For Official use only

GOVERNMENT OF INDIA
MINISTRY OF RAILWAYS
(Railway Board)

INDIAN RAILWAY STANDARD

CODE OF PRACTICE FOR

THE DESIGN AND CONSTRUCTION
OF MASONRY AND PLAIN CONCRETE
ARCH BRIDGES

(ARCH BRIDGE CODE)

ADOPTED –1941
INCORPORATING A & C SLIP NO. 7, YEAR : 2000

ISSUED BY

RESEARCH DESIGNS AND STANDARDS ORGANISATION

LUCKNOW - 226011

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 CONTENTS

PAGE No.
1. SCOPE … 1
2. DESIGN LOADS AND THEIR METHODS OF APPLICATION … 1
2.1 Dead Load … 1
2.2 Live Load … 1
2.3 Temperature Stresses … 1
2.4 Rib-shortening Stresses … 1
2.5 Shrinkage Stresses … 1
3. SHAPE OF THE ARCH RING … 1
4. THICKNESS OF ARCH RIB … 2
5. ANALYSIS OF STRESSES IN THE ARCH RING … 2
5.1 Conditions of Loading … 2
5.2 Method of Analysis … 2
5.3 Existing Arches … 2
6. ‘EFFECTIVE LENGTH’ OF ARCH RING … 3
7. ABUTMENTS FOR ARCH BRIDGES … 3
7.1 Thickness at the skew-backs … 3
7.2 Forces Acting on an Abutment … 3
7.3 Conditions of stability … 4
7.4 Foundations for Abutments … 4
8. PIERS OF ARCH BRIDGES … 4
8.1 Thickness at Top … 4
8.2 Forces Acting on the Pier … 4
8.3 Conditions of Stability … 5
8.4 Foundations for Piers … 5
9. DESIGN OF RETURN AND WING WALLS … 5
10. ECONOMY IN ARCH BRIDGE DESIGN … 5
11. TYPE OF MASONRY … 5
12. WORKING STRESSES … 5
12.1 Masonry Arches … 5
12.2 Plain Concrete Arches … 5
13. FOUNDATION PRESSURE … 5
14. SEISMIC EFFECT … 5
15. SKEW ARCHES … 6
16. WEEP HOLES … 6
17. FILLING OVER ARCHES … 6
18. STRIKING OF CENTRES AND APPLICATION OF LOAD … 6

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 Indian Railway Standard
CODE OF PRACTICE FOR
THE DESIGN AND CONSTRUCTION OF MASONRY AND
PLAIN CONCRETE ARCH BRIDGES
(Arch Bridge Code)

1. SCOPE may be neglected in designing or analysing

arches covered by this code.
1.1 This Code of practice applies to arch
bridges constructed of brickwork, stone or plain 2.3 Temperature Stresses: Temperature
concrete. Any revision or addition or deletion of stresses may be neglected in designing arches
the provisions of this Code shall be issued only in masonry or plain concrete, where rise-span
through the Correction slip to this manual. No ratio is not less than 1/3.
cognizance shall be given to any policy
2.4 Rib-shortening Stresses: In the
directives issued through other means.
design of arch bridges, allowance shall be
1.2 Open spandrel and reinforced concrete made for stresses due to rib-shortening under
arch bridges are excluded from the scope of thrust.
this code.
2.5 Shrinkage Stresses – Shrinkage
2. DESIGN LOADS AND THEIR stresses are neglected in the design of arch
METHODS OF APPLICATION bridges covered by this code. When the arch
is, however, built in plain concrete, steps shall
2.1 Dead Load - The dead load trans-
be taken to reduce shrinkage stresses by
mitted to the arch is assumed to act vertically.
concreting in strips and for spans exceeding
The horizontal component of the earth
6m, light reinforcements which may not be less
pressure acting on the arch ring may be
than 0.16 per cent of the area of concrete,
neglected.
shall be provided to resist residual shrinkage
2.1.1 The dead load shall include the weight stresses.
of the arch ring itself and all filling above it,
3. SHAPE OF THE ARCH RING:
also the weight of the road metal in the case of
road bridges and track and ballast in the case 3.1. In order to reduce the horizontal thrust
of railway bridges. and so to obtain economy in design of
abutments, piers and foundations, the rise of
2.1.2 For the purpose of calculations, the
an arch should be kept as large as possible. It
dead loads for various materials shall be taken
should not ordinarily be less than 1/3 of the
from IS:1911-1967. Schedule of Unit Weights
span but in no case less than 1/5.
of Building Materials.
3.1.1. For spans up to 12m clear, a simple
2.2 Live Load:
segmental or semi-circular curve may be
2.2.1 Live Load: The live load shall be the adopted as no marked advantage is obtained
appropriate standard of loading with by using multi-centred arches.
longitudinal and lateral distribution as laid
3.1.2. For spans exceeding 12m clear, the
down in the Bridge Rules.
shape of the arch axis should be designed in
2.2.2 Dynamic Effects : The Dynamic such a manner that the axis conforms as near
Effects Allowance shall be taken as specified as practicable to the equilibrium polygon for
in the Bridge Rules. dead load plus 50 per cent of the E.U.D.L
2.2.3 Horizontal Loads on the Arch: The covering the entire span
effect of the tractive effort and braking effect

