Lifetime-Oriented Structural Design Concepts- P5 ppt

2.3 Transport and Mobility 77 10 2 10 3 10 4 10 5 10 6 10 7 number of vehivles and axles per year 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 vehicle weight axle weight G [kN] 1270 kN n Fig. 2.55. Traffic records from the Netherlands recorded in 2006 periods of one or two years. In this case a further increase of these transports can be expected and it cannot be excluded that a significant percentage of these transports is overloaded. A possible increase in the number of such vehi- cles in combination with a possible overloading has especially to be considered for the development of future fatigue load models. A comparable development takes place in other European countries. Figure 2.55 shows the vehicle weight and axle load distributions recorded in 2006 near the harbour of Rotterdam in the Netherlands. It can be seen that the extreme values of the gross weight and also the extreme values of the axle loads are significant higher than the values of the Auxerre traffic (see Figure 2.24). The shape of the distribution shows that the heavy load transports lead in comparison with the Auxerre traffic to a new shape of the distribution which could be taken into account by splitting the distribution into a distribution for normal traffic and a distribution for heavy load transports. Additionally the transport industry is extremely interested in new trans- port concepts at present. In some European countries and also in some Ger- man federal states field trials take place with modular vehicle concepts, the so called Giga-Liners with gross weight up to 600 kN and a total length of 25.25 m [314]. Typical vehicles and the corresponding allowable axle loads are shown in Figures 2.56 and 2.57. These types of vehicles have significant higher transport capacities and can reduce the transport cost. At present it cannot be foreseen how the future traffic composition will change. Some people ar- gue that the new modular concept will reduce the total number of lorries on roads due to the higher transport capacity. On the other hand it has to be 78 2 Damage-Oriented Actions and Environmental Impact Vehicles acc. to the modular concept (gross weight up to 600kN) 25,25 m 16,50-18,25 m Current trucks in Germany (gross weight 400kN) Fig. 2.56. Heavy vehicles on the basis of the modular concept (Giga-Liners) 1,475 5,10 m 1,35 4,65 1,35 5,965 m 1,36 1,36 2,64 1,475 3,215 1,36 5,965 m 1,36 6,27 m 1,36 2,88 1,36 25,25 m 57 kN 74 kN 74 kN 65 kN 65 kN 65 kN 90 kN 90 kN 74 kN 92 kN 92 kN 54 kN 54 kN 78 kN 78 kN 78 kN Giga – Liner with gross weight of 600 kN Giga – Liner with gross weight of 580 kN Fig. 2.57. Axle spacing and allowable axle weights of ”Giga-Liners” considered that this new type of vehicle can not be loaded on trains, so that it can be expected that no significant reduction of the total road traffic will occur. First investigations [201] show that especially for bridges with longer spans the current European load model has to be modified, when the percentage of the new vehicles reaches 20% to 40% related to the to- tal heavy traffic. Furthermore at present no information is available regarding the driving of such vehicles in convoys, especially on routes with acclivities, and the possible overloading and wrong loading which can lead to higher axle weights. 2.3 Transport and Mobility 79 The new traffic concepts and development regarding heavy transports need new technologies to get more detailed information about the actual traffic situation and also a more close cooperation between the car industry and the authorities and experts for the development of realistic traffic models. The Weight in Motion (WIM) is a technology [407, 588] for the determination of the weight of vehicles without requiring it to stop for weighting. The system uses automated vehicle identification to classify the type of the vehicle and measures the dynamic tyre force of the moving vehicle when the vehicle drives over a sensor. From the dynamic tyre load then the corresponding tyre load of a static vehicle is estimated. The most common WIM device is a piezoelectric sensor embedded in the pavement which produces a charge that is equivalent to the deformation induced by the tyre loads on the pavements surface. Nor- mally two inductive loops and two piezoelectric sensors in each monitoring lane are used. The system can be used in combination with an automatic vehicle clas- sification system (AVC). Vehicles which do not meet the gross weight and axle weight requirements are notified with dynamic message signs. While in the USA this systems