ashlars with 80 cm longat the corners (8. Ashlars in the corner) (Fig. 8).Replacing earth with ashlars or rough stones in the corners. Wehave adopted average characteristics for the stone in the modelcalculation.

The problem with this solution is the availability of material,cost and workability of the stone.

Model 9. Earth walls 40 cm thick with internal reinforcementmade by reeds 6 cm in diameter every 40 cm vertically and hor-izontally (9. Reeds lattice) (Fig. 9).

Reinforcing walls by placing reeds as supporting struts just likesteel in reinforced concrete walls.

Despite being an international renown reinforcement tech-nique, there are some difculties to overcome: it requires theemployment of more expert workers and a much longer and com-plex construction process due to the need to build the wall withthe reeds inside; it is impossible to check the condition of the reedsbecause they are already inside the structure, so they are at risk ofbecoming moist and attracting insects or fungi; the discontinuitydue to the two different materials (reeds and earth) can make wallbecome weakened and cracks may appear [75].

The traditional analyzed braces are internationally standardizedwith local peculiarities. Models are generally used although someof them are more common in some countries. Models withoutbraces are possible only in areas without seismicity risk and notmore than one or two levels due to risk of collapse. Models 2.Woo-den beams embedded, 4. Ring beams, 6. Buttresses are common inSpain, Peru, Chile, Morocco, etc. Model 3. Tiranta aspada belongsto Albacete, Spain. Model 5. Reinforced ring beams is common inCuba, Morocco, etc. Model 8. Ashlars in the corner is also used inSpain and Morocco.

4. Experimental

We have obtained the following results for the differentmodels:

Efforts in the main directions with the three methods, sepa-rately for each hypothesis, load, load combination or altogether.

It is possible to analyze the damage rate, depending on the loadcombinations applied to models, taking into account where andhow much damage has been caused.

Construction is presented from two opposite viewpoints (Iso-metrics 1 and 2) to observe the entire structure. We analyze thestress on the three main components for the main axes (tensionSx, Sy and Sz).

4.1. Efforts

Analyzing the efforts obtained either from a load combinationor the whole load combination, we are able to measure the perfor-mance of the structure and see the areas where the force exceedsthe materials point of resistance.

As an example of the whole process, we present efforts obtainedfrom model 1A. Earth walls 40 cm thick without braces.

Linear static method under gravity loads and wind. We can see from the model that the largest strain is always con-centrate in the area of the upper joints between walls (Fig. 10).

Nonlinear static method, under the combination of gravity andhorizontal loads until collapse.

In the graphs, with the consecutive increases of load (load at

uilding Materials 30 (2012) 389399100%, 280%, 460% and 595%), there are consecutive increasesof the pressure in the construction (Figs. 1113).

Fig. 5. Model 5. Earth walls 40 cm thick with wooden beams 15 cm in diameter at

nd Building Materials 30 (2012) 389399 393Fig. 3. Model 3. Earth walls 40 cm thick with reeled braces in the corners on the topoor (wooden beams 15 cm diameter at 1 m from the inside corner) Tirantaaspada.

Q. Angulo-Ibez et al. / Construction a Dynamicseismic method.

Under earthquake conditions, there are clearly two types ofcommon failure in the soil based construction and that would leadto the collapse of the building either by wall overturning failure orother unstable elements: failure by bending and shear failure (seefailures at Section 1) (Fig. 14).

4.2. Damage rate

From calculating forces, we have obtained the damage rate,which allows us to check the areas where the material stops work-ing because it has exceeded its resistance. This is especially inter-esting in the non-linear structural analysis, for a load combinationand with consecutive increase in loads we can analyze the damagein each increase and its evolution. From this concept, we can devel-op two studies.

4.2.1. Evolution of damage according to increasing loadsWe study the models response according to consecutive in-

creases in loads, checking damage (areas and severity) that occursin the structure and its readjustment.

