Tasmanian Museum and Art Gallery: Assessment of sections of the timber structures: Final Report

The building fabric of the Tasmanian Museum and Art Gallery (TMAG) is being assessed in preparation for planned renovations. Part of this is assessment of the integrity and structural capacity of timber components of three areas in the TMAG complex, namely the 1824 Bond store, the 1869 Queen’s warehouse and the 1808 Commissariat store.

 This preliminary report describes the results of examinations of these buildings conducted in December 2010 and January 2011 by registered architect, Associate Professor Greg Nolan from the University of Tasmania’s Centre for Sustainable Architecture with Wood and an experienced timber grader, Mr Nigel Leigh-Jones. A spreadsheet of detailed results and images of elements and other items of interest accompany this descriptive report.

The timber work in the three areas was examined to:
• Establish the structural section and grade of individual members.
• Assess assembly and durability issues of individual members and connections.

• Make observations on the strength, stiffness and durability characteristics of the assemblies as structures.
• Determine the timber’s species and moisture content.

 The examination did not endeavour to determine the structural adequacy of the buildings or any connection in them. However, areas where the structural adequency needs to be confirmed by calculation or other means were noted.

 In addition to the impact of the condition of the individual elements noted during the examination, one are of critical and iimediate concern and five areas of general concern were noted.

 The area of critical and immediate concern is the support of beam C in the L2 of the Commissariat store. Its supports appear inadequate for the likely load applied and prone to 
unpredictable failure. This needs modelling and if necessary remedial work.

 Of the areas of general concern, two require modelling and examination in the short term.

These are:

 • The capacity of the main floor beams between grid 0 and grid 4 in L2 of the Queen’s warehouse. This area is in regular use as the children’s discovery area. While the beams were not in apparent distress, four of the beams in this area appear to have shear failures. Beam 1 has an apparent shear failure along most of its length.
 • The apex connection of truss 2 in L4 in the Bond store. The effective section of the primary rafter on one side of this joint is significantly smaller than in other trusses. While the possibility of failure of this joint appears low, its consequence is high.

 Three areas of general concern should be addressed through the design of modification to the buildings. These are
 • Water penetration to L1 and the ends of embedded beams in L4 in the Bond store. Decay will only continue at an increasing rate and lead to further deterioration in the building fabric unless water is excluded and the moisture content of the timber brought below about 16%.

 The support of joists on L1, L2 and L3 of the Bond store. Given the initial detailing of the building and shrinkage of elements, this has obviously been an on-going problem.

• In addition to beam C, the remainder of the floor in L2 of the Commissariat store, particularly the connections between all transverse beams and longitudinal beams.