BEHAVIOR OF HIGH PERFORMANCE STEEL AS SHEAR REINFORCEMENT FOR. Matthew S. Sumpter, Sami H. Rizkalla, and Paul Zia

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1 BEHAVIOR OF HIGH PERFORMANCE STEEL AS SHEAR REINFORCEMENT FOR CONCRETE BEAMS Matthew S. Sumpter, Sami H. Rizkalla, and Paul Zia Sami H. Rizkalla, sami_rizkalla@ncsu.edu (corresponding author), Matthew S. Sumpter, Matt.Sumpter@hotmail.com, Paul Zia, p_zia@yahoo.com, North Carolina State University Constructed Facilities Laboratory (CFL) 1 Campus Shore Dr. Raleigh, NC -, USA Author s Biographies ACI Member Matthew S. Sumpter received his B.Sc. and M.Sc. degrees from North Carolina State University, Raleigh, NC in and, respectively. Currently he is a practicing engineer in the Raleigh, NC area. ACI Fellow Sami H. Rizkalla is a Distinguished Professor of Civil and Construction Engineering in the Department of Civil, Construction, and Environmental Engineering, North Carolina State University. He serves as the Director of the Constructed Facilities Laboratory and NSF I/UCRC in Repair of Structures and Bridges at North Carolina State University. He is a fellow of ACI, ASCE, CSCE, EIC, and IIFC. An ACI honorary member and past president Paul Zia is a Distinguished University Professor Emeritus at North Carolina State University. He served as ACI President in 1, and is a member of several ACI committees including ACI, High-Strength Concrete; joint ACI- ASCE, Prestressed Concrete; ACI, Shear and Torsion; the Concrete Research Council; and TAC Technology Transfer Committee, serving as chairman of its ITG-. 1

2 1 1 ABSTRACT This paper describes the behavior of high performance steel as shear reinforcement for concrete beams. High performance (HP) steel is characterized by enhanced corrosion resistance and higher strength in comparison to ASTM A 1-1 Grade steel. The HP steel selected for this research is commercially known as Microcomposite Multistructural Formable (MMFX) steel, and conforms to ASTM A -. Nine reinforced concrete beams were constructed using No. (No. ) longitudinal bars and No. (No. ) stirrup bars. The main variables considered in this study are the stirrup spacing and type of reinforcing steel material. Test results indicate that using MMFX steel reinforcement increases the shear capacity and enhances the serviceability in terms of strength gain and reduction of shear crack width. Current design codes can conservatively be used for the design of HP steel using a yield strength of ksi ( MPa). Keywords High performance; high strength; concrete beams; shear; steel INTRODUCTION There is a growing interest in the use of high strength materials to reduce dead loads and consequently increase span length. However, not nearly enough research has been conducted on high performance steel in comparison to high strength concrete. High performance steel 1 conforming to ASTM A - has higher strength and better corrosion resistance in 1 1 comparison to conventional ASTM A 1- Grade 1 steel. As a result, the use of HP steel could reduce the amount of required reinforcement as well as enhance the corrosion resistance. This could potentially reduce the costs of material and labor for future structures and relieve reinforcement congestion. The commercially available Microcomposite Multistructural Formable (MMFX) steel, which conforms to ASTM A -, was chosen for this study. The

3 objective of this study was to determine the feasibility of using high performance steel as shear reinforcement for concrete members, particularly the member behavior under overload condition with the steel being at high stress levels. The research consisted of evaluating the behavior of beams reinforced with MMFX stirrups and longitudinal reinforcement, determining the capability of current design codes to predict the shear strength, assessing the capability of detailed analysis to predict the shear strength, and making design recommendations. 1 1 RESEARCH SIGNIFICANCE The behavior of concrete members subjected to shear and reinforced with high performance steel is not well defined. One concern is whether the high stress levels induced in the reinforcement may cause excessive cracking in the concrete. Another concern is how accurately the current design codes can predict the shear strength. This research complements the ongoing efforts at NC State University and elsewhere to provide design guidelines for the use of high performance steel in concrete structures EXPERIMENTAL INVESTIGATION Test Specimens The experimental program consisted of nine reinforced concrete beams divided into three main categories according to the type of reinforcing steel. The type of steel includes conventional 1 ASTM A 1- Grade 1 steel and ASTM A - steel. Within each category, the 1 1 stirrup spacing varied to reflect a minimum, intermediate, and maximum level of shear reinforcement as allowed by the ACI Code 1-. All beams had cross-sectional dimensions of 1x1 in. (x mm), with a total length of 1 feet (. m). In addition, all beams were provided the same longitudinal reinforcement ratio in order to keep the effect of dowel action constant. As a result, changes in the observed behavior could be attributed to either the high

