Life-cycle robustness of fastening systems

Fastening systems are an important part of the construction industry. The requirements of the future —faster and automatized construction, improved life-cycle performance and sustainability of infrastructure — will further promote their significance. However, the challenges associated with the safe and efficient design and assessment of such systems in the light of life cycle concepts requires new concepts. Life–cycle robustness is achieved when a (fastening) system is designed to maintain its intended function and required safety level for the full duration of its intended life time. The different characteristics of processes each element will face in course of time (damage, ageing, extreme events, changes in usage) in conjunction with the diversity in the intrinsic material properties form a demanding problem. Further complexity emerges when one realises that time is not simply a variable, but a factor permeating model choices. Different effects on the load side and properties on the resistance side develop differently in time, as does the dependence structure between variables. Spatial randomness of materials, such as concrete, requires careful modelling, even at a meso–scale. For a long–term analysis, where the influence of uncertainty on the safety level may dominate over the mean trend, robust design can prove decisive. On the computational side, challenges often appear since the computational costs of simulations and non–linear analyses may quickly prove infeasible. Suitable numerical techniques for small scale sampling, accounting for arbitrary distribution types and dependence structures, are yet to be developed. The realistic prediction of spatial randomness for now fails due to a lack of understanding regarding the physical basis of main input parameters. Within this contribution the authors present the general concept of life–cycle robustness and the expected prospects that arise from its application to fastening systems. A detailed discussion of the aforementioned challenges and review of the state of the art complement the paper

Load transfer mechanism of concrete screws

Even though the market and development for concrete screws has been increasingly rising in recent years, the load transfer mechanism of concrete screws has not yet been fully investigated. Therefore, different tests of concrete screws made of galvanized and stainless steel were performed in concrete C20/25 and C50/60. The main aim is to measure the strain along the embedment depth. This will be achieved by using strain gauges that get placed in a centrically drilled borehole through the concrete screw. To get a comparison to the mechanism of the screws the same process will be executed in threaded rods used as a part of bonded anchors. Due to the fact that the threaded cuts of concrete screws have geometrical similarities to bonded anchors, it was examined if the load transfer of both fasteners is related and may be compared. The results of the testing have shown that the load transfer mechanism of both fastener types is similar in low-strength concrete showing a concrete cone failure. In high strength concrete due to the mainly occurring steel failure the maximum measured strains at the maximum load step are not comparable. However, at lower load steps where the steel does not exceed the yield strength the results show a similar load transfer mechanism, too

seismic demands on nonstructural components anchored to concrete accounting for structure fastener nonstructural interaction sfni

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Applied and research based performance indicator database for highway bridges across Europe

Publicado em "Life-cycle of engineering systems: emphasis on sustainable civil infrastructure: proceedings of the Fifth International Symposium on Life-Cycle Civil Engineering (IALCCE 2016), ISBN 978-1-138-02847-0"Structural codes provide several practical principles and application rules such as the use of protective systems for material exposed in aggressive environment, the construction detailing aimed at avoiding the initiation of degradation, the maintenance actions to be regularly performed. Each construction, during its life cycle, will face with deterioration depending on several factors such as the environmental condition, the natural aging, the quality of the material, the execution of works and the planned maintenance. Therefore, several design procedures based on the prediction of the deterioration that will likely act on the structure will be developed in the framework of the international research. In addition, performance indicators for the present and future structural conditions on deterministic and probabilistic level will be defined and determined. It is extremely important to analyse such indicators in terms of used assessment frameworks, and in terms of the quantification procedure itself.COST (European Cooperation in Science and Technology

Gamma prediction models capturing the long term creep shrinkage performance of segmentally-erected prestressed box girder bridges

For creep-sensitive structures like statically in determined large bridges, it is essential to implement an efficient and realistic creep model for example in 3D Finite element considerations. Concrete creep, characterized by the gradual strain growth with time under a unit sustained stress applied at age t’, is generally calculated based on the given compliance function J(t, t’), where t is the current time. For stress level within the designed service strength, the concrete creep is assumed to follow the constitutive law of ageing linear viscoelasticity. In order to systematically study the main influence factors on bridge deflection measurements, which are known to show large scatter, a probabilistic analysis can be performed. Due to the associated computational costs such investigation are limited. The predictions based on these large-scattering basic variables (model inputs) are fraught with uncertainties and accordingly there is interest in alternative prediction models decoupled from complex analytical and numerical models, using measured structural responses. Gamma process considerations are such alternative methods. These approaches are suitable for capturing the structural behavior, like crack formation, bending, and surface strain, as well as previously mentioned long term creep shrinkage performance (can also be captured by traditional inspection and/or monitoring methods). The objective of this contribution is to illustrate the use of gamma process approaches for the prediction of the creep shrinkage performance of complex pre-stressed concrete bridges that incorporates uncertainties and makes predictions in terms of load rating and system-level more reliable with the help of structural health monitoring (SHM) data. The creep-shrinkage response of a statically in determined three span boxgirder bridge extracted (a) from a complex finite-element (FE) model, which is based on the gradual strain growth concrete creep, and (b) from structural health monitoring data, serves for the calibration and verification of the considered gamma process approaches. Finally, The ability of the Gamma process approaches to capture complex creep shrinkage processes in complex statically in determined will be critically examined

