Compressed Elements Research Articles

Structural response of cross-laminated timber compression elements exposed to fire

A set of novel structural fire tests on axially loaded cross-laminated timber (CLT) compression elements (walls), locally exposed to thermal radiation sufficient to cause sustained flaming combustion, are presented and discussed. Test specimens were subjected to a sustained compressive load, equivalent to 10% or 20% of their nominal ambient axial compressive capacity. The walls were then locally exposed to a nominal constant incident heat flux of 50 kW/m2 over their mid height area until failure occurred. The axial and lateral deformations of the walls were measured and compared against predictions calculated using a finite Bernoulli beam element analysis, to shed light on the fundamental mechanics and needs for rational structural design of CLT compression elements in fire. For the walls tested herein, failure at both ambient and elevated temperature was due to global buckling. At high temperature failure results from excessive lateral deflections and second order flexural effects due to reductions the walls' effective cross-section and flexural rigidity, as well as a shift of the effective neutral axis in bending during fire. Measured average one-dimensional charring rates ranged between 0.82 and 1.0 mm/min in these tests. As expected, the lamellae configuration greatly influenced the walls' deformation responses and times to failure; with 3-ply walls failing earlier than those with 5-plies. The walls' deformation response during heating suggests that, if a conventional reduced cross section method (RCSM), zero strength layer analysis were undertaken, the required zero strength layer depths would range between 15.2 mm and 21.8 mm. Deflection paths further suggest that the concept of a zero strength layer is inadequate for properly capturing the mechanical response of fire-exposed CLT compression elements.

Deformation Behavior of Powder Metallurgy Connecting Rod Preform During Hot Forging Based on Hot Compression and Finite Element Method Simulation

Powder-forged connecting rod with a complex geometry shape always has a problem with nonuniform density distribution. Moreover, the physical property of preform plays a critical role for optimizing the connecting rod quality. The flow behavior of a Fe-3Cu-0.5C (wt pct) alloy with a relative density of 0.8 manufactured by powder metallurgy (P/M, Fe-Cu-C) was studied using isothermal compression tests. The material constitutive equation, power dissipation (η) maps, and hot processing maps of the P/M Fe-Cu-C alloy were established. Then, the hot forging process of the connecting rod preforms was simulated using the material constitutive model based on finite element method simulation. The calculated results agree well with the experimental ones. The results show that the flow stress increases with decreasing temperature and increasing strain rate. The activation energy of the P/M Fe-Cu-C alloy with a relative density of 0.8 is 188.42 kJ/mol. The optimum temperature at the strain of 0.4 for good hot workability of sintered Fe-Cu-C alloy ranges from 1333 K to 1380 K (1060 °C to 1107 °C). The relative density of the hot-forged connecting rod at the central part changed significantly compared with that at the big end and that at the small end. These present theoretical and experimental investigations can provide a methodology for accurately predicting the densification behavior of the P/M connecting rod preform during hot forging, and they help to optimize the processing parameters.

Cone ice crushing tests and simulations associated with various yield and fracture criteria

ABSTRACTTo determine the most reliable numerical simulation parameters affecting the ice resistances, such as yield functions with relevant ice-breaking criteria, compressive volumetric hardening intensities and element sizes, numerical simulations for different parameters were compared with the crushing tests of cone-shaped ice specimens. The yield functions of crushable foam, Drucker–Prager and Mohr–Coulomb were taken into consideration with three different volumetric hardening intensities. The ice resistance variation was also studied for two finite element models with different element sizes. To realize ice breaking in numerical simulations, a damage variable was introduced to trigger fracture initiation and evolution. The nominal contact area-dependent energy per unit area as a damage to fracture was newly proposed from the test results composed of a crushing force versus indenter stroke. This new concept could be realized by applying the different nominal contact area-dependent fracture energies to finite elements along the vertical location.

