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  • 1.
    Wadi, Amer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Soil-Steel Composite Bridges: Research advances and application2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Soil-steel composite bridges are considered competitive structures being an economical alternative to similar span concrete bridges. This frequently stimulates practitioners to push their design limits and expand the different areas of application including their performance in sloping terrain. This also implies that most design methods are continuously being developed to address new market challenges and at the same time to seek for better design and construction.

    This thesis compiles the recent research efforts to advance the knowledge on the structural performance of soil-steel composite bridges (SSCB). The first part of the thesis investigates the performance of SSCB in sloping terrain, where numerical simulations are used to predict the behaviour of three case studies. This includes structural response under sloped soils and also avalanche loads (Paper I and Paper II). The research enabled to realize the importance of soil configuration around the wall conduit and its influence on the structural response. While the presence of surface slopes emphasizes the susceptibility of SSCB with low depths of soil cover, higher covers may help in reducing the influence of steep slopes and avalanche loads. It was also found that the downhill soil configuration has substantial effects on the flexural response. The findings of the study were also used to provide methods for preliminary estimates of normal forces under sloped soils and avalanches.

    To better understand the load bearing capacity of SSCB, the second part of this thesis deals with the behaviour of large-span structures. It includes the use of finite element method simulations (FEM) for the analysis and the prediction of a previous full-scale loading-to-failure test (Paper III). The study also presents response predictions on the ultimate capacity of a large-span structure pertaining to its ongoing preparation for a full-scale field test (Paper IV). The thesis also includes discussions and possible refinements on current design equations concerning buckling calculations and live load effects. The results of the study have allowed to realize the major role of the soil load effects on the subsequent formation of yield areas and failure loads. It is found that the load position has a direct influence on the ultimate capacity especially for large-span structures. The study also highlighted the variations in the distribution of the live load sectional forces in both the circumferential and the transverse directions of the corrugations. Furthermore, possible refinements are proposed on current design equations of which are believed closely relevant on the path for the design development of large-span structures.

  • 2.
    Chhang, Sophy
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. INSA de Rennes.
    Energy-momentum conserving time-stepping algorithms for nonlinear dynamics of planar and spatial Euler-Bernoulli/Timoshenko beams2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Large deformations of flexible beams can be described using either the co-rotational approach or the total Lagrangian formalism. The co-rotational method is an attractive approach to derive highly nonlinear beam elements because it combines accuracy with numerical efficiency. On the other hand, the total Lagrangian formalism is the natural setting for the construction of geometrically exact beam theories. Classical time integration methods such as Newmark, standard midpoint rule or the trapezoidal rule do suffer severe shortcomings in nonlinear regimes. The construction of time integration schemes for highly nonlinear problems which conserve the total energy, the momentum and the angular momentum is addressed for planar co-rotational beams and for a geometrically exact spatial Euler-Bernoulli beam.

    In the first part of the thesis, energy-momentum conserving algorithms are designed for planar co-rotational beams. Both Euler-Bernoulli and Timoshenko kinematics are addressed. These formulations provide us with highly complex non-linear expressions for the internal energy as well as for the kinetic energy which involve second derivatives of the displacement field. The main idea of the algorithm is to circumvent the complexities of the geometric non-linearities by resorting to strain velocities to provide, by means of integration, the expressions for the strain measures themselves. Similarly, the same strategy is applied to the highly nonlinear inertia terms. Several examples have been considered in which it was observed that energy, linear momentum and angular momentum are conserved for both formulations even when considering very large number of time-steps. Next, 2D elasto-(visco)-plastic fiber co-rotational beams element and a planar co-rotational beam with generalized elasto-(visco)-plastic hinges at beam ends have been developed and compared against each other for impact problems. Numerical examples show that strain rate effects influence substantially the structure response.

    In the second part of this thesis, a geometrically exact 3D Euler-Bernoulli beam theory is developed. The main challenge in defining a three-dimensional Euler-Bernoulli beam theory lies in the fact that there is no natural way of defining a base system at the deformed configuration. A novel methodology to do so leading to the development of a spatial rod formulation which incorporates the Euler-Bernoulli assumption is provided. The approach makes use of Gram-Schmidt orthogonalisation process coupled to a one-parametric rotation to complete the description of the torsional cross sectional rotation and overcomes the non-uniqueness of the Gram-Schmidt procedure. Furthermore, the formulation is extended to the dynamical case and a stable, energy conserving time-stepping algorithm is developed as well. Many examples confirm the power of the formulation and the integration method presented.

  • 3.
    Arvidsson, Therese
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Train–Track–Bridge Interaction for the Analysis of Railway Bridges and Train Running Safety2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, train–track–bridge interaction (TTBI) models are used to study the dynamic response of railway bridges. A TTBI model considers the dynamics of the train in addition to that of the track–bridge system. The TTBI model enables the assessment of train running safety and passenger comfort. In the bridge design stage, a moving force model is instead typically used for the train load. The main aim of this thesis is to use results from TTBI models to assess the validity of some of the Eurocode design criteria for dynamic analysis of bridges.

    A 2D rigid contact TTBI model was implemented in ABAQUS (Paper II) and in MATLAB (Paper III). In Paper V, the model was further developed to account for wheel–rail contact loss. The models were applied to study various aspects of the TTBI system, including track irregularities. The 2D analysis is motivated by the assumption that the vertical bridge vibration, which is of main interest, is primarily dependent on the vertical vehicle response and vertical wheel–rail force.

    The reduction in bridge response from train–bridge interaction was studied in Papers I–II with additional results in Part A of the thesis. Eurocode EN 1991-2 accounts for this reduction by an additional damping Δζ. The results show that Δζ is non-conservative for many train–bridge systems since the effect of train–bridge interaction varies with various train–bridge relations. Hence, the use of Δζ is not appropriate in the bridge design stage.

    Eurocode EN 1990-A2 specifies a deck acceleration criterion for the running safety at bridges. The limit for non-ballasted bridges (5 m/s2) is related to the assumed loss of contact between the wheel and the rail at the gravitational acceleration 1 g. This assumption is studied in Paper V based on running safety indices from the wheel–rail force for bridges at the design limit for acceleration and deflection. The conclusion is that the EN 1990-A2 deck acceleration limit for non-ballasted bridges is overly conservative and that there is a potential in improving the design criterion.

