Challenge 9

Challenge-9

Ans of question-1

Detail steps involved in calculation of the loads in piers

A.

1. i) Dead load-This load comprises of self weight of girders, pier caps and pier.
2. ii) SIDL- This load majorly comprises of weight of track plinth, rails, cables, cable trays, parapet etc.
3. B. Live load- This load comprises of the train (rolling stock) live load that runs on the superstructure.
4. i) OTOS (one track one side load)-

1. ii) OTBS (one track both side load)-

iii) BTOS (both track one side load)-

1. iv) BTBS (both track both side load)-

1. C. Braking load- The load comes into play when the train applies break while moving. It takes as 18 % of unfactored vertical load comes on pier due to breaking effect.
2. Traction load- The loads comes into play when the train starts to accelerate from rest. It is taken as 20% of the unfactored vertical load. It occurs opposite direction of breaking action.
3. E. Centrifugal force-

This load acts on curve spans, it shall be calculated with the actual maximum allowable speed of the train in curve according to plan radius of curvature.

Coefficient of centrifugal force=V^2/127R

Where, V= design speed of train in km/hour

R= radius of cord span in meters.

Generally CF is considered to act 1.83m above the rail level I,e the distance between C.G of train to rail level.

1. F. Wind load-
2. i) With out LL- This load comes into play when wind exerts load on the structure, in this case the wind pressure will very high, making it quite difficult for movement of LL.
3. ii) With LL- This load comes into play when wind applies force on the structure, in this case the wind pressure will be normal allowing the movement of LL.

Design Wind speed Vz= Vb * K1 * K2 *K3

K1,K2,K3= Certain geographical factors.

Vb= Regional basic wind speed in M/SEC

1. G. Earthquake load- This load comes into play during earthquake when the structures vibrates in the longitudinal direction, LL is not considered in that case as vibration don’t have any impact on the live load as it rolls away.
2. H. LWR force- The long welded rail, force act on the structure due to stress generated in the rail.it is generated by the expansion / contraction of rail due to increase/decrease in temperature. The LWR force are considered to be 0.8 ton/meter/track
3. Derailment load- This load comes into play when the live loads get derailed. In this case , the live load may get off the track and slide to the edge of the structure, on the live load may derail and topple on edge.

Load combinations-

Limit state	Loads	Symbol	IRS	IRS				IRS	IRS
			GI	GIIa	GIIb	GIIc	GIId	GIII	GV
		Checked for	Cracking stress	Stress	Stress	Stress	Stress	Stress	Stress
SLS Combinations	DL	DL	1	1	1	1	1	1	1
	Shrinkage & creep	SC	1					1	1
	Prestressing	PR	1	1	1	1	1	1	1
	SIDL	SIDL	1.2	1.2	1.2	1.2	1.2	1.2	1.2
	Earthquake	EQ		1	1
	Overall temp	OT						1
	Differential temp	DT						0.8
	Differential settlement	DS
	LL	LL		1.1	0.5		1
	Derailment loads	DR							1
	Wind loads					1	1
Limit state	Loads	Symbol	IRS	IRS				IRS	IRS
			GI	GIIa	GIIb	GIIc	GIId	GIII	GV
		Checked for	Cracking stress	Stress	Stress	Stress	Stress	Stress	Stress
ULS Combinations	DL	DL	1.25	1.25	1.25	1.25	1.25		1.25
	Shrinkage & creep	SC	1						1.25
	Prestressing	PR	1.15	1.40	1.40	1.40	1.40		1.40
	SIDL	SIDL	2	2	2	2	2		2
	Earthquake	EQ		1.60	1.25
	Overall temp	OT
	Differential temp	DT
	Differential settlement	DS
	LL	LL	1.75		0.70		1.40
	Derailment loads	DR							1.75
	Wind loads					1.60	1.25

Ans of question-2

Design codal provisions for piers of metro viaducts-

Check for shear-

shear stress enhancement factor, d= 1+0.05P/Ac

Where,

P=ultimate axial load in newtons

Ac=area of entire column section in mm^2

Fck=characteristic compressive strength of concrete.

According to table 15 of IRS-CBC 1997 ultimate shear stress in concrete as per percentage area of tension reinforcement and grade of concrete.

Ultimate shear stress, Vc=0.767N/MM^2

Depth factor S= 0.799

Enhanced ultimate shear strength of concrete, S*Vc*d N/MM^2

Shear reinforcement is required if V>S*Vc*d

If V<=Vc*S, Asv=0.4*b*sv/0.87fy

If V>S*Vc, Asv=b*Sv*(V+0.4-SVc)/0.87fy

Where,

ASv= C/S area of all the legs of the stirrups/links at a particular C/S.

Sv=spacing of the stirrups along the member.

B=Breadth of the section.

Confining reinforcement (for circular section)

Ash=0.09*S*Dk*(Ag/Ac-1) *Fck/fy or Ash=0.024*S*Dk*fck/fy

Take maximum value from above.

Where,

Fck=concrete grade

Fy=reinforcement grade

D= dia of pier

C= clear cover on either side

Dk= dia of pier core

Ac= area of concrete core

Ag= gross area of pier section.

S= pitch of spiral.