Compression Panels Research Articles

Properties of Lightweight Insulating Boards Produced from Triticale Straw Particles.

Insulating materials made from straw are becoming increasingly popular in the construction industry. Straw can be used in the construction of buildings as uncompressed straw chips or in the form of compressed panels. This study aimed to determine the possibility of manufacturing boards from straw particles with densities in the range of 150-400 kg/m3, allowing favorable mechanical properties while simultaneously providing high thermal and acoustic insulation properties. The study also analyzed the influence of the degree of carpentry density on the quality of the manufactured boards. The study shows that insulation boards can be produced from straw particles with satisfactory properties already at densities in the range of 200-150 kg/m3. Boards with this density have a compressive strength of 150 kPa, thermal resistance of 0.033-0.046 W/(m·K), and a sound absorption coefficient above 0.31.

Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls.

This paper describes an experimental investigation into the feasibility of using ferrocement jacketing, polypropylene fibers, and carbon fiber reinforced polymer sheets (CFRP) to enhance the shear resistance of unreinforced brick masonry. The study involved testing 12 wall panels in diagonal compression, three of which were strengthened using each of the above-mentioned techniques. The results showed that all three strengthening techniques led to a significant improvement in the shear resistance and deformation capacity of the unreinforced walls. Furthermore, the results showed that the strengthened walls exhibited a significant improvement in shear resistance and deformation capacity by a factor of 3.3-4.7 and 3.7-6.8, respectively. These findings suggest that ferrocement jacketing is a viable and highly effective method for strengthening masonry structures. Test results can assist in the decision-making process to identify the most suitable design and retrofitting solution, which could indicate that not only new materials, but also traditional methods and materials (ferrocement) could be interesting and effective, also considering their lower initial cost.

Variable compression panel thickness for concrete members under bending and torsion: Experimental study

An experimental study was conducted on the behaviour of eight reinforced and prestressed concrete beams subjected to combined action of bending and torsion. The beams were heavily reinforced in the longitudinal direction so that the height of the concrete compression zone under pure bending would be much larger than the concrete diagonal strut thickness under pure torsion and measurements were done so that behaviour of this compressive zone could be observed. The amount of the reinforcement was designed close to the over-reinforcement limits, as would happen if the cross-section dimensions of an actual structure would be minimized in the design. The ultimate resistances and beam deformations were compared against the results of a plasticity-based space truss model where the panel on the compressive side of the cross-section had variable thickness in order to account for the resultant force demands of both the bending and torsion. Most heavily reinforced beams failed in a brittle manner due to the ineffectiveness of diagonally cracked concrete to resist the high normal stresses arising from the bending. The proposed model gave better predictions than the classical model where the panel thickness was constant, and the results showed the significance of concrete strength reduction factor contribution in ultimate resistance of concrete members under combined bending and torsion.

Full Length Transverse Stiffener Under Compression

AbstractThe behavior of web panels in steel elements loaded in compression is characterized by buckling. Thus, their resistance is controlled by local or global buckling according to the slenderness. To limit the risk of instability which tends to reduce the resistance capacity of this type of compressed panels, transverse stiffeners are added. The resistance of the stiffened web panel is evaluated considering the instability of a column element in compression with a cross‐section composed by the stiffener and a part of the web. In order to observe the behavior of these stiffened sections, an experimental campaign was carried out on panels of two different dimensions stiffened over their entire height. Thus, various zones of stiffened or unstiffened panels are tested in double localized compression until failure. These tests are performed on welded panels of two different heights. The stiffeners are either in a central position or at the edge regarding the beam length. The stiffeners are welded over the entire height on both sides of the web and on the flanges of the panel. Some tests are performed on parts of panels without stiffeners to evaluate the unstiffened panel resistance to be used as reference. The results of the experimental tests are compared with those given by the finite element model using shell elements. The comparison makes it possible to calibrate the nonlinear model considering the elastic‐plastic behavior of materials and large displacements. The results are compared on the basis of displacement‐load curves and failure modes that define the behavior of the stiffeners in compression. They can be used to study the global resistance of the stiffened panels in compression zone of beam‐to‐column connections.

