Long span structures in Concrete and Steel

Long Span Structures
Garima Rajput
Rithika Ravishankar
Roshani Tamkhade
Rasika Dongare
Aishwarya Khurana
Nilesh Mane
Long Span Beams Long Span Trusses Portal Frames

Long span structures create unobstructed, column-free spaces greater than 30 metres (100 feet) for a
variety of functions.
Visibility Flexibility Large Scale Storage
Auditoriums
Stadiums
Exhibition halls
Manufacturing facilities
Aircraft hangars

for
Long Span
Buildings
Subject to
Bending
Funicular
Structures
Both tensile and
compressive forces
Pure tension or
pure compression
1. Girder
2. Truss (Depth
to span ratio
– 1:5 to 1:15)
3. Two-way grid
4. Two-way truss
5. Space truss
(Depth to
span ratio –
1:35 to 1:40)
1. Parabolic Arch
2. Tunnel vault
3. Domes
4. Cable stayed
roof
5. Bicycle wheel
6. Warped tension
surfaces

for
Long Span
Buildings
Subject to
Bending
Funicular
Structures
Both tensile and
compressive forces
Pure tension or
pure compression
1. Girder
2. Two-way grid
3. Truss (Depth
to span ratio
– 1:5 to 1:15)
4. Two-way truss
5. Space truss
(Depth to
span ratio –
1:35 to 1:40)
Pure Compression:
1. Parabolic Arch
2. Tunnel vault
3. Domes
Pure Tension:
1. Cable stayed
roof
2. Bicycle wheel
3. Warped tension
surfaces

Some of the oldest long span structures
dated back to the Roman civilization.
However, most long-span buildings then
were single level constructed using vaults
and domes.
By the late 20th century, durable upper
limits of span were established for these
types:
the largest covered stadium had a span of
204 meters (670 feet),
the largest exhibition hall had a span of
216 meters (710 feet),
and the largest commercial fixed-wing
aircraft had a 75–80 meter (250–266
foot) span hangar.
The major evolution in long span section-
active structures has occurred in the
aspect of shift from in-situ to precast
construction.
History and Evolution
Old-to-New long span structures
with their height and spans

Another method of classification of long span structures is
as follows
Form - Active
Systems of flexible,
non-rigid matter, in
which the
redirection of forces
is effected by
particular form
design and
characteristic form
stabilization
Systems of rigid,
solid, linear
elements, in which
redirection of forces
is effected by
mobilization of
sectional forces
Systems of short,
solid, straight lineal
members, in which
the redirection of
forces is effected by
vector partition, i.e.
by multidirectional
splitting of single
force simply to
tension or
compressive
elements
Section - Active Vector - Active Surface - Active
Cable Structures
Tent Structures
Pneumatic structures
Arch structures
Flat Trusses
Curved Trusses
Space Trusses
Beam Structures
Framed structures
Slab structures
Systems of flexible
or rigid planes able
to resist tension,
compression or
shear, in which the
redirection of
forces is effected
by mobilization of
sectional forces
Plate Structures
Folded Structures
Shell structures

Introduction
Beams greater than 30 meters in span are
said to be LONG SPAN BEAMS.
The use of long span beams results in a
range of benefits, including flexible,
column free internal spaces, reduced
foundation costs, and reduced steel
erection times.
Many long span solutions are also well
adapted to facilitate the integration of
services without increasing the overall
floor depth.
The design of long span steel and (steel -
concrete) composite beams is generally
carried out in accordance with the IS.
>30 meters
Conventional beam Long span beam

Types
Most common type of long span beams used today are: Plate Girders, and Beams with Web Openings.
The popular construction methodology is composite construction (steel + concrete)
The types of long span beams are:
1. Parallel beam approach
The parallel beam approach is
effective for spans up to around 14
m. Floor grids comprise two layers
of fully continuous beams running
in orthogonal directions. Services
running in either direction can be
integrated within these two layers,
so that services passing in any
direction can be accommodated
within the structural floor depth. A
further benefit is that, being fully
continuous, the depth of the beams
themselves is reduced without
incurring the expense and
complexity of rigid, full strength
connections .

