Experimental testing of innovative panel-to-panel connections for precast concrete building cores
Introduction
The primary purpose of the horizontal panel-to-panel connections in precast reinforced concrete (RC) building cores is to transfer vertical shear force between adjacent panels to allow composite action to be developed, such that individual panels can act together as one combined cross-section under lateral load. The amount of composite behaviour developed across adjacent panels will be dependent on both the stiffness and maximum strength of the connections. If the connections do not have sufficient strength, they will fail prematurely, hindering any composite behaviour between adjacent panels. Similarly, if the connections are too flexible, the panels will essentially act individually, also hindering composite behaviour developing.
Welded stitch plate (WSP) connections are a commonly used type of panel-to-panel connection for precast building cores in both Australia [1] and New Zealand [2]. WSP connections consist of individual steel plates that are cast into adjacent wall panels during fabrication, which are later connected together on site after the panels are erected by site welding a third ‘stitch’ plate to both cast-in plates. The number and capacity of WSP connections required in each storey is dependent on the configuration of the core and the intensity of the lateral design actions the building is required to withstand. An example of a typical WSP connection is shown in Fig. 1. These plates are typically recessed into the panel so they can be grouted over to achieve a smooth surface finish to the panel, in addition to providing fire resistance to the stitch plates during a fire scenario.
Wet joints are usually adopted, as an alternative to WSP connections, in situations where the vertical shear forces that need to be transferred between adjacent panels are greater than the capacity of the WSP connections. Wet joints consist of a cast in-situ portion of concrete that is poured between two adjacent precast panels. Well designed and constructed wet joints essentially allow a jointed precast building core to behave the same as an equivalent cast in-situ section. They are typically not preferred by contractors as they are significantly more expensive and slow the floor-to-floor construction cycle, which in some circumstances can effectively eliminate the cost advantage of adopting a precast concrete building core over a traditional cast in-situ core.
Previous studies identified in literature have assessed the behaviour of the stitch plate component of the connection in isolation [3], however no literature was identified that assessed the overall behaviour of WSP connections, including the shear stud connection between the cast in plate and respective precast panel. Other studies in literature have assessed panel connection plates that have friction connections built in, which then allow energy dissipation during lateral load response [4], [5], [6]. There has also been a number of studies developing rocking wall systems that are anchored to the foundations using an unbonded post-tensioning cable running down the centre of the wall, which have has mild steel connectors [7], [8] or friction plates [9] between the web and end panels that provide hysteretic energy dissipation to the system. Other innovative studies have included: bolted connections using vertical structural steel sections that are fixed to the ends of adjacent panels and bolted together [10], [11]; a unique solution where panels are connected using structural steel box plates in each corner of the panel, which are connected back to the panel reinforcement [12]; or interlocking steel channels that cast into the vertical edges of adjacent panels and later connected together using high strength bolts [13]. Wet joint research has also been previously undertaken in literature [14]. Unfortunately, the systems discussed above, and similar variants, have been perceived as unattractive by the local precast industry in Australia, and as a result, have never been adopted.
The first objective of this experimental study was to assess the behaviour of industry standard WSP connections and develop an experimentally verified design model for predicting the vertical strength and stiffness of these connections. The second objective of this experimental study was to develop two new alternative prototype connections for precast building cores, which were developed in conjunction with a local precast concrete company in Melbourne, Australia, in the hope that the proposed connections would be more attractive to the local industry. The first prototype connection, referred to as a grouted panel pocket (GPP) connection, was developed as an alternative to WSP connections and the second prototype connection, referred to as post tensioned corbel (PTC) connection, was developed as an alternative to wet joints. To this end, the GPP was developed with ease and speed of construction as the primary consideration, whereas the PTC was developed with strength and stiffness as the primary consideration.
This paper will firstly present an overview and results of the experimental testing performed for each connection specimen. The paper is then concluded with a detailed overview of the critical failure mechanism of each connection and the development of respective design models.
