Proceedings of the International Conference of Steel and Composite for Engineering Structures

A novel non-linear truss finite element specifically conceived to study an FRCM reinforcing package is presented. FRCM is modelled considering separately the central elastic fiber grid and the two upper and lower inelastic matrix layers; matrix and fiber are considered in a monoaxial state of stress, mutually exchanging shear stresses at the interface. The interface constitutive relationship assumed is trilinear with softening and residual strength; the element is thus constituted by three trusses (one elastic and two inelastic) linked with shear springs. The internal matrix layer exchanges also tangential stresses between reinforcement and substrate by means of elastic shear springs. The finite element is therefore characterized by 8 DOF, namely the longitudinal displacements of the three layers of the FRCM package plus that of the substrate, evaluated at the extremes of the element. The finite element performance is successfully validated against some available experimental datasets, relying into different FRCM strengthening packages bonded to rigid substrates and subjected to single lap shear tests.

This document presents an overview of the studies recently performed by the Authors regarding the numerical simulation of the bond behavior of Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) strengthening systems in case of applications to curved masonry structures. In the paper are indeed presented and compared among them the different numerical approaches carried out by the Authors and validated with respect to experimental tests. The numerical approaches concern both sophisticated and simplified Finite Element models and, moreover, analytical procedures. The comparison among them allows for underlining important issues to account for numerically analyzing the complex phenomena characterizing the interaction between FRP/FRCM strengthening systems and masonry substrate in case of curved structures. In particular, it is emphasized the influence of stresses acting normal to the substrate at the interface between strengthening and masonry in case of FRP, and between strengthening and matrix in case of FRCM, on the bond mechanism.

The application of Fiber Reinforced Cementitious Matrix (FRCM) composites for the reinforcement of building surfaces is more and more common, especially for masonry structures, thanks to their compatibility and the ability to reverse the intervention process. Various analytical and numerical models have been developed to replicate the bond behavior of this complicated system. However, most existing simplified models tend to focus on either the failure of the fiber-mortar interface or the mortar-substrate interface. The influence of mortar cracking and the presence of masonry joints are aspects that have not been extensively investigated. In this paper, we introduce a mathematical model that considers the failures of both the fiber-matrix and matrix-masonry interfaces, as well as the damage to the mortar matrix. We address the debonding problem by formulating an ordinary differential equation (ODE) system and employing a 2D bisection procedure after discretization along the bond length. Two scenarios are discussed, one with consideration of mortar joints and one without. Comparative analysis with existing experimental data and models reveals that the current model performs promisingly in predicting global stress-slip curves.

Fibre-reinforced polymer (FRP)-bonded concrete performance relies heavily on bond; therefore, bond-slip models have been developed with interfacial bond properties. Since the structural behaviour of the test specimens bonded with FRP and the failure mechanisms depend on these bond qualities, it is vital to know how sensitive they are. This work examines the interfacial bond-slip characteristics of a bond-slip model with two curves, an ascending and a descending curve, for their sensitivity. The results show that the fracture energy related to interfacial debonding significantly influences the maximum load capacity, while the shape of the ascending curve significantly influences the effective bond length. These results highlight the importance of considering the interfacial bond-slip properties when designing and evaluating concrete structures retrofitted with FRP.

Elastic local buckling strength of rectangular hollow section members is theoretically derived considering coupling of adjacent plate elements and shear bending interaction. The effects of boundary conditions, loading conditions, and member shapes on the buckling strength are investigated. Finally, approximate formulas for calculating the buckling strength depending on bending moment gradient, cross section ratio, and aspect ratio are presented.

The acoustic muffler development depends on optimizing its volume for high performance, it is of great importance in the industrial field to obtain a reduction in duct noise economically and efficiently. The main aim of this work is to optimize analytically the acoustic transmission loss (\({\text{TL}}\)) of the Basalt Fiber Reinforced Polymer laminated composite Double-Chamber Mufflers (BFRP-CDCM) because \({\text{TL}}\) is an essential characteristic of the muffler and is not based on the source or the termination impedances. The power transmission coefficient (\({\text{PTC}}\)) and the \({\text{TL}}\) of a muffler will be calculated. The method used to optimize the length of the acoustic muffler is the genetic algorithms (\({\text{GA}}\)) method. The sound pressure data is obtained from the exact solution of the governing equations of the muffler model in Matlab® software. Many mathematical simulations were performed of varying muffler lengths at multiple frequency ranges simultaneously. The results indicate that the \({\text{TL}}\) is optimized at the desired zone of frequency. This research supports the quick and active approach towards optimal design for BFRP-CDCM in a space constrains.

