Design-oriented Model Research Articles

Numerical-aided flexural-based design of fibre reinforced concrete column-supported flat slabs

The growing use of fibre reinforced concrete (FRC) for structural purposes has led several guidelines to include design-oriented models that allow the partial (and even total) substitution of the steel reinforcing bars. Among those, fibres as concrete reinforcement for elevated concrete flat slabs is gaining interest due to the identified technical and benefits and quantified sustainability enhancements. However, although this technology has already been used in buildings and its sufficient bearing capacity confirmed by real-scale experimental programs, its straightforward implementation is far from being consolidated. The latter is owing to the existence of several paramount aspects to be answered. One of those is the influence of the fib MC-2010 FRC post-cracking strength classification, including the combination of steel bars, on the mechanical response of these elements at ULS and SLS. In this context, a non-linear finite element model was implemented and validated by means of results from existing real-scale tests. Posteriorly, the model was used to design a new real-scale test to be performed within the context of the research project eFIB (from the Spanish, Optimization of Construction Processes of Structural Elements by using Fibre Reinforced Concretes). To this end, a parametric study was developed by considering several FRC post-cracking strength classes, using fibres as unique reinforcement or combined with steel meshes, to determine an optimum solution for flexure (which governs the main reinforcement requirements) based on the structural reliability index targeted for building construction. The model results and analysis permitted to derive relevant conclusions from the material design optimization point of view, which can be a reference for future similar experiences.

Hybrid regression and machine learning model for predicting ultimate condition of FRP-confined concrete

The accurate design-oriented model for concrete confined with fiber-reinforced polymer (FRP) is important to provide safe design of this composite system. In this paper, the response surface model (RSM) is coupled with support vector regression (SVR) for developing a novel hybrid model, namely RSM-SVR, with the aim of predicting the ultimate condition of FRP-confined concrete. Predictions obtained by the proposed model were compared with those by six empirical models and two data-driven models of RSM and SVR for database containing 780-test column results with circular cross section. Statistical analysis reveals that the proposed RSM-SVR model predicts the compressive strength and corresponding axial strain of the concrete confined with FRPs more accurately in comparison with the existing models. The results also show that RSM-SVR and SVR models provide stable predictions of strength and strain enhancement ratios for lateral confining ratio of >1 while the other models exhibit chaotic model error. The high accuracy and stable predictions by the proposed model are achieved based on its high flexibility and robustness in capturing the effect of lateral confining pressure as the interaction between the concrete core and FRP jacket in comparison with the existing models.

Assessment of the variability and uncertainty of using post-customer plastics as natural aggregate replacement in concrete

This paper presents a comprehensive assessment of the performance of concrete containing post-customer plastic as natural aggregate replacement. An experimental database of 370 individual concrete mix designs is collated from 60 studies and covers a large variety of plastic aggregate types and concrete mixing factors. This database is used to: evaluate the overall variability of plastic aggregate concrete (PAC), quantify the uncertainty of applying models developed for natural aggregate concrete (NAC) to predict the compressive strength of PAC, and to identify the influential PAC mixing factors. The database is also used to develop a new design-oriented model to predict the 28-day compressive strength of each type of PAC. A significant change in the failure mechanism of PAC at different strength grades is identified based on these analyses. Moreover, comparisons of mechanical properties of PAC with models given in major design codes for conventional NAC are performed. It is shown that the existing models cannot adequately predict PAC mechanical properties due to the significant differences in the characteristics of PA and NA.

Design-oriented strength and strain models for GFRP-wrapped concrete

The aim of this paper is to develop design-oriented models for the prediction of the ultimate strength and ultimate axial strain for concrete confined with glass fiber-reinforced polymer (GFRP) wraps. Twenty of most used and recent designoriented models developed to predict the strength and strain of GFRP-confined concrete in circular sections are selected and evaluated basing on a database of 163 test results of concrete cylinders confined with GFRP wraps subjected to uniaxial compression. The evaluation of these models is performed using three statistical indices namely the coefficient of the determination (R2), the root mean square error (RMSE), and the average absolute error (AAE). Based on this study, new strength and strain models for GFRP-wrapped concrete are developed using regression analysis. The obtained results show that the proposed models exhibit better performance and provide accurate predictions over the existing models.

