Keywords

1 Introduction and Background

Precast structure is widely used in low-rise housing projects, and the connecting joints and its mechanical performance for precast members are generally key issues for precast concrete structure. The advantages of this type of structure are time saving, better quality control, lower materials consumption [1], compared with traditional construction method, especially in those regions with insufficient building materials resource and poor construction condition but with rapid demand of housing construction market, such as Saudi Arabia [2]. Among various built or ongoing projects, the precast bearing wall structure is widely and successfully adopted [3], such as in Developmental Housing Programs initiated by National Housing Company in Saudi Arabia.

Fig. 1.
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Precast concrete bearing wall structure.

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For precast concrete bearing wall structure, the vertical structural members are off-site precast load bearing wall, while for external sandwich wall will be insulated inside to provide thermal resistance [4]. The foundation is usually casted on site with dowels embedded before installation of precast wall members. The precast wall will be connected to foundation through dowels and grouts after installation. The slab will be installed and supported on the precast wall and finally connected by dowels and grouts. See Fig. 1 for the structural system illustration.

The shear and tensile performance of precast wall horizontal joints are fundamental issues among the various research issues. Hofbeck et al. [5] conducted 38 push-off specimens tests with or without a pre-existing crack along the shear plane and reported a shear-friction theory to give a conservative estimate of the shear transfer strength of initially cracked concrete. Mattock et al. [6] analysed and concluded the influence of concrete strength, shear plane characteristics, reinforcement, and direct stress to the shear transfer strength of reinforced concrete and proposed the equation to estimate a proper shear-transfer strength. Harris et al. [7] tested 18 full scale horizontal joints under concentric compressive loading and reported the effect of reinforcement to prevent wall end splitting and the effect of joint length on the ultimate load carrying capacity and stiffness. Einea et al. [8] tested different types grout-filled steel pipe splices specimens considering influence of grout strength, rod bar size and pipe size, and found that high bond strength of reinforcing bars can be achieved by confining the grout surrounding the bars. Alias et al. [9] studied influence of anchorage length and sleeve inner diameter on the bonding and anchoring performance of the sleeves and found that sufficient anchorage length can ensure the safety and reliability of the joint, and the reduction of sleeve inner diameter will strengthen the constraint on the grout. Hosseini et al. [10] tested 21 grouted splice connectors with different spiral pitch distance under an increasing axial load and found the best performance of grouted pipe splice connectors was obtained at the spiral pitch distance of 15 mm, combined with the use of four vertical bars as shear keys. Soudki et al. [11] tested six full-scale specimens to investigate the behavior of mild steel connections for precast panels and found that properly designed mild steel connections for precast wall panels exhibit sufficient ductility and energy dissipation capacity and the use of shear keys across the interface of the connection significantly limits the slip mechanism and enhances the shear resistance. Tsoukantas et al. [12] proposed that the shear friction is one of three different mechanisms that transfer shear forces across uncracked interfaces in reinforced concrete members, including shear friction, cohesion between concrete surfaces across the interface, and dowel action crosses the interface. Soudki et al. [13] tested horizontal connections for precast wall panels subjected to reversed cyclic shear deformations combined with simulated gravity loads normal to the connection and found that the shear resistance of connections with post-tensioning, using either strands or bars, is mainly provided by friction at the dry pack grout-to-panel interface. Crisafulli et al. [14] proposed the shear strength design method for horizontal joints between precast wall members considering the friction and dowel action. Jiang et al. [15, 16] proposed a novel plug-in filling hole for steel bar lapping of precast concrete structure and reported the mechanism and the failure modes of the anchorage rebar, and presented the recommended anchorage length. Belleri et al. [17] studied the suitability of grouted sleeve connections as column-to-foundation joints for precast concrete structures in seismic regions and reported that grouted sleeves ensure a ductility and energy dissipation capacity similar to traditional connections.

