Bridges are a crucial part of the dense Dutch highway network. Almost 50% of the current bridges are built between 1960 and 1980 for an intended service life of 50 years and thus they might reach the end of their lifetime in the near future. This strongly indicates that a large challenge can be expected regarding infrastructural replacement. In current practice, the replacement of bridges within the highway network often leads to substantial traffic hindrance, which has a large negative impact on the Dutch economy. Therefore reduction of traffic hindrance – together with sustainability – is generally an important quality criteria in MEAT-procedures (Most Economic Advantageous Tender) for tender assignments. In order to prepare for the upcoming replacement challenge, there is a need for contractors, the government and product suppliers to invest in the development of a sustainable tender strategy now. The main objective of this thesis was to propose a tender strategy that incorporates sustainability and in particular the reduction of traffic hindrance into a technically feasible design. An extensive literature review has led to a quick bridge replacement strategy consisting of three time-reducing actions, listed according to their potential profit in construction time: 1. Select the Accelerated Bridge Construction (ABC) approach: By means of lateral sliding or transportation by SPMTs (Self-Propelled Modular Transporters) entire superstructures can be constructed off-site and transported to their final location in a matter of hours. 2. Retain the existing foundations: In terms of on-site construction time it would be beneficial to retain the existing foundations. Additionally, theory suggests that a profit in bearing capacity can be obtained compared to the current design codes, which might lead to the total elimination of additional foundation elements required. 3. Avoid intermediate supports: Less elements are required if intermediate supports are avoided in the new bridge design. This does however lead to longer spans, and to prevent additional groundwork activities from an increase in deck height a higher slenderness must be obtained. Furthermore, the new superstructure design must be as light as possible, not only to allow for foundation retainment, but also to facilitate transportation and speed of erection. In particular, the technical feasibility of these actions - both separately and combined - required more research. A case study considering a two-span plate bridge was used to investigate these strategy actions. Research was done into the obtainable profit in retained pile foundations and the application of UHPC in a slender and lightweight bridge concept. It was concluded that the proposed tender strategy has a high potential. Not only is the on-site reduction time diminished but the retainment of the existing foundations and the application of UHPC in a slender and lightweight superstructure may also lead to a highly sustainable design.

The Netherlands is a densely populated country with a congested road and railway network. Therefore more and more highways are widened and expanded. These wider highways create a demand for bridges which are suited for longer spans. These bridge solutions should constructed with a minimum of hindrance for other traffic. Rijkswaterstaat, also wishes to reduce the number of intermediate supports so the space underneath a viaduct can be used more freely. The currently most used solution to build a highway overpass without disrupting the traffic too much is a concrete viaduct consisting of prefabricated prestressed concrete bridge beams. But for spans longer than 60 meters those beams become too long and too heavy for transport by truck to the building site. Therefore the existing bridge solutions are reaching the maximum distance to which they can be built. The primary goal of this report is to find a concrete bridge solution with which it is possible to construct longer bridge spans in prefabricated concrete up to 100 meters. With such a bridge solution it is also possible to span a waterway or a small river in the Netherlands. A beam bridge in which the beam is composed of three parts is the most suitable solution to build these longer spans in prefabricated concrete. This solution can be constructed with relatively little hindrance for the other traffic. This solution is also relatively flexible in the shapes of bridge decks that can be constructed, skew bridges and wide bridge decks are both possible. The design of this beam bridge is extended and analyzed with a more detailed calculation. A bridge span of 100 meters is possible with a construction height of only 3 meters. This relatively slender design is possible because high strength concrete is used and because the bridge deck is designed to spread the traffic load efficiently over the full width of the bridge deck. The beam parts of this bridge can be transported by truck to its destination. A rough cost estimation shows that the designed solution is expensive compared to existing concrete beam bridges, but it is also possible that the designed solution has a lower cost price compared to existing solutions in steel. It is advised to continue the research to and development of the bridge design because of the possible lower cost price and because with this design, bridges can be constructed which currently cannot easily be constructed with the existing solutions.

