Performance of mechanical steel bar splices using grouted couplers under uniaxial tension
Introduction
Precast concrete (PC) structures have superior performance compared to conventional concrete structures because of their distinct advantages, such as saving construction time, decreasing cost, reducing the consumption energy, and increasing the quality of the members due to higher quality control [[1], [2], [3], [4]]. The grouted sleeve splices can be used to join PC members such as beam-to-beam, wall-to-wall, and column-to-column by connecting the upper and lower members, as shown in Fig. 1. The grouted sleeve splice is created by inserting connecting reinforcement bars into a sleeve and casting its cavity by using a high-compressive strength of grout material.
There are several ways to connect steel bars, such as grouted steel couplers and grouted sleeve tubes, using grouted sleeves or couplers and half-grouted couplers [[5], [6], [7], [8]]. Studies on the grouted sleeve splice have drawn the attention of researchers in recent years due to its advantages. For instance, the grouted sleeve splice has a special working mechanism, tolerance control, welding avoidance, and it is faster to be constructed [7,9,10], in addition to reducing CO2 emissions compared to the conventional splice method of reinforcement bar, due to reducing the required quantity of reinforcement steel bars [11]. The application of the grouted sleeve bar enhanced the performance of the internal precast beam-to-column connections under seismic zones [2]. Grouted splice connectors are used to confine the grout surrounding the bars of the grouted sleeve's inner hole to enhance the bond between the grout and bar [5,9]. Thus, increasing bonding strength can produce higher confinement and prevent splitting failure [12]. In addition, the alignment of the steel bar in a splice connection under tension test has significantly influenced the performance of the spliced bar [13]. Furthermore, the performance of the grouted splice is significantly affected by the mechanical properties of the grout material [5]. Therefore, the construction of new structures requires an effective splice method between steel bars to take account of the environment, safety, strength, and cost-efficiency to replace the conventional method.
The required splice length between the steel bars can be up to 50 times the bar's diameter [14], thereby the development length of the steel bars can cause a congestion issue, and may increase the cost as a result of increased steel quantity. The splice bar using coupler can contribute to facilitating site assembly in the PC member [15,16]. The effect of a single reinforcement bar on the bond strength between the bar and the grout material was investigated, focusing on the use of steel pipe. The results showed that a high bond strength can be achieved by applying an embedment length of at least 7 times the bar diameter inside the steel pipe [17]. The tensile strength of the steel bars, which were fabricated with embedment lengths of 7.0–7.5 times the bar diameter also reached the required strength [9] in ACI 318–19 [18]. Testing of the filled grout couplers showed typical modes of failure, including steel bar fracture failure, bonding failure between the steel bar and the grout material, grout-sleeve bonding failure, as well as sleeve tensile failure [5]. Based on the literature, there are various parameters that could affect the performance of the grouted sleeve such as (a) different grouting defects, (b) insufficient grout strength, (c) bonding strength between the steel bar and grout, (d) bonding strength between the grout and the inner surface of the sleeve of the steel pipe or coupler, (e) embedded length of steel bar inside the sleeve, (f) the alignment of a bar in a splice connector in-line or adjacent leading to the offset of the steel bar inside the sleeve, (g) the type of the coupler such as threaded, grouted sleeve, swaged, bolt-lock, headed’ couplers, (h) the mechanical properties and the characteristics of the couplers, (i) the mechanical properties of the bars, and (j) the shape of bolts or the shape and the material properties of the connectors, especially the connection area whether using the sleeve, only grout, or both. The eccentricity could be observed as a result of an adjacent alignment of bars, and this may affect the performance of the grouted connector. This study expands the experimental database of grouted splice couplers under uniaxial tension. Two types of couplers were examined, i.e., the short-threaded grout couplers and the long grout couplers, focusing on the effect of embedded bar length (Lb) and the bar eccentricity inside the coupler cavity. The performance in terms of strength, ductility, energy absorption, and failure mode were assessed. Apart from that, the compressive and tensile strengths of the grout material known as “Emcekrete HP 100” were investigated to determine the grout properties. In addition, this article presents detail explanation on the seismic requirements for the bar splices based on different design standards for practical application. Furthermore, an analytical model was proposed to estimate the ultimate tensile strength of the grouted splices considering the effect of the bar eccentricity in the coupler cavity.
