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This thesis is concerned with the use of semi-active suspensions in heavy vehicles to improve ride and reduce road damage. An introduction into the subject is given in chapter 1 and a review of the relevant literature is presented at the beginning of each main chapter. The development and modelling of a prototype, continuously variable semi-active damper for heavy vehicles is described in chapter 2. A proportional valve is used to generate the variable damping coefficient and the detrimental effects of the oil flow forces acting on the valve spool are studied. The force tracking performance of the damper is then examined for simple input conditions and the compliance of the hydraulic fluid is found to have a strong influence upon the response of the damper. The different vehicle and road models used in the thesis are described in chapter 3. In chapter 4, the performance of the prototype damper is investigated under realistic operating condition using a Hardware-in-the-Loop (HiL) test rig, with a single wheel station vehicle model. The prototype damper displays a phase lag of approximately 20ms between the demanded and achieved damping force. The semi-active suspension is found to be most effective in reducing the body accelerations relative to an optimum non-linear passive suspension. A theoretical investigation into the reduction of road damage through the use of active and semi-active suspensions is described in chapter 5. The relative performance of four linear state feedback control strategies is examined. The potential for reducing road damage by using a controller which directly regulates various measures of road damage is also studied. Significant improvements are predicted for the three controllers which assume the road inputs to the vehicle are correlated. However, these benefits are shown to diminish as the vehicle speed is reduced. It is concluded that the control of the dynamic tyre forces is an effective means by which to regulate road damage. Theoretical predictions of the benefits from wheelbase preview control are measured experimentally in chapter 6, using the prototype semi-active damper in a half-car HiL rig with a planar two axled heavy vehicle model. The benefits of preview control using the prototype semi-active damper are found to be less than theoretically possible due to the phase lag between the demanded and achieved damping force of the prototype damper. The final section of chapter 6 shows that the performance of the prototype damper can be improved further by having a theoretical simulation running ahead of the HiL vehicle. The theoretical simulation is used to predict the demanded damper force for the HiL vehicle and thereby compensate for the phase lag in the prototype damper. Conclusions and recommendations for further work are presented in chapter 7.

Prague ring road is one of the most important constructions of Prague and Central Bohemia. When completed, it will become one of routes with the heaviest traffic in the Czech Republic. In my thesis I deal with the past, present and future of Prague ring road. I have mentioned its individual parts as well as its links to urban circuit. The main focus is on the most problematic part of the circuit, namely the northwestern segment.