Old bridges in the Netherlands are reassessed to prove their structural safety because of the increased traffic loads. The Eurocode model for the shear capacity of prestressed concrete beams with sufficient shear reinforcement was found to be very conservative for small amounts of transverse reinforcement, which is typical for old bridges. Code provisions based on the modified compression field theory appear to be much more accurate (Bentz, Vecchio, & Collins,2006). On the other hand, these models make no distinction between flexural shear and shear tension failure, while 25% of the bridges consists of T-, I-, or box beams which are sensitive to shear tension failure. The aim of this thesis is to present a more accurate prediction for shear tension failure based on the modified compression field theory (MCFT). The report focuses on both the CSA-model and Response-2000. The CSA-model is a simplification of the MCFT for beams under the assumption that σ_z=0. The CSA-model shear resistance consists of a concrete and steel part. Response-2000 is a cross-sectional analysis program that works as a non-linear finite element analysis and not only takes into account bending but also shear.Response analysis of 32 beams (experiments of Xie (Xie, 2009), Choulli (Choulli, 2005), Hanson (Hanson & Hulbos, 1965) and Leonhardt (Leonhardt, Koch, & Rostasy, 1973)) have been made and compared with the experimental observations. The failure load is predicted with a mean ratio of 1.38 and a COV of 19% compared to the experiments. It was found that for small a/d-ratios predictions are more conservative. Failure mechanisms: rupture of the stirrups, crushing of the web concrete and slipping/major crack opening are found in Response. 87% of the failure mechanisms was predicted correctly compared to the experiments. The critical cross-section compared with the experimentally observed failure zone showed that 60% of the beams was predicted in the failure zone. The shear force in the cross section is resisted by reinforcement steel, aggregate interlock and the uncracked concrete, which were found to take up respectively 1/2, 1/6 and 1/3 of the shear force. The steel part is predicted accurately while the aggregate interlock part is underpredicted due to an over prediction of the crack spacing. The uncracked part is overpredicted for small amounts of reinforcement and underpredicted for larger amounts of reinforcement. The data of the Response analysis have been used to modify the CSA-model to a model solely describing shear tension failure. The comparison showed that the CSA-model underestimates the steel part, overestimates the concrete part, takes a to large cracked height and doesn't take into account the contribution of the uncracked part. From this comparison, modifications for β,θ,V_max,h_crack and ϵ_x are proposed using Response data and proposals from Esfandiari (Esfandiari & Adebar, 2009). The flanges are taken as uncracked and the contribution of the uncracked part is described with a linear elastic shear stress distribution. This has led to a proposal for a model that solely describes shear tension failure, where the most important addition is the contribution of the uncracked height. Calculations show that the model gives conservative predictions compared to the experiments (mean ratio of 1.36 and a COV 22%) and the predictions are almost the same as for Response. The parameters are predicted conservative compared to the Response-2000 predictions.

Vanuit Rijkswaterstaat is de wens om een snelle, verifieerbare methode te ontwikkelen voor het controleren van de veiligheid voor meerdere T-ligger constructies volgens huidige normen en inzichten. Hierbij dient rekening gehouden te worden met eventuele wijzigingen in de toekomst, welke door de huidige ontwikkelingen op het gebied van dwarskrachtonderzoek te verwachten zijn. Het is de verwachting dat op basis van verfijnde beoordelingen en verder fundamenteel onderzoek de ‘reserves’ middels een quickscan-aanpassing inzichtelijk gemaakt kunnen worden. Hierdoor zou een deel van de onderzochte kunstwerken mogelijk alsnog voldoen aan de veiligheidsnormen. Door diverse berekeningsmethoden met elkaar te vergelijken is getracht een methode te vinden welke simpel toepasbaar is, realistische resultaten voor dwarskracht en moment geeft ten gevolge van de verkeersbelasting en tevens conservatief is. Door deze te vergelijken met diverse Scia-berekeningen is een methode gekozen die het best aan de eerdergenoemde punten voldoet. Tevens zijn de invloeden van meerdere uitgangspunten met elkaar vergeleken. Nadat inzicht is verkregen in de manier waarop de belasting over de liggers is verdeeld, is een generiek systeem gemaakt, een zogenaamde quickscan. De quickscan maakt op een snelle manier duidelijk of de gekozen snede voldoende weerstand kan bieden aan de behorende belastingcombinaties. De quickscan is een generieke, eenvoudig toepasbare, conservatieve methode om ‘het kaf van het koren te scheiden’ voor de dwarskrachttoets, zonder dat daarvoor EEM-software nodig is, welke tevens de Scia-berekeningen zo goed mogelijk benadert. Om deze zo goed mogelijk te ontwikkelen is een beoordelingsprocedure gerealiseerd welke zich vormt tot de quickscan. Om inzicht te verkrijgen in de invloed