Technical Paper
BR-1887
Heavy Lift Crane Selection
Authors:
R.L. Mikut, Jr., P.E.
Babcock & Wilcox
Power Generation Group, Inc.
Barberton, Ohio, U.S.A.
Presented to:
ASCE Construction Institute
Summit
Date:
November 8-11, 2012
Location:
Fort Worth, Texas, U.S.A.
Heavy Lift Crane Selection
R.L. Mikut, Jr., P.E.
Babcock & Wilcox
Power Generation Group, Inc.
Barberton, Ohio, USA
Presented at:
ASCE Construction Institute Summit
Fort Worth, Texas, U.S.A.
November 8-11, 2012
Abstract
Many factors must be looked at simultaneously to properly select a heavy lift crane for a specific job. There are
various types of cranes including crawler, tower, ringer,
derricks and more. The type of crane, the size of the load,
site constraints, deductions from the listed crane capacity,
ground-bearing pressures, crane efficiency and rental costs
must all be taken into account. This paper will discuss how
to take all of these issues and constraints into account when
selecting the proper heavy lift crane. Knowing the weight
and dimensions of the component to be lifted is a critical
element, but there are many other items that should be considered. Site constraints may actually impact the selection
of the crane more than the lifted element itself. Also, when
sizing the crane, the weight of the rigging, the crane block,
line weight and other items below the boom point must be
added to the load weight. Another major factor affecting
crane selection is the ground-bearing pressure imposed by
the crane and the ground preparation needed. Costs must be
considered. Taking these and other factors into account, a
properly sized heavy lift crane is an important component
to completing a job safely and effectively.
Introduction
With the increasing size of component modules on
construction sites to reduce schedules and field labor costs,
mobile cranes are becoming more and more critical for the
completion of a successful job. The selection of a heavy
lift crane for a specific project application involves detailed
consideration of many factors that critically affect the load
handling capabilities on the job site. Historically speaking,
from an initial perspective, one may assume that a knowlBabcock & Wilcox Power Generation Group
BR-1887
edge of the geometry, size and rigging weight of the lifted
load is all that is required for heavy lift crane selection. In
fact, while this knowledge is critical to the overall selection
process, it is a small part of the required input.
There are many types of cranes available, each having
specific advantages and disadvantages. Proper crane selection can help reduce cost, schedule, and safety risks. Crane
selection is challenging because it often takes place early in
the planning stages of a project. Some of the elements to be
taken into account during the selection process are total load,
site constraints, deductions from the listed crane capacity,
ground bearing pressures, cost, efficiency and reliability. It
is important to choose an efficient, versatile crane that will
bring the greatest possible contribution to the job for the least
overall cost. This cost is likely a key component to the total
project cost, but it should also be measured against reliability,
redundancy, and ground preparation costs. There are many
computer programs and algorithms available to help in crane
selection, but the factors discussed in this paper should be
considered in addition to using these computer programs.
Types of Cranes
Cranes can be classified into several broad categories
such as mobile cranes, tower cranes, derricks, bridge/gantry
cranes, container cranes, barge cranes, etc. The most common cranes used at typical construction sites are mobile
cranes, tower cranes, ringers and derricks.
Mobile cranes, whether they are lattice boom crawler
cranes, hydraulic all-terrain cranes, or rough-terrain cranes,
are the backbone of the modern construction industry. Figure
1 shows an environmental retrofit project at a coal-fired
utility plant. This photo illustrates the different types of
1
heavy lift cranes that can be utilized on a job site. Lattice
boom crawler cranes typically range in capacity from 75 to
3500 t (68 to 3175 tm). They are extremely versatile with
options such as wheeled or hanging counterweights, fixed
jibs, luffing jibs, etc. With all of these options, a lattice boom
crawler crane can perform almost any job in the construction industry. Hydraulic all-terrain cranes typically range in
capacity from 20 to 650 t (18 to 590 tm). All-terrain cranes
are usually designed with the capability to drive on roadways
and highways, as well as from a rental yard to a project
site. They are usually higher in capacity than rough-terrain
cranes, but require more set-up time. All-terrain cranes
usually have their booms and counterweights transported
separately, and therefore, have a higher mobilization cost.
