Durability of timber structures in agricultural and livestock buildings

biosystems engineering 104 (2009) 152–160

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Research Paper: SEdStructures and Environment

Durability of timber structures in agricultural and livestock buildings R.A. Marin˜o, X.C. Carreira, M.E. Ferna´ndez*, C. Fernandez-Rodriguez Department of Agroforestry Engineering, University of Santiago de Compostela, Escuela Polite´cnica Superior, Campus Universitario, s/n. 27002 Lugo, Spain

article info This paper aims to determine the factors that most strongly influence the durability of Article history:

timber members in agricultural and livestock buildings. A sample of 133 agricultural and

Received 5 December 2008

livestock buildings was selected, including barns for housing different livestock species

Received in revised form

and other agricultural buildings such as storage buildings or hay barns. Every building was

29 May 2009

inspected in order to gather information about the timber structure. The following vari-

Accepted 16 June 2009

ables were analysed: timber species, service life of the structure, features, treatment,

Published online 17 July 2009

structural condition, type of product (round or sawn timber), structural system, joint design and service conditions (end use of the building, environmental conditions, ventilation). Timber durability was assessed based on the structural condition of the buildings, and the influence of the other variables on the condition of the structure was analysed. Data analysis revealed that the structural condition of the buildings studied was not affected by age or species. The factors with the strongest influence on the structural condition of the buildings were wood treatment, ventilation and the proper design of joints between timber members. Therefore, the durability of timber structures in the buildings studied was dependent on the construction practice, including the previous treatment of wood and the proper maintenance of the structure (ventilation, cleaning). ª 2009 IAgrE. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

For use as a structural material in buildings, timber must satisfy conditions that ensure the durability and good performance of the structure. Structural timber, as a general rule, should not be obtained from sapwood and should also show the appropriate degree of drying at the moment of construction, considering the service class for which it is designed. Usually, solid timber can be used in sawn or round form. The use of sawn or round timber is influenced by the building system used. The timber species used determines the strength properties and affects the cross-sectional size of structural members.

Because timber shows considerable natural resistance to degradation, time is not a factor causing decay. Such a resistance, combined with appropriate conditions in the building, makes timber a suitable material for building structures. The efficiency and durability of timber structures are appropriate for agricultural and livestock buildings. However, timber often degrades due to factors that may reduce the service life of the structure. Such factors are not inherent to the structure and composition of wood, as the knots are. Rather, such degradations are caused by the action of external abiotic and, mainly, biotic agents. The main abiotic agents are moisture, sudden weather changes (temperature and humidity), exposure to direct

* Corresponding author. E-mail address: [email protected] (M.E. Ferna´ndez). 1537-5110/$ – see front matter ª 2009 IAgrE. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biosystemseng.2009.06.009

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biosystems engineering 104 (2009) 152–160

