Partial Interaction Research Articles

08.25: The influence of the concrete slab on the behaviour of steel‐concrete composite joints for braced frames

ABSTRACTIn current practice, the design of seismic resistant steel‐concrete composite braced frames generally aims to ensure a structural behaviour for beam‐to‐column joints as close as possible to perfect hinges, hence preventing any kind of interaction with the bracing system. The global performance of steel‐concrete composite joints, on the other hand, is markedly affected by the structural interaction between the concrete slab and all the steel components at the beam‐to‐column intersection. This is especially true during seismic events, when compression forces can typically arise in the concrete slab in the vicinity of the column, leading to the occurrence of struts in contact with the column itself. As such, for appropriate design assumptions, it is thus necessary to fully understand the influence of the joint components interactions.To this aim, in this paper a refined Finite Element (FE) model representative of a hinged beam‐to‐column joint in a braced frame is implemented in the ABAQUS computer software and validated with experimental results. A full 3D solid modelling approach is first taken into account, with careful consideration for the geometrical and mechanical properties of each joint component, as well as for the corresponding contact interactions, including properly calibrated damage material models. After a preliminary validation of the FE modelling approach carried out towards earlier full‐scale experimental tests, a parametric FE study is proposed. By taking into account four different geometrical configurations for a reference steel‐concrete composite joint, in particular, being characterized by (i) absence of slab, (ii) presence of slab with partial interaction with the column (i.e. isolated slab), (iii) presence of slab with interaction (even with small gap on one side) and (iv) fully interacting slab, major FE outcomes are critically discussed. It is shown, in this regard, that the isolation of the slab is typically associated to important effects on the structural performance of the joint itself, compared to a fully interacting concrete slab.

Mean crack spacing modelling for RC tension elements

An approach for predicting the crack spacing of reinforced concrete tension elements is presented in this paper. Two well established methods, the mean strain and the stress transfer approaches (partial interaction) are combined through a newly proposed strain compliance principle. Through the assumption of a linear strain shape function governing the reinforcement strains in the stabilized cracking stage, the method enables the prediction of the mean crack spacing from the stress transfer approach. The strain compliance principle establishes the equality of the mean strains, estimated for a given loading level by a mean strain approach and the stress transfer approaches. The proposed approach requires a single data point, represented by a reinforcement ratio and bar diameter, that is denoted as a reference element and is further used to obtain the distance between cracks for any other tensile concrete element. A free-of-shrinkage tension stiffening law was employed for the evaluation of the mean reinforcement strains. A thorough investigation of this approach together with results for varying concrete compressive strengths, reinforcement ratio and bar diameters is presented. The new method was shown to give reasonably accurate results and most importantly, proposes a new way of investigating the cracking behavior of concrete elements.

Time‐dependent serviceability behavior of reinforced concrete beams: Partial interaction tension stiffening mechanics

The partial interaction (PI) mechanics of tension stiffening governs crack widening and the consequential deflection of reinforced concrete (RC) beams and, therefore, is essential in the serviceability design of RC structures. Both behaviors are dependent on the PI global load slip behavior of the tensile reinforcement relative to the surrounding concrete at a crack face, which in turn is dependent on the local PI material bond‐stress/slip relationship between the reinforcement and adjacent concrete. Due to the complexity of PI theory, it has been difficult to directly incorporate PI mechanics into design procedures. Consequently, empirical approaches to quantify effective flexural rigidities and crack widths are commonplace. While empirical approaches can be derived relatively simply for short‐term loading, the influence of concrete shrinkage and creep is difficult to incorporate. In this paper, pure mechanics‐based PI solutions to describe the crack spacing and tension stiffening behavior of RC beams subjected to long‐term loads are derived. They only require material properties and clearly show the interaction among shrinkage, creep and bond properties. They are simple enough to use directly in design and will help in the experimental derivation of the material properties. The results of these PI analyses are used in a companion paper to develop design rules for the time‐dependent serviceability deflection of RC beams and compared with test results.