Soft Spherical Tensegrity Robot Design Using Rod-Centered Actuation and Control

This paper presents the design, analysis, and testing of a fully actuated modular spherical tensegrity robot for co-robotic and space exploration applications. Robots built from tensegrity structures (composed of pure tensile and compression elements) have many potential benefits including high robustness through redundancy, many degrees-of-freedom in movement and flexible design. However, to take full advantage of these properties, a significant fraction of the tensile elements should be active, leading to a potential increase in complexity, messy cable, and power routing systems and increased design difficulty. Here, we describe an elegant solution to a fully actuated tensegrity robot: The TT-3 (version 3) tensegrity robot, developed at UC Berkeley, in collaboration with NASA Ames, is a lightweight, low cost, modular, and rapidly prototyped spherical tensegrity robot. This robot is based on a ball-shaped six-bar tensegrity structure and features a unique modular rod-centered distributed actuation and control architecture. This paper presents the novel mechanism design, architecture, and simulations of TT-3, an untethered, fully actuated cable-driven six-bar spherical tensegrity robot. Furthermore, this paper discusses the controls and preliminary testing performed to observe the system's behavior and performance and is evaluated against previous models of tensegrity robots developed at UC Berkeley and elsewhere.

INFLUENCE OF RESIDUAL STRESS ON THE STABILITY OF STEEL COLUMNS AT ELEVATED TEMPERATURES

Influence of residual stresses on the stability of steel columns with various sections at elevated temperatures has been studied. The potential effect of residual stresses on the stability of columns should be clarified, as the stability of compression elements in fire even without explicitly regarding residual stresses is not a straightforward phenomenon. Extensive numerical study was performed utilizing non-linear finite element method. Results for models ignoring and accounting for residual stresses were compared for different steel grades, various slenderness values, temperatures and section types. Results were compared with Eurocode method.

Tensegrity-inspired polymer nanocomposites

Investigating the design space available in nanofilled polymers is expected to produce materials with unique structure-property relationships. In this work, the concept of tensegrity is used as inspiration for microstructural design. Tensegrity is an elegant and efficient structural design, relying upon interactions between elements, specifically elements in compression which are connected through a tensioned web. In this embodiment, the nanoparticles are considered the compressive elements, and the polymer matrix, when suitably processed, is considered the tensioned web. Nanocomposite materials containing polymer-decorated hydroxyapatite nanoparticles were used to evaluate the tensegrity-inspired approach. Nanocomposite systems with a semi-crystalline matrix (polyethylene oxide) and an amorphous matrix (polymethyl methacrylate) were prepared and characterized with compatible polymer-decorated nanoparticles. The results showed that the nanocomposite with a semi-crystalline matrix was more promising as a candidate for producing the tensegrity-inspired microstructure and that the concept could produce improved thermomechanical properties in the glassy temperature regime.

Study of the stress-strain state of compressed concrete elements with composite reinforcement

The efficiency analysis of the application of glass composite reinforcement in compressed concrete elements as a load-carrying component has been performed. The results of experimental studies of the deformation-strength characteristics of this reinforcement on compression and compressed concrete cylinders reinforced by this reinforcement are presented. The results of tests and mechanisms of sample destruction have been analyzed. The numerical analysis of the stress-strain state has been performed for axial compression of concrete elements with glasscomposite reinforcement. The influence of the reinforcement percentage on the stressed state of a concrete compressed element with the noted reinforcement is estimated. On the basis of the obtained results, it is established that the glass-composite reinforcement has positive effect on the strength of the compressed concrete elements. That is, when calculating the load-bearing capacity of such structures, the function of composite reinforcement on compression should not be neglected.

