Academic literature on the topic 'Diagnosis of timber structures'

The paper presents a survey of state-of-the-art nondestructive and semi-destructive diagnostic techniques of testing timber structures and examples of their application. Nondestructive testing is a field of study which covers: identifying the mechanical and physical properties of materials and structural components, detecting material defects and discontinuities, and measuring the geometric dimensions of objects without affecting their performance. The nondestructive and semi-destructive methods are described in a systematic manner and the relevant equipment, technology and applications are discussed. The paper focuses on acoustic methods, resistance drilling techniques and radiography, which are suitable for detecting internal defects, decay and cracks, determining the location and dimensions of degraded areas and assessing the mechanical properties of structural timber members. Much attention is devoted to the techniques that are used in practice and have shown significant promise for future development. The results of several drilling resistance tests carried out on historic timber structures are presented.

Synthetic methods for the diagnosis of structures and particularly for their vulnerability assessment rely on simplified calculations and visual inspection. Their effectiveness strongly depends on an accurate calibration of the procedure by which data are collected. A recent methodology for the seismic vulnerability assessment of timber roofs in historical buildings has been applied to the Thun Castle during a study for its rehabilitation. The purpose was twofold: testing and calibrating the procedure on a heritage structure and estimating the capability of the roof structure to resist seismic action, as required in a zone of low but not negligible seismicity.

The paper presents an overview on the timber structures of the Royal Palace of Naples. Focusing on the roofs of the Historical Apartment, located at the second level of the palace, different structural typologies are illustrated. The structural identification was achieved starting from an extensive in situ survey, aimed at assessing materials, conservation state, geometries and static schemes. Therefore 3D FEM models of the study systems as whole were set up and the structural analyses carried out, allowing to catch the weaknesses in terms of strength and deformation capacities; the safety checks were performed according to Eurocode 5 provisions. Finally, on the basis of the acquired knowledge, the appropriate retrofitting techniques were suggested [1, . In particular, with reference to the Diplomatic Hall (II), details of the realized restoration interventions, based on mixed technologies, are presented [.

Grading of timber for structural purposes allows material with similar physical and mechanical properties to be grouped together. The groups are defined by specific strength values and indicate the basic working stresses and stiffnesses to be used for structural design purposes. In particular, visual strength grading bases the assignment of each timber element to a grade on the characteristics that are visually measurable (i.e. knots, slope of grain, annual ring width). Very similar principles are implemented for the in situ assessment of timber structures, as recommended for example by the Italian standard UNI 11119, that specifies the procedures for the diagnosis of timber members. Currently, however, European standards and most of the national standards on strength grading refer to timber elements with rectangular cross section, while in existing buildings, members with irregular cross section are extremely common. Thus, 10 different provenances (5 from Italy and 5 from France) of chestnut timber were sampled. More than 600 structural elements with wane were visually examined in laboratory and all the characteristics were collected. Bending tests were then performed on each timber element until failure, and bending strength, as well as modulus of elasticity and density, were determined. Here, the limitations for the main strength-reducing characteristics and the characteristic values (fifth percentile for bending strength and density and the mean value for modulus of elasticity) of chestnut timber with wane are presented.

Purpose – Deterioration of timber bridges can often be related to a number of deficiencies in the bridge elements, connectors and/or as a result of been in aggressive environments which they are exposed to. The maintenance cost of timber bridges is affected significantly by a number of deterioration mechanisms which require a systematic approach for diagnosis and treatment. Evaluating the risk of failure of these bridges is of importance in bridge performance assessment and decision making to optimize rehabilitation options. The paper aims to discuss these issues. Design/methodology/approach – This paper identifies common causes for timber bridge deterioration and demonstrates an integrated approach based on fault tree analysis to obtain qualitative or quantitative estimation of the risk of failure of timber bridge sub-systems. Level 2 inspection report for a timber bridge in Queensland, Australia has been utilized as a case study in this research to identify the failure modes of the bridge. Findings – A diagnostic tool for timber bridge deterioration will benefit asset inspectors, managers, and engineers to identify the type, size and the distress mechanisms in order to recognize the proper corrective measures either to prevent or to reduce further deterioration. Timber bridge maintenance is a major issue in Queensland, Australia. If a decision support tool can be developed, it will benefit road authorities and local councils. Originality/value – Timber bridge maintenance is a major issue in Queensland, Australia. If a decision support tool can be developed as initiated in this research paper it will benefit road authorities and local councils.