Types
2. Composite Beam with Web openings
Web openings are typically formed
in beams to allow services to pass
through the beam, reducing the
effective overall depth of floor
construction for a given spanning
capability or for aesthetic reasons
Span: 10 to 16 m.
The alternative way of forming the
web openings is simply to cut them
into the plate used to form the web
of a plate girder, or the web of a
rolled section.
The openings introduce a number
of potential failure modes not
found in solid web beams. Large
openings may require stiffening to
avoid instability (buckling) of the
web posts.
Failure
in
cellular
beam

Introduction

Failure in cellular beam
With stiffened web openings

Types
3. Tapered Girders
Tapered girders can be a cost
effective solution in the span
range 10 m to 20 m.
They are another solution that
allows services to be
accommodated within the
structural floor zone.
The depth of the girder
increases towards mid-span,
where applied moments are
greatest, and thereby
facilitating hanging services
under the shallower regions
near the beam supports. It is
also possible to form web
openings in tapered girders in
regions of low shear, towards
mid-span. These provide more
options for service integration .

Types
4. Stub girders
Stub girders are a Vierendeel
form of truss. The bottom
chord is typically formed from
a shallow open section (H-
beam), on which sit short
lengths (stubs) of deeper I-
sections.
The number of
elements/surfaces associated
with a stub girder may increase
the cost of fire protection
compared with simpler
solutions.
Spans in excess of 20 m can be
economically achieved.
Services and/or secondary
beams can pass through the
gaps between the beam stubs,
reducing overall construction

Types
5. Haunched Composite beams
Haunches may be added at the
ends of a composite beam to
provide moment continuity.
The stiffness and strength of the
connections mean that the rest
of the span can be shallower
(the bending moment diagram
is 'lifted' and the effective
stiffness of the beam
substantially increased), and
services passed under it. In
buildings where the services are
likely to need frequent
replacement (for example in
hospitals ), hanging the services
under the beams can be
advantageous.
Spans in excess of 20 m can
readily be achieved.

Types
6. Composite trusses
Composite trusses, which use the
concrete slab as the upper chord
in the final state, can achieve
spans in excess of 20 m. This
means they have been used when
very long spanning capability was
needed. The main disadvantages
are that during the construction
phase the truss may be rather
flexible (laterally), and that in the
final state the costs of fire
protection can be high given the
large number of surfaces to
protect. Clearly one of the prices
to pay for the spanning ability is
that fabrication cost is higher than
for a plain beam. Services can be
passed through the gaps between
the truss members to reduce
overall floor depth.

Construction drawingsPrecast concrete beam sections

Reinforced Concrete
(In - situ / Precast)
Timber, Laminated Timber
Glue-laminated timber can be
prefabricated using metal
connectors into trusses that span
up to 45 metres (150 feet)
Most economical forms: the pure
compression shapes of the
multiple-arch vault, with spans up
to 93 metres (305 feet), and ribbed
domes, with spans up to 107
metres (350 feet).
Used as industrial storage
buildings for corrosive materials
Metal
Structural steel
(Cut on site / Prefabricated)
Bending structures originally developed for
bridges, such as plate girders and trusses,
are used in long-span buildings. Plate
girders are welded from steel plates to
make I beams that are deeper than the
standard rolled shapes and that can span
up to 60 metres (200 feet)
Materials

Cleddau Bridge
• The Cleddau Bridge is a toll bridge
on the A477 road that spans the
River Cleddau between Neyland
and Pembroke Dock, Wales.
• Errors in the box girder design
caused it to collapse during its
construction in 1970.
Case study: Failure

• It failed during its erection by cantilevering segments of the span, out from the piers.
• The bridge was designed as a single continuous box girder of welded steel.
• The span that collapsed was the second one on the south side. The boxes were fabricated in
sections and moved over the previously built sections, aligned in place and welded.
• The collapse occurred when the last section of box for the second span was being moved out along
the cantilever.
• This section slid forward down the cantilever buckled, at the support and collapsed into the river
(Fig 2), killing four men, including the site-engineer.

• Investigation of collapse showed that the collapse was due to the buckling of the diaphragm at the
support (i.e., at the root of the second span being erected).
• The diaphragm was torn away from the sloping web near the bottom. This caused reduction in the
lever arm between flanges resisting negative bending moment at the support.
• The tendency of the bottom flange
to buckle was inevitably increased
by the reduction of the distance
between the flanges, as this
increased the force needed in each
flange to carry the moment with
the reduced lever arm.
• The support diaphragm was, in
effect, a transverse plate girder,
which carried heavy loads from
the webs of the plate girder at its
extreme ends and was supported
by the bearings as shown in Fig 3.

