Terms Of Flexural Stiffness Research Articles

Experimental and theoretical investigation of the structural behavior of reinforced glulam wooden members by NSM steel bars and shear reinforcement CFRP sheet

Abstract Reinforcing the wooden structural members is considered as a challenging matter to overcome the drawbacks of using wood in the construction field. The current investigation, therefore, presents an attempt to evaluate the effectiveness of utilizing steel bars as reinforcements in glulam timber beams using the near-surface-mounted (NSM) technique in conjunction with carbon fiber-reinforced polymer (CFRP) sheet wraps. A series of flexural testing was carried out until failure for both reinforced and unreinforced glulam members in a simple support system. Eleven specimens were examined in two groups to compare them with the control beam. Five reinforced glulam (RG) beams of the first group were reinforced with different schemes at tension and compression zones using the same bar size. The other five specimens of the second group were reinforced with shear reinforcement using fully wrapped strips made of CFRP sheet in addition to the same flexural reinforcement schemes as the first group. Each glulam beam has a span of 1.35 m and a rectangular section sized 85 mm × 175 mm. Based on experimental outcomes, theoretic modeling was provided to estimate the ultimate load capacity and bending rigidity of reinforcing glulam members. Though several theoretical predictions of flexural capacity were overstated when compared to experimental predictions, these disparities were frequently about 10%, confirming that the proposed theoretical model was accurate, and the mean of ultimate loading capacity and deflection between experimental and theoretical results were 1.01 and 1.09, respectively. Experimental results presented show that the RG beams performed much better than the unreinforced reference beams in terms of structural behavior, with improvements in ultimate load capacity ranging from 16 to 49%. On the other hand, the shear reinforcement for RG members slightly improved flexural performance, and the ultimate load capacity increased by 2–7%. Therefore, it was concluded that the NSM techniques using ordinary steel bars were effective ways in strengthening the glulam members in terms of flexural stiffness with increasing ultimate load capacity.

Use of Carbon and Basalt Fibers with Adhesives to Improve Physical and Mechanical Properties of Laminated Veneer Lumber

Climate change is one of the main factors influencing the research of environmentally friendly materials. This is why the use of engineering fibers as a reinforcement technique in wood, in order to increase its mechanical properties, has recently been investigated. This research presents the results obtained from the use of carbon and basalt fiber fabrics as a reinforcement for microlaminated Radiata Pine wood panels at a laboratory scale using the adhesives epoxy resin and polyvinyl acetate. Tests were carried out in comparison to the control boards, relating the physical properties obtained in terms of thickness swelling by 48 h-water immersion with a decrease of 19% for the polyvinyl acetate and carbon fiber matrix reinforcement, about the mechanical properties evaluated, a better performance was obtained for the epoxy resin and carbon fiber matrix reinforcement and in terms of flexural stiffness and strength (in flatwise), tensile strength and Janka hardness, with an increment of 31%, 38%, 56% and 41%, respectively.

Effect of Reinforcement Ratio and Bond Characteristic on Flexural Behavior of Carbon Textile-Reinforced Concrete Panels.

Textile-reinforced concrete (TRC) is highly anticipated as an alternative to reinforced concrete due to its ability to enable lightweight design, free formability, and improved ductility. In this study, TRC panel test specimens were fabricated and four-point loading flexural tests were performed to examine the flexural characteristics of TRC panels reinforced with carbon fabric, and to investigate the effect of the fabric reinforcement ratio, anchorage length, and surface treatment of fabric. Furthermore, the flexural behavior of the test specimens was numerically analyzed using the general section analysis concept of reinforced concrete and compared with the experimental results. Due to bond failure between the carbon fabric and the concrete matrix, the TRC panel showed a large decrease in flexural performance in terms of flexural stiffness, flexural strength, cracking behavior, and deflection. This low performance was improved by increasing the fabric reinforcement ratio, anchoring length, and sand-epoxy surface treatment of the anchorage. Comparing the numerical calculation results with the experimental results, the deflection of the experimental results was approximately 50% larger than the numerical calculation results. This is because the perfect bond between the carbon fabric and the concrete matrix failed, and slip occurred.