We will continue with the example model of paragraph 4. Ef-forts, 1A. Earth walls 40 cm thick without braces, under a combina-tion of gravity loads and horizontal wind until the collapse of themodel.

Fig. 4. Model 4. Earth walls 40 cm thick with wooden beams 15 cm in diameter atthe top of the walls. Ring beams.the top of the walls with reinforced corners. Reinforced ring beams.Worn out material usually comes from the top of the joints be-tween the walls, and progressively worsen as load increases, there-by collapsing the wall in two directions, thickness and height. Thecollapse of the wall occurs when the cracks penetrate the wallcompletely and the walls become independent without lateral sta-bility, so continuing to support loads will lead to collapse due tooverturning failure (Fig. 15).

Fig. 6. Model 6. Earth walls 40 cm thick with buttresses 80 cm long. Buttresses.

Fig. 7. Model 7. Earth walls 40 cm thick with built-up inside corners. Increasedinside corners.

4.2.2. Analysis of the models until their collapseWith same combination and increases, the exact load that col-

lapses each model can be compared.100% is the usual maximum load in the life of the building,

increasing loads until they collapse, thereby obtaining the collapseload for each model referenced in Table 2. With all the results andusing model 1A. Earth walls 40 cm thick without braces as a refer-ence, we can compare the overall response of each of the models.

This table gives a simple and direct comparison between themodels analyzed. They show the different performances, assessingand quantifying their effectiveness and also graphics for a betterunderstanding (Table 2) (Figs. 16 and 17).

The houses with cracks in the area of the Manchuela, Spain(which have served to dene the model) have been compared withthe respective structural models. Cracks were measured and col-lated with the results, matching in all cases (Fig. 18).

3. Tiranta aspada, 4. Ring beams and 5. Reinforced ring beams

the top of the corners due to the effect of being attached to eachother. As result, there is a redistribution of tension along the woo-den strut, acting only at the joint between the walls. But in the caseof model 3. Reeled brace better results are produced due to it beingbound and braced.

In the models 4. Ring beams and 5. Reinforced ring beams, theplacement of a wooden beam attached to the top of the earth wallsensures a greater join between the different walls and thus a betterstructure overall. Moreover, the ring beam provides a better shar-ing and distribution of the loads. These solutions slightly increasethe resistance to gravity loads and are the ones that work bestagainst horizontal loads.

The 6. Buttresses model, despite increasing the inertia of thewalls, this does not solve the problem of bracing the walls becauseof a awed joint, so weakness in the top of the joints between wallscontinues.

The model 7. Increased inside corners, although constructedsimultaneously with the walls and working together with in-creased resistant section in corners, it does not solve the problemof reinforcement between walls because of a awed joint. It just in-creases the resistant sections as in model 1B. Earth walls 60 cm

394 Q. Angulo-Ibez et al. / Construction and B5. Results and discussion

See the section below where we proceed to discuss results andmake comparisons between existing buildings and bibliography.

5.1. Collapse in the earth constructions without bracings

In the calculated models 1A. Earth walls 40 cm thick withoutbraces and 1B. Earth walls 60 cm thick without braces, regardlessof the load combinations and methods, it is possible to appreciatethat the greatest tension is found in the upper corners of the walls.If these tensions are greater than the resistance of the material,cracks will appear making walls independent and therefore start-ing the process of a building collapse due to lack of lateral stabilityin the walls.

In the model 1B. Earth walls 60 cm thick without braces, with a50% thickness increase of the walls (4060 cm) we see a signicantincrease in global resistance of the structure. As expected, increas-ing the section of the material increases its resistance in theseareas and therefore the overall resistance of the structure. With re-gard to gravity loads this is the model with the highest resistancedue to being the model with more area in its resistant section. Italso increases resistance to horizontal forces and has a greaterinertia against lateral overturning.

