Simple Design Model Research Articles

Axial Compression Performance of Concrete-Filled Steel Tubular Columns with Different D/t Ratios

The impacts of three diameter/thickness (D/t) ratios (21.22, 25.46, and 31.83) and concrete strengths (40 N/mm2, 50 N/mm2, and 60 N/mm2) on the strength capabilities of concrete-filled steel tubular (CFST) columns are investigated in this study. The central composite design (CCD) of the response surface methodology (RSM) was used to design the trials in order to complete the tests in a cost-effective manner. 13 (9 distinct tests) columns were evaluated according to the CCD experimental design, and the failure mode of the specimens, load–deformation behavior, and ultimate strength capacity were investigated. Concrete strength improves, resulting in a decrease in steel tube confinement on the core. Because the steel tube longitudinal compressive stress (fsl) increases as the D/t ratio lowers, the confinement is reduced by inhibiting the circumferential tensile stress (fsc). The Reynolds stress model’s, analysis of variance (ANOVA), Pareto chart, and contour plot demonstrated that the column D/t ratio, rather than the in-filled concrete strength, has a considerable impact on the CFST column’s strength capability. The proposed design models in different international codes and literature were evaluated for their effectiveness in predicting the strength capacities of CFST columns subjected to axial compression load. Using regression analysis, a simple design model was suggested to predict the axial strength capacities of CFST short columns, taking into account material strength and column shape. In comparison to other existing and suggested design models, the proposed design model of the present study delivers a more accurate and stable forecast.

Axial compressive behaviour of CFST column externally reinforced by CFRP strips – A design of experiments approach

The purpose of this research is to investigate the influence of CFRP strips wrapping scheme (partial wrapping) in strengthening of CFST column subjected to axial compression. To complete the experimental investigation in an economical way, the central composite design (CCD) of the response surface methodology (RSM) was used to design the experiments. Based on the CCD experimental model, 9 unique tests were performed and the failure mode of the specimens, load–deformation behaviour, ultimate strength and ductility behaviour were studied. The test results showed that externally bonding CFRP strips is an effective approach to restraining axial deformation and enhancing the ultimate capacity of the column under compression. By bonding three layers of CFRP strips, the deformation of the columns was restricted to a maximum of 55.78% and 50.27% compared to the column bonded with one layer, when set at spacings of 20 mm and 30 mm, respectively. The ANOVA, Pareto chart and contour plot of RSM revealed that the layers of the CFRP wrapping scheme was more significant than the strips spacing in increasing the strength capacity of the CFST column. The suitability of design models proposed in various literatures for predicting the strength capacities of CFST columns strengthened with CFRP wrapping scheme was also examined. A simple design model, derived considering the column geometry and material strength of column and CFRP composites, was proposed to predict the axial strength capacities of CFST short columns confined by CFRP strips by using regression analysis. The proposed design model provides a more accurate and reasonably stable prediction compared with other existing design models.

Accuracy of Dental and Industrial 3D Printers.

This in vitro study evaluated the dimensional accuracy of three 3D printers and one milling machine with their respective polymeric materials using a simplified geometrical model. A simplified computer-aided design (CAD) model was created. The test samples were fabricated with three 3D printers: a dental desktop stereolithography (SLA) printer, an industrial SLA printer, and an industrial fused deposition modeling (FDM) printer, as well as a 5-axis milling machine. One polymer material was used per industrial printer and milling machine while two materials were used with the dental printer for a total of five study groups. Test specimens were then digitized using a laboratory scanner. The virtual outer caliper method was used to measure the linear dimensions of the digitized 3D printed and milled specimens in x-, y-, and z-axes, and compare them to the known values of the CAD model. Data were analyzed with Kruskal-Wallis one-way ANOVA on Ranks followed by the Tukey's test. Milled specimens were not significantly different from the CAD model in any dimension (p > 0.05). All 3D printed specimens were significantly different from the CAD model in all dimensions (p = 0.01), except the dental SLA 3D printer with one of the polymers tested (Bis-GMA) which was not significantly different in two (x and z) dimensions (p = 0.4 and p = 0.12). The milling technology tested provided greater dimensional accuracy than the selected 3D printing. Printer, printing technology, and material selection affected the accuracy of the printed model.