are used in some states all over the country, in Eu- rope only in some countries these systems are used on special routes. First field trials with combined WIM and AVC methods take place presently in the Netherlands. The records demonstrate that besides the problem that the total weight of the vehicles exceed the permissible total weight there are also cases where the permissible total weight is not exceeded, but due to wrong loading of the vehicles the weight of single axles is significantly higher than the permissible axle weight. This can lead to excessive fatigue damage espe- cially in orthotropic decks of steel bridges and also in concrete decks. These new traffic records demonstrate that in the future a better cooperation be- tween bridge designers and truck producers is necessary. Strategies to avoid such overloading of single axles could be the implementation of immobiliser systems in trucks if single axles or the total gross weight of the truck are exceeded. 2.3.2 Aerodynamic Loads along High-Speed Railway Lines Authored by Hans-J¨urgen Niemann Shelter walls often accompany high-speed railway lines for noise protec- tion or to provide wind shelter for the trains. The walls consist of vertical cantilevered beams connected by horizontal panels. The pressure pulses from head and tail of the train induce a pressure load on the walls, which is in general smaller than the wind load. However, the load is dynamic which may cause resonant amplification. The load is furthermore frequent which may require design for fatigue. These issues are the topic of the following chapter. 80 2 Damage-Oriented Actions and Environmental Impact Fig. 2.58. Pressure time history at the track-side face of a 8 m high wall; at a fixed position; V = 234.3km/h, [573] 2.3.2.1 Phenomena As a train passes, a sudden rise and drop of the static pressure occurs. Struc- tures at the trackside, such as noise barrier or wind shelter walls, in turn experience a time variant aerodynamic load [777]. It is caused by the pressure difference over the wall sides facing the track and the rear face. The load in- tensity of this aerodynamic loading is proportional to the square of the train speed. Figure 2.58 shows a pressure time history measured at a fixed position at the trackside surface of a wall, 1.65 m above rail level. The wall distance to the track axis is a g =3.80 m. Typically, the head pulse starts with a posi- tive pressure which is followed by a negative pressure approximately identical in magnitude. The subsequent tail pulse is reversed and its amplitudes are smaller unless the train is short. For short vehicles, head and tail pulse may merge and the negative pressure may dominate. Additional pulses occur at inter-car gaps with amplitudes much smaller than head and tail pulses. The measured time history clearly depends on the train speed. If instead of the time history the load pattern along the wall is considered, it becomes inde- pendent of the train speed. Figure 2.59 gives an example. The pattern of the pulse sequence travels along the wall at the train speed. It provides a dynamic load on the wall structure within a narrow bandwidth of frequencies determined by the train speed V . Furthermore, a spectral de- composition shows that the distance Δx of the positive and negative pulses is related to the prevailing frequency. Figure 2.59 gives two values of Δx mea- sured at a track distance of a g =3.80 m at two different train speeds. The effect of the train speed is within the scatter of the experimental results. 2.3 Transport and Mobility 81 Fig. 2.59. Pressure distribution along the track-side face of a wall at two different train speeds [573] (a) (b) Fig. 2.60. Full scale tests performed along the high speed line Cologne-Rhine/Main: view of the trough; (a) measuring the train speed, (b) with measurement set-up at the eastern wall A spectral decomposition shows that the prevailing frequency f p is in the order of f p ≈ V 2.7Δx (2.64) Depending on the natural frequencies f n of the wall or any other trackside structure resonance may occur at a critical train speed V res ≈ 2.7Δxf n ,which in turn may cause considerable fatigue at rather few train passages. The 82 2 Damage-Oriented Actions and Environmental Impact maximal pressure amplitude measured at a train speed of 304 km/h= 84.6m/sisca.0.550 kN/m 2 . Typical wind loads are larger by a factor of 2 to 4. It has been argued that the load effect will become important only at very high speeds beyond 300 km/h (see [617]). In fact, the aerodynamic load does not dominate the design as long as the train speed is sufficiently below the