Important Structural Design Research Articles

Trans‐N‐alkylation Covalent Exchanges on 1,3,4‐Trisubstituted 1,2,3‐Triazolium Iodides

Abstract1,3,4‐Trisubstituted 1,2,3‐triazolium salts having either aliphatic or benzylic substituents at the N‐1 and N‐3 positions were synthesized in two steps involving: i) copper(I) catalyzed azide‐alkyne 1,3‐dipolar cycloaddition (CuAAC), and ii) N‐alkylation of the 1,2,3‐triazole intermediates. Trans‐N‐alkylation reactions in bulk and in the presence of excess methyl iodide were monitored by 1H NMR spectroscopy for each 1,2,3‐triazolium molecular model. By assigning the different formed species and their respective evolution with time, it was possible to conclude that trans‐N‐alkylation exchange reactions are significantly faster for benzylic substituents than for aliphatic ones. Furthermore, the exchange reactions are noticeably faster at the N‐3 position than at the N‐1 position most likely due to the steric hindrance induced by the neighboring C‐4 substituent. The kinetics of trans‐N‐alkylation reactions are thus influenced by both the chemical nature of the N‐1 and N‐3 substituents and the regiochemistry of the 1,2,3‐triazolium group. This provides important structural design rules to improve the properties of thermosetting covalent adaptable networks involving trans‐N‐alkylation of 1,2,3‐triazolium salts.

The effects of nozzle taper angle on in-nozzle flow and nozzle tip-wetting under flash boiling conditions

As an important structural design, the taper angle of an injector has been proved to have a significant influence on spray behavior under both subcooled and flash boiling conditions. However, present studies on taper angle mostly focus on the morphology of the far-field spray, the detailed in-nozzle process as well as the influencing mechanism have not been discussed. To illustrate how the taper angles influence the spray characteristics, backlit imaging method has been adopted on two-dimensional optical nozzles with different taper angle designs. Analyses have been made from in-nozzle bubble development to the unique tip-wetting phenomenon at the counterbore of the injector has been discussed in detail. A novel bubble index is proposed in this paper to describe the in-nozzle flow development. It is found that the design of the taper angle would have a significant impact on the in-nozzle pressure distribution, which would then result in different bubbling characteristics even under the same superheat index, and the contact mechanism between phase boundary and counterbore surface would change with different taper angle designs and tend to result in reverse tip-wetting tendencies under flash boiling conditions compared with subcooled conditions.

Optimization of a New Composite Multicellular Plate Structure in Order to Reduce Weight.

Currently, the most important structural design aims are weight reduction, corrosion resistance, high stiffness and vibration damping in several industrial applications, which can be provided by the application of advanced fiber-reinforced plastic (FRP) composites. The main research aim was to develop novel and innovative multicellular plate structures that utilize the benefits of lightweight advanced FRP and aluminum materials, as well as to combine the advantageous characteristics of cellular plates and sandwich structures. Two new multicellular plate structures were developed for the structural element of a transport vehicle. The first structure consists of carbon-fiber-reinforced plastic (CFRP) face sheets and pultruded glass-fiber-reinforced plastic (GFRP) stiffeners. The second structure consists of carbon-fiber-reinforced plastic face sheets and aluminum (Al) stiffeners. The second main goal of this research was the development of an optimization method of minimal weight for the newly developed all-FRP structure and the CFRP-Al structure, considering seven design constraints. The third main purpose was to confirm in a real case study that lightweight multicellular composite constructions, optimized by the flexible tolerance optimization method, provide significant weight saving (86%) compared to the all-steel structure. The added value of the research is that optimization methods were developed for the constructed new composite structures, which can be applied in applications where weight saving is the primary aim.

