Universität Stuttgart Institut für Werkstoffe im Bauwesen Crack moving test R. Eligehausen

Universität Stuttgart Institut für Werkstoffe im Bauwesen Crack moving test  Purpose of test: Evaluate the performance of anchors located in a crack whose width is cycled. The test conditions are intended to model an anchor located in the cracked zone of a reinforced concrete member which is loaded and unloaded during the service life.

Universität Stuttgart Institut für Werkstoffe im Bauwesen Increase of anchor displacements as a function of number of crack openings, expansion anchor type 1, Seghezzi (1985)

Universität Stuttgart Institut für Werkstoffe im Bauwesen p g M p + M g Beam / Slab on two supports

Universität Stuttgart Institut für Werkstoffe im Bauwesen Load case gLoad case p MgMg MpMp M p + M g Continous beam / slab

Universität Stuttgart Institut für Werkstoffe im Bauwesen Relationship between moment and crack width (schematic)

Universität Stuttgart Institut für Werkstoffe im Bauwesen Example of the development of the crack widths  w 1 and  w 2 during crack cycling (mean of 5 tests, bonded anchor, M8)

Universität Stuttgart Institut für Werkstoffe im Bauwesen Example of the development of the crack widths  w 1 and  w 2 during crack cycling (mean of 5 tests, bonded anchor, ¾")

Universität Stuttgart Institut für Werkstoffe im Bauwesen Example of the development of the crack widths  w 1 and  w 2 during crack cycling (mean of 5 tests, expansion anchor, ¾")

Universität Stuttgart Institut für Werkstoffe im Bauwesen Open the crack by a crack width w 1 = in. (0.3 mm). Apply a sustained tensile load of N w as calculated from Eq. (8-1). Cycle the crack width between the maximum crack opening width of w 1 = in. (0.3 mm) and the initial minimum crack width of w 2 = in. (0.1 mm). Open and close the crack 1000 times at a maximum frequency of 0.2 Hz. During cycling of the crack, keep the crack width w 1 constant. The crack width w 2 is expected to increase during the test (Fig. 8.1). The difference between the maximum and minimum crack widths during the 1000 cycles shall be at least in. (0.1 mm). If, at any time during the test, the value of w 1 – w 2 falls below in. (0.1 mm), either reduce the lower-bound load, increase the upper-bound load, or change both, until the minimum value of w 1 – w 2 = in. (0.1 mm) is restored. Note that an increase in the upper-bound load corresponds to an increase in the maximum crack width w 1 beyond in. (0.3 mm). Requirement according to ACI and AC193

Universität Stuttgart Institut für Werkstoffe im Bauwesen Requirement according to ACI and AC308 While maintaining the static load on the anchor within 5% of N w, cyclically load the test member as required to cause the crack width to alternate continuously between Δw 1 and the lower crack width Δw 2 = in. (0.1 mm) where Δw 2 is additive to the initial width of the crack as measured after installation of the anchor but prior to loading of the anchor. Open and close the crack 1,000 times at a maximum frequency of approximately 0.2 Hz. The crack width test requirements are illustrated in Figure 8.1. During crack cycling, adjustment of the force required to maintain the crack opening width Δw 1 constant shall be permitted. The minimum load applied to the test member shall be held constant during the crack cycling portion of the test. The crack opening width Δw 2 shall be permitted to increase (see Figure 8-1); however, the difference Δw 1 − Δw 2 shall be maintained as not less than in. (0.1 mm) for the duration of the crack cycling portion of the test.

Universität Stuttgart Institut für Werkstoffe im Bauwesen 1. The intent and conduct of the test for sensitivity of anchors to crack width cycling is identical in ACI and ACI The objective of the test is to cycle the crack between a crack width of in. (0.1 mm) and in. (0.3 mm), both being additive to the initial hairline crack width, while maintaining a constant tension load on the anchor. 3.Crack cycling shall be performed in such a manner that the reinforcing in the specimen does the work of closing the crack in each cycle. Therefore the test specimen has been described in detail. Adjustment of external force input corresponding to the lower crack width shall not be made during the test. The external force input corresponding to the upper crack width may be adjusted downward as necessary to maintain a minimum upper crack width of w 1 + w 0 where w 1 = in. (0.3 mm). In the event that the lower crack width increases such that the difference w 1 - w 2 is less than in. (0.1 mm), an increase of external force input corresponding to the upper crack width so as to preserve a minimum crack width differential of in. (0.1 mm) is required. 4.ACI 355 should strongly state again that the crack movement test should be performed as described under 3) above. 5. It is intended to write an article in ACI CI “How are anchors qualified for cracked concrete” in which the reasons for the different tests and their proper conduct will be explained. Crack moving test