Steel-concrete Joints Research Articles

Generalised fracture mechanics approach to the interfacial failure analysis of a bonded steel-concrete joint

Steel-concrete joints are often made by welded shear studs. However, this connection reduces the fatigue strength, especially in situations where locally concentrated loads occur with a large number of load cycles e.g. in bridge decks. In this paper the shear bond strength between steel and ultrahigh performance concrete (UHPC) without welded mechanical shear connectors is evaluated through push-out tests and a generalized fracture mechanics approach based on analytical and finite element analyses. The connection is achieved by an epoxy adhesive layer gritted with granules. In the tests, specimens made with various manners of preparation of the epoxy interlayer are tested experimentally. Numerical-analytical 2D and 3D modelling of a steel-concrete connection is performed without and with the epoxy interlayer. The model of a bi-material notch with various geometrical and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

STEEL-GLUED WITHOUT ANCHOR JOINT SHORT-TERM STRENGTH EXPERIMENTAL RESERCH ON ACRYLIC MODIFIED COMPOSITIONS

The central issue of the paper is the short-term adhesive strength dependence determining from the number of various technological factors and advanced acrylic composition selection for further elements constructions and without anchor joint adhesive development. The results of the experiments on determination the technological equipment without anchor joint strength, in the case of gluing steel plates to the concrete surface with modified acrylic adhesives, are conducted. Short-term strength of adhesive steel-concrete joints testing methods, as well as the determination of the main technological factors influence on the strength of without anchor joint on acrylic modified compositions, are described in detail. The experimental research on the concrete class, adhesive layer thickness and other structural fixing joint characteristics influence on the strength of adhesion are conducted. On the basis of research results, it was demonstrated that regardless from the type of the loading, the adhesive compound geometric characteristics, concrete physic and mechanical properties, the destruction of concrete-steel joint was occurred on the concrete surface. The obtained results of experimental research data can be used for attachment joints projecting and industrial technological lines development, as well as for further polymeric adhesive materials, widely applied in industrial and civil engineering, improvement.

Push-out tests for perfobond strip connectors with UHPC grout in the joints of steel-concrete hybrid bridge girders

This paper aims at examining the structural behavior of perfobond strip (PBL) connectors for steel-concrete joint of hybrid girders with ultra-high performance concrete (UHPC) as grout for such connectors. Twenty-four push-out specimens fabricated according to the design used for the connectors in the steel-concrete joint in a hybrid cable-stayed bridge have been investigated. Effects of several parameters such as (i) the interface bond between perforated plate and concrete, (ii) dowels inside the holes in the plate, and (iii) volume of steel fibers in the UHPC on the behavior of PBL were discussed in depth. Experimental results indicated that the use of a 2% volume fraction of steel fibers in the UHPC, increased the average bond strength at the plate/concrete interface and the shear resistant-capacity of concrete dowel by 82% and 50%, respectively, as compared to UHPC specimens without the fibers. The concrete dowel played an important role in developing the desired loading resistant-capacity of the PBL, and about 34–41% of the overall resistance of a standard PBL embedded in UHPC were supplied by the concrete dowel surrounding transverse rebar. The source of the achieved ductility of PBL was mainly determined by the action of transverse rebars, and the ductility in the specimens having transverse rebars was about eleven times the ductility of similar specimens without the rebars. Furthermore, the experimental ultimate strength values of PBL were compared with available equations in literatures published recently, and an analytical model for PBL/UHPC was developed and appropriate parameters were derived from present data and used to provide reliable prediction of ultimate resistant-capacity of PBL in the hybrid girders’ steel-concrete joints.

