Challenge 3

Ans of question no-1

■The sectional properties we need upfront for designing a metro viaduct are-

The area of structure, perimeter,bounding box in x direction and also y direction, centroid of structure with respect to X& Y axis,and MOI of the section about X & Y axis.

■The supporting software for identifying the sectional properties and designing them are STSSD pro.

Ans of question no-2

■Details steps involved to create the element in STAAD pro are-

1. to create the nodes with respect to slab width, height of web, mid of web.
2. go to isometric view and select the nodes from select menu and select the nodes which are drawn.
3. go to geometry and select transitional repeat from their select the no of steps and spacing with select the global Y direction and link the steps then click on ok.
4. from length of span devided by no of plate we get the plate length .
5. from view option select the top view, and select the right side nodes.
6. from geometry select transitional repeat and select the steps and spacing,no of steps and default speacing and then link the steps then click on ok button.
7. from geometry select add plate and the connect the nodes through plate nodes. And after creating one side plate then from transitional repeat create the all plate.
8. then create the support plate at both sides.
9. create the beam on transverse direction and the create the supports.
10. from properties create the slab thickness, web height.

■Inputs for sectional properties assigned-

After adding properties we see the details properties at right side.

go to isometric view and select the plate which need to be assigne .

select plate cursor and select the plate I,e slab portion or web portion then go to assign to selected plates then assign.

Ans of question no-3

SLS load combination for live loads are the factor of 1.1 along with impact factor.

With respect to impact factor the moment of this section are derived after get the critical plate and the load on this plate from there the moment of individual plate are calculated. And find the critical plate above which maximum moments come.

Ans of question no-4

Prestressing in girders:-

Prestressing is the process of introducing compressive strength to counteract the tensile stress. girders are the structure made in factory then fixed over pier cap through launching gantry. To get better quality and required less time to fix.

Advantages of prestress girders in metro projects are-

1.less time required for Erection .

2. Better quality control.
3. Lower maintenance cost.
4. No impact over weather condition.

Ans of question no-5

Prestressing losses-

Prestressing loss is the loss of stress in prestressed structure due to various factors like elastic shortening, anchorage slip etc.

Types of prestressing losses-

1. immediate I,e short term losses- these are 3 types (a) elastic shortening, (b) frictional losses, (c)anchorage slip.
2. Time dependent losses I,e long term- these are 3 types (a) creep,(b) relaxation,(c)shrinkage.

Elastic shortening happens when we release the stress then full compressive stress generated on structure, so the structure wants to shorten upto a limit, so losses in structure.

Ans of question no-6

Girders is being prestress during fabrication through prestressing tendon.

The following component use during prestressing are-

1. tendon.
2. anchorages.
3. tendon couplers.
4. ducting.

Ans of question no-7

Calculated the stress through resultant prestressing losses-

At first calculate the all individual losses through empirical formula, I,e friction loss anchorage slip etc. then calculate the applied force through formula, I,e =0.765Fpu*As*n*(1-loss)/1000KN.

Then calculate the stress at top and bottom of the structure. From resultant stress we deduct the resultant loss to get actual load goes on it.

Ans of question no-8

Step wise procedure of transverse analysis of open web structure of U girders-

At first create the transverse plate and find out the critical plate for moment, and check the results for sectional material stress, reinforcement stress, and allowable crack width as per permissible limit. and find out the M/Mu ratio which is equal to 1.

Ans of question no-9

Longitudinal analysis of open web structure-

At first create the longitudinal plate and find out the critical plate for moment, and check the results for sectional material stress, reinforcement stress, and allowable crack width as per permissible limit. and find out the M/Mu ratio which is equal to 1.

Final design moments and axial stress are extracted on the basis of maximum moments and axial stress on it.