Long‐ and short‐term serviceability behavior of reinforced concrete beams: Mechanics models for deflections and crack widths

Analysis and design of reinforced concrete (RC) flexural members at the serviceability limit state is complicated by the localized bond slip or partial interaction (PI) between tensile reinforcement and the surrounding concrete. Localized slip is responsible for crack formation, crack widening, and tension stiffening and is further complicated by the time‐dependent nature of concrete, which results in reduced tension stiffening and widening of cracks. Analysis techniques commonly applied in design are typically formulated on the assumption of full interaction between the reinforcement and the surrounding concrete. Hence, they do not simulate the behaviors observed in practice, but rather they correlate analytical predictions with experimental observations through the use of empiricisms, such as effective flexural rigidities and statistically derived expressions for crack widths. In this paper, it is shown how PI theory can be directly incorporated into elastic analysis procedures to develop simple expressions for flexural rigidities and crack widths under both instantaneous and sustained loading. The proposed approach should simplify not only the design process but also the development of design guidelines and material models, as it provides a simple rational method for investigating the time‐dependent flexural behavior of RC members.

Effect of steel bar corrosion on flexural behaviour through bond

Steel reinforcing bar corrosion is a major concern in reinforced concrete (RC) structures. Two problems have to be tackled: determining the rate of corrosion and determining the effect of corrosion on the behaviour of the RC structure, not just at the serviceability limit but also at the ultimate limit. This paper deals with the latter, that is, the quantification of the effect of a known amount of corrosion on the flexural capacity of RC beams at the ultimate limit state. A partial interaction numerical procedure is described for quantifying the effect of corrosion at the ultimate limit state. The procedure quantifies: the flexural capacity and ductility prior to debonding – that is, while the corroded bars are still acting as reinforcement; the onset of debonding; and the flexural capacity and ductility after debonding while the corroded bars are acting as tendons. It is shown through mechanics that the onset of debonding due to corrosion is not necessarily a major or catastrophic problem as the RC beam can still have significant strength and ductility, both of which are quantifiable.

Mutual plumage ornamentation and biparental care: consequences for success in different environments

Lay SummaryParental care and reproductive success of collared flycatchers were related to own and partner’s sexual ornaments in partial interaction with environmental conditions. In a brood size manipulation experiment, male wing patch size and female plumage brightness correlated with the partner’s feeding rate. Nestling quality correlated with male forehead patch size depending on breeding environment. These findings reveal a complex picture of relationships between the sexual ornament expression of parents and their parental care and success.

Influence of Shear Connection Distributions on the Behaviour of Continuous Steel-concrete Composite Beams

Background:In this work the behaviour of continuous steel-concrete composite beams with different shear connection distributions obtained from two design methods,i.e. Eurocode 4 and a proposed alternative approach, is analysed.Objective:For this purpose a finite element model specifically developed for the nonlinear analysis of steel-concrete composite beams is adopted. This finite element model includes material nonlinearity of slab concrete, reinforcement steel, beam steel as well as slab-beam nonlinear partial interaction due to the deformable shear connection. The inclusion of the partial interaction in the composite beam model provides information on the slab-beam interface slip and shear force and enables to model the failure of the shear connectors.Results and Conclusion:In this way it is possible to analyse and quantify the effect of shear connector distributions on the global and local response of continuous steel-concrete composite beams, both under service load levels and at collapse. Particular attention is focused on the ductility requirements on the shear connectors when varying the connection design approach and distribution.

Local vibrations and lift performance of low Reynolds number airfoil

The 2D incompressible Navier-Stokes equations are solved based on the finite volume method and dynamic mesh technique is used to carry out partial fluid structure interaction. The local flexible structure (hereinafter termed as flexible structure) vibrates in a single mode located on the upper surface of the airfoil. The Influence of vibration frequency and amplitude are examined and the corresponding fluid flow characteristics are investigated which add complexity to the inherent problem in unsteady flow. The study is conducted for flow over NACA0012 airfoil at 600≤Re≤3000 at a low angle of attack. Vibration of flexible structure induces a secondary vortex which modifies the pressure distribution and lift performance of the airfoil. At some moderate vibration amplitude, frequency synchronization or lock-in phenomenon occurs when the vibration frequency is close to the characteristic frequency of rigid airfoil. Evolution and shedding of vortices corresponding to the deformation of flexible structure depends on the Reynolds number. In the case of Re≤1000, the deformation of flexible structure is considered in-phase with the vortex shedding i.e., increasing maximum lift is linked with the positive deformation of flexible structure. At Re=1500 a phase shift of about 1/π exists while they are out-of-phase at Re>1500. Moreover, the oscillation amplitude of lift coefficient increases with increasing vibration amplitude for Re≤1500 while it decreases with increasing vibration amplitude for Re>1500. As a result of frequency lock-in, the average lift coefficient is increased with increasing vibration amplitude for all investigated Reynolds numbers (Re). The maximum increase in the average lift coefficient is 19.72% within the range of investigated parameters.