Strength of Circular Concrete Columns Reinforced with FRP Bars and Spirals

Circular cross section reinforced concrete columns are often used in structures of buildings, ports or bridges. Generally, for the installment of these constructions metal/steel reinforcement is being used. Corrosion of steel reinforcement is the main and one of the biggest problems reducing the durability of these structures and it is a reason of fragile disintegration of these structures. In the current period, the composite reinforcement is an alternative material for the production of reinforced concrete structures the mechanical characteristics of which are equal to or even better in comparison of the commonly used steel reinforcement characteristics, including tensile strength and resistance to corrosion at the extremely aggressive environment. Due to the lack of the researches, many design standards do not indicate or recommend the use of composite reinforcement in compressive elements or flexural elements in compressed zones. This article analyzes the possibilities of the use of composite reinforcement in axially crushed circular cross section columns.

Calculation methodology of reinforced concrete elements based on calculated resistance of reinforced concrete

Calculation methodology of reinforced concrete elements based on the calculated resistance of reinforced concrete is presented. The basic dependence which allows setting the strength of bending sections and non-central compressed elements is obtained. The proposed method for calculating reinforced concrete elements is based on the use of nonlinear diagrams of material deformation, the hypothesis of flat sections and deformation criteria for the destruction of materials. The basic equations of strength are reduced to dimensionless quantities and are tabulated. When compiling the tables, the formula proposed in Euroсode 2 was adopted as the diagram of concrete deformation, and for the reinforcement two linear Prandtl diagram was used. The calculated formulas of the proposed method fully correspond to the formulas of the classical resistance of materials, and make it possible to solve the most frequently encountered problems in the practice of modern construction. The reliability of the dependencies is experimentally confirmed. There are calculation examples of bending and non-central compressed elements by the developed methodology.

Strength and stiffness of cement-treated marine dredged clay at various curing stages

This paper evaluates the unconfined compressive strength (qu) and stiffness (G0) of marine dredged clay treated by ordinary Portland cement. Although the cement-treated marine dredged clays have been used as filling materials for construction or reclamation, many of previous studies were more applicable to soft foundation improvement methods such as deep cement mixing and jet grouting. This study aims to investigate how the qu and G0 of cement-treated marine dredged clay vary with water and cement contents at various curing times and to observe the relationship of the qu and G0. A series of unconfined compression and bender element tests were carried out for cement-treated Tokuyama dredged clay with different values of water and cement contents at various curing times, ranging from 5 h to 90days and the relationship between the qu and G0 was examined. Specific volume normalized by that at liquid limit were applied to facilitate parametric study. The study revealed that the behavior of qu with curing time are closely similar to that of G0, and a trend of development of qu and G0 change before and after 3days of curing time. The qu and G0 can be correlated with the normalized specific volume. The qu and G0 exhibits a linear relationship for the curing time. Based on these results, the empirical equations for estimating qu are proposed using G0 estimation equations and the relation between qu and G0. In addition, the applicability of formulas based on the relation of qu and G0 was evaluated using the relation of G0 and secant modulus (E50). It was confirmed that the G0 can successfully describe the improvement effect of cement-treated marine dredged clay and can be used to effectively predict the qu using the proposed formulas.

3D hybrid modelling of vascular network formation

We develop an off-lattice, agent-based model to describe vasculogenesis, the de novo formation of blood vessels from endothelial progenitor cells during development. The endothelial cells that comprise our vessel network are viewed as linearly elastic spheres that move in response to the forces they experience. We distinguish two types of endothelial cells: vessel elements are contained within the network and tip cells are located at the ends of vessels. Tip cells move in response to mechanical forces caused by interactions with neighbouring vessel elements and the local tissue environment, chemotactic forces and a persistence force which accounts for their tendency to continue moving in the same direction. Vessel elements are subject to similar mechanical forces but are insensitive to chemotaxis. An angular persistence force representing interactions with the local tissue is introduced to stabilise buckling instabilities caused by cell proliferation. Only vessel elements proliferate, at rates which depend on their degree of stretch: elongated elements have increased rates of proliferation, and compressed elements have reduced rates. Following division, the fate of the new cell depends on the local mechanical environment: the probability of forming a new sprout is increased if the parent vessel is highly compressed and the probability of being incorporated into the parent vessel increased if the parent is stretched.Simulation results reveal that our hybrid model can reproduce the key qualitative features of vasculogenesis. Extensive parameter sensitivity analyses show that significant changes in network size and morphology are induced by varying the chemotactic sensitivity of tip cells, and the sensitivities of the proliferation rate and the sprouting probability to mechanical stretch. Varying the chemotactic sensitivity directly influences the directionality of the networks. The degree of branching, and thereby the density of the networks, is influenced by the sprouting probability. Glyphs that simultaneously depict several network properties are introduced to show how these and other network quantities change over time and also as model parameters vary. We also show how equivalent glyphs constructed from in vivo data could be used to discriminate between normal and tumour vasculature and, in the longer term, for model validation. We conclude that our biomechanical hybrid model can generate vascular networks that are qualitatively similar to those generated from in vitro and in vivo experiments.

