US8177081 discloses a multi configurations crane system comprising:

- a crane base having a main boom pivot structure adapted to secure thereto a main boom of the crane and providing a horizontal main boom pivot axis for the main boom relative to the crane base,

- a main boom system adapted to provide multiple main boom configurations, said main boom system comprising:

- a lower main boom section having a first end connectable to said main boom pivot structure of the crane base to allow for luffing of the main boom in a luffing plane, and a second end opposite said first end,

- a top main boom section adapted to suspend a load from the main boom, e.g.

comprising an assembly of one or more sheaves for one or more winch driven cables from which said load is suspended,

- multiple lattice insert sections adapted to be inserted in said main boom, wherein said lattice insert sections each comprise a longitudinal axis, wherein said multiple lattice insert sections comprise:

- a set of multiple first insert sections, each having a first cross-sectional size providing a first moment of inertia in the luffing plane and a second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane,

- a set of multiple second insert sections, each having a second cross-section size different from said first cross-sectional size of said first insert sections and providing a third moment of inertia in the luffing plane that is different from said first moment of inertia in the luffing plane and providing a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane that is different from said second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane.

In US8177081 it is proposed to a first configuration of the crane wherein the main boom is composed of the lower main boom section, the top main boom section, and a single strand of multiple first insert sections between said lower and top main boom sections. It is explained in US 8177081 that for some hoist jobs and situations increased strength is desired. Therefore a second configuration is proposed, wherein the main boom is composed of the lower main boom section, the top main boom section, a lower region wherein two strands of first insert sections are arranged in parallel, an upper region wherein a single strand of second insert sections is present, a lower cross-beam that connects the lower ends of both first insert section strands to the lower main boom section, and an upper cross-beam that connects the upper ends of the two first insert section strands to the single second insert section strand. A first aspect of the present invention aims to provide an alternative or improved main boom system.

This aim is achieved by a crane system according to claim 1. In the inventive crane system the multiple lattice insert sections are adapted to be inserted as a single strand of multiple of lattice insert sections in the main boom.

The lattice insert sections each comprise a longitudinal axis. The lattice insert sections are each composed of longitudinally extending corner chords that are spaced from one another and are each parallel to the longitudinal axis of the insert section. Each of the corner chords is arranged at a corner of a cross-section of the insert section perpendicular to the longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section. Each corner chord is provided along the length thereof with joint members. Each lattice insert section is further composed of elongated rigid bracing members, e.g. hollow tubular steel bracing rods. These elongated rigid bracing members extend in the side planes of the insert section, wherein each elongated rigid bracing member has one end thereof connected to a joint member on one corner chord and has its other end thereof connected to a joint member on the other corner chord of the pair of corner chords.

In parallel axial end faces of each insert section the axial ends of the corner chords are provided with connector members, which connector members are adapted to interconnect the insert section to adjoining sections of the main boom. In the inventive crane it is envisaged that the multiple lattice insert sections are adapted to be inserted as a single strand of multiple of said lattice insert sections in said main boom. The mentioned multiple lattice insert sections comprise:

- a set of multiple first insert sections, each having a first cross-sectional size providing a first moment of inertia in the luffing plane and a second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane, and

- a set of multiple second insert sections, each having a second cross-sectional size greater than said first cross-sectional size of said first insert sections and providing a third moment of inertia in the luffing plane that is greater than said first moment of inertia in the luffing plane and providing a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane that is greater than said second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane.

In the inventive crane section, at least the second insert sections are modular as each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the second insert section is effected by a releasable fastener allowing for a disassembled transport mode of the second insert sections wherein the second insert sections have been disassembled into individual corner chords and individual elongated rigid bracing members, for example said releasable fastener being a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member.

For example individual corner chords and/or individual elongated rigid bracing members are dimensioned to be transported in a 40 ft. ISO freight container.

The inventive crane section also comprises multiple lattice transition sections, each comprising a longitudinal axis and comprising corner chords that extend non-parallel to this longitudinal axis. Each transition section has at a first axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the first cross-sectional size and is provided, at said first axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said first insert sections. Each transition section further has at a second axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the second cross-sectional size and is provided, at said second axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of the second insert sections. As will be appreciate by the skilled person the second insert sections have a greater resistance to buckling than the first insert sections. Due to the structure of the second insert sections the load bearing chords and bracing members are located in the corners and related side planes of the second insert sections which allows to make optimum use of these components in view of strength and resistance to buckling. At the same time the weight of each insert section is kept relatively low. Due to the modular construction of at least the second insert sections, these second insertion section can be envisaged with cross-sectional dimensions that would rule out transport by road if they were of non-modular or even another modular design.