Modern Techniques For Long Span Beams –
Precast Concrete
PRECAST BRIDGES
• BENEFITS TO OWNER
o Reduction in the duration of work zones
o Reduced traffic handling costs
o Reduced accident exposure risks
o Less inconvenience to the traveling public
• BENEFITS TO OWNER
o Reduced exposure to hazards
o Reduced accident exposure risks
o Fewer weather delays
o Lower costs

Benefits of using precast concrete beams
Quality and Corrosion Resistance Immediate Delivery and Erection No Curing Time

Long Span Beam + Truss
Typical multi girder system with x-type
intermediate cross frames and stay-in-place
formwork used for constructing a deck-slab
Curved roof trusses can be used to support structural decks
with a suspended ceiling. The natural open web of the steel
truss allows for the simple passage of services.
Long Span Beams Long Span Trusses Portal Frames+
Cross – over 1

Long Span Trusses

• A roof truss is a structure that includes one or multiple triangular units that include straight
slender members with their ends connected via nodes.
• Trusses are frame works in which the members are subjected to essentially axial forces due to
externally applied load.
• Bending leads to compression in the top chords (or horizontal members), tension in the bottom
chords, and either tension or compression in the vertical and diagonal members, depending on
their orientation.
External loads on the nodes Tension & Compression members
Introduction

Pitched Roof Truss
• A pitched roof truss has a bottom
chord with two inclined top chord
connected through gusset plates or
panels. Extra supports in the form of
struts are also added as per the
requirement.
•These trusses have a greater depth at
mid-span.
Pitched roof truss
Categories

• A pitched roof truss has a
bottom chord and a top chord
that run parallel to each other.
Extra supports in the form of
struts are also added as per the
requirement.
Parallel chord truss
Categories Parallel Chord truss

King post truss:
A king post is a central vertical post used in
architectural or bridge designs, working in tension
to support a beam below from a truss apex above
Queen post truss:
A queen-post bridge has two uprights, placed
about one-third of the way from each end of the
truss. They are connected across the top by
a beam and use a diagonal brace between the
outer edges.
Types of trusses

Pratt truss:
•In Pratt trusses, the web members are arranged in
such a way that under gravity load the longer
diagonal members are under tension and the shorter
vertical members experience compression.
•These trusses can be used for spans that range
between 6-10m.
Howe truss:
•The converse of the Pratt is the Howe truss. This is
commonly used in light roofing so that the longer
diagonals experience tension under reversal of
stresses due to wind load.
•These trusses can be used for spans that range
between 6-30m.
Types of trusses

Fink truss:
Fink trusses are used for longer spans having high
pitch roof, since the web members in such truss are
sub-divided to obtain shorter members.
Fan truss:
Fan trusses are used when the rafter members of the
roof trusses have to be sub-divided into odd number
of panels.
Scissor truss:
Scissor roof truss can particularly be found in
cathedrals. The upside here is that the ceiling gets
vaulted and you receive more space in the attic.
Types of trusses

Warren girder:
•Parallel chord trusses uses webs of the same lengths
and thus reduce fabrication costs for very long spans.
•Modified Warren is used with additional verticals,
introduced in order to reduce the unsupported length
of compression chord members.
Lattice girder:
•It is commonly made using a combination of
structural sections connected with diagonal lacing.
This member is more correctly referred to as a laced
strut or laced tie.
Types of trusses

Vierendeel truss:
The Vierendeel truss is a structure where the
members are not triangulated but form rectangular
openings, and is a frame with fixed joints that are
capable of transferring and resisting bending
moments.
K- type truss:
In the case of very deep and very shallow trusses it
may become necessary to use K patterns for web
members to achieve appropriate inclination of the
web members.
North light truss:
In the north light truss, skylights or openings are
provided to allow north light inside the structure.
Types of trusses

Types Of Loads
The following are the various types of
loads to be considered while
calculating the stresses.
• Dead Load
• Live Load
• Longitudinal Force
• Horizontal Forces
• Wind Load
• Seismic Load
Direction of load transfer in Trusses
Load Analysis

