A Thesis Presented to

Transcription

1 NONDESTRUCTIVE AND DESTRUCTIVE TESTING OF COVERED TIMBER BRIDGE MEMBERS A Thesis Presented to The Faculty of the Russ College of Engineering and Technology Ohio University In Partial Fulfillment of the Requirements for the Degree Master of Science by Sitdhichai Choamnak March, 1997

2 ACKNOWLEDGEMENTS I am very much indebted for Dr. Eric Steinberg, my advisor, for his advice and kindness. I would also like to thank the members of my thesis committee: Dr. Glenn Hazen and Dr. Hajrudin Pasic for their suggestions. I would like to thank Matthew Johnson for his helpful on preparation some specimens and suggestions the use of non-destructive testing apparatus. Finally, a very special thank to my parents, my friends, and the staff members of the Department of Civil Engineering for making my stay enjoyable.

3 CONTENTS ACKNOWLEDGEMENTS... iv CONTENTS... v... LIST OF TABLES....vii... LIST OF FIGURES x... CHAPTER 1 INTRODUCTION 1... CHAPTER 2 BACKGROUND 3... CHAPTER 3 TEST PROCEDURE Specimen preparation Nondestructive testing Compression test Flexural test Destructive testing Compression test Flexural test Moisture content CHAPTER 4 EXPERIMENTAL TEST RESULTS Nondestructive testing results Destructive testing results Allowable properties discussion 111

4 CHAPTER 5 CONCLUSION AND RECOMMENDATION.....I17 LIST OF REFERENCES APPENDIX A Linear regression for stress-strain curve of a compression test specimen APPENDIX B Linear regression for stress-strain curve of a flexural test specimen.....i24 APPENDIX C Nondestructive testing results for a compression test specimen......i26 APPENDIX D Nondestructive testing results for a flexural test specimen....i29 vi

5 LIST OF TABLES Table 2-1 Moisture content constants for Eq Table 2-2 Reduction factors for converting test results to allowable properties... 8 Table 4-1 Nondestructive testing result of flexural test specimens #3 and # Table 4-2 Nondestructive testing result of specimens # Table 4-3 Nondestructive testing result of specimens # Table 4-4 Nondestructive testing result of specimens # Table 4-5 Nondestructive testing result of specimens # Table 4-6 Nondestructive testing result of specimens # Table 4-7 Nondestructive testing result of specimens # Table 4-8 Nondestructive testing result of specimens # Table 4-9 Nondestructive testing result of specimens # Table 4-10 Destructive and nondestructive testing results of compression test specimen # Table Destructive and nondestructive testing results of compression test specimen # Table 4-12 Destructive and nondestructive testing results of... compression test specimen #3 41 Table Destructive and nondestructive testing results of... compression test specimen #4 42

6 viii Table 4-14 Destructive and nondestructive testing results of compression test specimen # Table 4-15 Destructive and nondestructive testing results of compression test specimen # Table 4-16 Destructive and nondestructive testing results of compression test specimen # Table 4-17 Destructive and nondestructive testing results of compression test specimen # Table 4-18 Destructive and nondestructive testing results of compression test specimen # Table 4-19 Destructive and nondestructive testing results of compression test specimen # Table 4-20 Destructive and nondestructive testing results of compression test specimen # Table Destructive and nondestructive testing results of compression test specimen # Table 4-22 Destructive and nondestructive testing results of flexural test specimens # Table 4-23 Destructive and nondestructive testing results of flexural test specimens # Table 4-24 Destructive and nondestructive testing results of

7 flexural test specimens # ix Table 4-25 Destructive and nondestructive testing results of flexural test specimens # Table 4-26 Destructive and nondestructive testing results of flexural test specimens # Table 4-27 Destructive and nondestructive testing results of flexural test specimens # Table 4-28 Destructive and nondestructive testing results of flexural test specimens # Table 4-29 Destructive and nondestructive testing results of flexural test specimens #lo Table 4-30 Destructive and nondestructive testing results of flexural test specimens # Table Destructive and nondestructive testing results of flexural test specimens # Table 4-32 Table 4-33 Base design values for visually graded dimension lumber Statistics of allowable 10% moisture content for compression test specimens Table 4-34 Statistics of allowable 10% moisture content for flexural test specimens