PurposeThe maintenance of original building materials is crucial to extending their lifetime and avoiding their repeated replacement in heritage buildings. In order to maintain the identity of built heritage and resolve possible deterioration over the years, special expertise is required to avoid possible materials decay and to preserve building elements in a way that allows them to function efficiently as originally intended.Design/methodology/approachAn expert system is created to identify the most effective method of repair for each specific building material and to propose the appropriate conservation methods for resolving different types of damages. Artificial intelligence is used to provide a systematic problem-solving technique that saves time and provides the most efficient conservation and preservation method for heritage building elements.FindingsThose expert systems could be generalized on similar historical structures to be used as a systematic guide for examining material, evaluating deterioration state and objectively suggesting their related repair techniques. Further deteriorated materials in heritage buildings should be investigated, such as stone and timber staircases, to provide a guide for usage by restoration and conservation authorities.Originality/valueUsing a user-friendly method, with special considerations to three major problematic building elements in terms of decay and material dysfunction in heritage structures, timber doors, iron gates, and ceiling paintings are selected for diagnosis and repair in an Egyptian heritage building.

The aim of the project that is described in this paper was to define a four-level timber frame survey mode of a historical building: the so-called “Andlau's Seigniory”, Alsace, France. This historical building was built in the late XVIth century and was in a stage of renovation in order to become a heritage interpretation centre. The used measurement methods combine Total Station measurements, Photogrammetry and 3D Terrestrial Laser scanner. Different modelling workflows were tested and compared according to the data acquisition method, but also according to the characteristics of the reconstructed model in terms of accuracy and level of detail. 3D geometric modelling of the entire structure was performed including modelling the degree of detail adapted to the needs. The described 3D timber framework exists now in different versions, from a theoretical and geometrical one up to a very detailed one, in which measurements and evaluation of deformation by time are potentially allowed. The virtually generated models involving archaeologists, architects, historians and specialists in historical crafts, are intended to be used during the four stages of the project: (i) knowledge of the current state of needs for diagnosis and understanding of former construction techniques; (ii) preparation and evaluation of restoration steps; (iii) knowledge and documentation concerning the archaeological object; (iv) transmission and dissemination of knowledge through the implementation of museum animations. Among the generated models one can also find a documentation of the site in the form of virtual tours created from panoramic photographs before and during the restoration works. Finally, the timber framework model was structured and integrated into a 3D GIS, where the association of descriptive and complementary digital documents was possible. Both offer tools leading to the diagnosis, the understanding of the structure, knowledge dissemination, documentation and the creation of educational activities. The integration of these measurements in a historical information system will lead to the creation of an interactive model and the creation of a digital visual display unit for consultation. It will be offered to any public to understand interactively the art of constructing a Renaissance structure, with detailed photos, descriptive texts and graphics. The 3D digital model of the framework will be used directly in the interpretation path, within the space dedicated to “Seigniory” of Andlau. An interactive touch-screen will be installed. It will incorporate several levels of playgrounds (playful, evocative and teaching). In a virtual way, it will deal with the different stages of building a wooden framework and clarify the art of construction.

Master’s thesis „Behavioral studies of the timber footbridges structures“ deals with static models of timber footbridges. This thesis mainly consists of the behavioral study of historical timber footbridge in the village of Černvír in Vysočina. Based on the actual design of the bridge a three-dimensional beam model was created. This thesis also includes two contemporary alternatives of timber covered bridges. The individual structural elements were assessed according to the applicable standards. To analyze the model FEM program SCIA Engineer 2012 was used.

