FLEXURAL BEHAVIOR OF SPUN CONCRETE POLES REINFORCED WITH GLASS FIBER REINFORCED POLYMER (GFRP) SALLY G. PALMER

Transcription

1 FLEXURAL BEHAVIOR OF SPUN CONCRETE POLES REINFORCED WITH GLASS FIBER REINFORCED POLYMER (GFRP) by SALLY G. PALMER FOUAD H. FOUAD, COMMITTEE CHAIR ROBERT W. PETERS TALAT SALAMA A THESIS Submitted to the graduate faculty of The University of Alabama at Birmingham, in partial fulfillment of the requirements for the degree of Master of Science BIRMINGHAM, ALABAMA 2010

2 FLEXURAL BEHAVIOR OF SPUN CONCRETE POLES REINFORCED WITH GLASS FIBER REINFORCED POLYMER (GFRP) SALLY G. PALMER CIVIL ENGINEERING ABSTRACT Steel-reinforced structural concrete has been used in civil engineering practice for many years. A primary concern with steel-reinforced structural concrete is corrosion. In marine environments, corrosion becomes an important factor and may impact the longterm durability of the conventional steel-reinforced structure. Concrete poles are commonly placed in severe marine or industrial environments that are conducive of corrosion. Traditionally, these poles are reinforced with steel material, which poses the certainty of corrosion and deterioration. Recently, various alternatives to the use of steel reinforcement have been studied. Alternative non-metallic reinforcement will increase the lifespan of the product, reduce maintenance needs, and result in a product that is more versatile and sustainable. Glass fiber reinforced polymer (GFRP) reinforcement demonstrates most of the advantages of steel reinforcement with few of the drawbacks. It is non-corrosive, non-magnetic, non-conductive, lightweight, and durable. Also, its availability and cost comparison to other steel reinforcement alternatives, such as carbon fiber reinforced polymer (CFRP) reinforcement, give it the potential economical advantage in civil engineering applications. This research work experimentally and analytically studied the flexural behavior of GFRP reinforced spun concrete poles. Four test specimens were designed and manufactured for the experimental portion of the research. During the testing of each ii

3 pole, certain parameters were investigated: cracking and ultimate moment, deflection, crack width and spacing, and failure mode. The analytical portion of the study used equations found in the literature to calculate the theoretical cracking and ultimate moment capacities. The calculation of the cracking moment capacity was computed using the elastic theory. The ultimate moment capacity was predicted based on strain compatibility and the internal force equilibrium. The results and performance of these poles were compared to those of the traditional steel-reinforced prestressed spun concrete poles, and to those of the spun concrete poles reinforced with CFRP. The results were also compared to recommended practical serviceability considerations for concrete poles. Lastly, a cost comparison analysis was performed among the three reinforcing materials considered in this study. iii

4 ACKNOWLEDGEMENTS The author is greatly indebted to Dr. Fouad H. Fouad, Chair of the Civil, Construction, and Environmental Engineering Department at The University of Alabama at Birmingham, for his supervision, support, and enthusiasm throughout her graduate studies and research. The author is also indebted to Valmont-Newmark, Inc., for providing the financial support for labor, manufacturing, and acquisition of the GFRP material needed for the construction of the test specimens at their pole production facility in Tuscaloosa, Alabama. Additionally, the guidance of Senior Engineer, Ron Albanese, along with the abundance of technical information is greatly appreciated. The author wishes to express gratitude to her committee, Dr. Robert W. Peters and Dr. Talat Salama, for their guidance and valuable discussion during the final stages of this thesis. The author also gratefully acknowledges the help of Dr. Ian Hosch and Dr. Christopher Waldron, as all their help and patient guidance throughout the research will be forever appreciated. Also, the author wishes to express appreciation to Richard Hawkins, Rachael Nelson, Jason Woodall, and Justin Sansing for their tremendous help during the experimental program. iv

5 Finally, the author would like to acknowledge the love and support received from her family throughout the journey. v

6 TABLE OF CONTENTS Page ABSTRACT... ii ACKNOWLEDGMENTS... iv LIST OF TABLES... ix LIST OF FIGURES... xi LIST OF ABBREVIATIONS... xv CHAPTER 1. INTRODUCTION General Background GFRP vs. Prestressing Steel GFRP vs. CFRP Advantages and Disadvantages of GFRP Serviceability Considerations Literature Review Objectives of Study Plan of Work Thesis Organization MANUFACTURING OF TEST SPECIMENS Introduction Materials Reinforcement Concrete Specimen Manufacturing Construction of the Cage Casting: Placing of the Concrete vi

7 2.3.3 Curing of the Specimens Control Cylinders Summary EXPERIMENTAL PROGRAM Introduction Specimen Instrumentation Test Setup Testing Procedure Testing Summary Test Specimen 6A Test Specimen 12A Test Specimen 12B Test Specimen 6B TEST RESULTS Introduction Data Collected Cracking Load Ultimate Load Deflection Crack Width Spacing Concrete Strain Failure Modes Summary ANALYTICAL PROGRAM Introduction Design Equations Cracking Moment Ultimate Moment Theoretical Results Cracking Moment Ultimate Moment DISCUSSION AND ANALYSIS Introduction Experimental vs. Theoretical vii

8 6.2.1 Cracking Loads and Moments Ultimate Loads and Moments Crack Width Deflection Concrete Strain Comparison Among Prestressed, GFRP, and CFRP Cracking Loads Ultimate Loads Crack Width Deflection Failure Modes COST COMPARISON ANALYSIS Introduction Cost Per Foot Comparison Cost Per Force Comparison Summary SUMMARY AND CONCLUSION Summary Conclusion Recommendations for Future Work LIST OF REFERENCES APPENDICES A B TECHNICAL DRAWINGS CONCRETE COMPRESSIVE STRENGTHS C CRACK SPACING DATA viii

9 LIST OF TABLES Tables Page 1-1 Study specific properties of rebar Physical properties of GFRP Aslan Physical properties of GFRP spiral Specimen coding details day concrete compressive strength data Experimental program details Experimental cracking loads Experimental ultimate loads Summary of deflection data Summary of crack width data Summary of crack spacing data Summary of compressive concrete strain data Summary of failures Summary of test results Theoretical cracking moments Theoretical ultimate moments Experimental cracking moment capacities ix

10 6-2 Comparison of theoretical and experimental cracking moments Experimental ultimate moment capacities Comparison of theoretical and experimental ultimate moments Comparison of experimental cracking loads and experimental ultimate loads Experimental load at 13 mils Experimental load at 3% deflection Comparison of experimental and ACI concrete strain Nominal rebar strengths of prestressing steel, GFRP, and CFRP Comparison of crack width at 2000 lbs for GFRP and CFRP Cost of GFRP reinforcement material Cost of CFRP reinforcement material Cost of steel reinforcement material Comparison of reinforcement cost per foot Comparison of reinforcement cost per force x

11 LIST OF FIGURES Figure Page 2-1 Typical stress/strain curve for GFRP rebar Aslan 100 GFRP Rebar GFRP spiral Showing slinky property of GFRP spiral Technical drawings showing 6 (left) and 12 (right) rebar Specimen dimensions Placing the prestressing steel into the plastic de-bonding tubes Inserting the GFRP rebar Tying the wire ties to keep the steel rings in place Placing the GFRP spiral Plastic chairs Four prestressed steel strands Finished cage of the specimen Pouring the concrete Placing the top mold Illustration of final product of reinforced spun concrete pole Residual slurry inside Specimen 6A at the tip (left) and at the butt (right) xi