8 LIST OF FIGURES Figure 2-1 The Radial. Tangential. and Longitudinal axes of wood with respect to growth rings and grain direction... 3 Figure 3-1 The Towne Lattice truss covered timber bridge Figure 3-2 A member taken from the bridge Figure 3-3 Some defects on a member 11 Figure 3-4 The nondestructive testing apparatus Figure 3-5 Transducers arrangements Figure 3-6 A divided compression test specimen and a divided flexural test specimen Figure 3-7 Width and Depth of a specimen Figure 3-8 The nondestructive testing of a compression test specimen Figure 3-9 The nondestructive testing of a flexural test specimen Figure 3-10 Destructive compression test Figure 3-11 Destructive flexural test Figure 4-1 Relation of compressive strength and dynamic modulus for compression test specimens #5 (Yellow poplar) Figure 4-2 Relation of compressive strength and dynamic modulus for compression test specimens #6 (Eastern hemlock)... 65

9 xl Figure 4-3 Relation of compressive strength and dynamic modulus for compression test specimens #7 (Eastern hemlock) Figure 4-4 Relation of compressive strength and dynamic modulus for compression test specimens #8 (Eastern hemlock) Figure 4-5 Relation of compressive strength and dynamic modulus for compression test specimens #9 (Eastern hemlock) Figure 4-6 Relation of compressive strength and dynamic modulus for compression test specimens # 10 (Eastern hemlock) Figure 4-7 Relation of compressive strength and dynamic modulus for compression test specimens # 1 1 (Eastern hemlock) Figure 4-8 Relation of compressive strength and dynamic modulus for compression test specimens #12 (Eastern hemlock) Figure 4-9 Relation of bending strength and dynamic modulus for flexural test specimens #3 (Yellow poplar) Figure 4-10 Relation of bending strength and dynamic modulus for flexural test specimens #4 (Yellow poplar) Figure Relation of bending strength and dynamic modulus for flexural test specimens #5 (Yellow poplar) Figure 4-12 Relation of bending strength and dynamic modulus for flexural test specimens #6 (Eastern hemlock)

10 xii Figure 4-13 Relation of bending strength and dynamic modulus for flexural test specimens #7 (Eastern hemlock) Figure 4-14 Relation of bending strength and dynamic modulus for flexural test specimens #9 (Eastern hemlock) Figure Relation of bending strength and dynamic modulus for flexural test specimens # 10 (Eastern hemlock) Figure 4-16 Relation of bending strength and dynamic modulus for flexural test specimens # 1 1 (Eastern hemlock) Figure Relation of bending strength and dynamic modulus for flexural test specimens # 12 (Eastern hemlock) Figure Relation of static compressive modulus and dynamic modulus for compression test specimens #5 (Yellow poplar) Figure 4-19 Relation of static compressive modulus and dynamic modulus for compression test specimens #6 (Eastern hemlock) Figure 4-20 Relation of static compressive modulus and dynamic modulus for compression test specimens #7 (Eastern hemlock) Figure Relation of static compressive modulus and dynamic modulus for compression test specimens #8 (Eastern hemlock) Figure 4-22 Relation of static compressive modulus and dynamic modulus for compression test specimens #9 (Eastern hemlock) Figure 4-23 Relation of static compressive modulus and dynamic modulus for

11 compression test specimens #10 (Eastern hemlock) Figure 4-24 Relation of static compressive modulus and dynamic modulus for compression test specimens # 1 1 (Eastern hemlock) Figure 4-25 Relation of static compressive modulus and dynamic modulus for compression test specimens # 12 (Eastern hemlock) Figure 4-26 Relation of static bending modulus and dynamic modulus for flexural test specimens #3 (Yellow poplar) Figure 4-27 Relation of static bending modulus and dynamic modulus for flexural test specimens #4 (Yellow poplar) Figure 4-28 Relation of static bending modulus and dynamic modulus for flexural test specimens #5 (Yellow poplar) Figure 4-29 Relation of static bending modulus and dynamic modulus for flexural test specimens #6 (Eastern hemlock) Figure 4-30 Relation of static bending modulus and dynamic modulus for flexural test specimens #7 (Eastern hemlock) Figure Relation of static bending modulus and dynamic modulus for flexural test specimens #9 (Eastern hemlock) Figure 4-32 Relation of static bending modulus and dynamic modulus for flexural test specimens # 10 (Eastern hemlock) Figure 4-33 Relation of static bending modulus and dynamic modulus for flexural test specimens #11 (Eastern hemlock) xiii

12 xiv Figure 4-34 Relation of static bending modulus and dynamic modulus for flexural test specimens # 12 (Eastern hemlock) Figure 4-35 Relation of bending strength and dynamic modulus for Yellow poplar Figure 4-36 Relation of static bending modulus and dynamic modulus for Yellow poplar Figure 4-37 Relation of compressive strength and dynamic modulus for Eastern hemlock.....lo0 Figure 4-38 Relation of static compressive modulus and dynamic modulus for Eastern hemlock Figure 4-39 Relation of bending strength and dynamic modulus for Eastern hemlock.....lo2 Figure 4-40 Relation of static bending modulus and dynamic modulus for Eastern hemlock......lo3 Figure Statistic of bending strength and dynamic modulus for Yellow poplar.....lo5 Figure 4-42 Statistic of static bending modulus and dynamic modulus for Yellow poplar Figure 4-43 Statistic of compressive strength and dynamic modulus for Eastern hemlock Figure 4-44 Statistic of static compressive modulus and dynamic modulus for Eastern hemlock