Temperatures and gradients in concrete Bridges: Experimental, finite element analysis and design

Aiming to introduce a simplified flexible design model for thermal actions in concrete bridge superstructures, experimental and finite element works were carried out in this study. From an experimental concrete box-girder segment, concrete temperature, solar radiation, air temperature and wind speed records for a complete one-year cycle were recorded and utilized. In addition, a thermal finite element model was conducted and verified, which was then used to conduct required parametric studies. Finally, the verified finite element model was used together with long-term climate history (from 1960 to 2013) of 10 cities in Turkey to propose the thermal actions' design models and procedure. Both positive and negative vertical temperature gradient models were introduced in terms of the top surface maximum temperature gradient, which is related to the solar radiation history of the region. In addition, simplified correlations and design procedure were suggested to evaluate the maximum and minimum mean temperatures of concrete bridges using the long-term maximum and minimum air temperatures.

Fire behaviour and design of hybrid fibre reinforced high-performance concrete columns subjected to uniaxial bending

This paper presents an experimental programme and a fire design model on hybrid fibre reinforced high-performance concrete (HPC) columns under ISO 834 heating curve. To date, there are very few experimental works on HPC columns subjected to eccentric loading under fire conditions. Therefore, a total of six specimens are tested to investigate the effects of load eccentricity and slenderness ratio on spalling and structural behaviour of HPC columns. Material properties including compressive strength, residual flexural strength and spalling behaviour under unstressed state but subject to transient heating are presented to get an overview of the performance of HPC. Following that, the test results of column specimens are discussed in terms of temperature distribution, mid-height deflection, axial deformation, failure mode and fire endurance. No spalling is observed in all the specimens owing to the synergistic effect of hybrid polypropylene and steel fibres. Test results show that mid-height deflection and axial contraction increase with an increase of load eccentricity. A simplified fire design model incorporating fibre reinforced concrete design is adopted based on 500 °C isotherm method. The model is verified with test data and it shows that 400 °C isotherm depth could provide safe and accurate predictions for HPC columns.

Experimental analysis and design strength models adopted by international guides for FRP-confined concrete columns subjected to axial compression

Carbon fiber jacketing is an efficient technique for increasing the strength and strain capacity of concrete circular and square section columns subjected to axial load, although confinement efficiency decreases for rectangular cross-section members. The research project BIA 2016-80310-P includes an experimental program on intermediate-size plain concrete specimens strengthened with carbon fiber jackets, mostly with square and rectangular cross-sections. The results, alongside others with similar characteristics from two databases published, are compared to predictions of four international guides. The incidence of the key parameters in the experimental results is analyzed, such as the aspect ratio of the section, the effective strain in FRP jacket attained at failure or the rounded corner radius. As a result, two efficiency strain factors are proposed, one for circular and another for rectangular specimens. The predictions contained in certain guides, based on a simple linear design-model, are improved by using the proposed efficiency strain factor for rectangular sections.

Computational analysis of axially loaded thin-walled rectangular concrete-filled stainless steel tubular short columns incorporating local buckling effects

This paper investigates the structural performance of concrete-filled stainless steel tubular (CFSST) columns composed of rectangular and square sections. A fiber-based mathematical model is developed to simulate the nonlinear performance of such columns loaded concentrically accounting for the local buckling of steel tube. An accurate lateral pressure model, as well as a strength degradation parameter are proposed based on the existing test results and incorporated in the mathematical modeling developed. A large test dataset is used to validate the accuracy of the numerical prediction. The mathematical model is employed to study the sensitivities of important column parameters on their axial behavior. The accuracy of the existing confinement model of rectangular CFST columns is evaluated in predicting the performance of CFSST short columns. Furthermore, the accuracy of the existing codified design models as well as and the simplified design model proposed in this study to quantify the ultimate compressive strength of such columns is investigated. An accurate artificial neural network (ANN) model along with the GUI feature is developed for the design engineers as a tool to predict their ultimate axial strengths.

