GB2488582A

GB2488582A - Building unit made from concrete panels and process for deploying said unit.

Info

Publication number: GB2488582A
Application number: GB1103621.7A
Authority: GB
Inventors: Roy Nield-Dumper
Original assignee: QUBE GROUP Ltd
Current assignee: QUBE GROUP Ltd
Priority date: 2011-03-03
Filing date: 2011-03-03
Publication date: 2012-09-05
Also published as: GB201103621D0

Abstract

Building unit made from concrete panels and process for deploying said unit.The process comprises: providing six concrete panels and joining them together to provide four walls 18, a roof 32 and a floor and including anchor points to allow the connection of lifting equipment and transporting the unit to a site. Anchor points are preferably provided on the upper edges of two walls which are left partially exposed by the roof . The unit may comprise apertures for doors and windows which are braced prior to transportation. A partition may also be included within the unit. The panels are preferably connected together using either: an â Lâ shaped bar which protrudes from one panel and is inserted into a corresponding recess of a second panel; welding together of metal protrusions embedded in two panels or using a bolt that goes through a through-thickness aperture in one panel and into a second panel. In use the unit comprises a prefabricated prison cell.

Description

Building unit and process for the assembly and transportation thereof

Field of the invention

The present application relates to building units and processes for the assembly and transportation thereof, in particular to building units for use in providing prison cells.

Background to the invention

For security reasons, prison buildings are often built with reinforced concrete (RC) as the primary structural material. In particular, precast reinforced concrete (PRO) is advantageous for the construction of prison cells, since it allows efficient production of multiple identical units.

PRO structures are usually built using one of two approaches. In the first approach, distinct RO members (columns, beams, walls and floors) are produced separately at the factory, and are then transported to, erected and assembled on site. The production of individual members may be relatively low in cost, but assembly on site is often time-consuming and inefficient.

The second approach is the factory production of pre-cast monolithic RO modules. For example, a block of four cells, comprising ceiling, outer walls and partition walls may be cast as a single monolithic RO block, and ultimately integrated as part of a prison structure. Mechanical and electrical ducts and fittings, as well as windows, doors, and even furniture may be pre-installed at the factory before delivery to site. Despite being very efficient, such a process is very costly because the blocks require very expensive specialised nioulds with limited usable life.

It is desirable to provide building units for prisons that may be produced at a low cost and installed quickly and efficiently.

Summary of invention

Therefore, at its most general, the present invention may provide a process for constructing a building unit from at least six concrete panels, and transporting the building unit to a site where it is deposited to form whole or part of a building structure.

In addition, the building unit may be partly or entirely fitted-out e.g. with one or more of the following: embedded mechanical and electrical installations, windows and doors, paint, flooring, furniture and toilet fixtures.

Thus, the building unit may be erected rapidly and efficiently, while its panel structure allows for flexibility in production and assembly, as well as carefully controlled costs.

In a first aspect, the present invention may provide a process for supplying a building unit to a building site, comprising the steps of: providing at least six concrete panels, joining the concrete panels to provide a building unit having a floor, a roof and four walls extending between the floor and the roof, providing anchor points on the building unit, for allowing the building unit to be connected to lifting equipment, transporting the building unit to a building site and depositing the building unit in a pre-determined location, to provide whole or part of a building structure, wherein the step of transporting the building unit to the building site comprises the step of attaching the building unit to the lifting equipment such that the building unit is suspended from its anchor points.

The term "concrete" is intended to cover any element that consists primarily of concrete.

However, the element may include other constituents, e.g. reinforcing bars, meshes and/or welded wire fabric. Thus, the term "concrete" covers e.g. reinforced concrete. In certain cases, the reinforcement may be pre-stressed and may take the form of pre-stressed wires, bars, or strands. Generally, the reinforcements may consist partly or entirely of steel.

The panels each define a plane, that is, each panel extends primarily in two dimensions, and only to a much lesser extent in a third dimension. Thus, the panels generally have two substantially flat opposed faces. However in certain cases, one or more of the panels may have additional features that extend outwardly from the plane of the panel.

For example, in certain embodiments, an arched structure may extend along one face of a panel, the arched structure bounding a space for housing e.g. pipework. The panels may include one or more apertures to provide windows or doors.

