Conventional Structural Elements Research Articles

Utilization of Bioactive Silk Protein in the Development of Optical Devices: Recent Advancements and Applications.

Typically, materials used to create optical devices have chemical and physical properties that have been precisely designed for a narrowly defined purpose, allowing for changes in design to account for device variability. There is a growing need for devices built of materials with changeable optical responses, as optical systems are incorporated into platforms with much functionality. Regenerated silk fibroin is described in this article as an enabling gadget with an active optical response as a result of the inherent characteristics of proteins. Silk's capacity for controlled movement, to swell and shrink reversibly, alter conformation and degradation that is customizable, impacts both the shape and the response of the optical structure-representative silk-based gadgets. The diversity of silk material is shown and discussed in this paper, concentrating on architectures that show reconfigurable behavior, an optical waveguide that is physically temporary and provides reversible responses. Finally, innovative research directions for silk-based materials and optical devices are presented in this paper. Since ancient times, silk, a natural biopolymer, has been used as a repair material in medicine. In the past 20 years, it has attracted a lot of interest to be used in several biomedical applications. Various healthcare items with silk as their substrate have been developed thanks to significant advancements in silk biomaterial research. Silk is a fabric created from spider and silkworm cocoons. Hierarchical structures and conventional structural elements are present in them. Different silk types can be produced using certain methods, such as films, fibers, microspheres, sponges, and hydrogels. The structural characteristics of secondary proteins present in silk can also be modified. This paper investigates the use of silk in biomedical and optical applications, and examines the technical trend in electronic fields.

Studying effects of interface surface roughness, mean particle size, and particle shape on the shear behavior of sand-coated CFRP interface

Carbon fiber-reinforced polymer (CFRP) composites can be considered an ideal alternative for conventional structural elements due to their superior benefits, such as high durability, satisfactory strength, and cost-effectiveness. This study is focused on interface shear behavior between sand-coated CFRP [spark plasma sintering CFRP (SPSCFRP)] and different types of sand with varying mean particle sizes (D50), and particle shapes [well-rounded (glass beads or GB), well-angular (glass powder or GP), and sub-rounded to sub-angular (natural sand)] under two levels of initial relative density. Four types of SPSCFRP surfaces with different levels of surface roughness, ranging from very smooth (VS) to highly rough (HR) were selected to perform interface shear tests. Analysis of sand-SPSCFRP data highlights an increase in surface roughness, mean particle size, angularity, and initial relative density resulting in mobilization of higher peak and critical-state friction angles. Rough SPSCFRP shows the most effective performance of the tested configurations in interface shear response. A critical value for normalized roughness (Rn) is observed (0.2≤Rcr≤0.5), within which the highest value of peak and critical-state friction angles is obtained. A well-pronounced post-peak reduction in shear stress of interfaces with Rn≥ 0.3 is observed. The peak and critical-state friction angles of sand-rough SPSCFRP interfaces are 15–32% and 11–32% higher than those of sand-CFRP interfaces, respectively. Given the same surface roughness and mean particle size, smaller peak and critical-state interface friction angles are mobilized for well-rounded sand than for well-angular sand. For the sand-SPSCFRP and sand-CFRP interfaces, the sand-structure design ratio (D.R.) ranges between 1.04 and 1.16 and 0.79–0.96, respectively. The average efficiency factor (E.F.) of the sand-SPSCFRP surfaces are 1.02 and 1.06, respectively, for medium-dense and dense specimens, while this value is much lower for sand-uncoated CFRP (∼0.8).

Non-linear behaviour and failure mechanism of bamboo poles in bending

The adoption of bamboo poles in construction can support the reduction of carbon dioxide emissions generated by the manufacture of conventional structural elements produced from unsustainable industrialised materials. This research focuses on the study of the nonlinear softening behaviour and failure mechanism of bamboo poles in bending through a series of experimental tests on Moso (Phyllostachys pubescens) bamboo and Finite Element simulations supported by digitisation techniques. The results indicate that this nonlinear behaviour is caused by the incremental development of cracks at the locations where the circumferential tensile capacity of bamboo is exceeded leading to the eventual failure of the pole. Also, the simulations in this study suggest that reinforcing bamboo poles with pretensioned stainless steel bands is ineffective in counteracting the development of significant circumferential tensile stresses and the associated longitudinal cracks. More generally, this work highlights the challenges and limitations of applying traditional methods of structural testing and design for manufactured components to a highly variable natural structural element and speculates whether modern digital technologies can be adopted to manage more effectively the effects of this inherent variability.