  • 4.
    Svedholm, Christoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Efficient Modelling Techniques for Vibration Analyses of Railway Bridges2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The world-wide development of new high-speed rail lines has led to more stringent design requirements for railway bridges, mainly because high-speed trains can cause resonance in the bridge superstructure. Dynamic simulations, often utilising time-consuming finite element analysis (FEA), have become essential for avoiding such problems. Therefore, guidelines and tools to assist structural engineers in the design process are needed.

    Considerable effort was spent at the beginning of the project, to develop simplified models based on two-dimensional (2D) Bernoulli-Euler beam theory. First, a closed-form solution for proportionally damped multi-span beam, subjected to moving loads was derived (Paper I). The model was later used to develop design charts (Paper II) and study bridges on existing railway lines (Paper III). The model was then extended to non-proportionally damped beams (Paper IV) in order to include the effects of soil-structure interactions. Finally, the importance of the interaction between the surrounding soil and the bridge was verified by calibrating a finite element (FE) model by means of forced vibration tests of an end-frame bridge (Paper V).

    Recommendations on how to use the models in practical applications are discussed throughout the work. These recommendations include the effects of shear deformation, shear lag, train-bridge and soil-structure interactions, for which illustrative examples are provided. The recommendations are based on the assumption that the modes are well separated, so that the response at resonance is governed by a single mode.

    The results of the work show that short span bridges, often referred to as `simple´ bridges, are the most problematic with respect to dynamic effects. These systems are typically, non-proportionally damped systems that require detailed analyses to capture the `true´ behaviour. Studying this class of dynamic system showed that they tend to contain non-classical modes that are important for the structure response. For example, the bending mode is found to attain maximum damping when its undamped natural frequency is similar to that of a non-classical mode.

  • 5.
    Heng, Piseth
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.

    In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.

    The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.

  • 6.
    Zhu, Jiqing
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Storage Stability and Phase Separation Behaviour of Polymer-Modified Bitumen: Characterization and Modelling2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer-modified bitumen (PMB) is a high-performance material for road construction and maintenance. But its storage stability and phase separation behaviour are still not sufficiently understood and need to be studied toward a more successful and sustainable application of PMB. In this thesis, the equilibrium thermodynamics and phase separation dynamics of PMB are investigated with the aim at a fundamental understanding on PMB storage stability and phase separation behaviour. The development of polymer modifiers for paving bitumen is reviewed. The phase separation process in unstable PMBs is captured by fluorescence microscopy at the storage temperature (180 °C). A coupled phase-field model of diffusion and flow is developed to simulate and predict the PMB storage stability and phase separation behaviour. The temperature dependency of PMB phase separation behaviour is modelled by introducing temperature-dependent model parameters between 140 °C and 180 °C. This model is implemented in a finite element software package and calibrated with the experimental observations of real PMBs. The results indicate that storage stability and phase separation behaviour of PMB are strongly dependent on the specific combination of the base bitumen and polymer. An unstable PMB starts to separate into two phases by diffusion, because of the poor polymer-bitumen compatibility. Once the density difference between the two phases becomes sufficiently significant, gravity starts to drive the flow of the two phases and accelerates the separation in the vertical direction. The proposed model, based on the Cahn-Hilliard equation, Flory-Huggins theory and Navier-Stokes equations, is capable of capturing the stability differences among the investigated PMBs and their distinct microstructures at different temperatures. The various material parameters of the PMBs determine the differences in the phase separation behaviour in terms of stability and temperature dependency. The developed model is able to simulate and explain the resulting differences due to the material parameters. The outcome of this study may thus assist in future efforts of ensuring storage stability and sustainable application of PMB.

  • 7.
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Sustainable Implementation of Electrified Roads: Structural and Material Analyses2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Given the promise of the Inductive Power Transfer (IPT) technology for eRoad applications, the potential challenges for a successful integration of dynamic IPT technology into the physical road structure are explored extensively in this research work. The Finite Element Method (FEM) is selected for studying the structural performance of an eRoad under operational conditions. In this, an energy-based finite strain constitutive model for asphalt materials is developed and calibrated, to enable the detailed investigation of the structural response and optimization of the considered eRoad. In the context of enabling both dynamic charging and autonomous driving for future electric vehicles, the influences to the pavement (rutting) performance by the changed vehicle behaviour are investigated as well. Moreover, to study the effect on the IPT system by the integration, the potential power loss caused within eRoad pavement materials is further examined by a combined analytic and experimental analysis. The direct research goal of this Thesis is therefore to enhance the possibility of a sustainable implementation of the eRoad solutions into the real society. At the same time, it aims to demonstrate that the road structure itself is an important part of smart infrastructure systems that can either become a bottleneck or a vessel of opportunities, supporting the successful integration of these complex systems.

  • 8.
    Du, Guangli
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Life cycle assessment of bridges, model development and case studies2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent decades, the environmental issues from the construction sector have attracted increasing attention from both the public and authorities. Notably, the bridge construction is responsible for considerable amount of energy and raw material consumptions. However, the current bridges are still mainly designed from the economic, technical, and safety perspective, while considerations of their environmental performance are rarely integrated into the decision making process. Life Cycle Assessment (LCA) is a comprehensive, standardized and internationally recognized approach for quantifying all emissions, resource consumption and related environmental and health impacts linked to a service, asset or product. LCA has the potential to provide reliable environmental profiles of the bridges, and thus help the decision-makers to select the most environmentally optimal designs. However, due to the complexity of the environmental problems and the diversity of bridge structures, robust environmental evaluation of bridges is far from straightforward. The LCA has rarely been studied on bridges till now.

    The overall aim of this research is to implement LCA on bridge, thus eventually integrate it into the decision-making process to mitigate the environmental burden at an early stage. Specific objectives are to: i) provide up-to-date knowledge to practitioners; ii) identify associated obstacles and clarify key operational issues; iii) establish a holistic framework and develop computational tool for bridge LCA; and iv) explore the feasibility of combining LCA with life cycle cost (LCC). The developed tool (called GreenBridge) enables the simultaneous comparison and analysis of 10 feasible bridges at any detail level, and the framework has been utilized on real cases in Sweden. The studied bridge types include: railway bridge with ballast or fix-slab track, road bridges of steel box-girder composite bridge, steel I-girder composite bridge, post tensioned concrete box-girder bridge, balanced cantilever concrete box-girder bridge, steel-soil composite bridge and concrete slab-frame bridge. The assessments are detailed from cradle to grave phases, covering thousands of types of substances in the output, diverse mid-point environmental indicators, the Cumulative Energy Demand (CED) and monetary value weighting. Some analyses also investigated the impact from on-site construction scenarios, which have been overlooked in the current state-of-the-art.

