Geert Lombaert

KU Leuven | ku leuven · Department of Civil Engineering

Natural frequencies are probably the most widely used modal characteristics in vibration-based monitoring. However, they can be highly influenced by temperature and this influence can completely mask the effect of even severe damage. This translates into a necessity for time-consuming data-normalization techniques to remove the influence of tempera...

In this work, a reinforced concrete slab bridge (instrumented and tested in 2018) is investigated. Based on field data, a finite element model of the bridge is calibrated. Model selection is performed both based on log evidence and posterior predictive capabilities. It is investigated if the models selected based on the log evidence also induce the...

This paper investigates how seismic metamaterials can mitigate environmental ground vibration in a wide frequency band (1 − 80 Hz). This is accomplished by placing surface resonators on the transmission path. Each resonator is composed of a vertical oscillator on top of a foundation. Detailed models based on two-and-a-half dimensional (2.5D) and th...

The current tendency to increase the lifetime of reinforced concrete (RC) structures creates concerns about their serviceability and safety. Reinforcement corrosion is the most common deterioration process in RC, which can severely decrease the structural capacity. Corrosion causes a reduction of the rebar’s cross section, cracking and spalling of...

Current practice is mostly focused on prescriptive design approaches where the performance of the structure in case of fire is assessed based on its performance in standardized fire tests. Those tests indicate whether the structural member can withstand standardized ISO 834 fire exposure for a certain code specified time. This method however does n...

This paper presents novel measurement data on the dynamic soil–structure interaction of an end-bearing pile foundation. The purpose is to assess the ability to predict the foundation impedances based on the small-strain properties of the soil obtained from site investigations. Measurements were performed in two stages of construction, allowing to a...

This paper presents a computational model for unreinforced masonry structures, where softening plasticity describes the behavior of the mortar joints, while a brittle phase-field model accounts for fracture in the bricks. The governing equations are derived in an energetic framework, ensuring variational and thermodynamic consistency, while taking...

The diffuse sound transmission through a wall or floor can be efficiently computed with a hybrid approach. The wall is then modelled deterministically as finite size effects and modal behaviour can be important in the considered frequency range, while the rooms carry a diffuse field and are modelled as stochastic subsystems. The finite element meth...

In this paper, the feasibility of structural health monitoring based on natural frequencies is investigated for a steel bowstring railway bridge in Leuven, Belgium. The data used in the study are obtained from an ongoing long-term monitoring campaign on the railway bridge and include acceleration measurements on the bridge deck and the arches. Duri...

One of the main causes of deterioration in reinforced concrete (RC) structures is corrosion of the steel rebars. Therefore, efficient and reliable monitoring techniques are crucial to assess the damage. The acoustic emission (AE) technique is a promising non-destructive technique (NDT) to obtain such results. The initiation of new cracks and propag...

Engineering problems are often characterized by significant uncertainty in their material parameters. A typical example coming from geotechnical engineering is the slope stability problem where the soil’s cohesion is modeled as a random field. An efficient manner to account for this uncertainty is the novel sampling method called p-refined Multilev...

We present a Bayesian framework for model-based optimal sensor placement. Our interest lies in minimizing the uncertainty on predictions of a particular response quantity of interest, with parameter estimation being an intermediate step for this purpose. By developing a methodology that targets prediction inference rather than parameter inference,...

A method to minimize the economic cost of the structural design of spatial reinforced concrete (RC) frame structures is presented. SAP2000 is used as computational engine, taking into account modelling aspects such as static soil structure interaction (SSSI). The optimization problem is formulated to properly reflect an actual design problem, limit...

Environmental vibrations induced by human activities such as traffic, construction or industrial manufacturing can cause disturbance among residents or to vibration sensitive equipment in buildings. In Sweden, geological formations of soft clay overlying a stiff bedrock are soil conditions prone to ground vibrations that are encountered both in urb...

This paper presents a novel strategy for structural topology optimization considering damage. In engineering practice, structures are typically designed to have a certain load‐bearing capacity, with a minimal material volume or cost. We aim to optimize the topology of a structure to have a minimal weight while guaranteeing a predefined load capacit...

