Mechanical properties on flexure and shear of commercially available timber beams

• Main Authors: De Guzman, Earl Marvin B., Go, Michael Stephen C., Tengki, Katrina C.
• Format: text
• Language: English
• Published: Animo Repository 2011
• Subjects: Wood > Testing; Strength of materials; Structural engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/10084
• Institution: De La Salle University

Wood construction has proven itself to be a feasible alternative to other existing forms of construction when it comes to providing economical houses that are of good quality. With the depletion of forests because of illegal logging, the Philippines implemented restriction in the country’s production of timber. Most of the lumber in the Philippines are imported, and in the market, harvest species of commercially available timber are not specified and only referred to as 2good lumber3. Thus the properties of good lumber are unknown to the structural designer, and the determination of its allowable mechanical properties would be a useful design aid. A lumberyard survey conducted in the lumberyards of Metro Manila showed that 44% of the commercially available timber is imported from other countries, while the other 56% comprise of lumber that is locally produced. Most of the results show that the specie of good lumber is unknown or a combination of different known species. Laboratory tests were done to determine the different mechanical properties of good lumber, and it was found that good lumber had moisture content ranging from 12-82% with an average of 25%, a relative density ranging from 0.236-0.743 with an average of 0.47, and a modulus of elasticity ranging from 2.61 to 16.41Pa, with an average of 8.15GPa. The modulus of rupture obtained from the flexure tests ranged from 5.7 to 63.5MPa, while the shear stress at failure ranged from 0.60 to 4.15MPa. A reduction factor of 2.1 was applied to the test results for bending and shear. The lower limit of the allowable bending stress was 11.0Pa, while that of the allowable shear stress was 0.77MPa. Specimens found to have the major defects were observed to have greatly affected the lumbers capacity for stiffness. Ratios of 53% and 63% were found for the bending and shear stresses of beams with major defects to those of beams without major defects. The results from the laboratory tests were compared to that of the known species in the NSCP particularly the species that had design values nearest to the values obtained for good lumber and it was found that good lumber in general would have values within the ranges for medium and moderately low strength group for 63% stress grades. However for beams with no major defects, good lumber can be further classified under the medium and moderately low strength group for 80% stress grades.