sunlight and fire. Abiotic agents can be avoided and generally do not cause serious damage. However, unsuitable environmental conditions (temperature and humidity) in the environment surrounding structural members are conducive to attacks by biotic agents (Carll and Highley, 1999; Brischke et al., 2008) and affect the service life of the building (Havirova and Kubu, 2006). The direct action of water on structural members produces the same effect; according to Liso et al. (2006), the climatic conditions must be taken into consideration. Because the environment of agricultural buildings, and particularly of livestock buildings, can be aggressive to building materials, the end use of the building is one of the aspects that must be taken into consideration (De Belie et al., 2000). Biotic agents are related to living organisms, such as insects, fungi and a variety of microorganisms. Biotic agents are the source of attacks that reduce the cross-sectional area of timber members and, consequently, the mechanical properties of such members (Fujihira et al., 1997), thus compromising the structural integrity of the building. Attack by biotic agents must be taken into consideration when using timber (Gaylarde et al., 2003). Insect attack is characterised by bore holes and tunnels, while attack by fungi and other microorganisms produces a variety of defects in wood, among which decay is the most important. A proportion of the fungi that degrade timber structures may come from green timber used during building construction (Wilcox and Dietz, 1997). Wood colour change can be caused by fungi and microorganisms, but also by abiotic agents, such as light or moisture. A method of preventing attack by abiotic agents is wood treatment, which favours wood preservation (Masse et al., 1991) and helps maintain the mechanical properties of wood (Yildiz et al., 2004). Another method of preventing decay is to avoid the conditions that favour the invasion and colonisation of wood by biotic agents. The direct action of water and moisture favour the development of fungi and of a number of microorganisms that cause wood decay. Ventilation helps maintain the appropriate temperature and humidity conditions. The direct action of water can be avoided by using structural solutions that ensure water does not reach the structural members of the building. The points of support of columns on the floor, the joints between columns and beams, and the joints between beams and load-bearing walls are particularly important areas where moisture can occur, causing problems to the structure. Consequently, particular attention must be paid to the design of these joints. If wood is appropriately used and all the factors mentioned are taken into consideration, the mechanical properties of wood remain unaltered over time (Horie, 2002; Leichti et al., 2005; Lin et al., 2007). The objective of this study is to determine the factors that most strongly influence the durability of timber members used in the structures of agricultural and livestock buildings.

2.

Materials and methods

Some characteristics of timber structural members affect the service life of the timber structure of a building. This study has determined the characteristics that affect the service life of timber structures used in agricultural and livestock buildings. These characteristics correspond to the variables

considered in this study and are shown in Table 1. The characteristics were related to building context, material characterisation, identification of degradation agents, identification of possible mechanisms of degradation and the effects of degradation, in line with the standard ISO 15686-2 (2001). Among such characteristics, the condition of wood was defined based on wood deterioration, considering the following degradations: bore holes, fungal decay, colouration and/or discolouration. The condition of the wood was the criterion used to assess the influence of the characteristics of timber structural members on the durability and service life of the structure. This information allows one to consider the agents or conditions that are likely to affect service life, corresponding to inherent performance level, design level, execution level, indoor environment, usage conditions and maintenance level (ISO 15686-8, 2008). After such characteristics were determined, a sample of agricultural and livestock buildings with timber structural members was selected in Galicia, Northwest Spain. The selected sample provided the information necessary to assess the variables considered in the analysis. The sample included 133 buildings. Table 2 shows a classification of the sample buildings, along with the number of buildings designated for each end use. Data collection was carried out through a survey and an on-the-spot inspection of each building. In addition to data pertaining to the variables considered, the survey gathered information about the farm where the buildings were located and about other aspects of the buildings. Fig. 1 shows an overview of the data collected. Wood deterioration was measured based on visual inspection of the elements. Visual inspection was aimed at searching for external signs indicative of the degradation mentioned, namely, fungal decay, bore holes, colouration and/or discolouration. Visual inspection is a widely used method for characterising or classifying timber (UNE 56544, 2007; UNE 56546, 2007). In order to carry out the inspection and to collect comprehensive information about the condition of the

Table 1 – Variables for assessing the durability of timber members in livestock buildings Variables pertaining to

Variable

Timber characteristics

Timber species Time in service: time elapsed from the assembly of the structure Features: knots, cracks, presence of pith Treatments Condition: bore holes, decay, colouration and/or discolouration

Characteristics of the structural solution used in the building

Type of timber used in the members: round or sawn timber Structural system: beam, truss, purlin System of connections and supports Service conditions: end use of the building, environmental conditions, ventilation

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biosystems engineering 104 (2009) 152–160

Table 2 – Number and end use of the buildings studied End use of agricultural and livestock buildings

No.

