Aging concrete structures: a review of mechanics and concepts

The safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges

Structural health monitoring of in-service tunnels

This work presents an overview of some of the most promising technologies for the structural health monitoring (SHM) of in-service tunnels. The common goal of damage or unusual behaviour detection is best pursued by an integrated approach based on the concurrent deployment of multiple technologies. Typically, traditional SHM systems are installed in problematic or special areas of the tunnels, giving information on conditions and helping manage maintenance. However, these methodologies often have the drawbacks of forcing the interruption of traffic for SHM system installation and monitoring only selected portions. Alternative solutions that would make it possible to keep the tunnel in normal operation and/or to analyse the entire infrastructure development through successive and continuous scanning stages, would be beneficial. In this paper, the authors will briefly review some traditional monitoring technologies for tunnels. Furthermore, the work is aimed at identifying alternative solutions, limiting or avoiding traffic interruptions

Topology Optimized Reinforced Concrete Walls Constructed with 3D Printed Formwork

The construction industry continually evolves to adapt to gains in knowledge, market pressures and new technologies. However, two promising new technologies, 3D printing and computational topology optimization, have not yet penetrated the civil engineering industry despite being important drivers of change in other fields. The aim of this study was the potential to overcome the major barriers to adoption of both technologies by using them in combination. Both theoretical and practical problems must still be addressed, but the potential impacts are significant: lightweight, architecturally pleasing, reduced volume structures. Two small-scale specimens were constructed and tested to demonstrate the feasibility of using additively manufactured (3D printed) formwork to construct complex reinforced concrete (RC) structures. The concept was shown to be viable. Areas were identified where further development is necessary before 3D printing can be used for large-scale cost-competitive formwork. An approach, based on the rule of mixtures, was proposed for applying computational topology optimization to RC structures. This was necessary because the computational topology optimization algorithm employed in this study assumes a structure is homogenous but RC structures are not. The approach was shown to work for optimizing an RC wall for force demands within the linear-elastic range of response. The sensitivity of optimization outputs to modeling parameters was investigated. The effects and interdependencies of mesh size, element type, number of optimization cycles, and target volume ratio on optimization outcome were demonstrated. The importance of ISO and “percent reduction” parameters on the process of importing the optimized geometry to ABAQUS was also demonstrated. Finally, a parametric study was conducted to examine the relationships between volume ratio and member strength and stiffness (volume ratio refers to the volume of the optimized structure divided by the volume of the original structure). The study used finite element models of topology optimized slender structural walls subjected to pseudo-static lateral force. It was shown that reductions in volume are not proportional to reductions in stiffness, as expected for slender walls that are flexure-dominated. Reductions in volume of 10 to 20% cause only approximately 3 to 7% reductions in uncracked member stiffness. These reductions in stiffness can be compensated for with use of modestly higher-strength concrete

Numerical modelling for safety examination of existing concrete bridges

Tese de mestrado integrado. Engenharia Civil. Universidade do Porto. Faculdade de Engenharia. 201

Iš anksto įtemptais bazalto pluošto strypais armuotų lenkiamųjų betoninių elementų įlinkių analizė veikiant ciklinei apkrovai

The behaviour of prestressed concrete beams reinforced with non-metallic reinforcement under cyclic loading is analysed in this doctoral thesis. Review on the advantages and disadvantages of non-metallic reinforcement is provided, strength properties and the most crucial parameter values, necessary for the development of the topic of this thesis, are investigated and determined. Arguments on why and at which certain situations the use of this reinforcement can be superior compared to steel are provided. A separate experimental program is developed to determine the behaviour of non-metallic reinforcement undergoing repetitive or cyclic loading. The effect of initial prestressing level and stress range caused by the cyclic load to the final number of load cycles endured is also analysed. Moreover, the influence of cyclic loading on the mechanical properties of concrete is being investigated in this study. The dissertation consists of introduction, three main chapters, general conclusions, the lists of references and author’s publications on the topic of the dissertation. The introductory chapter presents the problem formulation, the relevance of the thesis and research object, formulates the aim of the study, describes research methodology, scientific novelty and practical significance of the obtained results. Chapter 1 describes the fatigue phenomena and the main reasons causing fatigue to concrete and composite reinforcement. Besides, attention to static, cyclic creep of concrete and recommendations of the evaluation of these effects in design codes are reviewed. Chapter 2 is dedicated generally for the description of the proposed deflection calculation method based on the principles of structural dynamics concerning cyclic creep of concrete and a possible decrease in mechanical properties of composite reinforcement due to cyclic loading. A detailed calculation algorithm of the proposed method and general assumptions are provided. The 3rd and final Chapter describes in detail the experimental study performed investigating basalt fibre reinforced polymer bars and tests of BFRP prestressed concrete beam deflection estimation results which are compared to the proposed and other authors methods. The adequacy of proposed method is evaluated thru statistical analysis. The topic of the thesis has been published in 7 articles: 5 – in the jour-nals with an Impact Factor, 1 – in scientific journals of other international databases and 1 in the conference proceedings referred by the Clarivate Analytics Web of Science.Dissertatio