Material properties and compressive local buckling response of high strength steel square and rectangular hollow sections

An experimental investigation into the structural performance of compressed high strength steel (HSS) square and rectangular hollow sections is described in this paper. Both hot-rolled and cold-formed HSS sections were examined. In total six S460NH and five S690QH hot-rolled section sizes and three S500MC, two S700MC and four S960QC cold-formed section sizes were tested. The experimental programme comprised tensile coupon tests on flat and corner material, measurements of geometric imperfections, full cross-section tensile tests and stub column tests. The results of the experiments presented in this paper have been combined with other available test data on high strength steel sections, and used to assess the existing design guidelines for high strength steels given in Eurocode 3. The focus has been on the material ductility requirements, the Class 3 slenderness limit for internal elements in compression and the effective width formula for Class 4 internal elements in compression.Reliability assessments of the Class 3 slenderness limit (both the current value of 42 and a proposed value of 38) and the effective width formula for Class 4 internal elements in compression were carried out. The analysis indicated that, based on the assembled test data considered in this study, and the assumptions made regarding the statistical distributions of material and geometric properties, a partial safety factor greater than unity is required for HSS. Similar findings have also recently been presented for ordinary strength steels.

Notes on the AISC 360-16 Provisions for Slender Compression Elements in Compression Members

Compression member strength is controlled by the limit states of flexural buckling, torsional buckling, and flexural-torsional buckling, as applicable. These compression members may buckle globally or locally, depending on the overall column slenderness and the local plate element slenderness for the plates that make up the shape. If any of the plate elements will buckle at a stress lower than that which would cause the column to buckle globally, the local buckling of the plate will control the overall column strength. When this occurs, the column is said to be composed of slender elements. This paper will briefly discuss past specification provisions for slender element compression members and introduce the new provisions in the 2016 AISC Specification. It will present a simplification that reduces the number of constants that must be used and will present the specification requirements in an alternate format. Because the 2016 requirements result in different strengths than the 2010 requirements, figures are provided to illustrate the overall impact of these changes on column strength.

Ultimate Load Bearing Capacity of Web Members of Lattice Aluminium Structures Made of CHS Profiles