Ultrastrong and multifunctional aerogels with hyperconnective network of composite polymeric nanofibers

Three-dimensional (3D) microfibrillar network represents an important structural design for various natural tissues and synthetic aerogels. Despite extensive efforts, achieving high mechanical properties for synthetic 3D microfibrillar networks remains challenging. Here, we report ultrastrong polymeric aerogels involving self-assembled 3D networks of aramid nanofiber composites. The interactions between the nanoscale constituents lead to assembled networks with high nodal connectivity and strong crosslinking between fibrils. As revealed by theoretical simulations of 3D networks, these features at fibrillar joints may lead to an enhancement of macroscopic mechanical properties by orders of magnitude even with a constant level of solid content. Indeed, the polymeric aerogels achieved both high specific tensile modulus of ~625.3 MPa cm3 g−1 and fracture energy of ~4700 J m−2, which are advantageous for diverse structural applications. Furthermore, their simple processing techniques allow fabrication into various functional devices, such as wearable electronics, thermal stealth, and filtration membranes. The mechanistic insights and manufacturability provided by these robust microfibrillar aerogels may create further opportunities for materials design and technological innovation.

The validation of elastic modulus models: Code models and their modified versions

AbstractElastic modulus (E) estimation forms an important element in the methods used to predict concrete creep deformation, which is an important structural design consideration. A variety of differentEestimation models for concrete exist but there is uncertainty as to which of the models is the most accurate. This research study assesses the performance of models namely, the ACI 318, ACI 318 Simplified, Mendis et al., Rüsch et al., Carrasquillo et al., ACI 363, AS 3600, Omar et al., AS 3600, BS 8110, Alexander and Davis, SANS 10100, CEB‐FIP, and the EC 2. The included list of models is taken from national codes and includes their superseded and modified versions. TheEvalues of 108 specimens, whose properties differed (in aggregate type, cement type, concrete strength, and curing age), were measured. The actualEvalue was compared to each model's estimations to determine which were most accurate statistically using the coefficient of variation (ωj). The ACI 363 model was the most accurate out of the 16 models assessed, yielding an overallωjof 16%. The CEB‐FIP model was found to be the least accurate showing an overallωjof 31.8%. From the 16 models considered, it was recommended that the ACI 363 model be utilized by creep prediction models. In addition, it was found that not all modified estimate models produced better estimates.

Mechanical behavior of concrete-filled rectangular steel tubular composite truss bridge in the negative moment region

Concrete-filled rectangular steel tubular (CFRST) composite truss bridge is a new type of structure composed of a CFRST truss and concrete deck slab. This new type of bridge has the advantages of high structural force-transferring efficiency, rapid assembly construction speed and excellent total life cycle, which meets the construction concept of green, recyclable and sustainable development. Due to the broad application prospects, experiment on the flexural behavior of CFRST composite truss bridge in the negative moment region was reported by authors previously. This paper thus presents a finite element analysis (FEA) modelling verified by the reported test data to further investigate the detailed analytical behavior of this structure. The structural response and failure mechanism of CFRST composite truss beam in the negative moment region are studied. In addition, the important structural design parameters on the flexural performance of the CFRST composite truss beam are also investigated, including the height to span ratio, the brace-to-chord wall thickness ratio, the reinforcement ratio of steel reinforcements and prestressed tendons and the strength grade of concrete infill in chords. Finally, the reasonable structural design parameters range are proposed for the optimum design of the CFRST composite truss bridge. • Presenting a FEA modelling to investigate the detailed analytical behavior of CFRST composite truss bridge. • Structural response and failure mechanism on the flexural performance of the CFRST composite truss beam are investigated. • Reasonable structural design parameters range are proposed for the optimum design.

Fatigue-based topology optimization with non-proportional loads

Fatigue resistance is an important structural design criterion. In this work, we present a method for the topology optimization of structures subject to non-proportional cyclic loading with regard to fatigue criteria. The non-proportionality of the loading leads to a significant increase in computational cost with respect to topology optimization methods that only consider proportional loading, as a count of stress reversals must be performed for each point where fatigue damage is to be computed. To alleviate this expense, we take advantage of the common situation where the loading history can be expressed as a linear combination of a set of unit loads. Since we employ stresses to compute damage, the fatigue-driven problem shares the same difficulties as stress-based topology optimization problems, namely the onset of singular optima, the high non-linearity of damage with respect to the design variables, and a large number of points where damage is to be evaluated. We employ similar strategies to those of stress-based topology optimization to circumvent these difficulties. We demonstrate our method through several numerical examples, including a realistic-size 3-dimensional component.