The most popular theory about the shear transfer mechanism is that shear forces can be transferred by adhesion or friction at joint interfaces, shear-key effect at indented joint faces, dowel action of transverse steel bars, and the frictional resistance can be enhanced by the pullout resistance of tie bars properly placed across the joint [18]. In some cases, the compressive stresses coming from such as the self-weight of upper members can be considered. Due to the different construction details at interface, the consideration and design method for smooth, rough, or indented faces are distinguished [19]. The design methods for horizontal connection shear capacity for precast bearing walls differ in codes of America (Sect. 22.9 in ACI 318-19 [20], or Sect. 5.3.4 in PCI Design Handbook [21]), Europe (Sect. 6.2.5 in EN 1992-1-1:2004 [22]), and China (Sect. 9.2 in JGJ 1-2014 [23]). Without the contribution of normal compression stress, the shear strength equation in ACI 318-19 form is like that in JGJ 1-2014, which both ignores the effect of interface friction. In contrast the equation in EN 1992-1-1:2004 is with both concrete friction and dowel action considered.

When the wall panel is subjected to lateral loads, such as wind and seismic demands, the overturning moment at the bottom section will result in tension and compression at the opposite sides of the section. Yuan et al. [24] tested half grouted sleeve connections and found three types of failure mode are observed in the test, and the tensile is governed by the weakest of rebar tensile capacity, bond capacity between the rebar and the grout, or the thread connection tensile capacity. Eligehausen et al. [25] proposed a behavioral model to predict the average failure load of anchorages using adhesive bonded anchors and found that the basic strength of a single adhesive anchor predicts the pullout capacity not the concrete breakout capacity, and the group effects also revealed. Fuchs et al. [26] raised a model for the design of post-installed steel anchors or cast-in-place headed studs or bolts, termed the concrete capacity design (CCD) approach and a data bank including approximately 1200 European and American tests was evaluated. Obata et al. [27] studied on the effect of a free edge on the pull-out strength based on experiments and proposed a new method to estimate the cone failure strength using the theory of linear fracture mechanics. Xu [28] proposed a new analytical model based on the bond stress integration along the bar stress propagation length to predict the bar-slip behavior in RC beam-column joints under monotonic loading, considering the phenomena of combined axial pullout and transverse dowel action at the joints. Singhal et al. [29] proposed and studied headed dowel bars precast connection, and found that lower embedment depth lead to concrete cone failure, while higher embedment depth resulted in slip of bar. Zhou et al. [30] conducted a program to investigate the influence of bar embedment length and ratio of duct diameter to bar diameter on monotonic bond-slip response of stainless energy dissipation bars (ED bars).

The improved precast bearing wall structure is proposed, with light weight gauge steel members embedded in the wall, forming full length hole for dowels passing through, which can save up to 30% site assembly time and lower construction cost, especially for low rise buildings. Compared with current technologies which the ground floor precast wall connected with foundation and first floor wall separately, in the improved proposal, the ground precast wall connected with top and bottom members with one full length steel dowels. The traditional connection requires the precast panel reserved holes to match with foundation embedded dowels, while for the proposed connection, the hole is reserved in foundation, also during the precast wall manufacturing, the square hole will be formed with embedded Light Gauge Steel (LGS) double C-lipped section members. When assembling on site, the vertical connecting full-length dowels can pass through slab, precast wall, and finally the foundation one time. After grouted then the horizontal joints for wall-slab-wall and wall-foundation will be formed at the same time. See Fig. 2 for the connection details.

Fig. 2.
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Horizontal connecting joints: (a) Wall-Slab connection; (b) Wall-Foundation connection.

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In this paper, the shear and tensile performance of this joints are tested and the failure modes are compared based on ABAQUS finite element simulation approach. Based on the above research, the shear and tensile failure mechanism of horizontal joints is presented and the recommendations to increasing the horizontal joints strength capacity and ductile performance are proposed, which may provide practical guidance for future engineering practice.

2 Experimental Overview

2.1 Materials

The precast members of all precast specimens were made of concrete of cubic test strength class C35 while the cubic test strength class of grout materials is C50. All the reinforcement strength class is HRB400 with yielding strength of 400 MPa, while the LGS members is Q355 with yielding strength of 355 MPa. The concrete specimen compression test is tested on 200T compression-testing machine. The compression strength is 44.08 MPa for C35 specimen and 59.52 MPa for C50 specimen thus both is qualified. See Fig. 3 for the specimen testing results.

Fig. 3.
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Test values for compressive strength: (a) C35 specimens; (b) C50 specimens.

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2.2 Test Specimens Design and Manufacturing

Horizontal Connecting Joints Shear Test.