12 2-18 Cracks in Specimen 6A Circumferential cracks of Specimen 6B Scaling on Specimen 12A Cracking on Specimen 12A 9.5 ft from the butt The tip (left) and butt (right) of Specimen 12A Hollow interior of Specimen 12B Strain gauges 6 and 12 inches from the ground line Strain gauge orientation Dial gauges underneath the pole Tape measure to measure tip deflection Load cell pulley apparatus Tension load cell Data Acquisition System Overall test setup Recording data during testing Average experimental cracking loads for the two groups Average experimental ultimate loads for the two groups Load deflection curves for Specimens 6A and 6B Specimen 6A showing large deflections prior to failure Load deflection curves for Specimens 12A and 12B Specimen 12A showing large deflections prior to failure Load vs. crack width for Specimens 6B, 12A, and 12B xii

13 4-8 Spacing along Specimen 6A Final spacing along Specimen 6B Final spacing along Specimen 12A Final spacing along Specimen 12B Load vs. crack spacing for Specimens 6B, 12A, and 12B Load vs. concrete strain for Specimens 6A and 6B Load vs. concrete strain for Specimens 12A and 12B Shear crack between the supports of Specimen 6A Crushing of the concrete on Specimen 6A Shear crack between the supports of Specimen 6B Crushing of the concrete at the ground line of Specimen 6B Shear cracks between the supports of Specimen 12A Compression failure of Specimen 12A Shear cracks between the supports of Specimen 12B Concrete compression failure of Specimen 12B at midpoint Internal tensile and compressive forces at ultimate Cracking moment comparison for all specimens Average cracking moment comparison for the two groups Average ultimate moment comparison for the two groups Comparison of experimental cracking load to experimental ultimate load Crack width at 25% of ultimate load Load deflection curves for all specimens xiii

14 6-7 Average load deflection curves for the two groups Percent deflection of each group at 25% of ultimate load Prestressed, GFRP, and CFRP cracking loads Prestressed, GFRP, and CFRP ultimate loads Prestressed, GFRP, and CFRP tip deflections at failure Deflection curves of prestressed, GFRP, and CFRP, for 6 bars Deflection curves of prestressed, GFRP, and CFRP for 12 bars xiv

15 LIST OF ABBREVIATIONS A fi Area ith reinforcement A FRP Area of the FRP reinforcement rebar A s Area of the steel strands c C c Location of the neutral axis measured from the extreme compression fiber of the pole Compressive force of the concrete CFRP Carbon fiber reinforced polymer d i Distance of the ith reinforcement from the extreme compression fiber e i Distance of the ith reinforcement to the neutral axis f Stress of the i th reinforcement fei f fu Ultimate strength of the GFRP bars f r Modulus of rupture of the concrete f ' c Compressive strength of the concrete xv

16 F FRP Stress of the FRP rebar F s Stress of the steel strands GFRP Glass fiber reinforced polymer I g Gross moment of inertia Kc M cr Position of the centroid of the compressive stress block Cracking moment capacity M u Ultimate moment capacity SG y t Strain gauge Distance from the centroidal axis to the extreme tensile fiber of the section xvi

17 CHAPTER 1 INTRODUCTION 1.1 General Background There has been very little research performed on concrete poles reinforced with glass fiber reinforced polymer (GFRP) and other fiber reinforced polymers (FRP). Although a number of universities and research centers have conducted durability testing of GFRP bars (Concrete Protection Products, Inc. 2007), GFRP as a reinforcement in concrete is still a developing concept in the United States. Limited research has been conducted at The University of Alabama at Birmingham and elsewhere on concrete poles reinforced with carbon fiber reinforced polymer (CFRP); however, a viable alternative to steel reinforcement has yet to be established. Although GFRP is an economical alternative to steel, over carbon or aramid fibers, there is still a need for more research before this reinforcement can be used in the construction market. The life-cycle cost and long-term performance data are non-existent at this point. Also, lack of a national FRP design code in the United States has hindered the efforts of utilizing FRP as an alternative to steel reinforcement. 1

18 1.1.1 GFRP vs. Prestressing Steel Glass fiber reinforced polymer is non-corrosive; therefore, some of the design criteria are not as strict. The maximum crack width limitation can be relaxed because atmospheric conditions are not highly crucial to the performance of the structure (ACI 440.1R 2006). Steel is corrosive, and due to such properties, failure or replacement will most definitely be expected after maximum crack widths are reached, especially if used in aggressive marine or industrial environments. In 2002, The US Federal Highway Administration estimated $276 billion as the total annual direct cost of corrosion in the United States. The annual indirect costs are estimated to be approximately equivalent to these costs (Koch et al. 2001). GFRP is non-corrosive, non-conductive, and nonmagnetic. GFRP (similar to other FRP materials) does not yield and exhibits an elastic behavior until failure. If FRP reinforcement ruptures, the failure is sudden; whereas steel reinforced structures have ductility and warning prior to failure. Table 3.1 in ACI 440.1R (2006) shows that the density of glass fiber rebar ranges from 77.8 to lb/ft 3, which is 16% to 25% that of steel. This lower weight reduces the cost of transportation to the project site. Table 1-1 shows that the tensile strength of the GFRP used in this study has a comparatively lower tensile strength than prestressing steel. The elastic modulus of GFRP is lower than that of prestressing steel, which means it is stiffer and tends to deflect less. Also, the rupture strain of GFRP is lower. Unlike steel, there is very little information on the performance of structural members reinforced with GFRP. 2

19 Table Study specific properties of rebar Prestressing Steel GFRP CFRP Nominal Yield Stress (ksi) 243 N/A N/A Tensile Strength (ksi) Elastic Modulus (10 3 ksi) Ultimate Strain (%) Yield Strain (%) 1 N/A N/A GFRP vs. CFRP GFRP is more available in the market than CFRP; it is also less expensive on a level of straight quantity comparison. Table 1.1 shows that the tensile strength of CFRP is 300 ksi, whereas that of GFRP (used in this study) is 100 ksi. The elastic modulus of CFRP is about 3 times that of GFRP. Table 3.1 in ACI 440.1R (2006) shows that the typical densities of reinforcing bars between these two materials vary according to the specific product used. Table 3.2 in ACI 440.1R (2006) shows that the coefficients of thermal expansion also vary between these two reinforcing materials (ACI 440.1R 2006). Otherwise, the properties of these two materials are very similar. Neither of these materials is ductile; they are elastic until failure. Both materials are non-metallic, so they will not corrode. Both are relatively lightweight; each having a density of less than 150lb/ft 3 (ACI 440.1R 2006). 3

20 1.1.3 Advantages and Disadvantages of GFRP The advantages of GFRP include the fact that it has a high strength-to-weight ratio, which reduces shipping costs. Also, it has high durability, which means that the material will not likely be damaged during construction. Another benefit of using GFRP is its ease of installation (ACI 440.1R 2006). It is resistant to corrosion, rust, and rot; so it can withstand exposure to salt spray (e.g. northern areas) and high levels of moisture (e.g. near oceans) (Shalaby 2007). The specific GFRP rebar product used in this study is Aslan 100. The Aslan 100 brochure from Hughes Brothers, Inc., gives some additional product-specific benefits. It is impervious to chloride ion and low ph chemical attack. It is transparent to magnetic fields and radio frequencies and thermally non-conductive (Aslan FRP 2007). The disadvantages of GFRP include low transverse strength, and a low modulus of elasticity (ACI 440.1R 2006). The failure is somewhat brittle as the material does not yield prior to failure. It has a high coefficient of thermal expansion perpendicular to the fibers, relative to concrete (ACI 440.1R 2006) Serviceability Considerations Serviceability governs design restrictions and code limitation. Serviceability is defined as satisfactory performance under service load conditions (ACI 440.1R 2006). Service load conditions are typically defined as 25% or less of the ultimate load. This definition of the service load is specific to the pole industry. The major parameters that govern serviceability are crack width and deflection. Crack width is an important design 4

