Standard Historical Last Updated: Dec 23, 2022
ASTM C1531-16

Standard Test Methods for In Situ Measurement of Masonry Mortar Joint Shear Strength Index

Significance and Use

5.1 This test method provides a means of evaluating the horizontal in-plane shear behavior of mortar joints in existing unreinforced masonry assemblies (see Note 1).

Note 1: The masonry mortar joint shear strength index obtained by this test method can be related to the masonry wall shear strength by relationships contained in referencing Codes and Standards. For example, formulas relating shear index to wall shear strength are found in Chapter A1 of the International Existing Building Code and Chapter 11 of the Seismic Evaluation and Retrofit of Existing Buildings, ASCE Standard ASCE/SEI 41. The user of this standard is cautioned that these shear strength relationships are typically empirical relationships based on tests of early 20th-century unreinforced brick masonry. These relationships typically assume that wall shear strength is limited by shear of the mortar joints rather than shear through the units

5.2 For hollow ungrouted or solid unit masonry construction the shear strength index is measured only for the mortar bed joints vertically adjacent to the unit being tested. When testing hollow ungrouted masonry construction, the shear strength index is based on the horizontal interface between the mortar and the test unit and the masonry above and below the test unit. In the case of multi-wythe construction, the measured mortar joint shear strength index is applicable only to the wythe in which the test unit is located; no headers shall exist immediately above or below the test unit. The contribution of any existing collar joint mortar to the measured shear strength index is neglected, and this may lead to an overestimate of the shear strength index (see Note 2).

Note 2: Some documents that reference this test method, including ASCE/SEI 41, include a reduction factor to account for the contribution of a filled collar joint to the measured shear strength index.

5.3 The test procedure listed for Method A may be conducted as an extension of Test Method C1197. The two-flatjack test, conducted in accordance with Test Method C1197, provides half of the required test setup for Method A. At the completion of both the C1197 and the C1531 Method A test, one would know the deformability of the masonry at the test and the relationship between the expected joint shear strength index and the normal compressive stress.


1.1 These test methods cover procedures for the determination of the average in situ mortar joint shear strength index in existing unreinforced solid-unit and ungrouted hollow-unit masonry built with clay or concrete units. Three methods are provided:

1.1.1 Method A (with Flatjacks Controlling Normal Compressive Stress)—For determining mortar joint shear strength index when the state of normal compressive stress at the test site is controlled during the test using the flatjack method described in Test Method C1197. Horizontal displacement of the test unit is monitored throughout the test. The test setup for Method A is shown in Fig. 1.

1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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Book of Standards Volume: 04.05
Developed by Subcommittee: C15.04
Pages: 7
DOI: 10.1520/C1531-16
ICS Code: 91.080.30