Each panel is cast as a separate concrete element. Panels may be cast horizontally, that is, such that the plane of the panel is oriented horizontally during the casting process. In certain cases, however, the panel may be cast vertically, that is, such that the plane of the panel is oriented vertically during the casting process. Vertical casting may help improve the surface finish of the panel. In addition, vertical casting may allow for easier handling of the panel, for example, in cases where the panel includes one or more apertures that are bounded by relatively thin concrete elements.

Typically, the dimensions of the building unit are such that the distance between the inner faces of the floor and the roof of the unit is at least2m. The concrete in the panels generally has a thickness of at least 85mm, while the building unit as a whole typically weighs at least 17000kg.

In general, after being transported to the building site, the building unit is placed in an array together with other building units to provide a building. For example, building units may be stacked to a height of up to 8 units.

Surprisingly, it has been found that concrete building units may be pre-assembled by joining individual panels, and then transported and deposited at a building site. Up till now, it has been a long-held prejudice that sizeable concrete building units e.g. prison cells, may only be pre-cast as monolithic blocks, or assembled from panels on-site. It was not considered possible to assemble such building units from concrete panels off-site for transportation to the building site. Such a procedure was avoided, as it was thought that this would inevitably result in significant and uncontrolled cracking of the building unit.

In practice, it has been found that any cracking that occurs during transport, assembly and deposition (and possibly stacking on other building units) may be controlled to minimal values, which do not affect the performance or appearance of the building unit when it is integrated into the building structure. In fact, it has been found that the maximum crack widths may be controlled to within 0.3 mm within the panels as well as the joints, and in particular, crack width at the floor to wall joints may be controlled to within 0.1 mm.

The robustness of the building unit may be enhanced through control of a number of features of the unit.

One such feature relates to the arrangement and overlap of the panels, that is, the way in which one panel contacts an adjacent panel.

The building unit is configured such that the walls each have: * two longitudinal edge surfaces that extend from the floor to the roof; * a floor-side edge surface proximate to the floor; and * a roof-side edge surface that is proximate to the roof and that faces away from the floor.

The edge surfaces extend along the thickness of the panels used for the walls.

The roof-side edges are not necessarily covered by the roof In fact, it is preferred that roof is positioned in relation to the walls such that at least a portion of at least one roof-side edge surface is left uncovered by the roof, that is, this portion remains exposed.

For example, the building unit may be configured such that at least one edge surface of the roof is positioned against the inner face of one wall. Additionally or alternatively, the roof may have one or more cut-outs at its perimeter, such that at least a portion of a roof-side edge of a wall remains exposed.

This configuration may allow one or more anchor points to be mounted directly onto a wall, by securing the anchor point to the uncovered, exposed roof-side edge surface of that wall.

It is thought that mounting one or more anchor points directly on a wall allows the anchor points to be rooted deeply within the wall, thus improving the connection between the anchor points and the rest of the building unit, particularly when the building unit is suspended from the anchor points or deposited onto the pre-determined location. By contrast, if the anchor points are mounted on the roof, only a shallow connection is possible. Furthermore, by mounting one or more anchor points directly on a wall, the load carried by the joints between the roof and the walls may be reduced.

Preferably, one such exposed roof-side edge surface is provided on each one of a first pair of opposed walls, at least two anchor points being mounted on each exposed surface. Typically, the first pair of opposed walls are those walls having one or more apertures e.g. for a window or a door. Thus, the first pair of opposed walls may be considered to correspond to the front and back walls of the building unit.

The building unit has a second pair of opposed walls that extend between the first pair of opposed walls, that is, they may be considered to be cross walls. Preferably, the longitudinal edge surfaces of the second pair of opposed walls are positioned against the inner faces of the first pair of opposed walls. That is, the building unit is configured such that there is contact between the longitudinal edges of the second pair of opposed walls and the inner faces of the first pair of opposed walls. It is thought that this arrangement allows the cross walls to support the front and back walls of the building unit in their spaced-apart position, when the building unit is suspended from anchor points located on the front and back walls.

Preferably, at least one of the first pair of opposed walls comprises concrete that is reinforced with steel. The ratio of steel reinforcement to concrete generally depends on the number and size of any apertures present in the panel. Typically, at least one of the first pair of opposed walls has been cast vertically, that is, such that the plane of the panel extends vertically during the casting process.