critical. If however the critical speed is lower than the maximal track speed, resonant amplification will provide the dominant design situation. Fatigue damage occurred at protection walls along a high speed railway line in 2003. Previous investigations e.g. [36] had dealt with the static effect of the pulse and developed simplified design loads which cover the static action effect. However, they did not consider to model the loading process in view of the dynamic load effects. Therefore, additional investigations became necessary with a focus on the dynamic nature of the load. One issue concerned full-scale measurements of the aerodynamic load patterns along the wall and over the wall height, and the relation of natural wall frequency to the critical train speed. The following findings rely on the results of a campaign performed in 2003, see [573]. The measurements were performed along a concrete wall in order to avoid disturbances coming from the strong deformations of some of the walls. 2.3.2.2 Dynamic Load Parameters The streamlined shape of nose and tail, as well as the frontal area do not only determine the drag of the train but also the pulse amplitudes. As well, the nose length affects the distance between the pressure peaks. The ERRI-report [36] identifies three typical train nose shapes and gives load reduction factors as follows: freight trains k 1 =1, 00; express trains with V max = 220 km/h k 1 =0, 85; high speed trains (TGV, ICE, ETR) k 1 =0, 60. The dynamic stagnation pressure of the train speed clearly governs the aero- dynamic pressures. Figure 2.61 is based on the pressures at the track-side wall surface. The diagram relates the measured pressure peaks of the head pulse, positive and negative, to the dynamic head of the train speed: q = 1 2 ρV 2 (2.65) The relation is linear with a high degree of correlation, and it follows that pressure coefficients may be introduced as c p = p q (2.66) 2.3 Transport and Mobility 83 (a) (b) Fig. 2.61. 3 Effect of train speed stagnation pressure on the head pulse acting at the track-side face of a wall; (a) positive pressure; (b) negative pressure Figure 2.62 shows the pattern of the head pulse in terms of pressure coeffi- cients. The peak coefficients of ±0.15 are typical for the well shaped, slender nose of the ICE 3 train. The mean values are somewhat smaller. The detailed coefficients c p obtained for 152 train passages are: peak pressure maximum c p =0, 1499 mean pressure maximum c p =0, 1380 lowest pressure maximum c p =0, 1049 peak pressure minimum c p = −0, 1520 mean pressure minimum c p = −0, 1419 highest pressure minimum c p = −0, 1041 84 2 Damage-Oriented Actions and Environmental Impact Fig. 2.62. Pressure coefficients of the head pulse from 34 passages (at the track-side wall face) at 1.65 m above track level Fig. 2.63. Distance between the pulse peaks and the zero crossing (ΔL 1 = pressure maximum, ΔL 2 = pressure minimum) The dynamic effect is related to the distance between the pulse peaks. As is seen in Figure 2.63 a mean distance of Δx =6.9m is typical for the ICE 3 passing at a track distance of 3.80 m. At a train speed of 300 km/h, the related frequency is f p =4.5Hz. Natu- ral frequencies of light protection walls are in the same order of magnitude. Obviously, the critical train speed may happen and its dynamic effect may become important. 2.3 Transport and Mobility 85 Fig. 2.64. Head pulse in a free flow at various distances from the track axis [98] Fig. 2.65. Head pulse in the presence of a wall The results refer to a distance between the wall and the track axis of a g =3.80 m. This parameter plays an important role both for the amplitude of and the distance between peaks. Figure 2.64 shows the result obtained the- oretically regarding the pressure pulse in a free flow. As the track distance a g increases, the peak amplitudes max p and min p decrease whereas the separa- tion Δx between the pulse peaks increases. Theory predicts that in free flow without walls, the separation Δx depends linearly on the track distance a g , see e.g. [98] Δx = √ 2 a g (2.67) 86 2 Damage-Oriented Actions and Environmental Impact Experimental results can best be fitted by a slight modification: Δx =1.424 a 1.029 g (2.68) Figure 2.65 shows the head pulse in the presence of a wall for two different distances. The measurements at a track distance of 3.80 m and 8.30 m were performed simultaneously i.e. at identical train speeds at different walls, both 8 m high. The distance of the peaks at the wall decreases similar to the free flow case. However, the results indicate that the effect of the track distance