Fiber Reinforced Cementitious Matrix (FRCM) has gained more and more popularity for building strengthening applications. However, when dealing with curved structural elements, such as arches and vaults commonly found in masonry buildings, the relevant studies remain insufficient. The challenge lies in comprehending the intricate failure mechanisms within the FRCM composite and addressing the normal stresses induced by substrate curvature along the interface. In this study, we expand our previous model, capable of delineating both internal and external composite failures, to accommodate curved scenarios. This model leverages a two-dimensional bisection procedure, incorporating the impact of substrate curvature within the interface law. Non-linear behaviors in both the mortar and substrate are effectively addressed through a recursive elastic numerical algorithm. We introduce two distinct models, one considering the upper mortar layer and the other without it. These models are validated against existing experimental data, demonstrating their performance in predicting the bond behavior of FRCM systems under shear testing.

Fibre reinforced composite materials have been increasingly used in recent decades as reinforcement systems for masonry structures. Initially, externally bonded fibre reinforced polymer (FRP) sheets were mainly used in in structural applications. Subsequently, the use of composite materials with inorganic matrix (mainly, fiber reinforced cementitious matrix – FRCM) became widespread. Both systems present advantages and disadvantages that make them suitable in particular conditions and for specific practical applications. In any case, the structural effectiveness of such externally bonded reinforcements strongly depends on the composite-to-substrate adhesive capacity. The experimental behaviour of two different reinforcing systems (the first with organic matrix and the second having inorganic matrix) externally bonded to masonry pillars is compared in this paper.

Fiber reinforced polymers (FRP) have been increasingly popular over the past decades in civil engineering, even for the purpose of strengthening unreinforced brickwork. The primary aim of utilizing FRP on masonry walls is to enhance their strength and displacements. To strengthen cross walls and increase tensile capacity during an earthquake, it may be convenient to use externally bonded (EB) Glass-FRP strips. This strengthening system is affected by loss of bond with delamination of GFRP strips from surface of bricks.

The investigation’s findings regarding the bond between GFRP strips and modern brickwork masonry surfaces are presented in this paper. Pull-push shear tests were performed on brickwork specimens with different thickness of bed mortar joints strengthened by EB-GFRP strips. Failure’s modes are described with shear-slip laws and energy fracture values.

Detecting and locating damage is a crucial aspect of structural health monitoring. While Artificial Neural Networks (ANNs) have shown success in identifying damage in civil and mechanical structures, they come with certain limitations. However, enhancing the effectiveness of ANNs is achievable through adjustments in their architecture and training strategies. This study introduces a metaheuristic algorithm, specifically the Butterfly Optimization Algorithm (BOA), to optimize an ANN for predicting multiple damages in aluminum bars. Input parameters include natural frequencies, and output parameters consist of crack depths. The paper employs an enhanced Finite Element Model (FEM) to gather data through simulation, considering various crack depths. To gauge the dependability of this method, we gather experimental data from the examination of beams with varying crack depths. The results obtained are juxtaposed with comparable approaches employing metaheuristic algorithms like the Artificial Bee Colony Algorithm (ABC) and Genetic Algorithm (GA). The newly proposed approach demonstrates robust performance in predicting damage, showcasing its efficacy in comparison to alternative methods.

This paper presents an improved artificial neural network to predict the damage percentage in the test sample. The main objective is to show that the presence of holes and more generally of notches and other connection gaps lead to a weakening of the structure due to local overstresses, called stress concentrations. It is therefore good to avoid them, as much as possible. When the presence of stress concentrators is inevitable, it is necessary to know the stress concentration factor associated with each geometry, a notion introduced in this problem, in order to dimension the structures. Large holes result in high stress concentration factors. This behavior clearly shows that the presence of holes in a specimen is a place of stress concentration which can lead to the initiation and propagation of cracks. In this study, using an improved artificial neural network (ANN) model, we aim to predict the damage percentage in test samples with higher accuracy and reliability. This improved ANN integrates state-of-the-art algorithms (Arithmetic Optimization Algorithm-AOA, Balancing Composition Motion Optimization-BCMO and Jaya Algorithm), refined training methodologies and an extensive dataset of stress values of different sizes to ensure a more comprehensive and robust understanding of damage prediction, thereby contributing to more accurate assessments of the structural integrity and reliability of tested samples.

