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The seismic resilience of structures and infrastructures is affected by damage accumulation phenomena, mainly related to the type of hysteresis. Specifically, pinching drives the cyclic response of several building materials, such as reinforced concrete and masonry. Structural systems affected by pinching phenomena are prone to exhibit a dramatic increment of their displacement response after multiple cycles (e.g. repeated earthquakes). The authors estimate a reinforced concrete pier's response using truncated incremental dynamic analysis by concatenating three earthquake scenarios. The authors adopted a Bouc–Wen class hysteresis model to simulate the reinforced concrete pier's cyclic response, matching its experimental cyclic response. The current analysis proved that ductility and resistance primarily drive the seismic response after a single earthquake. However, the performance after multiple earthquakes strongly depends on the pinching, degradation and drift accumulation, which are generally neglected in standard design practices. [ABSTRACT FROM AUTHOR]

In the last decades, the majority of the existing infrastructure heritage is approaching the end of its nominal design life mainly due to aging, deterioration, and degradation phenomena, threatening the safety levels of these strategic routes of communications. For civil engineers and researchers devoted to assessing and monitoring the structural health (SHM) of existing structures, the demand for innovative indirect non-destructive testing (NDT) methods aided with artificial intelligence (AI) is progressively spreading. In the present study, the authors analyzed the exertion of various deep learning models in order to increase the productivity of classifying ground penetrating radar (GPR) images for SHM purposes, especially focusing on road tunnel linings evaluations. Specifically, the authors presented a comparative study employing two convolutional models, i.e. the ResNet-50 and the EfficientNet-B0, and a recent transformer model, i.e. the Vision Transformer (ViT). Precisely, the authors evaluated the effects of training the models with or without pre-processed data through the bi-dimensional Fourier transform. Despite the theoretical advantages envisaged by adopting this kind of pre-processing technique on GPR images, the best classification performances have been still manifested by the classifiers trained without the Fourier pre-processing. [ABSTRACT FROM AUTHOR]

Addressing the seismic vulnerability of infrastructures is critical, especially for those built before the introduction of the current seismic regulations. One of the primary challenges lies in retrofitting these buildings without interrupting their functionality. In this context, the use of exoskeletons for seismic retrofitting represents an effective solution. This approach increases the seismic resistance and ensures the continuous operation of the building during retrofitting. This advantage is especially crucial for critical infrastructures, such as airports. Nevertheless, traditional seismic assessment methods based on pushover analyses might not accurately predict the seismic capacity of complex infrastructures dominated by local vibration modes. To bridge this gap, the study proposes refining the multimodal pushover analysis tailored for seismic vulnerability assessments of large infrastructures with exoskeletons characterized by low modal participation ratios. The Foggia Airport case study exemplifies these points and highlights the practical applications of the discussed advancements. The authors compared two force distributions for push-over analysis, addressing the fine-tuning of exoskeletons to maximize their seismic resistance. [ABSTRACT FROM AUTHOR]

This paper compares three approaches for predicting the bridge response under moving vehicles. The first approach represents the vehicle as a concentrated moving load, while the second and third approaches simulate the vehicle using single (1-dof) and two (2-dof) degrees of freedom models, respectively. The vehicle–bridge models have been implemented following a finite-difference formulation. These models have been validated against the experimental displacement response of a mid-span prestressed reinforced concrete bridge. Parametric analyses have been conducted to investigate the impact of road roughness on the discrepancies between the models' predictions. An increasing level of road roughness, modeled according to ISO-8608, tends to conceal the mutual differences between the models' outcomes. Furthermore, a Monte Carlo simulation has been employed to fit the probability distributions of two indicators, comparing the bridge displacement responses in three roughness scenarios and considering variable velocity and vehicle characteristics. The primary objective is to assess whether there are scenarios where vehicle–bridge interaction modeling becomes indispensable for accurately estimating the vehicle's effect on the bridge response. The paper presents expressions for four probability density functions of the chosen metric, facilitating the comparison between the 1-dof and 2-dof models with the concentrated load approach. [ABSTRACT FROM AUTHOR]

This article attempts to define pinching of two structural joints, reinforced concrete (RC) and wood ones. In particular, the research outlines differences and analogies between pinching of an RC portal and a Light Timber Frame (LTF) wall. This is done by focusing on the concavity of pinching in their response under repeated cycles, which produces differences in the energy dissipation. The response of the two structural archetypes under pseudo-static and dynamic simulations is analysed using the Atan hysteresis model modification. The truncated incremental dynamic analysis (TIDA) of the two systems modelled as single-degree-of-freedom (SDOF) oscillators yielded the fragility curves, approximated by a lognormal cumulative distribution (CDF). The stability of RC under repeated cycles reveals its significant resilience compared to LTF structures. The examination of the fragility functions supports a discussion about the relation between the pinching concavity and the notion of structural resilience by introducing a robustness index ranging from 0 to 1. Ultimately, a parametric analysis of a fictitious structural system derived from the timber one by varying the concavity of the pinching path leads to the estimation of the robustness index as a function of the pinching concavity. [ABSTRACT FROM AUTHOR]

This paper estimates the effect of a pre-hole filled with high-damping material on the inelastic response spectrum of Integral Abutment Bridges (IAB) with pile foundation. The hysteretic response of the pile, described by a Winkler beam model, is obtained from the piece-wise definition of the subgrade stiffness, calibrated on experimental data. The pre-hole with damping pre-hole determines a reduction of the demand spectral acceleration. The force modification factors of the acceleration response spectrum of the bridge superstructure under a large set of strong/motion earthquakes are estimated. The force-reduction factors for the elastic design of IABs with damping pre-hole are proposed. [ABSTRACT FROM AUTHOR]

The flexibility of the foundation system significantly affects the seismic and operational performance of integral abutment bridges (IAB). The so-called pile isolation system can lead to higher flexibility in pile foundations. It consists in backfilling the pile hole with high-damping materials up to a certain depth from the surface level. However, the impact of this solution in increasing the lateral flexibility and reducing the seismic demand strongly depends on the scale factor and pile diameter. Most investigations on this topic are based on experimental tests on scaled pile specimens. This paper explores the pile isolation system's effectiveness by conducting a multivariate sensitivity analysis of the seismic demand of an IAB structural archetype. The IAB archetype is modelled as a Winkler beam with a piece-wise definition of the subgrade stiffness and equivalent viscous damping, simulating the responses of the soil and high-damping particles. The simulated data are then used to calibrate a probabilistic formulation of the seismic demand reduction due to the pre-hole. The formulation, calibrated following a Bayesian approach, is used to derive estimates of the q-factor associated with the damping pre-hole for possible use in engineering practice. The analyses demonstrate that pile isolation with high-damping material can be effective but possesses a limited dissipating capacity, with a seismic reduction factor of approximately 1 and 2. [ABSTRACT FROM AUTHOR]

The dynamic response of post-tensioned rocking walls in a mass timber building can be reduced to a single-degree-of-freedom (SDOF) model. In this model, the rocking wall panel is simplified as a rigid block, while the base rotation represents the degree of freedom of the entire structure. The paper presents an analytical approach to develop and calibrate this nonlinear model using shake table tests of a full-scale two-story building with CLT rocking walls. The experimental data are used to estimate the parameters of the governing equation using least-squares optimization. The correlation between the obtained parameters and the cumulative dissipated energy led to a nonlinear model with degradation behavior captured. After that, the calibrated model was used to assess the fragility functions of the structure under repetitive seismic events. [ABSTRACT FROM AUTHOR]

