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Main theme: Actions on FramesSHORT FLASH BACK FOR LOAD THEORY

Action of loading can be done from very different point of view. Perhaps the most frequent one is according to variability in time to:

Permanent load (ESC – dead load) the load has constant value, position and direction.

Variable load - (live load in the most ESC) even when one of prior meant attributes is not fixed – we obtain variable load).

According to the origin:

- self-weight, calculated from volume and density of actual material /in the same time it is permanent load/.

- Imposed load (furniture, people, rooms equipment etc.) /in the same time it is variable load/.

- Climatic loads (action of wind, snow) /in the same time it is variable load.

- Indirect actions (settlement, shrinkage of conc.)

- Accidental loads (diverse crashes, impact of a plane into sky draper, ship into pylon of a bridge etc. car crash into sup-port)

- Earthquake special design situation in earthquake hazard territories.

Actions (loadings) commonly

According the way of an Action:

Areal load unit [N/m2]

Linear load unit [N/m]

Point load (single force) unit [N]

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Of course we cannot forget statistical point of view:

Characteristic value – basic characteristic – by self-weight (densities of masses are given in EN 1991-1-1) will be not overrun in 95% of cases, by snow and wind e.g. the value will be not exceeded in 50 years (probability of overrunning = 0,02.)

Combined characteristic – used for different design situations and different limit states with 0 ,1 and 2 coefficients. Finally, we obtain design value (used by ULS).

Issues with loading of MBMS frames their structurall analyse and designHere, (when compared to members only) other significant loads have to be taken into account (wind, snow). Further complications could result from the unexpected implementation. There is definitely much more different loads here. Moreover, by application of a load we have to keep in mind the golden rule of design:

The minimum possible resistance R of a structure, (a member)

R ≥ E should be equal or over max. possible effect of the actual load = E in the actual section.

By structural analysis e.g. it means that the load should be arranged to the most unfavorable position for designed cross-section and actually investigated internal force. This principle is easy to apply by a simply supported beam, a little bit more difficult by running beams, and finally more complicated by MBMS frames.See the whiteboard: drawing I. T.All over the world, there are tendencies to simplify the structural analysis procedure without loss of its accuracy.

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Accidental loads are thought especially by structures like ridges, drapers etc.

Following videos shows us real cases of such load:

To presume accidental load –is not a guarantee of building safety. Not always the default conditions are fulfilled ..

For marked cross-section (CS) and action of M is important to place variable load in the marked position of the same square. Deflection line will help us to identify other places for increasing the M in the observed CS.

This matrix should be moved around the whole MSMB frame

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Other internal forces and deciding cross sections

Former demonstrated technique is not frequently used esp. by many times MBMS frames. Instead of this is so called chess technique used. In this case the vertical imposed load is distributed in a checkered manner (like checkered flag).

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The case with full load is deciding for M and V of marked cross – sections. By calculation of internal forces we cannot pass „empty frame“ case. This can provide an extreme stress in some cross – sections when combined with wind load, only. More later and in the practice of BL005.

Climatic loads - Snow loadEveryman knows, but how to calculate it?EN 1991-1-3 comes out from regions with typical climate, Details can be found in the National Annexes.

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National Annex contents for each region a relation between oversee level and the characteristic snowpack on the ground.

Firstly we have to understand the system of Eurocodes →→

Explained on BS basis. We have + CSN EN 1990 = Zaklady navrhovani konstrukci

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Possible complication by snow action:Snow fall

Snow drift (snow bank)

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Usually we need value of snow load on a roof „s“

Where:mi = shape coefficient of the roof,Ce = coefficient of exposition,

Ct = thermal coefficient ,Sk = characteristic value of snow load on the ground –

from the map or numerical expression. There are totally 8 zones with char. snow load from 0,7 to over 4 kN/m2 in the CZ.

The thermal coefficient Ct isused to account for the reduction of snow loads on roofs with high thermal transmittance (> 1 W/m2K), in particular for some glass covered roofs, because of melting of snow caused by heat loss. In such case is Ct < 1,0 in all other cases is Ct = 1,0. (Usual value.)

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Coefficient of exposition Ce

expresses possible increase or decrease of snow load on the roof due to action of wind (possible blowing off or on).

Shape coefficient mi

expresses influence of a roof shape on the mass of snow falling down or at opposite remaining on the roof.

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By MSMB frames structural analysis is snow load usually taken as uniform load on the roof (without drift and fall in the practice of BL005) and creates one loading case.

Increase of snowpack in time??

After „snow and collapse reach“ winter 2005/06 (more then 10 S-collapses) was the map of snowpack completely reworked. More detailed classification, higher snowpack values.

This winter I have seen at least 2 ‘snow collapsed’ structures apparently another increase of coded values?

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Action of Wind

One can presume the EN 1991-1-4 (action of wind) like EN 1991-1-3 (snow action) comes out from regional characteristics with typical basic wind data (velocity). The answer is in the same time Yes and Not. The reasons are: Wind action is much more complicated. The climate and wind character are changing instantaneously. The code claims design of building up to 200m of height. The code can be used both for static and dynamic action of the

wind. There is not official wind map for the whole Europe, now. (Was not found, everybody is speaking about upgrade of..)

Regional map was present in preliminary code, but in the final code disappears. And the major accent is given to National Annexes and to national Maps. Such actual map for CZ is on next screen.https://www.sublibrary.com/eurocode/eurocode-wind-load-maps-pdf

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Both Cdir and Cseason can be in the CZ approximate as 1,0

As we can see, the basic parameter of wind action is Basic wind velocity vb,0

[m/s].This have to be gradually modified with influence of:- Seasonal influence- Direction influence - Terrain roughness – global- Terrain orography - local- Height of designed building- Actual level over terrain (z)- Influence of turbulences ..- Etc.

Similarly to snow were wind maps in Eurocode countries in 2006 updated.

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Vm(z) is mean (average wind velocity in the actual place)C0(z) is coefficient of orographyCr(z) is coefficient of terrain roughness – depends on For basic idea only →→

How to find Co

Finally: qp(z) = ½ (vm2) . r .[1+ 7 lv(z) ]

Where qp(z) is actual pressure of wind in the level (z)lV(z) is influence of turbulence → more code or practices

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Another important point of view:what we want to design? Which influence (risk)of the wind is essential? Static support structure.Connection of used shell (cladding)

with static support structure .Other.

Structure shell (cladding) is blown out ..

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Finally quick look on papers for practice simplified calculation of wind action to solved MSMB frame.

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In practices of BL005: pressure of the wind blowing parallel with frames plane have to be transferred into single forces acting to marginal (external) joints of your actual frame. It is presumed that the action of wind blowing in perpendicular direction will be caught by some other (not calculated) bracing.

Thank you!!