The paper focuses on the formulation and solving technique of trusses with multi-freedom constraints loaded mechanically and thermally considering geometrically nonlinearity utilizing FEM with mixed primary unknown variable choice. For analysis of truss with dependent boundary conditions under thermal load using displacement-based FEM considering large displacement, it is needed to incorporate the expansion due to temperature change varying with the element’s length and the boundary relations of constraints to the FE stiffness equation for constructing the modified system of equations. To skip the incorporation process of temperature variation, in this research, a novel mixed form of finite truss element with temperature variation considering geometric non-linearity is established according to the mixed-based formulation. Utilizing the novel established element, the global equilibrium equation is built for the truss system according to the minimum total potential energy principle. The incorporation of multi-freedom constraints is done by using the Lagrange multipliers method to convert the boundary constraints. The mathematical technique based on the arc-length method has been implemented to establish an algorithm for solving a system of FEM nonlinear equations. Utilizing the incremental-iterative solution procedure established by the arc-length technique, the Matlab calculation program has been written to examine the buckling response of truss systems having boundary constraints under the action of simultaneous mechanical and thermal load.

Recently, the monitoring of FRP elements through damage detection has become one of the most important aspects of the use of Fiber-Reinforced Polymers (FRPs) in civil engineering, both in the rehabilitation of existing structures and in the construction of new ones. Non-destructive methods based on experimental vibration monitoring can adequately perform this task. FRP structures change their dynamics due to actual damage from defects, loss of integrity, and cracking of the FRP material due to overloading during service or damage. The response of Carbon-FRP lamina to vibration with damage has been studied experimentally, considering as damage variation pf frequency values due to tensile tests up to 80% of strength. Below are the changes in natural frequency values obtained from dynamic tests that are related to the degree of damage to CFRP laminas. A numerical model has been developed for a theoretical study of damaged CFRP laminas under vibration. The theoretical frequency values are compared with those obtained from experimental tests.

Our research focuses on optimizing soft robotic gripper designs by employing an innovative hybrid topology approach with the aim of creating lightweight and porous grippers. Addressing the complex challenge of multiscale, multilateral topology optimization, we use a hybrid technique that combines SIMP (Solid Isotropic Material with Penalization) for macroscale optimization and MSB (Metaheuristic Structural Binary Distribution) for microscale optimization. At the microscale, our efforts are directed towards enhancing Young's modulus for weight reduction, considering orthotropic materials. Numerical examples in our study illustrate the adaptability of the microscale design to spatial configurations within both macro and microstructures. Various scenarios in macrostructure design demonstrate an advanced approach to strain energy distribution at the macroscale. Our innovative hybrid approach, integrating SIMP as for the macro-scale and MSB for micro-scale design, enables optimal designs while significantly reducing computational costs. This design methodology has the potential to yield novel, durable, lightweight, and porous soft robotic grippers with exceptional elastic flexibility.

This paper proposes a simulation-based approach for probabilistic damage detection and quantification using vibration-based measurements. The method uses an Approximate Bayesian Computation (ABC) algorithm in which a Nested Sampling (NS) technique is introduced, which has the added advantage of guiding the parameters towards region(s) of high posterior density, especially in the first ABC-NS round. The ABC-NS algorithm gives the whole probability density function (PDF) of structural damage severities and a full characterisation of the posterior uncertainties in a reasonable computational time. Two numerical examples with different complexities were proposed to demonstrate the efficiency and the robustness of the ABC-NS sampler in terms of damage localisation and severity quantification.

Modern multistory buildings often incorporate steel and composite beams with web openings, offering various advantages. However, these openings can significantly diminish the shear and flexural strengths of the beams. The mechanical behavior of these beams is influenced by different shapes and sizes of openings in their webs. In this study, a numerical finite element analysis was conducted using Cast3m software to explore how the geometric characteristics of openings impact bisymmetric steel beam sections. The model accounts for material and geometric nonlinearities and is calibrated using analytical results from Eurocode 3. The parametric study revealed that, as height increases, the Vierendeel effect becomes more dominant compared to an increase in opening length.

Among the most common materials for resilient building construction and strengthening repair, composite-reinforced mortars (CRMs) have gained an increased attention, due to the enhanced durability, strength, and performance of cementitious materials involving various kinds of fibers, such as glass, carbon or basalt, within the cement matrix. At the same time, such innovative materials are reversible and sustainable, and can be easily applied on irregular substrates, and wet supports providing better performances at high temperature. In this context, the interfacial behavior of CRM-to-substrate systems represents a crucial aspect that must be studied to ensure the resilience and durability of strengthened structures, as increasingly investigated for direct single-lap or double-lap tests in a theoretical, computational and experimental sense. According to the main experimental findings from the existing literature on single-lap shear tests, this work analyses computationally the mixed-mode interfacial response of CRM-to-substrate single-lap shear specimens, as provided by the concrete damaged plasticity and cohesive crack models within a finite element environment. The matrix properties of the selected specimen are characterized by two different analytical approximations, namely, an exponential law available from literature, and a novel polynomial approximation, which is adequately calibrated for an accurate modelling of the softening response. The proposed model is validated systematically for different input parameters such as, the fiber stiffness, the fiber-matrix interfacial strength, and the specimen geometry, with an accurate prediction of the damage location, initiation and development, both from a local and global standpoint. The main results of this numerical work could provide useful insights for the design of CRM reinforcements and their potential applications, in an inexpensive way, instead of more costly experimental investigations.

