Cross-sectional Shape Research Articles

A Generalized Nonlinear Beam Element for Slender RC Members Using a Polygonization Section Approach—Part I: Theoretical Formulation

A mathematical model for RC beam elements is presented that falls into the category of distributed inelasticity models discretizing the cross-section in polygons (trapezoids, triangles). The models falling into these categories are considered to be able to describe in the best manner the inelastic behavior of the element across its whole clear length, since its response results from the numerical integration of the stiffnesses of its cross-sections, while presenting an ideal combination of accuracy, simplicity, and computational cost. The behavior of the cross-section is described through the constitutive relationships σ–ε of its materials for cyclic loading. The main objectives for the development of the proposed mathematical model are as follows: (a) the increased accuracy of the results compared to existing experimental ones; (b) the limitless generalization of its application, regarding of the cross-section shape; and (c) the elimination of the numerical problems presented by the application of other related models, a fact that leads to their impractical use in real three-dimensional structures. The proposed model falls under the category of distributed inelasticity models. This paper focuses on its initial version, which targets slender beam elements with negligible shear and bond-slip effects (i.e., with ribbed bars, sufficiently anchored). Thus, it is applicable to 2D and 3D framed structures that fulfill these conditions, while its modular structure allows for future adjustments for the inclusion of other effects.

EFFECT OF INNER BOUNDARIES GEOMETRY ON NATURALCONVECTION HEAT TRANSFER IN HORIZONTAL ANNULI

An analytical modeling of natural convection in physically-based analysis is developed for investigate free convective heat transfer in horizontal eccentric annulus between a circular outer cylinder and heated different shape inner envelope with used four models of the shapes of the inner cross section of (circular, triangular, square and hexagon inner boundary). The main objective of this paper was taking a composite model based on asymptotic solutions for three limiting cases: pure conduction, laminar boundary layer convection and transition flow convection. Laminar conditions up to Rayleigh number RaPi of 5×104 were investigated. By using data from MATLAB simulations for a wide range of two cylinder temperature difference in order to study the effects of annulus diameter ratio, Rayleigh number, and the cross section geometries of inner cylinder on the Nusslte number and the ratio of thermal conductivity. The numerical result illustrated for the circular the increasing the Rayleigh number leading to slightly increasing the non-dimensional Nusslte number with various value of annulus diameter ratio and when used the high annulus perimeter ratio (Po/Pi( about (4.5,2.6,1.6 and 1.175). There is rapid increasing in the non-dimensional ratio of thermal conductivity with increasing the Rayleigh number at the high values of (Po/Pi(, and the result showed that the non-dimensional ratio of thermal conductivity and the Nusslte number values of the (triangular, square and hexagon) less than in the case of circular inner boundary, but the hexagon model showed the Nusslte number more that than in the (triangular and square). the mathematical results compared with model developed by pervious numerical the model and data are in good agreement, with an average RMS difference of 10.6% for the circular annulus of dimensional Nusselt number (NuPi) and less than 4.9 % and 9.8% for the square inner geometry non-dimensional ratio thermal conductivity.

Measuring the behavior of the acoustic standing wave exiting a flue organ pipe: Is the decay sinusoidal or exponential?

Correctly predicting the playing frequencies of a musical instrument is dependent on the length of the resonator with the addition of an end correction. There are multiple theories describing this end correction, perhaps the simplest being that the end correction of a pipe is a physical extension of the sinusoidal pressure standing wave inside the pipe. However, recent optical imaging of the flow in a flue organ pipe found an unexpected exponential decay of pressure just outside of the pipe. This work looks to validate those findings acoustically. A flue organ pipe was played at the 1st, 5th, and 7th harmonics and the pressure just inside and immediately outside the end of the pipe played was measured using a zero-degree PU Match Microflown sound intensity probe. These measurements were fit to both exponential and sinusoidal curves and compared to the optical images. While an exponential trend is in fact apparent in some cases, the goodness-of-fit appears to be dependent on which harmonic is sounding. Future work includes exploration of a potential transitional region, assessing the impact of altered pipe geometry (both cross-sectional shape and size), and investigating potential sensor interference by using other measurement equipment.