The diploma thesis deals with building survey of the New synagogue in Velké Meziříčí. It is focused on diagnostics of timber structures using non-destructive and semi-destructive testing methods, such as visual inspection, moisture content measurement, penetration depth of a steel pin measurement and endoscopy. The aim of the thesis is to evaluate the condition of the timber structures according to the results of the building survey.

Key point to development of environmentally friendly timber structures, appropriate to urban ways of living, is the development of high-rise timber buildings. Comfort properties are nowadays one of the main limitations to tall timber buildings, and an enhanced knowledge on damping phenomena is therefore required, as well as improved prediction models for damping. The aim of this work has consequently been to estimate various damping quantities in timber structures. In particular, models have been derived for predicting material damping in timber members, beams or panels, or in more complex timber structures, such as floors. Material damping is defined as damping due to intrinsic material properties, and used to be referred to as internal friction. In addition, structural damping, defined as damping due to connections and friction in-between members, has been estimated for timber floors. The thesis consists of six main parts. The first part is entitled “Contexts”, and is composed of four chapters. A general overview of the wood material and its structural use in buildings is presented in Chapter 1. Chapter 2 gives a thorough literature review on comfort properties of (timber) floors. Chapter 1 and Chapter 2 serve as justifications for the motivation of this work, expressed in Chapter 3, and the aim of the work, expressed in Chapter 4. The next part “Backgrounds” briefly describes the basic theories used along the thesis, for the analytical studies (Chapter 5), the experimental studies (Chapter 6), and the numerical studies (Chapter 7). The part “State of the art” is a general literature review on damping (Chapter 8). A particular accent is set on the derivation of various damping prediction models. The “Research” part summarizes the original research work. Chapter 9 briefly presents the background and main findings for each study, and Chapter 10 concludes and proposes suggestions for further research. The studies are detailed in four journal papers, which are integrally reported in the “Publications” part. Paper I focuses on the evaluation of material damping in timber beam specimens with dimensions typical of common timber floor structures. Using the impact test method, 11 solid wood beams and 11 glulam beams made out of Norway Spruce (Picea Abies) were subjected to flexural vibrations. The tests involved different spans and orientations. A total of 420 material damping evaluations were performed, and the results are presented as mean values for each configuration along with important statistical indicators to quantify their reliability. The consistency of the experimental method was validated with respect to repeatability and reproducibility. General trends found an increasing damping ratio for higher modes, shorter spans, and edgewise orientations. It is concluded from the results that material damping is governed by shear deformation, which can be expressed more conveniently with respect to the specific mode shape and its derivatives. Paper II deals with the prediction of material damping in Timoshenko beams. Complex elastic moduli and complex stiffness are defined to derive an analytical model that predicts the hysteretic system damping for the whole member. The prediction model comprises two parts, the first related to bending, and the second related to shear. Selected experimental damping evaluations from Paper I are used to validate the model and obtain fitted values of loss factors for two types of wood. The good agreement of the derived model with experimental data reveals an efficient approach in the prediction of material damping. In Paper III, a semi-analytical prediction model of material damping in timber panels is described. The approach is derived from the strain energy method and input is based on loss factors, which are intrinsic properties of the considered materials, together with material properties and mode shape integrals, whose calculation can easily be implemented in most finite element codes. Experimental damping evaluations of three types of timber panels are performed. These are particleboards, oriented strand board panels and structural laminated veneer panels. Fair goodness-of-fit between the experimental results and the prediction models reveals an efficient approach for the prediction of material damping in timber panels with any boundary conditions, knowing only the loss factors and the mode shapes. In Paper IV, dynamic properties of two timber floors are experimentally evaluated by impact method. Each floor uses one specified type of connectors, either screws or nails. A numerical model is developed using constrained degrees-of-freedom for the modeling of connectors. Numerical analyses have been performed, and show good agreement with experimental results. A procedure is written using the commercial finite element software Abaqus to predict material damping from a strain energy approach. Estimation of structural damping is performed as the difference between the experimentally evaluated total damping and the predicted material damping. The contribution from floor members to material damping is extensively investigated, and the needs for better prediction of damping are discussed. Specific details of some aspects of the work are included in the “Appendix” part.