Structural performance of cross-laminated timber-concrete composite floors with inclined self-tapping screws bearing unidirectional tension-shear loads

This study investigated the structural performance of cross-laminated timber (CLT)-concrete composite floor with inclined self-tapping screws bearing unidirectional tension-shear loads. Five groups of push-out tests were conducted to evaluate the shear behavior of the inclined screw connector. The results showed the embedded depth of the inclined screw in the CLT had a significant influence on the shear performance of the connectors, and the vertical screws demonstrated enhanced ductility. Next, six groups of specimens were subjected to four-point bending tests to study their flexural behavior under various parameters. A screw spacing that was too small led to premature failure, whereas an increased section height greatly improved the bending performance of these specimens. One specimen in particular exhibited a plate-end shear enhancement accompanied by excellent performance in terms of flexural stiffness and bearing capacity. Furthermore, a computational optimization method for determining an effective bending stiffness of the composite floor was proposed based on ‘γ-method’. This approach expanded the application scope of traditional methods, and the calculated values were in good agreement with the experimental values. Finally, a simplified finite element model was established, and parametric finite element analysis verified that improving the shear efficiency of the connector could bring economic benefits.

The influence of infill density gradient on the mechanical properties of PLA optimized structures by additive manufacturing

The aim of this work is the development of a novel framework for structural optimization using bio-inspired remodelling algorithm adapted to additive manufacturing. The fact that polylactic acid (PLA, E = 3145 MPa (Young’s modulus) according to the supplier for parts obtained by injection) shows a similar parameterized behavior with ductile metals, in the sense that both materials are characterized by a bi-linear elastic-plastic law, allows to simulate and prototype parts to be further constructed in ductile metals at a lower cost and then be produced with more expensive fabrication processes. Moreover, cellular materials allow for a significant weight reduction and therefore reduction of production costs. Structural optimization algorithms based on biological phenomena were used to determine the density distribution of the infill density of the specimens. Several simple structures were submitted to distinct complex load cases and analyzed using the mentioned optimization algorithms combined with the finite element method and a meshless method. The surface was divided according to similar density and then converted to stereolitography files and infilled with the gyroid structure at the desired density determined before, using open-source slicing software. Smoothing functions were used to smooth the density field obtained with the remodeling algorithms. The samples were printed with fused filament fabrication technology and submitted to mechanical flexural tests similar to the ones analyzed analytically, namely three- and four-point bending tests. Thus, the factors of analysis were the smoothing parameter and the remodeling method, and the responses evaluated were stiffness, specific stiffness, maximum force, and mass. The experimental results correlated (obtaining accuracy of 35% for the three-point bending load case and 5% for the four-point bending load case) to the numerical results in terms of flexural stiffness and it was found that the complexity of the load case is relevant for the efficiency of the functional gradient. The fused filament fabrication process is still not accurate enough to be able to experimentally compare the results based of finite element method and meshless method analyses.

Characterisation of Electrical and Stiffness Properties of Conductive Textile Coatings with Metal Flake-Shaped Fillers.

Two conductive formulations containing different types of micron-sized metal flakes (silver-coated copper (Cu) and pure silver (Ag)) were characterised and used to form highly electrically conductive coatings (conductors) on plain and base-coated woven fabrics, the latter in an encapsulated construction. With e-textiles as the intended application, the fabric stiffness, in terms of flexural stiffness and sheet resistance (Rsh), after durability testing (laundering and abrasion) was investigated and related to user friendliness and long-term performance. Bare and encapsulated conductors with increasing amounts of deposited solids were fabricated by adjusting the knife coating parameters, such as the coating gap height (5, 20, 50, and 200 μm), which reduced the Rsh, as determined by four-point probe (4PP) measurements; however, this improvement was at the expense of increased flexural stiffness of the coated fabrics. The addition of a melamine derivative (MF) as a cross-linker to the Cu formulation and the encapsulation of both conductor types gave the best trade-off between durability and Rsh, as confirmed by 4PP measurements. However, the infrared camera images revealed the formation of hotspots within the bare conductor matrix, although low resistances (determined by 4PP) and no microstructural defects (determined by SEM) were detected. These results stress the importance of thorough investigation to assure the design of reliable conductors applied on textiles requiring this type of maintenance.