Experimental study on perfobond strip connector in steel–concrete joints of hybrid bridges

Perfobond strip (PBL) connectors, consisting of a perforated steel plate with steel rebar passing through the holes and embedded in concrete to transfer the shear action between the concrete and steel components, are increasingly used in composite and hybrid girders and columns. Though many studies on the behavior of PBL connectors can be found in the literature, the load transferring mechanism of PBL still needs further clarification because noticeable discrepancies can be found among the existing equations for predicting the shear capacity of the connectors. This paper presents an experimental study of the structural response of PBL connectors under push-out loading. Twelve push-out specimens fabricated according to the design used for the connectors in the steel–concrete joints in a hybrid cable-stayed bridge have been investigated. The behavior of the connectors, including the failure modes, ductility, and the components of the ultimate shear-resistant capacity, is discussed in depth. The results indicate that the mechanical properties of the PBL specimens are improved due to the bond at the interface between the perforated plate and the concrete. The transverse rebar located in the center of the steel plate hole is important for ensuring the connector's ductility. Furthermore, an analytical model and corresponding equation for predicting the ultimate resistance of PBL connectors with shear failure of the dowel are proposed, and the feasibility of the developed equation has been verified by the experimental results from related references.

Analysis of auxiliary ribs in steel–concrete joint of hybrid girder

The auxiliary ribs are utilized to reinforce the steel–concrete joints (SCJs) of hybrid girders. However, the demands of the ribs and the design of orthotropic steel decks with the auxiliary ribs are not addressed in design specifications. Solid element models are used to study the auxiliary ribs of the SCJ. The joints with and without auxiliary ribs are analyzed to clarify the demands and the reinforcing effects of the ribs. Stress dispersal efficiency of three typical auxiliary ribs is investigated. The trough–auxiliary rib (TA) joint is analyzed to check the steel deck design assumption and the approach to suppress stress concentration is discussed. The effective length of the auxiliary ribs is studied considering the geometric variations. Results show that the auxiliary ribs enlarge the steel deck and narrow the steel–concrete centroid deviation. The auxiliary ribs disperse about 50% axial force and the stress transmission of the joint is improved. The T-rib inserted in the trough is efficient to reinforce the SCJ with the effective length of 2–4 times the concrete slab thickness. The TA joint with abrupt tip suffers stress concentration and the safety margin of the steel deck is reduced. The joint is improved with about 60% hot spot stress decrease using the gentle tip with crossbeam constraint.

Research on Fatigue Load Parameters of Steel-Concrete Joint of Bridge Used for Highway Traffic and Light-Rail Traffic

This paper presents the calculation method for fatigue load parameters of light-rail traffic of the steel-concrete joints of Caiyuanba Yangtze River Bridge. Based on that the light-rail vehicles meet conforms to the normal distribution assumption, rain-flow counting method is adopted for the internal force amplitude of the steel-concrete joint induced by the light-rail traffic, which is then equivalent to fatigue load of constant amplitude according to linear cumulative damage criterion from Miner. With regard to design and research for similar bridges, this method can be referred to.

Research on Fatigue Load Parameters of Steel-Concrete Joint of Bridge Used for Highway Traffic and Light-Rail Traffic

This paper presents the calculation method for fatigue load parameters of light-rail traffic of the steel-concrete joints of Caiyuanba Yangtze River Bridge. Based on that the light-rail vehicles meet conforms to the normal distribution assumption, rain-flow counting method is adopted for the internal force amplitude of the steel-concrete joint induced by the light-rail traffic, which is then equivalent to fatigue load of constant amplitude according to linear cumulative damage criterion from Miner. With regard to design and research for similar bridges, this method can be referred to.

Experimental behaviour of heated composite steel–concrete joints subject to variable bending moments and axial forces

This paper presents the results of seven experimental tests performed at the University of Coimbra on a two dimensional composite steel–concrete beam-to-column sub-frame. These experimental tests were part of a global study of the robustness of composite steel–concrete open car park buildings under localised fire. The tested sub-frame was extracted from a composite open car park building, using the real cross-section dimensions of the beams (IPE 550) and the columns (HEB 300), and using bolts M30 grade 10.9 in the composite connection, and was subject to mechanical (bending and axial forces) and thermal loadings (constant temperature equal to 20°C, 500°C or 700°C; or linear increase up to 800°C). The interaction between the bending moment and axial load in the heated internal joint, after the loss of the column, is the objective of the tests. In order to reach this goal, the effect of the axial restraint to the beam was simulated: three tests were performed without any restraint to the beam, two tests with total axial restraint to the beam and two tests with a realistic axial restraint to the beam (spring restraint). The results of the seven tests are analysed and the behaviour of the joint is investigated and discussed in detail.

