DESIGN OF BOX CULVERT FOR RAILWAY EMBANKMENTS IN

DESIGN OF BOX CULVERT FOR RAILWAY EMBANKMENTS

• IN RAILWAYS BOX CULVERTS ARE THE STRUCTURES BUILT UNDERNEATH RAILWAY TRACKS FOR PASSAGE OF WATER AS WELL AS TRAFFIC. • THEY CAN BE OF MANY CONFIGURATIONS SUCH AS SINGLE BOX CULVERT, DOUBLE BOX CULVERT OR HIGHER.

RAILWAY TRACK OVER BALLAST EARTH FILL

FUNCTION OF HAUNCHES • ARE PROVIDED IN CIRCULAR TANKS AT CORNERS TO AVOID BURSTING PRESSURE. • WHERE SLAB DEPTH REQUIRED AT THE INTERIOR WALL IS MORE THAN 50 mm • SLOPE IS 1 V: 3 H • PROTECTION AGAINST IMPACT LOAD AND LATERAL THRUST OF PIPES. • FINALLY TO PREVENT LEAKAGE.

LOADS CONSIDERED IN DESIGN OF CULVERTS DEAD LOADS LIVE LOADS

DEAD LOADS WEIGHT OF TRACK AND BALLAST (5. 5 t/m for 25 t LOADING AND 5. 8 t/m FOR DFC LOADING) WEIGHT OF EARTH FILL WEIGHT OF BOX ITSELF

LIVE LOADS MAINLY TWO TYPES OF AXLE LOADS 25 t AXLE LOAD 32. 5 t DFC LOADING

DISPERSION OF RAILWAY LIVE LOADS: DISTRIBUTION THROUGH SLEEPERS AND BALLAST: THE SLEEPER MAY BE ASSUMED TO DISTRIBUTE THE LIVE LOAD UNIFORMLY ON TOP OF THE BALLAST OVER AREA OF CONTACT GIVEN BELOW: TYPE –I TYPE-II UNDER EACH RAIL SEAT BG 2745 mm x 254 mm 760 mm x 330 mm MG 1830 mm x 203 mm 610 mm x 270 mm THE LOAD UNDER THE SLEEPER SHALL BE ASSUMED TO BE DISPERSED BY THE FILL INCLUDING BALLAST AT A SLOPE NOT GREATER THAN HALF HORIZONTAL TO ONE VERTICAL AND DECK SLABS SHALL BE DESIGNED FOR BOTH TYPES OF SLEEPER

DISTRIBUTION THROUGH RC SLAB: WHEN THERE IS EFFECTIVE LATERAL TRANSMISSION OF SHEAR FORCE , THE LOAD MAY BE FURTHER DISTRIBUTED IN A DIRECTION AT RIGHT ANGLES TO THE SPAN OF SLAB EQUAL TO THE FOLLOWING: i) 1/4 SPAN ON EACH SIDE OF THE LOADED AREA IN THE CASE OF SIMPLY SUPPORTED , FIXED AND CONTINUOUS SPANS. ii) 1/4 OF LOADED LENGTH ON EACH SIDE OF THE LOADED AREA IN THE CASE OF CANTILEVER SLABS.

COEFFICIENT OF DYNAMIC AUGMENT (CDA) • AS THE AXLE IS NOT STATIONERY BUT MOVING HENCE LOADS ARE INCREASED BY CERTAIN FACTORS. • THE GIVEN RELATIONS ARE APPLICABLE FOR SPEEDS UPTO 160 KMPH. • FOR SINGLE TRACK SPANS CDA = 0. 15 + 8/6+L --------- (A) SUBJECT TO MAXIMUM OF 1

WHERE “L” IS LOADED LENGTH OF SPAN IN M FOR POSITION OF THE TRAIN GIVING MAX. STRESS IN THE MEMBER UNDER CONSIDERATION. IF THE DEPTH OF FILL IS LESS THAN 900 mm COEFFICIENT OF DYNAMIC AUGMENT SHALL BE EQUAL TO [2 - (d/0. 9)] x 1/2 x CDA WHERE d = DEPTH OF FILL IN m.

• IF THE DEPTH OF FILL IS 900 mm THE CDA SHALL BE HALF OF THAT SPECIFIED IN (A) SUBJECT TO A MAXIMUM OF 0. 5. • WHEN DEPTH OF FILL EXCEEDS 900 mm CDA SHALL BE UNIFORMLY DECREASED TO ZERO WITHIN THE NEXT 3 m.

CDA LESS THAN OR EQUAL TO 1 0. 9 m 1/2 CDA LESS THAN EQUAL TO 0. 5 FURTHER 3 m ZERO VARIATION OF CDA WITH DEPTH OF FILL

CURVATURE EFFECT UPTO 4 DEGREE CURVE • FOR 25 t AXLE LOADING ENHANCE LOAD BY 21%. • FOR DFC (32. 5 t AXLE LOAD) ENHANCE LOAD BY 34%.

• SEISMIC FORCES ARE NOT CONSIDERED IN THE DESIGN. • SWAY OF THE STRUCTURE IS ALSO NOT CONSIDERED.

LOADS ON A SINGLE BOX CULVERT WL 2/12 + WL 2/30 WL 2/12 + WL 2/20

THE STRUCTURE IS ANALYSED FOR DIFFERENT POSITIONS OF LOAD AND CRITICAL MOMENTS ARE CONSIDERED. NOW THE STRUCTURE IS DESIGNED FOR MAXIMUM MOMENTS BY MOMENT DISTRIBUTION METHOD. JOINTS A MEMBER AD AB MOMENTS DF DISTRIBUTE BALANCE B BA BC C CB CD D DC DA