    The study identifies the major structural and life-cycle scenario contributors to the selected impact categories, and reveals the effects of varying the monetary weighting system, the steel recycling rate and the material types. The result shows that the environmental performance can be highly influenced by the choice of bridge design. The optimal solution is found to be governed by several variables. The analyses also imply that the selected indicators, structural components and life-cycle scenarios must be clearly specified to be applicable in a transparent procurement. This work may provide important references for evaluating similar bridge cases, and identification of the main sources of environmental burden. The outcome of this research may serve as recommendation for decision-makers to select the most LCA-feasible proposal and minimize environmental burdens. 

  • 9.
    Sangiorgio, Filippo
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Safety Format for Non-linear Analysis of RC Structures Subjected to Multiple Failure Modes2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis treats the safety format for non-linear analysis of reinforced concrete (RC) structures subjected to multiple failure modes. The purpose is to identify questions which are poorly understood and ambiguous about the behaviour of structures that may fail due to a number of possible failure modes (e.g., bending, shear, buckling, crack propagation, fatigue) which might be used as a focus for the development of a more comprehensive approach to the evaluation of the structural safety level.

    Nowadays non-linear analysis in concrete structures cannot be considered only as a research tool to improve the understanding of structural behaviour, but it is also a useful mean to design more and more enhanced structures and to estimate the actual safety level in existing structures. As a consequence, semi-probabilistic safety formats for the non-linear analysis of RC structures are of great practical interest for structural engineers.

    Safety formats for non-linear analysis have mainly been tested on beams and columns subjected to normal forces and bending moments. Only recently there has been a noticeable effort in understanding whether available safety formats lead to the intended reliability when they are applied to structures that also may fail due to shear forces. However, the road ahead is still long and challenging.

    The definition of a suitable safety format involves the clarification of (i) which values of geometric and material properties should be used in the non-linear analysis, considering that they all influence both the resistance and the ultimate behaviour of the whole system, (ii) when the incremental process of non-linear analysis should stop, and (iii) how to derive from the failure load the ultimate load that can be carried by the structure with the safety margins that are required by the semi-probabilistic approach. This thesis considers in some sense all three of these aspects.

    The following major conclusions are based on the studies described in the appended papers: (1) the scatter of the shear capacity of RC slender members seems to be mainly due to the randomness of both tensile strength of concrete and shrinkage; (2) the structural behaviour at ultimate load of RC structures designed according to Eurocodes 2 is not unambiguous and may significantly vary depending on the structural system, load configuration, and capacity design; (3) the resistance of RC structures subjected to flexural and shear failure modes seems to be mainly influenced by the combination of mechanical properties of both longitudinal reinforcement and stirrups, and tensile strength of concrete; and (4) the resistance of RC structures subjected to multiple failure modes may have a general multimodal probability density function, in which each mode represents a specific failure mechanism.

  • 10.
    Gonzalez, Ignacio
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Application of monitoring to dynamic characterization and damage detection in bridges2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The field of bridge monitoring is one of rapid development. Advances in sensor technologies, in data communication and processing algorithms all affect the possibilities of Structural Monitoring in Bridges. Bridges are a very critical part of a country’s infrastructure, they are expensive to build and maintain, and many uncertainties surround important factors determining their serviceability and deterioration state. As such, bridges are good candidates for monitoring. Monitoring can extend the service life and avoid or postpone replacement, repair or strengthening works. The amount of resources saved, both to the owner and the users, by reducing the amount of non-operational time can easily justify the extra investment in monitoring.

    This thesis consists of an extended summary and five appended papers. The thesis presents advances in sensor technology, damage identification algorithms, Bridge Weigh-In-Motion systems, and other techniques used in bridge monitoring. Four case studies are presented. In the first paper, a fully operational Bridge Weigh-In-Motion system is developed and deployed in a steel railway bridge. The gathered data was studied to obtain a characterization of the site specific traffic. In the second paper, the seasonal variability of a ballasted railway bridge is studied and characterized in its natural variability. In the third, the non-linear characteristic of a ballasted railway bridge is studied and described stochastically. In the fourth, a novel damage detection algorithm based in Bridge Weigh-In-Motion data and machine learning algorithms is presented and tested on a numerical experiment. In the fifth, a bridge and traffic monitoring system is implemented in a suspension bridge to study the cause of unexpected wear in the bridge bearings.

    Some of the major scientific contributions of this work are: 1) the development of a B-WIM for railway traffic capable of estimating the load on individual axles; 2) the characterization of in-situ measured railway traffic in Stockholm, with axle weights and train configuration; 3) the quantification of a hitherto unreported environmental behaviour in ballasted bridges and possible mechanisms for its explanation (this behaviour was shown to be of great importance for monitoring of bridges located in colder climate) 4) the statistical quantification of the nonlinearities of a railway bridge and its yearly variations and 5) the integration of B-WIM data into damage detection techniques.

     

  • 11.
    Ülker-Kaustell, Mahir
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Essential modelling details in dynamic FE-analyses of railway bridges2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increased need to reduce the use of fossil fuels imposes higher demands on the efficiency of rail transportation. Therefore, an improved knowledge regarding the dynamic properties of railway bridges and infrastructure for railway traffic in general is required. Typically, increased train speed, longer trains and increased axle loads increase the dynamic response in railway bridges. Modelling details for bridge structures such as the flexibility of the foundations, radiation damping in the subsoil and the embankments as well as hysteretic effects in bridge bearings and the track superstructure are typically neglected. The reason for this is that suitable models which consider the influence of such effects in engineering calculations have not yet been implemented in the effectual design codes. This thesis is mainly based on a case study of a ballasted, simply supported steel-concrete composite bridge, which shows a considerable variation in the natural frequencies and damping ratios depending on the amplitude of vibration. Furthermore, the natural frequencies were found to increase significantly during the winter. It is well known that the dynamic properties of typical civil engineering structures are dependent on the amplitude of vibration. However, the fact that certain railway bridges exhibit such non-linear behaviour also for very small amplitudes of vibration has been shown only during later years. This has been verified by means of measurements of the free vibrations after train passages on three typical Swedish beam bridges for railway traffic. Possible sources to this amplitude dependency have been identified primarily in the bridge bearings and the track superstructure. Models of these structural components, based on the so called Bouc-Wen model, have been implemented in a commercial finite element program and was used in a preliminary study. The results indicate that roller bearings and pot bearings can give rise to a non-linear mode of vibration, characterised by two different states. At very small amplitudes of vibration (. 0:1m=s2), no movement over such bearings occur (state 1) since their initial resistance to motion is not overcome. Depending on parameters such as the longitudinal stiffness of the foundations and substructures, the beam height over the supports as well as the bearing type, there is an amplitude of vibration at which the initial resistance to motion is completely overcome (state 2). The bearings are then free to move, with a resistance characterised by the kinematic friction (pot bearings) or the rolling resistance (roller bearings). During the transition from state 1 to state 2, the frequency decreases continuously towards an asymptotic value and the damping initially grows considerably, from a value which corresponds quite well to the recommendations of the Eurocodes and then returns to a value similar to that in state 1. The preliminary study indicates that it is possible to design certain bridges so that this increase in damping is optimal over the relevant range of amplitudes of vibration.