A joint of lattice aluminium welded structure made of circular hollow sections (CHS) has been analysed. Aluminium alloy EN AW 6082-T6 was used. Calculation of ultimate load bearing capacity of lattice structure web member assumes check of element load bearing capacity for the following calculation situations:- calculation of ultimate load bearing capacity of compressed elements with the influence of buckling,- calculation of ultimate load bearing capacity of compressed elements with the influence of HAZ,- calculation of ultimate load bearing capacity of tensioned elements with the influence of HAZ,- calculation of ultimate element force in truss joint, depending on joint construction.The first three checks are independent of type and characteristics of truss chords. They depend only on elements connection manner and geometrical characteristics of web members. The fourth condition directly depends on relation of chord and web member characteristics, i.e. ratio of their diameters and tube wall thicknesses. The choice of joint geometry, gap between elements in joint as well as joint eccentricity are also important for ultimate force in web member. Check of K-joint ultimate bearing capacity is particularly needed for welded joints due to aluminium strength decrease caused by HAZ (Heat Affected Zone) effect.European standard EN 1999 for aluminium structures design has not defined ultimate load of web members regarding type and characteristics of joint connection.Value of ultimate force in web member of K-joint, depending on connection type, by means of expressions defined in EN 1993-1-8 (Design of steel structures - Part 1-8: Design of joints), has been analysed. Comparative analysis has been done by means of ANSYS modelling, taking into consideration real characteristics of aluminium alloy and ultimate load bearing capacity reduction in the vicinity of weld due to HAZ effect. The main goal of the paper is to analyse capability of expressions from EN 1993-1-8 for steel structures to be used in aluminium structures, having in mind quoted limitations.

Multistage Fiber Amplifier with Spectral Compression Elements for High-Energy Laser Pulse Generation

We consider general principles of spectral compression of parabolic pulses in nonlinear optical fibers. It is known that the variance analysis provides a way to describe correctly the evolution of the pulse parameters under the spectral compression. We propose a computational model of multistage amplifier with spectral compression segments incorporated. The model provides the possibility to amplify middle-power input pulses to obtain pulse energies of hundreds of nanojoules with such output spectral characteristics that provide the possibility for further effective enhancement. We also discuss a modification of the model that provides the formation of a parabolic envelope and linear frequency modulation of the output pulse.

Blind-bolted shear connections for axially compressed RHS columns strengthened with open sections

The process of implementing principles of sustainable development in building for existing structures is much more challenging than for new designs. This issue is particularly acute when it comes to improving the stability of an axially compressed bar elements made of rectangular hollow section (RHS). This paper presents the results of experimental and analytical studies that address the question whether blind bolts BOM may be an effective alternative to bolted fasteners in one-sided lap connections between strengthened bar and strengthening branches. The results of shear tests of single lap connections with blind BOM-R16-4 bolts prove that the structural properties of the tested joints are similar to the structural properties of connections with M16-8.8 grade bolts. Results of the parametric analysis carried out for a perfectly straight axially compressed RHS columns, symmetrically strengthened by two U-shaped branches indicate the special potential of BOM fasteners in applications for joining the walls of strengthened tubular bar and strengthening branches of open cross-section. The analytical results demonstrate that the lack of the main slip in the lap bearing connections of branches with BOM fasteners gains efficiency in strengthening of the axially compressed column in comparison with solutions using bolts. The results obtained provide the basis for the development of an efficient method of strengthening bar elements with closed cross-sections that is characterized by low energy expenditure, in accordance with the principles of sustainable building.

A minimal mass deployable structure for solar energy harvesting on water canals

This paper produces a design for a minimal mass, deployable support structure for a solar panel covering of water canals. The results are based upon the minimal mass properties of tensegrity structures. The efficient structure is a tensegrity system which has an optimal complexity (i.e. an optimal number of members) for minimal mass. This optimal complexity is derived in this paper, along with deployable schemes which are useful for construction, repairs, for Sun following, and for servicing. It is shown that the minimal structure naturally has deployable features so that extra mass is not needed to add the multifunctional features. The design of bridge structures with tensegrity architecture will show an optimal complexity depending only on material choices and external loads. The minimization problem considers a distributed load (from weight of solar panels and wind loads), subject to buckling and yielding constraints. The result is shown to be a Class 1 Tensegrity substructure (support structure only below the deck). These structures, composed of axially-loaded members (tension and compressive elements), can be easily deployable and have many port-able applications for small spans. The focus of this paper is an application of these minimal mass tensegrity concepts to design shading devices to prevent or reduce evaporation loss, while generating electric power with solar panels as the cover. While the economics of the proposed designs are far from finalized, this paper shows a technical solution that uses the smallest material resources, and shows the technical feasibility of the concept.