Rough-terrain cranes can range in capacity from 15 to 150 t
(14 to 136 tm). Unlike the all-terrain cranes, the rough-terrain
cranes usually only have four large wheels and are not meant
to travel on roadways. They require little set-up time and
are used primarily as yard cranes, site fabrication cranes, or
on smaller jobs. Rough-terrain cranes are usually brought
to site in a single assembly on a semi-trailer.
Tower cranes, ringers, and derricks are referred to as
fixed cranes because they remain in a stationary location
from mobilization to demobilization. These cranes are used
in more specialized applications, such as in areas with a
limited footprint. Even though they are in a fixed position,
they still require about the same space as a mobile crane to
assemble and disassemble.
This paper will primarily concentrate on lattice boom
crawler cranes, but many of the topics can be applied to all
types of cranes.
may in fact set the size of the crane for the entire project, it
is not the only consideration to be made. Additional factors
to consider are:
1.Dimensions of the largest module – Determining the
dimension of the largest module will provide insight
as to whether a jib attachment is needed at the top of
the boom. If a very large module is to be picked, then
a fixed jib or even a luffing jib may be needed to keep
the module away from the boom. The length of the
boom can also be increased to prevent the jib from
getting “boom bound.”
2.Crane reach – The required crane reach may actually
set the boom and/or jib configuration of the crane.
Site constraints often play a role when considering
crane reach. The farther the crane has to reach, the
more boom and/or jib that will be required to make the
reach. This reduces the overall capacity of the crane.
3.Weight of the module at the farthest reach point – A
module’s weight at the farthest reach point is directly
related to the crane’s reach because a minimum capacity will be needed at the farthest reach, which may
reduce the overall capacity of the crane due to the
additional lengths of the boom or jib. Also note that
just because the crane is capable of lifting 200 t (181
tm) at 50 feet, does not mean it will have the ability to
set 10 t (9 tm) at 200 feet.
4.Type of rigging required to lift the module – The
rigging concept and height of the rigging are factors
that affect the proper rigging choice. If spreader bars
are to be utilized or if the module is very wide, the
rigging will have to be fairly tall which increases the
overall headroom required to lift and set the piece.
The height of the boom tip is an important factor that
will be discussed throughout this paper.
5.Estimated versus actual calculated weights of the
module – Identifying how the weights were determined
helps to know what risk to take when sizing the crane.
If the module weights are all estimated, it would be
prudent to not select a crane that is at 99% of its capacity when lifting the module. However, if the weight
of the module is known, then using the crane’s full
capacity requires less risk. Determining the required
heaviest lift provides valuable information, such as
the size of crane block and the number of parts of line
required to make the lift. The number of parts of line
refers to the number of wire ropes running between the
boom tip and crane block to support the crane block
and the load hanging below it. This will be discussed
further in the deductions section.
Load
Site Constraints
Fig. 1 Multiple cranes on a construction site.
There are many factors to consider when first assessing a
project that requires a heavy lift crane. Most of these considerations relate to the loads that must be moved. Determining
the required heaviest lift is usually the first question asked.
Although the answer to this question is very important, and
2
Conducting an initial site review is often the first step in
crane selection. This can be done prior to knowing all of the
job details because many times the existing site conditions
may dictate the choice of crane rather than the actual loads
that will be lifted. The location of the site, access around
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and to the crane, existing soil conditions, underground
utilities, overhead lines, existing buildings, and prevailing
wind conditions, etc. all play major roles in the selection of
a heavy lift crane.
The location of the site may limit the size and type of
crane for the project. Heavy lift cranes add project cost and
require time to mobilize and demobilize. To limit these costs,
it is usually beneficial to choose a crane rental supplier close
to the job site. However, depending on the region, this may
limit the types and availability of heavy lift cranes.
