Lifetime-Oriented Structural Design Concepts- P3 pps

2.1 Wind Actions 17 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.95 Y(N )/Y ik 2.1x10 6 1.4x10 5 1.4x10 4 1.9x10 3 3.1x10 2 59 12 2.9 7x10 7 3.1x10 11 N 0.85 Fig. 2.4. Distribution of absolute frequencies of normalized gust responses into subsequent classes of different levels of effect Δσ =2·( M k W + N k A ) (2.18) is the reference value, M k an N k are characteristic internal forces of a con- struction component, W is the elastic section modulus, A is the loaded area. Stress levels between 0.9 ·Δσ and 1.0 ·Δσ can occure 2.9 times in 50 years in the statistical mean. A damage accumulation after Palmgren-Miner D =  i (N i /N ci )isper- formed in order to assess resistance of the considered component with respect to fatigue. Figure 2.5 shows an example taken from a fatigue analysis of the S - N c u r v e ( W ö h l e r c u r v e ) o f s t r e s s c o n c e n t r a t i o n c a t e g o r y 3 6 * Fig. 2.5. Comparison of the distribution of cyclic stress amplitudes with the S-N curve (W¨ohler curve) of stress concentration category 36* after [30] 18 2 Damage-Oriented Actions and Environmental Impact gust responses of steel archs of a road bridge. The considered cerb is suffi- cient to resist the repeated gust impacts. The application of the Equations 2.12 or 2.17 permits a detailed and safe method for the fatigue analysis of gust-induced effects at building structures. 2.1.2 Influence of Wind Direction on Cycles of Gust Responses Authored by R¨udiger H¨offer and Hans-J¨urgen Niemann Meteorological observations document that the intensity of a storm is strongly related to its wind direction. Figure 2.6(a) shows the wind rosette of the airport Hannover, Germany, as an example. The probability of the first passage of the same threshold value can strongly vary for different sectors of wind direction. That means that the risk of a high wind induced stressing of a structural component is different between the wind directions. The failure risk 5m/s 15 m/s 25 m/s 35 m/s 90 ◦ 0 ◦ 270 ◦ 180 ◦ 5m/s 15 m/s 25 m/s 35 m/s 90 ◦ 0 ◦ 270 ◦ 180 ◦ 5m/s 15 m/s 25 m/s 35 m/s 90 ◦ 0 ◦ 270 ◦ 180 ◦ 90 ◦ 0 ◦ 270 ◦ 180 ◦ 0.25 0.50 0.75 1.00 (a) (b) (c) (d) Fig. 2.6. Rosettes of wind quantities at Hannover (12 sectors, 50 years return pe- riod) (a) extremes of 10-minutes means of wind velocities at the airport of Hannover at reference height of 10 m above ground (b) extremes of 10-minutes means of wind velocities at a building location at building height of 35 m above ground (c) ex- tremes of gust wind speeds at a building location at building height of 35 m above ground (d) comparison of the load factors of the sectors; the largest load factor is valid for the design of the fa¸cade element after Figure 2.8 2.1 Wind Actions 19 of the structure or structural components is determined by the superposition of all probability fractions originating from the sectors of wind direction. Usually, codes follow the conservative approach to assume the same prob- ability of an extreme wind speed for all wind directions. In general, more re- alistic and very often also more economic results can be achieved if the effect of wind direction is considered. This can be done by employing wind speeds for the structural loading which are adjusted in each sector with a directional factor. Such procedure is in principle permitted by the Eurocode [32]. It is left to the national application documents to regulate the procedures. The wind load is a non-permanent load; within statical proofs of the load bearing capacity it is employed using a characteristic value, which is defined as a 98% fractile, and an associated safety factor of 1.5. A load level is required which is exceeded not more than 0.02 times a year in a statistical sense. Such value is statistically evaluated from the collective of yearly extremes of the wind speeds. The intensity of the wind load is deduced from the level of the wind speed, or more exact, from its dynamicpressure.Therelated statistical parameters are used to determine the characteristic value of the load. The wind load depends on the wind direction as the wind speed is differently distributed regarding their compass, and as the aerodynamic coefficients varies with respect to the angle of flow attack. Taking this into account the most unfavourable load can originate from combining a lower characteristic value of the wind speed, which might be associated to a directionalsector,andthe related aerodynamic coefficient for this sector. In order to evaluate completely the effect of the influence of the wind direction it is required to take the structural response into account, e.g. after [227]. In such procedure a response quantity, which is a representative value of the wind action, is evaluated with the restriction to limit its exceedance probability of its yearly extremes to a value lower than 0.02 instead of focussing on loads. Using this requirement the characteristic wind velocities related to the different sectors can be deduced. 