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4. THICKNESS OF ARCH RIB: (b) within the middle third if graphical or
other approximate methods are
4.1. The variation, if any, in the thickness of
adopted.
an arch from one section to another shall be
gradual and shall be fixed with due regard to 5.2. Method of Analysis: In analysing
the conditions of stresses, economy and masonry or concrete arches, the elastic
appearance. method of analysis should preferably be
adopted. Either purely analytical methods or a
For short spans, not exceeding 12m clear, a
combination of analytical and graphical
constant section of arch from crown to
methods may be used. In practice the simplest
springing may be adopted.
method would probably be a combination of
5. ANALYSIS OF STRESSES IN THE the analytical and graphical methods.
ARCH RING:
5.1. Conditions of Loading : In investiga- 5.3. Existing Arches:
ting the stability of the arch ring, it will be
sufficient to consider the following conditions of 5.3.1. Except in case of gauge conversion,
loading with regard to live loads – certification of existing arch bridges as per
para 4, chapter VI of Rules for the Opening of
5.1.1. For short spans not exceeding 12m a Railway shall be based on physical condition
clear, with a constant thickness of the arch of the structure.
ring, live load at the end 5/8 of the span.
5.1.2. For short spans not exceeding 12m When new types of locomotives and rolling
clear, with arch rings of variable thickness, stock are permitted to run on a section for the
investigation of stresses must be made at the first time, bridges should be kept under
three critical sections with the position of observation as considered necessary by the
U.D.L.specified in Clause 2.3.4.1 of Bridge Chief Engineer.
Rules as given in the Table-I below.
5.3.2. Heavier loading density or axle load
TABLE-I over those allowed at present shall not be
permitted on distressed arch bridges, unless
Moment they are rehabilitated. However, at the
Section Max. (+) Max. (-) discretion of the Chief Engineer, such heavier
trailing load/increased axle load may be
Crown Middle 1/4 of End 3/8 permitted on the existing distressed arch
whole span (both ends) bridges, if the strength of the arch bridge is
Quarter End 3/8 End 5/8 found safe after conducting load test on
Point (adjacent end) (opposite end) representative span as per the criteria
indicated in para 5.3.3.
Spring End 5/8 End 3/8
Line (opposite end) (adjacent end)
5.3.3. The load test shall be conducted on
5.1.3. For spans exceeding 12m clear, distressed bridge only after complete pressure
stresses shall be worked out throughout the grouting of the masonry. The criteria for
arch, the number of sections depending on the arriving at the safe load shall be:-
span of the arch.
(i) Under the proposed load the crown
5.1.4. The line of pressure under the condition deflection and spread do not exceed
of loading enumerated above shall everywhere 1.25 and 0.4 mm, respectively;
lie, (ii) There is no residual deflection or
(a) within the middle half of the arch ring, if spread after release of load; and
the line of pressure is determined (iii) There is no crack appearing on the
by elastic theory. intrados of bridge.