A piecewise linear transverse shear transfer model for bolted side-plated beams

The performance of bolted side-plated (BSP) beams is affected by the degree of transverse partial interaction, which is a result of the interfacial slip caused by transverse shear transfer between the bolted steel plates and the reinforced concrete beams. However, explicit formulae for the transverse shear transfer profile have yet to be derived. In this paper, a simplified piecewise linear shear transfer model was proposed based on force superposition principle and simplification of shear transfer profiles derived from a previous numerical study. The magnitude of shear transfer was determined by force equilibrium and displacement compatibility condition. A set of design formulae for BSP beams under several basic load cases was also derived. Then the model was verified by test results. A worked example was also provided to illustrate the application of the proposed design formulae. This paper sheds some light on the shear force transfer mechanism of anchor bolts in BSP beams, and offers a practical method to evaluate the influence of transverse partial interaction in strengthening design.

K-maxitive fuzzy measures: A scalable approach to model interactions

Fuzzy measures are powerful at modeling interactions between elements. Unfortunately, they use a number of coefficients that exponentially grows with the number of elements. Beyond the computational complexity, assigning a value to any coalition of a large set of elements does not make sense. k-order measures model interactions involving at most k elements. The number of coefficients to identify is reduced and their modeling capacity is preserved in real problems where the number of interacting elements is limited. In extreme situations of full redundancy or complementariness, it is mathematically proven that the complete fuzzy measure is both k-additive and k-maxitive. A learning algorithm to identify k-maxitive measures from labeled data is designed on the basis of HLMS (Heuristic Least Mean Squares). In a classification context, the study of synthetic data with partial redundancy or complementariness supports the idea that the difference between full and partial interaction is a matter of degree, not of kind. Dealing with two real world datasets, a comparison of the complete fuzzy measure and a k-maxitive one shows the number of interacting elements is limited and the k-maxitive measures yield the same characterization of interactions and a comparable classification accuracy.

Semi-empirical determination of gamma-ray kerma coefficients for materials of shielding and dosimetry from mass attenuation coefficients

In the present study, a semi-empirical formula for determination of gamma-ray kerma coefficient, k, has been developed. It based on the experimental total mass attenuation coefficient and the theoretical partial photon interaction probabilities. This semi-empirical technique has been applied to determining semi-empirical values of k for three elements, and 20 compounds and materials at different photon energy values; also, the theoretical values of this coefficient were calculated in the extended energy range from 1 keV to 100 MeV. The results showed that all kerma coefficient curves followed the same trend, regardless the material type. Shifting in kerma coefficient minima has been observed towards the high energy by increasing the average atomic number of sample. The results of the study have also shown that the proposed formula is simple and has potential application for determining the semi-empirical kerma coefficient of various elements, compound, and materials over a wide range of photon energy from 1 keV to 100 GeV.

Interaction between NiOx and MWСNT in NiOx/MWСNTs composite: XANES and XPS study

The current work presents the investigation of the interaction between NiOx and multi-walled carbon nanotube (MWCNTs) sidewall in NiOx/MWCNT nanocomposite, synthesized by electrochemical metal oxidation and dispersion method using the near edge X-ray absorption fine structure (XANES) and X-ray photoelectron spectroscopies. Scanning electron microscopy (SEM) illustrated that formation of the NiOx/MWCNT composite leads to decreasing of the NiOx sheets size and their dispersion among nanotubes. Comparison of the C K-edge XANES spectra of the initial high-purified MWCNTs with NiOx/MWCNTs indicates significant shape changes of the nanocomposite spectrum. Changes in π resonance and inter-resonance region of C K-edge XANES spectrum showed the appearance of new chemical bonds in the carbon nanotubes as result of formation of NiOx/MWCNTs nanocomposite, associated with partial chemical interaction of NiOx with CNT walls. The chemical state of Ni in the composite compound is 2+ and there is Ni with different oxygen surroundings in the NiOx/MWCNT nanocomposite.