Crane access presents a variety of questions. Can the
modules be brought directly to the crane? Are the modules
being fabricated next to the crane or being brought in on a
trailer? If the modules cannot be transported in or built near
the crane, how far does the crane have to reach to pick up
the module and how does it relate to the radius of the final
setting location? This last question is very important. If the
crane is sized based on just the weight of the module and
how far its final location is from the crane, then there could
be a major issue if the initial pick location of the module is
farther away than the final location. Another consideration
in crane access is whether there is adequate space for crane
assembly. Heavy lift cranes usually do not require significant space to build their superstructure, but they do need a
significant space in which to assemble their boom and jib
attachments. There are ways to build the boom and jib attachment in the air, but in terms of safety, cost and schedule,
it is preferred to lay out and build the boom on the ground.
Therefore, by adding the length of the boom and jib attachment, the length of space required to build the boom and jib
attachment is calculated. This area usually requires an assist
crane to help build the boom and the crane superstructure.
Also, the boom may need to be laid down periodically during
the job due to high winds, contract requirements, or repair
needs. Therefore, a boom laydown area should always be
available to a heavy lift crane within a reasonable amount
of time. Figure 2 shows the amount of space that is required
to lay down a boom of a heavy lift crane.
Existing soil conditions and underground utilities can also
determine the crane size or type. If the soil conditions are
poor or there are a lot of underground utilities, then it may be
prudent to select a crane that imposes a lower ground bearing pressure, such as a ringer crane. If this is impractical or
unavailable, then it will be necessary to improve the ground
conditions and/or move the existing underground utilities.
If the crane is to be put on a site where new underground
utilities are going to be installed, then it is necessary to take
into account where the new underground utilities will be
routed. Improving the ground conditions with filler material
or a crane pad may lead to selecting a crane with a smaller
footprint that will safely and adequately perform the required
lifting functions to save on ground preparation costs. This
may make using a larger crane with a smaller footprint more
practical than a smaller crane with a wheeled counterweight
or hanging counterweight with a larger tail swing and thus,
a larger footprint. Availability, cost and preference to the job
will dictate this choice.
Other existing site conditions, such as overhead power
lines or existing buildings, will likely dictate the type of
boom and jib attachment configuration. Overhead power
lines will either limit the location of the crane, or how far
it can rotate. Per OSHA regulation 1926.550(a)(15)(ii), for
power lines rated over 50 kV, minimum clearance between
the lines and any part of the crane or load shall be 10 ft plus
0.4 in. for each 1kV over 50 kV, or twice the length of the
line insulator, but never less than 10 ft. If the crane must
lift over buildings, it may make using a luffing jib more
appealing and/or necessary.1
Wind can be a factor in the selection of a heavy lift crane.
Tables are available that provide the allowable operating
conditions for a specific boom and/or jib combination. Table
1 is an example of a rating reduction table for various wind
speeds for a Manitowoc® 2250 crane with no counterweight
attachment.2
The wind affects the stability of the boom and load during
lifting operations. It can be observed in the table that the
more boom or jib length added, the more restrictions there
are on the operation of the crane. Failure to observe wind
conditions can cause the crane to tip or the boom to collapse.
These restrictions may limit the decision of how much boom
or jib to add if the heavy lift crane will be operating in a
high wind area.
Deductions
Fig. 2 Heavy lift crane with boom laid down.
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Crane load charts accompany every crane and provide
the capacities of the crane at a known radius. For most
heavy lift crane charts, this is defined as the gross load to
be lifted below the boom tip. Therefore when sizing a crane,
one cannot just look at the heaviest module at a radius and
compare it to the capacity of the crane at the matching radius.
Some deductions to consider along with the weight of the
modules are: weight of the rigging, weight of the block,
weight of the lines, weight of any jib or ball attached to the
lifted load point, wind restrictions, and the number of parts
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Table 1
Rating Reductions for Various Wind Speeds and Wind Gusts
When Equipped with Boom Only (Heavy Lift or Long Reach)
70 to 220
(21.3 to 67.1)
Boom Length ft (m)
Maximum Wind Speed
mph
230 to 260
(70.1 to 79.2)
270 to 300
(82.3 to 91.4)
310 to 330
(94.5 to 100.6)
Percent Rating Reduction
m/s
15
7
0
0
0
0
20
9
0
0
10
10
25
11
0
10
20
30
30
13
0
10
30
40
35
16
0
20
50
60
Above 35 mph (16 m/s)
OPERATION NOT PERMITTED
For operation in winds above 30 mph (13 m/s) with boom positioned above 80º, load block must weigh at least 4800 lb (2177 kg).