van de verkeersbelasting op de liggers en om deze conservatief te benaderen, zijn diverse berekeningsmethoden met elkaar vergeleken. Uit deze vergelijking is gebleken dat de beste benadering voor de verkeersbelasting de ‘verspreide methode’ is. Hierbij wordt de belasting gespreid of is deze niet afhankelijk van de locatie van de dwarsdragers. Met deze kennis is de quickscan Boon ontwikkeld. Deze kan worden uitgevoerd door enkele parameters in te vullen, zoals: de lengte van de ligger, het oppervlak van de ligger, het voorspanverloop, de dwarsdragers en door de ‘kritische’ sneden (belangrijke te toetsen sneden) van de ligger te bepalen. Daarna kan snel en slim inzichtelijk worden gemaakt wat de UC op deze sneden van de constructie is, en wat de consequenties van wijziging van uitgangspunten zijn. Uit het onderzoek is gebleken dat het tandemstelsel altijd op een hoek van 30 graden vanaf het gekozen punt tot hart rijstrook moet staan om de maximale dwarskracht in dat punt te vinden. Deze belastingsposities worden automatisch gevonden, waarna direct de dwarskracht en het bijbehorende moment berekend wordt met behulp van de verspreide methode. Hierdoor kan de constructieve beoordeling van de liggers snel inzichtelijk worden gemaakt. De quickscan Boon is een eenvoudig toepasbare, realistische, conservatieve beoordeling voor T-ligger constructies, welke inzicht geeft in de maatgevende belastingcombinatie en gemakkelijk te verifiëren is. De kracht van deze methode is dat door te variëren met diverse parameters (zoals capaciteitsaspecten, te toetsen snede en rijwegindeling) direct de invloed van deze parameters inzichtelijk kan worden gemaakt. Waar de resultaten conservatief en toch reëel zijn.

With the arrival of the Eurocode, the calculations regarding shear resistance, have become increasingly conservative compared to former concrete standards. For example in Voorschriften Beton 1974 (VB 74), a former concrete standard, a shear resistance combination of concrete, stirrups and prestress was allowed. Whereas the Eurocode assumes the shear resistance of the concrete is zero if it’s standalone contribution is insufficient. Meaning that once stirrups are required, the total applied shear stress is controlled by the stirrups. Prorail is the party in the Netherlands which is responsible for the construction and maintenance of the railway infrastructure. The change in regulations results in concerns for parties like Prorail and in particular to the shear resistance of concrete railway bridges constructed according to the VB 74. A through railway bridge consists of a relatively thin floor and two prestressed girders. Whenever a train drives over the floor, a great deal of the loading is spread in transverse direction, causing large shear forces and torsion in the two prestressed girders. Because this combination can be critical for the shear resistance, two prestressed through railway bridges, constructed according to the VB 74, are investigated in this master thesis. It is verified with hand calculations whether or not these existing structures can guarantee structural safety by considering three shear resistance checks; the risk of shear tension failure, capacity of the stirrups and resistance against fatigue. Ultimately it is concluded, that the largest unity check is 1,01 and that both bridges can guarantee structural safety regarding shear resistance. The reassessment of an through bridge, is an typical assignment for engineering firm such as Witteveen+Bos. But because hand calculations are too time consuming, the design loads are determined with SCIA Engineer (FEA program). However in the earlier days FEA programs were not available and torsion in the girders was derived from a set of differential equations (analytical solution). Because structural engineers from today completely rely on programs like SCIA, a comparison is drawn up between SCIA and the analytical solution for torsion in the girder. The plate, beam model 1A and 1B are the three types of models available in SCIA to model a through bridge. The plate model consists of a 2D-floor and 2D-girder, where the beam models form a combination of a 2D-floor and 1D-girder. But the plate and beam model 1B have in common that rigid connections are applied every ¼ meter between the girder and floor. The analytical solution is derived with the assumption that the bridge is divided into strips with a length of 1,0 meter, which is implemented in the plate and beam models by reducing the E-modulus of the floor to roughly a third (cracked floor). For the governing load combination, this leads to values for torsion, which remain 10-15%, 40% and 10% behind the analytical solution for respectively the plate and beam model 1A and 1B. The large deviation of beam model 1A is remarkable and can be explained from the fact that no rigid connections between the girder and floor are applied, resulting in a loss of bending and torsional stiffness of the girder. To conclude, the analytical solution is based on a number of assumptions, like no load distribution of the floor in longitudinal direction. In reality loads will be as well distributed in longitudinal as transverse direction and the analytical solution therefore needs to be considered as an safe upper limit.