VI-2
Note: The above criteria will be applicable to however, be ensured that a proper bond is
segmental and non-segmental arches of span established between the existing masonry and
4.5m to 15 m provided the span/rise ratio lies new material by suitable means such as
between 2 and 5 dowels and post grouting through grout holes
to be left while casting the jacket.
5.3.4. In regard to gauge conversion, the
certification for the safety of all the arch 5.3.5.5 In all cases of cracked masonry,
bridges, whether sound or distressed shall be whether in arches or in abutments and piers,
based on load test on representative type of that should be grouted under pressure to plug
bridges. The criteria for assessing the safe all the cracks before the additional material is
load shall be the same as specified in clause provided.
5.3.3 above, provided the following conditions
5.3.5.6 The space between the new arch ring
are also satisfied. Special cases, if any, may
and the existing arch, in the case of
be dealt with on individual merits by the
strengthening below the intrados of the arch
Railways in consultation with RDSO.
should be grouted under pressure for which
(i) The condition of masonry and its grout holes should be provided in the new arch
behaviour under test load are ring.
satisfactory.
6. ‘‘EFFECTIVE LENGTH’’ OF ARCH
(ii) Type of foundation and nature of soil on RING:
which it is founded are suitable.
6.1. The effective length shall be the full
length from skew back to skew back. Where
5.3.5. Strengthening of weak/distressed
however spandrel filling with masonry or
existing arches:
concrete is done in conjunction with the arch
5.3.5.1 For strengthening weak/distressed ring, so as to provide proper bonding between
arches method of jacketing at the intrados is the arch ring and the masonry or concrete in
preferable, if the resultant reduction in the the spandrel filling the effective length of the
waterway is permissible arch may be taken between the points
obtained by producing the inside vertical faces
5.3.5.2 In the case of strengthening over
of skew backs to cut the extrados as shown in
extrados of arch, the new arch ring should be
the sketch.
designed to take the entire load, viz.dead and
live loads.
5.3.5.3 In the case of strengthening below
intrados of arch, the new arch ring should be
designed as under:-
(a) To take the entire load by itself where
the existing arch has transverse
crack(s).
(b) To take the entire load by composite
action with the existing arch ring, where
the existing crack(s) are all longitudinal
or there are no signs of distress in the
existing arch, provided effective bond 7. ABUTMENTS FOR ARCH BRIDGES:
could be ensured between the old and 7.1. Thickness at the Skew-backs: The
new arch ring. thickness at the skew back should be
5.3.5.4 In the case of strengthening of determined with due regard to the shearing
abutments and piers of arch bridges, the stress produced by the horizontal thrust from
design should always be on the basis of the arch ring, which shall be assumed to be
composite action of the new material acting resisted by the combined friction and shearing
along with the existing one. It should, strength of the joint. The coefficient of friction

VI-3
in this case may be taken as 0.7 and the safe (c) Dead load plus live load on the entire
shearing stress as given in Clause 12. span.
7.2. Forces Acting on an Abutment: For each of the above conditions of loading,
the line of pressure in the course enumerated
7.2.1 The forces acting on an abutment are
above shall lie within the middle half of every
as follows:
section of the abutment. The stresses at any
(a) Reaction from the arch. section shall not exceed the working stresses
(b) Pressure of earth at back. specified in clause 12. The shearing stresses
at any place shall be assumed to be resisted
(c) Weight of abutment and overlying fill. by the frictional forces and safe shearing
(d) Water pressure and buoyancy – These strength of the masonry.
should be considered when depth of
water may exceed 6m the calculations 7.4. Foundations for Abutments.
being made both with and without the
effect of the water pressure and 7.4.1 Arches shall only be built where
buoyancy acting together. foundation conditions are such that there will
be no risk of unequal settlement or horizontal
7.2.2 In calculating the thrust of the arch ring movement.
for designing the abutment, Dynamic effects 7.4.2 The permissible pressure on the soil
may be neglected. shall not exceed that specified in Clause 13.

7.2.3 The total thrust from the live load may 7.4.3 The line of pressure shall lie within the
be assumed to be distributed over the whole middle third of the foundation and every effort
length of the abutment, or a length bounded by should be made to keep it as near the center of
lines drawn at a slope of 1` horizontal to 2 the base as possible, to ensure a uniform
vertical from the bottom edges of sleepers to distribution of pressure.
the section under investigation whichever 7.4.4 The depth of foundation shall be
length is less. Over this length, the thrust due determined by the Engineer with due regard to
to dead load may be assumed to have a the conditions at the site but should not,
uniform value, corresponding to that produced ordinarily, be less than 1.25 m.
by the maximum height of the filling.
8. PIERS OF ARCH BRIDGES.
7.2.4 The active earth pressure at the back of
an abutment (which adds to its stability) shall 8.1 Thickness at Top The thickness at
not be taken to be more than the pressure of a the top shall be adequate to accommodate the
3
fluid weighing 2353 N/m (240 kg/m ). This
3 skew backs on both sides and to resist the
pressure shall be assumed to act over a height stresses imposed under the most unfavourable
from bed level to springing only, due allowance conditions of loading.
being made for surcharge of the overlying fill.
No allowance shall be made for the surcharge 8.2 Forces Acting on the Pier.
due to the live load.
8.2.1 The forces acting on the pier are as
7.3. Conditions of Stability An arch follows:-
abutment shall be investigated for the following (a) reactions from the adjacent arches,
three conditions of loading:-
(b) weight of masonry and fill and the
(a) Dead load plus live load on 5/8 span weight of pier itself.
adjacent to abutment.
(c) Water pressure and buoyancy with the
(b) Dead load plus live load on the other same provision as for abutments in
5/8 span. Clause 7.2.

