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Patent Searching and Data

Document Type and Number:
WIPO Patent Application WO/2012/106650
Kind Code:
A building system and method comprising a combination of pre-cast structural elements. Corner joints include a centering pipe. Stairwell Wall Blocks and Hollow Core Planks are used for stairs. Elements are assembled with joint pins and finger shear keys.

Application Number:
Publication Date:
August 09, 2012
Filing Date:
February 03, 2012
Export Citation:
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International Classes:
Foreign References:
Attorney, Agent or Firm:
YEAGER, Rick, B. (Austin, TX, US)
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What is claimed is

1. A method of assembling a structure from precast elements, the method comprising

forming a plurality of wall joints by providing wall elements with cast fingers, the cast fingers including pipe sleeves,

providing a centering pipe having a first end which is larger than the diameter of the centering pipe, and inserting the centering pipe through the pipe sleeves, such that the first end is retained by the uppermost pipe sleeve or with a stop pin.


INVENTOR: David W. Powell


This PCT patent application is related to US Provisional Patent Application No. 61/439,346 filed by applicant on February 3, 2011, and claims the priority of that application.


This invention is related to a building system comprising a combination of pre-cast structural elements. BACKGROUND- Description of Related Art

This document describes a number of innovations in the construction of high quality precast concrete buildings using the LadderBlock™ wall system that has been described in previous applications by applicant, WO 2007/134073 and WO 2004/033810, which are incorporated by reference in this application.

Conventional construction generally consists either cast-in-place construction with obstructive and costly formwork, or of interconnected stick or panel framing that relies on diagonal bracing or shear walls for lateral stability.

It is highly desirable to introduce a building system that allows design flexibility while offering vast simplifications in both design and construction.


This specification describes an example set of joint configurations, the assembly process for building each joint type, and a detailed process for assembling a building using the LadderBlock wall system. Steps in this process are repetitive, and are planned and sequenced with the aid of a 3D model that is used to produce 3D erection drawings that are clear and concise. This innovate building process is executed by a small professional crew that advances the work with confidence, safety, and speed.


FIGS. 1-164 show example construction elements, modules, and structures.


Wall Joint Details, Features, and Assembly The description of system features and methods will begin with a review of the basic joint types, and of the innovative tools and methods that facilitate the assembly of each joint. Descriptions are for standard wall thicknesses of 150mm at interior walls and 250mm at insulated perimeter walls, but other wall thicknesses and configurations are obvious variations of the described embodiments.

Corner Joint

The most basic wall joint is a corner formed by two intersecting walls. Figure 1 shows the components required to build such a joint: two wall ends with precision cast fingers that interlace shown at a 300mm vertical spacing with a standard vertical erection tolerance of 30mm between fingers. Joint details are shown here for a cutaway section, where each wall is cut at 500mm from the center of the joint, so this and following details generally show what can be thought of as a 1 meter square joint "building block". In reality, the wall continues to a similar joint at the far end of the wall, and may have intermediate walls framing into it between its ends. The finger joint configuration shown is for a floor to floor height of 3.3 meters, where the walls support 200mm thick hollow core. By simple manipulation of the number of fingers and the depth of the top and bottom finger in the pattern, the set of details shown here can be used to build a wall of any height. Ideally, heights are adjusted in 300mm increments by the addition or omission of whole fingers, but any intermediate height can be delivered by also incorporating partial height fingers.

In addition to the two wall ends, a centering pipe and a vertical rebar pin are required to assemble the joint. Figure 2 shows two panel ends with their fingers laced together and aligned to allow the insertion of the centering pipe, which is shown partially inserted here. Figure 3 shows the centering pipe fully inserted, the rebar pin inserted through the centering pipe and through all of the interlaced fingers. The rebar pin is shown with a coupler pre-attached to the top of the bar, as would be installed at a joint that aligns with a wall intersection at the level above. The pin simply drops into an oversized hole that is predrilled in the slab, and is grouted in after the erection is complete and the crane is off the site. Note that the finger joint pattern leaves a gap at the base of the wall. This gap offers access required to make the connection of the vertical pin to the foundation or other supporting structure, and is ultimately filled in the grouting process described below.

Centering Pipe

The centering pipe is a simple but innovative tool that works well with the LadderBlock wall system to enable a superior method for assembling a precast building, as described in detail below. The centering pipe is made with a short length of nominal 25mm (1") diameter standard (Schedule 40) steel pipe that is flared at its top end. It naturally nests (Fig. 4) with a consistent fit but little free play into the nominal 32mm (1 ¼") diameter standard (Schedule 40) steel pipe sleeve that is cast into each finger joint. Both pipes are typically of galvanized steel, although they could be of other materials. They end up encapsulated in grout that further protects them from corrosion.