In embodiments the second insert sections may have a square or rectangular cross-section, so with four corner chords, with the dimension of the cross-section in width and in depth exceeding 3 meters. For example the second insert section may have a square cross-section of 4x4, 5x5, 6x6, 7x7, 8x8, or even 9x9 meters in practical embodiments. Of course rectangular cross-sections, wherein one of the width and the depth has a value between 3 and 9 meters and the other of the width and the depth has a value of between 3 and 9 meters may also be composed within the scope of claim 1. A rectangular cross-section may have a width that exceeds the depth, wherein the depth is seen generally in the plane of luffing motion. Equally the cross-section may be another polygonal cross-section providing more than four side planes, e.g. six or eight side planes.

Most preferably each second insert section only consists of said corner chords and said elongated rigid bracing elements configured to be releasably fastened between corner chords in said side planes of the section as far as the load bearing function of the second insert section is concerned.

The increased buckling resistance provided by the single strand of second insert sections for example allows to perform heavy load jobs with the main boom according to the second configuration. Herein the strand of second insert sections is located in the region where the highest buckling load is expected during the job. Lighter load jobs can then be performed with the main boom according to the first configuration. In the second configuration this single strand of second insert section is far more effective than the proposal of dual strands as in US8177081 in several aspects. For example the weight of the second insert sections of the inventive proposal to achieve a certain buckling resistance is far less than would be achieved if embodied to US8177081 as in the latter much of the structure is present close to the central longitudinal axis so not contributing in any significant manner to the resistance against buckling. The reduced relative weight has an impact on the effective hoisting capability of the crane in said second configuration, but also on shipping costs of the crane to the site of the hoisting jobs, to the assembly of the crane, etc.

In embodiments the first insert sections are non-modular, e.g. as their cross-sectional dimensions do not interfere with road transportation. For example a four side plane, square or rectangular, first insert section has no cross-sectional width and depth beyond 2.5 meters.

So in embodiments the first insert sections have the elongated rigid bracing members permanently secured to the joint members of the corner chords, e.g. by welding.

In embodiments all the corner chords within a first insert section and/or within a second insert section have the same cross-section. In other embodiments the corner chords within a first insert section and/or within a second insert have different cross-sections, for example corner chords located at the lower side of the main boom, seen in the luffing plane, being of larger cross-section than corner chords in the same insert section at the upper side of the main boom.

In embodiments the multiple lattice transition sections are also of modular design. Herein the transition sections have corner chords that extend non-parallel to the longitudinal axis and form side planes of the transition section. In these side planes elongated rigid bracing members are envisaged each having ends, wherein each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the transition section is effected by a releasable fastener allowing for a disassembled transport mode of the transition sections wherein these sections have been disassembled into individual corner chords and individual elongated rigid bracing members, for example said releasable fastener being a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member.

The inventive crane system may be of benefit, for example, for use at one site wherein a series of hoist job is to be performed in succession. Often, in such a series of jobs, one or a small number of hoisting jobs involve the hoisting of a load that is significantly larger or a load which has to be hoisted from and/or to a location which is significantly further from the position of the crane base than the remaining hoisting jobs. A commonly applied approach is then to provide crane system designed for the heaviest job and perform the entire series with said crane. However, the same crane operator may also be involved in hoisting jobs at another, second location that require the high capacity. The present invention, for example, allows to perform one or more heavy jobs at the first location with the crane system in the second configuration, and then remodel said crane boom in the first configuration to perform the lesser demanding jobs at said first location. The disassembled second insert sections can then be easily shipped to the second location, e.g. by road, train, and/or boat, and assembled there for use in conjunction with another crane.

The skilled person will appreciate that the inventive crane system allows for a large variety of methods of handle the crane system. The invention also relates to a crane system wherein the crane has a so-called back mast, and wherein the inventive approach is applied to back mast, possibly also in the same crane for the main boom as well.

For example the crane according to the invention comprises a crane base, a main boom and a back mast.

The crane base may for example be the chassis of a crawler crane, and/or a foot assembly of a ringer crane. The crane base optionally comprises rollers and/or slide shoes. Optionally, the crane base can absorb both pushing forces and pulling forces from the main boom and/or back mast of the crane.

