Week 10 Challenge

Aim:

To calculate the snow loads accumulated in the bridge and to apply it in Stadd Pro. model, design and analyse. 

Given: 

The span of the bridge = 10m.

The type of snow = Settled snow. 

The deck of the bridge is flat with ß <30°. 

The depth of accumulation of snow = 1250 mm. 

Introduction:

Bridge structures are subjected to snow load when the bridge is located in snowy regions. The type of snow resting on the structure is a major factor since the snow's age, dampness, sturdiness and slope determine the load. The snow load can be calculated as per IS 875 Part IV and IRC 6. Snow loads must be considered during the design phase in geographical locations where the structure is incidental to snow. 

Procedure: 

Part I: Calculation of snow load: 

As per IS 875 Part IV and IRC 6,  with the given data following is determined,

Γ = 3 kN/m³

Since the deck bridge is flat, ß < 30°, the shape coefficient µ = 0.8

S₀ = Γ x depth of snow x span of the bridge 

where, 

Γ = unit weight of snow on the bridge

S₀ = snow load

S₀ = 3 x 1.25 x 10 

S₀ = 37.5 kN/m

S = µ x S₀

where, 

S = Design Load due to snow

S₀ = Load due to snow

µ = shape coefficient

S = 0.8 x 37.5

S = 30 kN/m

Part II: Modelling and Analysis of Bridge in Stadd Pro. :

Step 1: Open Stadd Pro connect edition software -> create a new file with the units set to metric standards.

Step 2: Select the geometry tab and enter the values of the node in the y column in the node table as 0 and 7 respectively which will create two nodes. Add beam cursor in geometry tab -> connect these nodes creating a pier. 

Step 3: Select the beam using the beam cursor -> translational repeat in geometry tab -> translate the beam for 3 steps in the Z direction for 4m creating three more piers of the bridge -> Connect all the top nodes of the piers using add beam command in geometry.

Step 4: Select all the beams using the beam cursor -> translational repeat in geometry tab -> translate the beams for a step in the X direction for 10m creating piers on the other end of the bridge. Connect all the top nodes of the piers in a longitudinal manner using add beam command in geometry. Refer to figure 1.,

                                                                            Figure 1

Step 5: Select the end nodes along the width using the node cursor in geometry ( Refer to figure 2 ) -> translate repeat the nodes along the Z direction for a step for a length of 3m -> Connect the nodes using add beam cursor, Refer to figure 3. Repeat the same for the other end of the width of the bridge.

                                                                            Figure 2

                                                                            Figure 3

Step 6: Translational repeat -> select the highlighted node in Figure 4 and translational repeat it along the X direction for a step of 0.25 length -> Select both these nodes and translational repeat them along the Z direction for a step of 0.25 length -> Using add plate cursor connect these four nodes and create a plate. 

                                                                            Figure 4

Step 7: Select the plate -> translational repeat that plate along the X direction for 39 steps of 0.25 length each ( 10/0.25 = 40 since one plate is there 39 steps ). Select the created plates and translational repeat them along the Z direction for 71 steps of 0.25 length each ( 18/0.25 = 72 since one plate is there 71 steps ) Refer to Figures 5 and 6.

                                                                            Figure 5

                                                                            Figure 6

Step 8: Specification tab -> Select fixed and create foundation -> Assign this fixed foundation to the 8 nodes under the piers.

Step 9: Pier - In the Properties tab -> select define -> Circle -> 2 -> Assign to the piers -> close.

Step 10: Girders - In the Properties tab -> select define -> tapered -> F1=0.9m F2=0.4m F3=0.9m F4=0.5m F5=0.4m F6=0.5m F7=0.4m -> Assign to the highlighted beam in figure 7 and refer to figure 8 -> close.

                                                                            Figure 7

                                                                            Figure 8

Step 11: Deck - In the Properties tab -> select Thickness -> 0.9m -> Assign to all of the plates  -> close.

Step 12: In the loading tab -> Load case details-> click add -> Enter Snow load -> Click snow load and add -> Select member load and enter in W1 = -30 kN/m³ along the global Y axis and click add. 

                                                                            Figure 9

Step 13: These loads act on the girders, totally there are eight girders and the loads will act on the highlighted beams in figure 10., Apply this load to the girders of the bridge using the select beam cursor. Refer to Figures 9 and 10. 

                                                                            Figure 10

Step 14: Thus snow loads has been applied to the structure. Save the file and Run the analysis by -> Click analysis and design tab -> click define commands -> no print, click add -> click run analysis and check for errors after computation.

Part III: Results:

The results can be obtained after analysis of the model and can be viewed in the post-processing tab under the workflow section.,

The deflection of the Model can be seen below and the critical displacement is highlighted below., Critical Displacement = 1.165 mm. Refer to Figure 11.,

                                                                             Figure 11

 The Reaction of the Foundation can be seen below., Refer to Figure 12., 

                                                                             Figure 12

Bending Moment in Z direction -  Critical Bending Moment = 361.813 kN/m. Refer to Figure 13.,

                                                                             Figure 13

Bending Moment in Y direction - Critical Bending Moment = 242.141 kN/m, Refer to Figure 14.,

                                                                             Figure 14

Shear Force in Z direction - Critical Shear Force = 49.087 kN, Refer to Figure 15.,

                                                                             Figure 15

Shear Force in Y direction - Critical Shear Force = 205.723 kN, Refer to Figure 16.,

                                                                             Figure 16

The Plate results of the Model can be seen below.,

Bending Moment in X direction, Critical Bending Moment = 71.404 kN-m/m., Refer to Figure 17.,

                                                                             Figure 17

Bending Moment in Y direction, Critical Bending Moment = 10.98 kN-m/m., Refer to Figure 18.,

                                                                             Figure 18

Shear Force in X direction, Critical Shear Force = 0.417 N/mm² ., Refer to Figure 19.,

                                                                             Figure 19

Shear Force in Y direction, Critical Shear Force = 0.309 N/mm² ., Refer to Figure 20.,

                                                                              Figure 20

Thus Load calculation manually is done and analysis and result interpretation is done in Stadd Pro.