Passing the centering pipe through the precision precast finger joints on two interlaced adjacent fingers (Fig. 5) serves three valuable functions. First, it gives an easy tool for the alignment and "docking" of interconnecting panels. When the joint in Figure 5 is built, the first wall is in place and braced, either by connection to another perpendicular wall or by diagonal braces to the floor. The brace is only required for the first wall erected at each level, and there only temporarily. The elimination of the need for diagonal braces to stabilize every wall, as is standard of conventional precast construction, means that this building system offers a much safer and more productive jobsite by eliminating these obstructions to work and safe passage. When the second wall is hoisted into place, its fingers are floating free within the joint as it is aligned and the centering pipe is stabbed into the top finger of the hoisted panel. The top of the centering pipe is flared to prevent it from falling through the top finger, and the flare also presents something of an oversized nail head to facilitate driving the top of the pipe down with a hammer, if that is required to fully seat the centering pipe. Centering two adjacent finger sleeves, each of which is precision cast monolithically within its wall, naturally forces the alignment of the newly placed wall as it is lowered to bear along a pre -marked line on its supporting surface.

The second function of the centering pipe then comes into play. By engaging two rigid fingers, the pipe serves as a lateral brace to both walls, so the crane hoisting lines can be released immediately and the crane can go pick the next wall block. For the joint to fail would require the shearing of the steel pipe across the gapped joint. Where analysis shows that the connection of especially large panels or the expectation of especially large lateral forces during construction might require it, longer centering pipes can be specified to engage additional fingers and additional pipe shearing planes. Properly engineered for a given application, the centering pipe yields a safe and stable joint immediately. This allows the grouting process, which further solidifies and locks the geometry of the joint, to follow on after the erection of the structure is complete and the crane is off the site. As crane time represents a major expense, this innovation offers significant cost savings in comparison with conventional precast construction.

As soon as the final wall has been installed at a joint, the centering pipe serves its third function - as a hollow conduit for the passage of the vertical rebar joint pin (Fig. 6). Alternatively, the centering pipe could accommodate steel strands to enable the vertical post- tensioning of the assembly.

A further innovation is introduced in the detailing of variable length centering pipes. By producing centering pipes in length increments that are designed to engage two, three of four fingers (Fig. 7) the alignment and assembly of three and four wall joints can be safely accomplished without the need for supplemental shimming or bracing of the joined walls. Centering pipes are provided with holes that accommodate a steel stop pin, shown here as a J hook. Figure 8 shows a "four finger" centering pipe that is lowered through a cutaway section of the two topmost fingers of what will ultimately be a four wall finger joint. The centering pipe is held at that height by the stop pin so that it does not extend into the open joint, which awaits the insertion of the third wall. Once that wall is hoisted into position, the stop pin is moved to the next hole up on the centering pipe, which is lowered into the newly aligned third wall (Fig.9). When the fourth wall (shown in wireframe view in Figure 10) is hoisted into the joint, the stop pin is pulled and saved for re -use, and the centering pipe is lowered fully to engage the fourth finger and wall. Then the rebar joint pin is inserted, and work moves to the next joint to be assembled.

So each structural joint is built in three stages: it is positioned and temporarily braced by the centering pipe, it is threaded through with a continuous vertical rebar pin that is ultimately tied to the foundation, and then it is grouted solid to perform like monolithic construction, but in a fraction of the time and at a lower cost.

Insulated Corner Joint Where the corner joint of Figure 3 occurs at an exterior wall, the preferred embodiment of this system provides an insulated sandwich panel with an exterior concrete face. Figure 11 shows the components required to build such a joint. In this embodiment, the insulation and exterior face of wall nest into a 100mm deep ledge formed in the ground slab. This improves the water resistance of the assembly and serves to extend the insulation to below the floor level.

Figure 12 shows the two walls assembled and braced by the centering pipe, and Figure 13 shows the vertical rebar pin and coupler installed. As an alternative to the joint covers described in previous applications, this embodiment of the invention eliminates the joint cover by extending the insulation and exterior face of concrete as shown.

Two wall T Joints

A common T joint between two walls, one continuous and one intersecting, is shown in Figures 14 through 16. One insulated version of this joint, which forms a typical re-entrant corner in the sandwich wall exterior face, is shown in Figures 17 through 19.

Three Wall T Joints

The components required to build a three wall T joint are shown in Figure 20. These include the three walls, a four finger centering pipe, and the vertical joint pin. Although other assembly methods are possible, the preferred method places the wall with the topmost finger in the joint first (Fig. 20). Figure 21 shows the second wall, which offers the second finger from the top, installed. The centering pipe is installed through the top three fingers in the joint with the stop pin holding it above the gap that awaits a finger from the third wall, shown installed in Figure 22. Figures 23 through 25 show a comparable assembly of a three wall insulated T joint.

Three Wall X Joint

Figure 26 shows a joint configuration for walls that form a crossing or "X", where one wall is continuous across the joint and two others connect into the joint. Again, the first wall to be erected is typically the one that present the uppermost finger in the joint (Fig. 26). As with the three-wall T joint, the assembly of this joint utilizes the four finger centering pipe as shown in Figures 27 and 28.