Assumptions Behind Truss
Analysis
• Truss members are connected at
their ends only, and they are
connected by friction-less pins.
• So you don't have to consider any
secondary bending moment
induced do to force of friction.
• Truss is loaded only at joints.
• Weight of truss members can be
neglected, compared to load acting
on the truss.
Load Analysis

• Force developed in a truss member is
always axial. It can be either tensile,
or compressive.
• If a member is under tensile load, this
will be the direction of internal force
developed .
• So you can notice that, under tensile
load, internal force developed in the
member is directed away from the
joint.
• Similarly in case of compressive force,
the internal force developed in the
member is directed towards the joint.
Nature Of Load In Truss Members
Load analysis

Wood
Metal - Steel
Materials

Concrete – Precast /
Prestressed
Bamboo
Materials

While bamboo has been used for
centuries, the traditional methods of
lashing bamboo together are not
appropriate for the design of long
span trusses.
• These lashed connections don’t fully
utilize the full strength of bamboo
member.
• They rely solely on friction, the load
transfer between members is limited
and thus structures require more
members to do the same job that
one could if it were well connected.
• Finally complex geometries with
many members framing into one
node or three dimensional space
frames are difficult if not impossible
to construct.
Traditional Bamboo ConnectionLong Span Beams Long Span Trusses Portal Frames
Alternative MaterialsBamboo connections

• Since all fibers in a bamboo run parallel
once a bolt is placed through it and the
connection loaded in tension, the bolt acts
like a wedge and splits the bamboo.
• Also the puncture allows moisture to enter
the culm and accelerate decay
• Based on the proprietary nature of the
hubs, their installation requirements, and
the desire to develop cost effective, simple
connections, the research focused on an
alternate connection type to eliminate
these challenges.
Modern Bamboo Connection
These connections solve the issues of
complex geometries by joining the
members at a central hub. While they
provide a standardized connection
throughout a project, they are not
readily available.
Alternative MaterialsBamboo connections

• This connection requires filling several
hollow cells of the bamboo with concrete
and embedding a threaded rod.
• The new connection involves embedding a
common steel reinforcing bar into a mortar
filled bamboo culm and fillet welding
several of these members to a steel gusset
plate.
• The inner surface of the bamboo is
roughened to provide a bond between the
mortar and the bamboo while avoiding
puncturing the member.
• Because the rebar is embedded in mortar,
the load is transferred evenly across the
member’s cross section and can transfer
high axial loads to the bamboo.
• Finally, the incorporation of the steel
gusset plate makes the bamboo easy to
connect in any configuration desired
BAMBOO TRUSS
STEEL GUSSET PLATE
SECTION OF CONNECTIONLong Span Beams Long Span Trusses Portal Frames
Modern techniques Bamboo connections

Gatton Railway Bridge, Australia
Pratt truss design
Powerhouse roof, Boise
Fink truss design
Applications

Church roof, America
Scissor truss design
Industrial shed, England
North light truss design
Applications

Convention centre
Warren girder
Vierendeel bridge, Belgium
Vierendeel truss design
Applications

• Quick Installation- The primary advantage of a truss is
that it can be installed quickly and cost-effectively, even
even without heavy equipment to lift it into place.
• Increased Span- The unique properties of a triangular
object allow trusses to span across longer distances.
• Load Distribution- The shape of a triangle allows all of the
weight applied to the sides (or legs) to be redistributed
redistributed down and away from the centre. In trusses,
trusses, this transfers the entire weight of the roof to the
the outer walls.
• Accessibility- Since the bottom rail of a truss is typically
the ceiling of the rooms below, the triangular spaces of
of the trusses themselves form accessible paths for the
the installation of HVAC, electric and other utility
applications. The central void of a truss system is
generally the attic of a home, with the slope of the roof
roof forming the legs of the triangle.
Advantages Roof

• Transportation- Sometimes they are too big for a truck. In such
cases, specially designed truss trailers have to be used to haul the
structures around.
• Metal roofs-
I. Skilled labour is required to install metal roof trusses.
II. They are not energy efficient since they allow more heat to
from the structure.
III. When the metal is cut, drilled, scratched or welded, rust can
become a problem.
• Wooden roofs-
I. Wooden roofs are susceptible to fire.
II. Wood can rot or become infested with bugs if not maintained
treated properly.
Disadvantages Roof

