Assistant Professor of Civil Engineering, University of Texas at Arlington

Transcription

1 FRC Performance Comparison: Direct Tensile Test, Beam Type Bending Test, and Round Panel Test Shih Ho Chao (Presenting Author) Assistant Professor of Civil Engineering, University of Texas at Arlington Jae Sung Cho Doctoral Student, University of Texas at Arlington Netra B. Karki Doctoral Student, University of Texas at Arlington Nur Yazdani Professor of Civil Engineering, University of Texas at Arlington Presentation for Advances in Fiber Reinforced Concrete A Tribute to Gordon Batson at the ACI Fall 2008 convention in St. Louis, MO, November 2 6, 2008

2 OBJECTIVE To compare the performance of FRC materials when evaluated by three major types of material tests (Uniaxial ial Direct Tensile Test, Beam Type Tpe Bending Test, and Round Panel Test)

3 Uniaxial Direct Tensile Test This test can identify the key properties of FRC such as strain hardening or strain softening, elastic modulus, and stress versus strain relationships under tension, which is the fundamental property of FRCs [Naaman, Fischer, and Krstulovic Opara, 2007]. No standard test method available. High variation in post crack performance; generally needs to test many specimens to obtain reliable information.

4 Uniaxial Direct Tensile Test The high variation in post crack behavior is mainly due to the lack of control over the location of the crack (s)

5 Beam-Type Bending Test (Third-Point Loading, ASTM C1609) Widely used test method for evaluating the flexural performance of FRC. It is also the specified method in ACI for evaluating SFRC used for shear resistance in beams. ASTM standard C High variation in post crack performance; generally needs to test many specimens to obtain reliable information. Residual strength of a third point loaded beam shows poor reliability (C.O.V > 20%) [Bernard, 2002]

6 Beam-Type Bending Test (Third-Point Loading, ASTM C1609) The high variation in post crack bh behavior is mainly due to the lack of control over the location of the crack (s)

7 Centrally Loaded Round Panel Test (ASTM C1550) Diameter = 800 mm (31.5 in.) Thickness = 75 mm (2.95 in.)

8 Centrally Loaded Round Panel Test (ASTM C1550) Originally g ydeveloped for fiber reinforced shotcrete; can also be used for evaluating plate like members such as concrete slabs on grade. Panel experiences bi axial bending under central point load. ASTM standard C Low variation in post crack performance than beams (C.O.V is 4%~8%), thus a reliable test method [Bernard, 2002]. Cracks generally occur at same locations andpanel always breaks into three Cracks generally occur at same locations and panel always breaks into three segments upon failure.

9 Centrally Loaded Round Panel Test (ASTM C1550) Specimen size (diameter = 800 mm), plus the test setup, is too large to fit into most material testing machines. May lose the displacement measurement due to opened crack at large May lose the displacement measurement due to opened crack at large deflections.

10 Performance-Based Specifications Beam with Third Point Loading (ASTM C 1609) ACI > 0.9 P 1 L/300

11 Performance-Based Specifications Centrally Loaded dround dpanel l(astm C 1550) For example [Bernard, 2002]: Energy absorbed up to a deflection of 5 mm is used to indicate performance for applications in which crack control is important. Energy absorbed up to a deflection up to 40 mm is used to evaluate performance for applications where large cracks can be tolerated.

12 Experimental Program Mix proportion (by weight) Type 1 Cement Fly Ash (Class C) Sand Coarse Aggregate 20 mm (3/4") Water SSP104 Steel Fiber (or 0.04) Average Compressive Strength = 65.4 MPa (9.5 Ksi) Properties of Fiber Fiber Length (l) Diameter (d) Hooked-end steel fiber 1.6 in. (41mm) 0.03 in. (0.76mm) Aspect ratio (l/d) 53 Tensile Strength 150 ksi (1034 MPa)

13 Direct Tensile Tests

14 ASTM C 1609 Third Point Loading Bending Tests

15 ASTM C 1550 Round Panel Tests W 25mm (Vf = 1.5%) = 7260 J W 25mm (Vf = 0.5%) = 4760 J

16 Performance Comparison (Vf = 0.5%) Direct Tensile Test Degraded Strength after Cracking/Peak Strength = 15% Third Point Loading Bending Test Degraded Strength after Cracking/Peak Strength = 45% Round Panel Test Degraded dstrength th after Cracking/Peak kstrength th = 75%

17 Performance Comparison (Vf = 1.5%) Direct Tensile Test Elastic behavior up to first cracking, then followed by softening response Third Point Loading Bending Test Minor stress redistribution after first cracking, then followed by deflection softening response Round Panel Test Si ifi t t di t ib ti ft fi t ki Significant stress redistribution after first cracking (deflection hardening response up to 4 mm), then followed by deflection softening response

18 In Summary 1. The three major material evaluation methods (Uniaxial Direct Tensile Test, Third Point Loading Bending Test, and Round Panel Test) can give significant different performance for the same FRC material. 2. Further improvement of the material tests (especially Direct TensileTest Test and Third Point Loading Bending Test) to obtain higher level of reliability in post cracking performance is warranted.