Project 1

AIM:

To calculate the dead load, IRS live loads, Earth pressure load, wind load and seismic loads for the bridge structure at the Ahmedabad Metro rail project shown in the figure. 

 

INTRODUCTION:

The bridge structure is an underground metro rail station located in Ahmedabad. To this bridge, the following loads must be applied in Stadd Pro.

• Dead loads,
• Indian Railway live loads,
• Seismic loads,
• Wind loads ( Though the structure is located underground, manual calculation of wind load must be arrived at assuming that the bridge is located above the nominal ground level ),
• Earth Pressure loads.

Several manual calculations are required to arrive at the loads before applying them in Stadd Pro. With the help of IS code standards, these loads can be determined. In the following steps, these loads are arrived methodically and applied in Stadd Pro.

 

GIVEN:

Unit weight of soil = 18 kN/m³

Location of bridge = Ahmedabad 

Type of Structure = Underground Metro rail

Two-storey underground structure

Two railway tracks on either side of the station at the G-2 level

 

PROCEDURE:

 

Part I: Calculation of Dead Load:

 

Step1: The structure can be distinguished into 8 separate members. The Dead load of these members are calculated assuming that they are Reinforced Cement Concrete. 

Dead load = Area x Unit weight of the material (kN/m)

or

Dead load = Volume x Unit weight of material (kN)

 

Step2: The Dead load of the Diaphragm wall on either side of the station are calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Diaphragm wall are,  Refer to Figure 1

Length = 10m

Height = 20m

Thickness = 750mm

                                                                               Figure 1

Dead load = Volume x Unit weight of material (kN)

Dead load = 10 x 20 x 0.75 x 25

 

Dead load of Diaphragm wall = 3750 kN

The dead load of two Diaphragm walls = 3750 x 2

 

The dead load of two Diaphragm walls = 7500 kN

 

Step3: The Dead load of the Top slab of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Top slab are,  Refer to Figure 2

Length = 22m

Weight = 10m

Thickness = 1m

                                                                               Figure 2

Dead load = Volume x Unit weight of material (kN)

Dead load = 22 x 10 x 1 x 25

 

The Dead load of the Top slab = 5500 kN

 

Step4: The Dead load of the Intermediate slab of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Intermediate slab are,  Refer to Figure 3

Length = 22m

Weight = 10m

Thickness = 1.2m

                                                                               Figure 3

Dead load = Volume x Unit weight of material (kN)

Dead load = 22 x 10 x 1.2 x 25

 

The Dead load of the Intermediate slab = 6600 kN

 

Step5: The Dead load of the Bottom slab of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Bottom slab are,  Refer to Figure 4

Length = 22m

Width = 10m

Thickness = 2m

                                                                               Figure 4

Dead load = Volume x Unit weight of material (kN)

Dead load = 22 x 10 x 2 x 25

 

The Dead load of the Bottom slab = 11000 kN

 

Step6: The Dead load of the Platform slab of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Platform slab are,  Refer to Figure 5

Length = 13.5m

Width = 9.5m

Thickness = 0.7m

                                                                               Figure 5

Dead load = Volume x Unit weight of material (kN)

Dead load = 13.5 x 9.5 x 0.7 x 25

 

The Dead load of the Platform slab = 2244.375 kN

 

Step7: The Dead load of the Main Structural member of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Main Structural member are,  Refer to Figure 6

Length = 10m

Width = 2.5m

Thickness = 0.6m

                                                                               Figure 6

Dead load = Volume x Unit weight of material (kN)

Dead load = 10 x 2.5 x 0.6 x 25

 

The Dead load of the Main Structural member = 375 kN

 

The dead load of four Main Structural members = 375 x 4

The Dead load of the four Main Structural members = 1500 kN

 

Step8: The Dead load of the Main girders of the station is calculated below, 

 

Unit weight of the RCC = 25 kN/m³

The dimensions of the Main girders are,  Refer to Figure 7

Length = 10m

Width = 2m

Depth = 0.75m

                                                                               Figure 7

Dead load = Volume x Unit weight of material (kN)

Dead load = 10 x 2 x 0.75 x 25

 

The Dead load of the Main girders = 375 kN

 

The dead load of two Main girders = 375 x 2

The Dead load of the Main girders = 750 kN

 

Step9: The Calculated Dead loads are shown below, 

 

The dead load of two shear walls = 7500 kN

The Dead load of the Top slab = 5500 kN

The Dead load of the Intermediate slab = 6600 kN

The Dead load of the Bottom slab = 11000 kN

The Dead load of the Platform slab = 2244.375 kN

The Dead load of the four Main Structural members = 1500 kN

The Dead load of the Main girders = 750 kN

 

Part II: Calculation of Earth pressure load:

 

Step1: Assuming that the water table is at the Diaphragm wall toe level, the Earthpressure load on either side of the diaphragm wall is calculated as follows.,

 The formula for calculating the Earth pressure due to the soil acting on the exterior side of the diaphragm wall is as follows.,

 

K1 = k1 x Γ x h

 

where,

K1 = Earth pressure of the backfill soil located on the exterior side of the diaphragm wall,

k1 = Passive earth pressure coefficeint,

Γ = Unit weight of the backfill soil located on the exterior side of the diaphragm wall,

h = height of the soil from the Diaphragm wall toe level.