A simplified method for predicting early-age stresses in slabs of steel-concrete composite beams in partial interaction

Thermal effects due to the heat produced by cement reaction and shrinkage deformations affecting concrete generally results in stresses that can lead to early age cracking in the concrete slab of composite beams. This work provides a simplified approach for determining the time evolution of stresses developing at early age in curing concrete slabs of composite beams. Specifically, the method generally used in practice and based on a simple sectional analysis is extended to the case of steel-concrete composite beams in partial interaction. The time evolution of the force-slip relationship characterising the shear connector response as a result of the concrete curing process is also taken into account by means of a simple assumption corroborated by some experimental results available in the literature. The results obtained by applying the two proposed methods are compared to those achieved by means of the general practice-oriented procedure. Different types of cement, featuring a variable time evolution of the hydration process, are taken into account. Moreover, the effect of different external temperature at casting is also considered. It is worth highlighting that the proposed method enhances the predicting capability of the current practical ones, with almost no increase in calculation effort.

Time dependent behaviour of composite beams with partial interaction for different types of shear connectors

The structural behavior of composite steel concrete beams with long term deflection was investigated, taking in considerations several variables including degree of shear connectors 50%, 75%, 100%, and type of connectors including headed and hooked studs smooth or deformed. Five composite steel-concrete beams were tested each consist of steel section W12x35 and 300x100 concrete slabs. The composite beams were tested under uniformly distributed loads for different time interval up to 180 days. The results showed that the degree of interaction have significant influence on the long- term behavior of the composite steel concrete beam . When the degree of interaction decreased from 100% to 75% then to 50% the maximum long-term mid span deflection increased about 35.1% and 65.9% respectively at 180 days after loading. Also, the end slip increased about 67.5% and 112.4% respectively at 180 days after loading. The results showed that the type of the used shear connectors has slight influence on the long-term behavior of the composite steel concrete beams. For certain degree of interaction (75%)with using headed and hooked studs smooth or deformed the maximum long-term mid span deflection decreased about 7.1% and 11.7%at 180 days after loading, and the end slip decreased about 4.8% and 12.5% at 180 days after loading.

The Effects of Presented Media Types on Spatial Cognition Task Performance in Preschool Children

As the use of digital media is becoming more universal and is being used in early-childhood education, understanding the effects of digital media on development is required. The purpose of this study was to examine whether child performance on a spatial cognition task depends on the type of media used to present the task and if the effect of media type is different depending on child's age and sex. To do this, a spatial cognition task set (consisting of direction, rotation, symmetry, conjugation, and part/whole tasks) was prepared, and these tasks were presented to 60 3-, 4-, and 5-year-old children using paper- and tablet-based measures. Our results showed that the correct answer rate of task performance differed significantly when completing the task on a tablet than when completing the task on paper. Generally, response times when completing the tasks on a tablet was significantly shorter than when completing the tasks on paper. Although there was no interaction between the type of media and age, and partial interaction was found between the type of media and sex. This result implies an influence of digital stimulation on child performance on the spatial cognitive task. This study provides a basic understanding for follow-up studies to examine the consequences of exposure to digital stimulation.

Modelling of FRP-concrete bonded interfaces containing FRP anchors

Anchors made from fibre-reinforced polymer (FRP) composites can be used to delay the propagation of debonding cracks and enhance the deformability of FRP-to-concrete bonded interfaces. This paper presents a model for FRP anchors that is calibrated from tests on FRP-to-concrete joints anchored with FRP anchors. The anchor model is incorporated in a partial interaction model in order to simulate the behaviour of such anchored joints. Simulations of the relationship between load and slip compare favourably with tests results. Simulations also accurately represent the distribution of strain along the length of the FRP plate for FRP-to-concrete joints anchored with a single as well as multiple FRP anchors. The simulations are then extended to include the distributions of bond stress and slip along the FRP plate and they ultimately lead to a better understanding of the influence of anchors upon FRP-concrete bonded interfaces. Parametric studies are finally reported and they demonstrate the influence of the key FRP anchor model parameters.

