Transportation and Hosting of refabricates:
Twinned mast cranes
Truck cranes consists of chasis includinig mortar and pivoting upper part. These cranes are mobile and an travel on their own needs. Different features are:
1. Weight of the crane while travelling is 31.8 tonnes
2. Maximum height of hoisting hook is 36.6m
3. Crane can rotate through 360º.
Needs firm and compact soil.
These cranes are used mainly to serve the operation of manufacturing and storing areas in prefabrication plants.
Capacity 5T, Total weight 4.5T
Horizontal distance between 2 tracks is 7.8m
Maximum height is up to 11m
Mast height 10.9m and it can hoist up to 20 tonnes in operation.
These are wide spread hoisting devices,simple and cheap. Operation requires great skill and practice. Useful in hoisting prefabricates in vertical direction. Suspension load can be slightly moved forward by slackening the rear staying cable. Hoisting load is done by a winch.
Twinned mast cranes:
It is used for hoisting member to great height. It consists of two steel column assembled from sections and connected at top by bridging structure.
Hoisting capacity using two cranes each of 35-70T
Operation of the crane required minimum 16 workers.
The crane can be transferred but takes 1-2 days and is suitable fr high lifting but difficult to operate.
These are now a days replaced by 30T mast cranes hinged in 2 directions.
Highly efficient lifting machines
It is stable or movable
Suitable for prefabrication halls
These cranes have booms which can move in horizontal directions.
Prefabricated structurers are erected in coonvinient sections which when fixed correctly should be sufficiently rigid in all directions. Normal sequence of erection is
a. Structure units- external load bearing walls,columns,etc
b. Non structure units- internal walls,partition walls,etc
c. Floor panels, balconies, stair units
d. Specialized prefabricated units- chimney flumes. Ventilators, sanitary installation.
If the external walls are hand laid from small blocks or bricks, all necessary materials should be hoisted by crane and stacked near the ultimate position. The mansonry work is begun after the floor immediately above is laid.
The tolerances are comparatively strict and are normally coompliedwith the use of a skilled rection gang. The distance between the wals are measured with the steel tape and the thickness of joint with rule having mm scale.The accuracy is verified by means of surveying instruments after all joints are connected or erected.
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