This paper presents an optimization framework for steel trusses. The authors implemented a penalty-based approach to optimise the size, shape, and topology based on a dynamic grouping strategy to address the constructability challenges. The main contribution of the paper is the use of damped exponential constructability penalties. This approach ensures optimal designs by balancing structural complexity, through standardization in design, and minimizing the total number of members and variety of sections, with the overall structural cost. The paper also presents a detailed analysis that underscores the sensitivity of the optimization convergence to the algorithmic hyperparameters, emphasizing the role of cross-section assignments and stabilization of truss piece counts. The optimization framework is validated on a trussed roof structure based on the findings from the single truss optimization. The best truss topology proved to be the Howe truss configuration, highlighting its efficiency in meeting the defined objective function. • Constructability-based size, shape and topology optimization of steel trusses. • Penalty approach and dynamic grouping strategy for complexity minimization. • Sensitivity of the optimization to the penalty hyperparameters. • Application to planar trusses and a real tridimensional steel structure. • Howe truss is the optimal topology for the real roof structure. [ABSTRACT FROM AUTHOR]

This study examines the tensile behaviour of Ultra-High Performance Concrete (UHPC) specimens reinforced with varying steel fibre content and rebar diameters. An experimental campaign involving 18 reinforced UHPC specimens was conducted, following individual tensile response characterizations of UHPC and reinforcing steel. These specimens were designed and fabricated with threaded welded steel cages to transfer loads to the central measurement area. Force–displacement curves were measured to derive stress–strain curves for the UHPC component, evaluating the impact of reinforcement rebar and steel fibre content on UHPC's mechanical response. The analysis revealed that steel fibre volume content significantly influences the tensile response of UHPC reinforcement more than the steel bar diameter and yield strength. Comparing the strain in steel bars to the average strain in reinforced UHPC specimens indicated that post-cracking deformation concentrates at the crack. At the same time, the bond between reinforcement and UHPC remains intact in uncracked sections, allowing effective load transfer. UHPC specimens reinforced with 14 mm diameter steel bars displayed a significant horizontal segment in the descending phase of the stress–strain curve. In contrast, specimens with 18 mm or 22 mm diameter bars exhibit a progressive stress reduction at a nearly constant rate. Stress–strain curves of UHPC were fitted with a five-fold piecewise empirical model applicable to UHPC with a reinforcement ratio higher than 0.09%. The resulting model can be used to model the axial behaviour in UHPC, considering the effects of steel reinforcement. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical performance of ultra-high-performance concrete (UHPC) beam-to-beam joints in steel–concrete composite bridges, proposing an alternative to conventional reinforced concrete (RC) joints in continuous beams. The authors employed UHPC with steel end-plates and studs to connect the UHPC crossbeam with the steel beams and RC slab. These connections provides advantages like eliminating the need for on-site welding, , simplifying construction, and handling potential tolerance issues. The research includes full-scale experimental tests, a benchmark test on an RC joint, validation of finite element models, parametric analyses, and the development of analytical models to predict the joint's moment–rotation curve, initial stiffness, and ultimate bending capacity. Full-scale experiments revealed that the maximum longitudinal concrete stress in UHPC continuity joints occurs at the interface between the composite steel–concrete beam and the UHPC cross-beams, resulting in crack widths substantially below code limits. The parametric analyses identified critical factors affecting UHPC joint performance, such as concrete strength, steel yield strength, and horizontal stud dimensions. Additionally, the study validated existing formulations for predicting the capacity and stiffness of the joints against the results from the finite element (FE) parametric analyses. • Beam-to-beam connections with UHPC and shear studs for steel-concrete composite structures. • Full-scale experimental tests and FE model validation. • Sensitivity analysis of the stiffness and capacity on the design variables. • Calibration of a trilinear moment–rotation model. • Validation of analytical models for the rotational stiffness and ultimate capacity. [ABSTRACT FROM AUTHOR]

Pinching characterizes the hysteretic response of several structural systems. It is associated with a reduced dissipated hysteretic energy under cyclic loading and can significantly affect seismic performance, especially under repeated earthquakes. Although several scholars proposed advanced joint arrangements with reduced pinching, ordinary timber structures present pronounced pinching effects due to the local damage to the timber joints. This paper quantifies the impact of variable pinching on the seismic performance of a timber structural archetype. The authors modeled the hysteretic response of a light-timber framed assembly using an empirical hysteresis model and assessed the sensitivity of the displacement demand of the chosen archetype to pinching, number of earthquake repetitions, and spectral acceleration. The choice of an elementary structural archetype, rather than a more complex system, allows isolating the effects of pinching, which could otherwise be disguised by other phenomena, like force redistribution between structural assemblies due to plasticization. [ABSTRACT FROM AUTHOR]

This paper focuses on the optimum design of the e-CLT technology. The e-CLT technology consists in adding cross laminated timber (CLT) walls to an existing reinforced concrete (RC) infilled frame via asymmetric friction connection (AFC). The authors carried out quasi-static and nonlinear dynamic analyses. The RC frame is modeled in OpenSees by fiber-section-based elements with force-based formulation. The contribution of the infill is simulated using a degrading data-driven Bouc–Wen model with a slip-lock element while the AFC is modelled with a modified Coulomb model. Different types of infill, aspect ratio, scaling, and member size are considered. The benefits of using e-CLT technology are discussed and the ranges of optimum performance of the AFC are estimated. A comparison of the performance of traditional infills with the e-CLT system is presented. The authors provide optimum intervals of the ratio between slip force and in-plane stiffness of the CLT panel, following energy and displacement-based criteria. The seismic displacement demand under various seismic scenario is investigated. Correlations between the RC characteristics and the optimum design ratios bestow possible criteria for the design of the AFC. [ABSTRACT FROM AUTHOR]

Among the key benefits of using structural timber is its potential for reuse after being dismantled from an existing building. Recycling and reuse are central concepts in the circular economy. However, the installation and dismantling of structural elements often leave traces from previous use, such as holes from connectors like dowels or screws, internal piping and cabling. Therefore, it is crucial to develop methods to rigorously quantify the reduced load-bearing capacity of recycled beams due to potential holes using efficient and expedited methods akin to visual grading approaches. This work proposes a visual-based method for classifying recycled timber based on the geometric characteristics of the artificial holes. A stochastic mechanics-based numerical model was developed to predict the bending strength reduction of beams with random hole patterns and thus generate an extensive dataset for calibrating data-driven binary classification models. Machine learning and conditional classification models are used to determine if the reduction in bending strength is greater or less than 20%, being the predefined threshold value for reduced strength grading. An experimental campaign on timber beams with specific hole patterns, determined after experimental design, led to the numerical model validation and the calibration of thresholds for the conditional classification model, which relies on a single feature: the sum of the diameters of the holes in two beam regions. The study shows that with an elementary conditional model, high-performance metrics of the binary classification model comparable to machine learning techniques can be achieved. In other words, with a balanced dataset, accuracies over 80% in classifying the level of capacity reduction, greater or lesser than 20%, can be achieved simply by comparing the sum of diameters to a predetermined threshold. This method currently fills a regulatory and methodological gap in safely reusing structural timber. • Visual-based grading of recovered timber beams. • Comparison of visual-based classification models for structural grading. • Development of a simplified mechanics-based procedure for bending capacity assessment. • Generation of a dataset for model calibration using a stochastic Finite element model. • Experimental validation of the proposed mechanics-based procedure. [ABSTRACT FROM AUTHOR]

