The Comparison of Softwood and Hardwood Timber Properties - Research Paper Example

TITLE PAGE Abstract 3 1.0Introduction and objectives 4 1.1 Hypothesis 6 1.2 Methods and materials 6 1.2 Results 7 1.2.1 Deflection and loads 7 1.2.2 Deflection load plot 9 1.2.3Failure load plots 10 1.3Discussion 12 1.4 Conclusion 13 References 13 Abstract This begins by giving a brief introduction where the importance of the test is highlighted. The aim of this test was to compare properties of softwood and hardwood timber. The highest deflection of 0.35mm was for ash while the lowest was 0.16mm for meranti. Ash failed at the highest load of 2650N, while the failure loads for pine, redwood and meranti were 1800, 1100 and 800 respectively. 1.0Introduction and objectives Timber is a very popular engineering material because of its use in many countries as a traditional building material. There are several important factors that that need to be put into consideration when timber is being selected that include strength, appearance, the availability of species size and sections; the durability of timber and the ease of preservation and the cost of the timber. Strength grading can be used as a means of evaluating the strength a piece of timber where visual or machine methods can be used. In visual grading growth characteristics such as wane, wane, fissures, slope of grain, distortions, fungal and insect damage are used with the laid down Standards providing guidelines on the size, type and number of defects that is allowable for each grade. The relationships that exist between strength and stiffness properties of timber specimen provide the basis of machine strength grading. The experience bending or radiation type machines give the basis of the requirements for the machine strength grading system. There are two standard ways that the bending machine work: the first involve the application of a test load to each piece of timber when passing through the machine so that the strength or grade class is indicated by the maximum deflection or deformation. The other alternative is where there is a preset deflection where the minimum load to achieve the deflection gives the grade. Most system used for grading put emphasis on the species of the timber and there are many combinations of species and strength grades which have varied strength properties. As a way of simplifying design, species-grade combinations with similar strength may be grouped into strength classes and this ensures their interchangeability. This is an indication an engineer can do calculations on the basis of the strength class and any combination of the species and grade in the strength class can be utilized in the construction. The can be allocation of timber into strength classes visually by strength grade and species type consideration or use of machine grading by strength class limit. It therefore there is need for visual override so as to achieve the requirements in the growth characteristics of the pieces including fissures, wane, distortion, slope of grain, resin and bark pockets and knot diameter. Timber can be classified as hardwood (Angiosperms) or softwood (Gymnosperms) where hardwoods mainly are deciduous trees while the softwoods are coniferous trees. This classification does not factor in the physical properties but its basis is on the cell structure of the timber. In general hardwoods are more durable and possess high strength in comparison to the softwoods however there are exceptions cases (Keith F. et al 1999) where this general rule is not adhered to. In countries like the UK nearly three quarters of the timber used is softwood because its lower cost, its availability in addition to its ease of working. The trunk of the tree has the function of supporting the crown, which is the part that performs the role of food and seed production. The trunk enables minerals to move from the roots to the crown in addition storing the manufactured food. This means that as a whole unit the trunk offers structural support to the tree. The outer layer of the trunk which is known as the sapwood and is responsible for conducting and storing of food while the inner part named heartwood is dormant as it plays any role. Resin or gum production which gives protection to the reproductive layers of the tree against insect and fungal attack takes place in the heartwood. 