The actual shear capacity of existing reinforced concrete solid slab bridges, constructed before 1960 in the Netherlands, is subject of an extensive research nowadays, since additional sources, increasing the total shear capacity of concrete slabs, have been ascertained to be present. In addition, the increasing occurrence of human-induced earthquakes in the province of Groningen due to gas extraction, arises uncertainties regarding the seismic behaviour and earthquake resistance of existing bridges in this area. The Nieuwklap bridge is a reinforced concrete solid slab bridge located in the Groningen province, combining both characteristics under investigation. In the course of this research, the first two Levels of Assessment have been applied for the static analysis of the slab part of the deck of the Nieuwklap bridge, which was found to have sufficient shear and bending moment resistance under the application of the traffic loading defined by the current standards. The equivalent proof load tandems, that generate the same shear and bending moment stresses, for each load combination level have been found with both approaches, proving that localized phenomena at the area of load application are more intense when the field experiment takes place. Furthermore, by obtaining the equivalent tandem loading that leads to shear and flexural failure of the concrete slab, it has been concluded that flexural failure due to yielding of the reinforcement will occur first in case of exerting the collapse loading on the flexure-critical positions or on the shear-critical positions next to the end-supports. However, in case of applying the tandem loading on a shear-critical position next to a continuous support it is difficult to define which failure mode will precede. Regarding the seismic evaluation of the Nieuwklap bridge, the simplified fundamental mode method and a modal response spectrum analysis have been used. The bridge deck has been found to have adequate resistance against the vertical component of the seismic excitation, which cannot be considered critical, generating nearly the half stresses compared to the traffic load (LM1) combination defined by Eurocode 2. The piers and the pendulums supporting the bridge deck have been also evaluated against the two horizontal components of the seismic excitation, for two different earthquake return periods, discovering that they are able to withstand the generated forces without additional measures. Finally, from the performed modal analysis it has been obtained that movement of the bridge on the longitudinal direction can be observed in lower frequencies compared to the vertical and the transverse direction and that more than 10 modes are necessary in order to describe accurately the bridge behaviour. This Thesis describes the framework that can be used to prepare collapse tests at multiple Levels of Assessment, and for the seismic assessment of existing bridges in regions with recently initiated seismic activity.