Shell structures are material efficient structures capable of covering large spans with minimum weight. If concrete is used as the building material for the shell, it must be initially supported by a formwork. These generally rigid formworks, and their supporting falsework structure, are time and material consuming to construct. Recently, researche...

Reinforced concrete structures are often subjected to corrosion, inducing a decreasing reliability over time. This corrosion often exhibits spatial variation, which can be modelled by random fields. To improve the accuracy of the estimated reliability, measurements can be performed. In this work, focus will be on static strain data. Taking into acc...

Engineering problems are often characterized by significant uncertainty in their material parameters. Multilevel sampling methods are a straightforward manner to account for this uncertainty. The most well known multilevel method is the Multilevel Monte Carlo method (MLMC). First developed by Giles, see [1], this method relies on a hierarchy of suc...

The production and processing of building materials is responsible for a significant share of global greenhouse gas emissions. Nevertheless, in current building practice, a lot of material is wasted, because load-bearing structures are often grossly overdimensioned. Numerical optimization tools have the potential to reduce the consumption of struct...

Prestressed structures are commonly used all over the world. They might be subjected to degradation, such as corrosion of the prestressing steel. This can influence the resistance of these structures and induce early failure. Hence, prediction of the corrosion level is important in the assessment of existing prestressed structures. For this purpose...

The decay phase can have an important role in the behaviour and failure of the structure during and after a fire, and therefore, it should be properly defined. The most commonly used method to define natural fire exposure, the Eurocode parametric fire curve (EN 1991-1-2:2002), adopts a simplified linear approximation of the fire decay phase with a...

Before implementing a bridge monitoring strategy, a bridge manager would like to know the return on investment. Moreover, in order to spend the available budget as efficiently as possible, the monitoring strategy should be optimized, i.e., the type of measurements but also the time and locations at which these are performed. For this purpose, the V...

Quasi-periodic structures, as found in multi-span bridges, multi-bay and multi-storey buildings, are often characterized by a high modal density, even at low frequencies. This clustering of modes poses challenges in operational modal analysis, as well as in finite element model updating, where a pairing of experimental and numerically predicted mod...

This paper presents a dissipation‐based path‐following technique for the phase‐field approach to brittle and ductile fracture. This technique allows to compute the postpeak response of solids loaded by external forces and snap‐backs in the softening stage. By controlling the dissipated energy during loading, the solid is prevented from unloading el...

Stiff wall barriers can be effective in reducing the transmission of environmental ground vibration. As double walls are used in building acoustics in order to realize a high level of sound insulation, the potential of using double jet-grout walls in reducing ground vibration transmission is investigated in this paper. The three-dimensional free fi...

This paper reports on an extensive measurement campaign in a three-storey office building close to a ballasted track on embankment. Dynamic soil characteristics are determined by means of in situ geophysical tests. A coupled Finite Element-Boundary Element (FE-BE) model of the reinforced concrete building, accounting for soil-structure interaction,...

Predicting the dynamic response of long multi-span railway bridges with 3D element-based models is a computationally challenging task, especially if dynamic soil-structure interaction (SSI) is to be accounted for. In this paper, the wave finite element method (WFEM) is used to exploit periodicity. The methodology fully accounts for wave propagation...

A method to minimize the cost of the structural design of reinforced concrete structures using Biogeography-Based Optimization, an evolutionary algorithm, is presented. SAP2000 is used as computational engine, taking into account modelling aspects such as static soil-structure interaction (SSSI). The optimization problem is formulated to properly r...

The governing equations of the variational approach to brittle and ductile fracture emerge from the minimization of a non-convex energy functional subject to irreversibility constraints. This results in a multifield problem governed by a mechanical balance equation and evolution equations for the internal variables. While the balance equation is su...

Metaheuristic optimization algorithms are strongly present in the literature on discrete optimization. They typically 1) use stochastic operators, making each run unique, and 2) often have algorithmic control parameters that have an unpredictable impact on convergence. Although both 1) and 2) affect algorithm performance, the effect of the control...

The capability to analyze structures under static and dynamic loads is an essential skill for structural engineers. Structural analysis therefore is a key component in civil and architectural engineering education, where analytical methods are traditionally complemented by the use of (commercial) software packages. The latter are often closed sourc...