  • 12.
    Safi, Mohammed
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Life-Cycle Costing: Applications and Implementations in Bridge Investment and Management2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A well-maintained bridge infrastructure is a fundamental necessity for a modern society that provides great value, but ensuring that it meets all the requirements sustainably and cost-effectively is challenging. Bridge investment and management decisions generally involve selection from multiple alternatives. All of the options may meet the functional demands, but their life-cycle cost (LCC), service life-span, user-cost, aesthetic merit and environmental impact may differ substantially. Thus, life-cycle analysis (LCCA, a widely used decision-support technique that enables comparison of the LCC of possible options), is essential. However, although LCCA has recognized potential for rationalizing bridge procurement and management decisions its use in this context is far from systematic and the integration of LCCA findings in decisions is often far from robust. Thus, the overall objective of the work underlying this thesis has been to contribute to the development of sustainable bridge infrastructures while optimizing use of taxpayers’ money, by robustly incorporating life-cycle considerations into bridge investment and management decision-making processes.

    The work has introduced a full scheme for applying LCCA throughout bridges’ entire life-cycle. Several practical case studies have been presented to illustrate how an agency could benefit from use of a bridge management system (BMS) to support decisions related to the management of existing bridges and procure new bridges. Further developments include a comprehensive approach incorporating a novel LCCA technique, “LCC Added-Value Analysis”, which enables procurement of the most cost-efficient bridge design through a fair design-build (D-B) tendering process. A further contribution is a novel, holistic approach designed to enable procurement of bridges with the maximal possible sustainability (life-cycle advantages) under D-B contracts. The approach combines LCC Added-Value analysis with other techniques that make bridges’ aesthetic merit and environmental impact commensurable using an adapted concept named the willingness-to-pay-extra (WTPE).

    The systematic analytical procedures and potential of LCCA to deliver major savings highlighted in this thesis clearly demonstrate both the feasibility and need to integrate LCCA into bridge procurement and management decisions. This need has been recognized by Trafikverket (the Swedish Transport Administration), which has implemented a software tool developed in the research (BaTMan-LCC) in its bridge and tunnel management system (BaTMan). This thesis introduces readers to the field, considers BaTMan and the bridge stock in Sweden, discusses the developments outlined above and obstacles hindering further implementation of LCCA, then presents proposals for further advances.

  • 13.
    Le, Thanh-Nam
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Nonlinear dynamics of flexible structures using corotational beam elements2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The purpose of this thesis is to develop corotational beam elements for the nonlinear dynamic analyse of flexible beam structures. Whereas corotational beam elements in statics are well documented, the derivation of a corotational dynamic formulation is still an issue.

    In the first journal paper, an efficient dynamic corotational beam formulation is proposed for 2D analysis. The idea is to adopt the same corotational kinematic description in static and dynamic parts. The main novelty is to use cubic interpolations to derive both inertia terms and internal terms in order to capture correctly all inertia effects. This new formulation is compared with two classic formulations using constant Timoshenko and constant lumped mass matrices.

    In the second journal paper, several choices of parametrization and several time stepping methods are compared. To do so, four dynamic formulations are investigated. The corotational method is used to develop expressions of the internal terms, while the dynamic terms are formulated into a total Lagrangian context. Theoretical derivations as well as practical implementations are given in detail. Their numerical accuracy and computational efficiency are then compared. Moreover, four predictors and various possibilities to simplify the tangent inertia matrix are tested.

    In the third journal paper, a new consistent beam formulation is developed for 3D analysis. The novelty of the formulation lies in the use of the corotational framework to derive not only the internal force vector and the tangent stiffness matrix but also the inertia force vector and the tangent dynamic matrix. Cubic interpolations are adopted to formulate both inertia and internal local terms. In the derivation of the dynamic terms, an approximation for the local rotations is introduced and a concise expression for the global inertia force vector is obtained. Four numerical examples are considered to assess the performance of the new formulation against two other ones based on linear interpolations.

    Finally, in the fourth journal paper, the previous 3D corotational beam element is extended for the nonlinear dynamics of structures with thin-walled cross-section by introducing the warping deformations and the eccentricity of the shear center. This leads to additional terms in the expressions of the inertia force vector and the tangent dynamic matrix. The element has seven degrees of freedom at each node and cubic shape functions are used to interpolate local transversal displacements and axial rotations. The performance of the formulation is assessed through five examples and comparisons with Abaqus 3D-solid analyses.

  • 14.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Refining the fatigue assessment procedure of existing steel bridges2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis treats the fatigue assessment process of steel bridges. The purpose is to identify areas with potential of enhancement with an overall aim of attaining a longer service life. The aging bridge stock in Sweden and in many other developed countries is an impending economical burden. Many bridges have reached their expected service life and increased axle loads, speeds, and traffic intensity further accelerate the deterioration. An immediate replacement of all our bridges approaching their expected service life will not be possible. For economical and environmental reasons, effort should be put on extending the theoretically safe service life as far as possible.

     Fatigue is one of the major reasons limiting the service life of steel bridges .A specific example is the Söderström Bridge in Stockholm, Sweden. Fatigue cracks have been found in the webs of the main beams and theoretical assessments have shown an exhausted service life. As a mean to reduce the uncertainties in the theoretical assessments a monitoring campaign was started in 2008 and continued in periods until 2011. The first continuous period of 43 days of measurements in 2008 forms the experimental foundation for this thesis.

    A fatigue life prediction involves (i) an estimation of the load effect, (ii) an estimation of the resistance, and (iii) the selection of a prediction model. This thesis treats in some sense all three of them. Considering part (i), the load effect, a theoretical study on the influence of dynamics has been performed. The quasi static approach suggested in the standards does not necessarily reflect the true dynamic behavior of the structure. Performing a dynamic moving load analysis gives for all cases studied a more favorable fatigue life. A further enhancement of the assessment is to perform in situ measurements. The uncertainties related to dynamics, loads, and structural behavior are thereby captured in the response. Routines for processing the measured response and performing life predictions are treated, moreover the quality of the measured response.

