The structural behavior of a 640 m long stretch of the segmental lining in the north tube of the Koralm tunnel’s construction lot KAT3 is analyzed. Over a period of 3.5 years, circumferential normal strains were measured in nine measurement rings, each consisting of seven tubbings equipped with a centrally located strain sensor pair. A hybrid analysis combines the monitoring data with (visco)elastic modeling of concrete and steel as well as kinematics of slender circular arch theory. This allows for computing circumferential normal forces and axial bending moments at longitudinal sections through the measurement tubbings containing the strain sensor pairs. Cubic splines are used for circumferential interpolation between sensor positions and longitudinal interpolation between measurement rings. The obtained fields of internal forces are translated into fields of utilization degrees of both the reinforced concrete tubbings and the longitudinal joints consisting of plain concrete. The utilization degrees are illustrated in interaction diagrams. All computed pairs of normal force and bending moment – including those transmitted across reinforced tubbing sections – fall within the ultimate capacity boundary of the longitudinal joints. This is consistent with the interpretation that the longitudinal joints play a role in controlling lining stresses. This is particularly the case in highly utilized joints, where concrete exhibits nonlinear creep. This amplifies the overall deformability of the segmental tunnel ring, and thus provides a possibility for the lining to follow the deformation of the surrounding ground mass without activating overly high internal forces.

Ring 1945 in the north tube of Koralm tunnel construction lot KAT3, situated in the south of Austria, is equipped with 38 vibrating wire strain sensors. They are mounted on the inner and outer circumferential wire mesh of the precast concrete segments making up the tunnel ring, two each along one shell generator line. Corresponding uniaxial strain histories enter viscoelasticity theory, so as to deliver the evolution of mechanical stresses in the concrete next to the sensor positions. Outside the "Saint-Venant disturbance zones" close to the longitudinal joints, circumferential stresses associated with 14 sensors follow thin shell theory. Hence, they are converted into bending moments and normal forces associated with seven shell generator line positions. Spline-based interpolation between these seven locations evidences normal forces which are uniformly distributed along the ring, while bending moments exhibit a heart-shaped distribution. Insertion of corresponding functional relationships into the equilibrium conditions of shell theory yields quasi-uniform ground pressures along the tunnel shell circumference, while the ground shear patterns vary over time. During the first year, shear forces act from the spring-line to the top of the tunnel ring; and later, they act from top and bottom, respectively, towards the spring-line. Multiaxial stress states resulting from force-moment combinations at the longitudinal joints utilize 30 to 60% of the system's load-carrying capacity.

The demand for accurate characterization of slag-based CEM II concretes is becoming increasingly important as the construction sector shifts towards eco-efficient materials. Here, the basic creep behavior of slag-based CEM II concretes is traced back to mixture-invariant hydrate properties. Therefore, an experimentally validated three-step micro-viscoelastic model for CEM I/OPC-concretes is complemented by a Powers-Acker-type hydration model for CEM II and extended towards long-term creep, temperature activation, and moisture sensitivity. This model is used for a strain rate-based, aging viscoelastic analysis of two creep tests on distinctively different CEM II concretes; revealing that the shear creep modulus of CEM II hydrates is half as large as the one of ordinary Portland cement hydrates. This makes slag-based CEM II concretes especially suitable for applications such as precast segmental tunnel linings, where a faster stress relaxation under displacement-controlled conditions is beneficial.

This study addresses a critical gap in the literature by developing a unified analytical model for evaluating the stability and dynamic behavior of cylindrical sandwich shells with functionally graded nanocomposite face sheets and variable-porosity cores. The model incorporates graphene nanoplatelets (GNP) and carbon nanotubes (CNT) as reinforcements, with varying distribution patterns across the nanocomposite face sheets. The governing equations are derived using Hamilton’s principle, and an analytical approach based on the state-space method is applied to compute natural frequencies and critical buckling loads under classical boundary conditions. Verification studies confirm the model’s accuracy. The results highlight the significant effects of geometric and material parameters, including reinforcement and porosity distribution profiles, boundary conditions, and shell dimensions, on the buckling and free vibration responses of the structures. Notably, increasing the porosity ratio reduces the critical buckling load and natural frequencies, while a higher nanoparticle weight fraction enhances the fundamental frequencies and critical buckling load.