Analyzing the damage rate in the consecutive increases of loads,we observe that the crack starts at the top of the walls in the cor-ners. From one side of the wall, the crack advances as specic sec-tions of the wall buckle under the pressure, both transversely (wallwidth) and vertically (wall height). Finally, if the load that madeFig. 8. Model 8. Earth walls 40 cm thick with ashlars 80 cm long in the corners.Ashlars in the corners.although the joints between the walls crack, separating the wallsfrom one another, the braces supply some reinforcement allowingthe walls to continue to work together, limiting the collapse due tofailure in the joints.

The models 2. Wooden beams embedded and 3. Tiranta aspadaproduce a signicant increase in resistance against cracking atboth walls separate from each other continues, it causes the col-lapse of the structure.

This process corresponds to the usual failure of the soil basedconstruction mentioned in Section 1 due to low tensile strengthof earth.

5.2. Collapse in the earth constructions with braces

Each model of traditional brace brings different advantages anddisadvantages which are developed in this section. Not all modelssolve the problem of joints between walls in the upper part by thelack of tensile strength of the earth.

In the case of the following models 2. Wooden beams embedded,

Fig. 9. Model 9. Earth walls 40 cm thick with internal reinforcement made by reeds6 cm in diameter every 40 cm vertically and horizontally. Reeds lattice.

uilding Materials 30 (2012) 389399thick without braces.In model 8. Ashlars in the corner, reinforced corners with ashlars

strengthen the joints between the walls due to the higher tensile

nd BQ. Angulo-Ibez et al. / Construction aand bending resistance of stone instead of an earth based material.Stone is not a suitable material for tensile effort, so it could col-lapse too due to lack of proper bracing.

In model 9. Reeds lattice, the reeds have a high tensile and bend-ing resistance. This solution, like a reinforced concrete wall, in-creases the resistance of the structure against horizontal loadsdue to the horizontal and vertical bound, allowing each materialto perform the appropriate functions according to theircharacteristics.

Fig. 10. Linear static method under gravity loads and win

Fig. 11. Nonlinear static method, under the combination of gravity and horizontal

Fig. 12. Nonlinear static method, under the combination of gravity and horizontaluilding Materials 30 (2012) 389399 3955.3. Comparison of models according to the damage rate until collapse

From Table 2. Collapse load and reference rate:

Under gravity loads, the table shows that all models are in thesame range of values, with models braced slightly above unitydue to their walls being 40 cm thick. Here we highlight model1B. Earth walls 60 cm thick without braces, with an increase of20 cm thickness (50% thickness) increased by 25% the overall

d. Model 1A. Earth walls 40 cm thick without braces.

loads until collapse X axis. Model 1A. Earth walls 40 cm thick without braces.

loads until collapse Y axis. Model 1A. Earth walls 40 cm thick without braces.

nd B396 Q. Angulo-Ibez et al. / Construction aresistance of the structure against gravitational loads; the logi-cal consequence of this being that earth walls are the elementsthat transmit vertical loads. Therefore, increasing their thick-ness will increase the resistant area and hence its resistanceto these loads.

Under gravitational and horizontal loads (wind) we can see thatany bracing system substantially increases the overall resis-tance of the structure. While model 1B. Earth walls 60 cm thick

Fig. 13. Nonlinear static method, under the combination of gravity and horizontal

Fig. 14. Dynamicseismic method. Model 1A

Fig. 15. Nonlinear static method, under the combination of gravity and horizontal loaduilding Materials 30 (2012) 389399without braces increases the overall resistance by 39%, reinforce-ment with wooden struts increase the overall resistance tothese loads between 48% and 118% depending on the system.

Braces that one act at the corners considerably increase theresistance. Model 2. Wooden beams embedded increases by 48%,while model 3. Tiranta aspada has an increased resistance of 64%.This implies that with the same materials that oor slabs are made

loads until collapse Z axis. Model 1A. Earth walls 40 cm thick without braces.