Axial behaviour of FRP-confined rubberised concrete: An experimental investigation

This paper investigates the axial behaviour of square and circular concrete specimens confined by externally bonded Fibre Reinforced Polymer (FRP) jackets. Axial compression tests were performed on 96 regular and rubberised concrete specimens. The parameters considered were rubber content (0% and 60%), section shape (circular and square), FRP type (Carbon or Aramid) and the number of FRP layer (1, 2 and 3). The behaviour of the specimens in both axial and lateral directions, as well as their dilation characteristics, were investigated. The test results indicate that the confinement effectiveness of Aramid-FRP is better than that of Carbon-FRP. It is also shown that the detrimental effect of sharp corner on confinement effectiveness is less critical when using high rubber content as the element can develop large lateral expansion at unprecedented axial deformation. Large axial deformations can enable the development of highly ductile concrete elements. Existing design-oriented models fail to predict the behaviour of confined rubberised concrete with rectangular cross-section, indicating the need for developing more refined confinement models.

Design-oriented modeling of antenna structures by means of two-level kriging with explicit dimensionality reduction

The employment of full-wave electromagnetic (EM) analysis is a practical necessity in the design of contemporary antenna structures. This is because simpler models are generally not available or of limited accuracy. At the same time, EM-based design is computationally expensive. Consequently, the ways of accelerating tasks such as parametric optimization or uncertainty quantification have to be sought. A possible workaround that has been gaining popularity over the recent years is utilization of fast surrogates. Among these, data-driven models are the most popular due to their versatility and easy handling. Notwithstanding, the curse of dimensionality and utility requirements (e.g., having the surrogate valid over broad ranges of geometry and operating parameters) limit the applicability of conventional approximation approaches to antenna modeling. Recently proposed performance-driven methods, especially the nested kriging framework, allow for going beyond the capability of the standard techniques. This is achieved by an appropriate confinement of the model domain, defined to contain only high-quality designs with respect to the selected performance figures. This paper proposes a novel approach, which combines the main idea of the nested kriging, specifically, the first-level model as a tool for constructing the domain-defining manifold, as well as principal component analysis to reduce the domain dimensionality in an explicit manner. Comprehensive benchmarking using three antenna structures indicates superiority of our methodology over conventional techniques, but also nested kriging, in terms of the achievable predictive power. The latter is obtained without compromising design utility of the model as demonstrated through application case studies.

Compressive behavior for recycled aggregate concrete confined with recycled polyethylene naphthalate/terephthalate composites

Environmentally friendly recycled aggregate concrete (RAC) is a good alternative to natural aggregate concrete (NAC). The poor performance of RAC (e.g., relatively lower strength than its NAC counterpart) that limits its engineering application can be improved by the lateral confinement of fiber-reinforced polymer (FRP). A new type of FRP emerged in recent years and made from recycled polyethylene naphthalate (PEN)/terephthalate (PET) fibers has a large rupture strain (LRS, typically greater than 5%). It is ideal for confining RAC, especially to satisfy the ductility requirements of structures in earthquake zones. In this study, 40 RAC circular specimens wrapped with LRS FRP were tested for monotonic compressive behavior. The replacement ratio of recycled coarse aggregate and the confinement stiffness of FRP were experimentally studied. Test results indicate that the enhancement of compressive strength and strain of RAC is mainly affected by the confinement stiffness, but marginally affected by the replacement ratio. Furthermore, the results show that the design-oriented model and analysis-oriented model previously developed by the authors’ group for LRS FRP-confined NAC, can present satisfactory predication performance on LRS FRP-confined RAC. These findings not only provide design guidance for LRS FRP-confined RAC members, but also point to the possibility of the development of a sustainable structural system.

Design-oriented axial stress–strain model for partially fiber-reinforced-polymer-confined normal-strength concrete:

Due to the influence of “arching action” in fiber-reinforced polymer (FRP) partially confined concrete columns as a result of the unconfined regions, the confinement of the concrete columns wrapped...