4 performance steel or to the stirrup spacing. Two layers of three No. (No. ) bars were used in the bottom and one layer of three No. (No. ) bars was used in the top of the beam, with all stirrups of No. (No. ) bar size. The cross-section is shown in Figure 1. All transverse reinforcement contained closed stirrups with hooks extended by a distance of six bar diameters past the bend, as specified by the ACI Code Section.1. Longitudinal steel in the bottom layers were designed with a º hook at the end of the bar in order to ensure proper anchorage. The test matrix given in Table 1 labels beams using three parameters: type of longitudinal steel, type of transverse steel, and the spacing of the transverse steel in inches. The letter C indicates conventional Grade steel while M represents MMFX steel. For example, beam C-M- contains conventional Grade longitudinal steel and MMFX stirrups spaced inches ( mm) center to center. Casting and testing was organized into three beam sets, where each set contains three specimens and differs based on the transverse reinforcement spacing. Within a given beam set, the specimens change based on the combination of reinforcing steel material used. Set 1 beams have a shear span to depth ratio (a/d) equal to., while beams in Set and Set have a shear span to depth ratio equal to.. Material Properties The nine beams were fabricated using normal-weight concrete with an aggregate size of / in. (. mm). The average concrete compressive strengths at the day of testing ranged from - psi (- MPa). The concrete compressive strength was determined by testing x inch (x mm) cylinders, which were cast for each beam set and cured under the same conditions as the beams. Tension coupons of the HP and Grade steels were tested according to ASTM A -, and the stress-strain relationships are shown in Figure. The MMFX steel experienced linear behavior until a stress level of ksi ( MPa), followed by a negligibly small reduction

5 in the elastic modulus up to ksi, and then non-linear behavior to a maximum strength of 1 ksi ( MPa) at % strain. The yield strength, based on the.% offset method, is ksi ( MPa). The yield strength of the Grade was determined to be ksi ( MPa). Test Setup and Instrumentation The test setup was designed so that each beam could be tested twice. It consisted of a single applied load located closer to one end of the beam, with a portion of the beam cantilevered off the far support. After completion of the first test, the beam was rotated to test the remaining unstressed portion. Figure shows the test setup configuration for Sets 1,, and, respectively, while Figure is a photograph of a typical test. The loads were applied using a -kip ( kn) capacity MTS hydraulic actuator supported by a steel testing frame, which was securely anchored to the strong floor. The load was then transferred through two steel loading plates, which measured 1 thick and wide (.x1 mm). The beam was supported by steel plates measuring 1 thick and wide (.x1 mm), one with a steel roller in between, which served as a pin and roller condition for the tested beams. The support was located on the top of concrete blocks, which were securely anchored to the strong floor. The applied load was measured by a load cell while the crack widths, steel strains, and deflection were measured using PI gages, electrical resistance strain gages, and string pots, respectively. The PI gages included two rosettes attached to the side of the beam to measure the crack widths and corresponding strains. Each rosette consisted of three mm (. in.) PI gages with one placed horizontally, one placed vertically, and one placed diagonally at a º angle. Two mm (. in.) PI gages were also placed on the top surface of the beam, at either side of the loading plate, to measure the top concrete strain. An additional two mm (. in.) PI gages and two string pots were placed on the bottom surface of the beam, directly below the load point,

