BEAM ASSEMBLY AND SPACER ELEMENTS

Abstract

The present invention provides an assembly of orthogonal tension beams (4) in alternate horizontal layers for use in a tank, wherein at least some of the intersection points between the orthogonal tension beams are interconnected by vertical spacer elements (5) with bending stiffness and torsional flexibility as well as spacer elements suitable for said assembly.

Description

FIELD OF INVENTION

The present invention relates to tanks for storage and transportation of fluids such as hydrocarbons, including low temperature liquefied natural gas. This includes tanks for ships and floating offshore structures exposed to wave loads as well as gravity based offshore structures and land tanks exposed to earthquakes.

BACKGROUND OF THE INVENTION

Tanks may be designed in many different configurations, such as spheres, cylinders, cones and shells in general, as well as prismatic shapes. The principal advantage of prismatic shapes is that they nest closer to each other, minimising the volume taken up by such tanks. Simple prismatic tanks are far less efficient structurally as they rely on bending action for mobilisation of strength. Shells develop strength through direct tension in the plane of the shell. This develops greater strength for the same amount of material.

A more efficient design of prismatic shapes is to incorporate internal stays (tension beams). By developing stays as the main means of restraining the internal load or pressure, such prismatic staid tanks are comparable to shell shapes in structural efficiency. WO 2006/001711 A2 discloses such tanks and is hereby incorporated by reference.

Apart from developing structural strength the stays dampen sloshing induced by wave motion. The horizontal loads on the tension stays due to sloshing are absorbed by the beams and to limit bending the beams must be connected at each intersection. The beams are organised in alternate orthogonal layers.

Sloshing forces cause angular displacement of the stays in different layers. The torsion moments induced in the connections at each intersection will be extremely large in relation to a practical geometry of the connections if they provide a rigid restraint. A solution to this problem would be highly advantageous.

OBJECT OF THE INVENTION

The object of the present invention is to provide a connection between orthogonally intersecting beams in alternate layers. This connection must be able to absorb relative angular displacement of beams in alternate layers at the same time as anchoring the beams to the transverse beams above and below. In order to overcome the above-mentioned problem of a rigid restraint, a connection should have torsional flexibility in combination with sufficient shear strength and resistance to lateral bending.

In order to provide torsion flexibility in combination with sufficient shear strength and resistance to lateral bending the invention uses a connection in the form of a stub column having a cruciform cross section. The cruciform cross section may be of variable thickness and may also incorporate slots or indentations to optimise the stress distribution with respect to strength and fatigue. The cross section may also be modified to incorporate anything from three or more plates centred into a common axis.

The stub columns may be anchored by welding one or more base plates accommodating bolts, welds or other means of connection to the stays.

SUMMARY OF THE INVENTION

The object of the present invention is obtained by connecting transverse stays by a stack of stub columns flexible in torsion and rigid in flexure and shear. The invention according to the present application comprises:

An assembly of orthogonal tension beams in alternate horizontal layers for use in a tank, wherein at least some of the intersection points between the orthogonal tension beams are interconnected by vertical spacer elements with bending stiffness and torsional flexibility.

In the above-mentioned assembly, the beams may comprise webs and flanges.

In the above-mentioned assembly, the spacer elements are preferably connected to the beams by way of bolts, welds or any other suitable fastening means.

In the above-mentioned assembly, the spacer elements are preferably connected to the beams by the webs or flanges of the beams.

A spacer element for use in an assembly as described above, wherein said element has two base-plates connected by a plurality of plates intersecting through a common axis and where this axis intersects both the two base-plates.

A preferred spacer element is one wherein the plates intersecting are of a cruciform cross section and preferably have a common axis perpendicular to the base plates.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention will be described below with reference to the exemplifying embodiments shown schematically in the appended drawings, wherein:

FIG. 1 shows a perspective view of a cruciform spacer element;

FIG. 2 shows a horizontal cross section including a plan view of the base plate;

FIG. 3 shows some alternative cross sections of a spacer element;

FIG. 4 shows a side view of a cruciform spacer element;

FIG. 5 shows an assembly of cruciform spacer elements and beams anchored by the spacer element.

FIG. 6 shows a perspective view of the interior of a tank, featuring an assembly of tension beams.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the spacer element consisting of plates 1 forming a cruciform stub column and two base plates 2 with holes 3 to receive bolts for anchoring the spacer element to the intersecting stays/beams. The spacer element may be manufactured by die forging or fabricated from welded plate, extruded or rolled profiles.

FIG. 2 shows the spacer element consisting of the cruciform stub column shown in cross section, one of the base plates 2 shown in plane and the bolt holes 3 shown with bolts inserted.

FIG. 3 show alternative embodiments of the spacer element.

FIG. 4 shows an elevation of a spacer element with plates 1 forming a cruciform stub column element, two base plates 2 with holes 3 to receive bolts.

FIG. 5 shows typical details of an assembly of stays/beams 4 shown as I-beams and cruciform spacer elements 5 connected to the webs of the stays/beams 4.

FIG. 6 shows a perspective view of the interior of a tank, featuring an assembly of tension beams 4 connected by cruciform spacer elements 5 at their intersections.

Claims

1. A tank comprising an assembly of horizontal, orthogonally crossing tension beams the beams being interconnected at the crossing points, wherein at least at some of the crossing points, the orthogonal tension beams are interconnected by vertical spacer elements wherein the spacer elements permit relative angular displacement, while resisting shear and bending, between adjacent orthogonal beams.

2. A tank comprising an assembly according to claim 1, wherein the beams comprise webs and flanges.

3. A tank comprising an assembly according to claim 2, wherein the spacer elements are connected to the webs of the beams.

4. A tank comprising an assembly according to claim 2, wherein the spacer elements are connected to the flanges of the beams.

5. A tank comprising an assembly according to claim 1 anyone of claims 1-4, wherein the spacer elements are connected to the beams by bolts or welds.

6. A spacer element for use in a tank comprising an assembly according to claim 1, wherein said element has two base-plates connected by a plurality of plates intersecting through a common axis and where this axis intersects both the two base-plates.

7. A spacer element according to claim 6, wherein the plates intersecting are of a cruciform cross section and have a common axis perpendicular to the base plates.