13 XV Figure 4-45 Statistic of bending strength and dynamic modulus for Eastern hemlock Figure 4-46 Statistic of static bending modulus and dynamic modulus for... Eastern hemlock...i 10 Figure 4-47 Crushing at supports and load point when loading......i12

14 CHAPTER 1 INTRODUCTION Wood has been used as a construction material by man for many centuries before the use of steel and concrete. One of the important applications of wood in structures are bridges. Timber bridges have played a significant role to allow mankind to travel, to explore new lands, and to open transportation ways of an increasing society. Although, steel and concrete is more popular than wood in most structural applications, wood is still a viable constructional material because of its availability, its flexibility in use, and its economical price. In Ohio, only 135 covered timber bridges of the original 3850 exist today (Wood, 1993). Unfortunately, most of bridges have deteriorated after being in service for many years. Most of them have been taken out of service and replaced by concrete or steel bridges. Many of them have reduced load limits or have been rehabilitated with structural steel. Several of the remaining bridges are classified as historic. From an economic consideration, construction of a new bridge can cost a lot more than rehabilitation of the historic bridges. In order to determine rehabilitation procedures of the bridges and to avoid further degradation of these historic structures, the material characteristics of the bridges have to be studied. In this research, the material properties of some members removed from a covered timber bridge were evaluated. The stress wave technique, the most widely used

15 of nondestructive testing methods for wood, was used to determine the dynamic modulus of elasticity of each specimen removed fiom the members. To accomplish accuracy and correlation of the nondestructive testing method, the specimens were also destructively tested to obtain their strength and static modulus of elasticity. This work lays the groundwork for future field studies using the nondestructive technique to evaluate timber properties in situ. Once the properties of a timber bridge are determined, accurate analytical procedures can be employed to determine load ratings and rehabilitation methods, if necessary, can be evaluated. 2

16 CHAPTER 2 BACKGROUND Wood is a natural material and its properties are subjected to many influences such as moisture content, species, and density. In the engineering field, wood can be described as an orthotropic material. This means the mechanical properties of it are unique and independent in the directions of three perpendicular or principle axes. These axes are radial, tangential, and longitudinal (Figure 2-1). The radial axis is perpendicular to the grain in the radial direction of the growth rings, the tangential axis is perpendicular to the grain and tangent to the growth rings, and the longitudinal axis is parallel to the grain. / '. Grain Direction, axis Lonqitudinal axis Growth ring Figure 2-1 The Radial, Tangential, and Longitudinal axes of wood with respect to growth rings and grain direction

17 The mechanical properties of wood can be classified into three groups: (1) elastic properties, (2) strength properties, and (3) vibration properties. The elastic properties of wood can be described by modulus of elasticity, modulus of rigidity, and Poisson's ratio. The strength properties normally include compression parallel to the grain, compression perpendicular to the grain, shear strength parallel to the grain, bending strength or modulus of rupture, tensile strength perpendicular to the grain, tensile strength parallel to the grain, impact bending, toughness, and hardness. The vibration properties of wood primarily are the speed of sound and the internal friction. To evaluate the mechanical properties of wood, the institutions such as the American Society for Testing and Materials, the U.S. Forest Service, and other similar organizations have developed standardized test methods over the years. Most of these methods are performed by loading test specimens to their maximum strength. However, many researchers have examined methods to evaluate the mechanical properties of wood and wood members in structures without impairing the timbers' usefulness. These methods are known as nondestructive testing (NDT) procedures. These methods are primarily used to determine the existing state or quality of a material to be accepted or rejected from an industrial view point. For wood materials, the nondestructive testing method is used to evaluate mechanical properties and to detect the presence of discontinuities, voids, or decay of wood. Several techniques of the NDT method have been developed. These techniques include static bending, transverse vibration (Pellerin, 1965), stress wave, x-ray, and withdrawal techniques. These techniques have been used under laboratory conditions and in-place assessment of timber members. 4