Parameter Analysis on Wind-Induced Vibration of UHV Cross-Rope Suspension Tower-Line

This paper analyzes the influences of important structural design parameters on the wind-induced response of cross-rope suspension tower-line. A finite element model of cross-rope suspension tower-line system is established, and the dynamic time-history analysis with harmonic wave superposition method is conducted. The two important structural design parameters such as initial guy pretension and sag-span ratio of suspension-rope are studied, as well as their influences on the three wind-induced vibration responses such as tensile force on guys, the reaction force on mast supports, and the along-wind displacement of the mast top; the results show that the value of sag-span ratio of suspension-rope should not be less than 1/9 and the value of guy pretension should be less than 30% of its design bearing capacity. On this occasion, the tension in guys and compression in masts would be maintained in smaller values, which can lead to a much more reasonable structure.

Design of Top-hat Purlins for Cold-formed Steel Portal Frames

This paper considers the use of cold-formed steel top-hat sections for purlins in the UK, as an alternative to conventional zed-sections. The use of such top-hat sections could be viable for cold-formed steel portal framing systems, where both the frame spacing and purlin span may be smaller than that of conventional hot-rolled steel portal frames. Furthermore, such sections are torsionally stiffer than zed-sections, and so have a greater resistance to lateral-torsional buckling. They also do not require the installation of anti-sag rods. The paper describes a combination of full-scale laboratory tests and non-linear elasto plastic finite element analyses. The results of twenty-seven tests on four different top-hat sections are presented. In terms of stiffness, good agreement between the experimental and finite element results is shown. The finite element model is then used for a parametric study to investigate the effect of different thicknesses and steel grades. Design recommendations are provided in the form of charts. The use of the finite element method in this way exploits modern computational techniques for an otherwise difficult structural design problem and reduces the need for an expensive and time consuming full laboratory study, whilst maintaining realistic and safe coverage of the important structural design issues.

Public Health May Not Be Ready for Health System Change – But Neither Is the System Ready to Integrate Public Health

In response to the lead paper, the authors of this commentary propose that there are three fundamental sorts of reform for which Canada's healthcare system would need to provide evidence of progress before public health professionals should get fired up about lumping everything together inside the care system, to help it "transform." These three central changes - the adoption of an integrated data system, the provision of meaningful incentives for prevention, and important structural design changes - would be essential to enabling public health talent (and their skills) to be really useful and effective as staff within the care system. They argue that without clear evidence of this progress, such integration might well lead to the capture of the hearts, minds and energies of many well-intended public health professionals by purely clinical services management work, to the exclusion of proper upstream public health activities to uplift population health status and reduce inequalities more fundamentally.

Characteristics of CFRP retrofitted hollow brick infill walls of reinforced concrete frames

The mechanical characteristics of infill walls retrofitted with carbon fiber reinforced polymer (CFRP) sheets are really important for the realistic prediction of seismic performance of the vulnerable reinforced concrete (RC) frames retrofitted through CFRP strengthened infill walls. In this study, 36 hollow brick wall specimens were tested either under uniaxial compression or diagonal tension before and after retrofitting externally with CFRP sheets. The test parameters are the dimensions of the walls, the orientation of holes of bricks, the type of mortar, the amount of CFRP sheets and the details of strengthening application. At the end of the tests, a significant contribution of CFRP sheets on the mechanical characteristics of hollow brick walls was observed in terms of several important structural design parameters such as Young and shears moduli, axial and shears strengths as well as the deformation capacity. Finally, the strength and deformability characteristics of the walls and frames retrofitted with CFRP sheets were predicted analytically. The predictions were in good agreement with the experimental data.