In situations with spatial limitations where a bridge is desired, a skewed bridge is a solution. The bridge deck of a skewed bridge has the shape of a parallelogram, in which the angle that remains in the acute corners is defined as the skew angle. This thesis focuses on the design of reinforced concrete skewed slab highway bridges that are simply supported on discrete bearing pads. A parametric tool is created which, based on a set of values for input parameters, generates and analyzes bridge models created in a finite element method (FEM) software program. After analysis, results are summarized, which allows for a parametric study. The goal of this study is to develop knowledge for decision-making in early stages of projects. The influence of main geometric parameters (skew angle, bridge span length, bridge road width) on the load distribution in a skewed bridge is investigated, as well as the influence of FEM mesh element size, applied plate theory, traffic load configuration and support configuration. Another important parameter, being the bridge deck height, is set to be dependent to the span length at first. Skewed slab bridges tend to span from support to support in the shortest direction. This means that loads will concentrate in the obtuse corner. Resultant quantities, mainly bending moments and shear force in the obtuse corner, are studied on their relation with the different parameters. The obtuse corner load concentrations can require the bridge height to become larger than desired. A powerful measure is to add additional triangular sections (ATS) to the side of the bridge, which increases its width. This way, the road skew angle no longer equals the bridge skew angle. Load concentrations in the obtuse corners are reduced, which can result in a lower deck height, less reinforcement, or both. The effect of ATS addition on resultants is studied: great reduction is observed, even for relatively small ATS addition. In order to relate the bridge deck height to bridge geometry, a reinforcement study is conducted. A procedure is described for a certain cross-section, in which the resultants are known from models generated by the parametric tool. Starting point is the longitudinal bending reinforcement based on the crack width criterion, which is usually governing in bridge design. Next, required shear reinforcement is calculated. Following, the ultimate bending moment capacity is checked, which is found to be always sufficient for crack-width-based reinforcement design. Finally, optimization (different bar diameters, add or remove a reinforcement layer, deck height reduction) is investigated and applied if possible. Using the procedure described above, a case study is conducted. A highly skewed bridge (road skew angle of 20◦) is taken. Starting with 0◦, ATS is added in steps of 5◦. For each geometry, a model is created with the tool after which resultants are used for the reinforcement design. For a bridge span of 13.7 m and a road width of 8.3 m, the first bridge (no ATS, skew angle of 20◦) was found to lie beyond the limits of reinforced concrete. Two layers of 40 mm bars required fatigue-sensitive couplers, while detailing and proper anchorage would prove to be unconstructible. Increasing the cross-section also increased governing moments due to concrete self-weight and therefore is not an option. Addition of a 5◦ ATS resulted in a 900 mm high bridge deck, which seems possible to construct. Addition of 10◦ resulted in a 750 mm high deck, 15◦ into 600 mm and further ATS addition reduced deck height even more. Although it should be noted that ATS addition increases deck surface, a significant reduction in deck height can be obtained. ATS addition is shown to be a powerful measure. Depending on project situation, it can provide optimization and cost savings; the parametric tool is proven to be useful in investigating this.

In this thesis, existing concrete municipal slab bridges are regarded. Many of these bridges were designed and built in the 1960s and 1970s. These bridges are still in service, and subjected to higher and more frequent loads than at the time of design. This leads to uncertainties in the safety of these bridges. Many municipalities become increasingly aware of these uncertainties and want to verify their bridges according to current standards. Especially the shear assessment is critical, since some former codes do not contain shear checks. Municipalities usually do not have sufficient financial resources to investigate and recalculate all of their bridges. A Quick Scan model is a cheap and fast tool to do structural checks, or to classify a number of bridges for structural safety. A literature study and Finite Element Modelling research was performed in order to make the Quick Scan more accurate. In general, existing municipal bridges are not exposed to the same heavy traffic as governmental highways. Nevertheless, municipal bridges were calculated with the same load models as governmental bridges. For the assessment of existing municipal bridges research was done to the possibility of reducing the design loads of Load Model 1 (LM1) from the Eurocode. This