A structural optimization analysis of cable-driven soft manipulator

Cable-driven soft robots hold significant potential for surgical and industrial applications, yet their performance and maneuverability can be further enhanced through design optimization. By optimizing the design, factors such as bending angles, manipulator deformation, and overall functionality can be directly influenced, leading to improved interaction with the environment and more accurate task performance. This article presents a physics-based design optimization approach for cable-driven soft robotic manipulators, aiming to enhance bending performance through structural design enhancements. Four design criteria, namely, cross-sectional shape, material, gap shape, and gap size, are considered in the optimization process. Given the inherent nonlinearity of soft materials, finite element modeling techniques are employed to analyze the effects of modifying each design parameter on displacement and bending angle. The manipulator’s design is evaluated using ABAQUS/CAE, and an analysis of variance test is conducted to identify significant performance differences among the design parameters. The results reveal that material variation has the most substantial impact, followed by gap shape and gap size. Based on subsequent parameter optimization, Dragon Skin 10 is determined to be the optimal material for bending motion, while a trapezoidal gap shape is preferred. In addition, a genetic algorithm is utilized to select a maximum gap size of 8.87 mm. These findings provide valuable insights into key design principles for cable-driven soft manipulators, aiming to enhance flexibility and reduce actuation forces. By establishing a fundamental understanding of the relationship between morphology and motion capability, this methodology demonstrates an effective simulation-driven optimization approach that incorporates the nonlinear elastic behavior of materials to improve performance. Overall, this work establishes a framework for optimizing cable-driven architectures to suit various applications in the field of soft robotics.

Mesoscale modellings of axial compressive failure of geometrically-similar CFST columns at low temperatures

In this paper, a thermo-mechanical sequential coupling mesoscopic simulation method was established and verified, which considered the interaction between steel tube and meso-components of concrete due to the difference in thermal parameters, as well as the low-temperature effect on mechanical parameters. On the basis of heat conduction analysis, the damage evolution and failure mechanism of CFST column under axial compression were subsequently revealed, and the effects of low temperature (20, −30, −60 and −80 °C), cross-section size (160, 320, 480 and 640 mm), width-thickness ratio (27, 36, 53 and 107) and cross-section shape (square and circular) on axial compression performance and the corresponding size effect of CFST columns were quantitatively analysed. Research results show that the low-temperature action can enhance the nominal peak strength and residual strength of CFST column, but weaken the ductility. As the cross-section size increases from 160 to 640 mm, all the nominal peak strength, nominal residual strength and peak strain of circular CFST column decrease with the maximum reductions of 16.2, 28.7 and 16.9%, respectively. Besides, the low-temperature action can enhance the size effect on nominal peak strength of CFST column with the maximum increase of 68.8%. Whether at ambient or low temperature, the size effect on nominal peak strength of square column is stronger than that of circular one. The size effect behaviour on axial compressive peak strength at various temperatures can be also well described by the previous proposed prediction formula. The research results of this paper can provide reference for the engineering application of large-sized CFST columns in the extreme low-temperature environment.

Effect of flow channel cross-section shape on the performance of proton exchange membrane electrolysis cell

To study the thermal and mass distribution in proton exchange membrane electrolytic cells (PEMEC), a two-phase numerical model of a single-channel electrolytic cell was established. The polarization performance and gas-heat distribution in a single-channel electrolytic cell under five different flow channel cross-sections (rectangle, trapezoid, inverted trapezoid, triangle, and circle) were studied. The findings indicate that the inverted trapezoidal flow channel’s gas buildup effect is rather severe in both the catalytic and diffusion layers. In the trapezoidal flow channel, the temperature of the proton exchange membrane region is lower, and the electrochemical performance of the rectangular flow channel electrolytic cell is the best, with an improvement rate of up to 11.47%. The electrochemical performance of the triangular and circular flow channels is the worst.

Investigation into the Effects of Cross-Sectional Shape and Size on the Light-Extraction Efficiency of GaN-Based Blue Nanorod Light-Emitting Diode Structures

We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging them over emission spectra, polarization, and source positions inside the nanorod. The LEE decreased as rod size increased, owing to the nanorods’ increased ratio of cross-sectional area to sidewall area. We compared circular, square, triangular, and hexagonal cross-sectional shapes in this study. To date, nanorod LEDs with circular cross sections have been mainly demonstrated experimentally. However, circular shapes were found to show the lowest LEE, which is attributed to the coupling with whispering-gallery modes. For the total emission of the nanorod, the triangular cross section exhibited the highest LEE. When the angular dependence of the LEE was calculated using the FFP simulation results, the triangular and hexagonal shapes showed relatively high LEEs for direction emission. The simulation results presented in this study are expected to be useful in designing high-efficiency nanorod LED structures with optimum nanorod shape and dimensions.