The horizontal connecting joint was selected at the floor slab area between upper and bottom wall for shear test. In order to prevent the load from being eccentric during loading, the specimen was designed as a cross-type joint. As shown in Fig. 4, the dimensions of the floor slab are 150 mm*600 mm*1000 mm with a 60mm diameter corrugated pipe in the middle of the slab for reserved hole, and the dimensions of the wall slab on both sides are 200 mm*480 mm*1000 mm with LGS double C-lipped box section members embedded forming a reserved hole. When the wall slab was assembled with the floor slab, PE rods were padded on both sides of the wall slab for blocking, followed by insertion of dowel with C50 high-strength non-shrinkage grout.

Fig. 4.
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Design of shear specimens for horizontal connecting joint: (a) Top view; (b) Front view.

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Total of three specimens for shear test, named SKJ1, SKJ2 and SKJ3, were casted and the manufacturing process of the specimens is shown in Fig. 5.

Fig. 5.
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Shear test specimens with horizontal joint manufacturing progress.

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Horizontal Connecting Joint Tensile Test.

The horizontal connecting joint was selected at the connecting joint between the wall and the foundation. The specimen design is shown in Fig. 6.

Fig. 6.
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Design of tensile specimens for horizontal connecting joints: (a) Top view; (b) Front view.

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Fig. 7.
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Tensile test specimens with horizontal joint manufacturing progress: (a) Reinforcement fabricating; (b) Assembled and grouted specimens.

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The size of the foundation part is 200 mm*400 mm*1210 mm, with 60 mm diameter and 360mm depth metallic bellows embedded inside to form the holes for dowels and grout. The size of the wall panel is 200 mm*200 mm*400 mm, with LGS double C-lipped box section members embedded forming a reserved hole along the wall length direction. After the panel and foundation are assembled, the T14 dowels were inserted into the hole of panel and foundation, and finally the holes were fully grouted. During manufacturing, the PE rods were arranged on both sides of the joint to seal the grout. Total of three tensile specimens were casted for the horizontal connection tensile test, named SKL1, SKL2 and SKL3, respectively. The manufacturing process of the specimens is shown in Fig. 7.

2.3 Testing Devices

The horizontal joint shear test was carried out on a 500T electro-hydraulic servo long column pressure tester at the Structural Laboratory of Chongqing University, with a maximum load of 5000KN, an accuracy of ± 1% of the test force value and a measurement range that can reach 2% to 100% of the full scale. In addition to the pressure tester, the devices used in the test are load cells, DH3816 data acquisition system, pull-wire displacement transducers and strain gauges, etc. The horizontal joint tensile tests were carried out on a structural laboratory reaction frame at Chongqing University. The load was provided via a jack connected with an oil pump. Other devices used in the tests were load cells, DH5902 data acquisition system, pull-wire displacement gauges, strain gauges, etc.

3 Experimental Progress and Phenomena

3.1 Horizontal Connecting Joints Shear Test

SKJ1 Specimen Testing Results.

The SKJ1 specimen before loading is shown in Fig. 8. As shown in Fig. 9, when the load was increased to 233KN, a crack appeared on the left side of the south face of the SKJ1 specimen. The cracking location was observed at the joint where the PE rods is in contact with the wall. The reason expresses the phenomenon is that the PE rods may weaken the bonding effect between the old and new concrete interface, and this location can be regarded as a weak anti-shear interface.

Fig. 8.
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SKJ 1 specimen before loading

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Fig. 9.
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First crack in SKJ 1 specimen

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Fig. 10.
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LGS member in SKJ1 specimen test.

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When the load reached to 300kN, with the load increasing the above cracks continued to expand upwards. When the load increased to 330KN, cracks also appeared on the right side of the south side of the member (left side of the north side) one after another. When the load increased to 348.77KN, the cracks on the left side of the north side of the member expanded rapidly, accompanied by the sound of blowing up. The cracks had formed extending through cracks resulting in the member the load bearing capacity was rapidly reduced to 233.68KN, at which time the shear capacity of the concrete at the old and new interfaces was sharply reduced, and a small strain occurred in the interpolation bars running through the wall and floor slabs. After one side extending through cracks formed, the crack on the other side of the specimen also developed rapidly and the extending through cracks formed, thus double side cracks both appeared, which is also the reason for the second peak load, followed by a sharp drop in the load-bearing capacity of the specimen and the completion of the shear resistance of the old and new concrete interface of the specimen.