reduction can be done with the α- factor on variable loads. The possible reasons for this reduction is threefold. Firstly, municipal roads are significantly less exposed to heavy traffic compared to governmental highways. Therefore the chance of occurrence of the governing vehicle according to LM1 is decreasing. This assumption was supported by Weight-in-Motion measurements on a municipal road in Rotterdam. With the reliability index (β) for existing bridges in Consequence Class 2, this lead to a governing axle load of 225 kN, instead of the 300kN from LM1. The second reason for the reduction of the design load is the fact that municipal bridges usually have relatively small spans (5-20m). LM1 is designed to simulate a fully loaded bridge with a span of at least 20m. For small spans it can be useful to calculate with real occurring traffic, since axle distance is more important than axle loads only. A third (small) reduction is the fact that an existing bridge has a shorter reference period than a new bridge. This leads to smaller chances of the occurrence of the governing vehicle. New load models for small span municipal bridges were designed taking into account these reductions. The governing vehicle for small span bridges is a 5-axle vehicle with axle loads of 137,5-165 kN and axle distances of 140-175mm. Occurring shear forces due to these loads are higher than due to a long vehicle with higher loads, mora axles and greater axle distances. The new governing vehicle was used to determine the reduction factor α. This was determined by a comparative research in the Finite Element Modelling program RFEM. The resulting shear stresses and flexural stresses from the different load models were compared. For spans up to 11m the loads from LM1 can be reduced by an α factor 0,8. This factor increases linearly to a factor 1,0 for a 20m span. Besides the differences in loads and dimensions, municipal bridges also differ from governmental bridges in lay-out. In general, the distance from the carriageway to the edge of the slab is larger for municipal bridges due to the presence of a footpath or bicycle lane separated by a kerb. Bridges in 10 different municipalities were examined on lay-out. Roughly 58% of the municipal bridges in the Netherlands have significant edge distance (>1,2m) This leads to a difference in the force transmission, since the high axle loads from LM1 cannot occur near the edge of the slab. The influence of this edge distance for different spans was investigated with RFEM. Also, the variable and permanent loads were investigated separately to give insight in the resulting shear stress due to different loads. Distinction was made between slabs in cracked and uncracked state. Cracking has significant influence on the transverse force transmission of the axle loads. The transverse force transmission is influenced by the ratio between longitudinal and transverse stiffness, which was conservatively chosen as 1/3. Also, distinction was made between in-situ casted slabs and prefab slabs. The self-weight of in-situ casted slabs leads to a constant shear force on the support. A prefab slab was treated like a theoretical slab, where the self-weight leads to peak forces near the edge due to torsional moments near the edge. The critical edge distance was determined for different spans. For a cracked in-situ casted slab with an edge distance >1,5m, the middle of the slab is always governing in shear. An edge distance <0,7 leads to the edge of the support being governing in shear. Research by Eva Lantsoght to shear force in reinforced slabs under concentrated loads close to the supports was used for rules and assumptions based on experiments. These rules were used to get a better understanding of the results in RFEM, and to develop the Quick Scan Model. The Quick Scan model uses findings from literature research combined with findings from finite element modelling. The output is a Unity Check which can function as real structural shear check if the concrete compressive strength and steel yield strength are known. When only dimensions are known, the Quick Scan model can function as classification for a series of bridges in a municipality. The Quick Scan model was tested by a series of case studies, which did not yet lead to the verification of the model. Results from the Quick Scan model were compared to results from the FEM research. Occurring shear stresses in the Quick Scan model are conservative with a maximum error of 11%. With the possibility of lowering the reliability index β to 2,5 (‘disapproval’ level) and taking into account the possible error due to several uncertainties, the upper boundary of the Unity Check was found as 1,4. Bridges with a Unity Check: 1 < UC < 1,4 according to the Quick Scan model need further assessment or material testing in order to fulfil the requirements. Extensive research was done to loads according to the Eurocode (LM1) on slab bridges and the force transmission of these loads. The capacity of existing concrete slabs was investigated relatively brief. More research to the capacity side of existing concrete bridges is expected to be beneficial.

