Materials and Structures, 34, 59— Gantz, C.
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Lin, C. Wood and Fiber Science, 35, — Tseng, Y. Procc 10th World Conference on Timber Engineering, — Lee Jun-Jae Reliability analysis of deteriorated post member. Procc 8th World Conference on Timber Engineering, — Progress in Structural Engineering and Materials, 6, 94— Piazza, M. Journal of Building Appraisal, 3, — Zhang, H. Ferenc Divos ed.
Ramos, L. Engineering Structures, 26, — Machado, J. Determination of density profile by non-destructive methods. Revista Portuguesa de Engenharia de Estruturas 42, 15— Johnstone, D. EN Grippa, M.
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Scientific papers - Quantifying the Value of Structural Health Monitoring - COST Action TU
How to cite item. Finding References. Email this article Login required. About The Authors M. Plagiarism Detection Tool. Journal covered by. Use and distribution license. Wood biodegrades over time. Under the impact of external factors, wooden members undergo chemical and physical changes. Wood can be regarded as a durable material when it is completely immersed in water, and so protected against decomposition caused by aerobic fungi.
In nature, five basic chemical processes occur which reconvert a wooden material into carbon dioxide and water: oxidation, hydrolysis, dehydration, reduction and free radical reactions [ 3 ]. Table 1 shows major degradation pathways and the chemistries involved in the pathways [ 3 ].
All the above factors can be significant when testing wood samples taken from a retaining structure since the latter is exposed to the air, water and soil environment. Therefore, wood analyses should be based on more than one research technique to gain a deeper insight into the change of wood parameters over time in different environmental conditions [ 3 ]. In the considered case, since the structure was in service in the water environment and in saturated soils, the hazards can be divided into the following three main groups:.
If timber members are above the groundwater table, access to oxygen makes the activation of wood decomposing fungi possible. However, the long-lasting service of timber structures below the groundwater table does not prevent decomposition [ 5 ], and examinations have shown some of the pile foundations in Venice to be in extremely bad condition.
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This paper presents research methods which enable one to determine the condition and some parameters of a material which has been in service in the water-soil environment. For the best results, wood should be tested on different levels of detail, i. On the macrolevel, acoustic methods, drilling resistance method or laboratory tests of basic material parameters, such as density and moisture content, are used.
On the microlevel the cell wall of the wood is tested and different elements, such as hardwood, sapwood and annual rings, are identified [ 6 ], using, e. The considered timber sheet wall was made of tongue-and-groove jointed timber piles. The history of this structure is not well known because of its previous military use.
The timber sheet wall had been in service for about 70 years. In the Swina strait, fresh water fully or partially mixes with seawater due to the stratification. It can be assumed that the water environmental conditions correspond to low salinity seawater. After the timber sheet wall had been dug out and dismantled, its members were closely examined with regard to their original and current cross-sectional dimensions and to the quality of the wood.
In the photograph Figure 1 a,b of the dismantled members of the wall, one can see pile surfaces which were in service in diverse environmental conditions: completely embedded in the ground, stayed in water and stayed in the variable water-air environment. One can notice that the timber embedded in the ground, under the groundwater table, has preserved its constant volume. Bacteria destroy the cellulose very slowly, while the lignin remains constant, and water replaces the large cellulose molecules.
The original waterfront layout has been reconstructed, see Figure 1 c. The main objective of the work is to develop a methodology for testing of wooden structural members using non-destructive techniques. This is aimed at obtaining information which is necessary to assess the technical condition of the material in wooden members and to conduct a global structure analysis.
In particular, to carry out such analysis, it is required to estimate the values of mechanical parameters and to assess possible zones of destruction. The detailed aim is to compare the quality of wood subjected to various environmental conditions Figure 1 d. Unlike destructive tests, the tests belonging to the latter two groups do not affect or only slightly affect the properties of the tested sample, whereby the parameters of a wooden member can be determined with no detriment to its value.
Their undeniable advantage is also the mobility of the testing equipment, whereby tests can be carried out in situ when it is not possible to take samples for laboratory tests as in the case of heritage assets. Among the non-destructive and semi-destructive methods one can distinguish global testing methods e. In order to acquire detailed data on the values of the physical and mechanical parameters of wood both non-destructive and destructive methods should be used.
If the results yielded by the two testing methods are found to correlate, the data acquired in this way are fully sufficient for further static load analyses of the structural members or the whole building structure. Nevertheless, even using only non-destructive methods as in the case of, e. Thanks to the use of non-destructive methods one can also detect internal damage or flaws in the wood [ 9 ]. Among the non-destructive and quasi-non-destructive testing methods used to assess and diagnose timber structures, the most common are the ones presented in Table 2 , and also described in detail in, i.
The non-destructive and quasi-non-destructive methods can be divided into two groups: global testing methods e. Using acoustic testing methods, such as the ultrasonic and stress wave techniques, one can evaluate the properties of wood by analysing the velocity of wave propagation in the tested material. The methods can be used to estimate selected mechanical properties e. The basic parameter used in the acoustic methods is sound wave propagation velocity V , defined as follows:.
The dynamic modulus of elasticity is calculated from the formula:. The velocity of sound wave propagation largely depends on the structure of the material. In the case of wood, it depends on the grain direction being several times higher usually 3—5 times higher along than across the grain [ 10 , 12 ]. Other values than the above ones may indicate internal discontinuities in the material structure. The lower values of the velocity across the grain are due to the internal structure of this material on its way the wave encounters more cell walls, whereby the time in which it covers the distance increases, whereas in the longitudinal direction there are fewer barriers or they do not occur, whereby the velocity is higher.
Several kinds of devices are used for testing by means of ultrasonic or stress wave methods.
In this case study, two of them were used and the test results are presented in Section 3. The Fakopp Microsecond Timer Figure 2 a uses the stress wave technique. The test consists of exciting a stress wave with a single strike of a special hammer. The device probes are driven directly into the tested sample. There is no need to drill holes as in the case of other devices e.
The device measures the time of wave propagation between the two probes the receiving probe and the transmitting probe. Devices for testing by acoustic method: a Fakopp Microsecond Timer using stress wave; b Sylvatest Trio device using ultrasonic wave; c Sylvatest Trio device during test.
In the case of the ultrasonic technique, the measurement can be performed in two ways: directly and indirectly. The first way consists of transmitting a signal from the transmitting probe to the receiving probe, with the probes placed on the opposite sides of the tested sample. As regard the second way, there is no need to place probes on the opposite sides of the sample because the signal is registered as reflected the echo method.
Owing to this, the range of the applicability of this test widens since only a unilateral access is required which is useful when testing, e. Sylvatest Trio Figure 2 b , manufactured by the firm CBS-CBT, is another device which one can use to non-destructively evaluate the properties of wood [ 13 ]. The device measures the time needed for an ultrasonic wave to pass between transmitting-receiving probes placed against the tested sample, and the energy of this wave. In order to carry out the test the tips of the probes should be inserted into previously drilled holes each 5 mm in diameter and 10 mm deep.