Dairy cattle barn Beef cattle barn Sheep barn Rabbit barn Mink barn Hay barns and storage buildings Other uses: handling facilities, market premises, silos

33 22 5 7 4 30 32

structure, the following standards were taken as a reference: UNE-EN 1311 Round and sawn timber. Method of measurement of biological degradation (UNE-EN 1311, 1998); UNE-EN 844-10 Round and sawn timber. Terminology. Part 10: Terms relating to stain and fungal attack (UNE-EN 844-10, 1998) and UNE-EN 844-11 Round and sawn timber. Terminology. Part 11: Terms relating to degradation by insects (UNE-EN 844-11, 1998). Graphical and written information was collected for every farm and every building with a timber structure, and a specific database was developed to facilitate data handling and analysis. Two variables were used to measure the degradation: intensity and extent. The intensity is indicative of the severity of the attack on the members of the structure while the extent suggests the distribution of the attack. To quantify the intensity, degradation was divided in two groups: group A, which included fungal decay (white and/or brown rot), bore holes and tunnels; and group B, which included colouration and discolouration. Table 3 shows the assessment ratings used for visual inspection. Group A degradation was rated on a scale of 0–4 according to the presence of degradation in relation to the area of the structural element, as well as the depth of damage. Group B degradation was rated on a scale of 0–4 according to the area affected in relation to the total area of the element. Extent was rated on a scale of 1–5, according to the presence of degradation in relation to the percentage of structural elements attacked throughout the whole structure, as shown in Table 4. In addition, the relationship between the degradation and the characteristics of the structural system was established.

GENERAL FARM DATA Farm identification: Farmer’s name and address Production activity on the farm Farm buildings and end use of the buildings - Graphical information: general distribution of the buildings on the farm DATA FOR EVERY BUILDING WITH A TIMBER STRUCTURE General data: current use (including previous uses or future prospects) Age of the building Materials used Type of structural solution and specific characteristics Changes in the design of the structure, if any DATA PERTAINING TO TIMBER Timber species Time in service Treatments applied Condition: type of degradation Timber features (knots, checks) Degradation: relationship with the structure

Fig. 1 – Overview of data collected on every farm for every building.

Table 3 – Assessment of the intensity of degradation in the timber members studied Rating

Label

Description

Group A. White rot, brown rot, bore holes and/or tunnels 0 No attack No sign of attack is observed 1 Light attack Noticeable changes, but very limited in extent and location. Very shallow degradation at depths between 1 and 2 mm, located at isolated points or extending over small isolated areas (5 cm2) 2 Moderate Degradation extends over areas of up to attack 10 cm2 and a depth of 5 mm or in disseminated deeper areas 3 Severe attack Degradation extends over large areas (>10 cm2) with depths of up to 5 mm, and over more limited areas (<5 cm2) with depths of up to 10 mm 4 Collapse Generalised presence of damage over the entire area for depths of up to 5 mm, or localised at critical points for depths greater than 10 mm Group 0 1 2 3 4

B. Colouration and discolouration Negligible Affected area: below 5% Noticeable Affected area: 5%  S < 15% Significant Affected area: 15%  S < 40% Considerable Affected area: 40%  S < 60% Extensive Affected area: above 60%

The source of the degradation was related to the effects of the damage observed. For each type of degradation, the source of the degradation and its effects on the structure were identified. Fig. 2 shows the scheme used for data collection. This scheme summarises the information related to the identification of degradation agents, possible mechanisms of degradation, and effects of degradation (ISO 15686-2, 2001). In addition to fungal decay, bore holes and colouration and/or discolouration, the presence of cracks was taken into consideration. In some materials, the synergy between factors that affect the durability of materials can be very great (Marteinsson, 2003). The analysis was aimed at assessing the influence of the variables considered on the condition of the wood. More specifically, the analysis evaluated the influence of building use, timber species, type of product (round or sawn timber), treatment, age, environmental conditions (humidity, sunlight, action of water) and execution of the structure (supports, joints between elements) on the condition of the wood. Data were processed using the SPSS 15.0 statistical package for Windows

Table 4 – Assessment of the extent of degradation in the timber members studied Rating 1 2 3 4 5