• They are light, but strong- As they use small
timbers or beams of metal, the trusses would
would be light, but are strong enough to
handle loads thanks to the ridged triangles.
• Accessibility- They allow placement of
roadways on the structure itself, such as a rail,
rail, to be placed straight across it.
• Material usage- Because of its design, it makes
good use of limited construction materials to
to achieve strength that far outweighs its cost.
cost.
• Can be constructed in difficult site conditions-
These types of bridges can be built quickly in
in places where many other types cannot,
linking areas that other types will not work in.
Advantages Bridges

• They require high costs- While it is said that these
bridges’ design efficiently uses materials, it does use a lot
a lot of them. Building a truss bridge can be costly, and
and its upkeep requires time and money.
• Wastage of materials- Without the proper design and
work practice, constructing a truss bridge can result to
to waste of materials.
• Maintenance- Because of the amount of materials they
use, these types of bridges require a lot of upkeep.
• Complicated Design-The design of truss bridges can
become very complicated depending on the situation.
situation. The triangles have to be the perfect size and
and there has to be the perfect amount in order for the
the truss bridge to be safe.
Disadvantages Bridges

Case study

Howrah Bridge is a cantilever bridge
with a suspended span over the
Hooghly River in West Bengal, India.
• Address : West Bengal
• Total length : 705 m
• Opened : February 3, 1943
• Construction started : 1935
• Location : Howrah, Kolkata
• Architect : James Meadows
• Material : James Meadows
General Information Howrah Bridge

• Bridge type : Suspension type Balanced Cantilever
• Central span :1500 ft between centers of main towers
• Anchor arm : 325ft each
• Cantilever arm : 468ft each
• Suspended span : 564ft
• Main towers are 280ft high above the monoliths and 76 ft apart at the top
1500 ft325 ft 325 ft
468 ft 564 ft 468 ft
280 ft
Anchor Arm Cantilever Arm Suspended Arm Cantilever Arm Anchor Arm
General Information Howrah Bridge

• All members of the super structure comprise built up riveted sections with a combination of high tensile and
mild steel. No nuts and bolts.
• Road way beyond the tower is supported on ground leaving anchor arm free from deck loads
• Bridge deck comprises 71 ft carriage way and 15 ft footway projecting either side of the trusses and braced by a
longitudinal fascia girder.
• The deck system consists of cross girders hung with pinned connection.
• They support a continuous pressed steel system over which deck concrete is laid out.
Construction Howrah Bridge

A structure at least one portion of
which acts as an anchorage for
sustaining another portion which
extends beyond the supporting pier.
• A simple cantilever span is formed
by two cantilever arms extending
from opposite sides of an obstacle
to be crossed, meeting at the center.
• In a common variant,
the suspended span, the cantilever
arms do not meet in the center;
instead, they support a central truss
bridge which rests on the ends of
the cantilever arms.
• The suspended span may be built
off-site and lifted into place, or
constructed in place using special
travelling supports.
Cantilever Bridges Function

TEMPORARY PIER CLOSURE END
TYPICAL CONSTRUCTION SEQUENCE
• Some steel arch bridges are built using
pure cantilever spans from each side,
with neither falsework below nor
temporary supporting towers and cables
above.
• These are then joined with a pin, usually
after forcing the union point apart, and
when jacks are removed and the bridge
decking is added the bridge becomes
a truss arch.
• Such unsupported construction is only
possible where appropriate rock is
available to support the tension in the
upper chord of the span during
construction, usually limiting this
method to the spanning of narrow
canyons.
Construction

International airport,
China
Long Span Truss + Portal Frame
Long Span Beams Long Span Trusses +
Cross – over 2
Portal Frames

Reticular Loom
Cross – over 2
Portal Frames

Denver Union Station
Cross – over 2
Portal Frames

Portal Frames

Portal frames were first developed during the Second
World War and became popular in the 1960‘s
They are now commonly used to create wide-span
enclosures, where a clear space is required
uninterrupted by intermediary columns.
They were originally used because of their structural
efficiency, meaning that large spaces could be enclosed
with little use of materials and for a low cost.
They tend to be lightweight and can be fabricated off
site, then bolted to a substructure.
The portal frames themselves may be left exposed to the
internal space, and if carefully designed can be very
beautiful.
Materials used for portal frame is Steel or steel
reinforced precast concrete although can also
constructed using laminated timber such as glulam