Section snippets
Research significance
Despite widespread use of precast concrete walls and building cores in both Australia and New Zealand, research efforts into their lateral performance have mainly been directed towards rectangular precast walls, e.g. [15]. Limited research has been performed for building core systems and their connections, particularly whether the connections have enough stiffness to allow sufficient composite behaviour to develop. Recent large-scale experimental testing of precast building core systems
Test program
The experimental program consisted of three panel-to-panel component level connection specimens. These specimens were meant to represent the corner segment of a box-shaped precast concrete building core specimen (denoted S05), which was previously tested by the authors [16]. The connection specimens were tested in isolation and the loading was applied such that the connections were subject to pure vertical shear forces matching what would be seen in a system level response, as shown in Fig. 2,
Connection strength and general behaviour
Specimen J01 (i.e. WSP connections) had a maximum strength of 176 and 177 kN in the positive and negative loading directions respectively. The WSP connections exhibited a reasonably ductile failure mode (Fig. 9), allowing a fair amount of connection deformation and gradual decline in strength, due to yielding of the shear studs, before complete failure occurred due to fracturing of the shear studs.
Specimen J02 (i.e. GPP connections) had a maximum strength of 304 and 308 kN in the positive and
Specimen J01 – Welded stitch plate (WSP)
The failure mechanism of specimen J01 was yielding and fracturing of the shear studs. The maximum loading was governed by the yielding of the studs and then overall failure of the connection was due to fracturing of the studs. The specimen was able to develop its maximum load with minimal damage and cracking of each individual wall panel, as shown in Fig. 11. It was only after the maximum strength of the connection was exceeded and it was subjected to much larger displacement increments that
Suitability of the proposed new connections
This paper has presented the development and experimental testing of two new corner connections for connecting precast concrete building cores, which have been named the grouted panel pocket (GPP) and post tensioned corbel (PTC). The suitability of the connections was assessed by experimentally comparing their performance against a typical welded stitch plate (WSP) connection that matched industry standard construction practices in the Australasian region. The GPP and PTC connections had to
Summary and conclusions
This paper has provided an overview and detailed analysis of the experimental testing of three large-scale precast concrete building core panel-to-panel connection specimens. This included one specimen that had welded stitch plate (WSP) connections, which was the ‘baseline’ connection, and two specimens that were constructed using two new prototype connections developed by the authors. The first connection is the grouted panel pocket (GPP) connection and the second is the post tensioned corbel
CRediT authorship contribution statement
Scott J. Menegon: Writing - original draft, Conceptualization, Methodology, Investigation, Visualization. John L. Wilson: Writing - review & editing, Funding acquisition, Supervision. Nelson T.K. Lam: Writing - review & editing, Funding acquisition. Emad F. Gad: Writing - review & editing, Funding acquisition.
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 would like to thank the Brown family for their generous donation in establishing the Dr. William Piper Brown AM Scholarship, of which the lead author was the recipient. The authors would also like to thank Simon Hughes from Westkon Precast Pty Ltd for the valuable discussions that lead to the development of the connections presented in this paper.
Funding
This work was supported by the Australian Research Council (ARC) [grant number DP140103350, 2014].
References (32)
- et al.
Finite element analysis of the PreWEC self-centering concrete wall system
Eng Struct
(2016) - et al.
Seismic performance and design approach of unbonded post-tensioned precast sandwich wall structures with friction devices
Eng Struct
(2020,) - et al.
In-plane cyclic testing of precast concrete wall panels with grouted metal duct base connections
Eng Struct
(2019) - et al.
RC Walls in Australia: Reconnaissance Survey of Industry and Literature Review of Experimental Testing
Aust J Struct Eng
(2017) - et al.
Panel Connection Details in Existing New Zealand Precast Concrete Buildings
Bulletin of the New Zealand Society for Earthquake Engineering
(2016) - et al.
Ductile Steel Connections for Seismic Resistant Precast Buildings
J Earthquake Eng
(2003) - et al.
Friction dissipative devices for cladding panels in precast buildings
European Journal of Environmental and Civil Engineering
(2011) - et al.
Role of wall panel connections on the seismic performance of precast structures
Bull Earthq Eng
(2013) - et al.
Friction-based dissipative devices for precast concrete panels
Eng Struct
(2017) - et al.
Precast concrete wall with end columns (PreWEC) for earthquake resistant design
Earthquake Eng Struct Dyn
(2015)