Testing 7-Wire Strand for Prestressed Concrete - The State of the Art

S equipment and some experience in the details of its use are required to obtain the necessary degree of accuracy in testing 7-wire prestressed concrete strand, ASTM A416 is the Standard Specification for Uncoated 7-Wire StressRelieved Steel Strand for Prestressed Concrete. The Supplement to ASTM A416 covers Low-Relaxation 7-Wire Strand. AASHTO M203 is the same as ASTM A416. Testing equipment and procedures are covered by Section VII of ASTM A370. Definitions of terms common to 7-wire strand and prestressed concrete are given at the end of this paper. ASTM A416 addresses the following_ properties for stress-relieved strand: Section 3.1 Strand — The requirement of "... a center wire tightly enclosed by six helically placed outer wires .. ." means that the outer wires shall be neither overpreformed nor underpreformed. See comments near the end of "Modulus of Elasticity" and "Definitions." Section 5 Materials and Manufacture — This section does not require action by the testing agency. Subsequent tests will show whether or not the requirements of Section 5 have been met. Section 6.1 Breaking Strength— Minimum breaking strengths are tabulated in ASTM A416. Special problems in testing strand are discussed later in this paper under "Gripping a 7-Wire Strand." Section 6.2 Yield Strength — If a load-elongation curve is plotted, the yield strength can be read directly from it. If not, the yield strength can be obtained by the test described in Section 6.2.2 using equipment of the type dis-