Evaluation Methods for Traditional Houses in Dobrogea

Assessing the technical condition of earthen constructions is an extremely difficult task due to the fact that the materials, methods and techniques used in construction have been replaced by new materials and installation procedures. Although they have a fairly large share in the existing housing stock, earthen constructions have not benefited from the same interest in the field of construction. This paper proposes a review of the current assessment possibilities applicable to earthen constructions in relation to the current level of knowledge on a local and international level.


Introduction
The invention of Portland cement and the industrial revolution facilitated access to high-performance materials such as concrete or brick, but at the same time, the energy required to manufacture these materials is obtained from non-renewable and unsustainable sources.At the present time, the fossil fuels used in the industry are irreversible affecting the environment and there is an acute need for sustainable and ecological construction materials.A possible answer to this need can be earthen constructions, which by nature save energy right from the construction phase.The material is obtained locally, it does not need to be subjected to very high temperatures in furnaces and the installation does not require specialized labor.Any new or existing construction must meet safety and stability requirements.For this purpose, there is a legislative basis with the help of which new structures can be designed and erected or existing buildings can be reinforced.With the help of the current regulations, the technical condition of a construction made of reinforced concrete, masonry or wood can be assessed with high accuracy, but the same regulations do not cover constructions made of earth.

Traditional houses in Dobrogea
The Dobrogea area is of particular interest in the study of earthen constructions because it is an arid steppe-like land with very few resources that can be used in constructions.The traditional Dobrogea house is made with clay adobe, often without foundations and covered with reeds thatch.The architecture is simple, the houses most often have a central room from which access is made into two larger living rooms.The main facade has a porch from where access is made to the central room and has decorations or motifs specific to the area.The traditional household is completed by annexes with the role of kitchen, bathroom or storeroom, made in similar techniques as the house, although in certain areas these rooms are under the same roof as the living quarters.The traditional Dobrogea house has a rectangular shape and is about five meters wide by thirteen meters long with wall thickness that vary between 40 and 60 centimeters.The case study is carried out on a typical house from a village in Constanta County, which has three roughly square rooms, the side rooms having internal dimensions of about four meters, and the central room of about three meters.The thickness of the walls is 45 centimeters, the foundations are made of stone laid with clay mortar, continuously under the walls, roof and ceiling made of wood, covered by ceramic tiles.Some of the details may be observed in figures 1, 2, 3 and 4.