Explicit matrices for a composite beam-column with refined zigzag kinematics

This paper presents explicit expressions of the linear and geometric stiffness matrix, as well as the mass matrix and vector of equivalent nodal forces for a simple planar beam finite element based on the Refined Zigzag Theory. After a brief review of the theory, the matrices are derived via Hamilton’s principle and special anisoparametric (interdependent) shape functions. The \(C^{0}\)-continuous element shows remarkable accuracy in the analysis of composite laminated or sandwich beams and for particular structures with partial interaction of two or more subcomponents with interlayer slip.

Numerical simulation of external pre-stressed steel-concrete composite beams

External pre-stressing is often used in strengthening or retrofitting of steel-concrete composite beams. In this way, a proper numerical model should be able to trace the completely nonlinear response of these structures at service and ultimate loads. A three dimensional finite element model based on shell elements for representing the concrete slab and the steel beam are used in this work. Partial interaction at the slab-beam interface can be taken into account by using special beam-column elements as shear connectors. External pre-stressed tendons are modeled by using one-dimensional catenary elements. Contact elements are included in the analysis to represent the slipping at the tendon-deviator locations. Validation of the numerical model is established by simulating seven pre-stressed steel-concrete composite beams with experimental results. The model predictions agree well with the experimental results in terms of collapse loads, path failures and cracking lengths at negative moment regions due to service loads. Finally, the accuracy of some simplified formulas found in the specialized literature to predict cracking lengths at interior supports at service loading and for the evaluation of ultimate bending moments is also examined in this work.

A higher order model for inelastic response of composite beams with interfacial slip using a dissipation based arc-length method

An efficient one dimensional finite element model is developed for an accurate prediction of the inelastic response of steel-concrete composite beams with partial shear interaction using a higher-order beam theory (HBT). This is achieved by taking a third order variation of the longitudinal displacement over the beam depth for the two layers separately. The deformable shear studs used for connecting the concrete slab with the steel girder are modelled as distributed shear springs along the interface between these two material layers. A plasticity model based on von Mises yield criterion and a damage model are used to simulate the inelastic behaviour of beam materials. An arc-length method based on energy dissipation is employed to capture the post peak response successfully. The capability of the proposed model is assessed through its validation and verification using existing experimental results and numerical results produced by detailed finite element modelling of these beams.

Golgi-retained Cx32 mutants interfere with gene addition therapy for CMT1X

Numerous GJB1 gene mutations cause the X-linked form of Charcot-Marie-Tooth disease (CMT1X). GJB1 encodes connexin32 (Cx32), which forms trans-myelin gap junctions in Schwann cells. Most GJB1 mutations result in loss-of-function mechanisms, supporting the concept of gene replacement therapy. However, interactions between delivered wild type and endogenously expressed mutant Cx32 may potentially occur in the setting of gene replacement therapy. In order to screen for possible interactions of several representative CMT1X mutants with wild type Cx32 that may interfere with the functional gap junction formation, we established an in vitro screening method co-expressing in HeLa cells wild type Cx32 and one of eight different Cx32 mutants including A39P, A39V, T55I, R75W, M93V, L143P, N175D and R183S. Some of the Golgi-retained mutants hindered gap junction plaque assembly by Cx32 on the cell membrane, while co-immunoprecipitation analysis revealed a partial interaction of wild type protein with Golgi-retained mutants. Dye transfer studies confirmed that Golgi-retained R75W, M93V and N175D but not endoplasmic reticulum-retained T55I had a negative effect on wild type Cx32 function. Finally, in vivo intraneural delivery of the gene encoding the wild type Cx32 in mice bearing either the T55I or R75W mutation on Cx32 knockout background showed that virally delivered protein was correctly localized in mice expressing the endoplasmic reticulum-retained T55I whereas it did not traffic normally in mice expressing the Golgi-retained R75W. Thus, certain Golgi-retained Cx32 mutants may interfere with exogenously delivered Cx32. Screening for mutant-wild type Cx32 interactions should be considered prior to planning gene addition therapy for CMT1X.