Risk Evaluation of Steel Structure Corrosion in Soft Foundation in the East Coast of Zhejiang

The detection index and evaluation for foundation engineering’s corrosion are performed in accordance with the “Code for Highway Engineering Geological Investigation” or “Code for Investigation of Geotechnical Engineering”. For both steel pipe piles and concrete pipe pile joints, the codes don’t consider the dissolved oxygen, Anaerobic organism and other corrosion factors. In order to improve the durability of the pipe pile foundation in coastal region, taking the typical coastal soft soil characteristics in eastern Zhejiang as example and by observing the steel corrosion electrochemical potential variation in the hypoxic environment, this paper analyses the corrosion risk of steel structures in marine deposit soft soil, and puts forward the microbial and electrochemical corrosion mechanism of the steel structures in foundation engineering in coastal environment. This paper argues that the Sulfate-Reducing Bacteria corrosion evaluation is indispensable in geotechnical investigation, and therefore should be included into the Code.

The Influence of the Epoxy Interlayer on the Assessment of Failure Conditions of Push-Out Test Specimens

Connection between steel and concrete parts is frequently required in constructions where the steel-concrete joints are often realized by welded shear studs. In order to avoid stress concentrations, corrosion proneness, and other negative consequences of the welding process, steel-concrete connection without welded mechanical shear connectors is sought nowadays. Connection can be realized via an epoxy adhesive layer and gritted with granules. In the paper, the assessment of the push-out test configuration was performed from the generalized fracture mechanics point of view. The numerical-analytical modelling of a steel-concrete connection is performed without and with the epoxy interlayer, while 2D and 3D modelling is used. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. The model of a bi-material notch with various geometry, and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Various manners of preparation of the epoxy interlayer are tested experimentally. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

Experimental Investigation of the Influence of the Bond Conditions on the Shear Bond Strength between Steel and Self-Compacting Concrete Using Push-Out Tests

Steel-concrete joints are often provided with welded shear studs. However, stress concentrations are induced in the structure due to the welding. Moreover, a reduction in toughness and ductility of the steel and a decreased fatigue endurance of the construction is observed. In this paper the shear bond strength between steel and ultra-high performance concrete (UHPC) without mechanical shear connectors is evaluated through push-out tests. The test samples consist of two sandblasted steel plates with a thickness of 10 mm and a concrete core. The connection between steel and concrete is obtained by a 2-component epoxy resin. Test samples with a smooth adhesive layer are compared with those with an epoxy layer, which is applied with a toothed paddle and/or gritted with small aggregates. In this research, specimens prepared with river gravel, crushed stone, and steel grit are compared and also two different epoxy resins are used. During the tests, the ultimate shear force is recorded as well as the slip between steel and concrete. All test specimens exhibited a concrete-adhesive or concrete failure. Furthermore, test results show that the use of a more fluid epoxy resin improves the anchorage of the gritted aggregates in the adhesive layer, resulting in higher shear bond stresses. No significant difference is found between specimens, gritted with river gravel or crushed stone. Applying the adhesive layer with the toothed paddle in horizontal direction slightly improves the bond behaviour. Finally, the experimental results of the test members with a smooth epoxy layer without gritted aggregates, provide test data for a fracture mechanics approach, which uses a 2D numerical model of the test specimen, composed of steel, epoxy resin, and concrete.