This paper presents an efficient approach for the modal analysis of coupled soil-structure systems, for which the dynamic response is strongly influenced by the embedment in the soil. The methodology is based on a finite element-perfectly matched layer model that allows for the derivation of frequency-independent system matrices and the computation...

During recent years, thorough experimental and numerical investigations have led to an improved understanding of dynamic phenomena affecting the fatigue life and survivability of offshore structures, e.g., ringing and springing and extreme wave impacts. However, most of these efforts have focused on modeling either selected extreme events or sequen...

Modally reduced order models are commonly adopted in system inversion. Their observability requires specific attention, since these models only accurately describe the dynamic behavior of the underlying system in a limited frequency range. This paper elaborates a methodology to investigate the observability of modally reduced order models with unkn...

p>Existing concrete bridges can show signs of deterioration, e.g. due to corrosion, in which case the question arises whether these bridges still have an acceptable safety level. To obtain additional information about the state of the structure, different types of information can be gathered. However, the measurements performed are often not used d...

This book reports on the 13th International Workshop on Railway Noise (IWRN13), held on September 16-20, 2019, in Ghent, Belgium. It gathers original peer-reviewed papers describing the latest developments in railway noise and vibration, as well as state-of-the-art reviews written by authoritative experts in the field. The different papers cover a...

p>Many existing bridges are reaching the end of their technical service life. To estimate the remaining lifetime of reinforced concrete structures, it is important to assess the parameters of the corrosion process (i.e. parameters governing the corrosion propagation, but also parameters of the chloride or carbonation ingress). The level of corrosio...

p>Railway bridge KW51 in Leuven, Belgium, has been monitored since October 2018 with the aim of constructing a digital twin, i.e. a virtual representation that mimics the behaviour of the actual struc- ture. A linear finite element model of the bridge was updated using measurements carried out on the bridge. The pot bearings of the bridge, however,...

p>Numerical optimization has a large potential in the context of structural design, but practical applications remain scarce. Even metaheuristic algorithms, which are easy to use, are rarely adopted in practice. Possible explanations are the fact that for problems with many design variables, metaheuristic algorithms converge slowly, and that struct...

p>Railway bridge KW51 in Leuven, Belgium, has been continuously monitored since October 2018. During the monitoring, the bridge was retrofitted to resolve a construction error that was noticed during inspection. The aim of the measurements is twofold. First, the strain measurements on the bridge deck are used to validate virtual strain sensing, whi...

This paper presents the results of an operational modal analysis on a self-supporting antenna mast. The structure is instrumented with seismic accelerometers, which are moved in different setups for a detailed characterization of the mode shapes. In addition, eight strain gauges are installed, two at the bottom of each leg of the tower. Two particu...

Engineering problems are often characterized by significant uncertainty in their material parameters. A typical example coming from geotechnical engineering is the slope stability problem where the soil's cohesion is modeled as a random field. An efficient manner to account for this uncertainty is the novel sampling method called p-refined Multilev...

The governing equations of the variational approach to brittle and ductile fracture emerge from the minimization of a non-convex energy functional subject to irreversibility constraints. This results in a multifield problem governed by a mechanical balance equation and evolution equations for the internal variables. While the balance equation is su...

Structural optimization has been extensively studied for decades, motivated by expected savings in material costs and engineering efforts in the design of loadbearing structures. The potential of optimization methods in the construction sector is high, but practical applications remain scarce, which may be explained by the fact that most test probl...

In many countries concrete bridges are reaching the end of their service-life, showing signs of deterioration, e.g. due to corrosion. Hence, the question arises whether their safety level is still acceptable. To improve the estimate of the safety level, information extracted from different tests, e.g. proof-loading, operational modal analysis, etc....

Pre-posterior analyses can be used to determine the value of information (VoI) of inspection strategies. As such, decisions can be made on whether or not it is relevant to perform inspections and to what extent this is the case, before these are implemented. In this article, a pre-posterior analysis framework is developed for degrading (concrete) s...

Although wave-wave interaction phenomena in random seas have shown to lead to a departure from Gaussian statistics and therefore to a higher occurrence of extreme waves, they are usually not taken along in the assessment of the dynamic behaviour of offshore structures. Supported by a rapid increase of computational resources, the use of Computation...