18 5 Stress wave techniques are widely used to determine the material properties. Papers have been published on the use of the stress wave techniques for in-place evaluation of wood members. The projects included: the assessment of a timber roof in an 18h century mansion using ultrasonic impact (Lee, 1965), a section of Washington State University's football stadium, a school gymnasium (Hoyle and Pellerin, 1978), timber bridges (Hoyle and Rutherford, 1987), a test stand for aircraft (Neal, Browne, and Kuchar, 1985), a barn structure (Lanius and others, 1981), water cooling towers (Stewart and others, 1986), and wood utility poles (Anthony and Bodig, 1989). One viable stress wave technique utilizes ultrasonic waves. The ultrasonic wave can be used to evaluate the material property because the velocity of the ultrasonic wave traveling in a solid material depends on the density and elastic properties of the material. This technique is possible because ultrasonic waves are mechanical vibrations which propagate in any continuous material and travel with little loss. Theoretically, the velocity of an ultrasonic wave propagating in a structural material varies directly with the square root of modulus of elasticity and inversely with the square root of the density of the material. The speed of ultrasonic wave traveling in the structural material can be calculated from: where c = Velocity of ultrasonic wave in material

19 p = Density of the material E = The modulus of elasticity if the dimensions of the specimen are very large compared to the wave length, the velocity can be obtained from: where v = Poisson's ratio of the specimen Conversely, properties of the specimen are observable from the speed of ultrasonic wave transmission. When a pulse travels through a known distance of a specimen within a known time period, the velocity can be determined from: where c = Ultrasonic wave velocity s = Distance that ultrasonic wave travels through specimen t = Transit time The dynamic modulus of elasticity, Ed, can therefore be calculated by:

20 However, if Poisson's ratio affects the velocity of the pulse, the dynamic modulus of elasticity is calculated from: Although the stress wave techniques can assess the performance of wood, it was pointed out in the study by Lanius and others (1981) that NDT techniques need to be used on timber members in service, and those members should then be tested destructively to determine the accuracy of the NDT method employed. According to ASTM D (Standard practice, 1993), it is suggested that properties of specimens should be adjusted to a single moisture content, because the moisture affects the elastic and strength properties of timber. However, adjustments for more than five percentage points of moisture content are to be avoided due to decreasing accuracy of the suggested equation. The properties can be adjusted to a single moisture content by: where P1 = Property measured at moisture content MI

21 P2 = Property adjusted to moisture content ha MI, M2 = Moisture contents in percent a, p = Moisture content constants (Table 2-1) Table 2-1 Moisture content constants for Eq. 2-6 Property Modulus of elasticity (Es) Bending strength (Fb) Compressive strength parallel (Fc) a P Property values of timber determined from experimental testing are reduced to account for the variability of the properties. Therefore, the design properties or allowable properties are usually determined by using adjustment factors taken from Practice D-245. The allowable properties are based on the concept of the lower 5% exclusion limit. That means the allowable value is the value that 95% of the measured values exceed it. The factors are given in Table 2-2. Table 2-2 Reduction factors for converting test result to allowable properties

22 CHAPTER 3 TEST PROCEDURE The samples tested were part of the upper chord of a Towne Lattice truss covered timber bridge (Figure 3-1) located in Ashtabula County, Ohio. These bridge members were at least 95 years-old as best as records could tell. The bridge members were approximately 3" by 10" by 7' (Figure 3-2), and the species of the members were Yellow Poplar and Eastern Hemlock. The procedure of this test program began with preparing specimens by cutting the members to standard sizes for compression and flexural testing. The nondestructive testing was performed first, then the destructive tests were performed. After finishing both tests, the moisture content of the specimens tested were found by standard procedures. 3.1 SPECIMEN PREPARATION Flexural and compression test specimens were cut from the members. The members taken from the truss had some cracks, decay, termite infestation and peg holes (Figure 3-3) so the number of both specimens depended on the condition of each member. According to ASTM D-198 (Standard Methods, 1993), standard compression test specimens are to be 2" by 2" and 8" in length along the grain, and each of the flexural test specimens are to be 2" by 2" by 30" along the grain.

23 Figure 3-1 The Towne Lattice truss covered timber bridge - - Figure 3-2 A member taken from the bridge

24 Figure 3-3 Some defects on a member Each specimen was defined by a number. For example, specimen # 3-1 was the compression test specimen number 1 fiom member number 3, specimen # 3-bl was the flexural test specimen number 1 from member number 3. It is important to keep in mind that special care must be taken in preparing both compression and flexural test specimens. Both specimens were carefully cut to ensure that the end grain surfaces would be parallel to each other. Moreover, the ends of the compression test specimens were cut to be perpendicular to the longitudinal axis to prevent misalignment while testing. The specimens were stored in the laboratory, before testing, to obtain a consistent moisture content. 3.2 NONDESTRUCTIVE TEST The tests were performed to determine the dynamic modulus of elasticity of the specimens by using the nondestructive test apparatus shown in Figure 3-4.