Seismic testing and modeling of cylindrical electrical equipment with GFRP composite insulators

Glass fiber reinforced polymer (GFRP) composite is a desirable alternative to porcelain for insulators of cylindrical electrical equipment in electrical substation. However, mechanical properties of composite insulator in an event of earthquake are not fully known yet. This study aimed to investigate both the static and dynamic properties of GFRP composite insulators and electrical equipment through impact hammer test, quasi-static flexural tests and full scale shaking table tests. The flexural properties, in terms of flexural stiffness, damping and hysteretic behavior, were investigated, based upon which a mechanical model was proposed. Moreover, the possible failure modes were identified in order that a design and qualification procedure was recommended for engineering application. The procedure has been further validated by a full scale shaking table test of 1000 kV cylindrical composite electrical equipment.

Experimental investigation of multi-layered laminated glass beams under in-plane bending

Due to its relatively good safety performance and aesthetic benefits, laminated glass (LG) is increasingly being used as load-carrying members in modern buildings. This paper presents an experimental study into one applicational scenario of structural LG subjected to in-plane bending. The aim of the study is to reveal the in-plane behaviors of the LG beams made up of multi-layered glass sheets. The LG specimens respectively consisted of two, three and four plies of glass, bonded together by two prominent adhesives. A total of 26 tests were carried out. From these tests, the structural behaviors in terms of flexural stiffness, load resistance and post-breakage strength were studied in detail, whilst considering the influence of interlayer type, cross-sectional interlayer percentage and presence of shear forces. Based on the test results, analytical suggestions were made, failure modes were identified, corresponding failure mechanisms were discussed, and a rational engineering model was proposed to predict the post-breakage strength of the LG beams. The results obtained are expected to provide useful information for academic and engineering professionals in the analysis and design of LG beams bending in-plane.

Finite element modeling of cable galloping vibrations. Part II: Application to an iced cable in 1:2 multiple internal resonance

The aim of this paper is to validate the finite element formulations proposed in a companion paper for the study of the nonlinear dynamic behavior of cable structures. A well-known suspended cable in multiple 1:2 “internal resonance” conditions is herein considered. A uniform ice deposit, along the length of the cable, makes it prone to galloping vibrations under a steady wind flow. Different modeling strategies, relying on different assumptions regarding both the mechanical model as well as the aerodynamic response, are investigated and compared with results coming from analytical, semi-analytical and numerical models from the literature. The role of torsional and flexural stiffness terms, and of the initial undeformed configuration, is critically assessed. The results obtained show the significant effect coming from the adoption of a beam finite element formulation that includes the effect of torsional rotation in the evaluation of the aerodynamic loads.

Modeling and Analysis of GFRP Bridge Deck Panels Filled with Polyurethane Foam

This paper presents finite-element analyses and analytical models of innovative, small-scale, prototype deck panels examined under monotonic bending. The deck panels consisted of two glass fiber–reinforced polymer (GFRP) facesheets separated by webs formed from E-glass–woven fabric placed around trapezoidal-shaped, low-density, polyurethane foam segments. The proposed panel exhibited a higher structural performance in terms of flexural stiffness, strength, and shear stiffness than those of conventional sandwich panels. Analytical models were used to predict critical facesheet wrinkling in the sandwich panel. Furthermore, a three-dimensional model using simulation software was developed for analysis of the proposed panel system under monotonic four-point loading. The finite-element results in terms of strength, stiffness, and deflection were found to be in good agreement with those from the experimental results. A parametric study was also conducted to further evaluate the effects of the stiffness of the top facesheet fiber layers, the mass density of the polyurethane foam, the existence of web layers, and the introduction of an overlay above the top facesheet. A flexural beam theory approach was used to predict the flexural strength of the sandwich panel.