Optionally, the crane base comprises multiple outriggers, e.g. at least four outriggers, optionally at least eight outriggers. The outriggers are arranged at a distance (at least in horizontal direction) from the lower ends of the masts.

In an embodiment the main boom has, in the second configuration, a length of more than 50 meters, e.g. about 80 meters. For example the strand of second insert sections has a length between 20 and 40 meters.

In an embodiment the main boom and back mast are pivotally connected to the crane base. Optionally, the back mast has a length which is more than 50%, preferably more than 75% of the length of the main boom, preferably less than the length of the main boom.

If the inventive approach is used for both the main boom and the back mast of the crane, and both are brought into the mentioned second configuration to provide enhanced buckling resistance, a significant overall increase in hoisting capacity can be achieved, which cannot be achieved if only the cross sectional size of the main boom would be increased.

In embodiment the corner chords have a circular cross-section.

In another embodiment, e.g. in the second insert sections, the corner chords, or at least some corner chords, have an octagonal cross section. The octagonal cross sectional shape is advantageous with respect to bending stiffness and resistance to buckling. It also allows an easy connection to the elongated rigid bracing members. In embodiments the second insert sections having a second cross-sectional size greater than said first cross-sectional size of said first insert sections, includes each of the corner chords of the second insert sections being spaced from both the luffing plane and from a plane through said longitudinal axis and perpendicular to said luffing plane by a distance greater a corresponding corner chord of the first insert section is spaced from the luffing plane and from a plane through said longitudinal axis, respectively.

For example, the second insert section may have a similar shape as the first insert sections, e.g. square, rectangular, triangular. In this context corresponding corner chords may be defined as the corner chords on similar locations in such shape, e.g. on the same corners. For example, both the width and depth of cross-section of the second insert section may be greater than the width and depth of the cross-section of the first insert section.

For example, all outer sides of the cross-section of the second insert sections may be greater than corresponding outer sides of the cross-section of the first insert sections.

A second aspect of the present invention relates to a multi configurations crane system comprising:

- a crane base having a main boom pivot structure adapted to secure thereto a main boom of the crane and providing a horizontal main boom pivot axis for the main boom relative to the crane base, - a main boom, for example, comprising:

- a lower main boom section having a first end connectable to said main boom pivot structure of the crane base to allow for luffing of the main boom in a luffing plane, and a second end opposite said first end,

- a top main boom section adapted to suspend a load from the main boom, e.g.

comprising an assembly of one or more sheaves for one or more winch driven cables from which said load is suspended, - multiple lattice insert sections adapted to be inserted as a single strand or multiple parallel strands of multiple of said lattice insert sections in said main boom,

- a back mast system to form a back mast from which a ballast load is to be suspended during a hoisting job, wherein the back mast system is adapted to provide multiple back mast configurations, said back mast system comprising:

- a lower back mast section having a first end connectable to a back mast pivot structure of the crane base to allow for variation of the angle of the back mast in a back mast pivot plane, and a second end opposite said first end,

- a top back mast section adapted to suspend a ballast load from the back mast, e.g. comprising an assembly of one or more sheaves for one or more winch driven cables from which said ballast load is suspended,

- multiple lattice insert sections adapted to be inserted as a single strand of multiple of said lattice insert sections in said back mast, wherein said lattice insert sections each comprise a longitudinal axis, and wherein the lattice insert sections are each composed of longitudinally extending corner chords that are spaced from one another and are each parallel to said longitudinal axis of the insert section, each of said corner chords being arranged at a corner of a cross-section of the insert section perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section, wherein each corner chord is provided along the length thereof with joint members, and wherein the insert section is further composed of elongated rigid bracing members, wherein said elongated rigid bracing members extend in said side planes of the insert section, each elongated rigid bracing member having one end thereof connected to a joint member on one corner chord and having another end thereof connected to a joint member on the other corner chord of said pair of corner chords, wherein - in parallel axial end faces of each insert section - axial ends of said corner chords are provided with connector members, which connector members are adapted to interconnect said insert section to adjoining sections of the back mast, wherein said multiple lattice insert sections comprise:

- a set of multiple first insert sections, each having a first cross-sectional size providing a first moment of inertia in the back mast pivot plane and a second moment of inertia in a plane through said longitudinal axis and perpendicular to said back mast pivot plane,