Müller Verpress piles are driven displacement piles which inject grout at the enlarged tip of the pile into the surrounding soil. Performed full-scale tests were not able to be loaded the pile upon failure, as the pile can resist forces which are significantly larger than its design capacity. This type of pile is known for its large tensile capacity and it is used often to bear major loads in large structures, but the ultimate true capacity has not been identified yet. A better understanding in the behaviour of a MV pile can be crucial in an optimal design of such structures, as construction costs and obtained safety level can be reduced. From provided full-scale tests the uncertainties about the shape of the circumference of the injected grout body and the acting soil pressures have been reduced. Further a different relation is found between the mobilized shaft friction and the cone resistance. As the soil becomes stiffer and holds a larger cone resistance, more shaft friction is mobilized.A two-dimensional numerical model of a cross section of the pile is generated to obtain the actual shape of the circumference and the maximum shaft friction after installation. The measured grout discharges and mobilized shaft friction from pile tests were in the same range as the results obtained from this model, validating that the results of the model are within reason. All available full-scale tests were extrapolated by application of the model and generated similar capacities as the method by measured shaft friction, setting a minimum boundary for α_t at 1.4%. A second numerical model of a complete full-scale tested pile is successfully generated, including the adaptations of obtained parameters from the other model. The adaptations consist of a new circumference, different relation for EA and larger values for the maximum shaft friction. The model showed results which are in the same range as the analytical derivations regarding the course of forces and mobilized shaft friction. The modelled results do however differ slightly in value. This difference in results can be explained by the absence of detailed soil investigation. The lack of detailed geotechnical parameters would increase the accuracy of the model, as the model is very sensitive to variation in the geotechnical parameters. The produced adaptations of multiple parameters have proven however to be a better indication of the total capacity than the current norms. Therefore the norm can be adapted into a more progressive code based on the produced relations of this thesis. The adaptations in EA relation, circumference and mobilized shaft friction comprehend the behaviour of the Muller Verpress pile with a better understanding. Changing these parameters are preferred over the adaptation of the α_t factor, as the theoretical background remains in the design rule.

Recycled granular materials such as Recycled Concrete Aggregate (RCA) and Recycled Crushed Masonry (RCM) are widely used in The Netherlands as base layers in asphalt pavements. The lack of natural resources and the growing amounts of demolition waste made that the Dutch industries in the early 1980s started to explore the possibilities to use construction debris in road construction. Recently, the application of recycled materials in pavement structures has also found traction in South Africa. Due to differences in pavement design, however, the mechanical and environmental exposure of these materials will be more severe than in the Netherlands. This results in different challenges with respect to (long term) performance and material durability. Understanding the potential durability issues and the way durability affects pavement performance is crucial to successfully implement these materials in South African pavements. This research, conducted at Stellenbosch University, South Africa, involves laboratory testing to investigate the performance and durability aspects of recycled aggregates. By means of triaxial testing before and after durability simulation, it is aimed to address the extent of potential material breakdown and the influence this has on performance. Tests are conducted on RCA, RCM, MG65 and MG30. The latter two refer to a mixture of RCA and RCM, with a mass percentage RCA of 65% and 35%, respectively. In addition to the recycled materials, a commonly used crushed rock of G2 quality is tested as well to serve as benchmark. Monotonic triaxial tests, to obtain the shear parameters, are performed on all materials except the pure RCM. Permanent deformation triaxial tests, to gain understanding of the long term response to cyclic loading, are performed on RCA and MG65. Specimens are tested under different confinement and deviator stress levels. For the durability simulation, the South African Durability Mill (DMI) is used. The DMI enables durability testing of the full grading under soaked and dry conditions. After the tests, the milled specimens are sieved out to obtain the change in grading. The most important findings regarding granulate durability include that the breakdown in recycled materials is significant in comparison with the G2. Mainly the largest particle fractions are affected. Furthermore, for these particular resources of recycled granulates, the RCA suffers more breakdown than the RCM. The breakdown in the blends decreases with increasing masonry content, implying that the RCA is the most prone to mechanical damage. Considering the monotonic triaxial tests, substantial values of shear parameters are measured in all materials. The highest cohesion is measured in the MG30, while the highest internal angles of friction are measured in the pure RCA. The shear parameters in the recycled materials are in all cases higher than those for the G2. Differences in failure type (brittle versus plastic) are observed as well. Durability milling results in a small increase of the internal angle of friction and in a moderate decrease of cohesion. The latter is the most governing for the material’s compressive strength after milling, as this is decreased in all milled specimens. Still, the shear parameters of the milled specimens remain relatively high. In the permanent deformation triaxial tests, a decrease of performance can be observed in both the RCA and MG65. Delayed shear failure is observed in milled specimens tested at a deviator stress ratio (DSR) higher than 30%. Although the number of permanent deformation tests performed in this research is limited, 30% DSR seems the upper limit with respect to cyclic loading. This points out that monotonic triaxial testing alone is not sufficient for an adequate material characterization. A small linear elastic pavement analysis based on the tested materials, however, shows that the occuring DSR levels in a reference pavement caused by standard axles of 80 kN do not exceed 20% DSR, proving the potential of these materials for further studies.