Dissertação para obtenção do Grau de Mestre em Engenharia Civil – Estruturas e Geotecnia
This dissertation covers the study of historic timber roof structures in Transylvania area - Romania, the structures type, its elements and connection variety between them. Procedures to study a structure of this category are approached. It is also referred semi and non-destructive tests that can be done to better understand the present wood characteristics, and potential reparation or strengthening solutions for the structure in case it is necessary. Ultimately a case study is analyzed and some intervention solutions are proposed for a gothic structure type in the nave of Huedin Reformed church.

Increasingly complex architectural geometries present new challenges for structural engineers. Collaborative, digital workflows which integrate 3D parametric architectural models with Finite Element Modelling software grant structural engineers a higher degree of geometric versatility and influence during the preliminary design phase. Through integrated parametric design models – also labelled “co-rationalized” – structural engineers may not only easily respond to rapid model variations and unusual assemblies, but also inform the building design from inception. This thesis presents an example of a project executed in a co-rationalized manner through architectural and structural collaboration, using both digitally-integrated and analog models, for the design and construction of solid timber shells structures using Cross-Laminated Timber (CLT) panels. By exploring a co-rationalized design process, timber engineering details are identified and integrated into the architectural model, and the role of structural engineer takes an active rather than reactionary role in the preliminary design stages. The result of this process using integrated parametric models was the design, fabrication, and assembly of a folded plate wall prototype and three CLT panels with double curvature. This research demonstrates how collaboration and integrated modeling enables the realization of the architectural versatility that mass-timber has to offer, and the efficacy which co-rationalized design and integrated models can bring to orthodox and unusual structures alike. As a consequence, this research serves as a precedent for structural detailing-based generative architecture and collaborative work in the future.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

It is common practice in the analysis of structural frames, to either assume that the joints are pinned or rigid. In fact the real behaviour of a joint is neither pinned nor rigid, and lies somewhere between the pinned and rigid assumption. This is referred to as the semi-rigid behaviour. Semi-rigidity not only refers to the rotational behaviour of the joint as commonly studied, but also in axial and shear actions. The moment distribution between pinned and rigid analysis differs substantially and therefore a more accurate method of modelling the semi-rigid joint is necessary to predict the overall structure response. The level of semi-rigid behaviour varies in different joints due to the material, construction and type of connector. The degree of semi-rigidity can be determined through physical tests. The type of joint for this study is the Metal Plate Connector (MPC) for timber trusses, 6 chosen connector used in residential trusses. An extensive test program was carried out in this study. Four different types of joints of a Queen truss were tested. In addition, the effect of combined loads on the joint characteristics was investigated. The loading arrangement in the tests allowed independent control of the bending moment and axial load. A novel approach is adopted to measure displacement, using high-resolution digital photogrammetry and specially developed software. The data produced gave details of timber movement in cartesian co-ordinates and measurement of plate deformation. From these tests, semi-rigid bending moment and axial stiffness values were determined for use in the theoretical study. An attempt to measure shear stiffness is also presented. Further tests were carried out on full-scale trusses under two different load conditions. The theoretical work comprises two approaches to truss modelling. The first is an automated structural analysis program, which accounts for non-linear semirigid joint characteristics derived from the joint tests using the Foschi power function. The effects of stability and geometrical non-linearity are also implemented into the analysis. The second approach calculates truss response using Finite elements where 2-D planar elements were used to calculate the response of the truss. Parameters for the connection strength are derived from the joint tests. Moment stiffness and axial stiffness values of the connections were determined. Combined load tests showed that there is indeed a measurable effect on joint stiffness and capacity due to combined loads, some of which actually contribute to the stiffness, but also some which are detrimental. There is good correlation between the truss test results and the FE model using semi-rigid joints. However, results of the simpler non-linear frame analysis, did not compare so well, but nevertheless exhibited fundamental characteristics of the truss.