Technical evaluation of a traditional house from Dobrogea
A possible option for evaluating the technical condition of the construction would be to draw a parallel between it and a house made of brick, but using appropriate characteristic resistances for the materials used.Taking into account the provisions of the regulations in use for the evaluation of existing masonry constructions as well as the information from the specialized literature, the values of the R1, R2 and R3 indicators can be calculated according to the P100-3/2019 standard.For the calculation of the R1 indicator, the standard proposes an evaluation of the quality of the structural system, the quality of the structural materials, floor types, in plane configuration, the configuration in elevation and other aspects that contribute to the behavior of the structure and which will be detailed in the following lines.The quality of the structural system takes into account the type of structural system, the efficiency of the connections between the walls, the efficiency of the connections between the walls and ceiling and the quantity of masonry for the two main directions.Regarding these criteria, the following unfavorable aspects can be noted: the structural walls are made of unreinforced masonry, without reinforced concrete columns and beams, the floors are flexible, the coupling areas are made of unreinforced masonry, without reinforced concrete beams and lintels made of wood.The crossing of the walls is made only by weaving the masonry, and the connections of the wooden beams are made by friction only.These aspects lead to a reduced ductility and redundancy of the structural system with unfavorable behavior during dynamic loads.The coupling zones have low capacity both for axial stress and bending moment as well as from the shear force.The connection between the walls and floors is quite weak.The distribution of masonry is approximately equal on the two main directions as well as the density of the structural walls of approx.6.0% in both directions are favorable aspects that improve the behavior to seismic loads.The structure has vibration periods values approximately equal on the two directions.The materials used are unfired clay bricks (adobe), clay-based mortar and wood for the superstructure and stone with clay-based mortar for the foundations.The quality of bricks and mortar is poor, having low resistance characteristics, but also low durability over time, especially when exposed directly to atmospheric factors and humidity.As a positive aspect, it can be mentioned that the clay-based mortar has superior damping capacity during seismic actions compared to cement-based mortar.The quality of the wood is poor, although it is suitable for the importance class of the construction, but with little durability over time, especially in the case of water infiltration through the frame, being sensitive to the attack of wood-eating insects and fungi, at the same being highly combustible.The quality of the masonry execution is good and ensures a good behavior of the construction both to gravity loads and to seismic loads, and the absence of weak areas (niches or slits) reduces the risk of cracks.The floor and the roof are made of wood without sufficient rigidity in plane to ensure the compatibility of the structural walls deformations, they cannot redistribute the loads between the structural walls from the two directions and have a diminished role in preventing their overturning due to stresses perpendicular to their plane.The weak connections (by friction) between the wood and masonry elements mean that the loads in the walls cannot be properly transmitted through the ceiling to the adjacent walls, even if the ceiling has sufficient rigidity in plan.The regular shape, the low height regime, without withdrawals in plane or in elevation is a positive aspect because a construction with large differences between the dimensions of the two directions, as well as with significant withdrawals can have additional effects of general torsion.Other positive aspects are represented by the absence of significant vertical discontinuities in structural walls, gaps or indirect supports.Distances less than 5.00 meters between structural walls in both main directions, their height less than 3.00 meters and the ratio between the height and thickness of the walls with a value less than 12 make the structure less prone to failure with a uniform distribution of seismic forces without major concentrations of forces in certain structural elements.High story heights can lead to significant 2nd order effects and buckling of slender vertical members.Another negative aspect is represented by the fact that the walls are subjected to thrusts from the frame without having any elements to limit these effects and local failures may occur due to exceptional loads from gravitational or seismic loads.The foundation soil has sufficient resistance capacity, without large swellings or contractions, and the foundations have a suitable width to transmit the loads from the superstructure.The negative aspects of the foundations are represented by the small foundation depth that does not exceed the frost depth.They are influenced by the swellings and contractions of the ground subjected to freeze-thaw cycles.More than that, the material from which the infrastructure is made does not have sufficient resistance to deformation, not being able to take over stretching efforts from seismic actions or differentiated settlements.
There are no possible interactions with the adjacent buildings because the building is at a sufficient distance from the neighboring constructions, and the building does not have decorative elements that present a risk of collapse or partition walls and claddings with inadequate fastenings.However, as a negative aspect, the degradation of the heels can be observed with a considerable risk of the roof collapsing.
Taking into account all the aforementioned aspects, the R1 indicator can be appreciated at a value of 61 points out of a maximum of 100 and the building can be included in the RsIII seismic risk class.For the calculation of the R2 indicator, the standard proposes an evaluation of the degree of structural damage, taking into account the degree of damage of the vertical and horizontal elements.It can be appreciated that the vertical elements show moderate damage on less than 1/3 of their area (cracks) and the horizontal elements show serious damage with the affected area between 1/3 and 2/3 of the total area.By adding up these effects, a value of 65 points is obtained for the R2 indicator and the building can be included in the RsIII seismic risk class.For the calculation of the R3 indicator, the modes of failure associated with masonry constructions must be taken into account, namely eccentric compression failure, ladder failure and horizontal sliding failure.It also takes into account the global behavior of the structures and the possibilities of redistributing the loads that appear during a dynamic action.Starting from the evaluation of the mass of the entire structure and from the evaluation of the static loads acting on the structure, the basic seismic force can be determined.The value of the behavior factor for the unreinforced brick masonry structure has a maximum value of 1.5 according to the P100-3/2019 standard.This factor is related to structure's ability to dissipate energy and it can be considered that a building made of adobe has a lower dissipative capacity.In specialized literature, the minimum value of the characteristic resistance to compression accepted for brick in seismic areas is 5N/mm 2 [4].The studies carried out on unfired clay bricks indicate a maximum compressive strength of 3N/mm 2 , most of the times around 1.5N/mm 2 .The tensile strength is estimated at a value of 3% of the value of the compressive strength [1] [5] [6].Taking into account all the above as well as the peak value of the design acceleration of the area, the R3 indicator defined as the ratio between the capacity of the structure and the value of the basic seismic force has a maximum value of 60, which means that the building falls into the RsII seismic risk class.Using computer software (ETABS17) to model the structure we can clearly see the areas where the loads are concentrated.A common design problem of the traditional Dobrogea house is that the centre beam of the ceiling which in turn supports the roof rests on the transversal walls as seen in figure 5.One shortcoming of this approach is that the door openings are directly under the beam and the load is distributed by wooden lintels.That is why one of the most common place for cracks to appear is the transversal wall, above the door.Figures 6 and 7 show the two main vibration modes and the corresponding displacement values in millimetres.

Conclusion
The deficiencies encountered in traditional Dobrogea houses are largely influenced by the high loads placed on the transverse walls and the undersized foundations made of non-homogeneous materials.Most of them suffered some damage, sometimes major damage, but not total collapse, taking into account the major seismic events that happened in Romania, idea which is also sustained by the value of the R3 indicator.

Figure 5 .
Figure 5. Software modelling of the structure..