25 Two transducers Two transducer leads A hand held terminal Portable computer Figure 3-4 The NDT apparatus

26 13 The apparatus consisted of a V-Meter MklI, two transducers, two transducer leads, a hand held terminal, and a portable computer. The Figure 3-5 shows how the transducers can be arranged to observe the dynamic modulus of elasticity of the specimens. There are three ways of arrangement which are direct, semi-direct, and indirect or surface transmission. The direct transmission is the most satisfactory because pulses from the transmitter are propagated mainly in the direction normal to the transducer face. Therefore, the direct transmission was used in all tests. The V-Meter MkII generates an ultrasonic pulse in the transmitting transducer which is passed into a test specimen. The receiving transducer receives the pulse, and the V-Meter MkII measures the time that the pulse takes to pass through the specimen. The system uses this information to calculate the velocity and the modulus of elasticity. Water pump grease is applied between the transducers and the surface of the specimens to improve contact and minimize attenuation while transferring and receiving ultrasonic waves between the transducers and specimens. The density of the specimens is required to use in Eq. 2-4 for the nondestructive testing. After measuring the size and weight of the specimens, the densities were obtained from dividing the weight, in pounds, of the specimens by the volume, in cubic feet, of the specimens. The gain and pulse switch on the top panel of the meter were set to low positions to decrease the signal strength and pulse level for short distances. The data required by

27 the meter consist of Initialization items and Menu items. The NDT began with input of the Initialization items. 14 Direct Transmission 'i Transducer Semi Direct Transmission Indirect or Surface Transmission Figure 3-5 Transducers Arrangements

28 When the meter was turned on, the display showed " Contact transducers, then the Enter." The transducers were held together with grease applied on the contact surfaces, and the enter button was pressed to re-initialize (zero set) the system. This set the computer in the meter to read and save the time that ultrasonic wave passes through the transducers, grease, and cables so that it can be subtracted from readings which included a specimen. The density of the specimen was then entered to be used to calculate the modulus of elasticity. The moisture correction was set at 1 (velocity is multiplied by this factor), and a pulse rate of 10 pulses per second (trace plotting and display are updated for every fifth pulse) were used through the testing. After the Initialization items had been input, the Menu items were set in the main menu. The wave type menu was set to P type (compression wave). The S type, which is a transverse wave, was not used in the test program. The data were displayed and stored in English units. The " Calculate Vel " was selected and the distance of the specimen was required to be input as a constant in the meter so the system could calculate the velocity of the ultrasonic wave while it passed through the specimen. When the meter was run, the wave travel time was measured and the computer in the meter calculated the velocity and then the modulus of elasticity. All of the data input to the meter and the modulus of elasticity calculated by the meter were transferred via a RS 232 link to a computer to save the results for further analysis.

29 3.2.1 Compression Test Each compression test specimen, which were 2" by 2" by 8", were divided along the longitudinal axis to two sections. These sections are referred to as section one and section two (Figure 3-6). The side that is approximately parallel to the growth rings in cross section was defined as the width. Conversely, the perpendicular side was defined as the depth (Figure 3-7). Appendix C shows an example of result for a compression test specimen. Figure 3-6 A divided compression test specimen and a divided flexural test specimen

30 Depth m / +Width - Figure 3-7 Width and Depth of a specimen In Table C-1, "6-5a" refers to longitudinal direction of specimen 5 of member 6. "w" and "d" refer to width and depth, respectively. A number after "w" or "d" refers to section of specimen. The nondestructive testing was performed across the width and depth of each section and down the longitudinal axis of each specimen to obtain the dynamic modulus of elasticity(figure 3-8) Flexural Test Specimens 2" by 2" and 30" were used for flexural testing. Each flexural test specimen was divided along the longitudinal axis into ten sections, which were numbered one to ten. Each section was 3" in length (Figure 3-6). The width and the depth were defined in the same manner as the compression test specimens.

31 NDT across the Width and the Depth of a specimen NDT down the longitudinal of a specimen Figure 3-8 The NDT of a compression test specimen

32 The NDT across the Width and the Depth of a specimen The NDT down the longitudinal of a specimen Figure 3-9 The NDT of a flexural test specimen

33 The nondestructive test was performed across the width and depth of each section and down the longitudinal axis of each specimen (Figure 3-9). Due to the sensitivity of the meter, ten readings of modulus of elasticity were taken in each direction of both the compression and flexural test specimens. Appendix D shows an example of nondestructive test result for a flexural test specimen DESTRUCTIVETEST The destructive test was used for determining strength and static modulus of elasticity of the compression and flexural specimens. The flexural and compression test specimens were separately tested to develop a relationship with the dynamic modulus of elasticity Compression Test The compression test was performed on 2" by 2" by 8" specimens to determine the compression strength. The actual sizes of the specimens were measured by a caliper, and a digital scale, with an accuracy of gram, was used to obtain the weights of the specimens before testing to use in the calculation of the strength properties. The specimens were placed in the compression machine and subjected to axial compression loads applied at their ends. Figure 3-10 shows a compression specimen in

