**3. Test results and Discussion**

#### *3.1. Failure Modes*

As expected, two different failure modes, namely, the fracture of rebar and the pull-out failure of rebar, were found, as shown in Table 4.



Note: L represents the short-lapped-rebar splices, A represents the diameter of rebar, B represents the ratio of the length of the lapped-rebar splices to the suggested length of splices (550 mm for rebar with 12 mm diameter, 750 mm for rebar with 16 mm diameter, and 940 mm for rebar with 20 mm diameter) in GB 50010-2010 [19], C represents the number of specimens (i.e., 1, 2, 3, and 4) in each group, and 4 represents the specimens with strain gauges in machined grooves, as shown in Figure 4d.

For the specimen with 0.15 times of the suggested length in GB 50010–2010 shown in Table 4 [19] (LA-0.15), the bond strength between grout and rebar was strong enough to resist the tensile loading, and the failure mode for the fracture of rebar was shown, as shown in Figure 6a. Clearly, all anchored rebar fractured at the center of splices. In addition, a wide inclined crack appeared between the anchored rebar and embedded rebar at the anchorage end of the splice, as shown in Figure 6a. This may be attributed to the small eccentricity of tensile loading. For the specimens with 0.10 times and 0.05 times the suggested length in Table 4 (LA-0.10, LA-0.05), the bond strength between grout and rebar was not strong enough to resist the tensile loading, and the failure mode for the rebar pull-out failure was shown, as shown in Figure 6b,c.

**Figure 6.** *Cont*.

**Figure 6.** Failure modes of the short-lapped-rebar splices (**a**) Rebar fracture failure (L20-0.15) (**b**) Rebar pull-out failure (L20-0.1) (**c**) Rebar pull-out failure (L20-0.05) (**d**) Rebar fracture failure (L12-0.15).

In contrast, Specimen LA-0.1 or Specimen LA-0.05 shows the pull-out failure of rebar, as shown in Figure 6b,c. Clearly, the shear failure of grout mortar was shown. Note that spitted cracks were also found on the anchored rebar of Specimen LA-0.1.

As shown in Figure 6d, the rebar diameter had little effect on the failure mode in the shortlapped-rebar splices, but the development of cracks was influenced by the rebar diameter. For example, Specimen L12-0.15 shows smaller cracks than that of Specimen L20-0.15. This may be attributed to the decrease in area (diameter) and yielding forces of rebar.