In general, the building unit is configured such that if a plurality of such units are stacked to provide a building structure, the weight of the building structure is supported primarily by the first pair of opposed walls, which are arranged to transfer the load through to the foundations of the building. Thus, the first pair of opposed walls are typically thicker than the cross walls. For example, the first pair of opposed walls may each comprise concrete portions that are at least 110 mm thick, whereas the cross walls are typically at least 95 mm thick. In general, the roof is at least 85 mm thick, while the floor may be at least 125 mm thick.

In certain embodiments, the building unit comprises a fifth wall extending between the first pair of opposed walls. The fifth wall therefore has the same orientation as the walls of the second pair of opposed walls. Effectively, the fifth wall provides a partition within the building unit, such that the building unit may provide a plurality of internal rooms.

The presence of the fifth wall, at this orientation, may improve the stability of the building unit, when it is suspended by means of anchor points that are secured to the first pair of opposed walls. That is, the partition wall may support the first pair of opposed walls in their spaced-apart positions.

Typically, in the case where at least one wall has an aperture e.g. for a door or a window, a brace is fixed across the aperture (e.g. diagonally) before the building unit is lifted. This may help to maintain the structural integrity of the building unit, as well as reducing cracking.

The floor panel may be connected to the wall panels by projecting bars that go through grouted formed holes or tubes in the walls. Additionally or alternatively, the connection may also take the form of cast-in steel fittings, in both the top of the floor and the bottom of the wall, such as anchored plates or tubes, which are eventually joined by welding.

Since the floor panel will effectively hang from the walls during handling, the connections are typically configured and spaced such that the crack width across that joint is limited to within 0.1mm. The design of the floor itself allows also for the imposed loads during normal use of the finished structure.

The wall-to-wall connections may take the form of cast-in steel fittings, in both abutting faces of the walls, such as anchored plates, which are eventually joined by welding.

Bolted connections may also be used, whereby studs with washer plates go through holes in one wall and connect to anchors in the other wall. The design of the walls themselves allows for the vertical and stability forces to be transferred through the structure. In that regard and depending on the height of the finished structure and its loading requirements, the building units may need to be tied together as well.

The roof to wall panel connection, where the edge surface of the wall is positioned against the inner face of the roof, may take the form of a bolted connection, whereby stud bolts go through grouted holes in the roof and connect to anchors at the top of the wall. For the case where the edge surface of the roof is positioned against the inner face of the wall, the connection may take the form of cast-in steel fittings, in both the side of the roof and the top of the wall, such as anchored plates, which are eventually joined by welding.

In a second aspect, the present invention may provide a building unit having a floor, a roof and at least four walls extending between the floor and the roof, each one of the floor, the roof and the walls being provided by an individually-cast concrete panel, the building unit further having anchor points, such that the building unit may be connected to lifting equipment and suspended from its anchor points, wherein the building unit is configured such that any cracks formed when the building unit is suspended from the anchor points and re-deposited are less than 0.3 mm in width.

The panels of the building unit according to the second aspect of the invention may have one or more optional features of the panels used in the method of the first aspect of the invention. Similarly, the panels may be joined using any of the arrangements described in relation to the first aspect of the invention.

Detailed description

The invention will now be described by way of example with reference to the following Figures in which: Figure 1 is a plan view of a building unit according to a first aspect of the invention, with the roof removed.

Figure 2 is a plan view of the building unit of Figure 1, with the roof in place.

Figure 3 is a cross-sectional view of the building units shown in Figure 1, stacked to provide a building structure.

Figure 4 is a cross-sectional view of a joint between the base and a wall of the building unit of Figure 2.

Figure 5 is cross-sectional view of a joint between the roof and a wall of the building unit of Figure2.

Figure 6 is a cross-sectional view of a joint between the roof and another wall of the building unit of Figure 2.

Figure 7 is a plan view of a joint between two walls of the building unit of Figure 2.

Figure 8 is a cross-sectional view of the back wall of the building unit of Figure 2, showing reinforcement details.

Figure 9 is a further cross-sectional view of the back wall of Figure 8, showing the anchor points extending within the wall.

Figure 10 is a cross-sectional view of the front wall of the building unit of Figure 2, showing reinforcement details.

Figure 11 is a further cross-sectional view of the front wall of Figure 10, including bracing elements for the apertures.

Figure 12 is a further plan view of the building unit of Figure 2, including chains for lifting the unit.