34 2 1 the machine. The loads were applied through a plate acting on the full cross sectional area of the specimens and parallel to the grain of the specimens. Figure 3-10 Compression test The compression load, in pounds, was read and printed simultaneously every 0.01 inch of deformation, and the specimens were loaded at the rate of approximately 2,000 lblmin until failure occurred. The stresses were calculated by dividing the loads, in pounds, by the cross sectional area, in square inches, perpendicular to the load. The strains were obtained from dividing the shortening of the specimens by the original length. The modulus of elasticity was obtained by plotting linear lines to the initial portion of the stress-strain curves (Appendix A).

35 3.3.2 Flexural Test The tested specimens were approximately 30" in length along the grain, and 2" square in section. The actual size and weight were measured before testing. The specimens were set up in the machine (Figure 3-11) and tested with a span of 28" with the support ends free to move. The load was applied at the center of the span and was recorded simultaneously every 0.01 inch of deflection at mid span. The loading rate of approximately 2000 lblmin was applied continuously to the specimens until they failed. Figure Flexural test The flexural test was a measure of the strength of the material as a beam. When the loads were applied, the upper half of the specimens were in compression and the lower half of them were in tension. Midway between the upper and lower half of them were neutral axis where tensile and compression stresses were zero.

36 The data obtained from the test were used to calculate stresses by: where o = Stress in pounds per square inch, P = The load in pounds, h = Thickness or depth of the specimens in inches, b = Breadth or width of the specimens in inches, and L = Span between supports in inches Strains were calculated by: where E = Strain in inch per inch d = Deflection in inches The stresses and the strains obtained from the calculations of each specimen were plotted and are shown in Appendix B. The modulus of elasticity of each specimen was determined from the slope of the linear regression for the stress-strain data and is also shown in the Appendix B.

37 3.4 MOISTURE CONTENT Timber will absorb or release water, which affects the properties of the timber. Therefore, it's necessary to know the exact moisture content of the specimens. Moisture content is typically expressed as a percentage of the oven-dry weight. The oven-dry weight is obtained by drying the specimens in an oven at OC for a period until insignificant change in weight is observed. The moisture content is obtained by: MC = (Initial weight of specimen - dry weight of specimen) x 100 Dry weight of specimen (3-3) where MC = moisture contain expressed in percent In this test, the specimens were dried in an oven for approximately 24 hours after the NDT and destructive testing to obtained the moisture content. The initial weight of the specimen was theoretically the weight of the specimen after it was cut from the members. It was only used to calculated the density of the specimen. The actual initial weight of the specimens used for calculating the moisture content were measured after the NDT and destructive test had been done. Grease, that was applied during the NDT test, was wiped off as much as possible from the specimens before the weight of the specimens were measured. The initial weight of the specimen included the weight of grease on it. However, the weight of a grease sample did not change after drying it in an

38 oven overnight. Consequently, the weight of the specimens changed only because of a change in the water content of the specimens. The dry weight of the specimens were measured immediately after the specimens were taken out of the oven to minimize the chance of the specimens absorbing moisture from the surrounding environment. 25

39 CHAPTER 4 EXPERIMENTAL TEST RESULTS 4.1 NONDESTRUCTIVE TESTING RESULTS The nondestructive testing results are shown in Table 4-1 to Table 4-9. Unfortunately, the nondestructive testing equipment used in this test program was not working properly when it was used on the compression specimens #1 through #4. Therefore, there are no nondestructive results for the compression specimens #I through #4. However, the problem was discovered before the flexural specimens #3 and #4 were tested so Table 4-1 shows the nondestructive testing results of the flexural specimen #3, and the nondestructive testing results of the flexural specimen #4 are also shown in Table 4-1. Each table contains the species of the specimens (EH is Eastern Hemlock and YP is Yellow Poplar), density, moisture content, dimension, and mean of dynamic modulus of elasticity (Ed) along each direction of the specimens. Each value of Ed along the width and depth of the compression test specimen were the average of 10 readings of Ed from section 1 and 10 readings of Ed from section 2, but each value of Ed along width and depth of the flexural test specimens was obtained from the average of 10 readings of sections 1 through 10. The Ed along the grain of the compression and flexural test specimens were the mean of 10 readings along the grain of each specimen. Ed of each

40 27 direction for compression and flexural test specimen are shown in Appendix C and Appendix D, respectively. The meter can not read dynamic modulus of elasticity if there is a void in the specimen between transducers. "NO DATA" shows that there were some cracks in the specimen so the meter could not produce a reading. Most of Ed along width were less than Ed along depth and Ed along the grain were the highest values. However, some specimens had cracks or knots so that Ed along the width was higher than Ed along depth or Ed along the grain was lower than Ed along width and depth, or Ed was higher than usual (higher than 2 million psi). Ed along the grain were the most consistent and reasonable (more than 10E6 psi), and they were used to develop relationships with other properties of the specimens.