    The resistance, part (ii), in form of the fatigue endurance has a funda- mental influence on the fatigue life. As an attempt to reach a more adequate fatigue endurance a refined assessment of a typical joint is performed using linear elastic fracture mechanics (LEFM). A descriptive detail category is suggested which renders a somewhat more favorable resistance.

    Part (iii), the prediction model, is treated considering the safety format. A reliability-based model is suggested which enables a consideration of the uncertainties in each stochastic variable. Thereby, all aforementioned parts and uncertainties can be combined within the same prediction. The reliability-based model is used for a code calibration of partial safety factors to be used in semi-probabilistic assessments according to the standards.

    The implementation of the suggested procedures is shown with a numerical example. The outcome should not be generalized but the example clearly shows an increase in fatigue life with the proposed enhancements of the assessment procedure.

     

     

     

  • 15.
    Hedebratt, Jerry
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Industrial Fibre Concrete Floors: Experiences and Tests on Pile-Supported Slab2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pile supported floor slabs have often been designed solely in ultimate limit state ULS and then foremost with uniformly distributed loadings UDL. The investigation of serviceability limit state SLS has been of simpler nature, even according to the governing codes of practice.

    Often it has been minimum‑reinforced with the presumption that full friction to the supporting ground is present, whit‑out any inspection, which by the Swedish code of practice even more reduced the addition of crack reinforcement. The cracks have not been controlled, before they in fact have occurred. For pile supported floor slabs the ground support will be there still, at least for a time, after the casting. As the ground settles, as dehydration always will occur, and drainage and the covering roof the precipitation to reach the ground, the slab will often be completely free bearing between the piles. The minimum reinforcement is based on the assumption that only the upper layer is needed to reinforce due to dehydration shrinkage – despite that the whole floor section in time will obtain the same moisture profile and also shrinkage magnitude. One often excludes the influence of creep and temperature and the affect from external loading and local variance of restraints in calculations in the SLS. Research on behaviour in SLS has been modest; in spite of that the contractors and the client and finally the end‑user of the floors often suffer from these problems.

    It has by this thesis been established that the shrinkage of the concrete used for industrial floors is large 0.9‑1.1 ‰, and that the problem foremost arise from cracking and problems with joints and unevenness in the floor. The integrated method for design and production of industrial floors is a way to the solution, but requires that all involved assign to co‑operate to 100 %. Furthermore it is required that one selects the proper materials to the proper design and the proper production method. If one will save cost this will often be on materials; which will lead to reduced reinforcement content and reduced concrete thickness. This way is wrong and will in end make the client suffer economically. A way to solve this has been to cast the floors with steel fibre concrete SFC; from the beginning often a little bit thicker and with moderate steel fibre content and complementary reinforcement, compared to present execution. The competition from abroad has nevertheless shaped solutions that with thinner slabs and less traditional reinforcement and invalid design calculations compete on faulty grounds. This work demonstrates how this make the floor suffer in ULS and SLS.

    Trough full‑scale testing (half of a normally loaded industrial floor in matter of geometry) where a pile supported floor slab has been simulated by a flat‑slab floor cast in steel fibre concrete, it has been shown that the solution with steel fibre concrete performs well  in slabs for industrial floors. On one hand it gives the opportunity to production wise superior methods for placing concrete which potentially could gain the environment with reduced reinforcement content, and on the other hand SFC brings a ductile failure behaviour for loadings with much larger magnitudes than in normal ULS design, and further SFC provides with a stiffer response and with possibility to construct slabs with small creep deformation.

    Finally it has been established that, when it comes to short‑term point loadings (ULS) and with long-term point loadings (SLS) one can rely on the bearing capacity and the tough behaviour of SFC. And that one may exert an influence on both limit states, through variation of the SFC and the reinforcement content. This is shown for a real bearing structure, the pile supported industrial floor, and that in a safe way.

  • 16.
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Capacity assessment of arch bridges with backfill: Case of the old Årsta railway bridge2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The work presented in this thesis comprises the assessment of existing arch bridges with overlying backfill. The main objective is to estimate the load carrying capacity in ultimate limit state analysis. A case study of the old Årsta railway bridge is presented, serving as both the initiation and a direct application of the present research. The demand from the bridge owner is to extend the service life of the bridge by 50 years and increase the allowable axle load from 22.5 to 25 metric tonnes. The performed analyses show a great scatter in estimated load carrying capacity, depending on a large number of parameters. One of the factors of main impact is the backfill material, which may result a significant increase in load carrying capacity due to the interaction with the arch barrel. Based on theoretical analyses, extensive conditional assessments and the demand from the bridge owner, it was decided that the bridge needed to be strengthened.

    The author, in close collaboration with both the bridge owner and the persons performing the conditional assessment, performed the development of a suitable strengthening. The analyses showed a pronounced three-dimensional behaviour, calling for a design using non-linear finite element methods. Due to demands on full operability during strengthening, a scheme was developed to attenuate any decrease in load carrying capacity. The strengthening was accepted by the bridge owner and is currently under construction. It is planned to be finalised in 2012.

    The application of field measurements to determine the structural manner of action under serviceability loads are presented and have shown to be successful. Measured strain of the arch barrel due to passing train has been performed, both before, during and after strengthening. The results serve as input for model calibration and verification of the developed strengthening methods.

    The interaction of the backfill was not readily verified on the studied bridge and the strengthening was based on the assumption that both the backfill and the spandrel walls contributed as dead weight only. The finite element models are benchmarked using available experimental results in the literature, comprising masonry arch bridges with backfill loaded until failure. Good agreement is generally found if accounting for full interaction with the backfill. Similarly, accounting for the backfill as dead weight only, often results in a decrease in load carrying capacity by a factor 2 to 3. Still, several factors show a high impact on the estimated load carrying capacity, of which many are difficult to accurately assess. This suggests a conservative approach, although partial interaction of the backfill may still increase the load carrying capacity significantly.

  • 17.
    Enckell, Merit
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Lessons Learned in Structural Health Monitoring of Bridges Using Advanced Sensor Technology2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Structural Health Monitoring (SHM) with emerging technologies like e.g. fibre optic sensors, lasers, radars, acoustic emission and Micro Electro Mechanical Systems (MEMS) made an entrance into the civil engineering field in last decades. Expansion of new technologies together with development in data communication benefited for rapid development. The author has been doing research as well as working with SHM and related tasks nearly a decade. Both theoretical knowledge and practical experience are gained in this constantly developing field.