Fatigue represents a critical condition for infrastructure subjected to repeated cyclic loads, such as steel railway bridges. The literature offers several methods to estimate fatigue life, consisting of three main phases: cycle counting, fatigue damage criterion, and damage accumulation criterion. Applying S–N curves might not be conservative in the case of railway bridges subjected to traffic because the stress-time history is complex and cannot be reduced to a sinusoidal history. Additionally, the presence of a multiaxial stress state must be considered. Therefore, this work compares eight multiaxial fatigue damage criteria for evaluating fatigue life in a scenario between high and low-cycle fatigue. Specifically, the authors considered four low-cycle fatigue criteria, namely Smith–Watson–Topper (SWT), Kandil, Brown and Miller (KBM), Glinka, Fatemi and Socie (FS), and four high-cycle fatigue criteria, Crossland, Basquin and the methods recommended by Eurocode 3 and British Standard. The rainflow counting method in ASTM E1049-85 (2011) and Miner's rule for damage accumulation were used. The Polcevera railway steel bridge was selected as a case study. A 3D numerical model was developed for this purpose using Midas Civil software, taking into account the material non-linearity of the bridge's elements. Once the area with the highest stress concentration was identified, a detailed analysis was conducted to estimate the stress and strain time histories induced by train traffic. A sensitivity analysis was conducted after critically comparing the eight methods for predicting fatigue life to assess the impact of traffic parameters, train velocity, axle load, and convoy length on fatigue life. It has been found that the criteria considering axial stress tend to overestimate the number of fatigue cycles to failure compared to the criteria, including the effect of shear stress components. • Fatigue life assessment of steel arch bridge. • Effect of train velocity, axle load and train length. • Comparison of state-of-the-art multiaxial fatigue criteria. • The lowest fatigue life from methods including the shear effect. • Low-cycle fatigue criteria underestimate fatigue life accordig to Standards [ABSTRACT FROM AUTHOR]

This paper delivers a reliability-based method for the assessment of the elastic modulus (EM) of concrete in simply supported girders from dynamic identification. The correlation between the natural frequencies of the first bending modes and the concrete EM supports the use of the first natural frequency as a predictor of the EM value, which is a well-acknowledged indicator of the state of concrete. In the current application, the EMs of seven girders provide the prior state of knowledge about the considered bridge class, possibly to be obtained by more samples in working applications. The identified natural frequencies update the prior probability distribution of the EMs using Bayes inference. The resulting probability of exceeding a specific EM value expresses the degree of belief of the inspector in the obtained EM. The posterior probability, compared to a proper threshold, could be used in decision-making processes when prioritising the interventions in the maintenance plans. [ABSTRACT FROM AUTHOR]

Timber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years , ambient vibration tests have become very popular due to the many advantages they have over traditional forced vibration tests when dealing with civil engineering structures. Furthermore, sensitivity analyses and black-box" optimization algorithms can support the development of refined finite-element models that accurately predict the structures' responses based on the experimental modal parameters. However, applications of these methods and techniques to timber structures are scarce compared with traditional materials. This paper presents and discusses the findings of an experimental testing campaign on a lightweight timber floor. At first, each component of the assembly was tested separately under different boundary conditions. Then, the authors evaluated the behavior of the whole floor assembly. In a second step, the authors carried out a covariance-based sensitivity analysis of finite element (FE) models representative of the tested structures by varying the different members' mechanical properties. The results of the sensitivity analysis highlighted the most influential parameters and supported the comparison among diverse FE models. As expected, the longitudinal modulus of elasticity is the most critical parameter, although the results are very dependent on the boundary conditions. Then automatic modal updating algorithms tuned the numerical model to test results. As a concluding remark, the experimental and numerical results were compared with the outcomes of a simplified analytical approach for the floor's first natural frequency estimate based on current European standards. [ABSTRACT FROM AUTHOR]

Parametric identification of bridges using instrumented vehicles can be challenging, mainly due to the reduced length of the time series associated with the bridge span under test. This research discusses the practicability of a time-domain identification method based on the use of an instrumented vehicle. The highest cross-correlation between the bridge response from an elementary analytical model and the experimental one, acquired by a moving force-balance accelerometer, yields the unknown model parameter. The effect of vehicle-bridge interaction is removed by proper filtering of the signals. Specifically, the authors estimate the elastic moduli of seven prestressed concrete bridges and compare a subset of the results to the outcomes of static load tests carried out on the same bridges. There is a good correlation between the elastic moduli from the instrumented vehicle and those from static load tests: the method grasps the approximate value of the elastic modulus of concrete. Still, the data do not return an excellent match due to the bias in the estimation of the deflection shape—the paper remarks on the issues faced during the experimental tests and proposes possible enhancements of these procedures. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) floors often encounter vibration issues when employed in large spans bearing heavy loads, and the enhancement of their vibration performance frequently centres around achieving composite action. This study delves into the effectiveness of hybrid CLT-steel composite floors as potential substitutes for traditional, long-span CLT floors. A parametric model was developed using OpenSeesPy and validated with prior vibration experimental tests on hybrid and pure CLT floors. It was then employed in examining the sensitivities of the floors to various excitation scenarios via an integrated random walk model used to generate random dynamic responses. Two extreme boundary conditions: pinned–pinned and clamped–clamped, were also simulated to investigate the limits of the vibration response of the hybrid composite floor. The chosen metrics for assessment comprised fundamental frequency, vibration dose value, peak acceleration and velocity, response factor, as well as root-mean-square acceleration and velocity. These metrics were also juxtaposed against the predictions put forth by the new Eurocode 5 draft. Though the fundamental frequency of the much-stiffer hybrid composite floor was about thrice that of the bare CLT, the considerably lower damping of the former — about 60 % less, resulted in a comparable acceleration response with the CLT floor. Also, despite a 55% increase in fundamental frequency when the hybrid floor was simulated with clamped supports, the resulting serviceability metrics did not indicate a clear-cut performance improvement over the pinned boundary condition. The results highlight the leading influence of damping rather than bending stiffness and fundamental frequency on the serviceability metrics of hybrid CLT-steel composite floors. • Probabilistic model for simulating human-induced vibration of hybrid CLT-steel floors. • Experimental tests on CLT and hybrid CLT-steel floors. • Validation of an FE model in OpenseesPy using experimental modal parameters and human-induced vibration responses. • Montecarlo simulations assuming a random walk model. • Greater influence of damping on the vibration response of the hybrid CLT-steel floor than stiffness and fundamental frequency. [ABSTRACT FROM AUTHOR]