3rd Probabilistic Workshop Technical Systems, Natural Hazards

Modern engineering structures should ensure an economic design, construction and operation of structures in compliance with the required safety for persons and the environment. In order to achieve this aim, all contingencies and associated consequences that may possibly occur throughout the life cycle of the considered structure have to be taken into account. Today, the development is often based on decision theory, methods of structural reliability and the modeling of consequences. Failure consequences are one of the significant issues that determine optimal structural reliability. In particular, consequences associated with the failure of structures are of interest, as they may lead to significant indirect consequences, also called follow-up consequences. However, apart from determining safety levels based on failure consequences, it is also crucially important to have effective models for stress forces and maintenance planning ... (aus dem Vorwort

Probability and sensitivity analysis of strain measurements in FRP

Monitoring is an important issue for FRP strengthening systems in order to control their health state. Strain gauges are often used for this aim, but the measures to be utilised can be affected by various factors. In this paper the influence of various factors is taken into account, such as the characteristics of resin coating, the type of glue and the gauge length. The theoretical approach developed in previous work performed on a deterministic basis is extended here to the probabilistic field. The objective is to make a sensitivity analysis of the basic variables which can cause errors in strain measurements. Additionally, the effect of the deviation of the direction of the gauges from the longitudinal direction of the FRP sheets is considered and the existing approach is extended to take this into account. Copyright © 2004 John Wiley & Sons, Ltd

Nonlinear finite element analysis of continuous welded rail–bridge interaction: monitoring-based calibration

Continuous welded rail is of high interest to operators of railway infrastructure facilities because of the reduced maintenance work and better train driving dynamics it offers. However, the application of continuous welded rail, in particular associated with its interaction with the superstructures of e.g. bridges, requires special caution with regard to the rail stresses in the transition area between the structure and the free field. These stresses are not only influenced by thermal deformations of the bridges but also by the clamp systems between the rails and e.g. the bridge. In general, these connectors are represented by spring elements during modelling, which: (a) causes singularities in the stress distributions in the rails, and (b) cannot capture all the mechanical system changes occurring due to loading, thermal effects, etc. The target of this paper is to present an alternative way of modelling the connection between rails and bridge superstructure based on composite materials which can overcome the disadvantages of the spring model. In particular, a nonlinear model of the whole system was developed for ballasted and non-ballasted track. Special attention was paid to the calibration of rail–bridge interaction and boundary conditions using measured data and code specifications. The aim of this study was to use the results of in-situ measurements to analyse the admissible stress in rails due to their interaction with a bridge caused by temperature loading

Gamma prediction models for long-term creep deformations of prestressed concrete bridges

For long-span bridges as well as statically indeterminate frame structures it is essential to implement efficient and realistic prediction models for the long-term processes of concrete creep, shrinkage, and steel relaxation. In order to systematically study the main influential factors in bridge deflection measurements a probabilistic analysis can be per­formed. Due to the associated computational costs such investigations are limited. The predictions based on the highly scattered input parameters are associated with uncertainties. There is interest in alternative prediction models decou­pled from complex analytical and computationally expensive numerical models, using measured structural responses. A gamma process is an example of such an alternative method. This process is suitable for capturing evolving structural response quantities and deterioration mechanisms like crack propagation, corrosion, creep, and shrinkage, as reported in Ohadi and Micic (2011). The objective of this paper is to illustrate the use of gamma process approaches for the pre­diction of the creep and shrinkage performance of prestressed concrete bridges. The presented approaches incorporate uncertainties and make predictions more reliable with the help of structural health monitoring (SHM) data. The creep-shrinkage response of a prestressed box girder bridge serves for the calibration and evaluation of the considered gamma process approaches

Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys

Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations are restrained a recovery stress is generated by the SME. This recovery stress can be used to prestress a SMA applied as a strengthening material. This paper investigates the performance and the load deformation behavior of RC beams strengthened with mechanical end anchored unbonded Fe-SMA strips activated by sequentially infrared heating. The performance of a single loop loaded and a double loop loaded SMA strengthened RC beam are compared to an un-strengthened beam and a reference beam strengthened with commercially available structural steel. In these tests the SMA strengthened beam had the highest cracking load and the highest ultimate load. It is shown that the serviceability behavior of a concrete beam can be improved by a second thermal activation. The sequential heating procedure causes different temperature and stress states during activation along the SMA strip that have not been researched previously. The possible effect of this different temperature and stress states on metal lattice phase transformation is modeled and discussed. Moreover the role of the martensitic transformation during the cooling process on leveling the inhomogeneity of phase state in the overheated section is pointed out