A Simplified Design Model for Modular Steel Buildings Subject to Vapor Cloud Explosions (VCEs)

Background: Modular steel buildings (MSB) are extensively used in petrochemical plants and refineries. Limited guidelines are available in the industry for analysis and design of (MSB) subject to accidental vapor cloud explosions (VCEs). Objectives: The paper presents simplified engineering model for modular steel buildings (MSB) subject to accidental vapor cloud explosions (VCEs) that are extensively used in petrochemical plants and refineries. Method: A Single degree of freedom (SDOF) dynamic model is utilized to simulate the dynamic response of primary building components. Analytical expressions are then provided to compute the dynamic load factors (DLF) for critical building elements. Recommended foundation systems are also proposed to install the modular building with minimum cost. Results: Numerical results are presented to illustrate the dynamic response of (MSB) subject to blast loading. It is shown that (DLF)=1.6 is attained at (td/t)=0.4 for front wall (W1) with (td/T)=1.25. For side walls (DLF)=1.41 and is attained at (td/t)=0.6. Conclusions: The paper presented simplified tools for analysis and design of (MSB) subject accidental vapor cloud blast explosions (VCEs). The analytical expressions can be utilized by practitioners to compute the (MSB) response and identify the design parameters. They are simple to use compared to Finite Element Analysis.

Methodology for the Concept Design of Locally Reinforced Composites

Locally load-optimized fiber-based composites, the so-called tailored textiles (TT), offer the potential to reduce weight and cost compared to conventional fiber-reinforced plastics (FRP). However, the design of TT has a higher complexity compared to FRP. Current approaches, focusing on solving this complexity for multiple objectives (cost, weight, stiffness), require great effort and calculation time, which makes them unsuitable for serial applications. Therefore, in this paper, an approach for the efficient creation of simplified TT concept designs is presented. By combining simplified models for structural design and cost estimation, the most promising concepts, regarding the cost, weight, and stiffness of TT parts, can be identified. By performing a parameter study, the cost, weight, and stiffness optima of a sample part compared to a conventional FRP component can be determined. The cost and weight were reduced by 30% for the same stiffness. Applying this approach at an early stage of product development reduces the initial complexity of the subsequent detailed engineering design, e.g., by applying methods from the state of the art.

Influence of Pile Diameter and Aspect Ratio on the Lateral Response of Monopiles in Sand with Different Relative Densities

The large-diameter monopiles are the most preferred foundation used in offshore wind farms. However, the influence of pile diameter and aspect ratio on the lateral bearing behavior of monopiles in sand with different relative densities has not been systematically studied. This study presents a series of well-calibrated finite-element (FE) analyses using an advanced state dependent constitutive model. The FE model was first validated against the centrifuge tests on the large-diameter monopiles. Parametric studies were performed on rigid piles with different diameters (D = 4–10 m) and aspect ratios (L/D = 3–7.5) under a wide range of loading heights (e = 5–100 m) in sands with different relative densities (Dr = 40%, 65%, 80%). The API and PISA p-y models were systematically compared and evaluated against the FE simulation results. The numerical results revealed a rigid rotation failure mechanism of the rigid pile, which is independent of pile diameter and aspect ratio. The computed soil pressure coefficient (K = p/Dσ′v) of different diameter piles at same rotation is a function of z/L (z is depth) rather than z/D. The force–moment diagrams at different deflections were quantified in sands of different relative density. Based on the observed pile–soil interaction mechanism, a simple design model was proposed to calculate the combined capacity of rigid piles.

Nonlinear and elasto-plastic behaviors of cross-laminated timber (CLT) walls under lateral loads

The goal of this study was to evaluate the nonlinear and elasto-plastic load–displacement curves of cross-laminated timber (CLT) walls under lateral loads. The lateral resistance of CLT walls according to the predictive models from the current study and previous studies were compared with the experimental results. When the previous models accounting for the connection in one-direction resistance were compared to the experimental test results, up to a 99.8% difference was found. The current model accounted for the connections working as shear and tensile resistance in addition to the material properties of the wood laminas, design layout, behavior of the connection system, base condition, aspect ratio, geometric characteristics of the CLT wall panels, and vertical loads. The average differences between the lateral resistance properties of CLT walls calculated using the predicted and experimental curves ranged from 1.5% to 10.7%. In the simplified model for force-based design, the average differences were 11.6% for elastic stiffness and 1.6% for the yield strength of CLT walls.