Label Highly localised Localised Wide Generalised Total

Description Presence of damage on less than 20% of the pieces Number of pieces affected: 20%  N < 40% Number of pieces affected: 40%  N < 60% Number of pieces affected: 60%  N < 80% Presence of damage in more than 80% of the pieces

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biosystems engineering 104 (2009) 152–160

PRIMARY CAUSE

SINGLE CAUSE

SECONDARY CAUSE

TYPE OF DEGRADATION

EFFECT

Fungal attack Poor ventilation

Fungal attack

Construction of supports

Fungal attack

Construction of supports

Direct action of water

Construction of supports

Poor ventilation

Accumulation of animal manure

Fungal attack

Failure of supports

Reduction in crosssectional area

Swelling and shrinkage Swelling and shrinkage

Joints between structural members

Atmospheric humidity

Direct action of water

CRACKS

BORE HOLES

Insect attack Poor cleaning

Insect attack

Poor ventilation

Fungal attack

Solar radiation

Direct action of water

Fungal attack

Loss of functionality

DECAY

Pathway for biotic agents Pathway for agents of decay Surface shrinkage

COLOURATION

Solar radiation

Loss of aesthetic value DISCOLOURATION

Fig. 2 – Scheme for the identification of the relationship among the source of degradation, the type of degradation and its effect on the structure.

(copyrightª SPSS Inc., Chicago, IL, USA). The nonparametric Wilcoxon–Mann–Whitney test was used to determine whether there were differences among the variables considered, with regard to the degradation of the wood. A level of significance of 0.05 was used. Moreover, regression analysis was used to determine the degree of relationship between variables.

3.

degradation is related to the degraded area in the case of colouration and discolouration. For every building structure, a mean value, considering all its structural elements, was obtained. The intensity rating is shown in Table 3. The extent of degradation is related to the percentage of structural elements with degradation in any of the elements throughout a structure. The rating of extent is shown in Table 4. Table 6 includes two percentages. The first one is the percentage of observations (the number of buildings with a particular level of extent or intensity of degradation as a percentage of the total number of buildings studied). The second percentage is a cumulative percentage. In virtually half of the buildings, the extent of the defects was highly localised and affected less than 20% of the structural elements. More specifically, decay was wide or generalised in extent in only 10% of the buildings. The situation was worse for bore holes, because the extent of bore holes was wide or generalised in 20% of the buildings. Furthermore, in almost 7%

Results and discussion

Table 5 shows an initial classification of buildings according to end use, timber species, type of product (sawn or round timber) and wood treatment. Table 6 presents the extent and intensity of degradation, according to the assessment proposed in Materials and methods. The intensity of degradation is related to the degraded area and the depth of the damage, in the case of bore holes, as well as to the extent of decay. The intensity of

Table 5 – Percentage of buildings according to some of the variables considered End use of the building

Livestock housing Hay barns Storage buildings Other uses: handling facilities, market premises, silos Total

%

62.20 8.90 22.20 6.70

100.00

Characteristics of timber used in structural members Species

%

Chestnut Oak Eucalyptus Pine

35.60 9.60 36.30 18.50

100.00

Type of product

%

Treatment

%

Sawn

34.80

Treated

12.60

Round

65.20

Untreated

87.40

100.00

100.00

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biosystems engineering 104 (2009) 152–160

Table 6 – Percentage of buildings according to the extent and intensity of degradation observed in structural members Type of degradation