Figure 13 is a further plan view of the building unit of Figure 2, mounted on a trailer bed for travel.

Referring to Figure 1, the building unit 10 has a base 12 and six walls 14,16,18,20,22,24 upstanding from the base. The walls include a front wall 14 and a back wall 18, which together provide a first pair of opposed walls. Two cross walls 16,20 each extend between the front wall 14 and the back wall 18, to provide a second pair of opposed walls. The cross walls 16,20 and the front and back walls 14,18 provide external walls for the building unit 10.

The two remaining walls 22,24 are internal partition walls, which between them divide the building unit 10 into three sub-sections 26,28,30. The three sub-sections 26,28,30 provide a first prison cell 26, a second prison cell 28, and a service riser 30 for accommodating e.g. pipework.

The two internal partition walls include a cell partition wall 22 and a riser partition wall 24.

The cell partition wall 22 extends from the back wall 18 in the direction of the front wall 14 and abuts the riser partition wall 24. The riser partition wall 24 is integrally formed with the front wall 14, that is, it is cast in one piece, and is shaped to provide an arched structure extending from the base 12 of the building unit 10, along the inner surface of the front wall 14. Effectively, the front wall 14 and the riser partition wall 24 together provide a single panel.

The base 12 has a cut-out portion that corresponds to the cross section of riser 30.

Walls 14,16,18,22,24 are secured to base 12 by means of joints 31. The spacing of the joints 31 along the back wall and cross walls does not exceed I.3m.

Referring to Figure 2, the top cover slab 32 has a generally rectangular shape, but is configured to provide a cut-out portion 34, the shape of the cut-out portion 34 corresponding to the cross-sectional shape of the riser 30.

Each of the six walls 14,16,18,20,22,24 has an edge surface that faces away from the base 12. Of these edge surfaces, the edge surfaces corresponding to cross walls 16,20 and cell partition wall 22 are covered by the top cover slab 32. By contrast, the corresponding edge surfaces for front wall 14, back wall 18 and riser wall 24 remain exposed, i.e. uncovered by top cover slab 32. In fact, the inner faces of front wall 14 and back wall 18 are positioned against an edge surface of the cover slab 32.

Top cover slab 32 is secured to cross walls 16,20 and cell partition wall 22 by means of joints 36. Additional joints 37 secure the cover slab 32 to the front and back walls 14,18 and the riser wall 24.

The base 12, cover slab 32, front wall 14, back wall 18, cross walls 16,20, cell partition wall 22 and riser partition wall 24 are all made of concrete reinforced with steel mesh and/or reinforcement cages around apertures.

Referring to Figure 3, building units 10 are stacked to provide a building structure. Like numerals correspond to like features in Figures 1 and 2. The back wall 18 has two apertures 38a,b (only one is shown in Fig. 3), which provide windows for prison cells 26,28 respectively. The front wall 14 has two apertures 40a,b (only one is shown in Fig. 3), which provide doorways for prison cells 26,28 respectively.

Referring to Figure 4, the walls are secured to the base 12 by means of joints 31 comprising L-shaped bars 50. The L-bars have a first portion 50a extending into and along the base 12 and a second portion SOb extending into the wall. The second portion SOb of the L-bars is housed in grout tubes provided within wall. The grout tubes are grouted with fast-curing non-shrink grout, such as Tecro Speedsure. Gull wing bars 52 pass around the grout tubes and provide continuity of the reinforcement on either side.

Referring to Figure 5, the cover slab 32 is secured to the cross walls 16,20 and the partition wall 22 by means of joints 36 comprising a stud bolt 60 that passes through an hole 62 in the cover slab 32. The stud bolt 60 engages with an anchor 64 that is embedded in the wall. To prevent any splitting, U-shaped bars 66 pass around the hole 62, while gull-wing bars 68 pass around anchor 64.

Referring to Figure 6, the cover slab 32 is secured to front, back and riser walls 14,18,24 by means of joints 37 comprising cast-in fittings in both the wall and slab. Each cast-in fitting comprises a plate 70a,72a, each plate being welded to a respective anchor bar 70b,72b. Each pair of cast-in fittings from the slab and the corresponding wall is joined together by means of a further welded plate 74.