21 criterion for steel-reinforced concrete for aesthetic purposes. However, more crucially, a large crack width makes steel reinforcement susceptible to exposure, which can lead to deterioration. When using FRP, the Japan Society of Civil Engineers only considers aesthetics in setting a maximum allowable crack width of 0.02 inches (ACI 440.1R 2006). Canadian Standards set the maximum crack width of 0.02 inches for exterior exposure and for interior exposure when FRP is used (ACI 440.1R 2006). The American Concrete Institute (ACI) does not currently have any standards for crack width when FRP is used; however, the maximum crack width for steel reinforcement is inches (ACI 440.1R 2006). Deflection is more of a concern for FRP reinforced concrete than is crack width. Because FRP stiffness is lower than that of steel, deflections tend to be greater. Therefore, the ACI 440.1R (2006) requires the use of a direct method of deflection control. Short-term and long-term deflection should be considered in design. An acceptable deflection under service load conditions is 3% or less of the pole s free length. This standard limit for deflection is also specific to the pole industry. This thesis compares the results, obtained through experimentation, of GFRP to the current serviceability considerations for crack width and deflection. 1.2 Literature Review ISIS Canada in conjunction with the University of Manitoba conducted a GFRP durability study in 2005 (Onofrei 2005). The ISIS Canada project studied the effect of natural aging in the field of five GFRP reinforced concrete bridges that were constructed 5

22 in Canada. The ISIS Canada study concluded that time does not affect the adhesion of concrete to the GFRP reinforcement. The samples of the GFRP rebar taken from the bridges in the field were compared with original samples, which had been stored in the lab, and the resin and glass fibers did not show any signs of deterioration. Further analysis revealed that there was no non-reversible degradation, except for a few of the samples that were determined to have not completely cured prior to installation. The infrared analysis showed that any changes in the number of hydroxyl groups were due to sampling or the material heterogeneity, and not to a chemical degradation. Also, the X- ray analysis determined that no reaction occurred as a result of the diffusion of the GFRP compounds with the concrete. The study concluded that no deterioration of the GFRP occurred in the field, and that GFRP is durable in concrete. A study conducted at the University of Alabama (Lyons 2003) explored analytically the potential behavior and performance of CFRP prestressed spun concrete poles. Calculations found in the literature were used, and CFRP technology was researched and incorporated into the project. Lyons determined an overall design philosophy, established design and manufacturing guidelines for members reinforced with CFRP, and theoretically predicted the performance of such members. Although Lyons thesis was only theoretical in nature and no physical testing was performed to produce actual test data, it was determined through his research that CFRP prestressed spun concrete poles are structurally feasible. Also, the concrete wall thickness is allowed to be thinner, resulting in lighter-weight pole designs. 6

23 The University of Sherbrooke performed a research project involving fiber reinforced polymer poles (Metiche and Masmoudi 2007). The program investigated the flexural behavior of FRP hollow poles and theoretically predicted the behavior and deflection. Twenty-three tapered poles were manufactured with a filament winding process, using epoxy resin reinforced with E-glass fibers, and then subjected to flexural testing. Each pole had three different zones with varying geometrical and mechanical properties. These poles were made entirely of FRP material involving no concrete. The load deflection curve developed from experimentation was linear until failure. The theoretical linear model, based on the beam theory, was the most accurate in predicting the deflection behavior. This experimental program showed that the use of low linear density glass-fibers, over an epoxy resin material, improves the mechanical performance of GFRP poles in terms of flexural stiffness and increases the ultimate load carrying capacity. Fam (2008) wrote a paper introducing a pole of spun cast concrete inside a GFRP tube. The purpose of the tube was to replace the interior reinforcement and to protect the concrete from the environment. The concept of this idea was in response to the hollow GFRP pole, similar to that of Metiche and Masmoudi (2007), and the GFRP tube that was completely filled with concrete. The pole tested in this study was found to have the equivalent strength of a conventional pole of the same size with traditional reinforcement. This type of pole was also found to behave fairly elastically. The drawbacks of this type of pole include the fact that the only way to get the concrete into the tube is at either end and may not be practical for a pole of much longer dimension. The manufacturing 7

24 process required the entire specimen to be placed in a steel mold for spinning, thus adding another step to the manufacturing process. The pole in this study had the same cross section throughout the length of the pole, and the feasibility of a tapered pole of this design needs further exploration. Feeser and Brown (2005) state in their Guide for Design paper that, unlike steel, FRP rebar is not currently standardized across the manufacturing industry, so there is variance in the material properties among FRP manufacturers. This paper shows a section efficiency figure for GFRP designs for beams, and makes a comparison to CFRP. CFRP is much more efficient to use in the reinforcement beams due to the larger moment capacity it produces. It has been suggested that higher compressive strength concrete should be utilized when reinforcing with FRP in order to achieve efficient performance of the FRP. However, for tension-controlled sections, Feeser and Brown state that the use of high-strength concrete is less cost effective when only a single layer of reinforcement is used, unless the rebar is CFRP, and that adopting a reinforcement system with multiple layers would be more cost efficient. CFRP sections should be designed for compressioncontrolled failure, with the minimum reinforcement necessary. These researchers pose the question of whether the higher strength of CFRP would overshadow the cost, and they suggest that there is a need for a lifetime project cost benefit analysis. A dissertation at The University of Alabama at Birmingham (Shalaby 2007) studied the behavior of spun concrete poles reinforced with CFRP. In this research, the flexural behavior, deflection, crack width and spacing were theoretically explored and experimentally determined. Equations found in the literature were used and ANSYS 8

25 software was utilized to develop a finite element model of the specimens. The experimental program consisted of testing full-scale spun concrete poles reinforced with CFRP. The main objective of this research was to find a viable alternative to the spun concrete poles reinforced with the conventional prestressed steel. This thesis is similar to the research by Shalaby in that the same type and size of specimens were manufactured but GFRP reinforcement was been used in lieu of CFRP reinforcement. The results from this thesis are compared to Shalaby s work to further emphasize the behavior and performance of spun concrete poles reinforced with GFRP. 1.3 Objectives of Study The objectives of this research study are the following: 1. Evaluate the flexural behavior of spun concrete poles reinforced with GFRP reinforcement both analytically and experimentally. 2. Compare the results found through experimentation to theoretical values calculated using engineering equations in the literature. 3. Compare the experimental results of crack width and deflection to recommended practical serviceability considerations for concrete poles. 4. Compare the performance of spun concrete poles reinforced with GFRP reinforcement to the performance of conventional prestressed steel-reinforced spun concrete poles and to the performance of spun concrete poles reinforced with CFRP reinforcement. 9

26 5. Prepare an economic analysis comparing the cost of poles reinforced with the materials considered in this study. 1.4 Plan of Work In order to achieve the stated objectives, the concentration was on three main tasks: 1. Analytical Program The analytical portion of the study used equations found in the literature to calculate the theoretical flexural capacity. The calculation of the cracking moment capacity was computed using the elastic theory. The ultimate moment capacity was predicted based on strain compatibility and the internal force equilibrium. 2. Experimental Program Four test specimens were designed and manufactured for the experimental portion of the research. The variable among the poles was the number of longitudinal reinforcement bars. Two of the poles were reinforced with 6 bars, and the other two were reinforced with 12 bars. During the testing of the pole, certain parameters were investigated: cracking and ultimate moment, deflection, crack width and spacing, and failure mode. 3. Results and Analysis The experimental results of this study were compared to the theoretical values found in the analytical program. These results were also compared to currently recommended practical serviceability considerations for concrete poles. Also, the results 10