Data-driven initial peak crushing force prediction of hybrid tubes

Accurately predicting the initial peak crushing force (IPCF) of the CFRP/metal hybrid structure is of great significance for the high-efficiency energy absorption of energy-absorbing elements and ordered deformation of combined energy-absorbing devices. Due to the significant differences in material properties between CFRP and metal and the high complexity of cross-sectional shape, a combined method of machine learning and mechanism analysis is proposed for predicting the IPCF of CFRP/Al hybrid energy-absorbing tube. First, a high-precision finite element model validated by the axial and oblique experiments is conducted to generate the dataset for predictive analysis. Second, a sample space through the design of experiment (DOE) is established for data fitting between structural parameters and IPCF based on traditional response surface model (RSM). It is found that traditional RSM method can successfully predict the IPCF of the single-cell hybrid tube, but cannot effectively predict the IPCF of the multi-cell tube due to the strong coupling effect between inner and outer plates. To address the issue of the lack of accurate correspondence between structural parameters and IPCFs in multi-cell hybrid tube, the indicator of relative density is proposed to characterize complex cross-sectional features. Surprisingly, there is a strong correlation between relative density and IPCF where multi-cell tubes with the same relative density have almost the same IPCF. Third, different artificial neural networks (ANN) are trained by a pre-simulated IPCF database of CFRP/Al hybrid energy-absorbing tube depending on the parameter characterization scheme based on mechanism analysis. In order to enhance the network's performance, the optimal configuration parameters of the neural network, including the number of layers and nodes, are ascertained through a combination of K-fold cross-validation and the Grid Search method. As a result, compared with the traditional RSM and Kriging model, the IPCF of CFRP/Al hybrid energy-absorbing tube can be predicted in small samples with high accuracy using the optimal ANN model. Finally, Through the comparative analysis of the IPCF of hybrid tubes with reported multi-cell configurations, it is found that the prediction model proposed in this paper has good generalization ability, which can be used to predict more complex types of multi-cell tube configurations. The present study offers important suggestions for the overall control of multi-materials hybrid energy-absorbing tube and the ordered deformation of combined energy-absorbing devices.

금강유역권 축소모형농공구의 형태와 특징

These days, relics that used to have regional specificity tend to deviate from their specificity due to the active cultural property excavation research. It is necessary to recognize the newly identified area. Therefore, among the archaeological materials that strongly reflect regional specificity, we paid attention to the Miniature farming tools accumulated around the Geum River basin. The Miniature farming tools can be divided into ttabi type, cheolseo type, iron axe type, and sickle type. Data from the Geum River basin also show high excavation rates for Iron Axe type and sickle type, although the warm and cheolseo type are also identified. Cheoljun is one of the characteristic iron artifacts excavated from the Geum River basin. Compared to the Daegaya sphere, this was identified as a ttabi-type Miniature farming tool, and the plane shape and cross-sectional shape were considered to be more likely to have been produced under the influence of the Daegaya sphere rather than generated and produced within the Geum River basin. Iron axe-type Miniature farming tools are again divided into I-shaped and V-shaped in crosssectional form, and the I-shaped is the same as or similar to those confirmed in the Daegaya sphere, so it is thought to be highly relevant. On the other hand, the V-shaped is also excavated from the remains of the Proto-Three Kingdoms Period, which is confirmed around the Geum River basin, and is similar to the form of Iron axe, which has been produced and used for a long time, so it is thought that the traditional method was inherited. Although there is a limit to linking data excavated from the Geum River basin with Miniature farming tools excavated from the Daegaya sphere, data that are likely to have been produced in a manner similar to that of the Daegaya sphere in both plane and cross-sectional shapes were identified. From these data, it can be seen that there are also data that are more likely to have flowed into Baekje sphere from Daegaya sphere than from Baekje sphere.

The effects of the industrial transition on lower limb bone structure: A comparison of the inhabitants of Pecos Pueblo and present-day Indigenous peoples of New Mexico.