The present dissertation and its main subjects inquires into the pine and oak timber strength property changes-temperature relations. It also explores the behaviour of slender timber elements in axial compression at higher temperatures; and the comparative analysis of obtained results. The work seeks to accomplish the following major tasks: to obtain test data about the influence of high temperature on the properties of different natural – pine and oak – timber; to investigate the behaviour of slender timber elements under axial compression exposed to fire. Taking into account the investigated real fire effect to correct accordingly the existing in LST EN 1995-1-2 procedure for the fire resistance calculation of timber slender elements in compression. The dissertation consists of an introduction, five chapters, general conclusions, a list of references, a list of author’s publications on the dissertation subject, and 2 Annexes. Chapter 1 provides a literature review. It focuses on the publications inquiring into the loss of strength properties by timber at higher temperatures, the fire resistance of timber structures in compression. The chapter ends with the formulation of conclusions and the adjustment of research tasks. Chapter 2 offers the methodology of the research on strength properties of timber at higher temperatures, and the schemes of the developed testing equipment. Chapter 3 presents the procedure of the research on the behaviour of slender timber elements... [to full text]
Disertacijoje nagrinėjami pušinės ir ąžuolinės medienos stipruminių savybių pokyčių temperatūriniai sąryšiai bei medinių centriškai gniuždomų liaunų elementų elgsena veikiant aukštesnėms temperatūroms. Pagrindiniai tyrimo objektai yra Lietuvos spygliuočių ir lapuočių medienos savybių pokyčiai didėjant temperatūrai ir centriškai gniuždomų liaunų medinių elementų elgsenos veikiant kaitrai eksperimentiniai tyrimai bei rezultatų lyginamoji analizė. Darbe spręsti tokie pagrindiniai uždaviniai: gauti eksperimentinius duomenis apie aukštos temperatūros poveikį skirtingos natūralios – pušinės ir ąžuolinės – medienos savybėms, atlikti centriškai gniuždomų liaunų medinių elementų elgsenos ugnyje tyrimus. Atsižvelgiant į tyrinėtą tikrovišką gaisro poveikį patikslinti esamą EN 1995-1-2 medinių liaunų gniuždomų elementų atsparumo ugniai skaičiavimo metodiką. Disertaciją sudaro įvadas, penki skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai ir du priedai. Pirmasis skyrius skirtas literatūros apžvalgai. Jame pateikta darbų, kuriuose nagrinėjamas aukštesnės temperatūros veikiamos medienos, stipruminių savybių mažėjimas ir kuriuose pateikiami gaisro sąlygomis gniuždomų medinių elementų laikomosios galios tyrimų rezultatai. Pabaigoje formuluotos išvados ir disertacijos tikslai ir uždaviniai. Antrajame skyriuje pateikta medienos stipruminių savybių aukštesnėse temperatūrose tyrimo metodika ir sukurtų nestandartinių bandymo įrenginių schemos... [toliau žr. visą tekstą]

