Comparing the Building Code Sawn Lumber’s Wet Service Factors (CM) with Four Commercial Wood Species Laboratory Tests

Abstract

Indonesian Wooden Building Code (SNI 7973-2013) has adopted the National Design Specification (NDS) for Wood Construction since 2013. A periodic harmonization of the building-code-designated values (i.e., reference design values and adjustment factors) with the experimental data of commercial wood species is necessary. This study aimed to compare the building code’s wet service factors (CM) with the laboratory test of some commercial wood species. Since wood is weaker when its moisture content is high, the wet service factor (CM) must adjust the sawn lumber reference design values if the building serves in wet or aquatic environments. Four commercial wood species, namely pine (Pinus merkusii), agathis (Agathis dammara), red meranti (Shorea leprosula), and mahogany (Swietenia mahagoni), were subjected to mechanical property tests. To calculate the empirical CM values, the mechanical properties tests were conducted on air-dry and wet wood. Instead of testing the full-sized timber, which contains the growth characteristics and defects, this study chose clear-wood specimens to resemble the boundary condition of the ceteris paribus (other things being equal). The wet (water-saturated) specimens were immersed in water for 65 days, and the test was carried out when the specimen was still immersed. The test arrangement imitated the submerged wood as the worst-case scenario of the wet environment where the construction serves, rather than green or partially immersed timber. As many as 40 specimens were tested to compare each mechanical property’s wet service factor; thus, this study reported 200 specimens’ laboratory test results. The empirical CM values to adjust the modulus of elasticity, modulus of rupture, shear strength parallel-to-grain, tensile strength parallel-to-grain, and maximum crushing strength (CM = 0.59, 0.76, 0.65, 0.73, and 0.67, respectively) were significantly lower than SNI 7973-2013 designated values (CM = 0.9, 0.85, 0.97, 1, and 0.8, respectively). The empirical CM for the compression stress perpendicular-to-grain at the proportional limit and that at the 0.04″ deformation (CM = 0.66) were slightly lower than the designated values (CM = 0.67), although they were not significantly different. This study resulted in lower empirical CM values than the designated ones, which found that the building code lacked conservativeness. The lacked conservativeness is mainly attributed to the building code’s recent choices, e.g., (1) the wet service environment basis is the green timber rather than the fully water-saturated one, and (2) the ratio of near minimum (5% lower) distribution value is chosen as the CM value rather than the average of wet timber’s mechanical property divided by the air-dry one. This study proposes changing both recent choices to alternative ones to develop more safe and reliable designated CM values.

Structural Analysis of Self-Weight Loading Standing Trees to Determine Its Critical Buckling Height

“…This study assumed that the standing trees are round columns to simplify the buckling stress analysis. Two stress analysis methods can approach the round column buckling analysis: the Euler and the Ylinen formula as directed by Indonesian Wooden Building Code SNI 7973:2013 [35], which has adopted the National Design Specification (NDS) [36] since 2013 [28,29].…”

“…The allowable stress is the 5% lower exclusion limit of the strength corrected by the corresponding adjustment factors; thus, it represents the reference design values [27]. The adjustment factors accommodate the service environment condition effects on the mechanical properties compared to those resulting in the standardized condition laboratory tests [28,29]. When buckling occurs, a column structure can no longer maintain its original straight shape; the deformed shape resembles an arch curvature-like bending deflection (Figure 1), leading to the tree stem's instability failure.…”

“…This study aimed to analyze the safety factors related to the critical buckling height of decurrent and excurrent trees modeled as slender round columns using three different methods. The structural analysis of a tapered column following the Indonesian Wooden Building Code (SNI 7973:201) [35], which has adopted the National Design Specification for Wood Construction [36] since 2013 [28,29], is Method 1. Euler and Ylinen's formulas, already familiar to engineers [29,37,38], are required to analyze a column's buckling as specified by the legally current building code.…”

The Effects of Forest Operations and Silvicultural Treatments on Litter Decomposition Rate: a Meta-analysis

“…Wood has been a crucial renewable resource for mankind for millennia [1,2], and it also plays a key role in the framework of climate change mitigation, as it is a long-term carbon sink [3][4][5][6]. Forests provide not only wood as a renewable raw material but also present several other fundamental ecosystem services, for instance, hydrological protection [7][8][9] and biodiversity conservation [10,11].…”