27 and performance of these poles were compared to those of the conventional prestressed steel-reinforced spun concrete poles, and to those of the spun concrete poles reinforced with CFRP. Lastly, a cost comparison analysis was conducted among the three types of reinforced poles investigated in this study. 1.5 Thesis Organization This thesis consists of eight chapters. Chapter 1 is an introduction which gives general background information on the problem and presents the objectives of this study and the plan of work that was utilized in achieving those objectives. Chapter 2 discusses the materials used in the construction of the GFRP reinforced pole test specimens. It provides a brief description of the process involved in manufacturing the test specimens. The chapter ends with a discussion of the condition of the test specimens prior to testing. Chapter 3 provides an overview of the experimental program. This chapter discusses the instrumentation of the test specimens prior to testing. The test setup in the Structures Laboratory at The University of Alabama at Birmingham is described and documented. Also included is a detailed summary of the testing procedure. Chapter 4 provides the data acquired during testing and the details of how data were adjusted for accuracy. The data collected include the cracking load, the ultimate load, deflection, crack width and spacing, concrete compressive strain, and failure modes observed during testing. The chapter concludes with a summary of the test results. 11

28 Chapter 5 presents the analytical program. This chapter provides the equations used in the calculation of the theoretical values. It ends with the presentation of the theoretical cracking and ultimate moment capacities. Chapter 6 is a discussion and analysis section, the purpose of which is to compare the experimental results of cracking and ultimate moments to the theoretical results from the analytical program. It compares the experimental crack width and deflection to practical serviceability considerations currently recommended for concrete poles. This chapter also compares the experimental data of this project s spun concrete poles reinforced with GFRP to the conventional steel-reinforced prestressed spun concrete poles and to spun concrete poles reinforced with CFRP. Chapter 7 presents a brief economic analysis comparing the cost per foot and cost per force of poles reinforced with GFRP, CFRP, and conventional prestressing steel strand. Lastly, Chapter 8 summarizes the findings of this study. Conclusions are stated, and recommendations for future work are provided. 12

29 CHAPTER 2 MANUFACTURING OF TEST SPECIMENS 2.1 Introduction This chapter describes the materials used in the construction of the test specimens. It provides a brief description of the process involved in manufacturing the test specimens. This chapter also discusses the condition of the test specimens prior to testing. 2.2 Materials The major materials used in manufacturing the pole specimens include the two types of reinforcement (which comprise the cage) and the concrete. This section identifies the specific products and their properties used in the manufacturing of the test specimens Reinforcement There are two types of reinforcement used in the manufacturing of the test specimens: GFRP rebar and GFRP spiral. The GFRP rebar is the primary, longitudinal reinforcement that resists flexural bending. The GFRP spiral is the secondary, transverse reinforcement that resists shear stress. 13

30 The GFRP rebar used for the construction of the test specimens was manufactured by Hughes Brothers, Inc., in Seward, Nebraska under the commercial name of Aslan 100, which is more specifically vinyl ester matrix GFRP Rebar. The physical properties of the rebar are given in Table 2-1. Figure 2-1 shows the stress-strain curve for the GFRP Rebar given in the Aslan 100 Brochure (Aslan FRP 2007). Like all FRP material, the GFRP is linear elastic until failure. Figure 2-2 shows a close-up of multiple GFRP bars prior to their installation. Initially, it was planned that prestressing the GFRP bars for these test specimens would be one of the objectives. It is believed that prestressing the GFRP bars would have significantly improved the performance of the test specimens. However, prestressing of the GFRP bars was not incorporated in this study. There are two major factors that hinder the prestressing of GFRP bars: technology and cost. The physical technology used to prestress GFRP bars is not fully developed at this time, as the gripping devices (used in conventional prestressing) damage the GFRP reinforcement. Since prestressing FRP bars is not practiced in the United States, there was difficulty in obtaining the prestressing jack and anchoring devices at reasonable cost. Also, there was interest in evaluating the performance of non-prestressed GFRP bars, as this would result in more rapid and economical manufacturing. 14

31 Table 2-1 Physical properties of GFRP Aslan 100 Bar Size Cross- Sectional Area (in 2 ) Nominal Diameter (in) Tensile Strength (ksi) Tensile Modulus of Elasticity (10 6 psi) Ultimate Strain (%) # Figure 2-1 Typical stress/strain curve for GFRP rebar 15

32 Figure 2-2 Aslan 100 GFRP Rebar The GFRP spiral used for this study was also manufactured by Hughes Brothers, Inc. The physical properties of the spiral are given in Table 2-2. Figure 2-3 shows a close-up of the GFRP spiral prior to installation. Figure 2-4, provided by Hughes Brothers, Inc., illustrates the slinky property of the spiral (Hughes Brothers, Inc. 2009). The spiral was manufactured in three sizes for the specimen: 7, 9, and inch inner diameter measurements to spread the length of the pole. Table 2-2 Physical properties of GFRP spiral Bar Size Cross-Sectional Area (in 2 ) Nominal Diameter (in) Spacing (in) # c-c 16

33 Figure 2-3 GFRP Spiral Figure 2-4 Hughes Brothers, Inc. Showing slinky property of GFRP spiral. Oct 8, Concrete The spun concrete test poles were produced with a high-strength concrete mix at the Valmont-Newmark, Inc., spun concrete pole manufacturing plant in Tuscaloosa, Alabama. The concrete mixture used for this study contained a! inch aggregate size. It was a high-strength concrete that by centrifugally spinning the pole has a target 28-day compressive strength of 11,000 psi. The actual compressive strength of the concrete for 17

34 the plant on the days when manufacturing the test specimens took place is given in Section The specimen mold is spun at the rate of 20 times the acceleration of gravity (20G s), which forces the excess water out of the concrete mixture and makes the concrete much more dense. Fouad H. Fouad (1988) determined that through centrifugally spinning the pole, certain properties are developed: Higher compressive strength Higher modulus of elasticity Higher density Lower water/cement ratio Lower permeability Lower absorbability 2.3 Specimen Manufacturing The construction of the poles took place at the Valmont-Newmark, Inc., spun concrete pole manufacturing plant in Tuscaloosa, Alabama. Two poles were reinforced with six GFRP longitudinal bars, and the other two poles were reinforced with twelve GFRP longitudinal bars (see Figure 2-5). This is the only variable in the program. Figure 2-6 shows that the dimensions of these tapered poles were 20 feet in length, inches outer diameter at the butt, and 8.91 inches outer diameter at the tip. Full technical drawings of the two variations of design are included in Appendix A. Table 2-3 explains the coding of the test specimens. Specimen manufacturing has three major steps that are discussed in this section: the construction of the cage, which is the assembly of the 18

35 GFRP rebar and the spiral; the casting, which includes the placing of the concrete and the spinning process; and the curing of the specimens, which includes the testing of the control cylinders used to determine the concrete compressive strength at different ages. Figure 2-5 Technical drawings showing 6 (left) and 12 (right) rebar Figure 2-6 Specimen dimensions 19