. Earth walls 40 cm thick without braces.

s until collapse. Damage rate. Model 1A. Earth walls 40 cm thick without braces.

Table 2Collapse load and reference rate.

Gravitational Gravitational and horizontal

Collapse load (%) Reference rate (%) Collapse load (%) Reference rate (%)

1A. Earth walls 40 cm thick without braces 600 100 280 1001B. Earth walls 60 cm thick without braces 750 125 390 1392. Wooden beams embedded 600 100 415 1483. Tiranta aspada 600 100 460 1644. Ring beams 640 107 610 2183. Reinforced ring beams 685 114 610 2186. Buttresses 600 100 325 1167. Increased inside comers 600 100 305 1098. Ashlars in the corner 660 110 595 2139. Reeds lattice 600 100 595 213

Q. Angulo-Ibez et al. / Construction and Building Materials 30 (2012) 389399 397of (wooden struts), intertwining the corners at the top, greatly in-creases the overall strength of the structure in comparison with thesame building without any kind of brace. Simply acting directly ontop of the joints between the walls, the areas where a usual bend-ing failure would occur in an earth construction.

Models 4. Ring beams and 5. Reinforced ring beams double theglobal resistance of the model without braces increasing by118%. This is a result of monolithic structure and the redistribution

Fig. 16. Collapse load.

Fig. 18. Concordance between builof pressure. Beams placed at the top of the walls (wooden beams ofthe same characteristics and dimensions as oor slab beams) allowthe whole structure to work together in a more uniform distribu-tion of weight throughout the structure and increasing its overallstrength.

Model 6. Buttresses minimally increases the overall strength by16%. Despite the continuation of the walls with buttresses that in-crease the inertia, this model presents the same problems with the

Fig. 17. Reference rate.

dings and calculation models.

depending on the characteristics of the building and weight to beborne.

2011;25(4):174752.[17] Yetgin S, avdar , avdar A. The effects of the ber contents on the mechanic

[21] Dowling D. Adobe housing in El Salvador: earthquake performance andseismic improvement. In: Rose WI, Bommer JJ, Lpez DL, Carr MJ, Major JJ,

nd BTwo aspects of the braces which need to be checked are: correctanchoring between the reinforcing element and the wall to preventslippage and separation that would otherwise not work together;and in the case of wooden struts or reeds inside the walls, the con-trol of the composition, density and thickness of the walls to pre-vent moisture inside and the possible rotting of the woodreed.

Among the models that act only in the corners, 2.Wooden beamsembedded and 3. Tiranta aspada, do not show big differences.Although model 3. Tiranta aspada has more resistance and can becontrolled better due to the fact that it remains seen.

Models that act on the entire building, 4. Ring beams and 5. Rein-forced ring beams, are the ones with the best performance. They acton the whole structure and promote collaboration between allwalls and provide a better distribution of weight. It is necessaryto ensure that the joint between the wooden beams and the wallsis adequate therefore eliminating possible differential movement.This solution is part of all seismic guidelines of soil based construc-tions being reinforced horizontally or vertically.

Model 9. Reeds lattice is highly resistant thanks to the reinforc-ing of the reeds; but rotting can be a problem if the problem of hav-ing moisture inside the walls is not solved. In addition, recentstudies have shown that the discontinuities generated in the earthjoints between the different walls that also happens in the soilbased constructions without braces, so it does not increase itsoverall strength. Buttresses can be interesting in long walls with-out intermediate reinforcement for avoiding overturning failure.

Model 7. Increased inside corners has a minimal increase in theglobal resistance. It would be logical that increasing the resistantsection in the areas where collapse usually occurs (see model 1B.Earth walls 60 cm thick without braces) would increase the overallresistance. The problem with this solution is whether the increasedcorner is attached to the wall or not. Creating the increased cornerafter the walls were already built would cause them not to bestructurally sound and fulll their purpose. So in this constructionprocess, this model will work as model 1A. Earth walls 40 cm thickwithout braces.