Nonlinear numerical assessments for the in-plane response of historic masonry walls

This study examines the in-plane cyclic response of historic masonry elements using a micro modelling approach that incorporates damage-plasticity and surface-based cohesive-contact interface approaches. The nonlinear procedures adopted are validated against tests on dry and wet panels in diagonal compression and large walls under reverse shear-compression loading. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. Based on the validated models, followed by exploratory sensitivity studies, detailed parametric assessments are carried out. The parameter ranges are selected to cover historical masonry materials, consisting of bricks and mortar, and address both dry and wet conditions. Four typical failure modes, namely, flexural strut crushing, diagonal cracking, flexural toe crushing, and mixed sliding, in an order of increasing ductility, are quantified and discussed. It is shown that wet masonry walls have an average reduction of 16% in terms of stiffness and capacity compared with the dry counterparts. Although the failure modes in dry and wet wall pairs are similar, some cases are identified in which the weaker moisture-affected joint strength results in a shift to a more brittle mode. It is also shown that the ductility of the flexural strut crushing mode, which often governs the failure of historical masonry due to its low strength, is considerably overestimated in existing guidelines. Based on the results of the parametric investigations, analytical models for predicting the inelastic response are evaluated, and suggestions for modifications are proposed.

Structural Compressed Panel VAR with Stochastic Volatility: A Robust Bayesian Model Averaging Procedure

This paper improves the existing literature on the shrinkage of high dimensional model and parameter spaces through Bayesian priors and Markov Chains algorithms. A hierarchical semiparametric Bayes approach is developed to overtake limits and misspecificity involved in compressed regression models. Methodologically, a multicountry large structural Panel Vector Autoregression is compressed through a robust model averaging to select the best subset across all possible combinations of predictors, where robust stands for the use of mixtures of proper conjugate priors. Concerning dynamic analysis, volatility changes and conditional density forecasts are addressed ensuring accurate predictive performance and capability. An empirical and simulated experiment are developed to highlight and discuss the functioning of the estimating procedure and forecasting accuracy.

Stiffness Requirements for Longitudinal Stiffeners of Trapezoidal Box Girder Bottom Flanges

The reason for the widespread use of steel box girders is that they have high structural efficiency due to the high bending, high torsional stiffness and rapid erection. For bottom flange of the girders, the buckling behavior during production and erection due to compression strength can be a problem. The compression plate with longitudinal stiffeners typically renders an economic. The optimal design of longitudinal stiffeners is discussed. The results are based on 3-D FEA (ANSYS19.2) of many stiffened compression bottom flange models, the moment of inertia requirement of bottom flange longitudinal stiffener is investigated by studying the effect of many parameters as longitudinal stiffeners numbers, stiffener sections, plate aspect ratio and compression flange thickness. Also, the stiffeners effect on the compression panel plate stresses were studied by modeling girder with and without longitudinal stiffeners. The finite element method is useful as they can be used to study the plate with stiffeners in an economical way, and we don’t need experimental and laboratory tests.

ANALYSIS OF EFFICIENCY OF THREE-LAYER WALL PANELS WITH A DISCRETE CORE

Introduction: The paper addresses thin-walled three-layer plates and panels with cutouts, reinforced with an orthogonal grid of stiffeners or rectangular reinforcement plates parallel to the coordinate lines. In this case, the thickness of the entire structure is taken into account analytically using unit column functions. Purpose of the study: We aimed to build a mathematical model of deformation and develop a method for the analysis of the stability of thin-walled elastic isotropic three-layer plates and wall panels with a discrete core. Methods: Based on the mathematical apparatus of generalized functions using the Bubnov–Galerkin method, an eigenvalue problem is solved to determine the critical parameters of a compressed three-layer wall panel with a discrete core. Results: According to the suggested method, we perform a stability analysis of three-layer wall panels with different values of core stiffness and study the impact of the discrete core parameters on the buckling load, consumption of materials, and efficiency of three-layer engineering structures.