36 Table 2-3 Specimen coding details Specimen ID No. of Bar Conc. Bars Dia. (in) Bar Type Cover (in) Pole Outer Dia. (in) Pole Inner Dia. (in) Pole Length (ft) At Tip At Butt At Tip At Butt 6A 6B 12A 12B 6! GFRP ! GFRP Construction of the Cage The first step in the manufacturing process was construction of the cage. The following is a brief step-by-step description of the process. The casting mold was cleaned and prepared for construction. The GFRP spiral was placed in the mold and the four prestressing steel strands were inserted longitudinally, each at 90 degrees around the cross section. The steel strands were inserted into plastic de-bonding tubes during installation (see Figure 2-7), so they could be removed before testing. These steel strands were used only for the proper functioning of the mold. Figure 2-8 shows the installation of the GFRP Rebar. Steel rings were placed about every 30 inches inside the longitudinal reinforcement and tied to them with small wire ties (see Figure 2-9). It is crucial to note that these steel rings and the small wire ties were the only metal in the specimen during testing. The spiral was then stretched in three sections over the entire pole, spaced about 3 inches c-c (center to center). Figure 2-10 shows the spiral installation during the construction of the pole specimen. Small plastic chairs were added to ensure the that proper concrete cover was dispersed around the pole (see Figure 2-11). Then, the four steel strands were prestressed (see Figure 2-12) to hold the mold together during the 20

37 spinning process. Figure 2-13 shows the final cage assembly for the pole. Figure 2-7 Placing the prestressing steel into the plastic de-bonding tubes Figure 2-8 Inserting the GFRP rebar 21

38 Figure 2-9 Tying the wire ties to keep the steel rings in place Figure 2-10 Placing the GFRP spiral 22

39 Figure 2-11 Plastic chairs Figure 2-12 Four prestressed steel strands Figure 2-13 Finished cage of the specimen 23

40 2.3.2 Casting: Placing of the Concrete The concrete was poured onto the cage (see Figure 2-14), and the top of the mold was bolted on (see Figure 2-15). The mold was placed on the spinner for approximately ten minutes, and after spinning placed in the heat curing cell. Excess concrete was used to make control cylinders for testing compressive strength at different ages. Figure 2-16 shows an illustration provided by Valmont-Newmark, Inc., (Valmont Industries, Inc. 2010) of the final assembly of the product with all the materials. Figure 2-14 Pouring the concrete Figure 2-15 Placing the top mold 24

41 Figure 2-16 Valmont Industries, Inc. Illustration of final product of reinforced spun concrete pole Curing of the Specimens The curing of the test specimens took place at the Valmont-Newmark, Inc., spun concrete pole manufacturing plant in Tuscaloosa, Alabama. The pole specimens were allowed to sit for at least 24 hours before being extracted from their individual molds. They were then placed in the heat cell for curing. After 28 days, they were transported to the Structures Laboratory at The University of Alabama at Birmingham. Regarding the condition of the specimens, there were a few noticeable imperfections that are worth noting. All of the specimens, except for Specimen 12B, had residual slurry that had dried 25

42 inside the pole (see Figure 2-17). This is a typical result that occurs with spun concrete poles, and although it was bothersome cosmetically, it did not affect the strength or performance of the specimens. Figure 2-18 shows a few of the hairline cracks that Specimen 6A exhibited, which were not predicted to affect the behavior of the pole or the overall results of the testing. Figure 2-17 Residual slurry inside Specimen 6A at the tip (left) and at the butt (right) 26

43 Figure 2-18 Cracks in Specimen 6A Specimen 6B was in much better condition than its counterpart. The only defects were the few hairline cracks, that were circumferential in nature (see Figure 2-19). The cracks were not expected to play a role in the performance of the specimen. However, they were marked prior to testing so as not to be mistaken as new cracks during testing. 27

44 Figure 2-19 Circumferential cracks of Specimen 6B Specimen 12A had obvious scaling along 6 ft of the pole starting about 2 ft from the butt (see Figure 2-20). This scaling was placed on the tension side during testing, so as not to affect compression reading or strain gauge data. There was also a crack farther down on the pole approximately 9.5 ft from the butt, shown in Figure Figure 2-22 shows the tip and the butt of Specimen 12A. 28

45 Figure 2-20 Scaling on Specimen 12A Figure 2-21 Cracking on Specimen 12A 9.5 ft from the butt 29

46 Figure 2-22 The tip (left) and butt (right) of Specimen 12A Specimen 12B was in relatively pristine condition when it arrived from the plant in Tuscaloosa, Alabama. Aside from a few minor hairline cracks, the pole looked as expected, and its interior was slurry-free (see Figure 2-23). Figure 2-23 Hollow interior of Specimen 12B 30

47 2.3.4 Control Cylinders The concrete cylinder tests for the concrete batches on the days the specimens were manufactured are included in Appendix B. The 28-day compressive strengths for the cylinders are given in Table 2-4. Specimens 6A and 12A were manufactured on 12/9/09; Specimens 6B and 12B were manufactured on 12/14/09. The 28-day compressive strength for Specimens 6A and 12A was psi, and the 28-day compressive strength for Specimens 6B and 12B was psi. This information was used in the theoretical analysis. Table day concrete compressive strength data Manufactured Date 28 Day Date Gauge Reading 1 (lbs) Gauge Reading 2 (lbs) Gauge Reading 3 (lbs) 28 Day Strength 1 (psi) 28 Day Strength 2 (psi) 28 Day Strength 3 (psi) 28 Day Average (psi) 12/9/09 1/6/ /14/09 1/11/ Summary Four pole test specimens were manufactured at the Valmont-Newmark, Inc., spun concrete pole manufacturing plant in Tuscaloosa, Alabama. Table 2-5 gives details of the specimens. They were 20 feet long with two having 6 bars of longitudinal reinforcement and the other two having 12 bars of longitudinal reinforcement. The primary longitudinal reinforcement was GFRP Aslan 100, and the secondary transverse reinforcement was a GFRP spiral. These test specimens were used for the experimental program to determine 31

48 the behavior of GFRP reinforced spun concrete poles when subjected to full-scale flexural testing. Table 2-5 Experimental program details Specimen ID No. of Bars Bar Dia. (in) Bar Type Pole Outer Dia. Pole Inner Dia. Pole Concrete Conc. (in) (in) Length Strength (psi) Cover (in) At Tip At Butt At Tip At Butt (ft) 6A 6B 6! GFRP A 12B 12! GFRP

49 CHAPTER 3 EXPERIMENTAL PROGRAM 3.1 Introduction This chapter provides an overview of the experimental portion of this study. As discussed in Chapter 2, test specimens were manufactured at the Valmont-Newmark, Inc., pole manufacturing plant in Tuscaloosa, Alabama. The specimens were then delivered to the Structures Laboratory at The University of Alabama at Birmingham. This chapter discusses the instrumentation of the test specimens prior to testing. The test setup in the Structures Lab is described and documented. Also, this chapter gives a detailed summary of the testing procedure. 3.2 Specimen Instrumentation The strain gauges (SG s) used were N2A-06-20CBW-120, which were 2 long. The gauge length of strain gauges used on concrete should be at least 5 times the diameter of the largest aggregate in the concrete (Vishay 2005),! in the case of this study. However, it was decided to use 2 strain gauges identical to the ones used in Shalaby s (2007) study of concrete poles reinforced with CFRP. There were six strain gauges placed on the pole: one set of three 6 inches from the collar and the other set of three 12 inches from the collar (see Figure 3-1). Gauges 1 and 2 were placed directly on 33

50 the top of the pole, vertical. These gauges were expected to read equal to each other and to the maximum concrete compression forces of the pole during testing. Gauges 3 and 4 were placed approximately 25 degrees from vertical. Gauges 5 and 6 were placed 47 degrees from vertical. Figure 3-2 shows the strain gauge orientation on the cross section of the pole. There were two Fowler ultra logic 1 dial gauges (model LG ) placed underneath the pole at the collar supports (see Figure 3-3); these were used during the testing of Specimens 6A and 12A. For Specimens 6B and 12B, 2 Fowler ultra dig dial gauges (model ) were used at the collar supports. The dial gauges were changed on the last two tests, so that they did not have to be adjusted and reset during testing when deflection exceeded one inch. Also, there was a measuring tape attached to the tip of the pole to measure tip deflection (see Figure 3-4). Figure 3-1 Strain gauges 6 and 12 inches from the ground line 34