2.1.2.1 Wind Data in the Sectors of the Wind Rosette The maximum wind load effect on a structural component is resulting from the most unfavourable superposition of the function of the aerodynamic coeffi- cient and the dynamic pressure. Both variables are independent and functions of the direction of mean wind. The usual zoning in statistical meteorology into twelve sectors of 30 ◦ each is a sufficient resolution in order to include distri- bution effects. The prediction of the risk requires an analysis of the extreme wind velocities for each sector at the building location. If available a complete set of data is taken from a local station for meteorological observations near the considered building location. The wind statistics of a considered building location in the city of Hannover in Germany is shown in Figure 2.6(a) as an example. The wind rosette is evaluated from data collected at the observation station at the airport of Hannover. The terrain in the environment of the sta- tion is plain with a relatively homogeneous surface represented by a roughness 20 2 Damage-Oriented Actions and Environmental Impact Table 2.1. Conversion of the wind data of the observation station at the airport of Hannover into data for the building location Sectors of wind directions 0 ◦ 30 ◦ 60 ◦ 90 ◦ 120 ◦ 150 ◦ 180 ◦ 210 ◦ 240 ◦ 270 ◦ 300 ◦ 330 ◦ airport: 1 z 0 =0.05 m: v m (z =10m) in m/s 12.1 11.7 17.4 13.0 15.2 15.9 17.1 20.5 23.0 20.6 16.7 12.5 arena: 2 z 0 in m 0.44 0.27 0.31 0.24 0.24 0.08 0.10 0.11 0.36 0.36 0.36 0.35 3 k r · ln( z z 0 ) 0.96 1.03 1.02 1.05 1.05 1.20 1.16 1.15 1.00 1.00 1.00 1.00 4 v m (z =35m) 11.7 12.1 17.7 13.7 16.0 19.0 19.9 23.7 22.9 20.5 16.6 12.5 5 I u (z =35m) 0.229 0.206 0.212 0.201 0.201 0.164 0.171 0.174 0.218 0.218 0.218 0.217 6 gust factor v v m 1.540 1.494 1.506 1.485 1.485 1.409 1.423 1.429 1.520 1.520 1.520 1.518 7 v(z =35m) 18.0 18.1 26.7 20.3 23.7 26.8 28.3 33.8 34.8 31.2 25.3 19.0 of ca. z 0 =0.05 m in all of the sectors. The measurements have been conducted in a standard height of 10 m above ground level, cf. J. Christoffer and M. Ulbricht-Eissing [196]. N yearly extremes of the mean wind velocity v m are ranked in each sector F , and respective probability distributions are iden- tified. In the presented example distributions of Gumbel-typewereadapted. The occurrence probability of an extreme value in a year, which is lower than a reference value v m,ref ,iscalculatedfrom P (v m ≤ v m,ref )=F (v m,ref )=e −e −a(v m,ref −U) (2.19) In Equation 2.19 U is the modal parameter, and the parameter a describes the diffusion. The wind velocities with return periods of 50 years for all sectors are listed in Table 2.1, line 1. In opposite to the conditions at the observa- tion station, the building location is surrounded by a terrain with strongly non-homogeneous surface roughnesses. The effect of the varying roughnesses superpose the undisturbed conditions evaluated for the location of the obser- vation station. These additional effects influence the wind velocity in reference height, its profile and the profile of gustiness over height, which vary between the directions according to the respective roughness conditions of a sector. The surface roughnesses for each sector are required. The local roughness lengths z 0 of the surface roughness is analysed from aerial photographs over a radius of 50 to 100 times the height of the considered building, e.g. ca. 5 km in case of the considered stadium, Figure 2.7. Mixed profiles are evaluated for those sectors with significantly changing surface roughnesses; for approxima- tion an equivalent roughness length is adapted. The results are shown in line 2 of Table 2.1; the conditions within each sector are described by conversion fac- tors related to the undisturbed wind rosette. The factor in line 3 of Table 2.1 relates the mean wind speeds with a return period of 50 years at the building 2.1 Wind Actions 21 0° b 90° b/5 c =-1.4 p Fig. 2.7. Roughness lengths of the ter- rain in the farther vicinity of the building location [771] Fig. 2.8. Sketch of a building contour (top view) with b<2 h and