Construction of surrogate models for predicting the buckling strength of stiffened panels through DoE and RSM methods

PurposeExperimental mid/large scale testing of ship-like stiffened panels in compression is a quite expensive exercise that is not standard. Numerical simulations are preferred instead. Because of being relatively inexpensive (cost and time wise), most authors perform an exhaustive design space exploration arriving at a significant number of runs. This work demonstrates that the buckling response with respect to the nondimensional slenderness ratios may well be fitted with nine runs per stiffener geometry.Design/methodology/approachEfficient derivation of buckling strength formulas for stiffened panels through the employment of design of experiments (DoE) and response surface methodology (RSM) combined with numerical nonlinear experimentation over the entire range of practical geometries.FindingsThe surrogate model developed for T-bar stiffeners predicts accurately enough the ultimate stress in the practical design area, while the surrogate models for angle bars and flat bars demonstrate difference between 10 and 30% from common structural rules (CSR).Originality/valueTo the authors' best knowledge, the statistical-based formal and rigorous approach of DoE and RSM to obtaining buckling surfaces for stiffened panels is performed for the first time. The number of required observations per stiffener type has not been addressed yet as each work selects its own sampling scheme without formal reasoning. This work comes to frame the number of observations for efficient surrogate model building.

An adaptable algorithm to predict the load-shortening curves of stiffened panels in compression

ABSTRACT An adaptable algorithm is proposed in this study, which can predict the complete load-shortening curve of a stiffened panel subjected to uniaxial longitudinal compression. The algorithm provides an extension to existing empirical formulae initially derived for predicting the ultimate compressive strength of stiffened panels. Based on observations from a series of nonlinear finite element analyses, the compressive load-shortening behaviour of stiffened panels is idealised with a linear pre-collapse response, an arc-shaped nonlinear ultimate collapse region and an asymptotic post-collapse decay. The algorithm allows direct modification of the elastic stiffness, ultimate strain, ultimate strength and post-collapse characteristics of the load shortening curve. This enables the load shortening curve to incorporate characteristics specific to the type of stiffened panel under analysis. The capability of the algorithm is demonstrated through an application with the simplified progressive collapse method to calculate the ultimate ship hull strength of four merchant ships and one naval vessel.

Evaluation of the survivability of CFRP honeycomb-cored panels in compression after impact tests

This paper is oriented to the experimental research of the mechanics of the CFRP sandwich plates, glass and carbon fiber sample panels with a large-cell honeycomb core. The method for testing polymer composite sample plates in compression after impact (CAI) tests with joint use of a testing machine and a video system for deformation field registration was tested. Analysis of the experimental data obtained highlighted the impactive sensitivity zone for the test specimens. A quantitative assessment of the load-bearing capacity of glass and carbon fiber sample panels in CAI tests with the different levels of the drop weight impact energy was performed. Photos of samples after impact have been provided. Vic-3D non-contact three-dimensional digital optical system was used to register the displacement and deformation fields on the surface of the samples. The video system was used to evaluate various damage mechanisms, including matrix cracking, delaminations, and rupture of the damaged fibers. The paper studied the evolution of non-homogeneous deformation fields on the surface of the composite samples during the post-impact compression tests and analyzed the configuration of non-homogeneous deformation fields.

Postbuckling analysis and optimization of composite laminated panels using a novel perturbation-based approximation FE method

When composite laminated panels under compression are allowed to continuously loaded into the moderately deep postbuckling regime, further weight savings can be achieved. For this purpose, this work presents an optimization scheme for the design of postbuckling behavior of composite laminates. An efficient tool, termed the Koiter perturbation-based approximation FE method, is developed to obtain the postbuckling behavior of composite laminated panel. The initial postbuckling response is represented by the nonlinear predictor solved by the reduced order model, while the deformations in the moderately deep postbuckling regime are obtained by applying the correction phase under the design load. Five different indices, including the critical buckling load, postbuckling stiffness, stiffness residual, and in-plane and out-of-plane deformations under the design load, are proposed to assess various postbuckling performances of the compressed panel. The postbuckling indices can be flexibly selected to be either the objective or the nonlinear constraints in the lamination optimization. A genetic algorithm is subsequently used to determine the optimal lamination configuration for the most favorable postbuckling performance. The optimizations of composite laminates under uniaxial and biaxial compression for different boundary conditions are carefully studied and discussed with the consideration of initial geometric imperfections.