6 to measure the bottom concrete strain and deflection, respectively. Figure shows the locations of the instrumentation TEST RESULTS Test results were examined to determine the behavior of beams reinforced with high performance steel as transverse and longitudinal reinforcement compared to the behavior of beams reinforced entirely with Grade steel. Detailed test results and discussion can be found elsewhere. The nine beams were subjected to load that increased at approximately 1 kip (. kn) increments until failure. Failure was identified when the measured maximum load had dropped by more than %. Table shows the ultimate shear load for each beam, V exp. Shear Load-Deflection Behavior The shear load-deflection curves of Set 1 beams are found in Figure, with the maximum measured deflections approximately equal to. in. (1. mm). Figure shows the shear load- deflection curves for Set beams, which had maximum measured deflections of. in. (. mm). These relatively small deflections are due to the type of failure, which was primarily in shear. The experimental results also indicate that the stiffness of a beam set was almost identical, regardless of the type of reinforcement. In general, increasing the transverse reinforcement ratio, by reducing the stirrup spacing, increases both the load carrying capacity and deflection at failure. However, using different types of longitudinal and transverse steel within a given beam set only affects the ultimate load carrying capacity. Shear Load-Transverse Strain Behavior Strain in the transverse (vertical) direction was measured using vertical PI gages that were part of the strain gage rosette configuration shown in Figure. The shear load vs. transverse strain relationships for beam Set are shown in Figure, which is typical behavior of all sets. The

7 intersection of the tangent of the load-strain curve has been used to identify the initiation of the first shear crack. This load level estimated the concrete contribution to the overall shear resistance of the beam, V c,exp. In general, the measured shear cracking load for all tested beams ranged from - kips (1-1 kn), which is approximately '. fc bd using the measured concrete compressive strength at the time of testing each beam. The figure also shows two solid horizontal lines representing the concrete contribution, V c, based on the average measured concrete strength and the steel contribution, V s, based on a yield strength of ksi for the stirrups. The terms V c and V s were calculated based on ACI 1- equations - and -1, respectively. Figure indicates that the nominal shear strength, V n ( V c + V s ), is much lower than the measured values, which highlights the conservatism built into the code equations for shear. Beam sets with a higher transverse reinforcement ratio were slightly less conservative. Behavior of beam C-C- was approximately linear up to kips ( kn), which corresponds to yielding of the stirrups followed by non-linear behavior. Failure of C-C- occurred immediately after the yielding of the longitudinal rebar. This behavior is illustrated in Figure, which shows the shear load versus the longitudinal strain and transverse strain as measured by strain gages and PI gages, respectively. Yielding of both the transverse and longitudinal steel allowed significant deformation at the nodal zone, and lead to crushing of the concrete at the tip of the strut as shown in Figure. Behavior of beam C-M- remained fairly linear until the shear load level of kips ( kn), where the capacity appears to plateau. This is due to the characteristics of the MMFX steel, which has a much higher yield strain and strength in comparison to Grade steel. Beam M-M-, reinforced entirely with MMFX steel, behaved similarly to C-M- although was better

8 1 1 able to control crack width at a given load level in comparison to the other two beams. The high level of strain induced in the transverse and longitudinal steel allowed the compression strain in the diagonal direction to reach its ultimate value and lead to crushing of the concrete at the nodal zone, as depicted in Figure. This mechanism is demonstrated by the non-linear behavior, shown in Figure, before failure. These results indicate that failure was mainly due to the concrete and did not fully utilize the strength of MMFX shear reinforcement beyond ksi ( MPa). Crack Width Behavior Currently, the ACI Code neither limits the size of shear cracks nor provides a definitive guideline for the maximum flexural crack width. However, commentary in the current ACI Code 1- Section. suggests a value of.1 in. (.1 mm) for the maximum flexural crack, which was therefore used in this study as the limiting value. The geometry of two PI gages was used in order to determine the shear crack width, as detailed by Shehata in the following equation: ( D V g ct) ( V g ct) w= Δ Δ.l ε sinθ + Δ.l ε cosθ where ΔD, ΔV, Δ H are the measured PI gage readings in the diagonal, vertical, and horizontal directions, respectively, θ is the measured crack angle to the horizontal beam axis, l g is the gage length of the PI gage ( mm =. in.), and ε ct is the maximum tensile concrete strain (.1x - ). The average crack width, w, can be calculated based on the summation of crack width and the number of cracks passing through the PI gage rosette. In this analysis, the service loads are assumed to be % of the nominal shear capacity based on the ACI Code 1- with a yield strength of ksi (1 MPa). This corresponds to a service load stress of ksi ( MPa) in the stirrups.