An appropriate relationship between flexural strength and compressive strength of palm kernel shell concrete

This paper presents the determination of an appropriate compressive–flexural strength model of palm kernel shell concrete (PKSC). The direct and indirect Ultrasonic Pulse Velocity (UPV) measurements, with respective to mechanical properties of compression (cube) and flexural (slab) elements, of concrete at various mixes and water/cement (w/c) ratios were made. A total of 225 cubes and 15 slabs of the PKSC were casted for nominal mixes of 1:1:1, 1:1:2 and 1:11/2:3, and varying (w/c) ratios of 0.3–0.7 at interval of 0.1. The test elements were cured for 3, 7, 14, 28, 56 and 91days in water at laboratory temperature. The elements were then subjected to nondestructive testing using the Pundit apparatus for determination of direct ultrasonic wave velocity and the elastic modulus at the various ages. The cubes were subsequently subjected to destructive compressive test. The 28-day compressive strength–UPV and strength–age statistical relationships at w/c ratio of 0.5 determined from the velocity–strength data set in linear, power, logarithm, exponential and polynomial trend forms. The polynomial trend line in the form y=aln(x) at R2 value of 0.989, found appropriate, among others, was proposed for the formulation of the compressive strength–flexural strength model of PKSC at w/c ratio of 0.5.

Influence of Compression and Stiffness Apparel on Vertical Jump Performance.

Compression apparel alters both compression of the soft tissues and the hip joint stiffness of athletes. It is not known whether it is the compression elements, the stiffness elements, or some combination that increases performance. Therefore, the purpose of this study was to determine how systematically increasing upper leg compression and hip joint stiffness independently from one another affects vertical jumping performance. Ten male athletes performed countermovement vertical jumps in 8 concept apparel conditions and 1 control condition (loose fitting shorts). The 8 apparel conditions, 4 that specifically altered the amount of compression exerted on the thigh and 4 that altered the hip joint stiffness by means of elastic thermoplastic polyurethane bands, were tested on 2 separate testing sessions (one testing the compression apparel and the other testing the stiffness apparel). Maximum jump height was measured, while kinematic data of the hip, knee, and ankle joint were recorded with a high-speed camera (480 Hz). Both compression and stiffness apparel can have a positive influence on vertical jumping performance. The increase in jump height for the optimal compression was due to increased hip joint range of motion and a trend of increasing the jump time. Optimal stiffness also increased jump height and had the trend of decreasing the hip joint range of motion and hip joint angular velocity. The exact mechanisms by which apparel interventions alter performance is not clear, but it may be due to alterations to the force-length and force-velocity relationships of muscle.

Conceptual Design Optimization of Tensairity Girder Using Variable Complexity Modeling Method

Tensairity girder is a light weight inflatable fabric structural concept which can be used in road emergency transportation. It uses low pressure air to stabilize compression elements against buckling. With the purpose of obtaining the comprehensive target of minimum deflection and weight under ultimate load, the cross-section and the inner pressure of tensairity girder was optimized in this paper. The Variable Complexity Modeling (VCM) method was used in this paper combining the Kriging approximate method with the Finite Element Analysis (FEA) method, which was implemented by ABAQUS. In the Kriging method, the sample points of the surrogate model were outlined by Design of Experiment (DOE) technique based on Optimal Latin Hypercube. The optimization framework was constructed in iSIGHT with a global optimization method, Multi-Island Genetic Algorithm (MIGA), followed by a local optimization method, Sequential Quadratic Program (SQP). The result of the optimization gives a prominent conceptual design of the tensairity girder, which approves the solution architecture of VCM is feasible and efficient. Furthermore, a useful trend of sensitivity between optimization variables and responses was performed to guide future design. It was proved that the inner pressure is the key parameter to balance the maximum Von Mises stress and deflection on tensairity girder, and the parameters of cross section impact the mass of tensairity girder obviously.