Model 8. Ashlars in the corner, replaces the earth from the cor-ners with ashlars or rough stones. The increase of the tensile resis-tance of the stone, increases the global resistance of the structure.

Model 9. Reeds lattice, doubles the global resistance with an in-crease of 113%. Reeds, due to their high tensile and bending resis-tance, are responsible for supporting the tensile force in thestructure, working like steel bars in reinforced concrete, sewingand absorbing the tensile stresses.

6. Conclusions

The soil based constructions, and in particular rammed earthwalls and adobe, are vulnerable to tensile forces which are derivedmainly from important horizontal external loads. This is accentu-ated in the case of earthquakes: earthquakes with 0.20 g accelera-tion can bring soil based constructions without braces to the brinkof a collapse; and these kinds of earthquakes are frequent in area ofhigh seismic activity where people continue to live and build earthconstructions.

The common failure of these buildings comes from the top ofthe joint between walls, becoming independent, losing lateral sta-bility and giving way to collapse.

Traditionally, bracing systems have been used with the aim ofreducing this problem, which becomes more or less important

398 Q. Angulo-Ibez et al. / Construction awall by the reeds, can be a problem too.Model 8. Ashlars in the corner presents a good performance be-

cause of the higher tensile resistance of the stone than the earth.editors. Natural hazards in El Salvador. Geological Society of America; 2004.[22] Dowling D. Improved adobe mudbrick in application child-care centre

construction in El Salvador. In: 13th world conference on earthquakeengineering, Vancouver, Canada, Paper 705; August, 2004.

[23] Maz Equipo. La casa de adobe sismorresistente. El Salvador: AsociacinEquipo Maz; 2001.

[24] Flores L, Pacheco M, Reyes C. Algunos estudios sobre el comportamiento yrehabilitacin de la vivienda rural de adobe. Mxico: CENAPRED (CentroNacional de Prevencin de Desastres), Informe IEG/03/01; 2001.

[25] IAEE (International Association for Earthquake Engineering). Guidelines forearthquake resistant non-engineered construction, Tokyo: IAEE; 1986.

[26] Murty CVR, Charleson AW. Using the world housing encyclopedia to improvehouse earthquake safety. In: The 14th world conference on earthquakeproperties of the adobes. Constr Build Mater 2008;22(3):2227.[18] Barrionuevo R. Investigacin tecnolgica aplicada: domocaa. Informes de la

Construccin Julioseptiembre 2011;63:523.[19] Blondet M, Garcia GV, Brzev S. Earthquake-resistant construction of adobe

buildings. EERI/IAEE world housing encyclopedia; 2003.[20] Brzev S, Tomazevic M, Lutman M, Bostenaru Dan M, D Ayala D, Greene M. The

world housing encyclopedia: an online resource on housing construction inhigh seismic risk areas of the world. .Models 6. Buttresses and 7. Increased inside corners do not signif-icantly improve global resistance of the structure.

Therefore we recommend using models 4. Ring beams and 5.Reinforced ring beams as solutions for earth constructions.

As shown, the bracing of the walls signicantly increases theirability to withstand horizontal loads by creating an adequate jointbetween two walls. Braces are a necessity for global stability andmonolithic nature of the earth buildings, and is an essential secu-rity element in seismic areas.

Acknowledgment

The authors wish to express their Gratitudes to: Adolfo AlonsoDura, Ph.D. Architect, Professor of the University Institute of Heri-tage Restoration of the Polytechnic University of Valencia, for thecalculation program and his time.

References

[1] Dethier J. Down to earth: adobe architecture, an old idea, a new future, rutheaton, facts on le. New York; 1983.

[2] Easton D. The rammed earth house. White river Junction: Chelsea GreenPublishing Company; 1996.

[3] Lynne E, Adams C, et al. Alternative construction: contemporary naturalbuilding methods. Hoboken, NJ: John Wiley & sons Inc.; 2000.