9 The shear load-crack width relationships for beams with in. ( mm) stirrup spacing are given in Figure, which is typical behavior for all beams. The service load level based on % of V n,aci is also given in the figure. Results indicate that all crack width values are less than the ACI limit of.1 in. (.1 mm), regardless of the setup type or beam type. The two beams containing MMFX stirrups showed very small crack widths at the service load level in comparison to C-C-. This suggests that the direct replacement of conventional steel with MMFX steel significantly reduces the shear crack width at service load levels. The enhanced serviceability is believed to be from the better bond characteristics of MMFX steel due to their rib configuration. In comparison to conventional Grade steel, the ribs on typical MMFX bars show increased deformation as calculated from the relative rib area. Consequently, this would result in smaller cracks which are more widely dispersed. Since test results indicate that MMFX stirrups reduce the shear crack width at a service stress of ksi ( MPa), using high strength steel could allow for an increased service load level. Figure 1 shows a typical shear load-crack width relationship using a stirrup yield stress of ksi (1 MPa), which is % of the ksi ( MPa) yield strength proposed for MMFX steel. Results indicate that using a service load corresponding to a service stress of ksi (1 MPa) is acceptable for beams reinforced with MMFX stirrups. All beams reinforced with MMFX steel had smaller crack widths than beams reinforced entirely with conventional steel. In general, M-M beams had smaller crack widths at the higher service load level than C-M beams, although both types were within the.1 inch (.1 mm) limit. Beam C-C- had measured crack widths slightly exceeding the specified limit, which shows that a higher service stress level cannot be achieved for beams entirely reinforced with conventional steel without concerns for unacceptable cracking.

10 Mode of Failure Despite of the different shear span to depth ratios, every beam exhibited almost the same behavior during testing and up to failure. As expected, decreasing the amount of stirrup spacing increased the overall shear capacity of the member. Similarly, reinforcing the member with longitudinal MMFX rebars provided additional flexural strength and increased the shear compression capacity. The type of transverse steel had less influence compared to the type of longitudinal steel, although did create a slight increase in shear capacity. The typical mode of failure observed was shear compression failure, regardless of the type or ratio of transverse reinforcement. Failure was controlled by crushing of concrete in the nodal zone of the diagonal strut, which did not fully utilize the strength of the MMFX stirrups beyond ksi ( MPa). This behavior suggests that pairing high strength concrete with high performance steel would take better advantage of the high strength characteristics of the MMFX steel. For C-C beams, failure occurred after yielding of both the longitudinal and transverse reinforcement, which allowed significant deformation in the nodal zone and lead to crushing of the concrete at the tip of the diagonal strut. Beams reinforced entirely with MMFX steel, M-M, behaved similarly to C-M beams although were better able to control crack width at a given load level due to the high performance longitudinal steel. For both C-M and M-M beams, failure occurred once the compression strain in the diagonal direction reached its ultimate value and led to crushing of the concrete at the nodal zone. Cracking Pattern Initiation of the first flexural cracks typically occurred at an applied load level of 1 kips (. kn). Increasing the applied load caused propagation of the cracks and initiation of new flexural cracks along the span. Further load increase extended the existing flexural cracks into flexure-

11 shear cracks, as shown in Figure 1. After formation of the flexure-shear cracks, increasing the applied load caused an extension of the shear cracks and an increase of crack width within the span. In all cases, failure occurred due to local crushing of the concrete at the tip of the compression strut, which was close to the edge of the loading plate as shown in Figure. In general, failures of the tested beams were not explosive in nature. The applied load was maintained for significant deformation up to failure, as evidenced by the measured strain plateau for all beams. The cracking pattern at each load level was almost the same for all three beams of a given set. However, beams reinforced entirely with MMFX longitudinal and transverse steel typically had a larger number of small cracks dispersed along the span length than the other beams. This further suggests that the use of MMFX steel has the capability to distribute cracks and control crack width in comparison to conventional Grade reinforcement. Effect of the Steel Type The effect of the steel type is shown in Table by comparing the measured maximum shear load, V exp, for beams with the same stirrup spacing and thus, the same transverse reinforcement ratio. In this table, the measured shear stress was normalized with respect to the square root of the 1 concrete compressive strength, ' f c, to eliminate the effect of different concrete strengths. The 1 nominal shear stress for each beam, ν, was calculated as ν = V exp bd, where b is the width of the 1 beam taken as 1 in. ( mm), and d is the depth from the top compression fiber to the centroid of the steel and taken as 1 in. ( mm). The relative shear strength to ' f c for each 1 beam ranges from ' f c to ' f c, which is close to the maximum shear capacity range allowed by the ACI Code for a reinforced concrete section. Therefore, the current limit of

