Legenda
L = clear span [ mm ]
bt = point load width in bearing bar direction, fixed at 200 mm [ mm ]
bq = point load width in cross bar direction, fixed at 200 mm [ mm ]
Fp = point load [ kN ]
Fv = distributed load [ kN / m2 ]
ϒ = safety factor variable load [ - ]
mat = material [ - ]
t = bearing bar pitch [ mm ]
tcross = cross bar pitch [ mm ]
[ 1kN = approx.100Kg ]
Basis of design
- Calculations are based on quality standard RAL-GZ 638 and cover the situation with one span and one load acting on the grating. The load can be a point load in the middle of the span or a distributed load.
- To compensate for the reduction of strength and stiffness of the bearingbars due to the slids a reductionfactor is used when determining the moment of resistance 'W' or the moment of inertia 'I'. For pressure locked gratings type RR/RH a reduction factor v=0.9 is used. For welded gratings no reduction is used. ( RAL-GZ 638 par 4 a,b )
- Deflection of the gratings are limited by ulim = L*(1/200). When deflections are greather than 4.0 mm an indication message will appear which will warn for the possible hazard of stumbling ( RAL-GZ 638 par 4 )
- RAL-GZ 638 describes the spread of the load over the bearing bars. The number of bearing bars activated depend on the width of the point load and the spreading factor 'm' according RAL-GZ 638 table 1. This table represents values for m when the pitch of the grating is 33.33 x 33.33. For other pitches RAL-GZ 638 does not give values for 'm'.
Therefore, in addittion to RAL-GZ 638, For pitches other then 33.33 x 33.33 the spreading factor m is corrected with factor aspread = 33.33 / tcross with a maximum of aspread=1.2
- Selfweight is neglected in line with RAL-GZ 638
- Horizontal forces are not taken into account.
- RAL-GZ 638 does not cover (local) instability checks
Material characteristics
| Steel quality: |
S235 |
|
| Specific weight: |
7850 |
kg/m3 |
| Material factor: |
1.0 |
|
| Design yield stress: |
235 |
N/mm2 |
| Modulus of elasticity: |
210000 |
N/mm2 |
| Steel quality: |
S355 |
|
| Specific weight: |
7850 |
kg/m3 |
| Material factor: |
1.0 |
|
| Design yield stress: |
355 |
N/mm2 |
| Modulus of elasticity: |
210000 |
N/mm2 |
| Steel quality: |
AISI 304 / AISI 316L |
|
| Specific weight: |
7980 |
kg/m3 |
| Material factor: |
1.1 |
|
| Design yield stress: |
209 (230/1.1) |
N/mm2 |
| Modulus of elasticity: |
200000 |
N/mm2 |
| Steel quality: |
AW-5754/H22 |
|
| Specific weight: |
2755 |
kg/m3 |
| Material factor: |
1.1 |
|
| Design yield stress: |
118 (130/1.1) |
N/mm2 |
| Modulus of elasticity: |
70000 |
N/mm2 |
This calculation tool is to be treated as a help tool only, no rights should be derived from its results. All technical projects of platforms and traffic arteries must be based on qualified strength calculations by the project structural engineer.
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