Taiwan is located in a highly seismic zone and the historical “Dieh-Dou” timber buildings, constructed without following any code or standard, are prone to collapse under earthquake. These buildings are unique and represent the culture, heritage and art of Taiwan, therefore need to be preserved while minimizing unnecessary intervention that could damage their authenticity.
This research comprises a thorough investigation on the parameters influencing the seismic vulnerability of the Dieh-Dou timber frames in Taiwan, and propose a methodology of assessment and a strategy for strengthening validated through experimental testing and numerical analysis.
After review existing literature and post-earthquake surveys, the failure modes of the buildings are identified, showing that the dislocation of the elements of the frame from the joints is the primary source of damage. An experimental investigation is carried out comprising both rotational and translational tests on full scale joint specimens which, together with a parametric study undertaken with an appropriate FE simulation, demonstrates how both the rotational and translational stiffness of the joints play a key role in defining the behaviour of these structures.
Lateral force, response spectrum, and step-by-step pushover analyses are performed and compared with the post-earthquake survey of two Dieh-Dou buildings seriously affected by the 1999 Chi-Chi earthquake. The results show that the proposed FE modelling can successfully be employed to assess the vulnerability of the frames.
Based on a damage level approach, an assessment methodology is suggested that would allow to optimisation of the strengthening strategy, permitting protection these precious structures from future earthquakes while avoiding unnecessary interventions.

Microfluidic lab-on-a-chip (MLOC) technology is a promising approach for point-of-care (POC) diagnosis; low reagent consumption, high sensitivity and quick analysis time are the most prominent benefits. However, microfabrication of MLOCs utilizes specialized techniques and infrastructure, making conventional fabrication time consuming and difficult. While relatively inexpensive production techniques exist for POC diagnoses, such as replication of polymer-based (e.g., PDMS) microfluidic POC devices on lithographic molds, this approach has limitations including: further hydrophilic surface modifications of PDMS, inability to change lithographic mold Z dimensions, and slow prototyping. In contrast, stereo-lithographical (SLA) printing can integrate all of the necessary fabrication resources in one instrument, allowing highly versatile microfluidic devices to be made at low cost. In this paper, we report two microfabrication approaches of microfluidics utilizing (SLA) 3D printing technology: I) Direct SLA printing of channels and structures of a monolithic microfluidic POC device; II) Indirect fabrication, utilizing SLA 3D printed molds for PDMS based microfluidic device replication. Additionally, we discuss previous work providing a proof of concept of applications in POC diagnosis, using direct 3D printing fabrication (approach I). The robustness and simplicity of these protocols allow integrating 3D design and microfabrication with smartphone-based disease diagnosis as a stand-alone system, offering strong adaptability for establishing diagnostic capacity in resource-limited areas and low-income countries.

Abstract The dynamic behavior of elastic joints strongly affect the dynamic performance of a jointed mechanical system. The dynamic contacts introduced by joint clearances create a system with nonlinear characteristics. Special effort needs to be made to study jointed mechanical systems. This paper presents an integrated joint dynamics system, which can be used to predict the dynamic characteristics of a newly designed structure, or to analyze an existing jointed structure. This joint dynamics system can also be applied as a real time monitoring and diagnosis system when it is connected with a vibration measuring device. The joint dynamics system includes: 1) a theoretical model of jointed structures, in which the joint clearance and joint friction effects are considered; 2) a stochastic simulator which is used to generate vibration data and evaluate system dynamic characteristics; 3) a diagnostic monitoring algorithm for vibration state detection; and 4) a forecasting vibration control scheme. The joint dynamics system is applied to the dynamic analysis of a truss-cell unit structure. The results presented in this paper show that the joint dynamics system is effective.

<p>Near real-time damage diagnosis of building structures after extreme events (e.g., earthquakes) is of great importance in structural health monitoring. Unlike conventional methods that are usually time-consuming and require human expertise, pattern recognition algorithms have the potential to interpret sensor recordings as soon as this information is available. This paper proposes a robust framework to build a damage prediction model for building structures. Support vector machines are used to predict the existence as well as the probable location of the damage. The model is designed to consider probabilistic approaches in determining hazard intensity given the existing attenuation models in performance-based earthquake engineering. Performance of the model regarding accurate and safe predictions is enhanced using Bayesian optimization. The proposed framework is evaluated on a reinforced concrete moment frame. Targeting a selected large earthquake scenario, 6,240 nonlinear time history analyses are performed using OpenSees. Simulation results are engineered to extract low-dimensional intensity-based features that can be used as damage indicators. For the given case study, the proposed model achieves a promising accuracy of 83.1% to identify damage location, demonstrating the great potential of model capabilities.</p>