12 ' f c suggested by the ACI Code should be maintained for high performance steel since failure was controlled by the concrete compressive strength rather than yielding of the stirrups. The column showing % Relative Increase relates the percentage increase in shear strength of a beam to the previous beam in the same set. The column showing % Total Increase relates the percentage increase in shear strength of beams C-M and M-M, respectively, to beam C-C within the same set. In general, test results indicate very little increase in the shear carrying capacity due to the use of high strength stirrups. This behavior is due to the fact that Grade steel was substituted bar for bar in the design, rather than utilizing the high strength of MMFX steel. Also, the shear failure was controlled by crushing of the concrete strut and not yielding of the stirrups. The slightly higher strength capacity measured for the second and third sets were due to the longer shear span to depth ratio (a/d) used for testing. The use of a larger a/d ratio increases the ratio of the applied moment to shear, therefore making shear less critical. This load configuration allows more utilization of the shear reinforcement and causes a slight increase of shear resistance within the beam. In all beam sets, substitution of MMFX longitudinal reinforcement provided additional flexural resistance and therefore increased the overall capacity before failure. Effect of Stirrup Spacing To identify the effect of stirrup spacing, the normalized shear stress versus the measured transverse strain for beams completely reinforced with MMFX steel is shown in Figure 1, which is typical of all beam type behavior. In general, the behavior indicates that using a closer stirrup spacing increases the overall shear capacity of the beam. Furthermore, using a smaller spacing reduces the transverse strain at any given load level. 1

13 Code Predictions The maximum measured shear load, V exp, was compared to the predictions using the ACI 1- Code, the Canadian Standards Association (CSA A.-) Code, and AASHTO LRFD Bridge Design Specifications, and is given in Table. Based on the analysis, the CSA code gives the closest predictions to the measured shear capacity. The average measured-predicted shear ratio for the CSA is 1., compared to 1. for the ACI-1 and 1. for the AASHTO. However, using ACI equation - for the concrete contribution, V c, resulted in predictions almost equal to those of the CSA. It should be noted that all predictions for beams reinforced with MMFX stirrups used a yield strength of ksi ( MPa). The results indicate that the ACI 1- is capable to conservatively predict the shear capacity of beams reinforced with MMFX stirrups up to a yield strength of ksi ( MPa). Most of the current codes do not adequately account for the yield strength of the longitudinal reinforcement. This is evidenced by the predictions of the M-M shear strengths, which are shown to be equal to, or less than, C-M. While the codes can only discern differences between the two beams based on the concrete compressive strength, measured values indicate that beams with MMFX longitudinal rebars have higher strengths than beams reinforced with conventional rebars as given in Table ANALYTICAL MODELING The nine reinforced concrete beams were modeled using the program Response (RK). This program allows users to analyze beams and columns subjected to moment, shear, and axial loads comprised of virtually any type of beam geometry, material types, and material properties. The fundamental theory supporting the program is the Modified Compression Field Theory 1. In 1

14 order to accurately model the material properties of the reinforcing steel, the actual stress-strain characteristics of both the conventional Grade and MMFX steels were input to the program. Member response analysis and sectional analysis were both used in RK to predict the behavior of the beams. Member response calculates the full member behavior including the deflection and curvature along the member length, as well as predicted failure modes. The analysis was performed by specifying the length subjected to shear and any constant moment region. For this research, the constant moment region was zero while the shear span was,, and (, 1, 1 mm) for Set 1, Set, and Set, respectively. When predicting the strength of a beam in sectional analysis, the key parameter is selecting the location of the section. As recommended by Bentz 1, that distance was selected at a distance d v from the concentrated load, which can be taken as.d. The regions within a length d v to a discontinuity (D-region) do not follow the strain compatibility assumption. The Modified Compression Field theory, and consequently Response, assumes that a linear strain relation within the section is applicable. As a result, analysis on sections taken within the D-region will result in very conservative predictions. The predicted ultimate shear load based on Response analysis is shown in Table. The measured-predicted shear load ratio average is 1.1 with a standard deviation and coefficient of variation equal to.1, which is more accurate than the design codes predictions. Response is more accurate since it takes into account the additional resistance provided by the MMFX longitudinal reinforcement, and relies solely on the MCFT for analysis. 1 CONCLUSIONS Based on the experimental program, analysis of the data, and modeling of the behavior, the following conclusions have been reached: 1