Comparisons between Indigenous peoples over time and within a particular geographic region can shed light on the impact of environmental transitions on the skeleton, including relative bone strength, sexual dimorphism, and age-related changes. Here we compare long bone structural properties of the inhabitants of the late prehistoric-early historic Pecos Pueblo with those of present-day Indigenous individuals from New Mexico. Femora and tibiae of 126 adults from Pecos Pueblo and 226 present-day adults were included in the study. Cross-sectional diaphyseal properties-areas and second moments of area-were obtained from past studies of the Pecos Pueblo skeletal sample, and from computed tomography scans of recently deceased individuals in the present-day sample. Femora and tibiae from Pecos individuals are stronger relative to body size than those of present-day Indigenous individuals. Present-day individuals are taller but not wider, and this body shape difference affects cross-sectional shape, more strongly proximally. The tibia shows anteroposterior strengthening among Pecos individuals, especially among males. Sexual dimorphism in midshaft bone shape is stronger within the Pecos Pueblo sample. With aging, Pecos individuals show more medullary expansion but also more subperiosteal expansion than present-day individuals, maintaining bone strength despite cortical thinning. Higher activity levels, carried out over rough terrain and throughout adult life, likely explain the relatively stronger lower limb bones of the Pecos individuals, as well as their greater subperiosteal expansion with aging. Greater sexual dimorphism in bone structure among Pecos individuals potentially reflects greater gender-based differences in behavioral patterns.

Design and analysis of a nozzle-less twin-entry turbine volute for automobile application

Due to the increasing demand for improved fuel economy in passenger cars, recent internal combustion engines come with a turbocharger. Turbochargers are a method of engine downsizing that forces more compressed air into the combustion chamber, enabling a high power density. Two main types of turbines are commonly adopted in turbochargers; single-entry and multiple-entry. The multiple-entry type includes twin-entry and double-entry volutes. A twin-entry volute consists of two inlets with a divider that feed the entire circumference of a rotor whereas a double-entry volute has two separate inlets that feed the rotor separately. A twin-entry volute's design is based on a single-entry volute by merely placing a divider into the volute. The conventional design approach of a twin-entry volute gives relatively little consideration to the design aspects such as the divider's length, the divider's width, and the cross-sectional shape of the volute. The above-mentioned design aspects of a twin-entry volute have an impact on the performance of a turbine. This paper intends to design a new twin-entry volute with a specified divider length and width. The volute's profile is based on a single-entry volute. In addition, the performance of this twin-entry turbine is compared with the asymmetric double-entry turbine. The comparison of these configurations relies on consistent criteria, including the A/R ratio, mixed-flow rotor, and cross-sectional of the volute. The simulation was executed at two different turbine speeds; 30k RPM (50 %) and 48k RPM (80 %). The validation simulation shows great agreement with the experimental data with a Root Mean Square Error of less than 5 % for both speed lines. Based on the results obtained, the twin-entry turbine shows a lower swallowing capacity than the asymmetric double-entry turbine at both operating conditions. At both speed lines, the twin-entry turbine's efficiency begins to fall toward the end. The incidence angle of the twin-entry turbine is 24.4° at 50 % operating speed and -3.72° at 80 % operating speed. In both turbines, entropy generation reduces as the speed line increases, and both turbines exhibit a similar entropy generation at both speed lines. The existence of a horseshoe vortex near the hub surface and the tip leakage vortex near the shroud region of the blade substantially influence both the turbines' performance.

Critical issues in the moving reference frame CFD simulation of small horizontal axis wind turbines

Steady computational fluid dynamics with the Moving Reference Frame method has shown promise as a tool for assessing the aerodynamic performance of small horizontal-axis wind turbines, offering sufficient accuracy with low computational costs, thus supporting the development of these machines and facilitating their vital role in the growing distributed energy systems. However, accurately simulating the intricate low Reynolds number flow around the blades of these turbines remains a significant challenge, with certain critical issues yet to be fully resolved. Through a comparative literature review, this study firstly uncovered a lack of standardized simulation settings for small horizontal axis wind turbines, resulting in inconsistencies across different studies. Addressing this gap, the research delves into the critical issues identified, specifically the computational domain cross-section shape and size, discretization scheme accuracy, meshing criteria, freestream turbulence intensity, and turbulence modelling. To rectify these challenges, the study conducts a detailed sensitivity analysis of the aforementioned parameters applied on a well-documented turbine in the literature as a case study. For validation purposes, an empirical method is employed to correct the tunnel wall blockage effect on the case study turbine experimental data. This method is verified, and the correction of the closed test section tunnel data, notably, shows a significant blockage effect, contradicting the notion of insignificance for a blockage ratio of 11.8% in the literature. The analysis revealed how incorrect simulation settings can yield misleading results that initially may align with experimental data but fail to guarantee a reliable numerical setup for extending the study. Ultimately, this research furnishes best practice guidelines for establishing accurate simulation setups.