Feasibility Assessment of Stiff Seismic Base Absorbers

In this paper, a radically new concept of a Stiff Seismic Base Absorber (SBA) is proposed for seismic protection of multistory building structures. An inerter is first implemented, connecting directly the structure to the ground. This results in the decrease of the natural frequency of the structure, without decreasing its structural stiffness. Parallel, a negative stiffness-based absorber is used to increase the apparent damping behavior of the inerter. The additional mass of the SBA is connected to the structure with a negative stiffness (NS) element and to the base with a positive one. Also, an artificial damper is placed in parallel with each stiffness element. The design of the SBA includes the following novel features: (1) the SBA foresees variation in all stiffness elements, (2) the optimal system parameters are selected based on engineering criteria with proper constraints and limitations to the system dynamic responses, (3) the earthquake input motion is selected according to the seismic design codes, (4) a displacement-dependent non-linear configuration is proposed for the realization of the NS element, and (5) the detuning phenomena are observed via sensitivity analysis. Compared to other vibration absorbers, the SBA presents several advantages. An improved superstructure dynamic behavior is observed combined with small base displacements, in the order of a few centimeters. The drastically reduced base displacements render the implementation of the SBA feasible using conventional structural elements. As a result, the SBA is a realistic retrofitting option for seismic protection.

Constrained optimal design of seismic base absorbers based on an extended KDamper concept

In this paper, an extended KDamper (EKD) concept is proposed, for implementation as a seismic base absorber. The complexity of the EKD renders the conventional minmax (H∞) approaches ineffective. For this reason, a dedicated constrained optimization problem is proposed for the selection of the optimal system parameters. The EKD is designed according to seismic design codes and the constraints and limitations of the EKD components are evaluated based on engineering criteria. In order to better observe the efficiency of the proposed configuration, an acceleration filter is placed, as an additional constraint. Therefore, each set of optimized parameters of the EKD refers to the maximum structure acceleration, expressed as a percentage of PGA. A database of artificial accelerograms, compatible with the EC8 response spectra is generated. Sensitivity analysis is performed, and the effect of detuning is observed. Subsequently, the EKD is implemented as a seismic base absorber in a multi-story building. The performance of the proposed control strategy is compared not only to the original structure but also to the cases of conventional and highly damped base isolation systems, as well as to the KDamper. The EKD presents an improved superstructure dynamic behavior, comparable with a base isolated system. At the same time, the base relative displacement is drastically reduced, in the order of a few centimeters, rendering the implementation of the EKD feasible using conventional structural elements, without the need for special types of bearings. In addition, the base shear is reduced, as compared to the original structure, with the implementation of the proposed configuration, and thus, EKD can be considered a possible retrofitting option for seismic protection.

Recycling Aggregates for Self-Compacting Concrete Production: A Feasible Option

The use of construction and demolition wastes (C&DW) is a trending future option for the sustainability of construction. In this context, a number of works deal with the use of recycled concrete aggregates to produce concrete for structural and non-structural purposes. Nowadays, an important number of C&DW management plants in the European Union (EU) and other countries have developed robust protocols to obtain high-quality coarse recycled aggregates that comply with different European standards in order to be used to produce new concrete. The development of self-compacting concrete (SCC) is another way to boost the sustainability of construction, due to the important reduction of energy employed. Using recycled aggregates is a relatively recent scientific area, however, studies on this material in the manufacture of self-compacting concrete have proven the feasibility thereof for conventional structural elements as well as high-performance and complex structural elements, densely reinforced structures, difficult-to-access formwork and difficult-to-vibrate elements. This paper presents an original study on the use of coarse recycled concrete aggregate (CRA) to obtain self-compacting concrete. Concrete with substitution ratios of 20%, 50% and 100% are compared with a control concrete. The purpose of this comparison is to check the influence of CRA on fresh SCC as well as its physical and mechanical properties. The parameters studied are material characterization, self-compactability, compressive strength, and tensile and flexural strength of the resulting concrete. The results conclude that it is feasible to use CRA for SCC production with minimal losses in the characteristics.