Due to the shear resistance of the composite parts consisted of steel dowels, LGS double C-clipped box members, and grouts, the specimen still had a certain load-holding capacity after the two extending through cracks appeared, and the specimen load was kept fluctuation around a certain mean value at this time. At the same time, the LGS double C-slipped box members with grouts inside started sliding together was observed, as shown in Fig. 10.

Within the increasing displacement, the dowel inside the specimen finally appeared to be cut off, as shown in Fig. 11 at which point the specimen can no longer bear the load and the test program ends. As shown in Fig. 12, the damaged LGS double C-clipped box member appears tearing near the shear area with a large deformation of the dowel.

Fig. 11.
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The dowel was cut off in SKJ 1 specimen

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Fig. 12.
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The damaged LGS member and dowel of SKJ 1 specimen

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The test phenomena of other two specimen SKJ2 and SKJ3 were similar to specimen SKJ1 test. For SKJ2, it was observed that the first cracks appear at the loads of 205kN, and the cracks soon developed into extending through cracks at double sides. When dowel are involved in anti-shear progress, the slippage phenomenon was observed between the LGS members and precast members, and also between dowel and grout part, as shown in Fig. 13.

Fig. 13.
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LGS members slippage movement of SKJ2

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Fig. 14.
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LGS members buckling failure of SKJ3

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Fig. 15.
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Load displacement curves for horizontal joints shear specimens.

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For SKJ3, it was observed that the first cracks appear at the loads of 173kN, and one side extending through cracks appear at the loads of 282kN, and finally the double side extending through cracks appear at the loads of 332kN. The different phenomenon observed in SKJ3 specimen compared with another two specimen is that the failure mode of LGS member was buckling rather than slippage. The proper explanation for this phenomenon can be pointed to the empty space between LGS member and XPS insulation board due to the manufacturing deficiency. The failure diagrams of SKJ3 test specimen are shown in Fig. 14.

The load displacement curves for the three specimens in the horizontal connecting joints shear test are shown in Fig. 15, which can be read that the load displacement curves for the three specimens show the same regularity. The first peak loads for horizontal joint shear test specimens are listed in Table 1.

Table 1. First peak loads for horizontal joint shear test specimens.
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3.2 Horizontal Connecting Joints Tensile Test

SKL1 Specimen Testing Results.

As the test phenomena were similar for all three specimens, the experimental procedure for the SKL1 specimen is described in detail below. The tensile test of the horizontal joint connection between foundation and wall panel was carried out by controlling the oil pump for monotonic static tension, the SKL1 specimen before loading as shown in Fig. 16.

Fig. 16.
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SKL1 specimen before loading: (a) North side; (b) South side.

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When the load value reached 86kN, one crack appeared simultaneously on the south and north side of the specimen, at the location where the precast wall was connected to the foundation. When the load value reached 91kN, one horizontal crack appeared at the corner of the foundation of the specimen. The cracks continue to develop before the load value reaches the peak load. The specimen was pulled out within a short period of time after the peak load was reached, and the finally the failure of specimen was observed, as shown in Fig. 17. The final damage location of the specimen belongs to the foundation part, but there were also obvious cracks at the connection between the foundation and the wall panel.

The test phenomena of other two specimen SKL2 and SKL3 were similar compared with specimen SKL1 test. For SKL2 specimen, it was observed that the first cracks appear at the loads of 80kN at the PE rods location, and the cracks gradually developed into flaws until the loads reached 120kN. Soon the loads reached the peak loads and the strength capacity of the specimen rapidly decreased and the failure of specimen was observed, as shown in Fig. 18.

Fig. 17.
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Damaged SKL1 specimen: (a) South side; (b) North side.

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Fig. 18.
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SKL2 specimen tensile test failure diagram

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Fig. 19.
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SKL3 specimen tensile test failure diagram

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It was observed that the first cracks appear at the loads of 67.2kN also at the location of precast wall and foundation joint of SKL3. The cracks gradually developed into flaws and until the peak loads of 137.45kN was reached with the failure of specimen coming soon. The test progress diagrams of SKL3 test specimen are shown in Fig. 19.

