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Portable Bridges
 
 
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1.        GRSE is pioneer in manufacturing of Portable Steel Bridge in India. Since last 40 years GRSE has  manufactured & supplied this special type of bridge at various organisation. The design of this bridge was initially developed from original Bailey Bridge designed during 2nd World War.
 
2.        GRSE Portable Steel Bridges are designed on the unit construction principle, the base unit being a 3.048 meter (10 feet) long bay. These bays, when assembled together, create bridges of various lengths, in multiple of 3.048 m (10 ft).
 
3.        The bridge is 'through' type, having two main girders with the carriageway in between. The main girder is formed from steel panels, made of high tensile steel, of dimension 3048 mm (10 ft) (L) X 1448 mm (4 ft 9 in) (H) considering c/c. distance of pin joints, since each panel is connected to its neighbor panel thro' pin joints. The load carrying capacity of the side girders, depend on no. of panels and their configuration in the girder. The construction of girder may be single or double storey with one or more panels present in each storey depending on strength required. The construction of bridge is again denoted by configuration of panels in each girder e.g. SS, DS, TS, DD, TD etc, wherein 1st letter denotes no. of panel in each storey & 2nd letter no of storey i.e. Single Single, Double Single, Triple Single, Double Double etc. Sometimes chord reinforcement is added to top & bottom chords of panel for increasing the strength of girder of a given configuration and is denoted by SSR, DSR, DDR, TDR etc.
 
4.        Portable Steel Bridges are broadly classified based on the number of lanes and width of carriageway, as demonstrated hereunder.
Single Lane Standard Width      - Carriageway width 3.320 meter.
Single Lane Extra Width            - Carriageway width 4.250 meter.
Double Lane                              - Carriageway width 7.000 meter.
 
5.        The girders are connected crosswise by transoms, which are supported at bottom chord of lowermost panels of girders. Steel decks are laid over transoms to form the carriageway.
 
6.        The maximum clear span for a Single Lane portable bridge is presently 60.96 m (200 ft). The same for a Double Lane bridge is 48.77 m (160 ft). Span may be extended to any length beyond the above with multi-span bridges.
 
7.        GRSE offers a further variety of Portable Bridge for larger spans i.e. spans beyond 61 m (200 ft). It is Portable Steel Suspension Bridge, which covers a range from 61 m (200 ft) to 122 m (400ft). Both timber & steel deck versions are available.
 
8.        The Portable Steel Bridges cover a wide range of load class as per IRC 6, ranging from class 9R to class 70R (the heaviest class on Indian Roads). A chart is furnished below on various bridges produced by GRSE for ready reference.
 
SL NO TYPE OF BRIDGE ROADWAY WIDTH (M) IRC* LOAD CLASS MAX. SPAN (FT)
a. STANDARD WIDTH SINGLE LANE BRIDGE (STEEL DECK) 3.32 (i) UPTO 30R
(ii) 40R
(iii)70R

200
190
140

b. EXTRA WIDE SINGLE LANE BRIDGE (STEEL DECK) 4.25 (i) UPTO 30R
(ii) 40R
(iii)70R

200
180
140

c. DOUBLE LANE BRIDGE (STEEL DECK) WITH 10’ X 7’ PANEL

7.00

70R (NORMALLY)

160

d. SUSPENSION BRIDGE 3.277 CLASS 24 AS PER BRITISH MILITARY LOAD CLASSIFICATION

400

 
9.        The Portable Steel Suspension Bridges are capable of carrying load upto class 24R. When reinforced, they are also capable of carrying single vehicle of max. 40 MT (for timber deck)/ 30 MT (for steel deck) load, one at a time
 
10.        A tentative delivery schedule for all types of bridges is indicated below.
SL NO TYPE OF BRIDGE SPAN EXPECTED DELIVERY PERIOD
a. SINGLE LANE BRIDGE ALL 2 - 3 MONTHS
b. DOUBLE LANE BRIDGE ALL 6 - 8 MONTHS
c. SUSPENSION BRIDGE 240FT – 400FT 3 - 4   MONTHS
 
DOUBLE LANE PORTABLE STEEL BRIDGE
 
GENERAL DESCRIPTION
11.         GRSE has successfully developed Double Lane Portable Steel Bridge to allow an uninterrupted flow of high density traffic.
Mode of construction of this bridge is similar to GRSE Single Lane Bridge.

12.         The bridge is also of the "through" type, the roadway being carried between two main girders. The main girder is formed from steel panels of welded construction 3048 mm. (10 ft.) long x 2160 mm.(7 ft. 1 in.) high between pin holes, each panel being pin jointed to its neighbor end to end. The load carrying capacity of the girder can be increased by adding extra panels alongside and on top of the existing panels. The panels put alongside are known as trusses while row of panel put on top of panels is called storey. Girder made of three panels along side each other and one set of three on top is known as triple truss, double storey (TD in short).

13.         This construction can be reinforced by the addition of chord reinforcement to the top and bottom of each truss. The reinforced construction is annotated by the addition of the letter `R'. Construction TD when thus reinforced is termed as TDR.

14.         Illustration on such constructions of bridge girders are shown hereunder. The heaviest construction is termed as QDR (Quadruple Truss, Double Storey and Reinforced).
 
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15.         The girders are connected crosswise by transoms. These are long RSJs which rest on the bottom chord of the panels, and carry the roadways superstructure. They are tied to the panel chords by transom bolts and fix the trusses in position at the required distance apart.

16.         End posts, Male and Female, are provided for connecting to the female and male lugs at the ends of the panels of each truss of the bridge for distributing the shear forces due to the end reaction of the bridge. The end posts attached to the ends of each truss of bridge girder are supported on bearings which rest over base plates placed on the ground at each end of the span. The base plates are intended to spread the load from the bearings evenly over an area of ground.
Technical Specification
         (a) Carriageway width - 7.0 m.

         (b) Type of decking – Steel deck.

         (c) Maximum span suitable upto IRC - 70 R load class - 160 feet.
         (d) Design verification done by IIT-Kharagpur through FE analysis
         (e) Materials: SAILMA 410 HI (Load bearing members).
        (f) Advantages - Portability
- Easy to erect.
- Temporary / semi permanent use.
- Modular, pre engineered, pre fabricated components.
- Manufactured in ISO 9001/2000 certified unit.
- Over 30 years experience of manufacturing and providing bridging solution to BRO, State PWDs,   PSUs and IPPs.
- Product is patented.
Method of Erection & Launching
17.         The Portable Bridge is so designed that it can be completely erected on rollers on one side of the gap to be bridged and then launched across without the use of any temporary support within the gap. This is achieved by building on to the front end of the bridge a temporary skeleton cantilever structure, called "Launching Nose", which is constructed from the same standard components as the bridge. To raise the skeleton Launching Nose up for facility of landing on the far bank, a special component known as Launching Link is inserted in the bottom chord of the Panels of the skeleton nose. The nose is built up of such a length that when the whole structure is rolled forward, the tip of the nose lands on the rollers on the far bank before the point of balance is reached. Once the bridge is in position across the gap the Launching Nose is dismantled and the bridge jacked up of the rollers and lowered on to its permanent bearings on the abutments.