Curved portal frame (cellular beam)
Duo-pitch portal frame
Portal with crane
Types of Portal frames

Two-span portal frame Portal frame with external mezzanine

Where a pitch is required, portal frames can have a
mono pitch, or can have a double pitch with a rigid
joint at the apex.
Tied portal frame
Mono pitch portal frame

Other forms include; tied portal frames, propped
portal frames and multi-span portal frames which
very large areas.
Where the portal frame
includes a pitch, the wider the
span of the frame, the higher the
apex. To reduce the overall
height, a curved rafter
might be adopted, or a
mansard form.
A curved, or mansard form
increases the pitch of the roof
towards the eaves, where the
runoff is likely to be at its
greatest.

Portal frames are a type of structural frame, that, in their simplest
form, are characterized by a beam (or rafter) supported at either
either end by columns.
Portal frame structures are often clad with prefabricated
composite metal panels, incorporating insulation. Masonry
cladding may be provided at low level to give greater resilience
and security.
A secondary framework of purlins fixed to the rafters and rails
fixed to the columns provides support for cladding.
Generally, a building structure will be formed by a series of
parallel portal frames running down the length of the buildings,
typically 6 to 8m apart.
Single Skin Trapezoidal Sheeting
Double Skin Trapezoidal Sheeting
Typical Portal frame

Components Of Portal Frame
Typical Portal frame

Portal Frame Connections
The major connections in a portal frame are the eaves and apex
connections , which are both moment-resisting.
Portal frames are generally low-rise structures, comprising columns
and horizontal or pitched rafters, connected by moment-resisting
connections.
Members of portal frames are jointed by means of welding and bolting
so the joints of the frame could transfer moments also in addition to
the axial load
Construction

The legs or stanchions of the portal frame need connecting at the
bottom to a foundation.
Base Joint for Portal FramesConstruction

It is important that this joint is strong hence the use of wedge
shaped pieces called gusset pieces to strengthen and increase
the bolt area.
Ridge Joint for Portal FramesConstruction

It is important that this joint is strong hence the use of wedge
shaped pieces called gusset pieces to strengthen and increase
the bolt area.
Haunch Joint for Portal FramesConstruction

To help strengthen the framework and prevent
movement diagonal bracing is used.
Diagonal Bracing for Portal FramesConstruction

Imposed loads on roofs depend on the roof slope.
A point load, which is used for local checking of
roof materials and fixings, and a uniformly
distributed load, to be applied vertically.
In portal frames heavy point loads may occur
from suspended walkways, air handling units etc.
In certain situation it will be more appropriate to
use truss or lattice girder rather than a portal
frame.
Cranes impose both horizontal and vertical loads
on the structure, part of loading is due to dynamic
effects. The vertical load will be composed of a
load due to weight of the crane bridge. The
horizontal load due to crane surge and reaction
from the wheel.
DEAD LOAD (self weight)
SERVICE LOADS
CRANE LOAD
Types of LoadsLoad analysis

When a portal frame is close to the boundary,
there are several requirements aimed at stopping
fire spread by keeping the boundary intact:
• The use of fire resistant cladding
• Application of fire protection of the steel up to
the underside of the haunch
Two kinds of accidental loads are to be considered
• Impact of unusual loading
• Drifted snow
• The opening of the dominant opening which was
assumed to be shut.
Wind uplift may be important in terms of rafter
stability , but provided that adequate restraint can
be provided to stabilize the bottom flange of the
rafter near the apex
WIND LOAD
WIND LOAD
ACCIDENTAL LOADS
FIRE LOAD
Types of LoadsLoad analysis

Rafters are subject to high bending moments in
the plane of the frame, that vary from a
maximum ‘hogging’ moment at the junction with
the column to a minimum sagging moment close
to the apex. They are also subject to overall
compression from the frame action. They are not
subject to any minor axis moments.
Although member resistance is important, stiffness of the frame is also necessary to limit the effects
of deformed geometry and to limit the deflections.
Asymmetric or sway mode deflection Symmetric mode deflection
Bending MomentLoad analysis

Bending moment diagram under
asymmetric loading
Bending moment diagram under symmetric
loading

Long span structures in Concrete and Steel

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