- a set of multiple second insert sections, each having a second cross-sectional size greater than said first cross-sectional size of said first insert sections and providing a third moment of inertia in the luffing plane and/or back mast pivot plane that is greater than said first moment of inertia in the back mast pivot plane and providing a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said back mast pivot plane that is greater than said second moment of inertia in a plane through said longitudinal axis and perpendicular to said back mast pivot plane, wherein, at least the second insert sections are modular as each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the second insert section is effected by a releasable fastener allowing for a disassembled transport mode of the second insert sections wherein the second insert sections have been disassembled into individual corner chords and individual elongated rigid bracing members, for example said releasable fastener being a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member, - multiple lattice transition sections, each comprising a longitudinal axis and comprising corner chords that extend non-parallel to said longitudinal axis, wherein each transition section has at a first axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the first cross-sectional size and is provided, at said first axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said first insert sections, and wherein each transition section further has at a second axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the second cross-sectional size and provided, at said second axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said second insert sections, the back mast system providing a first configuration of the crane wherein:

- the back mast is composed of said lower back mast section, said top back mast section, and a strand of multiple first insert sections between said lower and top back mast sections, and the back mast system providing a second configuration of the crane wherein:

- the back mast is composed of said lower back mast section, said top back mast section, and a single strand of multiple second insert sections and a single first insert section or a single strand of multiple first insert sections, wherein one of said lattice transition sections is mounted at one end of said single strand of multiple second insert sections and wherein another one of said lattice transition sections is mounted at the other end of said single strand. In embodiments the second insert sections having a second cross-sectional size greater than said first cross-sectional size of said first insert sections, includes each of the corner chords of the second insert sections being spaced from both the luffing plane and from a plane through said longitudinal axis and perpendicular to said luffing plane by a distance greater a corresponding corner chord of the first insert section is spaced from the luffing plane and from a plane through said longitudinal axis, respectively.

For example, the second insert section may have a similar shape as the first insert sections, e.g. square, rectangular, triangular. In this context corresponding corner chords may be defined as the corner chords on similar locations in such shape, e.g. on the same corners. For example, both the width and depth of cross-section of the second insert section may be greater than the width and depth of the cross-section of the first insert section.

For example, all outer sides of the cross-section of the second insert sections may be greater than corresponding outer sides of the cross-section of the first insert sections. A third aspect of the present invention relates to a multi configurations crane system comprising:

- a crane base having an A - frame main boom pivot structure adapted to secure thereto an A - frame main boom of the crane and providing a horizontal main boom pivot axis for the A - frame main boom relative to the crane base,

- an A - frame main boom system adapted to provide multiple main boom configurations, said main boom system comprising:

- a lower main boom structure having a first end connectable to said main boom pivot structure of the crane base to allow for luffing of the main boom in a luffing plane, and a second end opposite said first end,

- a top main boom structure adapted to suspend a load from the main boom, e.g. comprising an assembly of one or more sheaves for one or more winch driven cables from which said load is suspended,

- two A- frame leg structures, each having a lower end connectable to the lower main boom structure and having a top end connectable to the top main boom structure,

- multiple lattice insert sections adapted to be inserted as a single strand of multiple of said lattice insert sections in each of the two A-frame leg structures of said main boom, wherein said lattice insert sections each comprise a longitudinal axis, and wherein the lattice insert sections are each composed of longitudinally extending corner chords that are spaced from one another and are each parallel to said longitudinal axis of the insert section, each of said corner chords being arranged at a corner of a cross-section of the insert section perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section, wherein each corner chord is provided along the length thereof with joint members, and wherein the insert section is further composed of elongated rigid bracing members, wherein said elongated rigid bracing members extend in said side planes of the insert section, each elongated rigid bracing member having one end thereof connected to a joint member on one corner chord and having another end thereof connected to a joint member on the other corner chord of said pair of corner chords, wherein - in parallel axial end faces of each insert section - axial ends of said corner chords are provided with connector members, which connector members are adapted to interconnect said insert section to adjoining sections of the main boom, wherein said multiple lattice insert sections comprise:

- a set of multiple first insert sections, each having a first cross-sectional size providing a first moment of inertia in the luffing plane and a second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane,

- a set of multiple second insert sections, each having a second cross-sectional size greater than said first cross-sectional size of said first insert sections and providing a third moment of inertia in the luffing plane that is greater than said first moment of inertia in the luffing plane and providing a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane that is greater than said second moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane, wherein, at least the second insert sections are modular as each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the second insert section is effected by a releasable fastener allowing for a disassembled transport mode of the second insert sections wherein the second insert sections have been disassembled into individual corner chords and individual elongated rigid bracing members, for example said releasable fastener being a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member,