Section snippets
Experimental methodology
In this study, short-threaded grout couplers (STGCs) and long grout couplers (LGCs) were used to serve as the connector splice for the deformed reinforcement steel bars of the diameter (db) 16 mm. Both types of couplers are suitable to be used in the reinforced and precast concrete structures to connect the steel bars with the sufficient embedded length. The short-threaded grout coupler (STGC) has the parallel threaded part with a 20 mm length in the lower end and a hole with the corrugated
The mechanical properties of grout materials
The compressive strength of the Emcekrete HP 100 grout material was evaluated in different ages. Table 3 presents the average results for three samples of different ages of the cube sizes of (100 × 100 x 100) mm. The average results of the ultimate tensile loads and ultimate displacements of grout sheet samples are 8.07 kN and 0.65 mm, respectively; see Table 4.
Load−displacement curves
The data were collected from the computer connected to the UTM machine directly, in addition to the data logger to produce the
Evaluation of the mechanical behaviour of grouted couplers
The stress criteria were used to define the design requirements of the splice reinforcement bars in the ACI 318-19 [18] and the American Association of State Highway and Transportation Officials (AASHTO) [34,35]. The mechanical splice in ACI 318-19 [18] was divided into Type 1 and Type 2. The strength of mechanical splice Type 1 and the full-mechanical connection (refer to AASHTO) [34,35] is required to improve a minimum of 125% the specified yield strength (fyd) of the splice reinforcement bar
An analytical model to predict the ultimate load of sample
The bonding force between the grout and bar and between the grout and the inner surface of the coupler will produce stress due to the applied tensile load. The stress can be uniform in the zero eccentricity of the bar, where the bar position will be at the centre of the coupler cavity. The stresses produced in the coupler wall and grout from the subjected load are shown in Fig. 16. The stresses might be tensile and compressive in the grout and sleeve walls during the reversals and uniaxial
The application of the splice bar and member behaviour
The performance of the embedded grouted couplers in concrete members can be enhanced due to restricting the coupler. Bond interaction significantly affects the local deformation in the reinforced concrete members. The plastic hinge mechanism and rotation capacity may be affected due to concentrating the inelastic deformations at the end of some types of the coupler. Therefore, the classification of the couplers according to their geometry is significant [15,36]. The type of couplers should be
Conclusions
In this study, the performance of the short-threaded grout couplers and long grout couplers were examined under uniaxial tensile testing to determine the influence of the coupler types, embedded bar lengths, and eccentricities due to the bar position. The following conclusions were made:
- 1.
The failure mode of the grouted couplers is significantly influenced by the bar embedded length and the eccentricity of the bar. The ductile failure type (I) can be observed in the STGCs has the Lb of greater
CRediT authorship contribution statement
Haider Hamad Ghayeb: Methodology, Formal analysis, Writing - original draft, Validation, Investigation. Hashim Abdul Razak: Project administration, Conceptualization, Resources, Funding acquisition. N.H. Ramli Sulong: Supervision, Funding acquisition, Resources, Writing - review & editing. Kim Hung Mo: Supervision, Funding acquisition, Writing - review & editing. Fuad Abutaha: Data curation. Meisam Gordan: Data curation.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors gratefully acknowledge the Faculty of Engineering, University of Malaya (UM) and the Ministry of Higher Education (MOHE), Malaysia, for funding this work under the Postgraduate Research Fund (PPP), Project No.: PG199-2015B and GPF071A-2018. The authors also sincerely thank Halfen Moment Company Sdn Bhd for supplying the coupler and grout materials to support this research.
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