An innovative modelling strategy is presented in this contribution to study the mechanical response of laminated doubly-curved shells with arbitrary shapes and advanced materials. The structure is described through differential geometry principles, allowing for an arbitrary variable thickness. Furthermore, a generalized isogeometric technique is adopted for the mapping procedure of the physical domain. The kinematic field variable is described according to the Equivalent Single Layer (ESL) and the Layer-Wise (LW) assumptions. The study also provides homogenization procedures for advanced materials like anisogrid, honeycomb, functionally graded materials, and carbon nanotubes, taking into account also the porosity effects. The Hamilton Principle is applied to determine the governing equations of the problem, accounting for arbitrary loading and boundary conditions, modelled with linear elastic springs. The Generalized Differential Quadrature (GDQ) method is used to determine the numerical solution, whereas an analytical approach is adopted in some multifield applications involving electric, thermal, and magnetic fields. Validation examples show the accuracy of the formulation for the prediction, with a reduced computational effort, of the static and vibrational response of the selected structures. A parametric investigation focuses on different geometries and materials. The higher-order theory-based two-dimensional formulation here proposed, is an efficient and valid alternative to widespread tools for accurately predicting the three-dimensional structural response of complex structural elements.

A new model for nonlinear static analysis of masonry domes subjected to point loads on the crown is presented. Its simplicity makes it usable in common practise by unexperienced users. Masonry is modelled with elastic hexahedral elements connected by 1D elements representing mortar joints, both meridian and horizontal, on which nonlinearities are concentrated. The aim is to simulate the nonlinear behaviour of domes under vertical loads by using a Finite Element commercial software equipped only with the simplest finite elements, namely point contacts and cutoff bars. The mortar joints nonlinearity is reproduced by two different models. The first of which accounts for elastic perfectly brittle point contacts under Heyman’s hypothesis of no-tension material. Whereas the second exploits elastic perfectly ductile cutoff bars, by which different tensile strengths and masonry orthotropy are considered. In this last model, to evaluate the increase in load carrying capacity, Fibre Reinforced Polymers (FRP) strips are applied. While in the first model, the position of plastic hinge is well defined at the expense of the ultimate load, in the second model, the plastic hinge is smeared in favour of a major precision and accuracy in the computation of collapse load. The models are benchmarked on a masonry dome experimentally tested. The procedure is validated by comparison of results with a wide range of Finite Elements, numerical approaches and limit analysis available in the literature for the same dome. By the analysis of nonlinear behaviour emerging from load-displacement curves, the robustness and simplicity of the procedure is proven.

This paper introduces an effective method for damage identification in engineering structures by analyzing alterations in natural frequencies. The study treats this problem as an optimization task, employing three newly developed optimizers: Mountain Gazelle Optimizer (MGO), Gazelle Optimization Algorithm (GOA), and Pelican Optimization Algorithm (POA). Finite Element Method (FEM) is utilized to model a 9-bar planar truss and a 25-bar space truss, simulating damage through a stiffness reduction factor. An objective function, incorporating both measured and calculated natural frequencies, is minimized using the three optimization algorithms. Numerical results demonstrate the accuracy of the proposed approach in identifying single and multiple damages in planar and space truss structures. The study contributes to the field of damage identification methods, providing a practical and efficient tool for maintaining structural safety and durability.

An analytical approach to describe FRCM coupons subjected to standard tensile tests is presented. The coupon is idealized assuming a mono-axial stress state and considering both matrix and fiber. Matrix and fiber interact at the common interface by means of tensile stresses. The fiber is supposed linear elastic, mortar is elastic perfectly brittle and the interface is characterized by a trilinear tau-slip law, where the first stage is elastic, the second involves linear softening and the third exhibits a constant tangential strength. A single second order linear differential equation - deduced from simple longitudinal equilibrium equations - governs the field problem in the three stages of the interface. The only independent variable is the slip at the interface and the solution can be obtained analytically. A priori it is not possible to know the position of the points where the interface exits one phase to enter into another and consequently a discretization with small elements is implemented. The closed-form solution is known for each element where the only variables to be defined are the integration constants of the differential equation solution of the differential equation. Depending on the state of cracking of the mortar, all the constants are derived by imposing suitable boundary conditions at the edges of the elements. The model is successfully validated against available experimental results and previously presented numerical models.