State-of-the-art monitoring equipment has been a key element of the New Austrian Tunneling Method (NATM) ever since its establishment and description in the 1960s. In particular so-called hybrid methods combining geodetic displacement measurements with material and structural mechanics modeling have provided access to the ground pressure distributions acting on the shotcrete tunnel shell and its utilization degree. Herein, we explore the effect of refined observation by five (instead of the classical three) geodetic laser reflectors positioned at so-called measurement points, as installed with the top heading of the tunnel Stein realized by the Austrian federal railways (& Ouml;BB) in the south of Austria: An analytical model for the equilibrium and the deformations of aging viscoelastic cylindrical shells is specified for the displacements recorded at the measurement points, and utilization is assessed in terms of (plastic) moment-force interactions. The corresponding results widen the perception of the fundamental load-carrying characteristics of the NATM: Rather than monolithically, the tunnel shell, due to the formation of plastic hinges, may act as a literally flexible mechanical system, well adapting to the heterogeneous behavior of the surrounding ground.

The New Austrian Tunneling Method (NATM) realizes an integrated ground-shell composite structure, namely a displacement-monitored shotcrete shell surrounded by rock bolt-reinforced ground. The present paper focusses on the shear transfer between ground and shell, as experimentally evidenced by direct shear tests of soil or rock samples moved over concrete surfaces. A multiscale analytical structural mechanics approach allows for translation of geodetical measurements into external and internal shell forces and stresses. Key ingredients of the approach are the continuum mechanics-related format of the Principle of Virtual Power, thin shell kinematics, i.e. virtual motions of rigid generator lines remaining orthogonal to the shell midsurface, and aging nonlinear viscoelasticity modeling of shotcrete. Application of the new method to Sieberg tunnel, an NATM benchmark example, shows that consideration of ground shear reduced the utilization degree of the shell by some 50%: Shell-to-ground shear transfer turns out as an essential feature of NATM tunneling.

With the aim to identify the mechanisms governing nonlinear basic creep of concrete under uniaxial compression, a micromechanics model is presented. Extending the affinity concept for nonlinear creep, it describes that every microcrack incrementally increases the damage of concrete, leading to a step-wise increase of its compliance. Experimental data are taken from the literature. Strain and acoustic emission measurements from a multi-stage creep test are used to develop the model. This includes identification of microcrack evolution laws for both short-term load application and sustained loading. Strain measurements from four single-stage creep tests are used for model validation. It is concluded that nonlinear creep of concrete is governed by two mechanisms: (i) stress-induced stick-slip transition of viscous interfaces at the nanostructure of cement paste, which is phenomenologically accounted for by the affinity concept, and (ii) microcracking-induced damage, which is of major importance once the stress exceeds some 70% of the strength.

BACKGROUND AND OBJECTIVE:In accordance with the latest aspirations in the field of bioengineering, there is a need to create a web accessible, but powerful cloud computational platform that combines datasets and multiscale models related to bone modeling, cancer, cardiovascular diseases and tissue engineering. The SGABU platform may become a powerful information system for research and education that can integrate data, extract information, and facilitate knowledge exchange with the goal of creating and developing appropriate computing pipelines to provide accurate and comprehensive biological information from the molecular to organ level.METHODS:The datasets integrated into the platform are obtained from experimental and/or clinical studies and are mainly in tabular or image file format, including metadata. The implementation of multiscale models, is an ambitious effort of the platform to capture phenomena at different length scales, described using partial and ordinary differential equations, which are solved numerically on complex geometries with the use of the finite element method. The majority of the SGABU platform's simulation pipelines are provided as Common Workflow Language (CWL) workflows. Each of them requires creating a CWL implementation on the backend and a user-friendly interface using standard web technologies. Platform is available at https://sgabu-test.unic.kg.ac.rs/login.RESULTS:The main dashboard of the SGABU platform is divided into sections for each field of research, each one of which includes a subsection of datasets and multiscale models. The datasets can be presented in a simple form as tabular data, or using technologies such as Plotly.js for 2D plot interactivity, Kitware Paraview Glance for 3D view. Regarding the models, the usage of Docker containerization for packing the individual tools and CWL orchestration for describing inputs with validation forms and outputs with tabular views for output visualization, interactive diagrams, 3D views and animations.CONCLUSIONS:In practice, the structure of SGABU platform means that any of the integrated workflows can work equally well on any other bioengineering platform. The key advantage of the SGABU platform over similar efforts is its versatility offered with the use of modern, modular, and extensible technology for various levels of architecture.