    This doctoral thesis presents lessons learned in SHM and sensory technologies when monitoring civil engineering structures, mostly bridges. Nevertheless, these techniques can also be used in most applications related to civil engineering like dams, high rise buildings, off-shore platforms, pipelines, harbour structures and historical monuments. Emerging and established technologies are presented, discussed and examples are given based on the experience achieved. A special care is given to Fibre Optic Sensor (FOS) technology and its latest approach. Results from crack detection testing, long-term monitoring, and sensor comparison and installation procedure are highlighted. The important subjects around sensory technology and SHM are discussed based on the author's experience and recommendations are given.

    Applied research with empirical and experimental methods was carried out. A state-of-the art-review of SHM started the process but extensive literature studies were done continuously along the years in order to keep the knowledge up to date. Several SHM cases, both small and large scale, were carried out including sensor selection, installation planning, physical installation, data acquisition set-up, testing, monitoring, documentation and reporting. One case study also included modification and improvement of designed system and physical repair of sensors as well as two Site Acceptance Tests (SATs) and the novel crack detection system testing. Temporary measuring and testing also took place and numerous Structural Health Monitoring Systems (SHMSs) were designed for new bridges. The observed and measured data/phenomena were documented and analysed. 

    Engineers, researchers and owners of structures are given an essential implement in managing and maintaining structures. Long-term effects like shrinkage and creep in pre-stressed segmental build bridges were studied. Many studies show that existing model codes are not so good to predict these long-term effects. The results gained from the research study with New Årsta Railway Bridge are biased be the fact that our structure is indeed special. Anyhow, the results can be compared to other similar structures and adequately used for the maintenance planning for the case study.

    A long-term effect like fatigue in steel structures is a serious issue that may lead to structural collapse. Novel crack detection and localisation system, based on development on crack identification algorithm implemented in DiTeSt system and SMARTape delamination mechanism, was developed, tested and implemented. Additionally, new methods and procedures in installing, testing, modifying and improving the installed system were developed.

    There are no common procedures how to present the existing FOS techniques. It is difficult for an inexperienced person to judge and compare different systems. Experience gained when working with Fibre Optic Sensors (FOS) is collected and presented. The purpose is, firstly to give advice when judging different systems and secondly, to promote for more standardised way to present technical requirements. Furthermore, there is need to regulate the vocabulary in the field.

    Finally, the general accumulated experience is gathered. It is essential to understand the complexity of the subject in order to make use of it. General trends and development are compared for different applications. As the area of research is wide, some chosen, specific issues are analysed on a more detailed level. Conclusions are drawn and recommendations are given, both specific and more general. SHMS for a complex structure requires numerous parameters to be measured. Combination of several techniques will enable all required measurements to be taken. In addition, experienced specialists need to work in collaboration with structural engineers in order to provide high-quality systems that complete the technical requirement. Smaller amount of sensors with proper data analysis is better than a complicated system with numerous sensors but with poor analysis. Basic education and continuous update for people working with emerging technologies are also obligatory.

    A lot of capital can be saved if more straightforward communication and international collaboration are established: not only the advances but also the experienced problems and malfunctions need to be highlighted and discussed in order not to be repeated. Quality assurance issues need to be optimized in order to provide high quality SHMSs. Nevertheless, our structures are aging and we can be sure that the future for sensory technologies and SHM is promising.

    The final conclusion is that an expert in SHM field needs wide education, understanding, experience, practical sense, curiosity and preferably investigational mind in order to solve the problems that are faced out when working with emerging technologies in the real world applications.  The human factor, to be able to bind good relationship with workmanship cannot be neglected either. There is also need to be constantly updated as the field itself is in continuous development.

  • 18.
    Selander, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Hydrophobic Impregnation of Concrete Structures: Effects on Concrete Properties2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydrophobic impregnations often referred to as water repellent agents, today mainly consisting of alkylalkoxysilanes, are often used on concrete to prolong the service life of the structure. This is accomplished by protecting the reinforcement bars from chlorides or by changing the moisture content inside. When the concrete is treated with a water repellent agent the properties of the surface layer becomes hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This change can reduce chloride ingress and stop heavy rain from penetrating through the surface layer.

    This thesis presents results concerning how the properties of concrete are affected by a hydrophobic impregnation. Moisture transport and fixation in the surface layer of the concrete are studied as well as the secondary effects of more practical use such as the effect on chloride ingress, water absorption and humidity level. It also presents results on how the penetration depth and concentration of the water repellent agent (i) depend on a number of parameters, and (ii) affect the outcome of the treatment. Water repellent treatments on a number of different concrete structures in Stockholm, ranging from tunnel to high-rice building, are evaluated as well.

    The three most important factors for the penetration of any water repellent agent into concrete are time, porosity and degree of saturation. A semi-empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. The depth and concentration have a major effect on the performance of the treatment.

    The moisture diffusion coefficient for a water repellent treated concrete is close to constant and not nearly as dependent on the relative humidity (RH) as for untreated concrete. Unlike untreated concrete, where capillary suction plays an important role for the moisture transport at high RH, the vapour transport is the dominant transport mechanism even at high RH for water repellent treated concrete.

    The moisture fixation is affected by a water repellent treatment and the effect is clearest at high moisture levels. The main reason for this is that the capillary porosity is affected by the treatment to a relatively high degree while the gel porosity to a large extent remains unaffected. A hypothesis is presented which suggests that the RH inside the concrete at the time of the treatment affects not only the depth and concentration but also in which range of pore radii the water repellent agent is present and active.

    The durability of hydrophobic impregnations can be divided into surface effects and in depth effects. The first is sensitive to the environmental and mechanical loadings and normally disappears within a year while the later can be long lasting if a sufficient depth is reached.

    Hydrophobic impregnations are not the answer to all problems in concrete related to moisture, but if correctly used it can prolong the service life of the structure which will lead to savings of natural resources and thus both economical and environmental savings for the community.

  • 19.
    Ilina, Elena
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Understanding the application of knowledge management to the safety critical facilities2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Challenges to the operating nuclear power plants and transport infrastructures are outlined. It is concluded that most aggravating factors are related to knowledge. Thus, of necessity, effective knowledge management is required.