Post-buckling behaviour in variable stiffness cylindrical panels under compression loading with modal interaction effects

Variable Angle Tow (VAT) composite panels, whereby fibre angle distributions vary continuously in-plane, have more scope for tuning structural properties than traditional straight fibre laminated composite materials. Currently, the geometrically non-linear response of such structures is typically modelled using path-following methods implemented in commercial finite element analysis. However the high computational cost given from both the incremental-iterative procedure and fine mesh required for accurate modelling of the variable trajectory of fibre direction, can be excessively time consuming. Driven by these shortcomings, we use a fast multi-modal Koiter asymptotic method for investigating the nonlinear buckling behaviour of VAT cylindrical panels in compression. In doing so, this paper provides new insight into the multi-modal description and nonlinear buckling mode interactions which are responsible for the highly nonlinear behaviour of cylindrical panels in compression with a particular emphasis on the nonlinear components in the mathematical asymptotic description. As such, through an extensive parametric virtual testing programme we construct, for each panel under investigation, an asymptotic solution projecting the equilibrium equations in the subspace of its first 30 buckling modes. Then, at several points of the resulting equilibrium path, the percentage contribution of each of these modes to the solution is measured. On the basis of the percentage obtained, those modes which give the largest contribution to the solution are identified. The main novelty of this work is that these results are used as a priori information for re-projecting the equilibrium equations into a new modal subspace to which only the buckling modes with the largest participation belong. Moreover, for the first time, we observe that in a multi-modal Koiter-inspired description the modal shapes giving the largest contribution to the asymptotic solution have the same degree of symmetry. In this way, for a generic panel under consideration, we show that it is possible to obtain a more computationally-efficient asymptotic description than current approaches. Finally, the new computed equilibrium paths are compared to benchmark results using the commercial finite element software ABAQUS and the computational advantages given by using a priori information in the asymptotic expansion are commented upon.

Computing Method Applicability Verification of Effective Width of Skin for Stiffened Panels in Compression

Computing Method Applicability Verification of Effective Width of Skin for Stiffened Panels in Compression

Wooden sandwich panels with prismatic core – Energy absorbing capabilities

Sandwich panels manufactured from wood and wood-based materials promote optimal management of natural resources, as they are obtained from renewable materials. For this reason numerous attempts are being made to use wood in the manufacture of light-weight layer composites exhibiting high rigidity and relatively low density. The aim of the study was to determine the energy absorption capacity in wooden sandwich panels with a prismatic core. This paper describes a method to manufacture a novel wood-based material with a prismatic core. Uniaxial compression tests and 3-point bending performed on the panels were discussed together with the method to determine the amounts of absorbed energy. Numerical models were presented for panels in compression and bending tests along with the method to calculate the results applying the Finite Element Method (FEM). These models were verified based on the results of experimental analyses to facilitate predictability for a new class of composite materials. It was shown that panels with a triple core are more resistant compared to panels with a single core. Moreover, these panels exhibit greater energy absorption capacity.

Sandwich assemblies of composites square hollow sections and thin-walled panels in compression

Abstract Sandwich structures were built up by two glass fibre reinforced polymer (GFRP) thin-walled panels and square hollow sections (SHS) in between through adhesive bonding or mechanical bolting. Experiments in compression were conducted in order to understand the failure modes including global and local buckling, load-bearing capacities, load-displacement curves and load-strain responses. Accordingly the effects of different connection methods and different spacing values between the SHS sections were clarified. Sudden debonding failure between GFRP panels and inner SHS columns was found on adhesively bonded specimens; while mechanically bolted specimens showed evident lateral deformation and progressive failure until the ultimate junction separation failure on the GFRP SHS columns. Local buckling was found on GFRP thin-walled panels of specimens with a larger spacing between the two SHS sections. Finite element analysis and analytical modelling were performed to estimate the load-displacement curves and the critical stress for the local buckling on GFRP thin-walled panels, where consistent agreements with experimental results were received.