Extent and intensity of degradation Extent

0

1

2

3

4

Decay Bore holes Discolouration Colouration

A% A% A% A%

48.5 43.1 67.7 45.4

21.5 10.7 7.7 15.4

20.0 18.5 4.6 14.6

6.2 13.1 5.4 14.6

3.8 7.7 8.4 8.5

Decay Bore holes Discolouration Colouration

B% B% B% B%

48.5 43.1 67.7 45.4

70.0 53.8 75.4 60.8

90.0 72.3 80.0 75.4

96.2 85.4 85.4 90.0

100.0 93.1 93.8 98.5

Intensity

0

1

2

3

5 0 6.9 6.2 1.5 – 100.0 100.0 100.0

Total 100.0 100.0 100.0 100.0 – – – –

4

Total 100.0 100.0 100.0 100.0

Decay Bore holes Discolouration Colouration

A% A% A% A%

48.5 42.3 67.7 55.4

27.7 23.8 15.4 20.0

12.3 16.9 6.9 9.2

7.7 11.6 6.9 12.3

3.8 5.4 3.1 3.1

Decay Bore holes Discolouration Colouration

B% B% B% B%

48.5 42.3 67.7 55.4

76.2 66.2 83.1 75.4

88.5 83.1 90.0 84.6

96.2 94.6 96.9 96.9

100.0 100.0 100.0 100.0

– – – –

A%: Percentage of observations. B%: Cumulative percentage.

of cases, bore holes affected all the structural elements in a particular building. A similar situation was observed for colouration, while discolouration tended to be less extensive. With regard to the intensity of degradation, almost half the buildings did not show any sign of attack, and colouration and/or discolouration were negligible. Only 7.7% of the buildings showed severe fungal decay, and 3.8% showed collapse or fungal decay covering the whole surface. For bore

holes, the percentages obtained for severe attack and collapse were 11.5%–5.4%, respectively. The first factor considered in the analysis was the influence of wood treatment. Fig. 3 shows that the intensity of degradation in treated wood never exceeded level 1, except for discolouration. For fungal decay, differences became more evident. Appropriate wood treatment can slow the expansion of biotic agents (Grace, 2003; Clausen and Yang, 2007), and the

100%

Percentage of buildings

80%

60%

40%

20%

Bore holes Level 0

Decay Level 1

Discolouration Level 2

Level 3

Treated wood

Untreated wood

Treated wood

Untreated wood

Treated wood

Untreated wood

Treated wood

Untreated wood

0%

Colouration Level 4

Fig. 3 – Intensity of degradation in buildings with treated and untreated wood.

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biosystems engineering 104 (2009) 152–160

Considering the type of product, significant differences were found between untreated sawn timber and untreated round timber, but only with regard to intensity and extension of bore holes (extent, Z ¼ 2.406, P < 0.05; intensity Z ¼ 2.518, P < 0.05). In this case, the presence of sapwood in the piece may favour colonisation by biotic agents (Ra˚berg et al., 2005). With regard to the end use of the building, significant differences were found for the extent and intensity of colouration and discolouration. Significant differences were found between buildings used as barns (colouration: intensity Z ¼ 2.942, P < 0.05; extent Z ¼ 2.250, P < 0.05; discolouration: intensity Z ¼ 3.119, P < 0.05; extent Z ¼ 3.233, P < 0.05) and buildings devoted to other uses, which served as handling facilities or market premises (colouration: intensity Z ¼ 2.048, P < 0.05; extent Z ¼ 2.514, P < 0.05; discolouration: intensity Z ¼ 3.290, P < 0.05, extent Z ¼ 2.514, P < 0.05). Each use of agricultural and livestock buildings has specific characteristics and certain agricultural environments (with regard to temperature, humidity or ventilation characteristics) can be aggressive to the building materials (Singh, 1999 and De Belie et al., 2000). In addition, humidity in the surrounding environment affects wood endurance (Kalamess, 2002). After we analysed the degradation in wood based on wood treatment, the influence of age on the condition of timber members was examined. Table 8 shows the correlation coefficient between the age of the structure and the intensity and extent of degradation. Because treated wood showed a significantly different pattern, wood treatment was defined as a control variable. At a significance level of 0.001, statistical significance was found only for the extent of discolouration and the intensity of fungal decay. Figure 4 shows the average age of buildings, considering the intensity of degradation. Two trends could be observed, one relative to colouration, discolouration and bore holes and the other relative to decay. Colouration, discolouration and bore holes are dependent on other factors (such as exposure to solar radiation or humidity) and the impact of such degradation accumulates over time. Therefore, it is foreseeable that there is more intense degradation in older buildings. Decay emergence is associated, in addition, with factors favouring the attack of biotic agents. In this way, high intensities of colouration, discolouration and bore holes may appear in older buildings, but a high intensity of decay could appear in newer buildings, if the conditions were suitable for the development of decay agents. Thus, it appears that, from Level 2 (moderate attack), decay is independent of time because it is more related to other factors that favour the development of the biotic agents responsible.