Ultrahigh Mobility in Polymer Field-Effect Transistors by Design

In this article, the design paradigm involving molecular weight, alkyl substituents, and donor-acceptor interaction for the poly[2,6-(4,4-bis-alkyl-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (cyclopentadithiophene-benzothiadiazole) donor-acceptor copolymer (CDT-BTZ) toward field-effect transistors (FETs) with ultrahigh mobilities is presented and discussed. It is shown that the molecular weight plays a key role in improving hole mobilities, reaching an exceptionally high value of up to 3.3 cm(2) V(-1) s(-1). Possible explanations for this observation is highlighted in conjunction with thin film morphology and crystallinity. Hereby, it is found that the former does not change, whereas, at the same time, crystallinity improved with ever growing molecular weight. Furthermore, other important structural design factors such as alkyl chain substituents and donor-acceptor interaction between the polymer backbones potentially govern intermolecular stacking distances crucial for charge transport and hence for device performance. In this aspect, for the first time we attempt to shed light onto donor-acceptor interactions between neighboring polymer chains with the help of solid state nuclear magnetic resonance (NMR). On the basis of our results, polymer design principles are inferred that might be of relevance for prospective semiconductors exhibiting hole mobilities even exceeding 3 cm(2) V(-1) s(-1).

Determination of elastic moduli effects on storey-drifts by fuzzy logic algorithm

Concrete compression strength is a standard input for obtaining the elastic modulus of concrete. Calculated values of elastic modulus for the same concrete strength may vary according to different codes throughout the world since the formulas of the elastic modulus are different. Elastic modulus is one of the important parameters for structural design. Storey-drifts are also among the important structural design criteria directly related to the elastic modulus. Different elastic moduli values may lead lateral storey-drift calculations to differ from the code requirements. More dependable elastic moduli definition results in more dependable storey-drift calculations. Fuzzy logic algorithm, which generates more dependable results in engineering problems, is applicable to solve this problem. This study investigates the effects of storey-drifts on structural design; upper and lower boundaries of elastic moduli are predicted using a fuzzy logic algorithm in order to determine the effects of the elastic moduli on the storey-drift limitations found in different design codes. The study considers various design codes that are obtained worldwide. Study results also show that using a range of values for the elastic moduli is a more dependable approach for structural design safety, and that dependable storey-drifts are crucially important for structural design.

Time-Periodic Stability of a Flapping Insect Wing Structure in Hover

The wings of insectlike flapping-wing micro air vehicles experience time-periodic inertial stiffnesses during flapping motion. By modeling the wing structure as a thin beam, a linear time-periodic assumed-modes analysis is developed. The equations of motion of a flapping wing undergoing out-of-plane bending and torsion are derived. The homogeneous assumed-modes equations are nondimensionalized. It is shown that the nondimensional strain stiffness varies with the ratio of the wing's nonrotating natural frequencies to the flapping frequency, whereas the nondimensional, time-periodic inertial stiffnesses vary with the amplitudes of flapping and feathering motion. The parametric stability of a representative wing is assessed by applying Floquet analysis to the nondimensional equations of motion, and a scalable stability diagram is presented. Parametric instabilities of the wing structure, caused by time-periodic stiffnesses, are characterized and plotted in the time domain. The effects of important structural design properties on parametric stability are examined.

Some aspects of the structural design of a mat foundation for various soil conditions

There are several important structural design parameters in the analysis of a mat type structure for a jackup mobile offshore drilling unit. These consist of dimensions for the mat, soil foundation types, and structural loads. Methods for determining the proper dimension of the mat structure, modeling the structure and its loading cases, modeling the soil conditions and a method for identifying critical load cases for each element and load case is presented. By using a database approach for the finite element output for all of the various loading cases, a rational approach is presented which solves the problem of sorting and analyzing all of the elements and load cases, ensuring that all are included and none of the critical cases are missed.

On the Shearing Deformation in Cross Section of Pure Car Carriers

It is well known that the racking phenomenon is the most important structural design problem for a ship having few transverse bulkheads. This paper reviews the results of study on the method of calculation of the racking deformation in the cross section of such a ship. First, the authors explain the method of estimation of deviation loads responsible for the racking. The authors define the deviation loads as differences between the actual loads and beam loads. The beam loads are assumed to be acting, proportionately to the resultant shear forces, on the cross section of each longitudinal strength member as an elastic thin walled beam. Secondly, the authors examine the distribution of racking as the shearing deformations in cross sections of a Pure Car Carrier, which is capable of carrying 3000 motor cars, by somewhat simplified structural idealization.