Referring to Figure 7, wall-to-wall connections are shown using the example of a joint 80 connecting the back wall 18 to cross wall 20. The joint comprises cast-in fittings in each wall. Each cast-in fitting comprises a plate 82a,84a that is welded to one or more respective anchor bars 82b,84b. Each pair of cast-in fittings from adjoining walls is joined together by means of a further welded plate 86.

Referring to Figure 8, the back wall 18 has apertures 38a,b to provide windows. The back wall has a thickness of 125mm and is cast vertically. It is reinforced by a steel mesh 42, shown in cut-away portions. Reinforcement cages made of longitudinal bars and links are used to reinforce the beams over and the columns between the windows.

Additional steel bars are also provided on the other edges of the apertures.

Referring to Figure 9, anchor points 92a,92b (also known as lifters) are located on either side of set of the two apertures 38a,38b. The anchor points comprise looped wires having an exposed looped portion that extends from an exposed edge surface of the wall, and an embedded portion that extends into the wall, past the apertures 38a,38b.

Referring to Figure 10, the front wall 14 has apertures 40a,40b to provide doorways for respective prison cells, and another middle aperture 40c for the riser. The front wall has a thickness of 125mm. Reinforcement cages 94 made of longitudinal bars and links are used to reinforce the beams over and the columns between the apertures.

Referring to Figure 11, anchor points 96a,96b are provided at the sections where riser wall 24 contacts front wall 14. The anchor points comprise looped wires having an exposed looped portion that extends from an exposed edge surface of the wall, and an embedded portion that extends into the wall, along the length of doorways 40a,40b.

Braces 97a,97b are provided diagonally across the doorways 40a,40b during the steps of handling and transportation of the building unit.

Referring to Figure 12, the building unit is lifted by connecting the anchor points 92a,92b,96a,96b on the front and back walls to the hook of a crane by means of chains 98a,98b,98c,98d. The connection between the anchor points and the crane hook is carried out such that during lifting, the crane is positioned directly over the centre of gravity of the building unit.

This allows the building unit to be lifted onto a trailer bed 100, as shown in Figure 13.

Key to Figures A -Bottom Slab -Connectors to walls B -lop Cover slab -Connections to walls C -Outline of top cover slab "dotted line" 0 -lop Slab supported on mid and end cross walls (110mm thick) E -Cover slab supported on mid and end cross walls (95mm thick) F -Continuity strip to screed G -Insulation Layer I cavity H-88 gull wing bars around grout tubes, 700 Lg J -612 projecting L-bars with 40 radius bend at locations.shown, into 40 1/Dia x 600mm deep grout tubes, holes grouted with tecro speedsure K-gap GPgrout L -M20 grade 8.6 stud bolt M -tapered hole in top slab 050-75mm, grouted N -10mm grouted joint P -288 U-bars around hole, 400 Lg 0-Rd20 combi anchor 183 Lg ref 6351-2.0-183 with 2-810 gull wing bars 500Lg R -lop slab to cross wall connection marked ® I -lop cover slab -connections to walls U -Top plate I O0x60x1 0 welded with 5mm fillet weld all around V -PIt 8Ox5OxlOmm, welded to 2-810, 400Lg bars with 5mm fillet weld EIS recess 60x100x30, grouted with Tecroc GP W -9 routed recess at top of wall X -lop slab to back and front wall connection marked Y -Wall to wall connections a no. per vertical joint Z -PIt 7OxlOOxj2mm with 2-6-12, 500Lg bars welded with 6mm fillet weld F/S AA -15mm gap, packed and welded F/S joint grouted 68 -4Oxl2Ox2Odp pocket to allow weld access on both sides CC -Back wall -reinforcement DO -Note: this wall shall be cast vertical. Thickness of wall 125mm FE -Links B8@100 FF -2-812 Top ElF 2-B-12 Bot ElF . GG -8503 mesh central :"i Fill 3-610 ElF JJ-1-B-12E/F : .. KK-B8links@Ioo LL -2-6-12 central under window MM -Reinforcement weight: 6503 mesh: 46kg; 612: 32kg; B10:10kg; 88 links: 11kg, Total = 100kg 4.1 % by weight of concrete *:*** NN-Backwall....rifters *...: PP -2-10 ton (2Dmm�xsm girth) open cast-in loop wires Halfen Ref P44VZMQ7 oh CL of * wall QQ -Note: Allow 2x1-M20 015 for propping RR -3-612 Top E/F 1-812 Bot E/F ll-2-BIOEIF UU-2-812E,p Key to Figures (cont.) W -1-625 across opening just for demoulding" WW-Reinforcement weight: A283 mesh: 33kg; 812: 50Kg; 610: 13kg; 625: 17; 68 links: 50 kg. Total = 163kg = 5.0% by weight of concrete XX -L60x60x6 brace across door opening fixed at each end with 2-M20 CIS. Brace to be fixed before first lift or handling of the assembled module, and shall only be removed after final erection on site. Note also that minimum concrete strength for handling of the assembled module is 30 N/mm2 VY -Note: Allow 2x1-M20 C1S for propping ZZ -Bottom slab 1k -Lifting of the assembled module 76 -Trailer bed ZC -Plank support ID -Travel * S S * *S