Abstract Conventional reliability test using accelerated test is not suitable for selection of high-reliability LSI device, because it needs high cost and long testing time. Then observation methods such as construction analysis have been used in a part of the test. Construction analysis can detect faults on leads, packages wires and chip surfaces. However, recent LSI device structures have multilayers one, and most part of faults exist in inner layers. The faults are due to LSI wafer process imperfection such as inaccurate process design or device structural defects. LSI process diagnosis has been developed for the quality and reliability evaluation with the observation of device structures. It consists of fault detection and estimation of risk that the faults cause to fail more than one of devices through many manufacturing lots. Typically, cross sectional SEM for observation and data base or theory of reliability for risk estimation are used in this method.

The method of vibration diagnosis for power plant equipment is generally used the modal method using impact hammer. However, it takes a long time to measure and verify the response frequency which is associated with the specific resonant frequency. Therefore, this research deals with the simpler method comparing to the measured modal characteristics using impact hammer. To find an efficient vibration control method, the flexural response of structure and rotating machinery such as turbine, pumps, and generator which are commonly encountering in power plant equipment. The used eccentric mass shaker is a very powerful and available vibration diagnosis method to carry out forced vibration test on structures as well as rotating machines by means of generating a harmonic load. Through the experimental verification using the proposed vibration diagnosis, it is helpful and useful for site experts and practical engineers to evaluate the vibration resonance in field audits.

Radioactive waste systems and structures (RWSS) are safety-critical facilities in need of monitoring over prolonged periods of time. Structural health monitoring (SHM) is an emerging technology that aims at monitoring the state of a structure through the use of networks of permanently mounted sensors. SHM technologies have been developed primarily within the aerospace and civil engineering communities. This paper addresses the issue of transitioning the SHM concept to the monitoring of RWSS and evaluates the opportunities and challenges associated with this process. Guided wave SHM technologies utilizing structurally-mounted piezoelectric wafer active sensors (PWAS) have a wide range of applications based on both propagating-wave and standing-wave methodologies. Hence, opportunities exist for transitioning these SHM technologies into RWSS monitoring. However, there exist certain special operational conditions specific to RWSS such as: radiation field, caustic environments, marine environments, and chemical, mechanical and thermal stressors. In order to address the high discharge of used nuclear fuel (UNF) and the limited space in the storage pools the U.S. the Department of Energy (DOE) has adopted a “Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste” (January 2013). This strategy endorses the key principles that underpin the Blue Ribbon Commission’s on America’s Nuclear Future recommendations to develop a sustainable program for deploying an integrated system capable of transporting, storing, and disposing of UNF and high-level radioactive waste from civilian nuclear power generation, defense, national security, and other activities. This will require research to develop monitoring, diagnosis, and prognosis tools that can aid to establish a strong technical basis for extended storage and transportation of UNF. Monitoring of such structures is critical for assuring the safety and security of the nation’s spent nuclear fuel until a national policy for closure of the nuclear fuel cycle is defined and implemented. In addition, such tools can provide invaluable and timely information for verification of the predicted mechanical performance of RWSS (e.g. concrete or steel barriers) during off-normal occurrence and accident events such as the tsunami and earthquake event that affected Fukushima Daiichi nuclear power plant. The ability to verify the conditions, health, and degradation behavior of RWSS over time by applying nondestructive testing (NDT) as well as development of nondestructive evaluation (NDE) tools for new degradation processes will become challenging. The paper discusses some of the challenges associated to verification and diagnosis for RWSS and identifies SHM technologies which are more readily available for transitioning into RWSS applications. Fundamental research objectives that should be considered for the transition of SHM technologies (e.g., radiation hardened piezoelectric materials) for RWSS applications are discussed. The paper ends with summary, conclusions, and suggestions for further work.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.