STATIC AND DYNAMIC ANALYSIS OF STIFFENED PLATE USED IN MACHINE TOOL COLUMN

STATIC AND DYNAMIC ANALYSIS OF STIFFENED PLATE USED IN MACHINE TOOL COLUMN

Deformations and damages of tunnels subjected to strike-slip faulting: Effects of tectonic stress and cross-sectional shape

Deep-buried tunnels are vulnerable to strike-slip faulting, the responses of which are complicated. However, the effects of tectonic stress and cross-sectional shape on behaviors of tunnels in strike-slip faults have not been detailly investigated. This study performs numerical modeling to study the deformations and damages of tunnels subjected to strike-slip faulting, focusing on the effects of tectonic stress and cross-sectional shape. A three-dimensional numerical model is applied, which is validated by the test from the previous study. Different lateral stress coefficients (from 0.5 to 3.0) and cross-sectional shapes of tunnels (circular shape, horseshoe shape, and egg shape) are modeled. The results show that tectonic stress and cross-sectional shape have a great influence on tunnel responses during strike-slip faulting. The failure mode of the tunnel is highly dependent on the tectonic stress. The tensile damage controls in low tectonic stress conditions, while compressive damage domains in high tectonic stress conditions. The tensile damage initials at the arch waist in the vicinities of fault planes, while the compressive damage mainly occurs at the tunnel vault and bottom in the whole fracture zone. Besides, tectonic stress has apparent effects on the transverse displacement of the tunnel axis and the compressive damage range. The H-shaped tunnel behaves the worst, experiencing the largest cross-sectional deformation, the largest compressive damage range, and the smallest required fault deformation for compressive damage.

Momentum transfer across an open-channel, turbulent flow

The distribution of stress generated by a turbulent flow matters for many natural phenomena, of which rivers are a prime example. Here, we use dimensional analysis to derive a linear, second-order ordinary differential equation for the distribution of stress across a straight, open channel, with an arbitrary cross-sectional shape. We show that this equation is a generic first-order correction to the shallow-water theory in a channel of large aspect ratio. It has two adjustable parameters – the dimensionless diffusion parameter, $\chi$ , and a local-shape parameter, $\alpha$ . By assuming that the momentum is carried across the stream primarily by eddies and recirculation cells with a size comparable to the flow depth, we estimate $\chi$ to be of the order of the inverse square root of the friction coefficient, $\chi \sim C_f^{-1/2}$ , and predict that $\alpha$ vanishes when the flow is highly turbulent. We examine the properties of this equation in detail and confirm its applicability by comparing it with flume experiments and field measurements from the literature. This theory can be a basis for finding the equilibrium shape of turbulent rivers that carry sediment.

Crashworthiness Analysis and Optimization of Thin-Walled Structures Based on the TSSA-LSSVM Surrogate Model

Thin-Walled Structures (TWS) play a crucial role in enhancing both the collision safety and lightweight characteristics of vehicles. Structural design and optimization have demonstrated significant potential in improving their crashworthiness and overall weight reduction. Several interconnected factors, including the cross-sectional shape and parameters of distinctive structural characteristics (known as induction grooves), impact the TWS’ resistance to collisions. Another critical aspect in the optimization of TWS design is striking the delicate balance between the surrogate model’s effectiveness and precision. Taking all these factors into account, this paper conducts an in-depth investigation into the cross-sectional shape, grooves, and other geometric attributes of various TWSs through a comparative analysis. It reveals that the thin-walled structure with a Double-Ribbed Rectangle cross-section (DR-TWS) proves to be the optimal choice, particularly in low-speed axial impact scenarios. Furthermore, we present an enhanced Least Squares Support Vector Machine (LSSVM) method, augmented with an adaptive [Formula: see text]-distribution Sparrow Search Algorithm (TSSA), referred to as the TSSA-LSSVM surrogate model. The optimized design of the DR-TWS is realized through the integration of the TSSA-LSSVM surrogate model with the adaptive hybrid multi-objective particle swarm optimization (AHMOPSO) algorithm. This paper not only provides substantial theoretical support but also offers valuable guidelines for the application of TWSs in the automotive industry.

Voids in type-IV composite pressure vessels manufactured by a dry filament-winding process

Type-IV high-pressure hydrogen-gas tanks for fuel-cell electric vehicles are made from carbon fiber-reinforced plastic. Their production involves wrapping a carbon-fiber-reinforced thermoset resin towpreg around a plastic liner to form a tank shape, followed by heating in an oven to cure the thermoset resin. The filament-winding process produces many voids in the tank that cause variations in quality and the product lifetime. In this study, the voids in the tank were classified according to their origin. A type-IV high-pressure hydrogen-gas tank with a burst pressure of 70 MPa was fabricated, and the voids produced in the tank were observed. The same filament-winding process was used to fabricate a plate and tank with a simple winding trajectory to identify the voids. The voids produced in the tank by the filament winding were categorized into six groups based on their location, cross-sectional shape, and size, showing the origin of the voids.