Lateral impact response of innovative hollow corrugated members

There has recently been a growing trend of replacing conventional structural elements by innovative components so as to achieve more resilient infrastructures. Owing to the recent benchmark study conducted at Monash University, it has been demonstrated that the ultimate compressive capacity of hollow box members consisting of self-strengthened corrugated plates is significantly more than those made of flat plates. However, the behaviour of hollow corrugated members subjected to lateral impact loading has never been investigated. This paper fundamentally reports the behaviour of members built up from four corrugated plates, which are butt-welded at the apexes of the section, under lateral impact loading. Three different types of corrugation profiles as well as two levels of impact energy are considered to investigate the influence of geometric parameters and impact energy level on the member behaviour. The samples are transversely hit by an indenter with defined weight dropping from desired height. It will be demonstrated that the corrugation shape may influence the peak impact force, stabilised post-peak forces, and contact duration. A numerical model is also developed and verified against the experimental results using ABAQUS. Good agreement between experimental and numerical results including recorded data histories and damage patterns is achieved.

Experimental Behavior of Innovative Hollow Corrugated Columns under Lateral Impact Loading

There has recently been a growing trend of replacing conventional structural elements by novel components to achieve more resilient infrastructure. Owing to the recent benchmark study conducted at Monash University, it has been demonstrated that the ultimate compressive capacity of hollow box columns consisting of self-strengthened corrugated plates is significantly enhanced compared to those made of flat plates. However, the behaviour of hollow corrugated columns subjected to impact loading has never been investigated. This paper reports the fundamental behavior of the columns built up from four corrugated plates, which are butt-welded together at the apexes of the section, under lateral impact loading. Three different types of corrugation profiles are considered to investigate the influence of geometric parameters and level of impact energy on the member behaviour. The samples are transversely hit by a 270kgweight dropping hammer from 5m height. Accordingly, the results of experimental tests conducted on large-scale corrugated columns with 1.8m height are addressed. The recorded data including the residual failure modes as well asimpact forces and global deformations time histories of corrugated columns are being compared with those obtained for a control specimen built from flat plates.

Geothermal Geotechnics for Urban Undergrounds

Underground urbanization as a prerequisite for sustainable development involves the design and construction of underground spaces in difficult ground and under very restricted conditions. Additionally, it offers the possibility of using ground structures also as thermo-active heat exchangers for heating and cooling of all kinds of buildings. This keynote paper focuses on near-surface geothermal geotechnics, i.e. energy piles and other energy foundations, energy walls, energy tunnels etc. This represents an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. Absorber pipes filled with a heat carrier fluid are installed within conventional structural elements (piles, barrettes, diaphragm walls, basement slabs or walls, tunnel linings), forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and for cooling in summer. Hence not additional elements have to be installed below surface. The primary circuit is then connected via a heat pump to a secondary circuit within the building. The paper deals with earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. For instance, several new metro stations in Vienna are equipped with this sustainable technology. Theoretical details, pilot research projects and case histories bridge the gap between theory and practice, and special applications reveal the wide field of geothermal geotechnics. Design recommendations are given. Finally, benefits of thermo-active ground structures and recommendations for promoting geothermal energy utilization are listed.

Heating performance characteristics of the ground source heat pump system with energy-piles and energy-slabs

Energy foundations and other thermo-active ground structure, energy wells, energy slabs, and pavement heating and cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. This paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Pipes, energy-piles and energy-slabs filled with a heat carrier fluid are installed under conventional structural elements, forming the primary circuit of a geothermal energy system. The ground source heat pump system with energy-pile and energy-slab presented high heating performance due to the stability of entering water temperature from the ground loop heat exchanger. The minimum COPs of the heat pump unit for the energy-pile and energy-slab system were 4.2 and 4.5, respectively. These results are higher than the minimum COP certification standard of 3.45 for a closed ground loop heat pump unit.

Thermo-active Ground-Source Structures for Heating and Cooling

Energy foundations and other thermo-active ground structures, energy wells, and pavement or bridge deck heating/cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. The paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Absorber pipes filled with a heat carrier fluid are installed within conventional structural elements (piles, barrettes, diaphragm walls, basement slabs or walls, tunnel linings), forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and for cooling in summer. Hence no additional elements have to be installed below surface. The primary circuit is then connected via a heat pump to a secondary circuit within the building. Benefits of energy foundations are also listed in this paper.