Fig. 20.
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Load displacement curves for horizontal connecting joints tensile test specimens.

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The load displacement curves for the three specimens in the horizontal joint tensile test are shown in Fig. 20, which can be read that the load displacement curves for the three specimens show the same regularity. The peak loads for horizontal joint test test specimens are listed in Table 2.

Table 2. First peak loads for horizontal joint tensile test specimens.
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4 Finite Element Simulation Analysis

4.1 Horizontal Connection Shear Specimen Simulation

Finite Element Models.

The horizontal joint shear specimens were modelled according to the specimens design, and the effect of PE rods sealing the joints space was ignored in the modelling. The complete model view and the meshing of the model are shown in Fig. 21.

Fig. 21.
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Finite element model of SKJ specimen: (a) Top view; (b) Axonometric view; (c) Meshing

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Materials Properties.

The materials used in the model are C35 and C50 concrete, Q355 LGS, XPS insulation and HRB400 steel reinforcement.

The concrete was modelled using concrete plasticity damage model (CDP) provided in ABAQUS, while the reinforcement and dowels were modelled using a bifold model, and the materials properties of the LGS and XPS are shown in Table 3.

Table 3. Linear elastic constitutive parameters for steel and XPS material.
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Contacts Setting.

Based on the horizontal joint shear test phenomenon, the slippage between the LGS members and the concrete can be observed. Thus, the contact between the LGS and the concrete is set as frictional contact. The interface between the C30 precast members and C50 grout is also subject to bond slip phenomenon and is set as frictional contact. The contact between the other components is shown in Table 4.

Table 4. Linear elastic constitutive parameters for each material.
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Loads and Boundary Conditions.

The boundary conditions for the horizontal joint shear test specimen are, with a point-surface coupling for loading at the top of the middle floor slab and fixed constraints at the bottom of the wall panels on both sides. The load is applied at the coupling point through displacement loading method, with a load value of 20 mm.

Numerical Analysis Results.

The overall stress cloud of the numerical model for the horizontal joint shear test specimen is shown in Fig. 22(a). The stress cloud of C35 concrete in the precast wall slab is shown in Fig. 22(b), where the maximum stress is 35MPa, which has reached the breaking strength. The stress cloud for the precast floor slab is shown in Fig. 22(c), where the maximum stress is generated at the corrugated pipe extraction hole in the middle of the floor slab, where the maximum stress reaches 35MPa.

Fig. 22.
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Numerical analysis stress cloud of SKJ specimen: (a) Overall view; (b) C35 precast wall member part; (c) C35 precast slab member part.

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The stress cloud for the LGS is shown in Fig. 23, in which the LGS double C-clipped member is considered as one single unit in the model and the welding joints between the C sections members are ignored. It can be observed from the stress cloud, yielding damage occurs in the LGS near the shear action area, which is complied with the failure mode of the specimens observed in the tests, as shown before. The stress cloud for the vertical dowel is shown in Fig. 24, which exhibits that its maximum stress is 400 MPa and occurs at the intersection of the precast floor slab and the precast wall panel, which is the same location where the dowels fail in the tests.

As the observation from experimental results and the failure mode agreement with finite model analysis, the LGS members embedded in the wall panel to provide tunnel for the dowels was involved in anti-shear progress after the concrete friction interface quits, which may not improve the shear strength capacity but provide more ductility. Moreover, the horizontal joints shear capacity equation in EN 1992-1-1:2004 is more reasonable with both concrete friction and dowel action considered, compared with that in American and Chinese codes.

Fig. 23.
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SKJ model LGS member stress cloud.

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Fig. 24.
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SKJ model LGS member stress cloud

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4.2 Horizontal Connecting Joints Tensile Specimen Simulation

Finite Element Models.

The numerical model of the horizontal joint tensile specimen and the meshing diagram are shown in Fig. 25, in which the PE rods were ignored in the model.

Materials Properties.

The materials used in this model are C35 and C50 concrete, Q355 LGS, HRB400 reinforcement and steel wire rope. The concrete is modelled using the concrete plastic damage model (CDP) provided in ABAQUS while the reinforcement and dowel is modelled using the bifold model, and the steel and steel wire rope are modelled using the linear elastic model with the following constitutive parameters as shown in Table 5.