Structural model updating, and model selection have been in the focus of intensive research for many decades and still represent a major challenge. In this paper, the Approximate Bayesian Computation (ABC) using a Nested Sampling (NS) technique is employed to deal with model updating and model selection issues. The proposed framework is based on simulations, it can update a single model but also to find the most likely model from a set of competing models. Moreover, instead of learning a single point estimates, the ABC-NS scheme learns a distribution over the unknown model parameters allowing us to quantify predictive uncertainty. The ABC framework offers the possibility to use different discrepancy metrics measuring the similarity between the measured modal data and the ones obtained from simulations. The performance and the robustness of the simulation-based inference procedure in structural dynamics are demonstrated through two numerical studies using modal data.

This paper investigates the application of topology optimization techniques to enhance damage tolerance in structural systems. The focus is on worst-case damage distribution scenarios, aiming to minimize the vulnerability of structures to localized damage. The study proposes a methodology that combines topology optimization with worst-case scenario analysis to identify optimal structural configurations. Considering cantilever beam structures under three distinct boundary conditions, with varying damage sizes, the paper identifies worst-case damage scenarios in both fully and topologically optimized structures. The results demonstrate the algorithm’s efficacy in identifying these scenarios and its adaptability to different structural shapes, boundary conditions, and damage sizes. Comparative analyses between fully and topologically optimized structures yield specific insights into the structures’ performance, equipping structural engineers and researchers focused on topology optimization with valuable information to enhance structural robustness and resilience.

The article presents the dynamic analysis of plane trusses with the imperfection in the length of elements. The establishment of the finite element method is formulated on the basis of a mixed model. To study plane trusses with element imperfection in length under dynamic loading, taking into account the geometrical nonlinearity, the establishment procedure of the calculation algorithm can be performed by assuming that the imperfection length is a parameter. The article proposes an approach based on mixed FEM formulation to solve the trusses with imperfection in the length of elements subjected to dynamic loads. The article establishes the dynamic equilibrium equation for the proposed mixed finite element formulation of trusses based on the compatibility equation considering the geometrical nonlinearity. The Newmark and iterative Newton-Raphson methods are applied in solving the nonlinear system of dynamic equations of trusses. The established incremental-iterative algorithm based on these methods is used to write a program for dynamic analysis with imperfections in element length in trusses. The obtained results verify the efficiency and accurateness of the mixed FEM formulation that proposed by authors in the dynamic analysis of trusses with imperfection in length.

The ever-increasing demand for advanced composite materials in industries like aerospace and automotive has spurred the drive to address their inherent weaknesses. This pursuit is facilitated by the availability of numerical simulations and artificial intelligence, offering a cost-effective means to comprehensively study various phenomena without excessive reliance on experimentation. While existing models in the scientific realm provide a foundation for composite material modeling, achieving results closely aligned with experimental data is often challenging due to the variation of the parameters and conditions. This present study introduces an innovative approach aimed at optimizing composite material performance and minimizing discrepancies between experimental and numerical outcomes. This approach leverages sophisticated optimization algorithms to fine-tune the Hashin damage parameters, resulting in a highly accurate model. Furthermore, the incorporation of an Artificial Neural Network (ANN) via an inverse problem based on Jaya’s algorithm solving strategy facilitates the prediction of optimal parameters, ensuring a significant reduction in error. This novel methodology presents a promising avenue for elevating the efficiency and reliability of CFRP composite materials in practical applications.

Structural Health Monitoring (SHM) aims to promptly detect defects and damage that affect the safety and operational quality of structures. Monitoring data helps to make timely and appropriate maintenance plans to maintain the safe working ability and efficient exploitation of the structure during its service life. SHM has been used for a long time in the aviation industry. Today, it is also applied to large scale structural systems, which is very important in modern construction. In Vietnam, SHM has been applied to a variety of structures such as large dams and large span bridges in recent decades. This study introduces an overview of some types of SHM being applied in Vietnam. Results of structural monitoring of actual projects, which are designed, deployed, installed, collected, analyzed and evaluated by the authors. The research contents of machine learning application for fault diagnosis, monitoring data processing are also introduced in this study.