The most common and practical connection between CLT walls can be realized with inclined screws. This choice avoids the realization of more elaborated half-lap or spline joints. The failure mechanism of CLT-to-CLT screwed connections is highly ductile. However, the epistemic and aleatoric uncertainties associated with the capacity estimation of the connection might lead to an undesired overstrength, compromising the expected hierarchy between failure mechanisms. This paper presents the results of an extended experimental campaign to estimate the overstrength of CLT-to-CLT screwed connections. However, the overstrength directly obtained from the experimental tests could be underestimated. In the experimental campaign, the same wood and screw stock is used, which might not represent the actual scatter of the material properties and construction uncertainties of the as-built connection (e.g., the screw inclination). Therefore, this paper attempts to provide a model-driven assessment of the overstrength factor, assuming more realistic values for the parameter uncertainties. The authors propose a method for removing the contribution of epistemic uncertainty to the model-driven estimation of the overstrength based on experimental tests with two Montecarlo simulations. Following the proposed method, the paper compares the overstrength estimations from the experimental tests to the predictions of analytical and nonlinear finite element models. This study has proven that an overstrength factor between 1.8 and 2 can represent the actual uncertainties in as-built CLT-to-CLT screwed connections. • Overstrength assessment of CLT-to-CLT screwed connections. • Proposal of a novel formulation for overstrength. • Experimental tests on CLT-to-CLT screw connections. • Epistemic and aleatoric uncertainties in the overstrength estimate. • Uncertainty propagation in analytical and FE models. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on structural verification and proposed improvements for an ancient masonry arch bridge. The research encompasses multiple stages, starting with a detailed survey utilizing LiDAR and aerial techniques to collect precise data on the bridge's condition. Mechanical inspections assess deterioration levels and identify critical areas requiring attention. Based on the gathered data, a structural model of the bridge is developed, considering geometric parameters and material properties. The model undergoes rigorous verification procedures to assess its seismic response and ensure compliance with safety standards. The analysis includes identifying potential collapse mechanisms, such as the formation of plastic hinges, which can lead to structural failure. The study proposes structural improvements to enhance the bridge's performance and safety. These interventions specifically target vulnerabilities identified during the verification process. They include additional support elements, reinforcing critical areas, and utilizing advanced materials to improve tensile strength and durability. The feasibility of the proposed retrofitting solutions will be proved by performing a cost analysis, while environmental impacts are evaluated through an environmental assessment (Lifecycle Assessment — LCA) in which all the main bridge refurbishment phases have been included. Finally, some of the advantages of bridge refurbishment measures are shown by comparing the proposed intervention with a bridge reconstruction in terms of costs and environmental impacts. The outcomes of this study contribute to the existing knowledge on the rehabilitation of masonry arch bridges and serve as a valuable reference for engineers and practitioners involved in preserving architectural heritage. • Multi-stage digital assessment of an ancient masonry bridge. • Non-linear analysis to identify potential collapse mechanisms. • Study of the interventions to enhance the bridge's performance and safety. • Additional cost analysis and environmental assessment (LCA). • Comparison among the proposed interventions compared, and reconstruction. [ABSTRACT FROM AUTHOR]

This paper attempts to formulate an expression for the estimation of equivalent viscous damping (EVD) for cross-laminated timber (CLT) structural archetypes as a function of ductility. The paper aims at contributing toward the direct displacement-based design procedure (DDBD) of CLT structures, which makes use of equivalent viscous damping and secant stiffness estimations as proxies for the estimation of the nonlinear behavior of structures. The available hysteretic models of CLT structures are very elaborate, and the inelastic time-domain simulations using hysteretic models are not easily manageable. Hence, the adoption of equivalent viscous damping is a crucial feature of any DDBD method. In this paper, the authors estimate the EVD of a set of 16 typologies of CLT buildings with an increasing slenderness ratio. The minimum of the squared error between the maximum drift of the elastic time-history and the hysteretic response gives the EVD. The extended energy-dependent generalized Bouc Wen (EEGBW) model, calibrated on experimental data, is used to predict the inelastic seismic response of the single CLT shear wall. The correlation between EVD and ductility is compared to existing EVD formulations referring to concrete and steel structures. [ABSTRACT FROM AUTHOR]

The article focuses on the assessment of a structural intervention using a simple Bayesian approach driven by subspace-based indicators. A permanent monitoring system installed in a monumental masonry structure, the basilica of Santa Maria di Collemaggio in L'Aquila Italy, continuously acquires vibration data. The results of modal identification are first reported and discussed. Then, the article delivers a damage detection procedure, tested on two sets of data measured by the façade accelerometers before and after the CLT (Cross-Lam Timber) roof connection, which are interpreted as damage and reference states, respectively. The application of Bayesian inference to a set of damage indicators for the assessment of the façade structural modification is presented and compared with the results of a non-parametric χ 2 -tests. A computation procedure for the built of a statistical reference model is proposed by discussing the issue of the choice of the reference data set. [ABSTRACT FROM AUTHOR]

The energy dissipation phenomenon of a high-temperature superconducting (HTS) magnetic levitation (Maglev) transport system is investigated by using a single degree of freedom generalized Bouc–Wen hysteresis model. The Maglev system under test consists of a bogie with HTS skaters, which interacts with permanent magnets distributed on the guideways; thanks to a passive and self-balanced magnetic interaction, the vehicle is suspended and guided in all phases of the motion, including zero speed. The response of the HTS skate is tested under pseudo-static cyclic load in the vertical and lateral directions. The parameters of the generalized Bouc–Wen (GBW) model are calibrated on the experimental hysteresis loops using an ordinary least squares–based algorithm. The vertical dynamics of the levitating HTS skate is affected by the magnetic field discontinuities of the guideway. The dissipated hysteretic energy is simulated to assess the dependence on the velocity and pattern of the magnetic field. The displacement response is obtained by solving the nonlinear differential equation representative of the moving HTS skater, modelled as a single degree of freedom system, whose interactions with the magnetic guideway are described by the identified GBW hysteresis law. [ABSTRACT FROM AUTHOR]

A critical analysis of the hysteresis models of wooden connections has led to an alternative analytical formulation of the pinching phenomenon. Starting from the generalized Bouc-Wen model, the six-degrees-of-freedom formulation has been extended to an eight parameters formulation, which is a better representative of the connection's cyclical degradation. The information given by the two additional parameters and also energy-dependency of the parameters provide a faithful representation of the actual hysteresis cycles of wooden connections. The model has been calibrated on experimental data, following an identification procedure, based on an Ordinary Least Squares (OLS) operator. [ABSTRACT FROM AUTHOR]

This paper proposes a data-driven model for predicting the code-based seismic vulnerability index calibrated on a dataset comprising almost 300 buildings. The vulnerability index, estimated following the Italian Seismic Code, involved rigorous investigations, including geometric surveys, experimental tests, and numerical modelling. Leveraging data from these investigations, encompassing approximately 15 categorical and numerical explanatory variables, the authors developed several regression and classification predictive models, such as Logistic Regression and Artificial Neural Networks (ANN). The optimal models perform binary classification to determine the categorization into two macro-classes, defined by an arbitrary vulnerability threshold. The ANN model stands out as the best performer. When adjusting the vulnerability threshold to obtain a balanced dataset, such a model achieves an accuracy higher than 85%. The paper also discusses the importance of each feature by calculating the SHapley Additive exPlanations (SHAP) values. The proposed model can aid decision-makers in allocating resources effectively to mitigate seismic risks of built environments. • Data-driven model for code-based seismic vulnerability assessment. • 15 explanatory variables are considered. • Regression models perform poorly. • Binary classification is the only reliable approach. • The ANN model has an 85% accuracy on binary classification with balanced dataset. [ABSTRACT FROM AUTHOR]

Timber structures are susceptible to sound propagation problems. The issue can be mitigated by decoupling structural components at connections level by means of polyurethane soundproofing interlayers. These layers are much softer than timber but, at the same time, they are characterized by higher friction coefficients. In this paper, an experimental investigation is carried out to characterize the mechanical behavior of insulated screw connections assessing the implications of the soundproofing layer use. Different interlayers, screw inclination angles and setups are considered. The load–slip behavior is studied, and a proper empirical model, suitable for performing push-over analysis of buildings involving soundproofed connections, is derived. The essential design parameters, namely the slip modulus, the strength and ductility, are determined and compared with existing models predictions, thus testing their accuracy. Substantial reductions in terms of stiffness, load-carrying capacity and ductility are observed in soundproofed connections. • Timber-to-timber connections with soundproofing interlayers are tested. • Soundproofing interlayers substantially reduce mechanical performances. • An alternative definition of the ultimate slip modulus is suggested. • An empirical model for the load–slip behavior is formulated and validated. • Withdrawal failure mechanism can be considered additive to the transversal mechanisms. [ABSTRACT FROM AUTHOR]

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University's laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated. • Tensile tests on 152 rebar welded joints. • Two groups: brittle (prevalent weld failure) and ductile (prevalent rebar failure). • Optimal configuration is R4V*: indirect butt joint with V coupler and additional butt weld. • R4V* has the minimum welding length with optimal ductility. • Probabilistic estimation of overstrength factors to prevent weld failure. [ABSTRACT FROM AUTHOR]