[4] McHenry Jr PG. Adobe and rammed earth buildings. New York: John Wiley &sons Inc.; 1984.

[5] McHenry Jr PG. The adobe story. Alburquerque: University of New MexicoPress; 2000.

[6] Minke G. Manual de construccin en tierra (Lehmbau-Handbuch). Editorial Finde Siglo; 2005.

[7] Oliver P. Earth as a building material today. Oxford Art J Arch 1983;5(2).[8] Rael R. Earth architecture. New York: Princeton Architectural Press; 2009.[9] Rodrguez MA, Saroza B. Determination of the optimum composition of adobe

brick for a school in Cuba. Mater de constr Abril-junio 2006;56:282.[10] Binici H, Aksogan O, Shah T. Investigation of bre reinforced mud brick as a

building material. Constr Build Mater 2005;19(4):3138.[11] Degirmenci N. The using of waste phosphogypsum and natural gypsum in

adobe stabilization. Constr Build Mater 2008;22(6):12204.[12] Galn-Marn C, Rivera-Gmez C, Petric J. Clay-based composite stabilized with

natural polymer and bre. Constr Build Mater 2010;24(8):14628.[13] Hall M, Djerbib Y. Rammed earth sample production: context,

recommendations and consistency. Constr Build Mater 2004;18(4):2816.[14] Hossain KMA, Mol L. Some engineering properties of stabilized clayey soils

incorporating natural pozzolans and industrial wastes. Constr Build Mater2011;25(8):3495501.

[15] Muntohar AS. Engineering characteristics of the compressed-stabilized earthbrick. Constr Build Mater 2011;25(11):421520.

[16] Turanli L, Saritas A. Strengthening the structural behavior of adobe wallsthrough the use of plaster reinforcement mesh. Constr Build Mater

uilding Materials 30 (2012) 389399engineering, Beijing, China; October, 2008.[27] Prez A. Manual tcnica para la produccin y construccin con adobe

natural. Cuba: Habitat; 2001.

[28] Roselund N. Buttresses, pilasters and adobe wall stability, workshop on theseismic retrot of historic adobe buildings: earthen building technologies.California; 1995.

[29] Woodward B. Mudbrick notes. 2nd ed. Wollombi, Australia: Earthways; 1996.[30] Borri A, Castori G, Grazini A. Retrotting of masonry building with reinforced

masonry ring-beam. Constr Build Mater 2009;23(5):1892901.[31] Adell JM. La fbrica armada. Madrid: Munilla-Lera; 2000.[32] Adell JM, Bustamante R, Dvila D. La vivienda de adobe sismorresistente con el

Sistema de Albailera Integral. Seminario Internacional SismoAdobe, Lima,Per; 2005.

[33] Adell JM, Lauret B. El sistema de albailera integral AllWall con BHH/BLOC+.Informes de la Construccin 2005;57:495.

[34] Adell JM, Bustamante R, Garca Santos B, Lauret S. The integral masonry systemwith earth-based materials: rubble based earthquake resistant at construction.In: Proceedings of international symposium on earthern structures, Bangalore,India; 2007.

[35] Blondet M, Torrealva D, Villa Garca G, Ginocchio F, Madueo I. Reforzamientode construcciones de adobe con elementos producidos industrialmente:estudio preliminar, PUCP, Lima, Per; 2004.

Memorias del XIII congreso nacional de ingeniera civil, Colegio de Ingenierosdel Per, Puno; 2001.

[48] Borri A, Castori G, Corradi M. Shear behavior of masonry panels strengthenedby high strength steel cords. Constr Build Mater 2011;25(2):494503.

[49] Faella C, Martinelli E, Nigro E, Paciello S. Shear capacity of masonry wallsexternally strengthened by a cement-based composite material: anexperimental campaign. Constr Build Mater 2010;24(1):8493.