15 Direct replacement of conventional Grade stirrups with MMFX stirrups increased the shear load capacity of flexural members and enhanced the serviceability in terms of distributing cracks and reducing crack width. This behavior may have been due to the better bond characteristics of the MMFX steel because of the rib configuration being different than Grade steel.. Direct replacement of conventional Grade longitudinal reinforcement with MMFX longitudinal reinforcement further increased the shear strength and enhanced serviceability.. Shear crack widths were within the allowable limit of.1 in. (.1 mm) using an increased service stress level of ksi (1 MPa) for all beams reinforced with MMFX steel.. The ACI, CSA, and AASHTO LRFD design codes can conservatively predict the shear behavior of concrete beams reinforced with high performance steel using a yield strength of ksi ( MPa).. The maximum shear resistance of a concrete section recommended by the ACI Code, ' fcbd, w should be maintained for high performance steel reinforcement.. Current research could not fully utilize the strength of MMFX stirrups beyond ksi ( MPa) since the failure was controlled by crushing of the concrete in the strut. Pairing high strength concrete with MMFX steel could provide a better utilization for the high performance steel.. Detailed analysis using the Modified Compression Field Theory, included in Response, provides accurate predictions of the overall shear strength of concrete members reinforced with HP steel. 1

16 ACKNOWLEDGEMENTS The authors would like to thank the MMFX Technologies Corporation for their financial support of this research project, and for supplying the reinforcing steel. Special thanks are also extended to Aruna Munikrishna for taking part in the fabrication and testing phases of the program. Finally, the authors extend thanks to the staff at the Constructed Facilities Laboratory, including Jerry Atkinson, Bill Dunleavy, and Amy Yonai for their invaluable help REFERENCES 1. ASTM A 1/A 1M- (). Standard Specification for Deformed and Plain Carbon-Steel for Concrete Reinforcement. ASTM International: West Conshohocken, PA.. ASTM A /A M- (). Standard Specification for Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement. ASTM International: West Conshohocken, PA.. ACI Committee 1 (). Building Code Requirements for Structural Concrete (ACI 1-) and Commentary (1R-). Farmington Hills: American Concrete Institute.. ASTM A - (). Standard Test Methods and Definitions for Mechanical Testing of Steel Products. ASTM International: West Conshohocken, PA.. Sumpter, M.S. (). Behavior of High Performance Steel as Shear Reinforcement for Concrete Beams. Masters thesis, North Carolina State University: Raleigh, NC.. Shehata, E.F.G. (1). Fibre-Reinforced Polymer (FRP) for Shear Reinforcement in Concrete Structures. PhD thesis, University of Manitoba: Winnipeg, Manitoba, Canada. 1

17 Seliem, H.M.A. (). Behavior of Concrete Bridges Reinforced with High- Performance Steel Reinforcing Bars. Ph.D thesis, North Carolina State University: Raleigh, NC.. Nilson, A.H., Darwin, D., & Dolan, C.W. (). Design of Concrete Structures (1th ed.). New York: McGraw Hill.. CSA Committee A. (). Design of Concrete Structures, CSA A.-. Rexdale, Ontario, Canada: Canadian Standards Association.. AASHTO LRFD (). Bridge Design Specifications and Commentary (rd Ed.). Washington, DC: American Association of State and Highway Transportation Officials.. Bentz, E.C. (). Response. Retrieved August,, from: 1. Collins, M.P., & Vecchio, F.J. (1). The Modified Compression Field Theory for Reinforced Concrete Elements Subjected to Shear. ACI Journal, v., n., pp Bentz, E.C. (). Sectional Analysis of Reinforced Concrete Members. PhD thesis, University of Toronto: Toronto, Canada. 1

