Abstract
Previously, numerous creep studies on wood materials have been conducted in various coupon-scale tests. None had conducted research on creep properties of full-scale wooden cross-arms under actual environment and working load conditions. Hence, this research established findings on effect of braced arms on the creep behaviors of Virgin Balau (Shorea dipterocarpaceae) wood timber cross-arm in 132 kV latticed tower. In this research, creep properties of the main members of both current and braced wooden cross-arm designs were evaluated under actual working load conditions at 1000 h. The wooden cross-arm was assembled on a custom-made creep test rig at an outdoor area to simulate its long-term mechanical behaviours under actual environment of tropical climate conditions. Further creep numerical analyses were also performed by using Findley and Burger models in order to elaborate the transient creep, elastic and viscoelastic moduli of both wooden cross-arm configurations. The findings display that the reinforcement of braced arms in cross-arm structure significantly reduced its creep strain. The inclusion of bracing system in cross-arm structure enhanced transient creep and stress independent material exponent of the wooden structure. The addition of braced arms also improved elastic and viscoelastic moduli of wooden cross-arm structure. Thus, the outcomes suggested that the installation of bracing system in wooden cross-arm could extend the structure’s service life. Subsequently, this effort would ease maintenance and reduce cost for long-term applications in transmission towers.
Highlights
Anisotropic materials has been widely used in many large structures such as bridges, buildings, pedestrian walkways and cross-arm in transmission tower
The creep properties of Balau wood timber cross-arms reinforced with additional braced arms was significantly reduced as compared to existing design wooden cross-arms
The implementation of bracing system in cross-arm structures display a good potential for application existing wooden cross-arms in latticed transmission tower
Summary
Anisotropic materials has been widely used in many large structures such as bridges, buildings, pedestrian walkways and cross-arm in transmission tower. Many studies reported that most wooden structures experienced premature failures after long period of service, especially when continuously exposed toward extreme weather [5,6,7]. These premature failures are contributed by creep and natural defect such as wood ageing process, which subsequently may lead to structural collapse [8,9,10,11,12,13]. Creep is a term referred to the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses They are divided into several phases starting from instantaneous deformation followed by primary (transient), secondary (steady-state) and tertiary (accelerated). Numerous creep studies of wooden materials have been carried out by many researchers in many ways including development of creep test rigs [17,18,19], and creep numerical analyses [20,21] and coupon tests [22,23]
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