Project 1
Aim: The aim of this challenge is to apply the dead loads,IRS live loads, wind loads, earth pressure loads and siesmic loads on the super structure and analyze it in Stadd select.
Here the model is already provided and only the loads have to be applied and analysed. From the provided drawing the structure is wholey constructed under ground, therefore the wind load effects will be null on the structure.
The model is one of the station buildings at Ahmedabad.
Ahmedabad comes under Zone - 3 as per IS 1893 part-1 seismic loads to be considered on the bridge.
There is an IRS siesmic code also for bridges and the load combinations given here are in compliance with IS 1893.
Intoduction:
The loads considered on the stadd model are
1. DL
2. IRS live load
The trains loads to be considered as per IRS are Metro train loads
Each car length is 21.1m
The distance between first axle to the last axle is 2.2+12.4+2.2 = 16.8 m
The spacing between two cars is 4.3m
3. Wind loads.
The wind loads shall not be considered here because the particular station model provided in an under ground station.
4. Earth pressure loads.
The earth pressure on the model, the construction of the structure goes stage wise, considering the procedure followed for construction of the station is open exacavation, the station struture is built and completely filled with soil.
As the structure will be built and filled the struture would act like a box with the slab at various level act like struts to entire outside wall, the earth pressure calculated here is as follows,
The earth pressure loads to be considered are calculated according to the following assumptions.
The desnsity of the soil here given is dry density ie. 18kN/m3
The saturated density of the soil = 21kN/m3
where as there is always a possibility that the soil shall get saturated completely and also,
The wate table at the particular station location is not mentioned.
As the station is completely underground and is 20 m from the ground level the water table here I have assumed as at 12m below the ground level
The various strate of the soil formations are not defined, the soil grains or the soil type is not defined, here I am assuming it as cohesion less and uniform soil formations through out the depth.
therefore the ka = 1- sin (phi)/ 1+ sin (phi)
phi - 30 degree
ka = 1-0.5/1+0.5= 0.5/1.5 = 0.333
gama = density of soil = 21kN/m3
The earth pressure taken is ACTIVE EARTH PRESSURE.
5. Seismic Loads.
According to IRS Seismic COde : 2017
Procedure
I. Dead Loads
The stadd model of the structure is already provided and entire structural properties are given as concrete therefore from the stadd model choosing the option self weight (-1) option and assigning to entire plate and beam model. This wiil generate the total dead load coming on the structure due to concrete.
From the model it can be seen that self wieght command is applied to the entire model.
II. IRS Live loads
The live loads on the model shall be run on the beam defined in the model. In the model we can see the location of the track.
There are two tracks on the wither side of the building.
Here two cars are defined
The total length of the vehicle defined is (2.2+12.4+2.2)x2 + 4.3 (spacing between two cars) = 37.9
The beam which defines the location of the left side track is at x @ 1.5m, y @ 3.5m
The beam which defines the location of the right side track is at x @ 19.5m, y @ 3.5m
The below model shows the defined loacation of the first load generation point.
III. Earth Pressure loads.
The following are the earth pressure loads applied on the model.
The calculations are shown in the introduction.
The following image shows the earth pressure loads applied on the plate element as area loads
IV. Seismic Loads
According to IRS seismic loading code, the vertical component need not be considered for area under zone - II and Zone -III.
Since Ahmedabad dose come under zone III, no vertical component shall be considered in the seismic load combinations.
The following are the loads and factors generated by stadd as per IS 1893 - 2016.
THE FOLLOWING ARE THE LOADS APPLIED ON THE STRUCTURE.
Load Cases:
The seismic loads shall be defined as the first load cases of all.
EQ load (1EQX+0.3EQZ)
EQ LOAD (0.3EQX+1 EQZ)
Dead load
Live load (this was not mentioned in the challenge but is considered here)
Earth pressure Load + water table was assumed at 12 below thw ground level
IRS train load (Metro train case).
The following combinations are also checked
EQ-1+DL+LL+EPL
EQ-2+DL+LL+EPL
Results:
BENDING MOMENT ON THE BEAM MEMBERS DUE TO IRS LOADING
THE FOLLOWING IS THE BENDING MOMENT DIAGRAM FOR THE BEAM MEMBERS
THE FOLLOWING IS THE SHEAR FORCE DIAGRAM FOR THE BEAM MEMBERS
PLATE STRESSES
PLATE STRESS RESULTS DUE TO EQ LOAS IN X DIRECTION
PLATE STRESSES DUE TO EQ-Z DIRECTIONS
THESE ARE THE STRESSES DUE TO EARTH PRESSRE
STRESSES ON THE PLATE DUE TO COMBINATION OF THE LOAD
EQ-X+DL+LL+EPL
STRESSES ON ENTIRE STRUCTURE DUE TO THE LOAD GENERATION 83
SIMILARLY OTHER CASE LOADS CAN ASLO BE OBTAINED
HERE LOAD GENERATION MAXIMUM MOMENT AND OTHER COMBINATIONS ARE COMBINED TOGETHER AND CAN BE DESINED.