This thesis examines the classic ride comfort vs. handling compromise when designing a vehicle suspension system. A controllable suspension system, that can, through the use of suitable control algorithms, eliminate this compromise, is proposed and implemented. It is a well known fact that if a vehicle suspension system is designed for best ride comfort, then handling performance will suffer and vice versa. This is especially true for the class of vehicle that need to perform well both on- and off-road such as Sports Utility Vehicles (SUV’s) and wheeled military vehicles. These vehicles form the focus of this investigation. The ride comfort and handling of a Land Rover Defender 110 Sports Utility Vehicle is investigated using mathematical modelling and field tests. The full vehicle, non-linear mathematical model, built in MSC ADAMS software, is verified against test data, with favourable correlation between modelled and measured results. The model is subsequently modified to incorporate hydropneumatic springs and used to obtain optimised spring and damper characteristics for ride comfort and handling respectively. Ride comfort is optimised by minimising vertical acceleration when driving in a straight line over a rough, off-road terrain profile. Handling is optimised by minimising the body roll angle through a double lane change manoeuvre. It is found that these optimised results are at opposite corners of the design space, i.e. ride comfort requires a soft suspension while handling requires a stiff suspension. It is shown that the ride comfort vs. handling compromise can only be eliminated by having an active suspension system, or a controllable suspension system that can switch between a soft and a stiff spring, as well as low and high damping. This switching must occur rapidly and automatically without driver intervention. A prototype 4 State Semi-active Suspension System (4S4) is designed, manufactured, tested and modelled mathematically. This system enables switching between low and high damping, as well as between soft and stiff springs in less than 100 milliseconds. A control strategy to switch the suspension system between the “ride” mode and the “handling” mode is proposed, implemented on a test vehicle and evaluated during vehicle tests over various on- and off-road terrains and for various handling manoeuvres. The control strategy is found to be simple and cost effective to implement and works extremely well. Improvements of the order of 50% can be achieved for both ride comfort and handling. AFRIKAANS : In hierdie proefskrif word die klassieke kompromie wat getref moet word tussen ritgemak en hantering, tydens die ontwerp van ‘n voertuig suspensiestelsel ondersoek. ‘n Beheerbare suspensiestelsel, wat die kompromie kan elimineer deur gebruik te maak van toepaslike beheeralgoritmes, word voorgestel en geïmplementeer. Dit is ‘n bekende feit dat, wanneer die karakteristieke van ‘n voertuigsuspensiestelsel ontwerp word vir die beste moontlike ritgemak, die hantering nie na wense is nie, en ook omgekeerd. Dit is veral waar vir ‘n spesifieke kategorie van voertuie, soos veldvoertuie en militêre wielvoertuie, wat oor goeie ritgemak en hantering, beide op paaie en in die veld, moet beskik. Die fokus van die huidige studie val op hierdie kategorie voertuie. Die ritgemak en hantering van ‘n Land Rover Defender 110 veldvoertuig is ondersoek deur gebruik te maak van wiskundige modellering en veldtoetse. Die volvoertuig, nielineêre wiskundige model, soos ontwikkel met behulp van MSC ADAMS sagteware, is geverifieer teen eksperimentele data en goeie korrelasie is verkry. Die model is verander ten einde ‘n hidropneumatiese veer-en-demperstelsel te inkorporeer en verder gebruik om optimale veer- en demperkarakteristieke vir onderskeidelik ritgemak en hantering te verkry. Ritgemak is geoptimeer deur in ‘n reguit lyn oor ‘n rowwe veldterreinprofiel te ry, terwyl hantering geoptimeer is deur ‘n dubbelbaanveranderingsmaneuver uit te voer. Die resultaat is dat die geoptimeerde karakteristieke op die twee uiterstes van die ontwerpsgebied lê. Beste ritgemak benodig ‘n sagte suspensie terwyl beste hantering ‘n harde suspensie benodig. Daar word aangedui dat die ritgemak vs. hantering kompromie slegs elimineer kan word deur gebruik van ‘n aktiewe suspensiestelsel, of ‘n beheerbare suspensiestelsel wat kan skakel tussen ‘n sagte en stywe veer, asook hoë en lae demping. Dié oorskakeling moet vinnig en outomaties geskied sonder enige ingryping van die voertuigbestuurder. ‘n Prototipe 4 Stadium Semi-aktiewe Suspensie Stelsel (4S4) is ontwerp, vervaardig,getoets en wiskundig gemodelleer. Die stelsel skakel tussen hoë en lae demping, asook tussen ‘n stywe en sagte veer binne 100 millisekondes. ‘n Beheerstrategie wat die suspensiestelsel skakel tussen die “ritgemak” en “hantering” modes is voorgestel, op ‘n toetsvoertuig geïmplementeer en evalueer tydens voertuigtoetse oor verskeie pad- en veldry toestande, asook tydens omrol- en hanteringstoetse. Die beheerstrategie is koste-effektief en maklik om te implementeer en werk besonder goed. Verbeterings in die orde van 50% kan behaal word vir beide ritgemak en hantering. / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