- multiple lattice transition sections, each comprising a longitudinal axis and comprising corner chords that extend non-parallel to said longitudinal axis, wherein each transition section has at a first axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the first cross-sectional size and is provided, at said first axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said first insert sections, and wherein each transition section further has at a second axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the second cross-sectional size and provided, at said second axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said second insert sections, the A- frame main boom system providing a first configuration of the crane wherein:

- the A -frame main boom is composed of said lower main boom structure, said top main boom structure, and said two A- frame leg structures which are each composed of a single strand of multiple first insert sections (11) between said lower and top main boom structures, and the main boom system providing a second configuration of the crane wherein:

- the A - frame main boom is composed of said lower main boom structure, said top main boom structure, and said two A- frame leg structures which are each composed of a single lower strand of multiple second insert sections and a single upper strand of multiple first insert sections, wherein one of said lattice transition sections is mounted between said upper and lower strands, and wherein another one of said lattice transition sections is mounted at a lower end of said lower strand connection said lower strand to said lower main boom structure or, optionally to a first insert section between said lattice transition section and said lower main boom structure. The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The drawing shows in:

Fig. 1 a possible embodiment of a crane system according to the invention, with the main boom system and a back mast system in the first configuration thereof,

Fig. 2 the embodiment of fig. 1 , with the main boom system and the back mast system in the second configuration thereof.

Fig.1 shows a crane 1 which is arranged at a hoisting location. The crane 1 comprises a crane base 2, a main boom 10 and a back mast 20.

In the embodiment of fig. 1 , the crane base 2 is for example the chassis of a crawler crane. Outriggers are not shown in fig. 1 for reasons of clarity, but they may be provided as needed. The main boom 10 and the back mast 20 are connected via a guy wire arrangement 3.

The crane 1 in this example further comprises one or more ballasts 4, 5. The main boom 10 and the back mast 20 are each pivotally connected to the crane base 2.

A crane hook 6 is suspended from the top of the main boom 10 by hoisting line 7. When a load is to be hoisted, the load is connected to the crane hook 6, thereby connecting the load to the main boom 10 via the hoisting line 7.

As illustrated in the example of fig. 1 , the back mast 20 may have a length of more than 50% of the length of the main boom 20. In the embodiment of fig. 1 , the main boom 10 comprises a lower main boom section 12 and a top main boom section 13.

In the embodiment of fig. 1 , the back mast 20 comprises a lower back mast section 22 and a top back mast section 23. The lower back mast section 22 has a first end 22a which is connected to the crane base 2 and a second end 22b.

In accordance with a possible embodiment of the method according to the invention, a first hoisting job in the series of hoisting jobs is carried out using the crane 1 in the configuration of fig. 1. The first hoisting job involves attaching a first load to the main boom 10 of the crane 1 , and subsequently hoisting the first load. After hoisting the first load, the first load is disconnected from main boom 10 of the crane 1.

As will be appreciated the inventive crane system can be brought in multiple alternative configurations, including the configuration illustrated in figure 2, wherein both the main boom system and the back mast system have been brought in the second configuration as explained herein. Herein both the main boom 10 and the back mast 20 have a region formed by second insert sections that provide a significant increase of strength, especially in view of buckling, and - as explained herein - at a relatively low weight so as to obtain an optimized load handling capacity of the crane 1 in this configuration.

It will be appreciated that in alternative embodiments the crane 1 for example has a main boom system in the second configuration thereof in combination with a back mast system in the first configuration thereof, or in another alternative configuration the main boom system is the first configuration and the back mast system in the second configuration.

The crane base 2 has a main boom pivot structure 2a that is adapted to secure thereto the main boom 10 of the crane and provides a horizontal main boom pivot axis for the main boom relative to the crane base so that the main boom 10 can perform a luffing motion in a vertical luffing plane.

As will be appreciated the main boom system is adapted to provide multiple main boom configurations, including a first configuration illustrated in figure 1 and a second configuration shown in figure 2.

The lower main boom section 12 having a first end 12a connectable to the main boom pivot structure 2a of the crane base 2 to allow for luffing of the main boom in a luffing plane, and a second end 12b opposite this first end 12a.

The top main boom section 13 is adapted to suspend a load from the main boom, e.g.

comprising an assembly of one or more sheaves 13a for one or more winch driven cables from which said load is suspended.