The vibration serviceability assessment of footbridges under pedestrian traffic requires a probabilistic approach considering the uncertainty in the dynamic behavior of the structure and the variability of multiple load parameters, such as the pedestrians' arrival time and step frequency. In view of engineering applications, a major challenge lies...

This paper focusses on topology optimization of support structures for metal-based additive manufacturing. Processes based on powder bed fusion are subjected to deformations during manufacturing due to large thermal stresses. Controlling these deformations by adding temporary support structures is essential in guaranteeing qualitative end products...

Fatigue is mostly the governing design criterion in girder steel bridges due to the presence of critical welded details. In this research, the hot spot stresses in welded cruciform duplex stainless steel joints are measured experimentally using digital image correlation as well as traditional strain gauges. They are also computed via FEM. The deduc...

Timber joist floors are widely applied in residential buildings. The accurate prediction of the sound radiated by timber joist floors is challenging due to the interaction between the impacting mass and the floor, orthotropy of the joist and plate components, the effects of the floor size and boundary conditions, etc. In the present work, state-of-...

Civil engineering applications are often characterized by a large uncertainty on the material parameters. Discretization of the underlying equations is typically done by means of the Galerkin Finite Element method. The uncertain material parameter can be expressed as a random field represented by, for example, a Karhunen–Loève expansion. Computatio...

This paper presents a geometric algorithm to investigate the theoretical observability of nonlinear systems with partially measured inputs and outputs. The algorithm is based on Lie algebra and applies to systems whose state and measurement equations are analytical and affine in all inputs. It investigates whether the system satisfies a necessary o...

This paper presents a novel algorithm for joint input-state-parameter estimation in structural dynamics. The algorithm is derived from an existing smoothing algorithm. In each time step, the system model adopted in the joint input-state-parameter estimation is linearized around the current state, yielding an algorithm similar to the extended Kalman...

When predicting the radiation of structure-borne sound into a room, it is often assumed that the generated sound field is diffuse. A diffuse field is by definition a random field, composed of a large number of statistically independent plane waves, the spatial phase of which is uniformly distributed and independent from the amplitude. It may repres...

Finite element (FE) model updating is often used as a non-destructive method to detect structural damage. Stiffness parameters of an FE model of the structure are calibrated based on experimental vibration data. If the desired spatial resolution is high, the problem is likely to be ill-conditioned and requires regularization. Tikhonov regularizatio...

Strained gridshells are reticulated shell structures that are erected from a flat grid of initially straight laths. The structural efficiency of a gridshell is determined by its shape, which is traditionally designed using form-finding techniques. However, these techniques are primarily used to generate structures in pure tension or compression for...

Practical structural engineering problems are often characterized by significant uncertainties. Historically, one of the prevalent methods to account for this uncertainty has been the standard Monte Carlo (MC) method. Recently, improved sampling methods have been proposed, based on the idea of variance reduction by employing a hierarchy of mesh ref...

Practical structural engineering problems are often characterized by significant uncertainties. Historically, one of the prevalent methods to account for this uncertainty has been the standard Monte Carlo (MC) method. Recently, improved sampling methods have been proposed, based on the idea of variance reduction by employing a hierarchy of mesh ref...

This paper focuses on topology optimization for additive manufacturing. In order to ensure that the optimized design is immediately manufacturable, it is essential to take into account the appropriate geometric constraints during the optimization. Two important constraints are minimum length scale and maximum overhang angle. A minimum length scale...

Practical structural engineering applications tend to exhibit a certain degree of uncertainty in their material parameters, loading forces and so forth. As such, the accurate quantification of the effect of those uncertainties is of capital importance. The standard Monte Carlo method is one of the most common sampling methods used to compute this e...

This presentation discusses an algorithm for simultaneously optimizing the size, shape and topology of reticulated shell structures subjected to distributed loads using gradient-based algorithms. To make the optimization problem compatible with such algorithms, it is reformulated in terms of continuous variables. Furthermore, more realistic loads a...

The potential use of pile barriers as a ground vibration mitigation measure is analysed through an efficient numerical model. The soil is modelled as an elastic half space, using the reciprocity theorem and specific Green’s functions for the layered half space, while the piles are treated as beam elements. After benchmarking the proposed model agai...