**1. Introduction**

Due to the application of quick-assembled rebar technology (i.e., grouted sleeve connections, metal or plastic duct connections, post-tensioned connections, and steel plate connections), the precast concrete structures were developed rapidly in China. As corrugated metal duct connections [1] and lapped connections with the spiral hoops [2] have the advantages of fast assembly, reliable connection, and convenient construction, they are widely utilized in the precast concrete structure.

Previously, corrugated metal duct connections [1] were mainly utilized for connecting the foundation and column in bridge engineering. Raynor et al. [3] first proposed a post-tensioned metal duct connection, and the experiment of metal duct connections under tension testing was performed. The results showed the metal duct connections exhibited high bearing capacity and good ductility. Matsumoto et al. [4] studied the bonding behavior of the corrugated duct connection, and a model for the anchorage length of rebar was suggested. Brenes [5] discussed the major parameters affecting the mechanical behavior of the corrugated duct connection, and a bond-stress-slip model was developed. Steuck et al. [6] evaluated the minimum anchorage length of large-size rebar in the corrugated duct connection. Galvis and Correal [7] proposed a model for the anchorage length of two or three bundles of metal ducts in the corrugated duct connection.

The corrugated duct connection was then developed in precast shear walls or frames, as shown in Figure 1 [8]. Here, a metal duct was first embedded in the formwork of the precast specimen, and the metal duct was closely connected to the embedded rebar with

**Citation:** Liu, Q.; Liu, X.; Chen, R.; Kong, Z.; Xiang, T. Experimental Study on Anchoring Performance of Short-Lapped-Rebar Splices with Pre-Set Holes and Spiral Hoops. *Metals* **2023**, *13*, 530. https://doi.org/ 10.3390/met13030530

Academic Editors: Andrea Di Schino and Claudio Testani

Received: 12 February 2023 Revised: 3 March 2023 Accepted: 4 March 2023 Published: 6 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

fixed iron wire. Then, the metal duct was bent to the outside of the formwork at the highest location for the later pouring of grout. Finally, the grout material was poured into the metal duct after the anchored rebar was inserted into the metal duct during the in-site assembly. Zhi et al. [8] experimentally investigated the seismic behavior of the corrugated duct connection with the lapped rebar splice in shear walls. Seifi et al. [9] found that the corrugated duct connection with a transverse confinement can effectively limit the development of cracks in seismic loading. In Tazarv and Saiidi [10] and Hofer et al.'s [11] cyclic testing, the good seismic behavior of the precast frames with the corrugated duct connection was exhibited.

**Figure 1.** Corrugated metal duct connections [8].

As discussed above, there is extensive research focusing on the mechanical behavior of the corrugated duct connection. However, the concrete near the zone of the connection is easily cracked. For this reason, Ma et al. [12] proposed a new type of lapped connection with spiral hoops and steel rod rotated holes, as shown in Figure 2. The stirrups with spiral hoops were embedded in the scope of overlapping reinforcement and were then preset in the formwork. After the pre-hardening of precast concrete, the holes with ribs were formed by pulling out the rotated steel rod. The experiment of the pull-out splice testing was then performed by Ma et al. [12] and Zhang [13], and the results showed this type of lapped connection can effectively connect precast shear walls. From the results of seismic testing, Gu et al. [14,15] pointed out the mechanical behavior of the precast shear walls with the lapped connection was similar to that of shear walls in cast. Based on Jiang et al.'s test [16], the precast shear walls with the lapped connection exhibited better ductility performance than that of shear walls in cast.

**Figure 2.** Lapped connection [12].

However, the spiral hoops and the steel rod rotated in the lapped connections are difficult to fix during the precast process, and the rotation of the steel rod may cause the cracking of the concrete. To solve this kind of problem, a new type of connection named the short-lapped-rebar splice is proposed in this study, as shown in Figure 3. Compared with Ma et al.'s method [12], the anchorage length in this new type of connection is shorter. In addition, the spiral hoops are welded on the embedded rebar to be fixed, and the metal duct avoiding the rotation of the steel rod is utilized. To investigate the mechanical behavior (i.e., failure mode, ultimate strength, and strain variation) of the short-lappedrebar splices, the experiment of the short-lapped-rebar splices with the pre-set holes and spiral hoops was tested in this study. A model for predicting the ultimate bond strength of the short-lapped-rebar splices is developed.

**Figure 3.** The short-lapped-rebar splices.