Table 7 – Percentage of buildings with treated timber members according to timber species, type of product and end use of the building Variable

Percentage of buildings

Timber species Chestnut Oak Pine

5.9 17.6 76.5

Total

100.0

Type of product Sawn Round

70.6 29.4

Total

100.0

End use of the building Barn Storage building

87.5 12.5

Total

100.0

efficiency of the preventive method can be improved by using timber with appropriate moisture content (Usta, 2006). The results of the Wilcoxon–Mann–Whitney test for the comparison between the percentage of buildings with treated wood and the percentage of buildings with untreated wood, according to the intensity and extent of degradation, suggest that the differences are significant in all cases (P < 0.05). In buildings with treated wood, a strong correlation was found between wood treatment and species, type of product, and end use of the building, as suggested in Table 7. In more than 70% of buildings with treated wood, pine was the species used; the type of wood product was sawn timber; and the building was used to house cattle. Because of the correlations found for buildings with treated wood, we analysed the observations made for buildings with untreated wood members. Timber species was the first variable studied, because the durability of wood against attack by biotic agents can differ according to species (Rodrı´guez Nevado, 1999 and Arango et al., 2006) or service conditions (Highley, 1995 and Natterer et al., 2000). This analysis did not reveal significant differences among chestnut, oak and eucalyptus members. Only pine seemed to behave differently with regard to the intensity of decay, for which significant differences were found between pine and chestnut (Z ¼ 2.546, P < 0.05), pine and oak (Z ¼ 2.211, P < 0.05) and pine and eucalyptus (Z ¼ 2.620, P < 0.05).

Table 8 – Correlation between age of timber members and intensity and extent of degradation Control variable

Treatment

Extent

Correlation Significance (bilateral) df

Intensity

Col.

Disc.

Bor.

Dec.

Col.

Disc.

Bor.

Dec.

0.064 0.468 127

0.239 0.006 127

0.205 0.020 127

0.172 0.052 127

0.086 0.332 127

0.216 0.014 127

0.031 0.725 127

0.265 0.002 127

Col.: Colouration; Disc.: Discolouration; Bor.: Bore holes; Dec.: Decay.

158

Average age of the timber structure (years)

biosystems engineering 104 (2009) 152–160

40 35 30 25 20 15 10 5 0-No attack. Negligible

1-Light attack. Noticeable

2-Moderate attack. Significant

3-Severe attack. Considerable

4-Collapse. Extensive

Intensity of degradation Colouration

Discolouration

Bore holes

Decay

Fig. 4 – Average age of timber structures in the buildings studied, according to the intensity of degradation.

Regression analysis was used to relate the intensity and the extent of degradation with the age of structural members. The analysed data fit a cubic curve estimation model (P < 0.05). The value of the regression coefficient R2 was low for all the correlated variables. The highest value was for the correlation between the intensity of bore holes and the age of the building (R2 ¼ 0.120, P < 0.05). The values obtained suggest that degradation did not increase with the age of the building; rather, degradation was more intense and extensive in buildings with a low average age. Given that age can only partially explain the condition of wood, there are other factors that determine the condition of structural timber (Horie, 2002; Leichti et al., 2005; Brischke, and Rapp, 2008). Table 9 shows data pertaining to the primary causes of degradation that define the condition of timber structures. The direct action of water brings about favourable conditions