51 Figure 3-2 Strain gauge orientation Figure 3-3 Dial gauges underneath the pole 35

52 Figure 3-4 Tape measure to measure tip deflection 3.3 Test Setup Testing was conducted at the Structures Laboratory at The University of Alabama at Birmingham. The setup was designed to be almost identical to that described in the CFRP dissertation by Shalaby (2007), in order for the data to be more comparable. There were two collars 3 feet apart fixing the pole at the butt. The load cell pulley was attached one foot from the tip of the pole and lifted the tip vertically, as a cantilever, with the specified loading. Figure 3-5 shows the load cell apparatus, which included the tension load cell (see Figure 3-6); both worked in combination with the Data Acquisition System, shown in Figure 3-7. Figure 3-8 shows the overall setup. 36

53 Figure 3-5 Load cell pulley apparatus Figure 3-6 Tension load cell 37

54 Figure 3-7 Data Acquisition System Figure 3-8 Overall test setup 38

55 3.4 Testing Procedure Testing for each specimen was conducted in two cycles. The first cycle brought the specimen to the first crack (cracking load), and the second cycle brought the specimen to failure (ultimate load). During the first cycle, the weight of the pole was found by applying load gradually until there were deflection and strain gauge readings. The loading was increased gradually by 100 lb increments until the first crack appeared. After each increment, the tip deflection and the two deflection dial gauge readings were recorded. Once the first (critical) crack appeared, its crack width was measured and its location was noted. The pole was then brought back to zero position, with no load or compressive strain. The second cycle started with increasing the load gradually until the crack re-opened, and then measurements were again taken. Load was increased in 100 lb increments up to 1000 lbs and then in 200 lb increments until failure. After each load increment, the crack locations and loads were noted, and the critical crack width was measured. Figure 3-9 shows the collection of data during testing. The pole was also constantly inspected during the testing for any other behavior. Failure modes and locations were noted and documented. 39

56 Figure 3-9 Recording data during testing 3.5 Testing Summary This section provides a specific step-by-step description of the testing of each specimen. The order in which the poles were delivered to the lab determined the order in which they were tested. This section specifies any variation from the set testing procedure and any other noteworthy occurrences. The loads given in this section are the loads reported by the Data Acquisition System; they are not reduced to account for the weight of the specimens. The deflections given are the tip deflections during testing, which were adjusted later to adjust for pole rotation about the collars. 40

57 3.5.1 Test Specimen 6A The first pole tested was Specimen 6A, which had 6 bars of longitudinal reinforcement. Load was applied gradually until the pole was perfectly level and the strain gauges began to show readings, at 600 lbs. This process determined the weight of the pole. Load was applied in 100 lb increments until the first crack occurred. The first crack formed at a load of 1190 lbs and 2.96 ft from the ground line. Tip deflection at this point was 4.5 inches. The load cell and the deflection dial gauges were reset to zero. Load was applied gradually again until 780 lbs, when the first crack re-opened. Unfortunately, there was not a crack width comparator in the lab, so no crack width data are available for this pole test. Load was further applied in 100 lb increments again until the second crack formed at 1220 lbs and 4.53 ft from the ground line. Failure occurred at 3600 lbs, where crushing of the concrete occurred at the ground line Test Specimen 12A The second pole tested was Specimen 12A. The first loading cycle started by raising the pole to zero, which required 611 lbs (weight of the pole). Load was added in increments of 100 lbs, and the first crack appeared at 1200 lbs at 6.5 inches from the collar with a crack width of inches. The second crack occurred at 1300 lbs at 19.5 inches from the collar with a crack width of inches. At this load, the crack width of the critical crack was inches. 41

58 The load and all gauges were reset to zero, and the second loading cycle began. Load was added gradually until the first crack re-opened, which occurred at 700 lbs, with a crack width of inches. Width measurements of the critical crack were taken at every load increment. Locations of new cracks were recorded every time a new crack appeared. Failure occurred at a load of 4400 lbs at 4.5 ft from the ground line Test Specimen 12B The third pole tested was Specimen 12B. There were a few mistakes and instrumentation malfunctions that occurred during the testing of this specimen. The pole was loaded to find the weight of the pole; then, the loading was increased by 100 lb increments. At 1100 lbs applied, before first crack, it was noticed that the Data Acquisition System had not been started, so no data were collected. The pole was unloaded, and the test was restarted. At 1300 lbs applied, the first crack appeared, which turned out to be 5 cracks. The first crack was recorded as 2.2 ft from the ground line, with a crack width of inches. The pole was unloaded, and then the next loading cycle began. Early on in the loading of this cycle, it was noticed that dial gauge 1 was stuck on itself, so it was not moving with the deflection of the pole. The pole was unloaded, the dial gauge was fixed, and the loading was restarted. Load was gradually applied until the applied load reached 1400 lbs, at which point it was noticed that strain gauges 2, 3 and 4 were not reading properly. The pole was unloaded, and suggestions about abandoning the test were discussed. The fifth cycle began and proceeded with no more problems. The pole was 42

59 loaded until failure with all the dial and strain gauges functioned properly. Failure occurred at 4140 lbs at the ground line Test Specimen 6B The fourth pole tested was Specimen 6B. This last test was almost flawless. The weight of the pole was found to be 600 lbs. The pole was loaded to first crack, which occurred at 5.25 ft from the ground line and measured inches. Then it was noticed that the Data Acquisition System had not been started. The loading was released, the Data Acquisition System was started, and the second loading cycle progressed normally until failure. The data presented in later chapters will be representative of this occurrence. Failure occurred at 3560 lbs at the ground line. 43

60 CHAPTER 4 TEST RESULTS 4.1 Introduction This chapter provides the data acquired during testing and the details of how data were adjusted for accuracy. Strain and loading data were recorded by the Data Acquisition System. Deflection dial gauges were used to measure movements at the support points in order to correct the tip deflections, which were measured by a tape measure. Crack comparators were used to measure crack width at specific load increments. The data collected included the cracking load, the ultimate load, tip deflection, crack width and spacing, concrete compressive strain, and failure modes observed during testing. A summary of the test results is given at the end of this chapter. 4.2 Data Collected In order to adjust the data for accuracy, the deflection was corrected according to the reading of the dial gauges, and according to the tape measure s zero point. The cracking and ultimate loads were adjusted to account for the weight of the test specimen. 44

61 4.2.1 Cracking Load As described in Chapter 3, the cracking load was determined by gradually and carefully increasing the load during testing until the first crack was observed. Also, the weights of the poles were determined at first by gradually increasing the load until a strain reading was reported by the Data Acquisition System. Although the weight is distributed along the length of the pole, this method is an acceptable approximation to negate the effects of the specimen weight. The experimental cracking loads for each pole are given in Table 4-1. The recorded cracking load is the value given by the Data Acquisition System. The specimen weight was subtracted from this value to yield the actual or corrected cracking load. The last column shows the average of the cracking loads for each specimen group. For Specimen 6A, the recorded cracking load was 1190 lbs; and by subtracting the specimen weight of 600 lbs, the corrected cracking load was found to be 590 lbs. For Specimen 6B, the recorded cracking load was 1200 lbs. The specimen weight was determined to be 600 lbs, so the corrected cracking load was calculated to be 600 lbs. For Specimen 12A, the first crack occurred at 1200 lbs. The specimen weight was determined to be 611 lbs, giving the corrected cracking load as 589 lbs. For Specimen 12B, the recorded cracking load was 1300 lbs. The specimen weight was determined to be 583 lbs, so the corrected cracking load was calculated to be 717 lbs. Table 4-1 shows that the cracking load for Specimen 6A was within 2% of Specimen 6B, and the cracking load for Specimen 12A was within 18% of Specimen 12B. Figure 4-1 illustrates the average experimental cracking loads for the two specimen 45