 

Assume that k1 = 0.5 and as per given Γ = 18 kN/m³.,

 

h = 20m ., Refer to Figure 1 for clarity on the dimensions of the Diaphragm wall.

 

K1 = 0.5 x 18 x 20 

K1 = 180 kN/m². 

 

The dead load of two Diaphragm walls = 180 x 2

The Earth pressure of two Diaphragm walls = 360 kN/m².

 

Part III: Calculation of Wind load:

 

Though the structure is underground, the calculation of wind load is done but the values are not applied to the analysis in Stadd Pro. 

 

Step 1: Basic Wind Speed (Vb):

From IS 875 Part 3 2015 Code book, On page number 6 from Figure 1, 

The basic wind speed in Mumbai can be identified as 39 m/s. 

Vb = 39 m/s   Refer to Figure 8 below.,

                                                                             Figure 8

Step 2: Factor K1:

Referring to table 1 of IS 875 Part 3 2015, for important structures and 39 m/s,

factor K1 is determined as 1.06

K1 = 1.06

 

Step 3:  Factor K2:

Referring to table 2 of IS 875 Part 3 2015, assuming the height of the bridge is 20m and the category 3 structure since Kankariya is an urban region with medium-rise buildings, 

Since the height of the bridge is 20m, and the category is type 3.,

from table 2 factor K2 is determined as 1.01

K2 = 1.01

 

Step 4:  Factor K3:

As per clause 6.3.3 IS 875 Part 3 2015 for upwind slope less than 3 degrees, 

factor K3 is determined as 1.00

K3 = 1.00

 

Step 5:  Factor K4:

As per Clause see 6.3.4 of IS 875 Part 3 2015, When the location is within a 60 km radius of the ocean, the cyclone factor is taken into account, but kankriya metro station is located far away from the coast,

thus factor K4 is determined as 1

K4 = 1.00

 

Step 6:  Design Wind Speed (Vz):

 

Vz = Vb x K1 x K2 x K3 x K4 

 

where,

Vz = 39 x 1.06 x 1.01 x 1 x 1

 

Vz = 41.7534 m/s 

 

Step 6: Wind Pressure (Pz):

 

Pz = 0.6 x Vz²

 

 

Pz = 0.6 x 41.7534²

 

The Calculated Wind Pressure Pz = 1.046 kN/m²

 

Part IV: Calculation of IRS Live load & Seismic Load:

 

The IRS Live Load and Seismic loads are directly applied to the Stadd Pro Model and Analysed. 

 

APPLICATION OF LOADS :

 

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

Step 2: Since the model is given in the question, the generation of the model will not be explained in the following steps.

DEAD LOAD APPLICATION :

Step 3: In the loading tab -> Load case details -> Click Add -> Enter the name as Dead Load and Click add -> Select Dead load case detail and click add -> Under Self weight -> enter the value as -1 in Global Y axis and click add.

Step 4: Select the generated Dead load and Click Assign to View, Thus the Dead load is assigned to the entire structure. 

IRS LIVE LOAD APPLICATION :

Step 5: In the loading tab -> Definitions -> Vehicle definition, click add -> Width= 1.8m, Metro Rail load details from IRC guidelines as 170kN - 0m, 170N - 2.2m, 170kN - 12.4m, 170kN - 2.2m. Refer to Figure 9 below.,

                                                                             Figure 9

Step 6: In the loading tab -> Load case details -> Generate a load type by clicking add -> primary -> enter Metro Rail and click add.

Step 7: In the loading tab -> Load case details -> Generate a load type by clicking add -> load generation -> click add -> Enter the number of loads to be generated as 62

( 10 + 21 ) / 0.5 = 62

( [[span of bridge + length of train] / increment length] ). 

Note: I tried giving lower values as well, but the analysis failed and the load generation of 10 steps only passed, thus the number of steps executed in the model is 10. 

The number of loads to be generated is 10 

Step 8: Click the generated load  -> add -> enter the coordinates as X=1.5, Y=3.5, Z=0 as the initial position and load increment in the Z direction as 0.5 m and the range in the Z axis as 10m.

Step 9: Click the generated load  -> add -> enter the coordinates as X=19.5, Y=3.5, Z=10 as the initial position and load increment in the Z direction as 0.5 m and the range in the Z axis as 10m. 

Step 10: The co-ordinates as the nodal points of the I - girder from where the metro rail will start and move along its length. Refer to Figure 10 & 11 below., Thus the IRS Live load is assigned to the structure. 