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8.2.2 The provisions regarding dynamic 11. TYPE OF MASONRY:
effects and distribution of thrust shall be the
11.1 Arch rings shall be constructed either
same as laid down for abutments in clause 7.2.
with voussoirs of precast cement concrete or
8.3 Conditions of Stability: sound durable building stone, or brick work in
first class bricks and 1:4 cement mortar. Plain
8.3.1 The stability of piers shall always be cement concrete cast in-situ may also be used
investigated for the following two conditions of in which case reinforcement shall be provided
loading:- as per Clause 2.5.
(a) when only one of the adjacent spans
12. WORKING STRESSES;
carries live load – This condition will
usually give the maximum stresses in 12.1 Masonry Arches
the masonry of the pier.
12.1.1 Where actual compression tests are
(b) When both adjacent spans carry live made, the maximum permissible compressive
load – This condition usually gives the stress in masonry shall not exceed one-eighth
maximum intensity of foundation of its crushing strength. Tensile and shear
pressures. stresses may be permitted upto one-fortieth of
the crushing strength.
8.3.2 The provision of Clause 7.3 regarding
the location of the line of pressure and the
12.1.2 In the absence of tests, sound brick-
stresses, apply to the piers also.
work in lime mortar, which has hardened, shall
8.4 Foundations for piers – These shall be assumed to have a crushing strength of
be governed by the same provisions as laid 4.3N per sq.mm (43.75 Kg per sqcm.) and
down for abutments in Clause 7.4. brick-work in cement mortar 6.9 N per sqmm
(70 kg. per sqcm.).

9. DESIGN OF RETURN AND WING 12.2 Plain Cement Concrete Arches – The
WALLS working stresses shall not exceed those laid
9.1 The return and wing walls should be down in the Indian Railway Standard “Concrete
designed in accordance with the Indian Bridge Code”.
Railway Standard “Code of Practice for the
design of sub-structure of bridges”. 13. FOUNDATION PRESSURE

10. ECONOMY IN ARCH BRIDGE 13.1 Owing to the wide variation in safe
DESIGN: bearing pressures on foundations in different
parts of India, it is not possible to specify
10.1 In the case of arch bridges in high permissible bearing pressures which will have
banks, the height of the springing, the length of universal application. Designs should be based
the arch barrel and, in the case of multiple on local conditions and permissible pressures
span bridges, the size of the span of the may be established on the basis of tests or on
arches should be so fixed that the total cost of pervious experience. Normally, foundations,
the bridge for the required water-way is a unless resting directly on rock, shall not be less
minimum. than 1.25m in depth. It is, generally, safe to
10.2 In order to avoid excessive lateral increase the permissible bearing pressure at
tension in the arch ring or excessive load on the rate of 17647 N/m2 (1800 kg per sqm) for
the ends of the barrel, the height of the parapet each additional metre of depth below 1.25 m.
wall above the crown of the arch should,
generally, not exceed 1000mm when the depth
of fill is considerable. 14. SEISMIC EFFECT:
14.1 Masonry or plain cement concrete
arches shall not be constructed in zone V.

VI-5
Masonry or plain cement concrete arches shall 18. STRIKING OF CENTRES AND
not be constructed with spans exceeding 6 m APPLICATION OF LOAD:
in Zone IV and 10m in Zone III.
18.1 The centers should not be struck before
15. SKEW ARCHES:
one week after the completion of the arch.
15.1 Skew arches shall be so constructed
that the courses are everywhere at right angles 18.2 After completion of any portion of the
to the lines of thrust. masonry of an arch bridge, the following
minimum periods of time as specified in Table-
16. WEEP HOLES: II below should be allowed to elapse before
16.1 Weep holes should be provided loads as specified therein may be imposed on
through abutments, wing or return walls, and that portion of the masonry:-
parapets, as may be necessary, adequate TABLE-II
arrangements being made to lead water to the
weep holes. 50% of 75% of Full
design design design
Description
17. FILLING OVER ARCHES: load load load
Ordinary 7 14 28
17.1 It is recommended that the depth of the cement mortar days days days
fill between the underside of the sleeper and and concrete.
the crown of the arch should not be less than
1 m. Rapid- 5 10 28
hardening days days days
17.2 Filling of a porous nature, such as cement mortar
brickbats or ballast, should be used to cover and concrete.
the whole extrados of the arch to a depth of at
least 300 mm over the crown.
17.3 Earth filling should be done in layers,
each being consolidated by ramming and by NOTES:
sprinkling with water. Black cotton soil should 1. The expression “load” means the total
not be used. calculated load with the appropriate Dynamic
effects allowance specified for the speed at
17.4 In existing arches the filling should be which the load is permitted to run.
disturbed as little as possible as, after a time,
the arch action in the filling relieves the arch 2. The above periods shall be suitably
ring of a considerable portion of the increased where the mean air temperature is
superimposed load. less than 160 C.

VI-6