becomes non-proportional in the presence of a wall. An analogous approxima- tion matches the test results Δx(a g )=6.9  a g a g,ref  0.653 (2.69) in which a g,ref =3.8 m is used as reference. The pressure amplitudes decrease with the inverse of the square of the track distance. Various empirical expressions take account of this theoretical result. The following formula developed in [36] is widely accepted: c p,max = k 1  2.5 (a g +0.25) 2 +0.025  (2.70) Introducing the pressure at a g =3.80 m as a reference, the peak pressure amplitude at any distance becomes c p,max (a g )=c a · c p,max (3.8) =  14.1 (a g +0.25) 2 +0.14  c p,max (3.8) (2.71) For a g =8.3 m, the formula gives a wall distance factor of c a =0.333. The experimental result is in this case a decrease by a mean factor of 0.3. The formula presented is a conservative estimate. The pressure varies over the wall height. Figure 2.66 is an example of a pressure pattern measured at a wall, 8 m high. The pressure intensity decreases at the upper end. This end effect coincides with a shift of the pulse peaks between wall foot and top, meaning that they do not occur simultaneously at each level. Figure 2.67 shows the time lag between head pulse maximum and mini- mum as it varies over the height of a 3.5 m wall. The measurements include various train speeds, the time lag has been transformed to V = 300 km/h. The maxima occur simultaneously at each level, whereas the minimum is not simultaneous but lags increasingly at higher levels. This will in general di- minish the dynamic load effect. A conservative approximation is to assume identical and simultaneous pulse patterns at each level. Finally, the pressure magnitudes depend on the wall height. The experiments show that the pres- sures measured at low levels are higher in magnitude at high walls compared to lower walls. The pulse between the walls apparently levels out more rapidly when the walls are low. A convenient wall height factor is: [...]... lead to limitation and loss of the function of the component, although structural stability is still assured (e.g in the case of airport taxiways) Internal damage is characterized by microstructural damage arising from microcracks (Figure 2.78), which influence the mechanical and physical properties of the concrete structure, and its structural integrity as a result While both types of damage go hand-inhand... which the pressure coefficients have been determined The results refer here to HW ref = 3.50 m 2.3.2.3 Load Pattern for Static and Dynamic Design Calculations The following expression summarizes the observed effects and may be applied to static and in particular to dynamic design calculations: q1k (x, z, ag ) = cWH (HW ) ca (ag ) cz (z) cp (x) ρ V2 2 (2.73) where: q the pressure at a distance x from the train... (with and without Deicing Agents) Authored by Ivanka Bevanda and Max J Setzer Frost and deicing salt attack are under the most detrimental environmental phenomena to be taken into account for durability design of concrete Frost attack with and without the presence of deicing salt is a dynamic effect that involves both a transport mechanism and a damage mechanism Setzer coined the term frost suction for... as loads for constructional measurement (Figure 2.74) From a technological point of view, durability is determined by minimum concrete composition requirements (water/cement ratio, cement content) The design concept was derived from current knowledge of deterioration mechanisms and correlations between exposure and resistance This simple approach does, however, have the major disadvantage that the application... after one winter at field station Meißen; scaling 260 g/m2 , visual degree of damage 21% 2.4.2.2 Damage Due to Frost Attack In keeping with the objective, both the external damage and the internal microstructural damage to the exposed concrete samples were determined The internal damage was determined by ultrasound pulse transit time measurement pursuant to [729] After two winters, there was no internal . the design as long as the train speed is sufficiently below the critical. If however the critical speed is lower than the maximal track speed, resonant amplification will provide the dominant design. Pattern for Static and Dynamic Design Calculations The following expression summarizes the observed effects and may be applied to static and in particular to dynamic design calculations: q 1k (x,. function of the component, although structural stability is still assured (e.g. in the case of airport taxiways). Internal damage is characterized by microstructural damage arising from microcracks