Flexural impact response of textile-reinforced aerated concrete sandwich panels

Abstract Mechanical response of textile-reinforced aerated concrete sandwich panels was investigated using an instrumented three-point bending experiment under static and low-velocity dynamic loading. Two types of aerated concrete: autoclaved aerated concrete (AAC) and polymeric Fiber-Reinforced Aerated Concrete (FRAC) were used as the core material. Skin layer consisted of two layers of Alkali Resistant Glass (ARG) textiles and a cementitious binder. Performance of ductile skin-brittle core (TRC–AAC) and ductile skin-ductile core (TRC–FRAC) composites was evaluated in terms of flexural stiffness, strength, and energy absorption capacity. The effect of impact energy on the mechanical properties was measured at various drop heights on two different cross-sections using energy levels up to 40 J and intermediate strain rates up to 20 s− 1. The externally bonded textile layers significantly improved the mechanical properties of light-weight low-strength aerated concrete core under both loading modes. Dynamic flexural strength was greater than the static flexural strength by as much as 4 times. For specimens with larger cross-sections, unreinforced-autoclaved AAC core had a 15% higher apparent flexural capacity. With 0.5% volume of polypropylene fibers in the core, the flexural toughness however increased by 25%. Cracking mechanisms were studied using high speed image acquisition and digital image correlation (DIC) technique.

Testing and Evaluation of Polyurethane-Based GFRP Sandwich Bridge Deck Panels with Polyurethane Foam Core

AbstractThis paper presents the evaluation of an innovative low-cost small-scale prototype deck panel under monotonic and fatigue bending. This new system introduces a trapezoidal-shaped polyurethane foam core with a thermoset polyurethane resin that has a longer pot life to facilitate the infusion process. The proposed panel exhibited a higher structural performance in terms of flexural stiffness, strength, and shear stiffness. The panels consist of two glass fiber–reinforced polymer (GFRP) facings with webs of bidirectional E-glass–woven fabric that are separated by a trapezoidal-shaped low-density polyurethane foam. The GFRP panels were manufactured using a one-step vacuum-assisted resin transfer molding process. The specimens studied were constructed in the Composite Manufacturing Laboratory in the Mechanical and Aerospace Engineering Department at Missouri University of Science and Technology. Small-scale prototype deck panels were tested both statically and dynamically in four-point bending to inves...

Performance of a lightweight GFRP composite bridge deck in positive and negative bending regions

This paper presents results from an experimental and analytical study of a newly developed lightweight composite bridge deck system composed of pultruded trapezoidal GFRP tubes and outer wrap. Panels with different grout materials and grouting patterns were evaluated and compared in terms of flexural stiffness. Two-span tests were performed on non-grouted and epoxy grouted panels to simulate a multi-girder bridge configuration and to evaluate their structural behavior in both positive and negative bending regions. Test results showed that the epoxy grouted panel meets the AASHTO deflection requirement (L/800) and performed well under service loads. An analytical model was developed to predict the load–deflection response of grouted and non-grouted panels at incremental load steps, even beyond the uncracked stage. The proposed model shows that shear deformation must be considered in order to accurately predict the behavior of GFRP panels in multi-girder bridges.

Efficient utilization of plastic waste through product design and process adaptation: A case study on stiffness enhancement of beams produced from plastic lumber

AbstractThe aim of the present work is the development of a method for structural reinforcement of beams obtained by in‐mold extrusion of plastics from solid urban waste. The beams obtained by in‐mold extrusion are commonly used for outdoor furniture and structures. The material used for such applications is mainly composed of low‐density polyethylene derived from bags and films, with small amounts of high density polyethylene and polypropylene, as well as traces of polyethylene terephthalate. This material is usually referred to as “plastic lumber.” Plastic lumber products have a low stiffness, which results in high deflections under flexural loads, particularly under creep loading. In this study, reinforcing rods of high aspect ratio were incorporated into plastic lumber beams in specific positions with respect to the cross section of the beam. The reinforcement of the plastic lumber beams with fine rods is introduced in the typical intrusion process used for the production of unreinforced beams. Glass fiber reinforced pultruded rods were chosen for this purpose from a preliminary evaluation of different materials. Different diameter glass fiber reinforced pultruded rods, including surface‐abraded systems to increase the roughness, were used for the reinforcement of plastic lumber beams. The reinforced beams were tested in terms of flexural stiffness, creep resistance, and pullout resistance of the embedded rods. The results obtained from the mechanical tests showed a significant enhancement of flexural stiffness and creep resistance behavior. The performance at higher stress levels was shown to be significantly dependent on the interfacial adhesion between rods and polymer matrix. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:133–142, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20131