fa¸cade el- ement exposed to a pressure coefficient c p = −1.4 [32] at the eastern fa¸cade in thecaseofwindsfrom0 ◦ location at a building height of 35 m of the stadium and the reference wind speed of the same return period at the location of the observation station in reference height of 10 m. The logarithmic law for the profile of the mean wind velocities is applied (Equation 2.20). The terrain factor k r is evaluated using an empirical relation (Equation 2.21). v m (z,z 0 ) v m (z ref ,z 0ref ) = k r · ln( z z 0 ) (2.20) k r =( z 0 z 0ref ) 0,07 · 1 ln(z ref /z 0ref ) (2.21) The wind velocities at the building location with a return period of 50 years are evaluated for each sector and are listed in line 4 of Table 2.1. As shown before, mean and gust wind speeds and the respective dynamic pressures are applied to determine equivalent loads which represent the result- ing wind loading for design procedures. The dynamic gust pressure is calculated from the mean dynamic pressure q m and the turbulence intensity I u . q =(1+2g · I u ·Q 0 ) · q m (2.22) The gust velocity in the last row of Table 2.1 is calculated from Equation 2.23, where g is the peak factor and Q 0 is the quasi-static gust reaction. Q 2 0 is also called background response factor after [32]. 22 2 Damage-Oriented Actions and Environmental Impact v =  1+2gQ 0 I u · v m (2.23) For simplicity Q 0 can consistently be determined from 2 gQ 0 = 6 assigning to Q 0 its maximum value 1. It has to be pointed out that the surface roughness is also affecting the turbulence intensity, as shown in line 5 of Table 2.1. The statistical evaluation for all sectors leads to a mean wind of 50 years return period of 23.8m/s at the building location. Figure 2.6(b) represents the rosette of mean wind speeds at the building location. In comparison of both wind rosettes, representing the building lo- cation and the location of the observation station, it can be concluded that the main character of the local wind climate is preserved but relevant changes due to the terrain roughness are introduced. 2.1.2.2 Structural Safety Considering the Occurrence Probability of the Wind Loading The wind load effect on a structure can be expressed in terms of a response quantity Y . For a linear, stiff structure without dynamic amplification, Y is calculated from: Y (Φ)= 1 2 ρv 2 Φ ·  A η p (r) · c p (r, Φ) · dA (2.24) in which: η p influence factor for the pressure p acting at the point on the surface of the structure; r - local vector; c p pressure coefficient at a point of the surface of the structure for a given wind direction Φ; ρ - mass density of air; A - pressure exposed influence area. A certain response force Y forms the basis for the determination of a char- acteristic wind velocity v ik , which is valid over the sector with the central wind direction Φ i . The starting point is v i,lim : Y i,lim (Φ i )=C Y (Φ i ) · 1 2 ρ ·v 2 i,lim (2.25) In Equation 2.25 the response Y i,lim is determined as an equivalent wind effect by use of the gust velocity v. The wind effect admittance depending on the wind direction Φ, C Y = C Y (Φ), is identical to the integral in Equation 2.24. It covers the distribution and the value of the aerodynamic coefficient within the influence area of the load as well as the mechanical admittance, which is the transfer from the dynamic pressure into the response quantity. This operation is conducted for a selected wind direction Φ i . In a second step the complete risk is evaluated as the exceedance probability of the response quantity Y , which adds up from the contributions from each sector. The safety requirements are met if the total risk has a value smaller than 0.02. In case of a risk larger 0.02 an increased value of the v i,lim enters into the iteration until a value smaller 0.02 is achieved. In an analogeous manner a 2.1 Wind Actions 23 decreased value of v i,lim is introduced aiming on an economical optimization if the first iteration yields a value much smaller than 0.02. The total risk of exceeding the bearable response quantity Y i,lim ,oras complementary formulation, the probability of non-exceedance of Y i,lim ,is proved within the following steps. The main idea of the procedure is to make use of combinations C Y (Φ) · 1 2 ρ · v 2 Φ,lim instead of a global C Y · 1 2 ρ · v 2 .A probability of non-exceedance of 0.98 of the applied force must be guaranteed forbothinthesectorsandintotal. C Y (Φ i ) · 1 2 ρ ·v 2 i,lim = C Y (Φ) · 1 2 ρ ·v 2 Φ,lim (2.26) The velocity limit v Φ,lim for a sector Φ results as v Φ,lim =  C Y (Φ i ) C Y (Φ) ·v i,lim =  1 a(Φ) · v i,lim (2.27) The effect of the direction of the wind on the wind effect is expressed through a directional wind effect factor: a(Φ)= C Y (Φ) C Y (Φ i ) (2.28) The probability P (v ≤ v Φ,lim )=F Φ (v Φ,lim ) of the non-exceedance of v Φ,lim within the sector Φ also applies for the response Y ≤ Y i,lim . F (v Φ,lim )can be calculated from the probability distribution of the mean wind velocity in the sector as given by Equation 2.19. The probability of the non-exceedance of the limit Y i,lim after Equation 2.25 under the condition of a certain v i,lim in sector Φ i is satisfied from a product (Equation 2.29) of all non-exceedance probabilities under the condition that the yearly extremes in the different sectors are statistically independent. P (Y ≤ Y i,lim )=P ((v ≤ v 1,lim )  (v ≤ v 2,lim )  ···  (v ≤ v 12,lim )) =  12 1 F Φ (v Φ,lim ) ≥ 0.98 (2.29) The considered value of the gust speed is adequate if the exceedance probabil- ity P (Y>Y i,lim ) is less or equal 0.02 which corresponds to the probability of non-exceedance of (1 − 0.02) = 0.98, Equation 2.29. Obviously, the condition P (Y = Y i,lim ) ≥ 0.98 must be observed in any sector. 2.1.2.3 Advanced Directional Factors The responses of a structure must be taken into consideration for the deter- mination of the relevant wind speeds and wind loads for each sector. This 24 2 Damage-Oriented Actions and Environmental Impact Table 2.2. Determination of a reduced characteristic suction force on the fa¸cade element after Figure 2.8 through the consideration of the effect of wind direction on loading. line 1: extreme gust speed at a building location at Hannover at build- ing height of 35 m; line 2: c p,10 -values at the considered fa¸cade element for wind flow from the respective directions; line 3: directional wind effect factor after Equa- tion 2.8; line 4: iterative determination of applicable wind speeds in sectors and associated non-exceedance probabilities in sectors; line 5: applicable fraction of codified standard load after the proposed method Sectors of wind directions 0 ◦ 30 ◦ 60 ◦ 90 ◦ 120 ◦ 150 ◦ 180 ◦ 210 ◦ 240 ◦ 270 ◦ 300 ◦ 330 ◦ 1 18.0 18.1 26.7 20.3 23.7 26.8 28.3 33.8 34.8 31.2 25.3 19.0 2 -1.4 -1.4 – – – -0.8 -0.8 -0.8 -0.6 -0.6 -0.6 -1.4 3 1 1 0 0 0 0.57 0.57 0.57 0.36 0.36 0.36 1 4 18.0 18.1 ∞ ∞ ∞ 35.5 37.5 44.8 58.0 52.0 42.2 19.0 0.98 0.98 1.0 1.0 1.0 0.98 0.98 0.98 0.98 0.98 0.98 0.98 18.2 18.3 ∞ ∞ ∞ 36.0 38.1 45.5 59.0 52.8 42.9 19.2 0.9985 0.9985 1.0 1.0 1.0 0.9985 0.9985 0.9985 0.9985 0.9985 0.9985 0.9985 5 0.194 0.196 – – – 0.434 0.486 0.694 0.874 0.701 0.462 0.216 can be achieved using the values of the wind effect admittance C Y (Φ)forthe respective sectors. The procedure of calculating the characteristic wind speed in the sectors is exemplified in Table 2.2 for a building located at Hannover, Germany. The fix- ing forces of fa¸cade claddings due to suction is considered. Figure 2.6 shows a topview sketch of a building cubus of 35 m height with fa¸cades oriented in northern, eastern, southern and western directions. The question is if reduced values of the suction forces at the cladding elements at the edge of the eastern fa¸cade can be adopted as the wind rosettes clearly indicate different wind ex- tremes when comparing the sectors, cf. line 1 in Table 2.2. Wind from eastern directions generate pressure forces at the element, whereas suction forces at the same element are generated through winds from all other sectors. Suction co- efficients from [26], Table 3, are used to describe the aerodynamic admittance in simplified terms. An element size of more than 10 m 2 is assumed. The pres- sure minimum — or maximum suction — occurs for northern directions and is described through the pressure coefficient c p = −1.4forh/b ≥ 5, h =35m. Southern wind directions generate a coefficient of c p = −0.8, c p = − 0.6isin- serted for western wind directions (cf. line 2 in Table 2.2). The directional wind effect factor a(φ) in line 3 after Equation 2.28 is calculated refering the sectorial pressure coefficents to the minimum pressure coefficient c p = c p,min = −1.4. The results of two iterations are listed in line 4. The first two rows represent v Φ,lim = v i,lim and the corresponding probability of non-exceedance F Φ,lim (v Φ,lim ) which remains 0.98 according to the probability of non-exceedance of the values given in line 1, or it is 1 in sectors 0 ◦ ,60 ◦ and 90 ◦ as only pressure instead of suction can occur here. The application of Equation 2.29 leads to P =0.8171 < 0.98. In a second iteration the extreme wind speeds are