Structural analysis of two King-post timber trusses: Non-destructive evaluation and load-carrying tests (original) (raw)
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Evaluation of Late Nineteenth and Early Twentieth Century Built-up Timber Trusses in Buildings
This paper presents an approach to understanding the characteristics, behavior, analysis, and repair of built-up timber trusses. Historic built-up timber trusses are generally made from dimensional lumber and usually have bolted connections and iron vertical rods. They are a product of the late 19th-century and early 20th century and are found in a range of commercial and institutional buildings. Their construction is distinct from earlier heavy timber trusses, and therefore presents a somewhat different set of evaluation criteria and repair strategies. Common problems with built-up timber trusses will be discussed, such as excessive deflection, splice failure, inappropriate repairs, and the lack of sway bracing. Examples from the author’s experience will be shown to illustrate the presentation. The examples are synthesized into a suggested structural evaluation approach, including visual cues to potential problems, modeling considerations, common errors in evaluation, and appropriate repair strategies. The approach is based on a philosophy of preservation engineering that seeks sensitive methods of strengthening and avoids unnecessary intervention.
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Zenodo (CERN European Organization for Nuclear Research), 2023
Maintenance is an essential task to extend the service life of buildings; and yet, not well attended in Uruguay. This fact has led to the development of timber structures with assorted problems related to humidity. The warehouse presented in this paper was built at the beginning of the 20th century. Its roof is supported by trusses, made of sawn timber pieces joined by traditional woodworking joints. Due to some roof leaks and a reform project that modified the structural loads, the owners requested us a roof inspection and rehabilitation proposal. To fulfill this, we set three objectives: first, to inspect the trusses; second, to characterize the timber-since no records of the original project were founded-; and third, to analyze the structure with the new loads. Developments: We started visually inspecting the trusses to detect the damage caused by biotic agents and to propose its reparation. Then, we estimated the timber mechanical properties destructively (by longitudinal compression tests of small-scale wood specimens) and non-destructively (by wave propagation testing techniques). Finally, we analyzed and checked the trusses in both the ultimate and serviceability limit states, after placing the projected new covering. Remarks and Conclusion: Since some of the encounters between the trusses and the walls showed active attacks of fungal rot (brown rot), we recommended the elimination of the damaged areas and the reinforcement of the corresponding joints. Based on the destructive and non-destructive tests, we estimated the mechanical properties of the timber to be those of a C24 strength class-though denser (610 kg/m³). Regarding the structural analysis, we observed that the new roof covering (new loads configuration) and the stresses fluctuation due to suction wind could critically affect the structural behavior of both the woodworking joints and the trusses elements.
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Proceedings of the VI International Conference on Structural Analysis of Historic Construction, SAHC08, 2-4 July 2008, Bath, United Kingdom, 2008
In-situ cyclic tests on an existing traditional timber truss were performed. The main goal of the tests was to evaluate the overall behavior of the timber truss under symmetric and non-symmetric loading. Moreover, the influence of the location of point loads application, without and with eccentricity relatively to joints, was assessed. The carrying tests were preceded by a visual and non-destructive inspection aiming to collect geometric data and to assess the decay level. The field tests results of a queen-post truss are presented and analyzed. A numerical model was developed to reproduce the test results.
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In the present work, the safety of existing traditional timber trusses is evaluated, with particular emphasis on the structural robustness. Traditional Portuguese timber trusses are analyzed probabilistically, using the information provided in the JCSS model code, combined with action and resistance models provided in the Eurocodes. Robustness is evaluated through introduction of a localized defect, simulating deterioration, construction error or damages. The comparison between the reliability index considering a defect and the corresponding index for an intact structure is defined as a measure of susceptibility to local damage. The reliability index is computed using Monte-Carlo simulation combined with linear elastic finite elements for different examples.
Behaviour And Rehabilitation Of Queen Post Timber Trusses:A Case Study
WIT Transactions on the Built Environment, 2003
The availability of a wooden queen post truss of the early nineteenth century has provided a unique opportunity to evaluate performances and need for restoration of these structures, and to assess the possible intervention procedures, resorting to both traditional and innovative (glued in steel bars) methods. The truss has been characterized geometrically and statically, and its material (Abies alba Mill) has been classified. The damages have been identified using non-destructive test methods, and the actual performance of each timber element of the truss has been assessed by means of full scale loading tests in the elastic field. The same type of tests has been carried out on those components that had undergone restoration. The data gathered in the diagnostic phase have provided the input values for numeric simulations aimed to propose a predictive model for the truss. These simulations have been validated against the results of load tests, carried out both under static and cyclic (low-frequency) loads. Results show, on the one hand, the opportunities for intervention on this kind of structures offered by innovative connections exploiting glued in bars, and, on the other hand that the static behaviour of t h~s type of truss requires a rather sophisticated approach to be satisfactorily predicted.
International Journal of Heritage Architecture: Studies, Repairs and Maintence, 2017
The National Museum in Stockholm is Sweden's leading museum of art and design. Behind the now closed doors of the National Museum and its construction coverings a renovation project is taking place, which began in 2014 and will be completed in 2018. The renovation project will create a modern museum, a brighter atmosphere for the arts and for its visitors. Part of the renovation project was to design and upgrade the timber roof structure for new loads according to Eurocode 5. As the roof structure was originally built in 1860, it was important to evaluate the condition and mechanical properties of the original load-bearing timber members. The roof structure, which is of main interest, comprises roof trusses and lantern structures. The main aim of the project regarding the timber roof structure in the National Museum was a safety verification in both the ultimate state (ULS) and the serviceability limit state (SLS). The preliminary capacity calculations for the roof structure showed that the roof members were under the new load conditions (with increased loads due to security and environmental requirements) utilized above 100%. Therefore, an investigation into the properties of the old timber members and connections was of vital importance. The need for non-destructive testing (NDT) of structural timber is well known under the name of strength grading and the concept has been used for many years to classify timber with respect to mechanical performance. The stress wave technique used in the project was based on commercial instruments such as FAKOPP®. The timber quality investigation for the attic roof structures showed that the material was generally in very good condition. As a result, according to SS-EN 338-2009, the timber strength could be assigned strength class C27-C30. Based on the results of the investigation, further design of strengthening works and refurbishment of the roof structure were being undertaken.
Diagnosis and analysis of two king-post trusses
Sahc2008 Structural Analysis of Historic Construction, 2008
An accurate geometric and mechanical evaluation of two king-post trusses, based in grading results with data gathered from NDT as well as from mechanical evaluation, followed by full-scale tests were performed. The trusses were reassembled in laboratory and submitted to a series of cyclic tests under symmetric and asymmetric loading. Strengthening techniques evaluated in precedents research steps were used in a second phase of the carrying tests.