Motivated by the water layer-coated nanoscale bone mineral crystals and the elastoplastic behavior seen at the extracellular scale, we develop a six-step hierarchical micromechanics model for the elastoplasticity of cortical bone. For that purpose, the Eshelby problem-based concentration-influence tensor concept is generalized for a multi-scale situation, quantifying the mechanical interaction between elastic and plastic strains between material phases across six orders of magnitude in observation scale. This hierarchical interaction scheme is complemented by non-associated Mohr-Coulomb plasticity assigned to the mineral crystal phases, and a return-mapping algorithm which adapts classical computational mechanics approaches for the realm of semi-analytical continuum micromechanics. Founded on elastic and strength properties of molecular collagen and hydroxyapatite, the model passes experimental validation against ultrasonic and quasi-static tests at the extrafibrillar, extracellular, extravascular, and cortical observation scales, across different tissues and species. It reveals cortical bone strength to increase nonlinearly with the vascular porosity, and to depend bi-linearly on the extracellular mass density, while elucidating plastic spreading events at the nanocrystal scale, which are fundamentally different in tensile and compressive loading.

Physical exercise has been shown to induce positive reactions in bone healing but next to nothing is known about how it affects the nanostructure, in particular around implants. In this study, we established this link by using small-angle X-ray scattering tensor tomography (SASTT) to investigate nanostructural parameters in 3D such as mineral particle orientation and thickness. As a model system, rat femoral bone with a bio-resorbable implant (ultra-high purity magnesium) was used. One half of the rats underwent treadmill exercise while the other half were moving freely in a cage. At two- and six-weeks post-surgery rats were sacrificed, and samples were taken. Our results point to an earlier start and stronger remodeling when physical exercise is applied and to a stronger reorientation of the mineralized collagen fibers around the implant. This study reveals the nanostructural response of bone with bio-resorbable implants to physical exercise. Understanding this response is very important for designing post-surgery treatments. Statement of Significance Physical exercise is known to have beneficial effects on the human body and is often incorporated into the recovery process following orthopedic surgeries. While the response of bone to physical exercise is well-documented, the structural response of bone to early exercise after implant placement, particularly its impact on the nanostructure, has not been extensively studied. In this study, we identify the effects of physical exercise on the bone nanostructure and the remodeling process around a bioresorbable implant. These findings could help develop tailored physical exercise strategies for post-surgery recovery in patients.

The New Austrian Tunneling Method (NATM) essentially rests on observational information concerning displacements measured in selected positions at the inner surface of shotcrete tunnel shells. The combination of these measurements with advanced material and structural mechanics, in the course of so-called hybrid methods, have successfully delivered, for more than 20 years, practically relevant estimations of internal and external forces and corresponding degrees of utilization. The reliability of the latter, however, may crucially depend on the used material model. Based on a recently proposed analytical structural mechanics model [Acta Mech 233, 2989-3019 (2022)], and focusing on the benchmark example of measurement cross section MC1452 of the Sieberg tunnel, driven in the 1990s in Miocene clay marl, the present paper compares the estimations of forces and degrees of utilization arising from differently refined constitutive concepts, namely (i) aging elasticity, (ii) aging linear viscoelasticity, and (iii) aging nonlinear viscoelasticity. It turns out that only the consideration of aging nonlinear viscoelastic material behavior provides access to realistic values for the degree of utilization, being lower than one. Simpler material models would indicate local material failure, which was not observed in situ.

In this article, an exact analytical method for the free vibration analysis of functionally graded (FG) graphene platelet (GPL)-reinforced composite (GPLRC) sector cylindrical shells is presented by considering Levy-type boundary conditions for the first time. The analysis relies on the use of the Halpin–Tsai micro-mechanical model for evaluating the material properties of the graded layers of the shell with three different grading patterns. Mathematical modeling of the Levy-type cylindrical shell is based on the Hamilton principle and the Sanders first-order shear deformation theory (FSDT). The governing equations of the composite shell are analytically solved using the state-space method. The validity of the proposed analytical method is demonstrated by the excellent agreement between the obtained results of the exact analytical solution and the results available in the literature. Furthermore, some parametric studies are conducted to reveal the effects of variations in boundary conditions, GPL distribution patterns, GPL weight fraction, and geometrical parameters such as shallowness angle, length-to-radius ratio, and thickness on the free vibration behavior of the shell structure. Natural frequencies and mode switching are reported for different mode numbers.