Modelling of Flexible Adhesives in Simple Mechanical States with the Use of the Darijani-Naghdabadi Strain Tensors and Kirchhoff-de Saint-Venant Elastic Potential.

Practical aspects of modelling of flexible adhesives with the energy conjugate measures of stress and strain of the Darijani–Naghdabadi (D-N) family are discussed. A possibility of description of materials exhibiting non-linear physical characteristics with the use of non-linear geometric relationships and linear elastic constitutive law is considered. Nominal stress vs. stretch relations are specified in cases of simple tension and simple shear with the use of the Kirchhoff–de Saint-Venant elastic potential and D-N energy conjugate stress and strain measures. Obtained theoretical estimates were compared with experimental results of simple tension and simple shear tests performed on Sika PM polyurethane (Cracow, Sika Poland). The deformation rate was fixed in order to minimize the influence of viscosity. Values of parameters in the definition of the D-N strain tensor were optimized in order to provide good agreement between model predictions and experimental results. Observed discrepancies indicate that the proposed approach is not appropriate for constitutive modelling of the PM polymer. The presented approach is proposed to be used as a simple design model providing practical formulas describing the behavior of materials of non-linear characteristics in chosen mechanical states. Admissible values of exponents are discussed regarding its bijectivity in a limited range of variation of principal stretches.

A simple parametric design model for straight-tube Coriolis flow meters

A 1D numerical model of a straight-tube Coriolis meter has been implemented and used to generate a simple and intuitive parametric relationship to predict sensitivity. This model is intended to aid the design of such meters and avoid the need to run a large number of time-consuming simulations. Three parameters were identified as being instrumental in determining the sensitivity of a meter: dimensionless bending stiffness (Σ̃), proximity to the Euler buckling limit (R̃) and the dimensionless sensor spacing (χ̃). Parametric relationships for sensitivity (dimensionless time-lag) and natural frequency were developed. These equations allow for the complete and rapid design of a straight-tube Coriolis meter with insignificant computational effort. The parametric model was validated against 11 experimental data sets, covering a range of flow conditions, tensions and materials. In all cases, the parametric model performed well, reporting a typical error of 2 to 5%.

Design model for concrete-filled steel tube columns under full and local compression loads

The structural behaviour of concrete-filled steel tubular columns subjected to full and local compression loads was investigated. Experiments were performed on 18 columns with different cross-sectional slenderness ratios. The experimental parameters were the local compression area ratio and the slenderness ratio. The strength index, stiffness and ductility index of the columns were obtained through experimental tests. The results revealed that the local compression area ratio and slenderness ratio are key parameters that considerably affect the strength capacity of columns subjected to full and local compression loads. Design models provided in various international codes and various studies were used to validate the experimental results. Furthermore, the suitability of these design models for predicting the strength capacity of columns subjected to full and local compression loads was examined. Finally, through regression analysis, a simplified design model was developed for predicting the strength capacity of columns under full and local compression loads.

Об использовании результатов положительного опыта в цифровой экономике аграрного производства

The article substantiates the necessity and possibility of using it in the digital agricultural economy as one so far underestimated object of its development: scaling the results of positive experience in organizing agricultural production using traditional long-used technologies (past experience). On the example of a simple design model of production costs, a methodological scheme for selecting potential participants for the exchange of positive results of their experience in organizing agricultural production is shown. Among the main problems hindering the wide dissemination of positive experience in the organization of agricultural production, one should consider the lack of the necessary motivation in the conditions of market relations for the exchange of positive results of the experience accumulated by agricultural producers.