Automatic Change-based Diagnosis of Structures Using Spatiotemporal Data and As- Designed Model

abstract: Civil infrastructures undergo frequent spatial changes such as deviations between as-designed model and as-is condition, rigid body motions of the structure, and deformations of individual elements of the structure, etc. These spatial changes can occur during the design phase, the construction phase, or during the service life of a structure. Inability to accurately detect and analyze the impact of such changes may miss opportunities for early detections of pending structural integrity and stability issues. Commercial Building Information Modeling (BIM) tools could hardly track differences between as-designed and as-built conditions as they mainly focus on design changes and rely on project managers to manually update and analyze the impact of field changes on the project performance. Structural engineers collect detailed onsite data of a civil infrastructure to perform manual updates of the model for structural analysis, but such approach tends to become tedious and complicated while handling large civil infrastructures. Previous studies started collecting detailed geometric data generated by 3D laser scanners for defect detection and geometric change analysis of structures. However, previous studies have not yet systematically examined methods for exploring the correlation between the detected geometric changes and their relation to the behaviors of the structural system. Manually checking every possible loading combination leading to the observed geometric change is tedious and sometimes error-prone. The work presented in this dissertation develops a spatial change analysis framework that utilizes spatiotemporal data collected using 3D laser scanning technology and the as-designed models of the structures to automatically detect, classify, and correlate the spatial changes of a structure. The change detection part of the developed framework is computationally efficient and can automatically detect spatial changes between as-designed model and as-built data or between two sets of as-built data collected using 3D laser scanning technology. Then a spatial change classification algorithm automatically classifies the detected spatial changes as global (rigid body motion) and local deformations (tension, compression). Finally, a change correlation technique utilizes a qualitative shape-based reasoning approach for identifying correlated deformations of structure elements connected at joints that contradicts the joint equilibrium. Those contradicting deformations can help to eliminate improbable loading combinations therefore guiding the loading path analysis of the structure.Dissertation/ThesisDoctoral Dissertation Civil and Environmental Engineering 201

Serviceability and post-failure behaviour of laminated glass structural elements

Glass structures are being built ever more frequently all over the world, in a growing architectural trend towards light, transparency and sustainability. The engineering design of laminated glass elements being profoundly influenced by properties of interlayers, this multi-scale research highlights some among the key elements on the hyperelastic and viscoplastic response of such synthetic materials. Results and new discoveries are interpreted to better model and predict the response of laminated glass structures: examples are provided for design applications to post-failure safety assessments, structural design and cold-bending techniques. Still, in a vastly unknown field, a growing market and foggy regulatory framework, many challenges and research opportunities remain to be dealt with

Experimental characterization and numerical modelling of the impact behavior of PVC foams

Background Polyvinyl chloride (PVC) foams are widely used in crashworthiness and energy absorption applications due to their low density and the capability of crushing up to large deformations with limited loads. This property is due to their particular constitutive behavior: the stress-strain curve is characterized, after an initial yield or peak stress, by a relevant plateau region followed by a steep increase due to foam densification. Furthermore, the mechanical response of PVC foam is strongly strain rate dependent. Objective This work aims to characterize the mechanical behavior of PVC foams and to develop a complete constitutive model for impact and energy absorption applications. Methods Compressive tests are carried out at different speeds on PVC foam samples having different relative densities. Quasi-static and intermediate strain rate tests are performed by a pneumatic machine, while high strain rate tests are conducted by means of a Split Hopkinson Pressure Bar. The uniaxial stress-strain curves are used to calibrate the visco-elastic and visco-plastic constitutive model. In particular, the material behavior is divided into two parallel branches: the former describes the elasto-plastic behavior, while the latter accounts for the visco-elastic one; the plastic branch also includes a multiplicative term accounting for the strain rate sensitivity of the base material. Results The tests highlight a strong compressibility of the foam with negligible lateral expansion. The energy absorption efficiency, as well as the densification strain, is evaluated. The material model is also implemented in Finite Element (FE) simulations of puncture impact tests, validating the results of the calibration procedure. Conclusions The calibration of the visco-elasto-plastic material model offers a physically consistent identification of the constitutive response of the PVC foams, showing an effective characterization of the impact behavior of the material