A CASE STUDY OF ERECTION OF 72 MET SPAN TRUSSES:

Project Detail- A unit of PLATE MILL (a type of steel plant).

Building detail – One of Big workshop type shed (see photo) of size 120MX80mX7-13.5M, called COOLING BED.

Design Load -

1. DL of Building including self wt

2. Imposed load – wind speed 50m/s and seismic zone no V

3. Service load – Light weight crane was to be attached to truss bottom cord – a special crane like 2 directional monorails called – UNDER SLUG (See the attached photo) of load capacity -10 tones to run in X – Y direction. One set of crane will run over 5 sets of trusses. And load of small piping works and cable trays will come there.

4. Live load

Structural Material -Bottom chord and top inclined chord of trusses are made of 2MC400 as I sections. In between 2MC200 Box are used as ties and struts.

Designer/ Contractor / Client – Dr. FADNIS was the sole designer under whom all plant of Rs. 200 crores construction works were run. All work was done by mainly M/s Patron (then). Client was the eminent tycoon of Steel and Textile.

Fabrication –

1. Trusses were fabricated in three pieces each of 24 met lengths.

2. Then those were brought by long body trailers to the place

3. And assembled in a jig (form template) just on their axes.

4. Total wt of truss including all gussets and cleats etc is estimated 35 ton.

5. Duration for one truss fabrication was 7days.

Erection-

1. Total 21 grids at 6.00mets distances of single bay was their. Ht of truss was 6.50mets.

2. Columns ht at the base plate was 7.00m.

3. As trusses finally assembled at site, and were laying on the leveled earth surface.

4. Each truss was griped in tackles which were made by MC200Box both side (as shown in photos) tightened with long stud bolts in 2 parallel lines along its length. First was of 48 m at 1/3rd ht from bottom chord and second was of 24 m at 1/3rd depth from apex. This safety is taken against buckling of trusses while erection.

5. Total lifting wt including wt of tackles, D-shackles and slings was estimated 45 tons for one truss.

6. One lighter Crane of 20ton capacity was used to turn up the laying truss vertically before lifting by two heavy cranes. Sling was fixed at centre (apex).

7. Main 2 cranes of 75 tons were used to lift up the trusses (see clips)

8. Placement of cranes as well as hooks of sling was kept in such a manner (as shown in photos) that total truss can be lift up in balance.

9. Here main remarkable thing was seen that truss was not lifted simultaneously by both cranes in synchronized manner. They were taken small-small lifts of approximate 0.3 to 0.5m by one after another crane, alternatively. In this manner risk factor was low. Because action of two cranes may differ at a time and chances of accident may be more. Delhi metro Launchers accidents - 2-3 times are the example of simultaneous (synchronized) method.

10. Finally trusses were rest over tubular section (600dia pipes – in pairs spaced at 2.0m) columns. Base plates were of 25mm thickness with extra ribs.

11. Supports are fixed by bolts. One side round holes sizes and other side slotted holes with 25 mm tolerance were given.

See the Sequence of Lifting of one 72m truss. In Middle one small crane is turning up the laying truss.

Two bigger cranes are lifting then one by one with small lift of 0.30 to 0.50m alternatively. One truss lifted in one day. (See the full preview by opening each clip in photo viewer (jpg)

This is OLD Plant (South Korea) showing crane attachment to trusses

UNDER SLUG Crane rolling over Bottom Chord of Trusses

UNDER SLUG Crane rolling over Bottom Chord of Trusses