Design-oriented axial stress–strain model for partially fiber-reinforced-polymer-confined normal-strength concrete

Due to the influence of “arching action” in fiber-reinforced polymer (FRP) partially confined concrete columns as a result of the unconfined regions, the confinement of the concrete columns wrapped with discrete FRP strips is less efficient when compared with full wrapping schemes. This study comprehensively investigates the difference of the the confinement mechanism between fully and partially FRP confined circular normal-strength concrete and thus presents a new design-oriented model to predict the stress–strain relationships of partially FRP confined normal-strength concrete. The formulas used to determine the strength and corresponding strain of several key points on the stress–strain curves are also proposed by the regression analysis according to a reliable test database from the relevant literature. Besides, another selected database including 100 FRP partially wrapped circular concrete columns is also collected for model verification. The results show that better performance can be achieved by the new model compared with the selected models in predicting the ultimate conditions of partially FRP confined concrete. Finally, some specimens are chosen to assess the performance of the new model in predicting the complete axial stress–strain curves. The comparisons reveal that satisfactory accuracy and good agreement can be achieved between the theoretical predictions and experimental observations.

Analysis-oriented models for FRP-confined concrete: 3D interpretation and general methodology

An important application of fibre-reinforced polymer (FRP) composites in structural engineering is to confine concrete. In contrast to actively confined concrete, the stress-strain curve of FRP-confined concrete can have a second ascending branch when sufficient confinement is applied. Numerous analytical models have been proposed to predict the axial stress–strain behaviour of FRP-confined concrete. These models can be classified into two categories: (a) analysis-oriented models and (b) design-oriented models. In this paper, a 3-dimensional geometrical approach is proposed to interpret the general theory of analysis-oriented models based on three general equations. This approach provides an intuitive perspective to understand the analysis-oriented models and the mechanism of FRP-confined concrete. With this approach, a systematic methodology for calibrating analysis-oriented models is demonstrated, and the parameters in design-oriented models are justified. This methodology can also be applied to build analysis-oriented models for other concrete-type materials.

Design-oriented model for circular F-STC stub columns subjected to axial compression

A fiber-reinforced polymer (FRP)-steel composite tubed concrete (F-STC) column is formed by wrapping FRP sheets around a steel tubed concrete column (STC). Both the strength and deformability of the core concrete are improved by the FRP-steel composite tube and the steel tube is prevented from corrosion. A number of studies have been conducted on the prediction of stress-strain behavior of FRP-confined concrete columns and steel tube-confined concrete columns. However, few models focus on the concrete under combined confinement of FRP and steel tube. This paper presents an analytical study on the design-oriented model for F-STC columns. To determine the confining stress, the stress distribution of steel tube was firstly analyzed and the equivalent stress was obtained. In addition, a strain efficiency factor was proposed for the prediction of rupture strain of FRP. Then the peak condition and ultimate condition of F-STC columns were investigated and related predicting models for the load bearing capacity and deformation were proposed. Finally, design-oriented models were proposed for F-STC columns with different types of axial load-strain curves and generally coincided well with the existing test results.

Design-oriented computationally-efficient feature-based surrogate modelling of multi-band antennas with nested kriging

Design of modern antenna structures heavily depends on electromagnetic (EM) simulation tools. EM analysis provides reliable evaluation of increasingly complex designs but tends to be CPU intensive. When multiple simulations are needed (e.g., for parameters tuning), the aggregated simulation cost may become a serious bottleneck. As one possible way of mitigating the issue, the recent literature fosters utilization of faster representations, or surrogates, of the system at hand. Notwithstanding, conventional models are severely affected by the curse of dimensionality. In practice, modelling of antenna structures described by no more than a few parameters over narrow parameter ranges is possible. In the context of the structural complexity of modern antennas, this is hardly acceptable. This paper presents a novel technique for cost-efficient design-oriented modelling of multi-band antennas. Our approach integrates a recently reported nested kriging framework and the response feature technology. This combination enables rendering of reliable surrogates valid within broad ranges of geometry parameters while using small training data sets. Benchmarking against conventional modelling methods demonstrates superiority of the proposed framework in terms of both the predictive power of the surrogate and its setup cost. Design applications for antenna optimization are discussed as well.