The process of designing cementitious layers (weakly and strongly cemented) against fatigue distress in road structures is well accepted. Research and field investigations with the aid of the Heavy Vehicle Simulator (HVS) revealed, however, that almost all weakly cemented subbase layers undergo non-traffic and traffic¬associated cracking and eventually degradation of the cemented material into a granular state (post-cracked phase). It is therefore very important to analyse these layers in the post-cracked phase and to incorporate the results of this analysis in the design, for both new and rehabilitation designs. The investigations revealed that the rate of degradation of these materials is largely dependent on traffic loading and the moisture conditions within the pavement layers. The purpose of this study is to investigate the behaviour of weakly cemented subbase layers in road structures mainly under a bitumen base between 90 mm and 140 mm thick. This behaviour includes both pre-cracked and post-cracked phases. It is shown that the fatigue life of bitumen base layers is mainly governed by the condition of the weakly cemented subbase layers. In Chapter 1 a brief historical review is given of the development of fatigue distress criteria of the cementitious layers. It is shown that the maximum horizontal tensile strain at the bottom of these layers is the main distress criterion in the pre-cracked phase. Unconfined compressive strength and durability requirements are also discussed. Some aspects of the current design methods are outlined in Chapter 2. The concept of equivalent granular states in the post-¬cracked phase of cementitious layers was derived from HVS test findings. However, before this document no behavioural prediction models were available to quantify accurately the post-cracked state of these layers. The actual mechanisms of distress were also not clear. In Chapter 3, a detailed investigations and analysis of ten dif¬ferent HVS tests at four different sites in Natal are discussed. The purpose of the analysis, is firstly to illustrate the powerful method of full-scale accelerated HVS-type testing and secondly to indicate the importance of the upper subbase layer, the initial condition of the in-situ structure, the importance of water condi¬tions within the pavement structure, and finally the different states of behaviour of this type of road structure, including predictions of future behaviour based on linear elastic theory. The characteristics of the weakly cemented upper subbase layer are shown to be of paramount importance in the final behaviour of these structures. In Chapter 4 a method of analysing the behaviour of mainly weakly cemented layers in the post-cracked phase is proposed. This method arises from the HVS testing discussed in Chapter 3, and may be regarded as the most important improvement on the current method discussed in Chapter 2. The analysis incorporates the determination of the effective elastic moduli of weakly cemented subbase layers, including both the wet and the dry periods during the structural design period of these layers. In Chapter 5 the effect of relatively weak interlayers within asphalt base structures is discussed and evaluated. The analysis incorporates the relative position and thickness of the inter layer during both wet (low modulus) and dry (high modulus) conditions. A summary and detailed discussion, together with recommendations for future research, are given in Chapter 6. The need for the incorpo¬ration of durability (erodibility) criteria for weakly cemented materials is also discussed. More research should be done on the effects of accelerated curing compared with normal curing methods. This investigation includes aspects of soil-lime-cement reactions together with delayed compaction techniques to reduce shrinkage cracking. The need for better quality control as well as improved construction techniques for weakly cemented materials is also discussed. This thesis also contains two appendices. In the first of these detailed photographic records of the different HVS tests and performances are given. In the second appendix an example of an input computer program to plot the three dimensional behavioural model is given. / Dissertation (MEng)--University of Pretoria, 2009. / Civil Engineering / unrestricted