New strategy of substructure method to model long-span hybrid cable-stayed bridges under vehicle-induced vibration

Hybrid cable-stayed bridges consist of steel and concrete bridge segments, of which steel–concrete joints are of great importance and raise strong research interest. Due to the limitation of the traditional methods, i.e., the member finite element (FE) method and Mixed Dimensional Coupling (MDC) method, the present study proposes a substructure method to model long span bridges. The current application of the substructure method is to extract some specific parts of the whole structure to refine and analyze them. Different from the routine substructure approach, here the entire structure is modeled in detail and divided into many substructures. All the substructures are then condensed into super-elements except the concerned part. The application of the method is then illustrated through numerical studies of the vehicle–bridge coupling vibration of the Jingyue Yangtze River Bridge with a main span of 816 m. The entire bridge is first divided into many substructures with a reasonable length. Among them, the concerned substructure with 23.8 m in length including the steel–concrete joint is modeled in detail but not formed into super-element, while all the other components are modeled in detail and formed into super-elements using the component mode synthesis (CMS) method. All the components including both the super-elements and non-super-elements are then assembled into a complete and fine full bridge model. Finally, the model is used for the vehicle-induced dynamic analysis under deterministic traffic flows. The results show that the joint works well, and the transition between the steel girders and concrete beams is very smooth.

Failure Conditions from Push-Out Tests of a Steel-Concrete Joint: Experimental Results

Steel-concrete joints can suffer from premature fail due to inadequate shear bond between the two surfaces. In this paper the shear bond strength between steel and self-compacting concrete (SCC) without mechanical shear connectors is evaluated through push-out tests. The test samples consist of two sandblasted steel plates (10 and 6 mm) and a concrete core, with connection between steel and concrete obtained by a 2-component epoxy resin, gritted with granulates. During the tests, the ultimate shear force is recorded as well as the slip between steel and concrete. All test members exhibited a concrete - adhesive failure, and indicate nominal shear bond stresses between 2.20 and 4.22 MPa. In addition, a substantial difference in measured shear bond stresses is found between the 6 and 10 mm steel plates, indicating unwanted secondary effects with the 6 mm plates. During testing, maximum slip values between 0.02 and 0.05 mm are recorded. In addition to the experimental tests, shear stress distribution in the epoxy – concrete interface is examined by finite element analysis (FEA). In this way, a non-uniform stress distribution between steel and concrete is found with the maximum shear value about 2.5 times higher than the nominal shear stress value. The FEA combined with the experimental results provide a reasonable understanding of the shear induced failure conditions at a steel-concrete joint, and create test data for a fracture mechanics approach.

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part II: Parametric study and comparison with the Eurocode 4 proposal

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part II: Parametric study and comparison with the Eurocode 4 proposal

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part I: Finite element modelling and validation

The paper concerns the modelling of rigid and semi-rigid steel-concrete composite joints under monotonic loading through use of the Abaqus program, a widespread finite element code. By comparing numerical and experimental results obtained on cruciform tests, it is shown that the proposed modelling allows a good fit of the global joint response in terms of moment-rotation law. Even the local response in terms of stresses and strains is adequately predicted. Hence, this numerical approach may represent a useful tool for attaining a better understanding of experimental results. It may also be used to perform parametric analyses and to calibrate simplified mechanical models for practical applications. rn

Analytical evaluation of the moment-rotation response of beam-to-column composite joints under static loading

The analysis of steel-concrete composite joints presents some particular aspects that increase their complexity when compared to bare steel joints. In particular, the influence of slab reinforcement and column concrete encasement clearly change the moment-rotation response of the joint. Starting from an energy approach developed in the context of steel joints, an extension to composite joints is presented in this paper that is able to provide closed-form analytical solutions. In addition, the possibility of tri-linear or non-linear component behaviour is also incorporated in the model, enabling adequate treatment of the influence of cracked concrete in tension and the softening response of the column web in compression. This methodology is validated through comparison with experimental tests carried out at the University of Coimbra.

Modelling of steel-concrete composite joints

Modelling of steel-concrete composite joints