Operational modal analysis methods have been proven especially useful to identify existing structures and infrastructures under serviceability conditions. However, the installation of sensing systems for monitoring continuously an ever larger number of existing constructions has motivated significant efforts towards the automation of the available methods. Within this framework, the present paper introduces a new paradigm for the automatic output-only modal identification of linear structures under ambient vibrations, namely the intelligent automatic operational modal analysis (i-AOMA). It exploits the covariance-based stochastic subspace (SSI-cov) algorithm for the output-only identification of the modal parameters and its workflow consists of two main phases. Initially, quasi-random samples of the control parameters for the SSI-cov algorithm are generated. Once the SSI-cov algorithm is performed for each sample, the corresponding stabilization diagrams are processed in order to prepare a database for training the intelligent core of the i-AOMA method. This is a machine learning technique (namely a random forest algorithm) that predicts which combination of the control parameters for the SSI-cov algorithm is able to provide good modal estimates. Afterward, new quasi-random samples of the control parameters for the SSI-cov algorithm are generated repeatedly until a statistical convergence criterion is achieved. If the generic sample is classified as feasible by the intelligent core of the i-AOMA method, then the SSI-cov algorithm is performed. Finally, stable modal results are distilled from the stabilization diagrams and relevant statistics are computed to evaluate the uncertainty level due to the variability of the control parameters. The proposed i-AOMA method has been applied to identify the modal features of the Al-Hamra Firduos Tower, an iconic 412.6 m tall building located in Kuwait City (Kuwait). The final results well agree with a previous experimental study, and it was also possible to identify two new vibration modes of the structure. The implemented open-source Python code is made freely available. • Automatic operational modal analysis assisted by machine learning. • Quantification of the uncertainty due to the variability of the control parameters. • Open-source Python-based code for intelligent automatic operational modal analysis. • Modal identification of an iconic tall building, the Al-Hamra Firduos Tower. [ABSTRACT FROM AUTHOR]

Glue-line tests provide the shear resistance and failure mode of samples extracted from laminated timber products. Several papers questioned the practical use of such tests affirming the lack of correlation between the capacity of the beam and the outcomes of glue-line tests. However, no studies provide a probabilistic framework for interpreting glue-line tests. This paper presents and discusses the largest database of glue-line tests ever published, consisting of approximately 17000 tests on glued laminated timber (GLT) beams, carried out at the Treteknisk, the Norwegian Institute of Wood Technology (Norway). This database has been used to develop in Abaqus a stochastic FE model to predict the shear capacity of glued laminated timber beams (GLT) using advanced modelling concepts, including discrete cracking and plasticity. The authors examine the dependence of the shear capacity on the beam size to assess the shear size effect in GLT components. The methodology is based on Montecarlo simulations. The mechanical properties of the elementary volumes composing the beam are assigned using a random field model calibrated on the glue-line tests. • Screw reinforcement for timber specimens under compression perpendicular to grain. • Experimental tests on 54 specimens with different geometry and load conditions. • Validation of the capacity model according to the Eurocode 5 proposal. • The model does not seize the failure mechanism by the screw tips. • The model is slightly conservative for the failure by the load steel plate. [ABSTRACT FROM AUTHOR]

Defining a reference shear wave velocity profile (V s) is crucial for seismic-hazard assessment and seismic response analysis. However, selecting a reference velocity profile is not straightforward, mainly because of the high variability of shear wave velocity in complex formations. This study considered 26 shear wave profiles from downhole tests carried out in the Laga Basin (Gran Sasso, Central Apennines), where the soil can be categorised as complex owing to the chaotic succession of turbidite and Quaternary continental deposits. Downhole tests and stratigraphy were used to (i) develop a probabilistic model for predicting the shear wave profiles calibrated on the collected test data and (ii) propose an outlier detection method for estimating the first fundamental frequency of the deposit from horizontal-to-vertical spectral ratio (HVSR) analyses. Specifically, the stochastic shear wave model provides the uncertainty of the first fundamental frequency estimated from downhole tests based on a simplified mechanics-based formulation. The defined bounds, were forward uncertainty propagation following a Monte Carlo approach, have been used to define the criteria for outlier detection in HVSR frequency assessments, given an approximate estimate of the equivalent depth. • Reference Vs profiles for complex soils. • Down-Hole seismic site characterisation. • Probabilistic model for predicting the shear wave profiles. • Outlier detection method for estimating the first fundamental frequency from HVSR. [ABSTRACT FROM AUTHOR]

Thanks to the axial resisting contribution, inclined screw connections offer a mechanical advantage over connections with purely transversely loaded fasteners. However, the strong coupling between the axial and the transversal behaviour of the screw makes it challenging to predict the actual connection behaviour. Moreover, the presence of polyurethane interlayers for soundproofing or OSB interlayers of light-frame buildings between main members may increase the bending moment component interacting with the axial force in the screw, thus reducing the connection failure load. This paper experimentally assesses the behaviour of steel-to-timber connections, and a parametric finite element model of Winkler non-linear beam is presented and validated. Finally, a simplified analytical model for capacity prediction is presented. The results of the approach currently provided by the Eurocode 5, of an additive model and the proposed analytical model, are then compared with the results of 500 finite element analysis. • Timber-to-steel connections with soundproofing and OSB interlayers are tested. • Interlayers reduce slip modulus more than strength. • Non-linear beam on foundation model is suitable for screws connections. • Bending moment interacts with axial force reducing the connection capacity. • An elementary capacity model is validated on 500 finite elements analysis results. [ABSTRACT FROM AUTHOR]

Within seismology, geology, civil and structural engineering, deep learning (DL), especially via generative adversarial networks (GANs), represents an innovative, engaging, and advantageous way to generate reliable synthetic data that represent actual samples' characteristics, providing a handy data augmentation tool. Indeed, in many practical applications, obtaining a significant number of high-quality information is demanding. Data augmentation is generally based on artificial intelligence (AI) and machine learning data-driven models. The DL GAN-based data augmentation approach for generating synthetic seismic signals revolutionized the current data augmentation paradigm. This study delivers a critical state-of-art review, explaining recent research into AI-based GAN synthetic generation of ground motion signals or seismic events, and also with a comprehensive insight into seismic-related geophysical studies. This study may be relevant, especially for the earth and planetary science, geology and seismology, oil and gas exploration, and on the other hand for assessing the seismic response of buildings and infrastructures, seismic detection tasks, and general structural and civil engineering applications. Furthermore, highlighting the strengths and limitations of the current studies on adversarial learning applied to seismology may help to guide research efforts in the next future toward the most promising directions. [ABSTRACT FROM AUTHOR]

This paper compares numerical and analytical predictions for the shear capacity of fibre-reinforced concrete beams based on experimental literature tests. The authors compared the outcomes of a FE model using the DamageTC3d constitutive model, a literature formulation, and the current proposal of the Eurocode 2 draft for fibre-reinforced structures. The paper evaluates the sensitivity of the beam response to the fracture energy G f , modified after the Model Code 2010 formulation. The investigation reveals a dependence of the estimated fracture energy on the beam size. Furthermore, the comparison between the numerical estimates and the analytical predictions using the MC2010 and the current EC2 draft proves that the error is substantially independent of the model selection but is strongly affected by the specific case study. This fact confirms the absence of weaknesses in the numerical modelling and highlights the aleatoric uncertainties of the experimental data. • Numerical and analytical prediction of the shear capacity of fibre-reinforced concrete beams; • Investigation based on the experimental tests by Minelli et al. • Simulating the shear size-effect in fibre-reinforced concrete beams; • Understanding the role of the fracture energy in size-effect phenomena; • Verification of the Eurocode 2 draft formulation against numerical predictions; [ABSTRACT FROM AUTHOR]