                                                                             Figure 10

                                                                             Figure 11

EARTH PRESSURE LOAD APPLICATION :

Step 11: In the loading tab -> load case details, click add -> Plate load -> hydrostatic load -> enter 180 kN/m² (Calculated Earth pressure on the Diaphragm wall ) in W1 with X Global axis and Interpolate along Y Global axis. Select the plate using the Select plate command from the Select tab -> Click Add. Refer to Figure 12.,

                                                                             Figure 12

Step 12: In the loading tab -> load case details, click add -> Plate load -> hydrostatic load -> enter -180 kN/m² (Calculated Earth pressure on the Diaphragm wall, - minus is added such that load acts from the exterior side of the diaphragm wall) in W1 with X Global axis and Interpolate along Y Global axis. Select the plate using the Select plate command from the Select tab -> Click Add. Refer to Figure 13.,

                                                                             Figure 13

Step 13: The load's green portion is due to the earth pressure on either side of the diaphragm wall. Refer to Figure 14., Thus Earth Pressure load is applied to the Structure. 

                                                                             Figure 14

SEISMIC LOAD APPLICATION :

Step 14: In the loading tab -> Definitions -> click seismic definitions and add -> select IS 1893 Part 1 2016 -> enter these Following values  and Click generate.,

City = Ahmedabad 

Response Reduction Factor = RC building with Special Moment Resisting Frame 

Importance Factor = Important Building 

Soil Type = Medium Soil

Structure Type = RC MRF

Damping ratio = 5%

Foundation Depth = 20m

The above values are assumptions made based on IS 1893 Part 1 2016 and as per the given data.,

Step 15: Select the generated definition and click add -> Select Self-weight and enter the value as 1 and Click add, such that the base shear will be calculated.

Step 16: In the loading tab -> Load case details -> Generate a load type by clicking add -> primary -> enter EQX and click add. 

Step 17: Select the Load case EQX and click add -> Select Seismic load and enter the value as 1 in Factor along the X direction and Click add.

Step 18: In the loading tab -> Load case details -> Generate a load type by clicking add -> primary -> enter EQY and click add. 

Step 19: Select the Load case EQY and click add -> Select Seismic load and enter the value as 1 in Factor along the Y direction and Click add.

Step 20: In the loading tab -> Load case details -> Generate a load type by clicking add -> primary -> enter EQZ and click add. 

Step 21: Select the Load case EQZ and click add -> Select Seismic load and enter the value as 1 in Factor along the Z direction and Click add.

Step 22: In the loading tab -> Load case details -> Generate a load type by clicking add -> define combinations -> enter the name as combination EQX -> For EQX load case enter factor 1, For EQY load case enter factor 0.3, For EQZ load case enter factor 0.3, such that load case EQX being dominant in this combination -> Click add.

Step 23: In the loading tab -> Load case details -> Generate a load type by clicking add -> define combinations -> enter the name as combination EQY -> For EQX load case enter factor 0.3, For EQY load case enter factor 0.1, For EQZ load case enter factor 0.3, such that load case EQY being dominant in this combination -> Click add.

Step 24: In the loading tab -> Load case details -> Generate a load type by clicking add -> define combinations -> enter the name as combination EQZ -> For EQX load case enter factor 0.3, For EQY load case enter factor 0.3, For EQZ load case enter factor 0.1, such that load case EQZ being dominant in this combination -> Click add.

Step 25: Thus Seismic load 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.

Thus the structural analysis of the given data has been done and the results are interpreted below.

 

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 = 15.958 mm. Refer to Figure 15.,

                                                                             Figure 15

 The Reaction of the Foundation can be seen below., Refer to Figure 16., 

                                                                             Figure 16

Bending Moment in Z direction -  Critical Bending Moment = 72.357 kN/m. Refer to Figure 17.,

                                                                             Figure 17

Bending Moment in Y direction - Critical Bending Moment = 2.237 kN/m, Refer to Figure 18.,

                                                                             Figure 18

Shear Force in Y direction - Critical Shear Force = 263.463 kN, Refer to Figure 19.,

                                                                             Figure 19

Shear Force in Z direction - Critical Shear Force = 4.166 kN, Refer to Figure 20.,

                                                                             Figure 20

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

Bending Moment in X direction, Critical Bending Moment = 2019.029 kN-m/m., Refer to Figure 21.,

                                                                             Figure 21

Bending Moment in Y direction, Critical Bending Moment = 2022.254 kN-m/m., Refer to Figure 22.,

                                                                             Figure 22

Shear Force in X direction, Critical Shear Force = 0.759 N/mm² ., Refer to Figure 23.,

                                                                             Figure 23

Shear Force in Y direction, Critical Shear Force = 0.574 N/mm² ., Refer to Figure 24.,

 

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