In the first configuration the main boom 10 is composed of the lower main boom section 12, the top main boom section 13, and a single strand of multiple first insert sections 11 between the lower and top main boom section 12, 13. The first insert sections 1 1 are embodied as lattice insert sections and adapted to be inserted as a single strand of multiple of lattice first insert sections 1 1 in the main boom 10.

As generally known in the art, the first insert sections 1 1 may be of non-modular design, so all components being rigid and permanently jointed. Other modular or foldable designs of the first insert sections are also possible, e.g. to facilitate transportation thereof.

The lattice first insert sections each comprise a longitudinal axis.

In this example it is envisaged that the lattice first insert sections are of a square cross- sectional shape, as is rather common in the art, e.g. with a width and depth of the insert section of 2.5 meters.

The lattice insert sections 11 are each composed of four longitudinally extending corner chords that are spaced from one another and are each parallel to the longitudinal axis of the insert section. Each of said corner chords is arranged at a corner of the square cross-section of the insert section 11 seen perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section 11. Each corner chord is provided along the length thereof with joint members. Each insert section 1 1 is further composed of elongated rigid bracing members, both diagonal bracing members and transverse bracing members (so at an incline to the chords and perpendicular to the chords). These elongated rigid bracing members extend in the side planes of the insert section.

Each elongated rigid bracing member of the insert sections 1 1 has one end thereof connected to a joint member on one corner chord and has another end thereof connected to a joint member on the other corner chord of said pair of corner chords.

As is common in the field, in parallel axial end faces of each insert section 1 1 , axial ends of the four corner chords are provided with connector members, which connector members are adapted to interconnect said insert section 11 to adjoining sections, so either another insert section 11 , the top section 13, or the lower section 12, of the main boom 10.

It will be appreciated that in the set of multiple first insert sections 11 , each first insert section 1 1 has a first cross-sectional size, here defined by the width and the depth of the square cross-section (with the depth seen in the luffing plane between the front and back side planes and with the width seen between the two lateral side planes of the sections 11), providing a first moment of inertia in the luffing plane and a second moment of inertia in a plane through the longitudinal axis and perpendicular to the luffing plane.

It will be appreciated that the main boom 10 can be made to length by inclusion of the desired number of first insert sections 1 1.

Figure 2 illustrates the reconfiguration of the crane 1 , wherein the main boom 10 is composed of the lower main boom section 12, the top main boom section 13, and a single lower strand of multiple second insert sections 31 and a single upper strand of multiple first insert sections 11. A lattice transition section 34 is mounted between these upper and lower strands. Another lattice transition sections 32 is mounted at the lower end of the lower strand and connects to a first insert section 11 that is mounted between this lower lattice transition section 32 and the lower main boom section 12. The multiple lattice second insert sections 33 are adapted to be inserted as a single strand of multiple of said lattice second insert sections 33 in the main boom 10. The second insert sections 33 each comprise a longitudinal axis.

In this example it is envisaged that the lattice second insert sections 33 are of a square cross-sectional shape, as is rather common in the art, however with a width and depth of the insert section 31 exceeding the width and depth of the cross-section of the first insert sections 11. For example the width and depth of the second insert section may be 4x4, 5x5, 6x6 meters.

The lattice insert sections 31 are each composed of four longitudinally extending corner chords that are spaced from one another and are each parallel to the longitudinal axis of the insert section 31. Each of said corner chords is arranged at a corner of the square cross- section of the insert section 31 seen perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section 31. Each corner chord is provided along the length thereof with joint members. Each insert section 31 is further composed of elongated rigid bracing members, both diagonal bracing members and transverse bracing members (so at an incline to the chords and perpendicular to the chords). These elongated rigid bracing members extend in the side planes of the insert section 31.

Each elongated rigid bracing member of the insert sections 31 has one end thereof connected to a joint member on one corner chord and has another end thereof connected to a joint member on the other corner chord of said pair of corner chords. As is common in the field, in parallel axial end faces of each insert section 31 , axial ends of the four corner chords are provided with connector members, which connector members are adapted to interconnect said insert section 31 to adjoining insert sections 31 or to one of the transition sections 32, 34 of the main boom system. These large cross-section second insert sections 31 are each modular as each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the second insert section 31 is effected by a releasable fastener allowing for a disassembled transport mode of the second insert sections 31 wherein the second insert sections have been disassembled into individual corner chords and individual elongated rigid bracing members. In a preferred embodiment the releasable fastener is a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member. So, the multiple second insert sections 31 of the main boom system each have a second cross-sectional size that is significantly greater than the first cross-sectional size of each of the first insert sections 1 1 of the main boom system. Each second insert section 31 has a third moment of inertia in the luffing plane that is greater than said first moment of inertia in the luffing plane of the first insert sections 1 1 and a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said luffing plane that is greater than the second moment of inertia of the first insert sections 1 1 in a plane through said longitudinal axis and perpendicular to said luffing plane.