에너지슬래브 적용 지열원 열펌프 시스템의 성능 특성에 관한 실증 연구

Energy foundations and other thermo-active ground structure, energy wells, energy-slab, and pavement heating and cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. This paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Pipes, energy slabs, filled with a heat carrier fluid are installed under conventional structural elements, forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and a heat sink in summer. The geothermal heat pump system with energy-slab represented very high heating and cooling performance due to the stability of EWT from energy slab. However, the performance of it seemed to be affected by the atmospheric air temperature.

Steady‐state characteristics on a single‐phase buck rectifier with improved input‐current waveform

AbstractA single‐phase buck rectifier applying pulse width modulation (PWM) creates a large amount of low‐order harmonics flow out in the input current. A high‐inductance inductor must be used to reduce the pulsations of the DC inductor current and to produce a sinusoidal input current. To address this, the authors propose a single‐phase buck rectifier with improved input current waveform by adding a switch for back flow of the DC inductor current to the conventional structural elements. In this paper, the main circuit configuration and operating theory of the proposed rectifier are explained, and its effectiveness is confirmed through experimental results and simulations. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 56–65, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20330

Energy foundations and other thermo-active ground structures

Energy foundations and other thermo-active ground structures, energy wells, and pavement heating represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimised maintenance. The paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Absorber pipes filled with a heat carrier fluid are installed within conventional structural elements (piles, barrettes, diaphragm walls, basement slabs or walls, tunnel linings), forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and for cooling in summer. Hence no additional elements have to be installed below surface. The primary circuit is then connected via a heat pump to a secondary circuit within the building. ‘Free cooling’ may even run without a heat pump. The paper describes heat transfer in the ground, and between absorber fluid and concrete/soil. Temperature-induced changes of soil properties or of foundation behaviour are also discussed, and recommendations for design and operation are given. Pilot research projects and case histories bridge the gap between theory and practice, and special applications reveal the wide field of geothermal geotechnics.

Surface free energy and its effect on the elastic behavior of nano-sized particles, wires and films

Atoms at a free surface experience a different local environment than do atoms in the bulk of a material. As a result, the energy associated with these atoms will, in general, be different from that of the atoms in the bulk. The excess energy associated with surface atoms is called surface free energy. In traditional continuum mechanics, such surface free energy is typically neglected because it is associated with only a few layers of atoms near the surface and the ratio of the volume occupied by the surface atoms and the total volume of material of interest is extremely small. However, for nano-size particles, wires and films, the surface to volume ratio becomes significant, and so does the effect of surface free energy. In this paper, a framework is developed to incorporate the surface free energy into the continuum theory of mechanics. Based on this approach, it is demonstrated that the overall elastic behavior of structural elements (such as particles, wires, films) is size-dependent. Although such size-dependency is negligible for conventional structural elements, it becomes significant when at least one of the dimensions of the element shrinks to nanometers. Numerical examples are given in the paper to illustrate quantitatively the effects of surface free energy on the elastic properties of nano-size particles, wires and films.

Pressure induced stability: from pneumatic structures to Tensairity®

Structural stabilization by a pressurized fluid is very common in nature, however hardly found in technology. Car tires, hot air balloons, airships and airhouses are among the few technical exceptions, which are stabilized by a compressed medium, typically air. Restricted by simple geometries and a very limited load bearing capacity these pneumatic structures could succeed only in very specialized applications. Nevertheless, prospective concepts ag has systematically investigated pneumatic structures during the last few years. As a major result, it was demonstrated that almost any shape can be made with pneumatic structures and that astonishing structures such as the pneumatic airplane Stingray can be realized even with low air pressure. On top of that, Airlight Ltd. in close collaboration with prospective concepts ag has recently developed the fundamental new structural concept Tensairity. The synergetic combination of an inflated structure with conventional structural elements such as cables and struts yields pneumatic light-weight structures with the load bearing capacity of steel girders. Thus, complex forms and high strength open up many new opportunities for pressure induced stability in technology. An overview of these recent developments is presented and the close relationship of pneumatic structures with biology is outlined.