Implementing product design assessment with sandwich-like architecture: A case study in an automotive company

Product design-oriented models are a decision-making problem with multiple criteria based on the assessment of product design factor that represent engineer judgments and customer desires, and are used to adapt to increasing competition and high levels of customization. Thus, in this work, a “sandwich-like” architecture and a hybrid integrated approach including triangle fuzzy numbers, quality function deployment, and the LeaderRank algorithm are respectively proposed to express and assess product designs more effectively. Additionally, the proposed approach is a measure study which can determine the design requirements, the relationships between product design and customer requirements, and the correlations among product values. The fuzzy analytical network process and LeaderRank algorithm are employed to evaluate the product design requirements and interaction between the product value and the uncertainty that exists in expert judgment. Besides, a case study is selected as an example to illustrate the “sandwich-like” architecture in the product design stage, and a priority analysis is performed to assess the importance degrees of product designs for customer needs, thereby providing optimization for product design and an effective approach to improve the product value.

Axial compressive behavior of concrete-filled FRP-steel wire reinforced thermoplastics pipe hybrid columns

This paper presents investigations on a new column form, namely, concrete-filled fiber-reinforced polymer-steel wire reinforced thermoplastics pipe (FRP-SRTP) columns (CFFSCs) which consist of a SRTP tube with an outer FRP confinement system and concrete filled in the core area. A series of axial compression tests were performed on CFFSCs, and parameters including the number of FRP layers, the FRP fiber type and the clear spacing of the FRP rings were investigated. The test results demonstrate that the concrete-filled SRTP tube columns have an excellent ductility and the outer FRP confinement system provides efficient confinement to CFFSCs. The dilation behavior of the concrete in CFFSCs with polyethylene terephthalate FRP is different to that of the concrete in CFFSCs with carbon FRP. Four existing design-oriented models are adopted to generate the ultimate axial stresses and their corresponding strains of concrete in CFFSCs. By comparing the test results and the theoretical predictions, it is found that the existing models provides inaccurate predictions for CFFSCs. The new column form is particularly suitable as a form of standing support for underground mines, where a novel supporting system requires both a large deformation capacity and a good structural integrity.

A New Design-Oriented Model of Glass Fiber-Reinforced Polymer-Reinforced Hollow Concrete Columns

Hollow concrete columns (HCCs) reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals are considered an effective design solution for bridge piers, electric poles, and ground piles because they use less material and maximize the strength-toweight ratio. HCC behavior is affected by critical design parameters such as inner-to-outer diameter ratio, reinforcement and volumetric ratios, and concrete compressive strength. This paper proposes a new design-oriented model based on the plasticity theory of concrete and considering the critical design parameters to accurately describe the compressive load-strain behavior of GFRP-reinforced HCCs under monotonic and concentric loading. The validity of the proposed model was evaluated against experimental test results for 14 full-scale hollow concrete columns reinforced with GFRP bars and spirals. The results demonstrated that the proposed design-oriented model was accurate and yielded a very good agreement with the axial compressive load behavior of GFRP-reinforced hollow concrete columns.

Behaviour of FRP tube-concrete-encased steel composite columns

Fibre-reinforced polymer (FRP) tube-concrete-encased steel (FTCES) column, which consists of an FRP tube, encased steel section and concrete filled between them, attracts the attention of more and more researchers since it has excellent corrosion resistance, superior strength, stiffness and ductility. However, experimental studies on FTCES columns are relatively limited compared with other composite columns, such as concrete-filled-steel-tube columns. Moreover, existing analytical models predicting the load-strain relationships on the FTCES columns were all design-oriented models. A scientifically more rigorous analysis-oriented model is required to explain the complicated physical conditions at the interface among concrete, encased steel and FRP tube, which should consist of a concrete dilation model based on equilibrium and compatibility conditions. Herein, to understand more thoroughly and simulate the uni-axial performance of FTCES columns, an experimental study, consisting of 41 specimens has been conducted. The main parameters are FRP tube thickness, encased steel shape and ratio. Moreover, an analysis-based path dependent load-strain model, previously developed by the authors for the FRP tube-confined concrete columns, has been modified for the FTCES columns. The validity of the proposed model is confirmed by the good agreement obtained between the measured axial load-strain curves of FTCES columns and the theoretically proposed values.