Due to the open centered structure of the second insert sections 31 , with corner chords and bracing members all located in the side planes and corners and with a simple, relatively lightweight, and readily assembled and disassembled design, an optimized load handling capacity of the main boom 10 and thus of the crane 1 can be achieved with a single strand of second insert sections 31 in the main boom. As explained this is considered beneficial over a dual parallel strand design.

In another configuration of the main boom 10, the entire region between the top main boom section 13 and lower main boom section 12 is made up by a single strand of second insert sections 31 with provision of the mentioned lattice transition sections 32, 24 at the lower and upper end of said single strand of sections 31.

The lattice transition sections 32, 34 of the main boom system each comprise a longitudinal axis. In these sections 32, 34 the four corner chords extend non-parallel to this longitudinal axis as the general shape formed by side planes of the section 32, 34 resembles a truncated pyramid. Each transition section 32, 34 has at a first axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the first cross-sectional size of the first insert sections 11 and is provided, at said first axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said first insert sections 1 1. Each transition section 32, 34 further has at a second axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the second cross-sectional size of the second insert sections 31 and is provided, at said second axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said second insert sections 31.

As explained herein the inventive approach discussed above in the context of the main boom 10 of a crane, may also be implemented in a back mast 20 of a crane having one or more back masts in combination with a main boom 10. Again the result is a multi-configurations design, now of the back mast 20 that allows to effectively alter the practical design of the back mast 20, e.g. to include a single strand of large cross-section second insert sections in the back mast to enhance the strength, and in particular the buckling resistance of the back mast 20. In figure 1 the back mast 20 is illustrated in its first configuration. Herein the back mast 20 is composed of a lower back mast section 22, a top back mast section 23, and a single strand of multiple first insert sections 21 between these lower and top back mast sections 22, 23.

The back mast is pivotal relative to the crane base 2 about a pivot structure 2b providing a horizontal pivot axis. Here said axis is parallel to the pivot axis of the main boom, so that the luffing plane and a back mast pivot plane coincide. In some cranes two back masts are provided that diverge from the crane base 2, with non-parallel pivot axes so that each back mast has its own back mast pivot plane that does not coincide with the main boom pivot axis.

As generally known in the art, the first insert sections 21 may be of non-modular design, so all components being rigid and permanently jointed. Other modular or foldable designs of the first insert sections are also possible, e.g. to facilitate transportation thereof.

The lattice first insert sections 21 each comprise a longitudinal axis.

In this example it is envisaged that the lattice first insert sections are of a square cross- sectional shape, as is rather common in the art, e.g. with a width and depth of the insert section of 2.5 meters.

The lattice insert sections 21 are each composed of four longitudinally extending corner chords that are spaced from one another and are each parallel to the longitudinal axis of the insert section. Each of said corner chords is arranged at a corner of the square cross-section of the insert section 21 seen perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section 21.

Each corner chord is provided along the length thereof with joint members. Each insert section 21 is further composed of elongated rigid bracing members, both diagonal bracing members and transverse bracing members (so at an incline to the chords and perpendicular to the chords). These elongated rigid bracing members extend in the side planes of the insert section. Each elongated rigid bracing member of the insert sections 21 has one end thereof connected to a joint member on one corner chord and has another end thereof connected to a joint member on the other corner chord of said pair of corner chords. As is common in the field, in parallel axial end faces of each insert section 21 , axial ends of the four corner chords are provided with connector members, which connector members are adapted to interconnect said insert section 21 to adjoining sections, so either another insert section 21 , the top section 23, or the lower section 22, of the back mast 20. It will be appreciated that in the set of multiple first insert sections 21 , each first insert section 21 has a first cross-sectional size, here defined by the width and the depth of the square cross-section (with the depth seen in the back mast pivot plane, here coinciding with the luffing plane, between the front and back side planes and with the width seen between the two lateral side planes of the sections 21), providing a first moment of inertia in the back mast pivot plane and a second moment of inertia in a plane through the longitudinal axis and perpendicular to the back mast pivot plane.