Fig. 25.
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Finite element model of the SKL specimen: (a) Axonometric view; (b) meshing diagram.

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Table 5. Linear elastic constitutive parameters for each material.
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Contacts setting.

The contact relationship between the components is set as shown in Table 6, based on the horizontal joints tensile test damage phenomenon.

Table 6. Physical component contact Settings
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Loads and boundary conditions.

To comply with the horizontal joint tensile test specimen, the bottom of the foundation is set as the fixed end and the load is applied to the three vertical dowels through displacement loading method, with an applied displacement value of 10 mm.

Numerical analysis results.

The overall stress cloud of the horizontal joint tensile finite element model is shown in Fig. 26, and the overall displacement cloud is shown in Fig. 27, which shows that the interface between the precast wall member and the foundation is the weak interface prone to be damaged.

The stress clouds for each component of the horizontal joint tensile test specimens are shown in Fig. 28. The stress cloud for the C35 precast member shows that the foundation concrete formed an inverted triangular failure zone, which is the same as the phenomenon observed in test results as shown before. The stress cloud of the reinforcement mesh of the foundation shows that the reinforcement near the vertical dowels reflects shear yielding failure mode, as shown in Fig. 29, which is complied with the test. The stress cloud for the C50 grout part shows that damage occurred in the C50 grout part at the junction of the foundation and the precast wall panel. The fracture failure at the junction of the foundation and the precast wall panel was observed on the N side of the specimen, as shown before. Similarly, it can be read that the C50 high-strength grout at this location also exhibits a high stress status, which is complied with test results.

Fig. 26.
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SKL specimen stress cloud

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Fig. 27.
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SKL specimen displacement cloud

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Fig. 28.
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Stress cloud diagram of SKL specimen: (a) C35 precast member; (b) C50 grout member.

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Fig. 29.
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Stress cloud diagram of SKL specimen: (a) Foundation rebar mesh; (b) LGS member.

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5 Conclusions

In consideration of construction and manufacturing efficiency and economics, the improved precast bearing wall structure was proposed, with light weight gauge steel members embedded in the wall forming full length hole for dowels passing through fast, especially for low rise buildings. The shear and tensile behavior of the horizontal joints for the novel precast bearing wall structure were studied through experimental and numerical investigation in this paper. Three identical specimens for horizontal joints shear and tensile tests were tested. The shear test specimens were designed from the wall-slab-wall connection part while the tensile test specimens were designed from the wall-foundation connection part. The finite element models of both type specimens are verified and calibrated with the experimental results using ABAQUS. The following conclusions are made based on the work in this research:

  1. 1.

    Horizontal joints shear numerical analysis complies well with the test results. The main failure mode is the interface friction failure at the joints between old and new concrete. For insulated precast panels, the insulation layers exposed to grout materials and the PE rods for sealing will weaken the interface friction shear performance. After the friction interface quit the work, the joints move into the second phase anti-shear behavior with the main mechanical performance contributed by the dowels as well as the LGS hole with grouts. The joints have good performance in shear behavior and the LGS will also contribute to ductile performance. A better approach to improve the horizontal joints shear ductile performance is to increase the dowel diameters or decrease the dowel space while the way to improve the joints shear capacity is to improve the friction interface condition such as using indented face or use studs to improve the friction action.

  2. 2.

    Horizontal joints tensile numerical analysis complies well with the test results also. The main failure mode is that the failure starts from the joints between old and new concrete and then ends in the final tensile fracture of the joints, such as concrete cone failure as observed in the experiments. The PE rods for sealing also will weaken the joints interface tensile performance. During the test, the dowels and the LGS members with grouts work jointly until the program ends, which can be concluded that the horizontal joints of proposed novel type of precast bearing wall are reliable.

  3. 3.

    For insulated precast sandwich panels, it is recommended to manufacture the insulation layers inside of the precast members to avoid any contact with grouts leading to the weakening of the joints interface friction.

  4. 4.

    For the proposed novel precast bearing wall, further efforts should be devoted to exploring the seismic performance of the precast member joints. Also, the coupling of axial, shear and bending interaction of the joints may present further insights into the practical.