This article develops an enhanced UHPC-grout shear connection for steel-concrete composite bridges with precast decks. The primary improvement is the use of ultra-high performance concrete (UHPC) as the connection grout. To validate the constructability and the mechanical performance of the new connection, two series of experimental tests (including grouting tests and push-out tests) were conducted. Results from the grouting tests show that both the pressure grouting method and the self-levelling grouting method are applicable to inject the UHPC grout into the channel void of the connection. Results from the push-out tests indicate that the advanced properties of UHPC allow for a significant improvement of the shear resistance of the adhesive connection over traditional cementitious grouts. The ultimate shear capacity of the adhesive connection is controlled by the interface shear strength between the embossed steel and the UHPC grout, with a cohesion value of approximately 5.87 MPa. Meanwhile, the residual frictional resistance can be taken as approximately one-half of the ultimate resistance. The results of the finite-element analysis show that the trilinear model is reasonable to simulate the shear-slip laws of the embossed steel-grout interface and the rough concrete-grout interface.
Steel-concrete composite bridges using prefabricated full-depth deck panels allow modular construction and greatly minimizing traffic impacts. Shear stud clusters embedded in shear pockets are usually used to create composite action between concrete deck slabs and steel girders (Figure
Full-depth precast deck system with stud clusters as the shear connection.
One potential solution to these problems is the use of linear or surface connections rather than point connections. One promising detail is the “connection by adhesion, interlocking, and friction” (also referred to as “adhesive connection”) that was first proposed by Thomann [
Details of adhesive connection: (a) first generation; (b) second generation.
The second generation of the adhesive connection is shown in Figure
Mechanisms of shear resistance of the adhesive connection.
The resistance of the adhesive connection to longitudinal shear is dependent on the adhesion and friction between the connected materials. A significant amount of research has already been carried out on interface behavior. For the interface between the embossed steel plate and cement paste, Thomann and Lebet [
This study aims to provide a new generation of the adhesive connection, referred to as the “enhanced UHPC-grout shear connection.” The primary improvement is the use of UHPC as the connection grout. Compared to traditional cementitious grouts, UHPC has good dimensional stability, exceptional durability, and mechanical properties [
The UHPC used in this study is a commercially available product in China. Table
Relative weight ratios to cement in the mix design.
Cement | Fine sand | Silica fume | Highly active admixture | Superplasticizer | Steel fiber | Water |
---|---|---|---|---|---|---|
1.0 | 1.1 | 0.25 | 0.28 | 0.05 | 0.22 | 0.2 |
The mechanical properties of UHPC were determined according to GB 50010-2010 [
The grouting of UHPC into the channel void of the connection may be realized by two methods: (1) pressure grouting from the channel end; (2) self-levelling grouting from the top pockets. To compare the constructability and compactness of two grouting methods (Figure
Two grouting methods: (a) pressure grouting; (b) self-levelling grouting.
Figure
Test setup for pressure grouting from the channel end (dimensions in mm).
Figure
Test setup for self-levelling grouting from the top pockets.
The grout quality using the pressure method is shown in Figure
Inspection of quality of pressure grouting. (a) Interface of acrylic sheet. (b) Interface of steel plate. (c) Grout inlets. (d) Grout outlets.
Self-levelling grouting: (a) grouting process; (b) grouting quality.
Two sets of push-out testing of adhesive connectors were conducted, including three specimens with the HMP grout and seven specimens with the UHPC grout. The parameters of the specimens are listed in Table
Parameters of adhesive shear connectors.
Specimen | Grout material | Compressive strength of grout (MPa) | Holes in steel rib |
---|---|---|---|
HPM-1 | HPM | 72 | w/o |
HPM-2-H | HPM | 72 | w/ |
HPM-3-H | HPM | 72 | w/ |
UHPC-1 | UHPC | 120 | w/o |
UHPC-2 | UHPC | 120 | w/o |
UHPC-3 | UHPC | 125 | w/o |
UHPC-4 | UHPC | 125 | w/o |
UHPC-5-H | UHPC | 125 | w/ |
UHPC-6-H | UHPC | 115 | w/ |
UHPC-7-H | UHPC | 115 | w/ |
All push-out specimens have the same outside dimensions, as shown in Figure
Geometry of push-out test specimens (dimensions in mm). (a) Plan view. (b) Front view. (c) Side view.
Figure
Fabrication of push-out test specimens.
Figure
Test setup and instruments.
The specimens were first loaded under force control. The loading procedure was 0 kN ⟶ 50 kN ⟶ 0 kN ⟶ 200 kN ⟶ 400 kN ⟶ 600 kN. Afterward, the force control was replaced with displacement control, with a loading speed of 0.005 mm/s until the maximum loading capacity was reached. Afterward, a loading speed of 0.015 mm/s was imposed until failure.
The failure mode of push-out specimens is affected by many parameters. According to the previous study of Papastergiou and Lebet [
In this study, all specimens failed along the embossed steel-grout interface, exhibiting a typical mode of shear failure (Figure
Typical failure mode of push-out test specimens: (a) top face; (b) bottom face.
Figure
Development of confinement due to uplift.
The shear-slip curves of all specimens are shown in Figure
Shear-slip curves: (a) specimens without holes in steel rib; (b) specimens with holes in steel rib.