    Knowledge management theories are reviewed in their historical perspective as a natural extension and unification of information theories and theories about learning. The first line is identified with names as Wiener, Ashby, Shannon, Jaynes, Dretske, Harkevich. The second line – with Vygotsky, Engeström, Carayannis.

    The recent developments of knowledge management theorists as Davenport, Prusak, Drew, Wiig, Zack are considered stressing learning, retaining of knowledge, approaching the state awareness of awareness, and alignment of knowledge management with the strategy of the concerned organizations.

    Further, some of the details and results are presented of what is achieved so far. More specifically, knowledge management tools are applied to the practical work activities as event reporting, data collection, condition assessment, verification of safety functions and incident investigation. Obstacles are identified and improvements are proposed.

    Finally, it is advised to continue to implement and further develop knowledge management tools in the organizations involved in various aspects of safety critical facilities.

  • 20.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Predicting shear type crack initiation and growth in concrete with non-linear finite element method2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     

    In this thesis, the possibility to numerically describing the behaviour that signifies shear type cracking in concrete is studied. Different means for describing cracking are evaluated where both methods proposed in design codes based on experiments and advanced finite element analyses with a non-linear material description are evaluated. It is shown that there is a large difference in the estimation of the crack width based on the calculation methods in design codes. The large difference occurs due to several of these methods do not account for shear friction in the crack face.

    The finite element method is an important tool for analysing the non-linear behaviour caused by cracking. It is especially of importance when combined with experimental investigations for evaluating load bearing capacity or establishing the structural health. It is shown that non-linear continuum material models can successfully be used to accurately describe the shear type cracking in concrete. A method based on plasticity and damage theory was shown to provide accurate estimations of the behaviour. The methods based on fracture mechanics with or without inclusion of damage theory, overestimated the stiffness after crack initiation considerably. The rotated crack approach of these methods gave less accurate descriptions of the crack pattern and underestimated the crack widths. After verification of the material model, realistic finite element models based on plasticity and damage theory are developed to analyse the cause for cracking in two large concrete structures. The Storfinnforsen hydropower buttress dam is evaluated where the seasonal temperature variation in combination with the water pressure have resulted in cracking. With the numerical model the cause for cracking can be explained and the crack pattern found in-situ is accurately simulated. The model is verified against measurements of variation in crest displacement and crack width with close agreement. The construction process of a balanced cantilever bridge, Gröndal Bridge, is numerically simulated and a rational explanation of the cause for cracking is presented. It is shown that large stresses and micro-cracks develop in the webs during construction, especially after tensioning the continuing tendons in the bottom flange. Further loads from temperature variation cause cracking in the webs that is in close agreement with the cracking found in-situ. The effect of strengthening performed on this bridge is also evaluated where the vertical Dywidag tendons so far seem to have been successful in stopping further crack propagation.

     

  • 21.
    Wiberg, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Railway bridge response to passing trains: Measurements and FE model updating2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today’s railway bridges are analysed in more detail for moving loads due to the increase in speeds and axle loads. However, these numerical analyses are very time consuming as they often involve many simulations using different train configurations passing at different speeds and many considerations to take into account. Thus, simplified bridge, track and train models are often chosen for practical and time efficient simulations.

    The New Årsta Railway Bridge in Stockholm was successfully instrumented during construction. A simplified 3D Bernoulli-Euler beam element FE model of the bridge was prepared. The FE model was first manually tuned based on static load testing. The most extensive work was performed in a statistical identification of significantly influencing modelling parameters. Consequently, parameters to be included in an optimised FE model updating, with consideration also to synergy effects, could be identified. The amount of parameters included in the optimisation was in this way kept at an optimally low level. For verification, measurements from several static and dynamic field tests with a fully loaded macadam train and Swedish Rc6 locomotives were used. The implemented algorithms were shown to operate efficiently and the accuracy in static and dynamic load effect predictions was shown to be considerably improved.

    It was concluded that the complex bridge can be simplified by means of beam theory and an equivalent modulus of elasticity, and still produce reliable results for simplified global analyses. The typical value of an equivalent modulus of elasticity was in this case approximately 25% larger than the specified mean value for the concrete grade in question.

    The optimised FE model was used in moving load simulations with high speed train loads according to the design codes. Typically, the calculated vertical acceleration of the bridge deck was much lower than the specified allowable code value. This indicates that multispan continuous concrete bridges are not so sensitive to train induced vibrations and therefore may be suitable for high speed train traffic.

    Finally, the relevant area of introducing the proposed FE model updating procedure in the early bridge design phase is outlined.

  • 22.
    Bayoglu Flener, Esra
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Static and dynamic behaviour of soil-steel composite bridges obtained by field testing2009Doctoral thesis, comprehensive summary (Other academic)
  • 23.
    Mattsson, Hans-Åke
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Integrated Bridge Maintenance: Evaluation of a pilot project and future perspectives2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The trend in many countries is to outsource maintenance with competitive tendering. The design of the tender is then a crucial issue. A new type of tendering contract, called "Integrated Bridge Maintenance", was introduced in one experimental area in Sweden. In this case the preventive bridge maintenance is separated from the standard road maintenance contract. The ideas behind these changes are that the new approach can increase efficiency through a combination of in­creased specialization, economies of scale and through giving the private contractor a greater degree of freedom concerning exactly what to do and exactly when to do it. A pilot project has been running since 2004 for all bridges in Uppsala County with about 400 bridges and since 2007 for all bridges in Örebro County with about 700 bridges.

     

    The experiences and lessons from this pilot project are presented in this thesis together with guidelines on how to procure Integrated Bridge Maintenance in the future. An important feature of the contract was that it contained a combination of specific measures that the contractor should carry out and properties of the bridges that the contractor was responsible to maintain. This created a balance between predictability and flexibility for the contractor. The contractor could make long term planning for the work. The client was satisfied because of increased com­petence and a low price. The latter can partly be explained by the possibility for the specialised bridge crew to receive additional work from other clients. As information about old bridges always is incomplete a partnering structure needs to be built into the contract. Experi­ence has also shown that a conscious policy to maintain long run competition is important. The general conclusion is that the project was seen as successful and as creating more "value for money".

     

    To manage a bridge stock optimally from a life cycle perspective is a very complex task, since the condi­tions for the individual bridge can vary greatly from place to place which the answers from the research questions indicate. Besides following-up and evaluating the Integrated Bridge Maintenance projects a number of research questions have been studied.