for the development of fungal decay and, to a lesser extent, of colouration and cracks. Other key causes of decay can be construction deficiencies (contributing to the penetration of moisture) and poorly designed supports of beams, columns, or beam-column joints. Cracks can originate at these types of joints and hinged connections. Colouration is caused by fungal attack and bore holes are made by insects. Incorrect maintenance of structural elements, such as poor cleaning, may facilitate insect attack and decay. Poor ventilation (which affects the relative humidity of the environment where the structural member is located) primarily causes colouration, but can also facilitate decay and, to a lesser extent, cracks. Fig. 5 shows the primary causes of the different types of degradation that defined the condition of the timber structures studied. The most serious degradation, fungal decay, could be avoided in 80% of the cases because decay was

Table 9 – Percentage of buildings according to the primary cause of degradation in timber structural members Primary cause

Percentage of buildings according to type of degradation Decay

Direct action of water Column support Beam support Beam-column joint Hinged connection Fungus-insect assoc. Fungal attack Insect attack Swelling and shrinkage Atmospheric humidity Solar radiation Poor cleaning Poor ventilation

Bore holes

Checks

Colouration

% Total

Discolouration

65.38

0.00

14.10

19.23

1.28

100

100.00 72.73 50.00 0.00 25.00 27.78 0.00 0.00 11.40 0.00 20.00 37.88

0.00 0.00 0.00 0.00 75.00 0.00 100.00 0.00 0.00 0.00 80.00 0.00

0.00 9.09 50.00 100.00 0.00 0.00 0.00 100.00 60.53 0.00 0.00 19.70

0.00 18.18 0.00 0.00 0.00 72.22 0.00 0.00 26.32 0.00 0.00 42.42

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.75 100.00 0.00 0.00

100 100 100 100 100 100 100 100 100 100 100 100

biosystems engineering 104 (2009) 152–160

results suggest that the use of local resources and of the timber species present in the local environment (both round and sawn timber) can be a good option for low-cost agricultural buildings if timber is treated, regardless of the end use of the building.

100%

Percentage of buildings

90% 80% 70% 60% 50% 40%

Acknowledgements

30% 20% 10% 0% Decay

Bore holes

Cracks

Construction deficiencies Interior and exterior environment

Colouration

Discolouration

Poor maintenance Attack by biotic agents

Fig. 5 – Causes of degradation in the timber structures studied.

caused by construction deficiencies or poor maintenance of the structure. Bore holes were less dependent on the construction of the building, but were dependent, to a great extent, on appropriate structure maintenance. These results suggest that, in addition to wood treatment, construction deficiencies and poor maintenance of the structure in service strongly influenced the deterioration of the timber structures of a building.

4.

159

Conclusions

The structural condition of the timber buildings studied is good. Constructions that can be considered collapsed because the intensity of decay and bore holes reached Level 4 accounted for 5% of cases, while constructions with severe damage (Level 5) accounted for 8–11%. About half the inspected buildings do not present any type of insect attack. The end use of buildings or the timber species used in the structure does not appear to affect the condition of the structure. Neither is age a determining factor in the structural condition of the building. Consequently, the service life of timber structures is related less closely to age than to other factors. Three factors affect the condition and service life of timber structures: wood treatment; appropriate design of structural joints; and appropriate ventilation and frequent cleaning. Treated wood decreases the intensity of bore holes by 82% and the intensity of fungal decay by 94%. Correct ventilation and good maintenance decrease decay by 45%, bore holes by 21% and cracks by 17%. The appropriate design of joints between members, together with the use of roof joints that avoid the direct action of water, can decrease fungal decay by 38%. The service life and the condition of timber structures are dependent on appropriate construction practice, including previous wood treatment and proper maintenance. The service life and condition of timber structures are not dependent on timber species or on the end use of the building, which do not determine the service life of the structure. These

This research has been funded by the Spanish Ministry of Science and Technology within the framework of Research Project BIA 2004-07146 ‘Validation of Resistograph as a Tool for the Assessment and Characterisation of Structural Timber’.

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