Week 1 Challenge
Ans.
The following data has been given along with Cross-section of a Box Girder :
- Width of Brideg deck=10.2m
- Span of Bridge=12m
- Pier Size (circular) Diameter =2.5m
- Seismic Zone ......Zone IV
- Wind Speed..........47Km/hr
- Unit weight of soil =19kN/m3.
Aim and Introduction: The aim is to do structural analysis using Staad Pro Software. For this, primary requirement is to find out the dead load of the box gider bridge. The Box Girder is Symmetrical about C/L of girder ,shown as A'-A' in Fig 1. The box girder is made up concrete ,hence unit weight is taken as 25kN/m3.
Procedure :
- The width of deck slab varies from 8.40m to 11.400m as shown in Fig 1 but in this problem the width has been given as 10.2m. Hence the value of 'A' (refer Fig1) is (10.2-8.4)/2=0.90m.
- For simplicity in calculation, the weight of half portion is calculated with dimension shown in Fig1 and will multiplied by 2 to find dead load of the bridge.
The portion has been marked as A,b,C,D,E,F and G and calcaltion done in tabluar form as shown in Table 1. The lenght of slant portion of box girder has been calculated takinhg into account of slope which is 1:2.5.
| Table 1 : Calculation of Deal Load per length of Bridge | |||||||
| Sl no. | Designated Portion | Length in mm | Thicknes /depth in mm | Area in mm2 | Area in m2 | Unit weight kN/m3 | Weight kN/m |
| 1 | 2 | 3 | 4 | 5=3*4 | 6=5/1000000 | 7 | 8=6*7 |
| 1 | A | 900 | 225 | 202500 | 0.2025 | 25 | 5.0625 |
| 2 | B | 1370 | (225+350)/2 | 393875 | 0.393875 | 25 | 9.8469 |
| 3 | C | 269 | 350 | 94150 | 0.09415 | 25 | 2.35375 |
| 4 | D | 1200 | (350+225)/2 | 345000 | 0.345 | 25 | 8.625 |
| 5 | E | 1361 | 225 | 306225 | 0.306225 | 25 | 7.65563 |
| 6 | F | 2100 | 250 | 525000 | 0.525 | 25 | 13.125 |
| 7 | G | 1821 | 200 | 364200 | 0.3642 | 25 | 9.105 |
| Total | 55.7738 | ||||||
| For whole cross section,Weigth per length of span= 2*55.7738=111.5476say 111.55 kN /m | |||||||
The span of Boc Girder bridge is 12m.
Hence the dead load of the box girder which is 111.55kN/m ,will act along span as shown in fig2.
The Analysis has been performend by Sttad Pro. Figure 3 shows the general description with span of 12m.
Figure2 with Span and Suppoert adopted.
Figure 4 With property of rectangular Size assumed for calculation purpose .The Size was taken as 0.01m*0.01m because while adopting 0.001m*0.001m error was observed.
Figure 4 with assumed property
Figure 5 Shows with loading of dead load of Box Girder with 111.55kN/m
Figure5 With dead Load of Box Girder along span.
The analysis was performed and attached 4 pages as pdf.
The figure 6 & 7 show different attributes of deflection and bending moments
Fig 6
Fig 7 Bending moments
The above data will be incorporated in bridge design taking into accout of live loads and seismic fores/wind loads.