BASIC RIGGING - Usmra.com

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BASIC RIGGING

MSHA REGULATIONS


56/57.16007 Taglines, Hitches, and Slings


(a) Taglines shall be attached to loads that may
require steadying or guidance while
suspended.


(b) Hitches and slings used to hoist materials
shall be suitable for the particular material
handled.


56/57.16009 Suspended Loads


Persons shall stay clear of suspended loads.


TOOLS OF RIGGING


Hoists


Cranes


Slings


Special
lifting

devices




HOISTS AND CRANES


Different types of
hoisting equipment


Manual and
powered devices


underhung and top
running cranes


monorails


various types of jig
cranes

SLINGS


Main purpose is to suspend a load from a
hoist


Commonly made of wire rope or welded
link chain


Can be constructed from fiber
rope,synthetic webbing or metal mesh


Most slings are assembled by sling
manufacturers


Can be assembled at the job site

The rigging system


Load


Sling


Hoisting equipment


Rigger (Designer and
Operator of the
system)


= Single, complex
rigging system

The Rigger


Must apply intelligence, common
sense and experience


Anticipate what will happen when the
load is moved


Thought process must take place
before the work is started


Must answer the following
questions
…..

Questions that must be
answered by rigger


What is to be done with the
load?


What tools are needed?


Do the tools have the
capacity to handle the loads
and forces involved?


Questions that must be
answered by rigger


How can the hookup be made?


What will happen when the load
is first moved?


What will be the travel path of
the load to reach the desired
location?


Questions that must be
answered by rigger


How will the load be set down at the
desired location?


What other factors are involved
(weather, electrical wires, sloping
grades, visibility)?


Are additional personnel needed to
control the load safely during the
process?

Planning a rigging system


Determine the weight of the load


Locating the center of gravity of a load


Distinguishing the force components
(horizontal and vertical) at work in a
diagonal force(loads at some angles other
than 90 degrees to the horizontal)


Limitations of each component of the
rigging system

Determining the weight of
the load


Shipping paper


Manufacturers information attached
to the load


Catalogs or blueprints


Tables of weights from
manufacturers or handbooks


Make sure the weight has not
changed

Volume & Area Formulas

Calculating an allowable
load


Determine the breaking strength of
the rope


Load which will cause the rope to break


Refer to standard tables in rigging
handbooks


Listed according to the diameter and
kind of rope


Design or safety factor usually 5

Calculating an allowable
load


Find the load limit by dividing the
breaking strength of the rope by the
design factor


Example
-


If the table indicates that the breaking
strength of the rope you are using is
27,000 pounds. Dividing this figure by
the design factor of 5 gives you a 5400
pound maximum allowable load.


Determine the center of
gravity


The point at which the load will balance


Whole weight of the load is considered
concentrated at this balance point


When suspended from a point, the load
tends to move so that the center of gravity
is directly below the point of support.


Make sure the center of gravity is located
directly below the hoisting hook


Determine the center of
gravity


Stable load


Balanced about its center of
gravity


Directly below the hoisting hook


Unstable load



has a tendency to tip or topple


Creates a hazard to personnel and
equipment

Before Lifting any load
check for hazards


If not directly below
the hook the load is
unstable


If the sling is free to
slide across the hook
the center of gravity
will shift directly
below the hook


If two slings are used
one will assume the
greater share of the
load



Before Lifting any load
check for hazards


The sling must not be
attached to the load at
a point lower than the
loads center of gravity


Exception to this
rule when lifting
loads on pallets or
skids


Then apex of sling
must be above the
center of gravity



Determining the center of
gravity


Marked on the load by manufacturer


Located in catalogs or blueprints


Some objects have lifting lugs


Calculate or estimate it


Make an educated guess and
correct through trial and error
before making the lift

Procedures to determine
center of gravity


Connect slings and hoist based on
estimate of object’s center of gravity


Take up slack in slings or hoist


Lift the load just enough to check stability


If stable, continue to lift


If unstable, lower load and adjust the
rigging


Lift point should be moved closer to
end that dips


Repeat until load is stable


Horizontal Force


Very often sling legs are attached at
an angle less than 90
0


Then a horizontal force is added to
the vertical force


Resulting Combined force is greater
than the weight of the load


Horizontal force increases as the
angle becomes smaller

Horizontal Force


When a sling
angle is 30
0
the
total force is
twice that of the
load


Sling Angles of
45
0

are not
recommended

Horizontal Force


Horizontal forces act
on the load causing
damage by
compression or
buckling


Horizontal forces are
absorbed by using a
spreader beam making
the sling legs between
beam and load vertical


Sling Components


Hooks


Coupling Links


Fittings


Sling Legs


Can be assembled at the job site but must
use recommended components and
assembly procedures


May also require some sort of weight test

Hook Hazards


Attachments should never be field welded to a
hook


Heat should not be applied in an attempt to
reshape a hook


Can reduce strength of hook


Could result in hook failure at loads lower than the
rated load


If handles or attachments are required they
should be obtained from the hook
manufacturer

Purpose of a latch?


Purpose is to retain slings in the hook


Not intended to support the load


Should be sturdy enough to retain the sling
if the moving load should catch on
something


Latches are used to close the throat opening


Must be provided on hoist and crane hooks

Reasons For Removing a
Hook From Service


Hook throat has increased by
more than 15%


Wear exceeds 10% of the
original hook section
dimension, or there is a bend
or twist of more than 10%
from the plane of the unbent
hook


Hook shows cracks,
excessive nicks, or gouges

Factors Affecting Wire
-
Rope
Strength


Three major signs of loss of strength


Flat spots worn on outer wires


Broken wires


reduction of rope diameter


Other factors that can reduce strength


Bending the rope over a curved surface


Temperature


Corrosion and environment


Rope fittings or terminations

Bending The Rope Over A
Curved Surface


Normal curved surfaces that ropes are
curved over include sheaves, pins and
other curved surfaces


The rope is subjected to bending stress


Reduces rope efficiency/nominal strength
by a certain percentage


Efficiency depends upon the:


D = Diameter of curved surface


d = Nominal diameter of rope

Example (You will need to refer
to Fig. 2
-
5 and Table 2
-
1)


Fiber
-
core 6 x 37
wire rope, 1” in
diameter (d)


Sheave with a 30”
diameter (D)


D/d ratio is 30/1


Efficiency is 95%


Load Rating
dropped 95% from
83,600 lb. To 79,420
lb.



Wire Rope Clips


Two basic designs


U section contacts dead end of the rope


Tends to crush some wires


Affects strength if u
-
bolt clip is installed wrong


Fist Grip can be installed either way


Use only forged steel for lifting slings

Removal From Service


Rope Distortion such as
kinking, crushing,
unstranding, birdcaging
or core protrusion


Heat Damage from any
source


Look for damage from
weld and weld splatter


Cracked or deformed
end fittings(hooks
particularly)


Corrosive failure of one
wire adjacent to end
fitting


Removal From Service


One broken or cut strand


Pitting due to corrosion


For Single Wire Rope Either:


10 broken wires in a section the length of one
rope lay


5 broken wires in one strand within a distance
of one rope lay

Chain Hazards


Similar force acts on
the links if the chain
is knotted or twisted


Never shorten a
sling by twisting or
knotting


Never use bolts and
nuts or other
fasteners to shorten
a sling