The cost of a road construction over its service life is a function of the design, quality of construction, maintenance strategies and maintenance operations. Unfortunately, designers often neglect a very important aspect which is the possibility to perform future maintenance activities. The focus is mainly on other aspects such as investment costs, traffic safety, aesthetic appearance, regional development and environmental effects. This licentiate thesis is a part of a Ph.D. project entitled “Road Design for lower maintenance costs” that aims to examine how the life-cycle costs can be optimized by selection of appropriate geometrical designs for the roads and their components. The result is expected to give a basis for a new method used in the road planning and design process using life-cycle cost analysis with particular emphasis on road maintenance. The project started with a review of literature with the intention to study conditions causing increased needs for road maintenance, the efforts made by the road authorities to satisfy those needs and the improvement potential by consideration of maintenance aspects during planning and design. An investigation was carried out to identify the problems which obstruct due consideration of maintenance aspects during the road planning and design process. This investigation focused mainly on the road planning and design process at the Swedish Road Administration. However, the road planning and design process in Denmark, Finland and Norway were also roughly evaluated to gain a broader knowledge about the research subject. The investigation was carried out in two phases: data collection and data analysis. Data was collected by semi-structured interviews with expert actors involved in planning, design and maintenance and by a review of design-related documents. Data analyses were carried out using a method called “Change Analysis”. This investigation revealed a complex combination of problems which result in inadequate consideration of maintenance aspects. Several urgent needs for changes to eliminate these problems were identified. Another study was carried out to develop a model for calculation of the repair costs for damages of different road barrier types and to analyse how factors such as road type, speed limits, barrier types, barrier placement, type of road section, alignment and seasonal effects affect the barrier damages and the associated repair costs. This study was carried out using a method called the “Case Study Research Method”. Data was collected from 1087 barrier repairs in two regional offices of the Swedish Road Administration, the Central Region and the Western Region. A table was established for both regions containing the repair cost per vehicle kilometre for different combinations of barrier types, road types and speed limits. This table can be used by the designers in the calculation of the life-cycle costs for different road barrier types.

The goal of the diploma thesis is to design and to assess a solution of a northern bypass of the road I/23, which will divert a transit traffic from Rosice. The town is situated approximately 25 kilometers west of Brno, in the South Moravian region. Three variants are worked out. The variant A and the variant B connects smoothly with a bypass of a neighboring village Zastávka. The variant A then copied a route designed in a local development plan and goes through a built-up part of the town Rosice in the area of the street Na Mýtě. The variant B is designed to avoid passage through this area and bypasses Rosice in north, behind a housing estate Kamínky. The variant C is designed in case an absence of a bypass of the village Zastávka. It connects with existing road I/23 in the village Zastávka in the area of an intersection of streets Lipová – Stará osada. The goal of the bypass is to divert the current transit traffic from Rosice

The proper densification of the separate pavement layers forms an integral part of road construction. Many problems, are, however, experienced in this area. Because of a lack of knowledge the compaction of untreated roadbuilding materials in problem situations is usually approached on a ''trial and error'' basis rather than basing possible solutions on scientific evidence of the collective influence of the material properties and site conditions. The purpose of the study was to place the compaction of untreated roadbuilding materials on a more scientific basis. An investigation was therefore launched to determine the effect of measured material properties on their compactability. A non-standard vibratory compaction test was used to compact the samples in one layer. New test parameters to quantify the shape and texture of the material were also developed, namely the shakedown bulk density and the shape factor. The CBR values of the materials at moulding moisture content were determined for each material for a range of densities and moisture contents. The maximum dry densities (MOD) (vibratory and mod. AASHTO) and optimum moisture content (OMC) (vibratory and mod. AASHTO) were also determined. The measured values were then evaluated in terms of the following physical properties of the materials: grading, Atterberg limits, linear shrinkage, shakedown bulk density (SBD), loose bulk density (LBO), shape factor (SF) and specific rugosity (Srv). In the extensive laboratory study of 21 different untreated roadbuilding materials, varying from TAB classes A-7-6 to A-1, it was found that both the maximum dry densities and moisture regimes can be quantified in terms of the grading, liquid limit and linear shnnkage of the materials. These relations were modelled by means of regression analysis. Besides this a general bearing capacity model was found for all these materials where the CBR is a function of the dry density and moisture content of the material. This model was further refined to take account of the influence of shape and texture of the particles so that it is possible to determine reasonable estimates of the bearing capacity for a range of densities and moisture contents from the grading, Atterberg limits, linear shrinkage, shakedown bulk density and shape factor. This investigation has shown that physical laws govern both the compactability and bearing capacity of untreated roadbuilding materials, irrespective of their composition or nature, making it possible to approach the compaction of untreated roadbuilding materials in a more generalised manner. / Thesis (PhD)--University of Pretoria, 1991. / gm2014 / Civil Engineering / unrestricted

see document / Master of Science