1.
LONG SPANSTRUCTURE’S

2.
LONG SPAN STRUCTURE’S
Structures with span larger than 15-20 meters are regarded to as Long Span Structures.
For Such structures span is unable to be achieved with ordinary R.C.C. construction.
Generally long spans result in flexible, column-free internal spaces, reduces substructure
costs and time to erect the structure.
*DEFINATION
*COMMON STRUCTURAL SYSTEMS FOR LONG SPAN STRUCTURES
Long span Beams
Long span Trusses
Long span Roof structures
• Tensile structures
• Folded Plates
• Shell structures
• Portal Frames

3.
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.
Types of Long Span Beams
• Parallel Beam Approach
• Composite Beams with Web Openings
• Cellular Composite Beams
• Tapered Girders
• Haunched Composite Beams

4.
LONG SPAN BEAMS
*Parallel Beam Approach
The parallel beam approach is effective for spans up to around 20 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.

5.
LONG SPAN BEAMS
*Composite Beams with Web Openings:
Web openings are typically formed in beams to allow services to pass through the beam.
This enables the structural and service zones to occupy the same space, thereby reducing
the effective overall depth of floor construction for a given spanning capability. Openings
may also be formed for aesthetic reasons, for instance with cambered beams used to
support a roof. Composite beams with web openings have been shown to be a cost
effective solution for spans in the range 15-30m.

6.
LONG SPAN BEAMS
*Cellular Composite Beams:
Cellular beams are a form of beam with multiple regular web openings , formed by
splitting two rolled sections longitudinally, to form two Tee sections. The two Tees, which
may not come from the same donor section are then welded together to form an I-section
with web openings which have a characteristic shape (normally, but not necessarily,
circular).

7.
LONG SPAN BEAMS
*Tapered Girders:
Tapered girders can be a cost effective solution in the span range 15 m to 25 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.

8.
LONG SPAN BEAMS
*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 rather than passing them through holes in the webs, or through a truss, can be
advantageous. Spans in excess of 20-30 m can readily be achieved.

9.
LONG SPAN TRUSSES:
A truss is essentially a triangulated system of straight interconnected structural elements.
The most common use of trusses is in buildings, where support to roofs, the floors and
internal loading such as services and suspended ceilings, are readily provided. The main
reasons for using trusses are:
• Long span
• Lightweight
• Reduced deflection (compared to plain members)
• Opportunity to support considerable loads.
Types of Long Span Trusses:
• Pratt Truss
• Warren Truss
• North Light Truss
• Saw Tooth Truss
• Fink Truss

10.
LONG SPAN TRUSSES:
Pratt Truss:
Pratt trusses are commonly used in long span buildings ranging from 20 to 75 m in span. In a
conventional Pratt truss, diagonal members are in tension for gravity loads. This type of truss
is used where gravity loads are predominant. An alternative Pratt truss is shown where the
diagonal members are in tension for uplift loads. This type of truss is used where uplift loads
are predominant, which may be the case in open buildings such
It is possible to add secondary members to:
•Create intermediate support points for applied loads
•Limit the buckling length of members in compression.
as Aircraft hangers.

11.
LONG SPAN TRUSSES:
Warren Truss:
In this type of truss, diagonal members are alternatively in tension and in compression. The
Warren truss has equal length compression and tension web members, and fewer members
than a Pratt truss. A modified Warren truss may be adopted where additional members are
introduced to provide a node at (for example) purlin locations.
Warren trusses are commonly used in long span buildings ranging from 20 to 100 m in span.
This type of truss is also used for the horizontal truss of gantry/crane girders.
Warren Truss

12.
LONG SPAN TRUSSES:
North Light Truss:
North light trusses are traditionally used for short spans in industrial workshop-type
buildings. They allow maximum benefit to be gained from natural lighting by the use of
glazing on the steeper pitch which generally faces north or north-east to reduce solar gain.
On the steeper sloping portion of the truss, it is typical to have a truss running perpendicular
to the plane of the North Light truss, to provide large column-free spaces.
Fink Truss:
The Fink truss offers economy in terms of steel weight for short-span high-pitched roofs as
the members are subdivided into shorter elements. There are many ways of arranging and
subdividing the chords and internal members.
This type of truss is commonly used to construct roofs in houses.

13.
LONG SPAN TRUSSES:
General Geometry:
For efficient structural performance, the ratio of span to truss depth should be chosen in
the range 10 to 15. The architectural design of the building determines its external
geometry and governs the slope(s) given to the top chord of the truss. The intended use of
the internal space can lead either to the choice of a horizontal bottom chord. For an
efficient layout of the truss members between the chords, the following is advisable:
•The inclination of the diagonal members in relation to the chords should be between 35°
and 55°
•Point loads should only be applied at nodes
•The orientation of the diagonal members should be such that the longest members are
subject to tension (the shorter ones being subject to compression).

14.
LONG SPAN TRUSSES:
Types of Truss Member sections:
Many solutions are available. Choice of members depends on the magnitude of the
internal forces, ease of connections between members, aesthetics and any necessity to
connect prefabricated truss sections on site. When selecting members, the out-of-plane
buckling resistance will be important, together with resistance under reversed loading, for
example, uplift.
For large trusses and heavy loads, typically found in transfer trusses in buildings, members
may be rolled sections. Nodes are usually welded. Any necessary connections are
completed with bolted splices within the length between nodes.

15.
LONG SPAN TRUSSES:
Types of Connections:
For all the types of member sections, it is possible to design either bolted or welded
connections. Generally in steelwork construction, bolted site splices are preferred
to welded splices for economy and speed of erection. Where bolted connections are used,
it is necessary to evaluate the consequences of 'slack' in connections. In order to reduce
these consequences (typically, the increase of the deflections), solutions are available such
as use of preloaded bolts.
Hollow sections are typically connected by welding whilst open sections are connected
by bolting or welding, which will usually involve the use of gusset plates.

16.
LONG SPAN TRUSSES:
Examples: Gallery of Machines Paris (span=112m height=45m)

17.
LONG SPAN TRUSSES:
Examples: Hong Kong Convention and Exhibition Center (span= 80m)

18.
LONG SPAN TRUSSES:
Examples: Hong Kong Stadium (span=100m and 60m)

19.
LONG ROOF STRUCTURES:
Portal Frames:
A portal frame building comprises a series of transverse frames braced longitudinally. The
primary steelwork consists of columns and rafters, which form portal frames, and bracing.
The end frame (gable frame) can be either a portal frame or a braced arrangement of
columns and rafters.
The light gauge secondary steelwork consists of side rails for walls and purlins for the roof.
The secondary steelwork supports the building envelope, but also plays an important role
in restraining the primary steelwork. Portal frames can span from 20-100m.

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