41 Table 4-1 The Nondestructive testing result of flexural test specimens # 3 and # 4 Species Specimen Density (PCF) MC?/.> Along Width Distance (in) Ed (10E6psi) Along Depth Distance (in) Ed (10E6psi) Along Grains Distance (in) Ed (10E6psi) YP 3-bl 3-b2 3-b3 3-b NO DATA b 1 4-b2 4-b

42

43

44 .= m ~ m o o r n ~ o m a m lll m m c n w - m v m o m o "?=??"?""9999 "a, 4-,,--,,,,, a lll w 0 m m 0 0 O P O O m m O m ~ ~ m a Q P m N ' 0 a - m - m m m m M $ s 283 lll w E o m o o o o o o o o o m ~ m o m m m m w o o N N N m N m N N - r n N C- ab+rnmcnmmbmce m b P J W z z m - "99999"? Y M & 8 agg. + n z& "Q ~0 ~ m m ~ m m m oo ~ w NNNNrnNNN-N m ~ m 00 """"=???"9=?" zzzzzz2zzzz N~NNNNNNNNN.+ P m -C;'3=?"?"7 +mm* &.Pbp,.bT+T+ PPPb ill k V)

45 Table 4-5 The Nondestructive testing result of specimens # 8 Species Specimen Density (PCF) MC (%> Along Width Along Depth Distance (in) Ed (10E6 psi) Distance (in) Ed (10E6 psi) Along Grains Distance Ed (in) (10E6 psi) EH bl 8-b OOO OOO NO DATA NO DATA

46

47

48 Table 4-8 The Nondestructive testing result of specimens # 11 Species Specimen Density (PCF) MC ('?A> Along Width Distance Ed (in) (10E6 psi) Along Depth Distance Ed (in) (10E6 psi) Along Grains Distance Ed (in) (I 0E6 psi) EH bl 11-b2 11-b

49 Table 4-9 The Nondestructive testing result of specimens # 12 Species Specimen Density (PCF) MC ('/.I Along Distance (in) Width Ed (1 0E6 psi) Along Distance (in) Depth Ed (1 0E6 psi) Along Distance (in) Grains Ed (1 0E6 psi) EH bl 12-b2 12-b3 12-b SO

50 4.2 DESTRUCTIVE TESTING RESULTS The properties determined through the destructive testing of the specimens were adjusted to a moisture content of ten percent by equation 2-6. This moisture content was chosen because the specimens were typically within five percentage points of a ten percent moisture content. Reduction factors, taken from ASTM D-245, were used to determine the to expected allowable properties of the specimens at a 10% moisture content. The allowable values of the properties are the design values to be used for timber design. The factors for the moisture content equation and the reduction factors to determine allowable values are listed in Table 2-1 and Table 2-2, respectively. The destructive testing results of the compression specimens are shown in Table 4-10 to Table The tables contain species, density, original moisture content, compressive strength parallel to the grain (Fc), static modulus of elasticity (Es), dynamic modulus of elasticity (Ed), adjusted properties values at 10% moisture content, allowable properties values at 10% moisture content, and statistics of each value. The values of Fc were the maximum values of the stresses obtained from stress-strain relationships in Appendix A and the values of Es were slope of the linear regressions for stress-strain relationships in Appendix A also. The allowable 10% moisture content for the compressive strength, Fc, of the compression test specimens of Yellow poplar are high (2,000-3,000 psi) compared to the highest design allowable values (900 psi) in Table The allowable values of Fc of Eastern hemlock are also high (2,000-3,000 psi but the highest tabulated allowable

51 3 8 value is 1200 psi) compared to the highest design allowable values in Table However, the means of static modulus of elasticity, Es, of Yellow poplar and Eastern hemlock are low compared to the allowable values. However, the means of the dynamic modulus of elasticity, Ed, of Yellow poplar and Eastern hemlock are reasonable.