The uplift (
Slip-uplift curves: (a) specimens without holes in steel rib; (b) specimens with holes in steel rib.
Due to the restraint of surrounding concrete slabs, the uplift cannot be released completely. Hence, the normal stress is created by the confinement effect. Figure
Slip-normal stress curves.
From the comparative analysis of the test data listed in Table The presence of holes in the steel rib can significantly increase the shear resistance of the adhesive connection [ Compared with the HPM grout, the utilization of UHPC grout can significantly increase the shear resistance of the adhesive connection by approximately 50% The uplift of the connections with UHPC grout is much smaller than those with HPM
Ultimate shear capacity of push-out test specimens.
Group | Specimen | Ultimate shear capacity (kN) |
---|---|---|
Specimens without holes in steel rib | UHPC-1 | 1280 |
UHPC-2 | 1300 | |
UHPC-3 | 1500 | |
HPM-1 | 1050 | |
UHPC-4 | 1850 | |
Specimens with holes in steel rib | UHPC-5-H | 3050 |
HPM-2-H | 2250 | |
HPM-3-H | 1600 | |
UHPC-6-H | 2360 | |
UHPC-7-H | 3000 |
In the present study, all FE analyses were performed using the commercial software package ANSYS (Release 10.0). Figure
FE model of push-out test specimen. (a) 3D view. (b) Plane view.
In the push-out testing of this study, the failure of the specimens was controlled by the interface shear failure, while no apparent damage was observed in the concrete block and the UHPC grout. For this reason, the concrete block, the UHPC grout, and the steel plate were treated as elastic materials in the FE analysis. The moduli of elasticity of normal-strength concrete, UHPC, and steel were taken as 30 GPa, 49 GPa, and 200 GPa, respectively. Poisson’s ratios of normal-strength concrete, UHPC, and steel were set to be 0.2, 0.2, and 0.3, respectively.
According to the
Constitutive laws of interfaces: (a) basic law; (b) steel-grout interface; and (c) concrete-grout interface.
The parameters in the constitutive law of equation (
Parameters in constitutive laws of two interfaces.
Interface | ||||
---|---|---|---|---|
Embossed steel-grout interface | 5.5 | 2.1 | 0.39 | 4.00 |
Rough concrete-grout interface | 6.1 | 2.6 | 0.31 | 4.00 |
The shear-slip curves obtained from the FE analysis are plotted in Figure
Comparison between numerical load-slip curves and test results.
The maximum stresses in the steel plate and the concrete block are shown in Figure
Maximum stresses in steel plate and concrete block.
The height of the embossed steel rib (
Influence of rib height on interface capacity.
Linear relationship between rib height and shear capacity.
Based on the test results, the ultimate shear capacity of the adhesive connection is controlled by the interface shear strength between the embossed steel and UHPC grout [
Based on regression analysis of the test data, the cohesion value can be taken as 5.87 MPa for the embossed steel-UHPC grout interface. The residual frictional resistance can be taken as approximately one-half of the ultimate resistance.
In this study, the experimental tests showed that the UHPC-grout shear connection has the potential to be used in accelerated bridge construction. It is believed that the UHPC-grout shear connection is a promising option for the design of steel-concrete composite bridges. However, more research should be carried out in the following aspects to promote its use in practice: As pointed out by Diógenes et al. [ Transversal prestressing, which is often applied in the bridge deck, is expected to have a favorable effect on the connection’s resistance [ The shear connection should resist the horizontal shear force and prevent vertical separation or uplift of the concrete slab from the steel girder. It is necessary to study the uplift effect in the UHPC-grout strip shear connection. The grouting compactness of UHPC in the channel void of the connection is of vital importance. More research should be conducted to study the constructability and compactness of different grouting methods.
This study aims to provide the third generation of adhesive connection, referred to as the “enhanced UHPC-grout shear connection.” The primary improvement is the use of UHPC as the connection grout. Two series of tests were performed to validate the constructability and the mechanical performance of the new connection. The following conclusions can be drawn: Both the pressure grouting method and the self-levelling grouting method are applicable to inject the UHPC grout into the channel void of the connection. By comparison, self-levelling grouting is better than pressure grouting, in terms of the convenience in construction and grout quality. The advanced properties of UHPC allow for a significant improvement of the ultimate capacity of the adhesive connection. Compared with the HPM grout, the utilization of UHPC grout can significantly increase the shear resistance of the adhesive connection by approximately 50%. Meanwhile, the presence of holes in the steel rib can generate a “dowel effect” that significantly increases the shear resistance of the adhesive connection. The ultimate shear capacity of the adhesive connection is controlled by the interface shear strength between the embossed steel and the UHPC grout, with a cohesion value of approximately 5.87 MPa. Meanwhile, the residual frictional resistance can be taken as approximately one-half of the ultimate resistance. The results of FE analysis show that the trilinear model is reasonable to simulate the constitutive laws of interfaces, and the shear capacity of the adhesive connection increases proportionally with the height of the embossed steel rib.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Zhang Y and Zheng H conceived and designed the experiments. Zheng H and Tang M performed the experiments and numerical simulation. Zheng H and He Z analyzed the data. Zhang Y, Zheng H, and He Z wrote the manuscript.
This work was supported by the Outstanding Youth Foundation of Jiangsu Province, China (no. BK20180063) and the National Natural Science Foundation of China (no. 51778137).