3D-printing allows for fluid-controlled linear actuators with unconventional shapes

BackgroundPneumatic actuators are widely used in applications like (medical) robots, or prostheses. Pneumatic actuators require a complex manufacturing process and are produced in standardized dimensions to reduce costs. Over the last decade 3D-printing has emerged as a cost-effective and efficient production method in medical applications. 3D-printing can also function as a cost-efficient alternative production method for pneumatic actuators. ObjectiveThe goal of this research is to study the possibility of creating a pneumatic linear actuator with 3D-printing. Furthermore, the aim is to use the advantage of 3D-printing to create pneumatic actuators with non-circular cross-sections. MethodologyTo evaluate the performance of a 3D-printed pneumatic actuator, a test setup was designed and built to measure the leakage and sliding friction force. Furthermore, two pneumatic actuators with a non-conventional cross-sectional shape were designed and their performance was tested and compared with a 3D-printed cylindrical pneumatic actuator, since these tests only ran once, the results are more a guideline. During the manufacturing of the cylinders, no post-processing techniques were used. ResultsThe functioning of a 3D-printed circular pneumatic actuator was proven with low static leakage rates of 2.5%, low dynamic leakage rates of approximately 1%, and a maximum friction force of ▪. Furthermore, the results show that it is possible to print functioning pneumatic cylinders with a non-cylindrical concave cross-section. The non-conventional cylinders were tested up to ▪ with maximum dynamic leakage of ▪. ConclusionThis study demonstrates a method to create functional pneumatic linear actuators with 3D-printing. It was possible to create 3D-printed actuators with a conventional shape, e.g. circular and unconventional shapes e.g. stadium/oval shape and a kidney shape. The leak rates for conventional and unconventional shapes were in the same range. This opens up the world for more design freedom in pneumatic actuators.

Stress and strain relations of RC circular, square and rectangular columns externally wrapped with fiber ropes

This study explores the potential use of low-cost natural fiber reinforced rope polymers (FRRP) to improve the compressive behavior of circular, square, and rectangular reinforced concrete (RC) specimens. A total of 42 specimens were tested under monotonic axial compression in three groups. Groups were formed to differentiate specimens with different cross-sectional shapes such as circular, square, and rectangular. The findings demonstrate that FRRP can effectively boost the compressive behavior of RC columns. Circular specimens with three-layer hemp FRRP exhibited a 200% increase in compressive strength and a 270% improvement in corresponding strain. Cotton FRRP provided a 117% boost in compressive strength and a 233% enhancement in strain. In square specimens, three-layer hemp FRRP resulted in a 110% rise in compressive strength and a 186% increase in strain, while cotton confinement yielded improvements of 95% and 144%, respectively. For the square and rectangular specimens, the improvement in the compressive behavior was reduced compared to the circular specimens because of stress concentrations near corners. Moreover, the study showed that the hemp FRRP confinement outperformed the cotton confinement. The investigation also revealed that the existing analytical models were inadequate in predicting the mechanical properties of RC confined with natural FRRP. Therefore, the study introduces novel equations to predict the compressive strength and corresponding strain for both hemp and cotton confined concrete in various cross-sectional types. These proposed equations exhibit a good level of accuracy in predicting the compressive strength and corresponding strain.

Operational modal analysis, seismic vulnerability assessment and retrofit of a degraded RC bell tower

This paper presents damage assessment through Operational Modal Analysis (OMA) and Finite Element (FE) model updating of the bell tower of the church of Castro in Bergamo, Italy. The tower is a 39 m high reinforced concrete structure with hollow cross-section and double-curved shape. The research was dictated by the need to identify the actual damage state of the structure, which was found through visual inspections. Piezoelectric accelerometers were used to record the ambient vibrations in subsequent test setups, using the roving technique for system identification. A detailed FE model was created with shell elements and calibrated to match the system identification results. A simplified beam model was then developed based on the modal analysis results of the detailed model. A sensitivity analysis was performed to identify the most influential model parameters on the modal characteristics of the system. Subsequently, the optimal values of these parameters were determined by an optimisation procedure carried out using a typical global optimization algorithm. The updating results allowed assessment of the actual condition of the bell tower and its seismic vulnerability. Finally, a seismic strengthening solution was recommended.