1.1 Hypothesis HO There is no difference in the strength and stiffness between softwood and hardwood. specimen H1 hardwoods have high strength and stiffness when compared to softwoods 1.2 Methods and materials In this experiment flexural load frame and load ring and a deflection gauge were the necessary apparatus. The distance between the two supports of the load frame were measured and it was designated as (L). The end grain structure for the four specimens that had been selected underwent examination and this was used in making on the orientation that would provide the highest resistance to deflection. This was done bearing in mind that there will be greater resistance when the force is applied normally to the grain. In the process of performing this experiment it was necessary to waer safety goggles. Each specimen was placed in the flexural load then secured in position; the deflection gauge was then placed under the sample as central as possible in a manner that it could touch the bottom of the sample. The dials were then adjusted to zero reading. The loads were applied in turn the 50N being the first with increments of 100N adding up to 450N while the deflection was being recorded in the first column of the recording for every increment. The load was then released and there was a repeat of the same procedure with the initial load of 50N and 100N increments up to 450N and another set of values were recorded in second column of the recording sheet. After the second set of recordings the same procedure was repeated so as to obtain the values recorded in the third columns of the recording sheet but for this third time the load were not released. The load was then increased in steps of 250N so as to have the deflection at 700N, 950N--- till the point of breakage of the specimen. 1.2 Results 1.2.1 Deflection and loads From table 1 it can be observed that the meranti wood sample had an average deflection of 0.013mm when a load 50N was applied while the average deflection for 450N was 0.085mm. in table it is observed the average deflection in the redwood sample when 50N, 150N, 250N, 350 and 450N were 0.01mm, 0.027mm, 0.043mm, 0.06mm and 0.07mm respectively. For pine wood sample the deflection recorded when 50N, 150N, 250N, 350 and 450N loads were applied was 0.1mm, 0.022mm, 0.034mm, 0.045mm and 0.055mm respectively as can observed in table 3. From table 4 it is observed that the deflection caused by a force of 50N in the ash wood was 0.006mm while for a load of 450N the deflection was 0.047mm. Table 1. Meranti test results Length between supports (L) = 285 (mm) Specimen dimensions 30mm x 5 mm Specimens Meranti Load Deflection (mm) 1 2 3 Average 50 0.01 0.014 0.014 0.013 150 0.028 0.032 0.033 0.031 250 0.046 0.05 0.051 0.049 350 0.064 0.068 0.069 0.067 450 0.083 0.086 0.087 0.085 700 0.16 950 Fail Failure load(N) 800 Table 2 Redwood test results Length between supports (L) = 285 (mm) Specimen dimensions 30mm x 5 mm Specimen Redwood Load Deflection (mm) 50 0.008 0.011 0.011 0.01 150 0.026 0.027 0.028 0.027 250 0.042 0.044 0.044 0.043 350 0.059 0.06 0.061 0.06 450 0.076 0.077 0.077 0.077 700 0.134 950 0.28 Fail Failure load(N) 1100 Table 3 Pine test results Length between supports (L) = 285 (mm) Specimen dimensions 30mm x 5 mm Specimen Pine Load Deflection (mm) 1 2 3 Average 50 0.008 0.011 0.011 0.01 150 0.021 0.023 0.022 0.022 250 0.033 0.034 0.034 0.034 350 0.044 0.045 0.045 0.045 450 0.055 0.055 0.055 0.055 700 0.084 950 0.0113 1200 0.147 1450 0.193 1700 0.28 1950 Fail 2200 Failure load(N) 1800 Table 4 Ash test results Length between supports (L) = 285 (mm) Specimen dimensions 30mm x 5 mm Specimen Ash Load Deflection(mm) 1 2 3 Average 50 0.003 0.008 0.008 0.006 150 0.015 0.019 0.019 0.018 250 0.027 0.029 0.03 0.029 350 0.036 0.038 0.038 0.037 450 0.046 0.047 0.047 0.047 700 0.07 950 0.092 1200 0.111 1450 0.133 1700 0.157 1950 0.195 2200 0.252 2450 0.35 Fail Failure load (N) 2650 1.2.2 Deflection load plot From figure 1 it can be seen that the timber with the highest deflection was ash with the maximum deflection being 0.35mm. There was lower values for the other timber types with maximum deflection of 0.28mm in both pine and redwood while merante had a value of 0.16mm. Another observation that can be made from the figure is that ash is the most stiff timber even though its failure occurred with the highest deflection. On the other hand redwood and meranti had almost the same stiffness as their graphs are almost coinciding even though the later meranti failed at a much lower load. Comparison of the redwood and pine graphs it can be seen that even though the two specimens failed after achieving the same deflection of 0.28 the later is stiffer than the former. Figure 1: Deflection load line graphs 1.2.3Failure load plots From figure 2 it is clear that meranti was the weakest specimen as its failure occurred at the lowest load of 800N. The largest load of 2650 was sustained by the ash specimen. When pine and redwood were compared in terms of failure load the later is seen to be stronger as it could with stand a load of up to 1800N compared to 1100N the maximum which was the failure load of former even though the two types of timber failed at the same deflection. Figure 2: Failure load bar graphs Figure 3: Deflection load graph for elastic region 1.3Discussion From the test result it had been observed that ash is the stronger of the two specimens as it failed at the highest load of 2650. It is also observed that ash was the stiffest specimen. This can be very important aspect in engineering work where structural components are supposed to sustain high loads with little deflection. This may be applicable where a beam is required to span a certain length without using any column to support it like in halls where column may not be desired as they may be regarded as barriers. It is also important to note that the area, shape and the orientation with respect to the applied force also play a major role in determining the deflection and the maximum load that can be sustained. 