S * S * ** * * * ****

0Se555 * S 5S5.S * *

Claims

Claims 1. A process for supplying a building unit to a building site, comprising the steps of: providing at least six concrete panels, joining the concrete panels to provide a building unit having a floor, a roof and four walls extending between the floor and the roof, providing anchor points on the building unit, for allowing the building unit to be connected to lifting equipment, transporting the building unit to a building site and depositing the building unit in a pre-determined location, to provide whole or part of a building structure, wherein the step of transporting the building unit to the building site comprises the step of attaching the building unit to the lifting equipment such that the building unit is suspended from its anchor points.
2. A process according to claim 1, wherein the distance between the inner faces of the floor and the roof of the building unit is at least 2 metres.
3. A process according to claim I or claim 2, wherein the thickness of the concrete in the panels of the building unit is at least 85mm.
4. A process according to any one of the preceding claims, wherein the total weight of the building unit is at least 17000kg.
5. A process according to any one of the preceding claims, wherein the building unit is configured such that during lifting, transporting and depositing of the building unit, the maximum width of any cracks formed does not exceed 0.3 mm.
6. A process according to any one of the preceding claims wherein the building unit is configured such that each of the four walls has a roof-side edge surface that is proximate to the roof and that faces away from the floor, the roof being positioned in relation to the walls such that at least a portion of at least one roof-side edge surface is left uncovered by the roof, to provide an exposed surface.
7. A process according to claim 6, wherein one such exposed surface is provided on each of a first pair of opposed walls, at least two anchor points being mounted on each exposed surface.
8. A process according to claim 7, wherein at least one wall of the first pair of opposed walls has an aperture e.g. for a window or a door.
9. A process according to claim 8, further comprising the step of fixing a brace across the aperture prior to the step of lifting the building unit.
10. A process according to any one of claims 7 to 9, wherein the building unit includes a second pair of opposed walls that extend between the first pair of opposed walls, the second pair of opposed walls having longitudinal edge surfaces that extend from the floor to the roof, the longitudinal edge surfaces abutting the inner faces of the first pair of opposed walls.
11. A process according to any one of claims 7-10, wherein the building unit comprises a fifth wall extending between the first pair of opposed walls, the fifth wall providing a partition within the building unit.
12. A process according to any one of the preceding claims, wherein a first one of the panels comprises a cast-in L-shaped bar, the L-shaped bar being positioned such that one end protrudes from the first panel, and a second one of the panels comprises an elongate recess extending along the plane of the second panel, and wherein the step of joining the first and second panels comprises inserting the end of the L-shaped bar that protrudes from the first panel into the recess provided in the second panel.
13. A process according to any one of claims 1-11, wherein at least two panels comprise cast-in metallic fittings, the step of joining the panels comprising welding together the metallic fittings of two such panels.
14. A process according to any one of claims 1-11, wherein the step of joining the panels comprising providing a through-thickness aperture in a first one of the panels and further providing securing means embedded in a second one of the panels, and subsequently passing one end of a bolt through the through-thickness aperture of the first panel and causing the securing means to engage the end of the bolt.
15. A building unit having a floor, a roof and four walls extending between the floor and the roof, each one of the floor, the roof and the walls being provided by an individually-cast concrete panel, the building unit further having anchor points, such that the building unit may be connected to lifting equipment and suspended from its anchor points, wherein the building unit is configured such that any cracks formed when the building unit is suspended from the anchor points and re-deposited are less than 0.3 mm in width.