Most bridges in the Western European road networks are ageing. The vast majority of about 90% of these bridges have reinforced concrete as a building material. The traffic intensity, as well as the axle, and the average vehicle weight have increased since these structures were opened to traffic. Furthermore, the structural (design) codes have changed over the years. Therefore, there is a need to investigate if existing structures meet the safety/reliability level described by the current codes. However, a frequently faced problem in practice is that the original design calculations and technical drawings of a large percentage of the existing bridges are unknown or lost. Especially for bridges in the lower road network, often designed for the lower load classes B/45 and maintained by a local government, the documentation is missing. The national road network, designed for load classes A/60 is maintained by the national government and faces the same problem but to a lesser extent. Bridges within this scope have different detailing rules and execution practices than used nowadays. Plain reinforcement was in general used which is bend-up at a support. Therefore, the study is twofold: first, Reverse Engineering is applied to determine the reinforcement of existing reinforced concrete slab bridges, second the capacity margin of RE bridges are examined with the current assessment codes. A Reverse Engineering-tool is developed to automate the dimensioning of the required reinforcement according to the former design codes. This tool uses the year of design, load class and the geometric dimensions of the bridge as input parameters. A parametric study is performed to examine bridges from different design periods. Consequently, the Reverse Engineering-tool is used to assess the Reverse Engineered bridge according to the current assessment codes. The validation of the model shows for the majority of the Reverse Engineered bridges that the Reverse Engineered reinforcement is slightly less than the reinforcement amounts from the technical drawings. This proves a conservative approach where the actual structural capacity is underestimated. Consequently, an assessment of the Reverse Engineered bridge can be performed with sufficient robustness.The computer code ran with the input parameters having a normal distribution, showed the largest effect for the uncertainty in the design year and load class especially around 1940 and 1962. Therefore, the design year and load class are crucial in Reverse Engineering and assessment of an existing bridge. The capacity margin of the Reverse Engineered bridges is assessed according to the current Eurocode based design codes. The traffic- and permanent load including load factors according to the general assessment codes from the NEN8700/NEN8701 and the RBK-1-1, and the decentralised load model from TNO are applied. The assessment with the Eurocode including the load factors from the NEN8700 showed Unity Checks for bending moment at the mid-supports and mid-spans of larger than 1.0, where the Unity Checks for shear forces resulted below 1.0. The assessment with the Decentralised load model showed Unity Checks for bending moment at the mid-supports and mid-spans and shear force below 1.0. In case the amount of support reinforcement is based on the amount of span reinforcement, the bending capacity margin at the mid-supports is insufficient for large spans. Significant bending capacity margins are obtained in structural design of RC slab bridges in the period 1930-1970. The main contribution of this research is that bridges designed between 1940 and 1962 show the most critical Unity Checks for bending in the assessed period. In this period account the following design methods: The dynamic amplification factor introduced in the GBV1940 for concrete bridges, the traffic load class from the VOSB1933, the N-method to determine the cross-section capacity and the effective width method from the GBV1940 and from the Guyon Massonnet method.The capacity margin for shear is found to be almost independent of the design period. Here can be concluded that the slenderness of the bridge deck is the main contribution in the shear capacity. Bridges designed in the period 1940-1962 with the support reinforcement based on the span reinforcement and with a span length >10m designed for load class B/45 or with a span length of >11m designed for load class A/60, form the group with the most critical bending capacity. However, the size of the group of former bridges designed according to these conditions is unknown.From the results can be concluded that bridges designed between 1940-1962 with RE reinforcement are found to be legally unsafe for bending according to the parametric assessment with the Eurocode.

The role of the slab mechanism compressive membrane action is investigated, during the direct loading of a beam integrated in a prestressed deck bridge.