increased in such a way that the total probability 2.1 Wind Actions 25 of non-exceedance after Equation 2.29 results to be larger or equal to 0.98. The third and fourth row in line 4 of Table 2.2 represent a valid solution for which P =0.9866 and results larger than the required value of P =0.98. The codified standard design procedure requires a reference wind speed of v ref =25m/s irrespective the wind direction. The calculation of a gust speed after the wind profile for midlands ([26], Table B.3) leads to a characteristic gust speed of v =41.3m/s at building height of 35 m. The standard suction force for the considered element — without any consideration of the influ- ence of wind directions — must be calculated as Y = 1 2 ρ · v 2 · c p · A.The applicable characteristic suction force after Equation 2.25 — with consider- ation of the influence of wind directions — can be calculated as a fraction (c p (φ) · v 2 φ,lim )/(c p,min · v 2 ref ) of the standardized characteristic value. The quotient is listed in line 5 of Table 2.2, and it is represented in Figure 2.6, (d). The largest factor in line 5 must be applied. The respective characteris- tic velocity is ca. 59 m/s but the associated characteristic suction force after Equation 2.26 is lower than the standard suction force after the code. The reason is in the application of the much higher pressure coefficent — or lower suction coefficient — of c p = −0.5 for wind in the sector 240 ◦ instead of c p = −1.4. The procedure can also be adopted for a fatigue analysis after Equation 2.9. 2.1.3 Vortex Excitation Including Lock-In Authored by J¨org Sahlmen and M´ozes G´alffy Vortex excitations represent an aerodynamic load type which can cause vibrations leading to fatigue, especially for slender bluff cylindrical structures — bridge hangers, towers or chimneys. The nature of air flow around the structure depends strongly on the wind velocity and on the dimensions of the structure. Accordingly, different wind velocity ranges can be defined, depending on the value of a non-dimensional parameter called the Reynolds-number Re = ¯uD ν . (2.30) Here, ¯u represents the mean wind velocity, D is the significant dimension of the body in the across-wind direction — for cylindrical structures, the diameter —andν =1.5 ·10 −5 m 2 /sisthekinematicviscosityofair. In the Reynolds-number range between 30 and ca. 3 · 10 5 , vortices are formed and alternately shed in the wake of the cylinder creating the von K ´ arm ´ an vortex trail (Figure 2.9) and giving rise to the lift force — an alter- nating force which acts on the structure in the across-wind direction. The nature of the vortex shedding and of the lift force is considerably influenced by the wind turbulence I u = σ u ¯u , (2.31) 26 2 Damage-Oriented Actions and Environmental Impact Fig. 2.9. Von K ´ arm ´ an vortex trail formed by vortex shedding where σ u denotes the standard deviation of the stochastically fluctuating wind velocity u. In a smooth wind flow, i. e. if the wind turbulence is low (I u ≤ 0.03), the across-wind force is a harmonic function of the time t: F l (t)= ρ¯u 2 2 DC l sin 2πf s t. (2.32) Here, F l denotes the lift force per unit span, ρ =1.25 kg/m 3 is the density of air, C l is the dimensionless lift coefficient and f s = S ¯u D (2.33) is the frequency of the vortex shedding, also called the Strouhal-frequency. The non-dimensional coefficient S in (2.33) is the Strouhal-number which depends on the shape of the structure; its value for cylinders is S ≈ 0.2. In a turbulent flow, the excitation frequencies are distributed in an interval around the mean frequency, the width of the interval depending on the turbulence. When the Strouhal-frequency approaches one of the natural frequencies f n of the structure 1 and the structure begins to oscillate at higher ampli- tudes because the resonance, an aeroelastic phenomenon, the so-called lock-in effect occurs. This results in the synchronization of the vortex shedding pro- cess to the motion of the excited structure (Figure 2.10), acting as a negative aerodynamic damping, and can lead to very large oscillation amplitudes. Con- sequently, the lock-in effect can play an essential role in the evolution of the fatigue processes in the damage-sensitive parts of the structure. The width of the lock-in range is zero for a fixed system and increases with increasing oscillation amplitude. As the amplitude depends on mass and damping, these system-parameters have a large influence on the lock-in effect. This influence can be numerically catched by introducing the dimensionless Scruton-number Sc = 2μδ ρD 2 , (2.34) where μ denotes the mass of the structure per unit length, and δ is the structural logarithmic damping decrement. The width of the lock-in range is 1 Generally only the first natural frequency is of practical importance. [...]