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CHAPTER 2
Research Program and Findings
2.1 Research Approach 2.2.1 ASTM A1035 Reinforcing Steel
The focus of the experimental phase of this study was on The data obtained for A1035 bars in this study are gener-
the use of ASTM A1035 (2009) reinforcing steel since it cap- ally consistent with those reported by others as summarized
tures both behavioral aspects of interest (i.e., it has a very in Section 1.3.2. That is
high strength and no discernable yield plateau). The project
identified aspects of reinforced-concrete design and of the · Values of yield ( fy) and ultimate ( fu) strengths were consis-
AASHTO LRFD specifications that may be affected by the use tent from batch to batch and bar size to bar size. The average
of high-strength reinforcing steel. Design issues were priori- ultimate strength was fu = 163 ksi having a COV of only 3.9%
tized and an integrated experimental and analytical program across all specimens. The average rupture strain exceeded
was designed to develop the data required to permit the inte- 0.10 and had a COV of 28%.
gration of high-strength reinforcement into the LRFD speci- · The use of the ASTM A1035-prescribed 0.2% offset method
fications. This program included parametric, experimental, for establishing yield strength results in an average yield
and analytical studies in addition to a number of "proof tests" strength, fy = 129 ksi (COV = 4.6%). Stress corresponding
intended to validate existing LRFD provisions when applied to a strain of 0.007 resulted in the most consistent (COV =
to higher strength reinforcing steel. Table 3 provides a sum- 4.0%) value of yield strength, fy = 133 ksi.
mary of the primary aspects addressed in this study and the · Yield and ultimate strength values remained essentially
approach by which they were addressed. Subsequent sections unaffected by bar size.
of this chapter discuss each experimental and/or analytical · Regardless of the manner by which yield stress was deter-
program in turn. mined, the condition fu > 1.25fy was satisfied in all cases.
· Calculated values of modulus of elasticity, Es, determined
as secant modulus at 60 ksi were very consistent, averaging
2.2 Mechanical Properties 28,137 ksi (COV = 7.1%).
of Reinforcing Steel · All bars tested exhibited linear behavior through stress levels
Table 4 provides a summary of all reinforcing bar grades of at least 70 ksi.
and sizes tested as part of this study. Batch numbers are
underlined and the specimens in which each batch was uti- A Ramberg-Osgood (R-O) function was established for
lized are also indicated. Appendix A provides summaries of each batch of reinforcing steel that was used in a number of
all tests conducted and axial stress-strain curves obtained from subsequent analyses reported in this work. The R-O function
all bars tested. All tension tests were conducted in compliance is given in Equation 7 (Ramberg and Osgood 1943). The
with ASTM E8 and were conducted on full bar sections (not parameters, A, B, and C, established using a nominal value of
machined coupons). Es = 29,000 ksi are given in Appendix A. The general form of
As reported in Appendix A, A1035 bars and A496 and A82 the resulting R-O curve is shown in Figure 3.
wire exhibit no discernable yield plateau. A615 and A706
exhibit clearly defined yield plateaus and A955 stainless steel
1- A
grades exhibit a clear "abrupt change of stiffness," but no f = 29, 000 A + 1 f pu ( ksi
i) (Eq. 7)
defined plateau. 1 + ( B )C C
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Table 3. Research approaches taken with respect to various aspects of
this study.
Experimental
Aspect of Study Analytical Notes
Parametric Proof Tests
Mechanical properties 47 batches including 8 steel
X
of reinforcing steel grades and 13 bar sizes tested
Flexural 6 large-scale beam tests and
X X
reinforcement extensive parametric analysis
Fatigue X 2 large-scale beam proof tests
5 large-scale beam tests and 4
Shear reinforcement X
AASHTO Type I girders
Shear friction
X 8 full-scale proof tests
behavior
Compression
X Extensive analytical study
members
Bond and
X 18 full-scale proof tests
development
Deflections Considered X Integration of flexural data into
Crack widths with flexure X extensive parametric studies
Table 4. Reinforcing steel tested in this study and its use in specimens.
ASTM Bar
Batch Number and Test Specimen Use
Designation Size
1: SR1 to SR5; 3: Type I-1 to
A1035 #3 1B: P1035-3B 2: Type I-4
P1035-3A 1-3*
A1035 #4 1: all H; P1035-4A 1B: P1035-4B
1: F1; F3; D5-1; D5-2; all H; all
A1035 #5 2: F4; F6; D5-3; D5-4
fatigue
A1035 #6 1: F2 2: F5
A1035 #8 1: D8-1; D8-2; SR1 to SR4; all H 2: D8-3; D8-4; SR5
1: D5-1; D5-2, 2: D5-3; D5-4; 4: all H;
A615 #3 3: all P615
D8-1, D8-2 D8-3; D8-4 all fatigue
1: F1 to F3; 3: Type I-1
A615 #4 2: F4-F6 4: Type I-4 5: all P615
SR1 to SR4 to Type I-3
A706 #4 1: tension tests only 2: tension tests only
A706 #6 1: tension tests only 2: tension tests only
A706 #8 1: tension tests only 2: tension tests only
A496 D4 1: tension tests only
A496 D8 1: tension tests only
A496 D12 1: tension tests only
A496 D20 1: tension tests only
A496 D31 1: tension tests only
A82 W4 1: tension tests only
A82 W8 1: tension tests only
A82 W12 1: tension tests only
A955 (316) #4 1: tension tests only
A955 (316) #6 1: tension tests only 2: tension tests only
A955 (316) #8 1: tension tests only
A955 (2205) #4 1: tension tests only 2: tension tests only
A955 (2205) #6 1: tension tests only 2: tension tests only
A955 (2205) #8 1: tension tests only
A955 (N32) #4 1: tension tests only
A955 (N32) #6 1: tension tests only
A955 (N32) #8 1: tension tests only
Notes:
*
No test data are available for A1035 #3 batch 3 bars; no additional samples accompanied the bar order.
Test specimen labels:
D5-1, D5-2, D5-3, D5-4, D8-1, D8-2, D8-3, and D8-4: beam splice specimens; H: hooked specimens; F1,
F2, F3, F4, F5, and F6: flexural specimens; P615, P1035-4A, P1035-4B: shear friction specimens; SR1,
SR2, SR3, SR4, SR5: reinforced-concrete shear specimens; Type I-1, Type I-2, Type I-3, and Type I-4:
AASHTO Type I girder shear specimens.