     

    Is Integrated Bridge Maintenance a successful method to increase the effectiveness and to increase the standard in bridge maintenance alternatively increasing the service life for the bridge stock at an optimal cost, i.e., will IBM lead to lower LCC? It is difficult to answer this question with exact numbers after so short time, but so far the opinion is that the effectiveness has increased. How can a bridge stock develop over a long time e.g. 15 years? Based on historical data one can calculate, for instance, new construction rate, demolition rate and average age for the bridge stock. This information could together with different future scenarios be a basis for different bridge management strategies for the actual bridge stock. What is the real service life for a bridge? Survival analysis for the different types of bridges in the actual bridge stock will give a good estimate of the different expected service life. Why and at which age are bridges de­molished? Two main reasons were found in this study: deterioration process of the bridge had gone too far and/or load bearing capacity was too low, and road were rerouted. What is the real service life for a bridge edge beam, one of the most often repaired element of Swedish bridges? Survival analysis of edge beams located on different types of roads will give a good estimate of the different expected service life.

     

    How should a long-term contract for bridge maintenance and specially Integrated Bridge Maintenance be procured? The bridge manager should have a good understanding of the answers on the research ques­tions above when the tender documents are to be prepared for the actual bridge stock. Thereafter the area that the contract should cover could be chosen, a good balance between properties and measures, defining the working cycle for properties, a flexible partnering structure in the contract and a suitable length of the contract (x years) inclusive an option (+ y years) and finally good incentives in the contract.

     

    To sum up, the main purpose with the doctoral project has been reached. A model for procurement of bridge maintenance has been developed; see the projects in Uppsala and Örebro. The contractor has deve­loped more effective methods for bridge maintenance. The doctoral project has been a step closer to the end goal of reducing the society’s costs for bridge maintenance in the future. The bridges should be func­tional to the lowest possible cost during its expected service life (LCC). The doctoral project has also con­tributed with new knowledge in the area of bridge maintenance, the actual development of a bridge stock over time, real service life for road bridges in Sweden and survival analysis.

  • 24.
    Pettersson, Lars G.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Full Scale tests and Structural Evaluation of Soil Steel Flexible Culverts with low Height of Cover2007Doctoral thesis, monograph (Other scientific)
  • 25.
    Stenbeck, Torbjörn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Promoting Innovation in Transportation Infrastructure Maintenance: Incentives Contracting and Performance Based Specifications2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Knowledge of what action that is needed to drive innovation at a desired speed is in demand in civil engineering and its related maintenance. 1. What measures to stimulate innovation have been tested? 2. How much innovation has been achieved by contracting? 3. How much innovation was achieved by performance-based specifications? 4. How can cost models contribute to innovation? Methods include qualitative and quantitative methods that have been timed and mixed to optimize their merits. Sweden, France, USA and Canada have used as research ground.

    Technology transfer, multi-criteria evaluation, variant bidding, idea mailbox, weatherregulated payment, contests and earmarked funds for innovative projects were some of the method beside and within contracting and performance-based specifications that have been tested.

    Contracting as such has cut costs in Sweden but not in North America. Neither Sweden nor North America has noticed any increase of innovation, rather the contrary. The savings have primarily been achieved by cuts on staff and by using standardized, less expensive and less advanced machinery. Contracted highway maintenance provinces in Canada and Sweden on average had about 50 % higher costs than inhouse provinces and Washington State. The difference is reduced to 26 %, when corrected by weather and the higher traffic in the contracted provinces. Prestige, politics and competitivity made it difficult to extract economic data from private contractors, and even from the public owners and may explain the contradictory results in previous studies. The internally driven innovation appears small and incentives to innovation weak in inhouse systems, but contrary to expectation even less in contracted systems.

    Performance-based specifications (PBS), such as Design-Build (DB), have reduced delivery times and kept the budget better than traditional contracts, but quality, lifecycle cost and technical progress was rarely analyzed and even less confirmed in the literature, why a multiple case study was carried out. The result was that three out of four PBS cases delivered lower quality in the long run or showed higher costs already on the opening day, when compared to a traditional contract alternative.

    Cost models contribute to innovation by making regions with different conditions comparable and provide tools for rational planning and decision making. One model for how highway maintenance costs depend on snow, bridges and traffic and one model for how bridge maintenance costs depend on size and age were elaborated. Models included in contracts, e.g. to allow a contractor to reduce the weather risk, appear to have contributed to a more successful contracting rollout in Sweden than in Canada.

    France provides experience of how inhouse innovation contests and industry-own patent-like routines can promote innovation. After the first two years with an incentive contract, Banverket received 10 % better quality measured as train delay and 20 % better quality measured as the number of technical errors at no cost. A lesson learnt is that the success of performance-based specifications depends on how well the owner can describe and define the contracts, how compliance is measured and how deviations are handled, i.e. how the contractor is penalized for non-fulfillment or awarded for excess delivery

  • 26.
    Broms, Carl Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Concrete flat slabs and footings: Design method for punching and detailing for ductility2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Simple but still realistic physical models suitable for structural design of flat concrete plates and column footings with respect to punching are presented.

    Punching of a flat plate is assumed to occur when the concrete compression strain at the column edge due to the bending moment in the slab reaches a critical value that is considerably lower than the generally accepted ultimate compression strain 0.0035 for one-way structures loaded in bending. In compact slabs such as column footings the compression strength of the inclined strut from the load to the column is governing instead. Both the strain limit and the inclined stress limit display a size-effect, i.e. the limit values decrease with increasing depth of the compression zone in the slab. Due respect is also paid to increasing concrete brittleness with increasing compression strength.

    The influence of the bending moment means that flat plates with rectangular panels display a lower punching capacity than flat plates with square panels – a case that is not recognized by current design codes. As a consequence, punching shall be checked for each of the two reinforcement directions separately if the bending moments differ.

    Since the theory can predict the punching load as well as the ultimate deflection of test specimens with good precision, it can also treat the case where a bending moment, so called unbalanced moment, is transferred from the slab to the column. This opens up for a safer design than with the prevailing method. It is proposed that the column rotation in relation to the slab shall be checked instead of the unbalanced moment for both gravity loading and imposed story drift due to lateral loads.

    However, the risk for punching failure is a great disadvantage with flat plates. The failure is brittle and occurs without warning in the form of extensive concrete cracking and increased deflection. Punching at one column may even initiate punching at adjacent columns as well, which would cause progressive collapse of the total structure. A novel reinforcement concept is therefore presented that gives flat plates a very ductile behaviour, which eliminates the risk for punching failure. The performance is verified by tests with monotonic as well as cyclic loading.

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