It will be appreciated that the back mast 20 can be made to length by inclusion of the desired number of first insert sections 21.

Figure 2 illustrates the reconfiguration of the crane 1 , wherein the back mast 20 is composed of the lower back mast section 22, the top back mast section 23, and a single strand of multiple second insert sections 41 and here a strand of just one first insert section 21. It will be appreciated that for a longer back mast also a single strand of multiple first insert sections 21 can be integrated in the back mast in combination with the strand of sections 41.

A lattice transition section 44 is mounted between these upper and lower strands. Another lattice transition sections 42 is mounted between the strand of insert sections 41 and the top back mast section 23.

The multiple lattice second insert sections 41 are adapted to be inserted as a single strand of multiple of said lattice second insert sections 41 in the back mast 20.

The second insert sections 41 each comprise a longitudinal axis.

In this example it is envisaged that the lattice second insert sections 41 are of a square cross-sectional shape, as is rather common in the art, however with a width and depth of the insert section 41 exceeding the width and depth of the cross-section of the first insert sections 21. For example the width and depth of the second insert section may be 4x4, 5x5, 6x6 meters, etc. The lattice insert sections 41 are each composed of four longitudinally extending corner chords that are spaced from one another and are each parallel to the longitudinal axis of the insert section 41. Each of said corner chords is arranged at a corner of the square cross- section of the insert section 41 seen perpendicular to said longitudinal axis so that each pair of adjacent corner chords defines a side plane of the insert section 41.

Each corner chord is provided along the length thereof with joint members. Each insert section 41 is further composed of elongated rigid bracing members, both diagonal bracing members and transverse bracing members (so at an incline to the chords and perpendicular to the chords). These elongated rigid bracing members extend in the side planes of the insert section 41.

Each elongated rigid bracing member of the insert sections 41 has one end thereof connected to a joint member on one corner chord and has another end thereof connected to a joint member on the other corner chord of said pair of corner chords.

As is common in the field, in parallel axial end faces of each insert section 41 , axial ends of the four corner chords are provided with connector members, which connector members are adapted to interconnect said insert section 41 to adjoining insert sections 41 or to one of the transition sections 42, 44 of the back mast system.

These large cross-section second insert sections 41 are each modular as each connection of an end of an elongated rigid bracing member to a joint member on a corner chord of the second insert section 41 is effected by a releasable fastener allowing for a disassembled transport mode of the second insert sections 41 wherein the second insert sections have been disassembled into individual corner chords and individual elongated rigid bracing members. In a preferred embodiment the releasable fastener is a fastener pin that is insertable through aligned holes in the joint member and the end of the elongated rigid bracing member. So, the multiple second insert sections 41 of the back mast system each have a second cross-sectional size that is significantly greater than the first cross-sectional size of each of the first insert sections 21 of the back mast system. Each second insert section 41 has a third moment of inertia in the back mast pivot plane that is greater than said first moment of inertia in the back mast pivot plane of the first insert sections 21 and a fourth moment of inertia in a plane through said longitudinal axis and perpendicular to said back mast pivot plane that is greater than the second moment of inertia of the first insert sections 21 in a plane through said longitudinal axis and perpendicular to said back mast pivot plane.

Due to the open centered structure of the second insert sections 41 , with corner chords and bracing members all located in the side planes and corners and with a simple, relatively lightweight, and readily assembled and disassembled design, an optimized load handling capacity of the back mast 20 and thus of the crane 1 can be achieved with a single strand of second insert sections 41 in the back mast.

In another configuration of the back mast 20, the entire region between the top section 23 and lower section 22 is made up by a single strand of second insert sections 41 with provision of the mentioned lattice transition sections 42, 44 at the lower and upper end of said single strand of sections 41.

The lattice transition sections 42, 44 of the back mast system each comprise a longitudinal axis. In these sections 42, 44 the four corner chords extend non-parallel to this longitudinal axis as the general shape formed by side planes of the section 42, 44 resembles a truncated pyramid. Each transition section 42, 44 has at a first axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the first cross-sectional size of the first insert sections 21 and is provided, at said first axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said first insert sections 21. Each transition section 42, 44 further has at a second axial end face thereof a cross-section perpendicular to the longitudinal axis that corresponds to the second cross-sectional size of the second insert sections 41 and is provided, at said second axial end face, with connector members at axial ends of the chords of the transition section so as to allow for connection to one of said second insert sections 41.