[50] Luccioni B, Rougier VC. In-plane retrotting of masonry panels with brereinforced composite materials. Constr Build Mater 2011;25(4):177288.

[51] Papanicolaou C, Triantallou T, Lekka M. Externally bonded grids asstrengthening and seismic retrotting materials of masonry panels. ConstrBuild Mater 2011;25(2):50414.

[52] Priestley MJN, Seible F. Design of seismic retrot measures for concrete andmasonry structures. Constr Build Mater December 1995;9(6):36577.

[53] Su Y, Wu C, Griffth MC. Modelling of the bondslip behavior in FRP reinforcedmasonry. Constr Build Mater 2011;25(1):32834.

[54] Willis CR, Yang Q, Seracino R, Grifth MC. Damaged masonry walls in two-waybending retrotted with vertical FRP strips. Constr Build Mater2009;23(4):1591604.

Q. Angulo-Ibez et al. / Construction and Building Materials 30 (2012) 389399 399[36] Orta B, Adell JM, Bustamante R, Garca A, Vega S. Ensayo en lima (Per) deedicio de adobe sismorresistente construido con el sistema de albaileraintegral. Informes de la Construccin 2009;61:515.

[37] Blondet M, Torrealva D, Villa-Garcia G, Ginocchio Fy Madueno I. Uso demateriales industriales para la construccin de viviendas seguras de adobe.Memorias del congreso internacional earthbuild 2005, NSW: faculty of design,architecture and building, University of Technology, Sydney; 2005.

[38] Blondet M, Vargas J, Tarque N, Velasquez J. Experimental study of syntheticmesh reinforcement of historical adobe buildings, vol 2. SAHC2006, MacmillanIndia Ltd., New Delhi; 2006.

[39] Blondet M, Aguilar R. Seismic protection of earthen buildings. Conferenciainternacional de ingeniera ssmica, Lima, Per, Agosto; 2007.

[40] Blondet M, Vargas J, Tarque N. Available low-cost technologies tos improve theseismic performance of earthen houses in developing countries. In: The 14thworld conference on earthquake engineering, Beijing, China; October, 2008.

[41] Blondet M, Vargas J, Patron P, Stanojevich M, Rubios A. A humandevelopment approach for the construction of safe and healthy adobehouses in seismic areas. In: Kerpic08 learning from earthen architecture inclimate change international conference, Paper code 45, Cyprus InternationalUniversity, Lefkosa; September 2008.

[42] Blondet M, Vargas J, Tarque N, Iwaki C. Construccin sismorresistente entierra: la gran experiencia contempornea de la ponticia universidad catlicadel per (seismic resistant earthen construction: the contemporary experienceat the ponticia universidad catlica del per). Informes de la ConstruccinJulioseptiembre 2011;63:523.

[43] Torrealva D, Acero J. Refuerzo ssmico de vivienda de adobe con malla exteriorcompatible. Memorias del seminario internacional de arquitectura,construccin y conservacin de edicaciones en tierra en reas ssmicas,SismoAdobe, PUCP, Lima, Per; 2005.

[44] Zegarra L, Quiun D, San Bartolom A, Giesecke A. Reforzamiento de viviendasde adobe existentes. Primera parte: ensayos ssmicos de muros u. Memoriasdel XI congreso nacional de ingeniera civil, Colegio de Ingenieros del Per,Trujillo; 1997.

[45] Zegarra L, Quiun D, San Bartolom A, Giesecke A. Reforzamiento de viviendasde adobe existentes. Segunda parte: ensayos ssmicos de mdulos. Memoriasdel XI congreso nacional de ingeniera civil, Colegio de Ingenieros del Per,Trujillo; 1997.