Model Predictive Path-Following Control of Snake Robots Using an Averaged Model

We propose a new simplified model for the control design of snake robots and apply it to a path-following control design using model predictive control (MPC). While MPC has an advantage in that inequality constraints can be explicitly considered in control design, most of the previous simplified models are still too complex to apply to MPC since the models include joint angles as time-varying parameters. Thus, we exclude joint angles using the averaging method to construct a simpler model. Another feature of the proposed model is that it can be derived from the original complex model without parameter identification using simulation data and without assuming straight-line movements. In addition to inequality constraints on joint angles and the frequency of joint motions, we impose constraints on the change rates of these variables in our MPC design since the averaged model is derived by assuming that these variables slowly change. Furthermore, we introduce a soft constraint to decrease the effects of approximation error of the simplified model on the control performance. The effectiveness of the control system is verified in both simulations and experiments.

Liquefied natural gas storage tank simplified mechanical model and seismic response analysis

In this study, a scale model of a liquefied natural gas (LNG) storage tank was designed to carry out a shaking table test, the main position of insulation layer on tank and the site effect were investigated under different ground motions. The test results show that there is an obvious interaction between the insulation layer and the liquid-solid coupling position of the storage tank, and the seismic response of the tank was related to the frequency of the ground motions, the site effect should be considered when analysing the seismic response of liquid-solid coupling structures. Based on the test results, a simplified mechanical model for the seismic design of LNG storage tanks that considered the insulation layer was constructed, and the simplified mechanical model was verified via a numerical simulation method. Moreover, based on the results of the 16 × 104 m3 LNG storage tank simplified mechanical model, the base shear and bending moment were reduced by 20%–25% on average, the acceleration and displacement of the inner tank wall were reduced by 40% on average after filling the insulation. In the seismic design of large scale LNG storage tanks, considering the damping effect of insulation is helpful to save design capital, and ignoring the damping effect of insulation will make the design conservative.

CAFE: An Instructional Design Model to Assist K-12 Teachers to Teach Remotely during and beyond the Covid-19 Pandemic.

The impact of the COVID-19 global pandemic on schools was massive and unprecedented. Many schools were forced to close, and teachers were forced to deliver their instruction online with a very short notice. To assist K-12 teachers to teach remotely, a simple instructional design model, CAFE (Content, Activities, Facilitation, & Evaluation), was created. This article describes the context in which CAFE was created and the three stages of improvement it went through from a simple instructional design table to the instructional design model. It also shares a reflection on the creation and characteristics of CAFE and finally, it ends with the introduction of the CAFE model.

Validation of a simplified model for liquid propellant rocket engine combustion chamber design

The combustion phenomena inside the thrust chamber of the liquid propellant rocket engine are very complicated because of different paths for elementary processes. In this paper, the characteristic length (L*) approach for the combustion chamber design will be discussed compared to the effective length (Leff) approach. First, both methods are introduced then applied for real LPRE. The effective length methodology is introduced starting from the basic model until developing the empirical equations that may be used in the design process. The classical procedure of L* was found to over-estimate the required cylindrical length in addition to the inherent shortcoming of not giving insight where to move to enhance the design. The effective length procedure was found to be accurate within ± 10%.

Safety Concept for Textile-Reinforced Concrete Structures with Bending Load

In most countries, for the production and execution of concrete structures with textile reinforcement, building owners must have a general approval (e.g., “abZ” in Germany) or an individual license (e.g., “ZiE” in Germany). Therefore, it is quite common for building authorities to request experimental tests that evaluate the ultimate limit state (ULS) and the serviceability limit state (SLS). However, these experimental tests are detailed, time-consuming and expensive. A practical and simple design model would help to reduce the number of tests needed and would offer structural planners a useful tool. An important aspect is that such design model must fulfil a set of reliability requirements in order to guarantee an adequate safety standard. To this end, probabilistic calculations are required. For the setup of such model, different parameters must be considered, namely the effective depth d and the tensile failure stress of the textile ft for the concrete compressive strength fc. This article presents the probabilistic calculations needed to attain a general safety factor γT that satisfies all the safety requirements for the textile reinforcement of concrete structures with bending load.