1.4 Conclusion From the experiment it was observed that hardwoods were stronger than soft woods as they could withstand higher loads. Hardwoods were observed to be stiffer and these make them desirable for use in beams with long spans. Therefore the null hypothesis that there is no difference between hardwoods and softwoods is not true. References BS 4978 (1988). Visual Strength Grading of Softwood. London. The Encyclopedia of Wood. Keith F. et al (1999).Wood Engineering and Construction Handbook, New York, McGran-Hill, Inc. LST EN 518 (2000) Structural Timber Grading – Requirements for Visual Strength Grading Standards. The Encyclopedia of Wood(1989) . New York, Sterling Publishing Co., Inc. Calculations 1. Calculation of E The dimensions of the four specimens are b= 50mm d= 300 From I = The 2nd moment of area for the four specimens = 11250mm4 E for meranti Taking the load of 150N where the average deflection = 0.031mm Using equation (1) and Substituting I = 11250mm4 P = 150N δm = 0.031 and L = 285mm E = = 207429N/mm2 E for redwood Taking the load of 350N where the average deflection = 0.06mm Using equation (1) and Substituting I = 11250mm4 P = 350N δm = 0.06mm and L = 285mm E = = 250067N/mm2 E for pine Taking the load of 250N where the average deflection = 0.034mm Using equation (1) and Substituting I = 11250mm4 P = 250N δm = 0.034mm and L = 285mm E = = 315211N/mm2 E = = 315211N/mm2 E for ash Taking the load of 350N where the average deflection = 0.037mm Using equation (1) and Substituting I = 11250mm4 P = 350N δm = 0.037mm and L = 285mm E = = 405515N/mm2 From the calculation ash wood is the stiffest with E= 405515N/mm2 The dimensions of the four specimens are b= 50mm d= 300 From I = The 2nd moment of area for the four specimens = 11250mm4 E for meranti Taking the load of 150N where the average deflection = 0.031mm Using equation (1) and Substituting I = 11250mm4 P = 150N δm = 0.031 and L = 285mm E = = 207429N/mm2 E for redwood Taking the load of 350N where the average deflection = 0.06mm Using equation (1) and Substituting I = 11250mm4 P = 350N δm = 0.06mm and L = 285mm E = = 250067N/mm2 E for pine Taking the load of 250N where the average deflection = 0.034mm Using equation (1) and Substituting I = 11250mm4 P = 250N δm = 0.034mm and L = 285mm E = = 315211N/mm2 E = = 315211N/mm2 E for ash Taking the load of 350N where the average deflection = 0.037mm Using equation (1) and Substituting I = 11250mm4 P = 350N δm = 0.037mm and L = 285mm E = = 405515N/mm2 From the calculation ash wood is the stiffest with E= 405515N/mm2 From the modulus of elasticity calculations which sample is stiffer? Hardwoods generally have a greater strength than softwoods, name one exception. Yellow pine. 2. What are the main applications for hardwoods and softwoods in construction? Hard woods are used in structural application like beams and column and where the timber is exposed hursh external environmental conditions. Softwoods find application in construction of elements that require less strength and are not exposed to harsh environmental conditions. 3. Define the term “coefficient of thermal expansion”. This can be defined as the increase in length of a unit length of a material when the temperature is increased by a unit value. 4. Describe the function of the following: Cell Type Function Vessels (hardwoods) They have dissolved end and play the conducting role Fibres (hardwoods) There are also the fibre cells which are long and thin and have tapered ends and provide additional support Tracheids (softwoods) The cells are vertically aligned in the trunk and they provide support allowing food to be conducted through Rays Their major function is to store food in addition of providing lateral support 5. Draw a diagram to illustrate where the forces of compression and tension acting on the timber sample during the static bending test. On which side did failure occur? Failure occur in the tensile side of specimen 6. Define the terms “Modulus of Elasticity” and “Modulus of Rupture”. Modulus of elasticity is the measure of elasticity of specimen in the elastic region while modulus of rapture is a measure of stress at failure load. 7. For the two samples tested calculate the “Modulus of Rupture”. (Show calculations). Modulus of Rupture (Nmm2) = 1.5 P x L / Width x depth2 (2) Where; P = Load at failure (N) L = Length between sample supports (mm) Modulus of rupture for redwood P = 1100 L = 285 Width x depth2 = 5x302 = 4500 1.5x1100x285/4500 = 104.5N/mm2 Modulus of rupture for ash P = 2650 L = 285 Width x depth2 = 5x302 = 4500 1.5x2650x285/4500 = 251.75 N/mm2 8. What is the minimum percentage of moisture that will allow fungi to attack timber? The minimum moisture content is 20% Read More