Control system for a continuous compaction large square baler

Bale density impacts the cost to harvest, aggregate, store and transport hay or biomass. To achieve legal transport weight limits in many countries, the large square bale (LSBe) wet basis density should be approximately 240 kg·m−3. Current large-square balers (LSBers) create density by employing a reciprocating plunger to apply pressures in excess of 700 kPa to the bale face, but densification by a reciprocating plunger is inefficient because of the intermittent manner that the pressure is applied. What is explored here is an alternative bale densification method that uses an auger and conical compaction rollers to compact material in a continuous fashion. Compared to conventional LSBers, this new baler concept has the potential to create high-density bales with a machine that is less complicated and lighter weight. An important component of this baling mechanism was a closed-loop control system developed to achieve a desired bale density, as well as control bale separation and bale length. The control system varied bale chamber compression panel pressure to alter auger force and subsequent bale density. Using this control system enabled the baler to achieve dry basis densities ranging from 166 to 334 kg·m−3 with auger forces less than 44 kN, nearly a fifteen-fold reduction in force compared to a conventional plunger type LSBer.

Nudging Axially Compressed Cylindrical Panels Toward Imperfection Insensitivity

Abstract Curved shell structures are known for their excellent load-carrying capability and are commonly used in thin-walled constructions. Although theoretically able to withstand greater buckling loads than flat structures, shell structures are notoriously sensitive to imperfections owing to their postbuckling behavior often being governed by subcritical bifurcations. Thus, shell structures often buckle at significantly lower loads than those predicted numerically and the ensuing dynamic snap to another equilibrium can lead to permanent damage. Furthermore, the strong sensitivity to initial imperfections, as well as their stochastic nature, limits the predictive capability of current stability analyses. Our objective here is to convert the subcritical nature of the buckling event to a supercritical one, thereby improving the reliability of numerical predictions and mitigating the possibility of catastrophic failure. We explore the elastically nonlinear postbuckling response of axially compressed cylindrical panels using numerical continuation techniques. These analyses show that axially compressed panels exhibit a highly nonlinear and complex postbuckling behavior with many entangled postbuckled equilibrium curves. We unveil isolated regions of stable equilibria in otherwise unstable postbuckled regimes, which often possess greater load-carrying capacity. By modifying the initial geometry of the panel in a targeted—rather than stochastic—and imperceptible manner, the postbuckling behavior of these shells can be tailored without a significant increase in mass. These findings provide new insight into the buckling and postbuckling behavior of shell structures and opportunities for modifying and controlling their postbuckling response for enhanced efficiency and functionality.

Compressive failure of quasi-static indented CFRP/aluminium honeycomb sandwich panels

The present study examines sandwich panels, which are made of carbon fiber facesheets with aluminium honeycomb core and focuses on how varying factors (skin thickness, layup, core density and diameter of hemispherical indenter) are affecting collapse of artificially damaged panels in edgewise compression. Damage in the middle of sandwich specimens was introduced using quasi-static indentation. Hemispherical indenters of two diameters, namely, 20 mm and 150 mm, were applied. The residual strength was estimated through the edgewise compression test of damaged specimens. The study demonstrated that increase of the honeycomb density led to decrease in the safety margin in structure. Thicker skins may also lead to a catastrophic propagation of indent.

Digital image correlation analysis of vertical strain for corrugated fiberboard box panel in compression

This work was aimed at examining the overall contributions to displacement of panels of compressed boxes, such as panel compression strain and flap and crease displacements. 3D digital image correlation (DIC) was used to analyse motion of side panels of corrugated fiberboard regular slotted containers. The vertical displacement and the vertical component of strain of the panel face during box compression test were examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in‐plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in‐plane panel compression behaviour. Detailed study of two box designs in three representative test cases was presented, which in future could be extended to other box designs. At peak load, the in‐plane compression of the panels, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 3% to 6% of total crosshead displacement for the test cases. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 48% to 59% of total crosshead displacement for the different cases. The analysis showed that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in‐plane stiffness of a box.