Realistic estimation of stresses in segmented tunnel linings is a challenge tackled herein by means of a hybrid, i.e. computational-experimental, approach. Thermistor-equipped vibrating wire strain gauges were installed (i) into concrete samples undergoing one year-long uniaxial creep tests under the environmental conditions of the tunnel site, and (ii) into the tubbings making up the tunnel lining of the Koralm tunnel. The data obtained from the creep tests allow for calibration and validation of an integro-differential thermo-viscoelastic model. The creep function combines a power-law for short-term creep with a logarithmic law for long-term creep. The corresponding relaxation function is determined by means of Laplace-Carson transformation, inversion, and back-transformation. This is the basis for translating the circumferential strain histories measured in the tubbings of Ring 2013 in Koralm tunnel KAT3 into circumferential and longitudinal stress evolutions. They are mainly due to mechanical ground-shell interactions. The corresponding degree of utilization increases during the first four months after ring installation, and remains virtually constant thereafter. Stress fluctuations due to seasonal temperature variations play only a minor role. With regards to a long-term prognosis, it is very interesting to note that the strain measurements recorded in the tubbings, when plotted as function of the logarithm of time, follow bi-linear trends. These trends can be extrapolated to 150 years, the targeted service life of newly built tunnels in Austria. Throughout this period, the viscoelasticity-based estimates of the stresses in the vicinity of the strain sensors stay temporally constant, at some 40% of the strength of concrete.

We here introduce an analytical model for a preclinical femur-implant compound structure. This model extends standard Euler-Bernoulli-Saint-Venant theory by closed-form expressions for such shear stresses in thin-walled components, which arise from elastic material properties changing at the interfaces between bone and implant materials. Particularly noteworthy are stress singularities occurring at the generators of the cylindrical implants, which intersect the long axis of the bone shaft. This is fully consistent with observed major reorientations of bone fibrils following the implantation event, so that our novel mechanical model clearly indicates a case of micro-mechanobiology.

Organisms generate shapes across size scales. Whereas patterning and morphogenesis of macroscopic tissues has been extensively studied, the principles underlying the formation of micrometric and submicrometric structures remain largely enigmatic. Individual cells of polychaete annelids, so-called chaetoblasts, are associated with the generation of chitinous bristles of highly stereotypic geometry. Here we show that bristle formation requires a chitin-producing enzyme specifically expressed in the chaetoblasts. Chaetoblasts exhibit dynamic cell surfaces with stereotypical patterns of actin-rich microvilli. These microvilli can be matched with internal and external structures of bristles reconstructed from serial block-face electron micrographs. Individual chitin teeth are deposited by microvilli in an extension-disassembly cycle resembling a biological 3D printer. Consistently, pharmacological interference with actin dynamics leads to defects in tooth formation. Our study reveals that both material and shape of bristles are encoded by the same cell, and that microvilli play a role in micro- to submicrometric sculpting of biomaterials. Bristleworms possess dedicated cells that can synthesize highly stereotypical bristles with sub-micrometric precision. Here, Ikeda and colleagues shed light on the underlying dynamics of cellular protrusions, revealing an extension-disassembly cycle that resembles a 3D printer.

There is a need to develop an integrated computational platform that will contain both datasets and multiscale models related to bone (modelling), cancer, cardiovascular diseases, and tissue engineering. The SGABU platform is a robust information system capable of data integration, information extraction, and knowledge exchange, with the goal of designing and developing suitable computing pipelines to give accurate and adequate biological information from the patient's molecular to organ level. Datasets integrated into the platform are directly obtained from experimental and/or clinical studies and are mostly in tabular or image file format. Multiscale models range from models that can be described using partial or ordinary differential equations, to complex models that use finite element modelling. The majority of the SGABU platform's simulation modules are built as Common Workflow Language workflows. This implies creating a CWL implementation on the Functional Engine Service backend and creating an acceptable User Interface. The key advantage of SGABU platform is the utilization of new, contemporary, modular, and unique technology for various levels of architecture.