Boom may be blown over backwards if this precaution is not observed.
of line. Figure 3 shows a heavy lift crane making a lift with
rigging weighing 20 t (18 tm) and a crane block weighing
nearly 20 t (18 tm). This is an additional 40 t (36 tm) to the
weight of the module being lifted with still other items to
consider such as the weight of the number of parts of line.
The weight of rigging could be estimated from previous
jobs or it could be sized and calculated if enough is known
about the module. The weight of the block can be found in
the crane load charts, but it should be requested from the
crane supplier to know the exact size and weight of block
that will be arriving on site with the crane. The weight of
the lines is conservatively determined by taking the boom
tip height multiplied by the number of parts of line and then
multiplied by the weight per foot of line. The number of parts
of line is determined by using the given available line pull
capacity of the hoist line and dividing it into the heaviest
load that is to be lifted. This heaviest load to be lifted needs
to include the component weight along with the weight of
the rigging and crane block. For example, if the total load
to be lifted is 85 t (77 tm) and the crane has a line installed
with a maximum of a 15 t (14 tm) line pull capacity, then at
minimum, six parts of line would be needed to lift the load.
Another deduction is the weight of anything attached to
the boom tip such as a rooster sheave, a whip line, and ball.
This is usually a single part line (whip line) running off of a
single sheave attached to the boom or luffing jib tip. It is used
to lift lighter items and has a faster line speed which allows
for quicker erection times. The weight of the whip line is
usually negligible since the ball will likely be pulled nearly
to the rooster sheave during the heavy lift operations. If lifting from the boom and a fixed jib is attached, then the fixed
jib along with the rigging hanging from it must be deducted
from the listed capacity of the boom. As discussed earlier,
wind can also be a major deduction. If lifting in higher winds,
proper deductions must be made to the capacities of certain
boom and jib combinations. Finally the number of parts of
line may be a deduction to the capacity of the crane in two
ways. First, the weight of the lines themselves is a deduction
that needs to be accounted for in the total weight below the
boom tip. Second, if the total number of line parts equipped
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on the crane have a capacity lower than the listed capacity of
the crane, then the capacity of the number of lines governs.
Ground-Bearing Pressures
The existing soil conditions and the bearing pressures
imposed on them by cranes have become increasingly scrutinized in the construction industry. Crane manufacturers and
rental suppliers typically use software to help calculate the
loads imposed by a specific crane, with a specific configuration, that is lifting a specific load, at a specific radius. This
will only provide one scenario out of the many dynamic
loads that the crane will induce throughout the duration of a
construction project. The ground-bearing pressures should be
considered at various lifting radii, swing angles, and loads to
find the worst-case scenario. The heaviest load picked may
not cause the worst ground-bearing pressure and therefore,
is an ill-advised assumption to make.
The allowable ground-bearing pressure, if given, or the
limitations of the crane mat might dictate the crane selection.
In general, the larger the capacity of a crawler crane, the
higher the ground-bearing pressure will be induced. There
are some options to help reduce the ground-bearing pressures imposed, such as wider tracks or track arrangement.
For example, the Manitowoc 18000 has two very large tracks
similar to most crawler cranes, whereas the Manitowoc
21000 has a system of eight tracks which help to better
distribute the load to the crane pad. Therefore, although the
Manitowoc 21000 has a higher capacity, it usually induces a
lower ground-bearing pressure than the Manitowoc 18000.
Another option to help reduce the loading is to add a sled
or wheeled counterweight to the back of the crane. These
backend counterweights add significant capacity to the crane,
but they also help in keeping the crane from leaning forward
and therefore, decreases the ground-bearing pressure of the
crane. This must be compared against the loading induced
by the wheel counterweight or sled which may impose a
greater ground-bearing pressure than some of the lower
capacity cranes.
