Elsevier

Engineering Structures

Volume 207, 15 March 2020, 110239
Engineering Structures

Experimental testing of innovative panel-to-panel connections for precast concrete building cores

https://doi.org/10.1016/j.engstruct.2020.110239Get rights and content

Highlights

  • Strength/stiffness of stitch plate connections depends on the stud configuration.

  • The innovative grouted panel pocket is a tested alternative for stitch plates.

  • Grouted panel pocket was 1.7 times stiffer and stronger than the stitch plate.

  • The innovative post tensioned corbel is a tested alternative for wet joints.

  • Post tensioned corbel was greater than 40 times stiffer than the stitch plate.

Abstract

This paper presents the experimental testing and results of a recent study into panel-to-panel connections for jointed precast concrete building cores. Panel-to-panel connections are typically used to transfer vertical shear forces between adjacent panels to allow the individual panels to act as one combined composite cross-section. The experimental program consisted of three specimens, each constructed using a different type of connection. The first specimen was the ‘baseline’ specimen and was constructed using ‘industry standard’ welded stitch plate (WSP) connections. The second and third specimen were constructing using two new prototype connections, which were developed by the authors and are referred to as grouted panel pocket (GPP) and post tensioned corbel (PTC) connections. These connections were developed such that precast concrete building cores could be constructed without the use of wet joints or site welding, which are both costly aspects in precast wall construction. The experimental assessment showed both connections were stronger and stiffer than the baseline WSP connection. The paper is concluded with a detailed overview of the critical failure mechanism of each connection and the development of respective design models that could be used to predict the design performance of the connections.

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].

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