... the number of high speed railway lines will increase also significantly These developments have to be considered for realistic lifetime oriented design concepts especially with regard to the fatigue damage of structures and structural members The basis of such design concepts is the realistic modelling of actions The clauses 2.3.1 and 2.3.2 exemplify the modelling of actions with regard to the static... Traffic Loads on Road Bridges Authored by Gerhard Hanswille For a realistic lifetime oriented design especially with regard to the fatigue damage of structures and structural members realistic models for traffic loads are needed These models have to cover several special aspects, because long time prognoses for the whole design life of a structure are necessary, e.g 100 years for bridges Traffic loads on road... Sahlmen and Anne Spr¨nken o u Climatic conditions (e.g air temperature, solar radiation, wind velocity) cause a non-linear temperature profile within a structure or a structural component and stress due to thermal actions is induced For the design and lifetime analysis of many engineering structures (e.g bridges, cooling towers, tall buildings, etc.) thermal effects, in combination with moisture and chemical... For the optimization of lifetime analysis a numerical algorithm is 36 2 Damage-Oriented Actions and Environmental Impact needed to describe the physical thermal load scenario on an observed structure or structural component A realistic temperature field, based on experimental data, has to be modelled to simulate the thermal transmission and moisture flux within a material with the final aim to determine... directly affected by external interference effects The local climatic conditions at the site (e.g air-temperature, surface temperature, humidity, cloudiness, etc.) as well as the properties of the observed structural component control the intensity of the total thermal action Surface colour and characteristic (colour, roughness, layer thickness of the wall, etc.) for example control absorption, reflection... interaction of all discussed parameters are implemented and non-stationary effects are taken into account 2.2.3 Test Stand Authored by J¨rg Sahlmen and Anne Spr¨nken o u For the analysis of thermal actions on structural elements under free atmospheric conditions a test stand with different test objects is performed On the roof of the IA-Building of the Ruhr-University Bochum three different test plates, made... critical wind velocity (2.37) with a half width Δu depending on the oscillation amplitude Ay according to a simple parabolic function (Figure 2.12) The parabola is defined by three points, P1 , P2 and P3 , obtained from fits to the experimental data The fit of the model parameters to the experimental data has been performed by simulating the vortex-induced vibrations in the time domain, on a finite-element... deterioration starts or proceeds As a consequence the deterioration over time leads to a reduction of stiffness of the structure The implementation of affected non-linearities due to thermal loads in the design process and lifetime analysis is still part of ongoing research The numerical modelling of the temperature effects on structures based on experimental results are in the focus of this chapter 2.2.2... whole design life of a structure are necessary, e.g 100 years for bridges Traffic loads on road bridges are a good example, where several aspects must be considered for the development of lifetime oriented design concepts 2.3.1.1 General In this case it should be pointed out, that especially for actions on bridges the models must cover current national and European traffic data and future developments due . the sectors; the largest load factor is valid for the design of the fa¸cade element after Figure 2.8 2.1 Wind Actions 19 of the structure or structural components is determined by the superposition of. velocity) cause a non-linear temperature profile within a structure or a structural com- ponent and stress due to thermal actions is induced. For the design and life- time analysis of many engineering structures. if the effect of wind direction is considered. This can be done by employing wind speeds for the structural loading which are adjusted in each sector with a directional factor. Such procedure is