The direct displacement-based design (DDBD) is based on the equivalence between the nonlinear hysteretic response of a structure and a simple linear oscillator with equivalent viscous damping (EVD). Typically the EVD is calibrated for different types of structures as a function of the ductility. However, those simple relationships exhibit a huge dispersion and uncertainty since the specific properties of the structural system are not considered. This work proposes an original approach for estimating the EVD of infilled reinforced concrete (RC) frames. We focus on a ductility demand corresponding to an ultimate limit state and we investigate the effect of the properties of infilled RC frames on the EVD. A data-driven hysteresis model proposed by the authors in a previous research is implemented in OpenSees to represent the nonlinear response of infill panels. The optimal EVD at the ultimate limit state is computed using an extensive series of time-history analyses (THAs) on a dataset of 14 infilled RC frames. Afterwards, an empirical correlation law for the estimate of the optimal EVD is calibrated as a function of the geometrical and mechanical properties of infilled RC frames. This formula is meant to be a practical tool for a preliminary design of infilled RC frames. A comparison with the EVD estimated by quasi-static tests and the EVD of bare frames is made. The methods and results presented in this work may be the basis for more robust predictions of the EVD of infilled RC structures. • Equivalent viscous damping (EVD) of infilled RC frames from time-history analyses. • Empirical formula for EVD as a function of geometrical and mechanical properties. • Comparison of optimal EVD for infilled and bare frames. • Comparison of optimal EVD from time-history analyses and quasi-static cyclic tests. • Hysteresis model for infilled RC frames implemented in OpenSees. [ABSTRACT FROM AUTHOR]

Visual inspections generally represent the initial step of the safety assessment of bridges. In particular, steel railway bridges are particularly prone to corrosion phenomena. Therefore, visual inspections provide the geometric characterization of the conservation state of each structural member, in particular, the size reduction originating from the progress of corrosion. Nonetheless, the geometric definition of corrosion is not directly related to structural safety, depending on the damage location. The paper quantifies and discusses the uncertainties in the safety assessment of trussed bridges associated with the unknown effect of damage location on the stress distribution, given initial knowledge of the number and intensity of damaged members. Is it possible to preliminary assess the structural safety for typological structures without knowing the effect of damage location on the stress re-distribution? This paper discusses these aspects by randomly simulating damage scenarios in a finite element model of a historic steel bridge. The model, validated against the experimental modal parameters and measured deflection under train transit, is used for estimating bidimensional fragility curves as a function of the damage intensity and the number of damaged members. Finally, a safety domain can support the preliminary safety assessment of typological steel railway bridges. • Reliability analysis of a steel bridge. • Effect of random corrosion on structural reliability. • Model validation from displacement measurements under train transit. • Model validation from ambient vibration data. • Proposal of a practical fragility chart for vision-based assessments. [ABSTRACT FROM AUTHOR]

The dynamics of roadway bridges crossed by vehicles moving at variable speed has attracted far less attention than that generated by vehicles travelling at constant velocity. Consequently, the role of some parameters and the combination thereof, as well as influence and accuracy of the modelling strategies, are not fully understood yet. Therefore, a large statistical analysis is performed in the present study to provide novel insights into the dynamic vehicle–bridge interaction (VBI) in braking conditions. To this end, an existing mid-span prestressed concrete bridge is selected as case study. First, several numerical simulations are performed considering alternative vehicle models (i.e., single and two degrees-of-freedom models) and different braking scenarios (i.e., soft and hard braking conditions, with both stationary and nonstationary road roughness models in case of soft braking). The statistical appraisal of the obtained results unfolds some effects of the dynamic VBI modelling in braking conditions that have not been reported in previous studies. Additionally, the use of machine learning techniques is explored for the first time to develop surrogate models able to predict the effect of the dynamic VBI in braking conditions efficiently. These surrogate models are then employed to obtain the fragility curve for the selected prestressed concrete bridge, where the attainment of the decompression moment is considered as relevant limit state. Whilst the derivation of the fragility curve using numerical simulations turned out to be almost unpractical using standard computational resources, the proposed approach that exploits surrogate models carried out via machine learning techniques was demonstrated accurate despite the dramatic reduction of the total elaboration time. Finally, the accuracy of the numerical (physics-based and surrogate) models is evaluated on a statistical basis through comparisons with experimental data. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling of screws loaded in compression inserted into timber members. Screws are often used as a reinforcement in timber structures. However, under compression forces, they are prone to axial buckling. The current model for the screw buckling, enclosed in the EC5 proposal, is based on the general framework of EC3 for the instability of compressed steel members. The main shortcomings of the current formulation for the buckling of screws are the following. (1) The analytical expression for calculating the theoretical buckling load does not follow the observed modes. (2) Due to the need for dedicated studies, the value of the imperfection coefficient is arbitrarily chosen. This paper fills the above gaps. Firstly, a simple analytical expression for predicting the buckling of screws is proposed and validated against experimental and finite element (FE) findings. Furthermore, the formulation adopts a more accurate expression for lateral deformation based on experimental observation. Secondly, a FE model calibrated on experimental tests is used to estimate the defect coefficients of the instability curves as a function of the amplitude of the geometric defects of the screw, expressed as a fraction of its length. Finally, a Markov chain Monte Carlo analysis is carried out to simulate the capacity of screws with different sizes, assuming the uncertainty of all input parameters sampled from suitable probability distributions. The results are used to validate the proposed deterministic capacity model and estimate the uncertainty factors of the design equation. • Buckling model for compressed timber screws. • Analytical model for the theoretical buckling load. • Numerical validation of the analytical model. • Experimental tests and numerical model calibration. • Calibration of the imperfection coefficients from Monte Carlo analysis. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of screw reinforcement on the capacity of timber members under compression perpendicular to the grain. The predictions of existing capacity models are compared to the experimental results of 39 timber specimens, distinguished by different load, screw and geometric configurations. Current capacity models assume two failure mechanisms, mainly characterized by their location, i.e. the contact area of the applied load (first mode) or the screw tips (second mode). However, the experimental tests reveal that the second mode never occurs despite the model predicting the occurrence of the second mode in more than half of the tested specimens. Additionally, the experimental tests show the fallacy of existing models in accurately estimating the capacity associated with the second failure mode. Parallely, the model appears to be relatively conservative for the first failure mode. • Screw reinforcement for timber specimens under compression perpendicular to grain. • Experimental tests on multiple specimens with different geometry and load conditions. • Validation of the capacity model according to the Eurocode 5 proposal. • The model does not seize the failure mechanism by the screw tips. • The model is slightly conservative for the failure by the load steel plate. [ABSTRACT FROM AUTHOR]