Data-driven ultimate conditions prediction and stress-strain model for FRP-confined concrete

Fiber Reinforced Polymer has been widely used in the retrofit of existing structures and the construction of new structures. The ultimate conditions and stress–strain model of FRP-confined composites are critical to structural design and prediction of structural response, especially under extreme loads such as earthquakes. In this paper, a data-driven neural network prediction model for ultimate conditions and stress–strain constitutive relation of FRP-confined concrete is proposed, and the validity and accuracy of the model are verified. A uniaxial compression database containing 169 FRP-confined normal concrete cylinders is collected from the open literature, and the quality of the database is examined and evaluated in detail. Based on the feed forward neural network technology, a prediction model for the ultimate conditions of FRP-confined normal concrete cylinders is established. Configurations and hyper-parameters of the network are carefully analyzed, and the optimal model is used for prediction and comparison. Besides, a uniaxial stress–strain model for FRP-confined concrete is established using a neural network with a recursive structure. The prediction accuracy of the proposed model is proven to be superior to the existing design-oriented models. The data-driven neural network prediction models developed in this paper can provide a rapid prediction and design for FRP-confined composites.

Shear tab connection with composite beam subjected to transient-state fire temperatures

Purpose This study aims to develop a rational model to predict the thermal axial forces developed in shear tab connections with composite beams when subjected to transient-state fire temperatures. Design/methodology/approach Finite element (FE) models are first developed in ABAQUS and validated against experimental data available in the literature. Second, a parametric study is conducted to identify the major parameters that affect the behavior of shear tab connections with composite beams in the fire. This includes beam length, shear tab thickness, shear tab location, concrete slab thickness, setback distance and partial composite action. A design-oriented model is developed to predict the thermal induced axial forces during the heating and cooling phases of a fire event. The model consists of multi-linear springs that can predict the stiffness and strength of each component of the connection with the composite beam. Findings The FE results show that significant thermal axial forces are generated in the composite beam in the fire. This is prominent when the beam bottom flange comes in contact with the column. Fracture at the toe of the welds governs the behavior during the cooling phase in most FE simulations. Also, the rational model is validated against the FE results and is capable of predicting the thermal axial forces developed in shear tab connections with composite beams under different geometrical properties. Originality/value The proposed model can predict the thermal axial force demand and can be used in performance-based approaches in future structural fire engineering applications.

Component based Finite Element Design of Seismically Qualified Joints

This paper describes the principles of Component Based Finite Element Modelling (CBFEM) and the system response quantity and application features for design of prequalified joints for seismic applications. The elements are analysed by geometrically and materially non-linear analysis with imperfections (GMNIA). The proper behaviour of components, e.g. of bolts, anchor bolts, welds etc., is treated by introducing components representing its behaviour in term of initial stiffness, ultimate resistance and deformation capacity. To show this process a contribution is prepared, which summarises the history of achievements of FEA application in structural connections. Contribution shows the currents trends in advanced modelling of connection components and differences of the research oriented and design-oriented models. Both have their roles in advanced analyses.

A simple and efficient control allocation scheme for on-ground aircraft runway centerline tracking

To achieve a high performance level during ground operations, the lateral dynamics of an aircraft must be controlled using all available actuators (rudder, nose-wheel steering system, engines and brakes) and under various constraints, which gives rise to a challenging allocation problem. To address this issue, a simple yet accurate design-oriented on-ground aircraft model is first developed. It takes into account the effects of aerodynamics, thrust and tire–ground interactions, both laterally and longitudinally, and for several runway states. It is validated on a high-fidelity Airbus simulator and a complete set of numerical values representative of a commercial aircraft is given, as well as design objectives, so as to provide the control community with a challenging benchmark. After an extensive literature review and an evaluation of the pros and cons of many existing control allocation techniques, a novel and easily implementable algorithm is then developed, which meets actuator and implementation constraints. It automatically manages the trade-off between two antagonistic objectives, namely minimizing the control effort and attaining the maximum virtual control. Its validation on both the design-oriented model and the high-fidelity simulator shows promising results.