62 groups. This figure shows that the specimen group with 12 bars of longitudinal reinforcement has an approximate 10% higher cracking strength than the specimen group with 6 bars. However, looking at the individual cracking loads, it is apparent that the cracking loads for all the specimens are relatively close to one another. Table 4-1 Experimental cracking loads Specimen ID Recorded Cracking Load (lbs) Specimen Weight (lbs) Corrected Cracking Load (lbs) Average Cracking Load (lbs) 6A B A B

63 800 Cracking Load (lbs) Bars 12 Bars Figure 4-1 Average experimental cracking loads for the two groups Ultimate Load The ultimate loads for each test specimen are summarized in Table 4-2. The ultimate load reported was determined the same way as the cracking load, described in the previous section. For Specimen 6A, the recorded ultimate load was 3600 lbs. After subtracting the weight of the pole, 600 lbs, the corrected ultimate load for the specimen was 3000 lbs. Similarly, for Specimen 6B, the recorded ultimate load was 3560 lbs. By negating the effect of the specimen weight, 600 lbs, the actual ultimate load for the specimen was 2960 lbs. For Specimen 12A, the recorded ultimate load was 4400 lbs, and after eliminating the effect of the pole weight, 611 lbs, the actual ultimate load was 3789 lbs. For 47

64 Specimen 12B, the recorded ultimate load was 4140 lbs. The weight of the pole was 583 lbs, so the corrected ultimate load was 3557 lbs. The experimental ultimate loads for the two types of specimens were expected to be similar. The ultimate load of Specimen 6A was within 2% of Specimen 6B; the ultimate load of Specimen 12A was within 7% of Specimen 12B. Figure 4-2 shows the average ultimate loads for the two groups. This figure shows that the specimen group with 12 bars of reinforcement provided for a 23% increase in the ultimate load over the group with 6 bars of reinforcement. Table 4-2 Experimental ultimate loads Specimen ID Recorded Ultimate Load (lbs) Specimen Weight (lbs) Corrected Ultimate Load (lbs) Average Ultimate Load (lbs) 6A B A B

65 Ultimate Load (lbs) Bars 12 Bars Figure 4-2 Average experimental ultimate loads for the two groups Deflection For all four specimens, the device used to measure tip deflection was a soft tape measure, so the zero reading varied from pole to pole, but was adjusted for later. After loading the pole to the point of eliminating the weight of the pole, the total deflection again needed to be adjusted. Also, allowing for pole rotation at the collars, the readings of the dial gauges were taken into account and adjusted for. These dial gauges had to be removed when the loading was at 75% of predicted failure to prevent damage to the equipment. An average deflection adjustment per pound was estimated past this point in order to have a more accurate representation of the deflection data. Figure 4-3 plots the load deflection curve for Specimens 6A and 6B. Figure 4-4 shows the large deflections of Specimen 6A prior to failure. 49

66 For Specimen 6A, as stated previously, the cracking load was 590 lbs, and at this load, the deflection was 0.8 inches. The curve for Specimen 6A is representative of a bilinear curve. Up to the cracking load, the deflection is relatively stiff. Past this point, the specimen becomes inelastic and deflects at a greater rate. The final deflection recorded at the ultimate load of 3000 lbs was 23.2 inches. For Specimen 6B, the cracking load was 600 lbs, and at this load, the deflection was 2 inches. In Figure 4-3, it can be seen that the curve for Specimen 6B is likewise a bi-linear curve, separated by the point at which the cracking load is reached. The deflection recorded at the ultimate load of 2960 lbs was 32.7 inches A 6B 3000 Load (lbs) Tip Deflection (in) Figure 4-3 Load deflection curves for Specimens 6A and 6B 50

67 Figure 4-4 Specimen 6A showing large deflections prior to failure Figure 4-5 shows the load deflection curves for the specimens with 12 bars of longitudinal reinforcement. Figure 4-6 shows the large deflections of Specimen 12A prior to failure. For Specimen 12A, the cracking load was 589 lbs, and at this load, the deflection was 0.9 inches. The bi-linear curve for Specimen 12A can be analyzed in two parts. Up to the cracking load, the curve is stiffly increasing. Past this point, the specimen becomes inelastic and deflects at a greater rate. The final deflection recorded at the ultimate load of 3789 lbs was 28.7 inches. For Specimen 12B, the cracking load was 717 lbs. At this cracking load, the deflection was 1.4 inches. Like all the specimens tested, it can be seen in Figure 4-5 that 51

68 the pole is relatively stiff until it reaches its cracking load. After the cracking load is reached, the pole deflects steadily at a faster rate than prior to this point. During testing, the last deflection reading, taken at 3217 lbs, was 20.3 inches. A tip deflection reading for Specimen 12B was not taken at the ultimate load; however, an educated prediction using the data estimated the deflection at the ultimate load for Specimen 12B to be 22.6 inches. An approximation of the deflection up to the failure load is included in the graph as a dashed line. Table 4-3 gives a summary of the deflection data stated in this section A 12B 3000 Load (lbs) Tip Deflection (in) Figure 4-5 Load deflection curves for Specimens 12A and 12B 52

69 Figure 4-6 Specimen 12A showing large deflections prior to failure Table 4-3 Summary of deflection data Deflection (inches) Specimen ID At Cracking At Ultimate 6A B A B

70 4.2.4 Crack Width Crack width of the critical crack was measured after each load for each specimen except for Specimen 6A. Load vs. crack width curves for the data available are shown in Figure 4-7. The graph presented is from the 2nd cycle of loading starting when the critical crack re-opened. The graph shows that as more load is applied, the crack width increases. The crack width measurements for Specimen 6B were taken of the first crack that appeared at 5.25 ft from the ground line. This may or may not have been the widest crack on the pole since it was further from the ground line, but since not every crack was measured, it is assumed to be the critical crack. For Specimen 12A, the measurements were taken of the first crack, which appeared at 6.5 inches from the ground line. For Specimen 12B, the measurements were taken of the first crack, which appeared at 2.2 ft from the ground line. All of the cracks measured were at different locations on the poles. Of course a crack that appeared later during testing might have been larger; however, since not all the cracks were measured, the first crack that appeared was taken to be the widest. It can be seen in Figure 4-7 that the maximum crack widths recorded for Specimens 6B and 12A were 16 mils, and the maximum crack width for Specimen 12B reached 25 mils. However, crack width data collection was terminated at different points for each specimen, so Table 4-4 shows a comparable summary of the crack width measurements taken at 50% of each specimen s respective ultimate load. 54

71 B 12A 12B Load (lbs) Crack Width (mils) Figure 4-7 Load vs. crack width for Specimens 6B, 12A, and 12B Table 4-4 Summary of crack width data Specimen ID 50% of Ultimate Load (lbs) Crack Width (mils) 6B A B Spacing Tabulated data of spacing at every load increment are given in Appendix C. A summary of selected points is stated within the text, and the final crack spacings for each specimen are summarized in Table

