Introduction

Gorgan is located in the North of Iran between the Caspian sea and the Alborz mountains where the climate is mostly Mediterranean (with average rainfall of 432.1 mm and RH between 62.5% and 74%). It is considered to be a heritage city because of its history and historic buildings some of which contain solid wood structural elements.

This paper evaluates the structural integrity of one of the most important historic building in Gorgan, called the House of Bagheri which is a tourist site and is designated as a Cultural Heritage Construction. The strength of decayed wood members is measured by using both a nondestructive stress wave method and a static laboratory measurement to quantify mechanical properties.

The House was built approximately 150 years ago with a floor area of 3000 m2 (Eimanian, 2001) and is now under repair. Solid wood was utilized extensively for structural members including beams, columns, rafters, roofs and floors in association with other traditional materials i.e. brick and cob (a mixture of clay and straw). Doors and windows are completely wooden and are well preserved. Due to long exposure to the natural environment, some faults have developed including decay of wooden members.

Figure 1. A view of the House of Bagheri.

The building is a collection of several main parts and yards. A small pool is located in the centre of each yard surrounded by buildings. Although there is a one-storey building in this complex, it is mainly built on two-stories with a few steps between floors (Fig. 1). The buildings have nearly the same architectural characteristics and the plan of one building is shown in Figure 2.

Figure 2. A plan of one building of the House of Bagheri.

This building possesses a rectangular structure and used construction materials which were essentially brick and cob in the shear walls and solid wood in the principal structural elements. Its main defects have been previously reported by Madhoushi & Eimanian (in press). Degradation caused by weathering (sunlight and rainwater splashing), decay and insect attack have led to damage and faults in the building. It is now under repair and most defective structural elements have been substituted by new members.

Today, repair and restoration of historic buildings is a major challenge for society (Lourenco et al. 2006). The conservation and repair of these mostly timber buildings is important due to the unique response of timber structural members under seismic loading (Ceccotti et al. 2006, Tampone & Messeri 2006). Previous studies conducted on historic wood buildings showed that moisture and fungal decay could be considered as the main source of damage (Ronca & Gubana 1998, Pasanen et al. 2000). However, it was shown by Madhoushi & Eimainan (in press) that in the House of Bagheri, insect and weathering damage as well as fungal decay are the source of degradation.

The stress wave technique is one of the methods used widely for the inspection of load-bearing timber members. Previous studies (Haines et al. 1996, Machek et al. 2004) show that there are good relationships between static MOE (Modulus of Elasticity) and dynamic MOE. These relationships depend on species, grain direction and existence of defects.

The fundamentals of the stress wave method and its applications have been explained by Pellerin & Ross (2002). This method can be applied in the evaluation of members in timber structures (Ross & Pellerin 1994) and decayed wood (Ross et al. 1996). A previous investigation (Madhoushi et al. 2006) showed that this method might be used for assessing the decay of Iranian hardwoods and it was suggested as an in situ evaluation technique for decayed wooden members of historic structures.

Figure 3. Measuring the transmission time of stress waves.

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