[46] Zegarra L, Quiun D, San Bartolom A, Giesecke A, Reforzamiento de viviendasexistentes de adobe. proyecto centro regional de sismologa para amrica delsur (CERESIS) cooperacin alemana al desarrollo (GTZ) ponticiauniversidad catolica del peru (PUCP). Memorias del XII congreso nacional deingeniera civil, Colegio de Ingenieros del Peru, Huanuco; 1999.

[47] Zegarra L, Quiun D, San Bartolom A. Comportamiento ante el terremoto del23-06-2001 de las viviendas de adobe reforzadas en moquegua, tacna y arica.[55] Alonso Dur A. Un modelo de integracin del anlisis estructural en entornosde cad para estructuras de edicacin. Doctoral thesis. Department ofcontinuum mechanics and structural theory, school of architecture,Polytechnic University of Valencia, Valencia; Diciembre, 2003.

[56] De Mazarredo Aznar L. Calibrado de modelo de dao escalar con ensayosexperimentales aplicado a materiales friccionales. Research paper ofdepartment of continuum mechanics and structural theory. School ofArchitecture, Polytechnic University of Valencia, Valencia; Septiembre, 2011.

[57] Hanganu AD, Barbat AH, Oate E. Metodologa de evaluacin del deterioro enestructuras de hormign armado. Monografa CIMNE n 39, Julio; 1997.

[58] Oliver J. Modelado de la suracin en estructuras de hormign. MonografaCIMNE, n 15, Enero; 1993.

[59] Oller S. Modelizacin numrica de materiales friccionales. Monografa CIMNEn 3, Enero; 1991.

[60] Oller S. Fractura mecnica. Un enfoque global, CIMNE, Barcelona; 2001.[61] Oate E, Hanganu A, Barbat A, et al. Structural analysis and durability

assessment of historical construction using a nite element damage model.CIMNE, Barcelona; 1996.

[62] Rauch M, Kapnger O. Rammed earth (lehm un architektur). Basel: Birkhauser;2001.

[63] Bauluz G, Barcena P. Bases para el diseo y construccin contapial. Madrid: Ministerio de Obras Pblicas y Transportes; 1992.

[64] Normativa de construccion con tierra neozelandesa NZ 4297;1998.[65] Font F, Hidalgo P. Arquitecturas de tapia. Castelln: Collegi Ocial

dAparelladors i Arquitectes Tcnics de Castell; 2010.[66] Walker P, Keable R, Martin J, Maniatidis V. Rammed earth, design and

construction guidelines. BRE Bookshop; 2005.[67] Guigou C. La tierra como material de construccin. Colegio Ocial de

arquitectos de Canarias; 2002.[68] Hidalgo O. Bamb, el regalo de los dioses. Bamboscar2@007mundo.com,

Bogota.[69] Moromi IN. Informe de la investigacin de propiedades del bamb.[70] Kumar A. Bamboo for sustainable development. In: INBAR Proceedings n 7,

Netherlands; 2002.[71] Regueiro y Gonzles-Barros M. Conferencia sobre normativa tcnica de piedra

natural. Instituto Geolgico y Minero de Espaa. .[72] Cdigo tcnico de la edicacin. Documento bsico de seguridad estructural

acciones de la edicacin.[73] NCSE-02, Norma de construccin sismorresistente: parte general y edicacin.[74] Villanueva J, Arte de Albailera. Ocina de don francisco martnez dvila.

Madrid; 1827.[75] Getty Trust JP. In: Proceedings of the getty seismic adobe project 2006

colloquium. Getty Center, Los Angeles; 1113 April, 2006.

Traditional braces of earth constructions1 Introduction2 Calculation methods: description of the model, materials and loads3 Traditional analyzed braces4 Experimental4.1 Efforts4.2 Damage rate4.2.1 Evolution of damage according to increasing loads4.2.2 Analysis of the models until their collapse

5 Results and discussion5.1 Collapse in the earth constructions without bracings5.2 Collapse in the earth constructions with braces5.3 Comparison of models according to the damage rate until collapse

6 ConclusionsAcknowledgmentReferences