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be transferred from the bottom of the crawler through the
crane pad to existing grade. How one is to analyze these
loads, and how these loads will act on the existing soils
to give an allowable ground-bearing pressure are other
areas needing further research. The load from the crane is
a transient load and not a permanent load. Therefore, using calculations that are reserved for permanent building
foundations seems very conservative. As stated in Cranes
and Derricks, “Presumptive soil-bearing capacities used
for building foundation design are often over-conservative
when applied to crane supports. Buildings present longterm loads to the ground, so that allowable soil capacity
must reflect a degree of settlement control not necessary for
crane use.” 4 A new standard would hopefully provide more
certainty within the construction industry. The levelness of
the crane pad is specified by the crane manufacturer for the
crane. This is usually around 0.5 in. vertically for every 10
ft horizontally. Depending on the existing site conditions, it
may be easy to create a level pad, or it may come at a large
cost. The larger the crane pad, for a crawler crane with a
wheeled counterweight for example, it may be more difficult
to maintain throughout the duration of the job, and should
be considered while planning the project.
Cost
Cost is a major determining factor during the selection of
a heavy lift crane because it usually is a major component of
the total project cost. Essentially, the higher the capacity of
Fig. 3 Heavy lift crane, rigging and load.
Bearing pressures induced by crawler cranes can be
lessened to an extent by distributing them with crane mats.
Figure 4 shows an example of a large timber crane pad built
for a heavy lift crawler crane. Crane mats are usually hardwood timber mats, but can be made out of steel, composites
and other materials. The mats can be stacked in layers to
increase distribution of the loads. Each layer should be laid
perpendicular to the layer above or below it to help distribute
the load. Crane mats are usually placed on a layer of compacted fill, usually crushed rock, to create a level pad and to
serve as a way to continue to distribute the crane loading to
the existing grade. The loading imposed by the crane when
making a lift is usually a triangular distributive loading due
to the crane leaning towards the direction of the boom.
There are many suggestions as to how to distribute the
load through the layers of crane mats and compacted fill.
They range from using finite element analysis to analyze it as
a beam on elastic foundation, to using assumptions to make
the triangular distributive loading as a rectangular distributive loading. Placing additional layers of crane mats on top
of the first layer adds even more assumptions and unknowns
to the analysis. David Duerr’s 2010 paper, Effective Bearing Length of Crane Mats, gives one approach as to how
to handle the distribution of crane loads and compares the
existing methods currently being used.3At present, more
research into this topic is required on how the loads should
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Fig. 4 Crane pad.
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the crane and the more accessories added, such as a luffing
jib or wheeled counterweight, the higher the rental rate. The
higher rental rate also usually means a higher mobilization
and demobilization cost. As previously stated, the location
of the crane supplier to the location of the job site will also
have an effect on the mobilization and demobilization costs.
Another cost to consider is the time required to erect the
crane and have it hook-ready for the job to start. This cost
adds man-hours to the job which may be included in the
mobilization cost, but it should be clarified with the rental
house as to how the crane will be erected and disassembled.
Rental rates also vary throughout the year based on the
season, the rental demand, and other factors.
Another cost outside of the rental and mobilization cost
is the expenditure for the crane pad and/or ground improvements that will be needed. This cost may include multiple
layers of crane mats and/or a crushed gravel pad. This is an
additional cost depending on the site and the duration of
the job that may affect the crane selection from one with a
wheeled counterweight to a larger capacity crane with no
wheeled counterweight. This would lead to a smaller crane
pad, but will likely lead to a higher crane rental rate or possibly a thicker pad due to the larger crane. These costs should
all be considered to select the most efficient and economical
crane for the job.
Crane Efficiency
Crane efficiency involves selecting a crane that uses at
least 85% of its rated capacity throughout the duration of
the project. This optimizes the rental rate of the crane. If a
selected heavy lift crane is to be used to set structural steel,
but is only at 40% capacity for all of its lifts, then the crane
is too large for the job and is not an efficient use of resources.