Influence of cross-section on the strength of timber beams

This paper investigates the strength and deformation characteristics of lightweight timber composite beams manufactured with six different cross-sectional profiles in comparison with readily available laminated veneer lumber (LVL) and glued-laminated (Glulam) beams. All engineered profiles comprised solid timber or LVL flanges and three-ply plywood webs. The number of webs varied from one to four. The beams had an overall depth of 290 mm and were either 88 mm or 106 mm wide. A study was conducted to provide a comparison of the beam designs and to determine possible effects of cross-sectional configuration and connection details on the structural properties of the beams. To enable a realistic analysis, 12 beams were replicated for each design. The individual components of the beams were tested prior to assembly to obtain the modulus of elasticity and shear modulus and were grouped to provide an even distribution of the material properties. The addition of extra webs to the I-beam profile significantly enhanced the bending and shear capacity of the beam while maintaining a high strength to weight ratio. The boxed I-beam proved to be the most efficient to manufacture and displayed superior structural performance compared with the rest of the profiles in terms of flexural stiffness and bending and shear capacity. The experimental results confirmed the significant contribution of the shear deflection to the total deflection of the I-beams, box beams and even solid section beams.

Coupled mechanics and finite element for non‐linear laminated piezoelectric shallow shells undergoing large displacements and rotations

AbstractA theoretical framework is presented for analysing the coupled non‐linear response of shallow doubly curved adaptive laminated piezoelectric shells undergoing large displacements and rotations. The formulated mechanics incorporate coupling between in‐plane and flexural stiffness terms due to geometric curvature, coupling between mechanical and electric fields, and encompass geometric non‐linearity effects due to large displacements and rotations. The governing equations are formulated explicitly in orthogonal curvilinear co‐ordinates and are combined with the kinematic assumptions of a mixed‐field shear‐layerwise shell laminate theory. Based on the above formulation, a finite element methodology together with an incremental‐iterative technique, based on Newton–Raphson method is formulated. An eight‐node coupled non‐linear shell element is also developed. Various evaluation cases on laminated curved beams and cylindrical panels illustrate the capability of the shell finite element to predict the complex non‐linear behaviour of active shell structures including buckling, which is not captured by linear shell models. The numerical results also show the inherent capability of piezoelectric shell structures to actively induce large displacements through piezoelectric actuators, by jumping between multiple equilibrium states. Copyright © 2005 John Wiley & Sons, Ltd.

The application of holographic interferometry to the measurement of flexural modulus under a uniform moment.

The accurate measurement of the flexural modulus of composite sheet materials is essential in the analysis of composite structures subject to bending loads. The bending of thin symmetric sandwich laminate plates is characterized by a matrix containing four independent terms. In the past, little attention has been given to the direct measurement of these terms. In the present paper, a new method is devised for loading a uniform bending moment or a uniform twisting moment to a symmetric sandwich laminate plate. Holographic interferometry was used as a means of determining the curvatures in a thin orthotropic sheet. The flexural modulus is obtained from the moment-curvature relation. Finally, the experimental result of the deformed shape for another loading condition is compared with the result of FEM using flexural stiffness terms derived from our experiment. Both results have a good agreement. Direct measurement could be the only practical means of accurately deriving the flexural stiffness terms.

Determination of the flexural stiffness of carbon composite plates by holographic interferometry

A method of measuring the flexural stiffness properties of anisotropic thin plates is presented. Three rhombic plates cut at different orientations from the test sheet are loaded in bi-axial bending, and the resulting deflections are recorded as fringe patterns using optical holography. Curvatures determined in the chosen coordinate system and related to the bending moments are used to calculate the flexural stiffness terms. The results of tests on cross-ply carbon fibre reinforced plastic material are in good agreement with laminated plate theory.