18 TABLES Table 1: Specimen test matrix Beam ID Spacing, in (mm) a/d f c ' psi (MPa) Set 1 Set Set C-C- (.) C-M- (1). (.) M-M- (.1) C-C- (.) C-M- (). (1.) M-M- (.) C-C- (.) C-M- (.). (.) M-M- (.) Table : Test results and the effect of the steel type Beam ID V exp kips (kn) ν psi (MPa) ν / f'c % Relative Increase % Total Increase C-C- 1. () (.). - - C-M-.1 () (.1)..%.% M-M-. () 1 (.)..%.1% C-C-.1 () (.). - - C-M- 1. () (.)..%.% M-M- 1 () (.)..% 1.% C-C-.1 () 1 (.). - - C-M-. () (.)..%.% M-M- () (.)..%.% 1

19 Table : Design code predictions ID V n kips (kn) ACI CSA LRFD V exp / V n V n kips (kn) V exp / V n V n kips (kn) V exp / V n Set 1 Set Set C-C-.1 (1) 1.. () 1.. (1) 1. C-M-. (1) 1.. () () 1. M-M-. () 1.1. () 1.. () 1. C-C-. () 1.1. () 1.1. () 1. C-M-. () 1.1. () 1.. () 1. M-M-. () () 1.. () 1. C-C-. () 1.. (1) 1.1. () 1. C-M-. () 1. ().. (1) 1. M-M-. () 1. 1 () 1.. (1) 1.1 Average Standard Deviation Coefficient of Variation Table : Response results Beam ID V n kips (kn) V exp / V n Set 1 Set Set C-C-. () 1. C-M-. ().1 M-M- (). C-C- 1. (1) 1. C-M-. (). M-M- (). C-C-. () 1. C-M-. () 1. M-M- (). Average 1.1 Standard Deviation Coefficient of Variation.1.1 1

20 FIGURES # (No.) # (No. ) 1" ( mm) " (1 mm) 1" ( mm)." (. mm) Figure 1: Beam cross-section 1 1 MMFX 1 Stress (ksi) Grade Stress (MPa) Strain Figure : Stress-strain relationship of HP and Grade steel

21 P # (No. ) Bars # (No. ) Stirrups 1" ( mm) " ( mm) " (1 mm) x y 1" ( mm) " (1 mm) x y Set 1 1 ( mm) ( mm) Set ( mm) ( mm) Set ( mm) ( mm) Figure : Test setup configuration Figure : Typical test setup picture 1

22 P1- P- P- Strain gages Pi-gage S1- Pi-gage rosette P- P- String Pot (a) Side view D1- D1- (b) Crosssection view (c) Legend 1 Figure : Instrumentation Deflection (mm). 1. M-M- Shear Load (kips) C-C- C-M- Shear Load (kn) Deflection (in) Figure : Shear Load-Deflection relationship, Set 1

23 Deflection (mm). 1. C-M- M-M- Shear Load (kips) C-C- Shear Load (kn) Deflection (in) 1 Figure : Shear Load-Deflection relationship, Set M-M- Shear Load (kips) Yielding C-C- V s C-M- Shear Load (kn) 1 V c Transverse Strain Figure : Typical Shear Load-Transverse Strain relationship, Set

24 Longitudinal Strain Shear Load (kips) Transverse Strain Shear Load (kn) 1 C-C Strain Figure : Shear Load-Strain relationship for beam C-C- (a) Typical diagonal crack at failure (b) Concrete crushing at nodal zone Figure : Typical failure pictures

25 Crack Width (mm) M-M- Crack width =.1" Shear Load (kips).v n,aci Shear Load (kn) C-M- Crack width =.1" C-C- Crack width =." Crack Width (in) 1 Figure : Shear Load-Crack Width relationship, Set (f s = ksi) Crack Width (mm) M-M- Crack width =." Shear Load (kips) C-M- Crack width =." C-C- Crack width =.1".Vn,ACI 1 Shear Load (kn) Crack Width (in) Figure 1: Shear Load-Crack Width relationship, Set (f s = ksi)

26 Figure 1: Flexure-shear cracking M-M- (a/d =.) M-M- (a/d =.) M-M- (a/d =.) Transverse Strain Figure 1: Normalized Shear Stress-Transverse Strain