Another issue may be that only one heavy module is
dictating the crane size for the entire job. In this case,
there are a few options. One option is to try to reduce the
size of the only large module into a few smaller modules;
however, this may not always be possible as in the case of
steel trusses or vessels. A second option would be to select a
smaller crane to perform the majority of the work, and then
a larger second crane is used to set the large module. Extra
mobilization costs, scheduling issues, site constraints, and
other costs may make this option cost prohibitive. Another
option is to consider using a crane with a wheeled counterweight or a sled that could be install or removed when
needed. The counterweight could be utilized at a later point
in the project to limit rental costs while the base crane does
the remainder of the work. This option would require a sizable amount of space to place the crane and an increased
pad size, but could keep rental costs down and increase the
efficiency of the crane.
Another way to increase the speed and overall efficiency
of the crane is to use the whip line over a rooster sheave.
This should be used for lighter lifts since it only has one or
two parts of line, and therefore, has a higher line speed than
a main block which will have multiple parts of line.
6
Using a belly block is another option to try to increase
the efficiency of the crane. If the crane has a luffing jib or
fixed jib attached, it could still have a block hanging from
the main boom. If it is within the capabilities of the crane,
the heavy module could be lifted with this block while the
luffing jib or fixed jib make the lifts for the lighter parts of the
project. The weights of the accessories above the boom tip
must be deducted when analyzing the use of the belly block.
Crane Reliability
The need for complete reliability of the cranes on a job
will vary depending on scope and schedule. Even if a job
has a large amount of float in the schedule and is not on the
critical path for the overall project, the crane selection needs
to take into account the reliability of the crane. If the job
involves lifts in which schedule is critical, then crane reliability is much more important to the crane selection process.
This may come at a premium rental rate, but it should bring
less risk to the overall job.
If a single crane is to be used as the only crane on the
job site, it may be worthwhile to consider the premium rate
to keep the crane continually operating. If the crane breaks
down in this case, then the majority of the work will halt
because materials cannot be delivered to the areas where
they are required.
The availability of spare parts and components such as
engines, pumps, cables, sheaves, and boom inserts is also
important. Some components of the crane could have lead
times up to two to three months, especially if the crane is
manufactured overseas. Renting from a supplier that stocks
these major parts may require higher rental costs, but may
lessen the impact of crane maintenance. The benefit of additional service and response time should be a factor in the
crane selection decision.
Although crane reliability may not show in the rental cost
of the crane, it should be analyzed when considering the total
cost of a project. Benefits can be gained by utilizing a crane
that has been properly maintained over its lifetime and has
spare parts available if needed. The reliability of the crane is
extremely important regardless of whether the lifts are on the
critical path because each lift should be considered critical
and important to the schedule. Therefore, the lowest rental
cost may not be the best overall cost for the job.
Conclusion
Heavy lift crane selection is a complex process. There
are a variety of issues that must be taken into account simultaneously to select the best crane for the job. The existing
site constraints may have more influence on crane selection
crane than the actual loads to be picked. When considering
the loads, all deductions must be used to determine the correct crane capacity. The ground-bearing pressure must also
be analyzed to ensure that the existing soil conditions can
handle the imposed loads. The construction industry would
greatly benefit by more investment in research on calculating
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ground-bearing pressures and the formation of a standard
calculation. After the crane has been selected, the rental rates
should be analyzed based on multiple factors and not just the
lowest cost. It is expected that more advanced algorithms
and crane selection programs will continue to be developed
to incorporate additional variables to assist in the heavy lift
crane selection process.
References
1.U.S. Occupational Safety and Health Administration,
OSHA Standards for the Construction Industry, Chicago, Illinois, 2010.
2.Wind Conditions, Manitowoc Cranes, Inc., Folio
1678, 2000.
3.Duerr, D.P., Effective Bearing Length of Crane Mats,
Crane & Rigging Conference, Houston, Texas, 2010.
4.Shapiro, H., Shapiro, J., and Shapiro, L., Cranes and
Derricks, McGraw-Hill Companies, Inc., Fourth edition, 2010.
Manitowoc is a registered trademark of Manitowoc Crane
Companies, LLC.
Copyright© 2012by Babcock & Wilcox Power Generation Group, Inc.
a Babcock & Wilcox company
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Disclaimer
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