Multiple physical variables potentially affect the friction coefficient of Asymmetric Friction Connections (AFC). This paper discusses the cyclic response of a class of AFC subjected to repeated load protocols. Two phenomena are observed. First, the friction coefficient, initially higher due to wear phenomena and moment-axial force-shear force interaction, stabilizes after multiple cycles. Second, the test repetitions on the same specimen show that the friction coefficient at the beginning of the loading protocol is higher than that observed at the end of the antecedent load protocol. The experimental data prove that the dissipated energy during the current load test, temperature, and the specimen's history affect the friction coefficient. This paper presents two probabilistic friction models calibrated using a Bayesian approach. The first engineering-oriented model is dependent on the dissipated hysteretic energy. The second includes the measured temperature as a model regressor to estimate its possible role in the response. The proposed probabilistic models can be used to predict with satisfactory accuracy the friction coefficient in Coulomb-like hysteresis models of AFCs. • Repeated experimental cyclic tests on Asymmetric Friction Connections (AFC). • Temperature effects on friction response. • Bayesian probabilistic model for the friction coefficient of AFC. • Description and evolution of the e-CLT technology. • Pros and Cons of AFC devices. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular (CFST) columns are increasingly used around the world because they offer two significant advantages. The first one is the composite action of the steel tube and infilled concrete, which enhances the strength and ductility of the columns. The second one is the use of the steel tube as a permanent formwork for concrete casting, which allows saving construction time and costs. Although considerable research and several experimental tests have been carried out on CFST columns, there is not a probabilistic model for the evaluation of their axial capacity yet. Additionally, the effects of the axial load eccentricity and debonding have received little attention so far. Within this framework, the present paper proposes a physics-based probabilistic model to predict the ultimate axial capacity of CFST columns, which is developed as the sum of a deterministic part and a probabilistic correction term, together with two additional corrective models to describe its reduction due to load eccentricity and debonding, which are developed coherently with the axial capacity model as probabilistic correction terms. The accuracy of the proposed models is compared with that of existing capacity equations already in use within technical standards and available literature. Additionally, this study provides uncertainty factors to allow using the proposed capacity model for design applications. Thanks to their very good accuracy and compact form, the proposed models are suitable to be included within technical standards. On the other hand, differently from common deterministic models, they can also be updated as new experimental data are available. A case study with the derivation of fragility curves for a CFST bridge column shows a possible application and the advantages of the proposed model. • Probabilistic model for the axial capacity of Concrete Filled Steel Tubes (CFST). • Capacity reduction factors for load eccentricity and debonding. • Bayesian model calibration using all available data from the literature. • Comparison between formulations from literature and technical standards. • Calibration of uncertainty factors corresponding to different reliability levels. [ABSTRACT FROM AUTHOR]

• Novel empirical hysteresis model based on a data-model driven approach. • First data-driven approach in modelling the hysteresis of timber-based structures. • The experimental cyclic response is needed for the model formulation. • A step-by-step optimization problem defines the evolution of the backbone curve. • The maximum displacement during the cycle is the hysteretic evolutionary parameter. • Publication of the MATLAB and Python code implementations of the hybrid hysteresis model. This paper presents a novel computational approach to empirical hysteresis modelling applied to timber-based structures based on a combined data model-driven strategy. While the backbone curve is simulated using the experimental cyclic response based on a step-by-step optimization problem (data-driven approach), analytical functions describe the re-loading curves (model-driven approach). Empirical hysteresis models developed so far for timber structures are model-driven. However, the backbone curves can exhibit a highly irregular non-smooth trend, difficult to mirror using analytical formulations. The challenge in mirroring the experimental backbone using closed-form formulations has led to an extended set of parameters to be calibrated in existing literature models This paper presents a novel approach to the empirical hysteresis model, where the experimental data are directly involved, as a whole, in the model formulation. This model aims to be a possible trade-off between model complexity and accuracy. A reduced number of parameters needed to describe the re-loading paths is counterbalanced using an entire subset of the experimental data. The paper delivers the developed Matlab and Python codes for further implementation as a user-defined element within a Finite Element software. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of timber plasticization on the ultimate lateral capacity of rocking Cross-Laminated Timber shear walls with different characteristics. Simplified capacity models predict a CLT wall ultimate capacity by multiplying the hold-down ultimate resistance by its distance to an assumed pivot point, often coincident with the panel edge. However, timber plasticization at the interface with the foundation can significantly reduce the lever arm of the hold down reaction. This paper aims at assessing the effect of timber plasticization and panel characteristics (geometry, width, presence of openings, etc.) on the position of the pivot point, expressed by the dimensionless lever arm τ , namely the ratio between the distance of the hold-down geometrical axis from the compressed timber resultant and the distance between the hold-down geometrical axis and the panel edge. An extended covariance-based sensitivity analysis of several Finite Element (FE) models, representing all the CLT shear wall design variability was carried out. The FE model, developed in Abaqus, has been calibrated on the experimental cyclic response of a CLT wall panel. Among the chosen parameters, the sensitivity analysis proved that the most significant ones affecting τ are two: the ratio between the hold-down reaction and the maximum resistance of the compressed timber, and the width of the opening. Accordingly, the authors estimated an elementary empirical regression equation based on the FE model results for predicting the dimensionless lever arm (τ) in the capacity equation of CLT panels. The use of this elementary formulation allows the designer to estimate with considerable accuracy the lateral capacity of a CLT panel given the panel geometry, the ultimate resistance of the hold-down, the compression strength of timber perpendicular to the grain and the vertical load. Almost all points used for the linear regression fall within the confidence bounds, thus proving the accuracy of the proposed empirical formula for the dimensionless lever arm. • An elementary capacity model is obtained using a hybrid FEM-Analytical approach. • A FE model has been calibrated on the experimental cyclic response of a CLT wall. • The plasticization of the CLT floor base of the wall limits the wall capacity. • In-plane deformability of CLT wall with door openings influences the wall capacity. • Platform framed buildings wall capacity rapidly decrease with door opening length. [ABSTRACT FROM AUTHOR]

Friction-based dampers are a valid solution for non-invasive seismic retrofitting interventions of existing structures, particularly reinforced-concrete (RC) structures. The design of friction-based dampers is challenging: underestimating the slip force prevents the full use of the potential of the device, which attains the maximum admissible displacement earlier than expected. By contrast, overestimating the slip force may cause delayed triggering of the device when the structure has suffered extensive damage. Therefore, designing the appropriate slip force is an optimization problem. The optimal slip force guarantees the highest inter-story drift reduction. The authors formulated the optimization problem for designing a specific class of friction-based dampers, the asymmetric friction connection (AFC), devised as part of the ongoing multidisciplinary Horizon 2020 research project e-SAFE (Energy and Seismic AFfordable rEnovation solutions). The seismic retrofitting technology involves the external application of modular prefabricated cross-laminated timber (CLT) panels on existing external walls. Friction dampers connect the CLT panels to the beams of two consecutive floors. The friction depends on the mutual sliding of two metal plates, pressed against each other by preloaded bolts. This study determines the optimal slip force, which guarantees the best seismic performance of an RC structural archetype. The authors investigate the nonlinear dynamic response of a coupled mechanical system (RC frame-friction damper) under a set of strong-motion earthquakes, using non-differential hysteresis models calibrated on the experimental cyclic responses. The solution of the optimization leads to the proposal of a preliminary simplified design procedure, useful for practitioners. • e-CLT is a seismic retrofit system for RC frames developed within Horizon 2020. • Proposal of a simplified design strategy for e-CLT. • Modeling of the response of an RC frame equipped with the e-CLT friction connection. • Experimental tests and calibration of a Coulomb-like hysteresis model. • Optimization of the slip force in the friction connection. • The optimum slip is associated with the yielding displacement of the RC frame. [ABSTRACT FROM AUTHOR]

The piles represent the most vulnerable structural components in Integral Abutment Bridge (IAB). They must adsorb the thermal deformation and the seismic loading transferred from the superstructure to the substructure. The use of pre-holes filled with high-damping material represents a possible solution for enhancing the dissipative performance of reinforced concrete (RC) piles in IABs. This paper presents the experimental tests of four RC pile specimens backfilled with different damping material to assess their effect on the soil-structure hysteretic response. The authors developed a physical hysteresis model of the soil-pile interaction to assess the optimum length of the damping pre-hole. Firstly, the model is calibrated to the experimental tests. Then the authors extrapolated the hysteresis models to full-scale specimens to estimate their optimum design in practical applications. • Experimental tests of piles with pre-hole filled with high-damping material. • The use of rubber particles or foam reduces pinching effects due to soil and reinforced concrete. • The experimental backbone is independent of the damping features of the soil. • Development of a physical hysteresis model of the soil-pile interaction based on a Winkler plane beam. • The optimum length of the pre-hole ranges between 0.1% and 0.15% the pile length. [ABSTRACT FROM AUTHOR]