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55 @ 10% MC Es (1 0E6 psi) Table 4-13 Destructive and nondestructive testing results of compression test specimens # 4 Species Specimen Density (PCF) MC (%) Fc (psi) Es (10E6 psi) Ed (10E6 psi) Corrected Values Fc (psi) for 10% MC Es (1 0E6 psi) Allowable values Fc (psi) YP , ,741.OOO 5, , , , , , , , , , , ,031.OOO 6, , ,23 1.OOO 6, , NODATA NO DATA NODATA NODATA NODATA NODATA NODATA NO DATA NO DATA NODATA NODATA NODATA NODATA NO DATA NODATA NODATA NO DATA NODATA NO DATA 5, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Avg. Std. Dev. COV , NODATA NO DATA NO DATA 5, ,

56

57 @ 10% MC Es (10E6 psi) Table 4-15 Destructive and nondestructive testing results of compression test specimens # 6 Species Specimen Density (PCF) MC (%) Fc (psi) Es (1 0E6 psi) Ed (1 0E6 psi) Corrected Values Fc (psi) for 10% MC Es (1 0E6 psi) Allowable values Fc (psi) EH , , , , , , , , , , , , , NO DATA , , , , , , , , , , , , , , , , , , , , , , , , Avg. Std. Dev. COV , , , , ,

58

59 @ 10% MC Es (1 0E6 psi) Table 4-17 Destructive and nondestructive testing results of compression test specimens # 8 Species Specimen Density (PCF) MC (%) Fc (psi) Es (1 0E6 psi) Ed (1 0E6 psi) Corrected Values for 10% MC Allowable values Fc (psi) Es (10E6 psi) Fc (psi) EH , , , , , , OOO , , , , , , , , , , , , Avg. Std. Dev. COV , , ,

60

61

62

63 hj 10% MC ES (1 0E6 psi) Table 4-21 Destructive and nondestructive testing results of compression test specimens # 12 Species Specimen Density (PCF) MC (%) Fc (psi) Es (1 0E6 psi) Ed (1 0E6 psi) Corrected Values Fc (psi) for 10% MC Es (1 0E6 psi) Allowable values Fc (psi) EH , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Avg. Std. Dev. COV , , ,

64 5 1 Table 4-22 to Table 4-31 contain species, density, moisture content, bending strength (Fb), bending static modulus of elasticity (Es), dynamic modulus of elasticity (Ed), adjusted properties values at 10% of moisture content, allowable properties values at 10% of moisture content, and statistics of each value for the flexural specimens. The bending strength of the flexural test specimens of both species (4,000-5,000 psi) are very high compared to typical allowable values. The means of bending static and dynamic modulus of elasticity are reasonable for both species.

65

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73 Table 4-30 Destructive and nondestructive testing results of flexural test specimens # 11 Species Specimen Density (PCF) MC (%I Fb (psi) Es (1 0E6 psi) Ed (1 0E6 psi) Corrected Values for 10% MC Fb Es (psi) (10E6 psi) Allowable 10% MC Fb Es (psi) (10E6 psi) EH 11-bl 11-b2 11-b , ,361 SO , I , , , , , , Avg. Std. Dev. COV , , ,

74 Table 4-31 Destructive and nondestructive testing results of flexural test specimens # 12 Species Specimen Density (PCF) MC (%) Fb (psi) Es (10E6 psi) Ed (10E6 psi) Corrected Values for 10% MC Es (10E6 psi) Allowable 10% MC Fb (psi) Es (10E6 psi) Fb (psi) EH 12-bl 12-b2 12-b3 12-b , , , , , , , , , , , , Avg. Std. Dev. COV , , ,

75 6 2 The data used for plotting Figures 4-1 to 4-34 were obtained fiom Tables 4-10 to Each figure shows an equation of linear regression for the data. Figure 4-1 to Figure 4-8 show the relationship between compressive strength, Fc, and dynamic modulus, Ed, (along the axis parallel to the grain of the compression test specimens). The results of Ed for specimens 1, 2, 3, and 4 are not available as mentioned earlier. The bending strength was plotted versus the dynamic modulus, along the grain of the flexural test specimens, in Figure 4-9 to Figure To determine a relationship between the compressive static modulus and the dynamic modulus, the compressive static modulus were plotted versus dynamic modulus in Figure 4-18 to Figure The bending static modulus was also plotted versus the dynamic modulus in Figure 4-26 to Figure The relationships of the dynamic modulus with the strength properties show variability within a member. Most of them are promising except the relationships of compressive strength versus dynamic modulus for compressive test specimens # 7 (Figure 4-3) and # 11 (Figure 4-7) and the relationships of bending strength versus dynamic modulus for flexural test specimens # 3 (Figure 4-9), # 5 (Figure 4-1 I), and # 11 (Figure 4-16). These relationships were poor because there were cracks in some specimens of the members. The relationships between mechanical properties and the dynamic modulus of elasticity for each species are shown in Figure 4-35 to Figure Figure 4-35 is bending strength versus dynamic modulus for Yellow poplar. The equation of the linear regression for the relationship is Fb = Ed Figure 4-