72 Spacing measurements were taken only at the end of the test for Specimen 6A, so most of the cracks had re-closed and were not recorded. It is believed that the spacing data for Specimen 6A are not representative of the actual spacing because of the ambiguity in the crack spacing data collection. Figure 4-8 shows the spacing of the cracking for Specimen 6A. Cracks appeared from the ground line, running along 16.4 ft of the pole. The spacing from the ground line to 4 ft was approximately 6 inches; and from 4 ft to 16.4 ft, the spacing increased to 8.3 inches. Figure 4-8 Spacing along Specimen 6A For the remaining poles, spacing measurements were taken throughout the testing process until 75% of the predicted ultimate strength was reached. For safety reasons, there were no measurements taken again until the pole was unloaded. For Specimen 6B, at 900 lbs (30% of ultimate load), spacing was approximately one foot. At 1000 lbs (33% of ultimate load), spacing was 6 inches. Figure 4-9 shows the final spacing of Specimen 6B. Cracks appeared from the ground line, running along 14.3 ft of the pole. The top 56

73 right picture shows the region from the ground line to 4 ft; the bottom left picture is the tip of the pole. The spacing from the ground line to 4 ft was 3.2 inches; and from 4 ft to 14.3 ft, the spacing was 4.7 inches. Figure 4-9 Final spacing along Specimen 6B For Specimen 12A, at load 789 lbs (21% of ultimate load), the spacing was about 6 inches. When the load reached 1589 lbs (42% of ultimate load), the spacing decreased to 5 inches. Cracks appeared from the ground line, running along 16 ft of the pole. The final spacing of Specimen 12A is shown in Figure The top right picture shows the region from the ground line to 4 ft; the bottom left picture is the tip of the pole. The spacing from the ground line to 4 ft was 3 inches; and from 4 ft to 16 ft, the average spacing was 3.9 inches. 57

74 Figure 4-10 Final spacing along Specimen 12A For Specimen 12B, at load 817 lbs (23% of ultimate load), the spacing was approximately one foot. At load 1417 lbs (40% of ultimate load), spacing was about 5 inches. The final spacing of the pole is shown in Figure 4-11, and it can be seen that the cracks appeared from the ground line to 14.5 ft on the pole. The top right picture shows the region from the ground line to 4 ft; the bottom left picture is the tip of the pole. The spacing from the ground line to 4 ft was 2.8 inches; and from 4 ft to 14.5 ft, the spacing was 3.4 inches. Figure 4-11 Final spacing along Specimen 12B 58

75 Figure 4-12 shows load vs. crack spacing for Specimens 6B, 12A, and 12B. As the load increases, spacing decreases as more cracks form along the pole. This figure shows the average crack spacing at various loads from the ground line to 4 ft from the ground line. This is the region that experienced the highest bending moment. Of the three specimens, Specimen 12A had the least crack spacing, which corresponds to the crack width data of it having the greatest crack width B 12A 12B Load (lbs) Crack Spacing (in) Figure 4-12 Load vs. crack spacing for Specimens 6B, 12A, and 12B 59

76 Table 4-5 Summary of crack spacing data Average Final Spacing (in) Specimen ID From GL to 4 ft From 4 ft to End 6A B A B Concrete Strain Figure 4-13 shows the load vs. compressive strain curve for Specimens 6A and 6B. The inconsistency between the two curves is a result of the variation in the testing processes described in Chapter 3. The Data Acquisition System had not been started until the second cycle of loading for Specimen 6B. For Specimen 6A, the maximum compressive reading shown by SG2 at the cracking load of 590 lbs was 89x10-6. The strain at the ultimate load of 3000 lbs was 2082x10-6, given by SG2. For Specimen 6B, the cracking load was 600 lbs. Unfortunately, the Data Acquisition System had not been started to collect data until the second loading cycle, so the concrete strain at the cracking load is not available. However, during the second loading cycle, the strain in the concrete at 600 lbs, registered by SG2, was 5x10-6. The strain at ultimate was given by SG2, reading 2016x

77 4000 6A 6B 3000 Load (lbs) Concrete Strain (10 ⁶). Figure 4-13 Load vs. concrete strain for Specimens 6A and 6B Figure 4-14 shows the load vs. compressive strain curve for Specimens 12A and 12B. The curves show that strain behaviors throughout the tests were very similar. For Specimen 12A, the cracking load was 600 lbs, and the concrete strain reading at this load shown by SG2 was 130.3x10-6. The concrete strain, given by SG2, was 2418x10-6 at the ultimate load of 3789 lbs. For Specimen 12B, the specimen was loaded to the cracking load of 717 lbs, where the concrete strain given by SG2 was 129x10-6. At the ultimate load of 3557 lbs, the compressive strain was 2385x10-6, given by SG2. 61

78 A 12B 3000 Load (lbs) Concrete Strain (10 ⁶) Figure 4-14 Load vs. concrete strain for Specimens 12A and 12B Table 4-6 highlights the critical points of the load strain curves for all the test specimens. The compressive concrete strains at cracking for Specimens 6A and 6B were not comparable to each other because of the inconsistencies between the two test procedures described in Chapter 3. However, the table does show that the concrete strains at ultimate for Specimens 6A and 6B were within 4% of each other. For Specimens 12A and 12B, the concrete strains at cracking were within 1% of each other. Also, for the group with 12 bars, the strains at ultimate were within 2% of each other. 62

79 Table 4-6 Summary of compressive concrete strain data Concrete Strain (10-6 ) Specimen ID At Cracking At Ultimate 6A B A B Failure Modes There were two modes of failure observed during testing: shear cracking and crushing of the concrete from compression. Figure 4-15 shows the shear crack that Specimen 6A developed between the supports at a load of 1060 lbs. Figure 4-16, taken after all load was released, shows the crushing of the concrete, which occurred at a load of 3000 lbs. This reaction occurred at the ground line; and the ultimate strain, reported by SG2, was 2082x

80 Figure 4-15 Shear crack between the supports of Specimen 6A Figure 4-16 Crushing of the concrete on Specimen 6A Specimen 6B experienced shear cracking and concrete compression. At load 1100 lbs, a shear crack appeared within the collar supports (see Figure 4-17). At the ultimate load of 2960 lbs, with a strain reading given by SG2 of 2016x10-6, the concrete began crushing at the collar (see Figure 4-18). 64

81 Figure 4-17 Shear crack between the supports of Specimen 6B Figure 4-18 Crushing of the concrete at the ground line of Specimen 6B Specimen 12A developed shear cracks between the supports at load 1989 lbs (see Figure 4-19). The specimen also experienced crushing of the concrete on two sections, first at load 3789 lbs at 4.5 ft from the ground line (about 0.75 ft long), and then a few load increments later at 2 ft from the ground line (about 1 ft long). The concrete strain at this ultimate point was 2418x10-6, given by SG2. Figure 4-20 shows the classic failure-- crushing on the compression face. 65

82 Figure 4-19 Shear cracks between the supports of Specimen 12A 66

83 Figure 4-20 Compression failure of Specimen 12A Specimen 12B experienced shear cracking between the supports, which occurred at load 1817 lbs (see Figure 4-21). Crushing of the concrete at the ground line on the compression face of the specimen occurred at load 3557 lbs. The concrete strain at this point was 2385x10-6, given by SG2. Also, crushing on the specimen s compression face at its midpoint occurred at 3802 lbs (see Figure 4-22). 67

84 Figure 4-21 Shear cracks between the supports of Specimen 12B Figure 4-22 Concrete compression failure of Specimen 12B at midpoint Each test showed the same sequence of events prior to failure: 1. first crack appeared 2. shear cracks formed between the supports 3. concrete crushed from 68