• Pseudo-static cyclic tests on Cross-Lam Timber (CLT) and Light Timber Frame (LTF) shear walls. • Decomposition of the post-elastic displacement into sliding, rocking and deformation components. • Similarity of the two structural responses due to the same resisting mechanism. • A capacity model based on the sole hold-down reaction seizes the overall cyclic response. • The estimated overstrength factors manifests the intrinsic differences between the two structural systems. Cross Laminated Timber (CLT) and Light Timber Frame (LTF) shear walls are widespread constructive technologies in timber engineering. Despite the intrinsic differences, the lateral response of the two structural systems may be quite similar under specific connection layouts, boundary constraints, and size of the shear walls. This paper compares the experimental cyclic responses of CLT and LTF shear walls characterized by the same size 250×250cm, and loaded according to the EN 12512 protocol. The rigid-body rotation of the shear walls prevails over the deformation and rigid-body translation in the post-elastic displacement range. As a consequence, a capacity model of the two systems based on the sole hold-down response accurately seizes the observed cyclic response, despite ignoring the other resisting contributions. The authors examine the differences exhibited by the CLT and LTF shear walls and the related error corresponding to a capacity model based on the sole hold down restraints. Additionally, it is assessed the overstrength of the CLT panel and LTF sheathing to the shear walls collapse due to the hold-down failure. The estimated overstrength factor is the most meaningful difference between the two structural systems in the considered experimental layouts. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental campaign in Macerata (Italy). In the first step, the research addresses the site characterization by presenting the in situ and laboratory examinations results. In a second step, the study focuses on the more in-depth interpretation of the raw signals acquired by the SDMT in the 100 m deep borehole. The cross-correlation between SDMT signals represents the standard method to estimate the velocity of the shear waves. The authors attempted to assess any dependency of the shear wave velocity on the wavenumber by applying a moving bandpass filtering to the signals acquired in the 100 m deep borehole. In seismic engineering practice, the standard mechanical models of soils are representative of non-dispersive media. This assumption originates from the scarcity of experimental investigations on the dispersion laws of soils and the confidence in dispersion's possibly negligible effect. However, a purely non-dispersive medium does not exist, and all media do show some dispersion features: the phase velocity of shear waves may depend on the wavenumber. • Geotechnical characterization of a site in Macerata (Italy). • Estimate of the velocity of propagation of the shear waves using the seismic dilatometer. • Estimate of the dispersion curves of the shear waves. • The dispersion curves tend to infinity as the wavenumber tends to zero and lower to zero as the wavenumber raises. • The standard estimate of the shear waves may lead to a conservative soil classification. [ABSTRACT FROM AUTHOR]

• Reliability methods drive the assessment of overstrength ratios in Cross Laminated Timber structures. • There is a satisfactory agreement between the experimental lateral response of Cross-Laminated Timber panels and the simulations based on the Extended Energy-dependent Generalized Bouc-Wen model. • Given a certain failure probability, the overstrength factor is estimated as the ratio between the failure Peak Ground Acceleration of the ductile and brittle system. • The obtained overstrength ratios range between 1.5 and 2.5. • The obtained overstrength ratios are in accordance with those obtained by other scholars following non-probabilistic approaches. The ductile collapse mechanisms of structures should be less resistant than the brittle mechanisms to ensure a ductile seismic response: in this way, the ductile mechanisms activate before the brittle ones. This sort of chronological law of collapse is obtained in the design phase by providing a proper "overstrength" to the brittle mechanisms. The realization of overstrength plays a crucial role in the design, and several studies endeavoured to estimate the best overstrength factors, defined as the ratio between the characteristic load-carrying capacity of the non-ductile element and the characteristic load-carrying capacity of the ductile element. In this paper, the conventional definition of overstrength is discussed and compared to a probabilistic definition based on reliability methods. The probabilistic definition of overstrength drives the assessment of the overstrength factors of Cross-Laminated Timber buildings using a sort of indirect approach. The Extended-Energy dependent generalized Bouc-Wen model is used to estimate the nonlinear seismic response of a set of Cross-Laminated Timber shear walls with different ductility. The results are compared with the existing formulations, attempting to draw correlations possibly useful in the design phase. [ABSTRACT FROM AUTHOR]

• Long-term monitoring of seven modes in the frequency range 0–5.5 Hz using a modal tracking algorithm. • Detection of negative temperature-natural frequencies correlations. • Notable decreasing of the natural frequencies over time due to progressive loss of stiffness: approximately 0.1 Hz in two years. • Detection of frequency veering and mode interaction phenomena due to temperature fluctuations. • Presence of both positive and negative correlations between temperature and the crack amplitude. The Santa Maria di Collemaggio basilica is a 13th-century masonry masterpiece. The restoration works following the 2009 earthquake in L'Aquila included the installation of a permanent monitoring system. Crack gauges monitor a few significant cracks that appeared during the 2009 earthquake. Force-Balance accelerometers record the dynamic response of the entire structure. The dynamic response to ambient excitation leads to the estimation of the modal parameters. The current paper reports the outcomes of two years of static and dynamic monitoring from 1/1/2018 to 31/12/2019. The authors correlated the outdoor temperature and relative humidity to both the amplitude of the cracks and the modal parameters. The temperature deeply affects the static and dynamic response of the basilica. However, the linear correlations between the temperature and the structural response are diverse. There are cracks which stretch when the temperature rises and cracks which act oppositely. Natural frequencies lower when the temperature rises, while the same modes exhibit modal interaction phenomena. Furthermore, the natural frequencies of the basilica are not stationary but are moderately declining across the years. The basilica is a complex structure, where the different constitutive behaviour of three different materials, masonry, steel and timber may yield a varied structural response. The authors attempt to provide a qualitative interpretation of the observed behaviour, namely the detected correlations to the outdoor temperature, the lowering of the natural frequencies across the years and mode interaction phenomena. [ABSTRACT FROM AUTHOR]

The authors examined the dynamic behaviour of seven concrete box-girders of the A24 Italian motorway. The bridge spans derive from the same design and are nominally identical. However, they manifest a varied dynamic response, imputable to several factors. Some discrepancies may originate from the construction time, due to geometrical irregularities and unlike concrete curing. Others may descend from the time-degradation, soil-substructures interactions and other modifications in the boundary restraints, like the substitution of the original rack and roller bearings with multi-directional pots. The first bending mode shape is negligibly affected by the specific bearing, and the corresponding natural frequency has a marked dependence on the values of the Elastic Modulus, obtained from static load tests. The Least-Squares fit between the Elastic Modulus from static load tests and the first natural frequency matches with the corresponding expression of a simply-supported beam model. Conversely, the second mode shape, which is mainly torsional, is likely to be more sensitive to the bearings. The authors endeavored to estimate the values of two equivalent torsional springs, representatives of the actual restraint conditions by maximizing the Modal Assurance Criterion (MAC) between analytical and experimental mode shapes. The analytical mode shape is the solution of the equation of motion for free torsional vibration, with warping stiffness and warping inertia both neglected. The obtained values reported as the ratio between torsional stiffness of the boundary spring and the torsional stiffness of the beam cross-section yield the estimate of the vertical restraint offered by the two different typologies of bearings: the rack and roller and the multi-directional pot. The study encompasses the analysis of the outcomes of the dynamic identification and an elementary model updating. [ABSTRACT FROM AUTHOR]