Four Wall X Joint

Where four separate walls all connect into the same joint, the centering pipe is a great facilitator of the work. Figure 29 shows the first two walls in place, with the four finger centering pipe dropped into two fingers, waiting for the third wall to be set in place so the pipe can drive down into the third finger, as shown in Figure 30. The fourth wall is centered using the centering pipe to complete the joint (Fig. 31). Note the two formed recesses in the base of the third and fourth walls. These combine to provide access to the wall base connection of the vertical pin, and standard wall base blockouts provide similar access at each joint that would otherwise be enclosed and inaccessible. The wall base blockouts will later be filled in the grouting process, and will then generally be concealed by a depth of floor screed and a baseboard or skirting.

Beam End on Corner Joint It is a common condition for a beam to frame into a wall corner. The beam end shown in Figure 32 will more often than not be the free end of a beam that is a cantilevered extension from another wall block, or it could be an independent precast beam. In either case, the free end of the beam is generally placed on a bearing pad that is of the same 30mm thickness as the erection tolerance between fingers. The joint around the pad is then typically filled in the grouting process. Figure 33 shows the beam in position, and the three finger centering pipe inserted into the top joints and held at that level by the stop pin. The assembly is completed as shown in Figure 34.

Beam Cantilevered from Corner Joint

A similar joint occurs where a beam intersects a wall corner, but cantilevers from it as an extension of the wall rather than framing into it as a separate element, as shown in Figure 35. Figure 36 shows the two walls aligned and braced by the centering pipe, and Figure 37 shows the rebar joint pin installed.

Beam Continuous over Wall Joint

Where a beam crosses the end of a wall, and where the vertical tie down of that wall to the supporting structure is desired, the joint can be built with the components shown in Figure 38. Figure 39 shows the beam set and positioned with the centering pipe, which is shown not yet fully inserted. The vertical tie down of the assembly to the foundation is provided through a vertical sleeve in what is effectively a single tall finger, as shown in Figure 40.

Simple combinations or obvious variations of the corner, T, X, and beam joints described above are sufficient to build any wall structure.

Stair and Suspended Floor Construction

Stairwell Wall Blocks

An example of a precast stairwell that is built using the joint details described above is shown in Figure 41. The upper level walls appear to float in this image because the hollow core planks, upon which the upper walls bear, are omitted from this view to more clearly show the walls.

These walls are joined like any other, but they carry added features for support of the precast stair units. Note the horizontal slots in the back wall of the stairwell, where the landing will be. These slots are held back from each corner of the stairwell to avoid interference with the wall joint. To provide erection tolerance, they are 25mm taller than the precast "tongue" that extends from the each precast stair landing and bears in the slot. Also note the holes formed in the tops of the beams and wall at the front of the stairwell, and the hole drilled in the slab at the center of the ground level stair entrance. These are to receive vertical rebar pins that will be dropped into sleeves in each precast stair unit as it is erected, and are later grouted.

The other key feature of these walls yields the closure of the continuous horizontal wall joint within the stairwell as shown. Note that the tops of the back and side walls shown in Figure 41 are raised, over the full width of the back wall and the inner half of the side walls. The height of the concrete curbs shown on each sidewall is equal to half of the hollow core depth and half of the wall width, so these curbs are 100mm high and 75mm wide. The back wall is raised across its full width because it effectively has a curb on both faces; it is a dividing wall between back-to-back stairwells. Each of the upper walls also has a similar extension of its base, so the curbs bear on one another at mid-height of the hollow core floor that surrounds them.

Precast Stair Blocks

Figure 42 shows a set of precast stair blocks in what would be their supported positions, but the walls have been omitted for clarity. This set uses three block types: the ground floor stair, the upper floor stair, and the return stair. The ground floor stair block has a squared first riser and a vertical base extension below the typical riser height, where the extension depth is equal to the height of the planned floor screed. This yields a first riser height that is the same as remainder of the risers. The ground floor stair block also has a precast bearing tongue extension that inserts into the back wall for support as described above. The tongue is notched at the left edge with a horizontal erection tolerance relative to the slot in the back wall. The upper floor stair unit is identical, except that its base extension reaches down to the support beam that is omitted from this view. The full width of the stair unit bears on the supporting beam or wall, but it must share the bearing surface with the hollow core that builds the floor at each level, so it stops just short of the beam or wall centerline. At the center of each precast stair unit, a dowel tongue extends another 75mm to cover the full width of the supporting beam as shown. The dowel tongue is cast with a sleeve that receives the vertical pin described above, and the abutting hollow core units are notched with an erection clearance to receive the tongue. Two return stair units are shown in Figure 42. They extend from the mid-height landing to the floor level above; they feature a dowel tongue that is similar to that of the upper floor stair block (Fig. 43), and a bearing tongue at the landing that is notched in symmetry with the other stair blocks (Fig. 44).

The top edges of upper floor stair and return stair units are detailed to interface with the hollow core planks that share their supports (Fig. 45), and they top out at an elevation that is above the top of hollow core by a height equal to that of the planned floor screed. Figure 46 is a cross section that shows the pinned and bearing connections that support the precast stair units; where a single stairwell is being built, the back wall notches extend only halfway through the wall as shown. Where back-to-back stairwells are being built, as in a duplex or office arrangement, the back wall features a full slot to receive precast landing tongues from both sides of the wall (Fig. 47).

Hollow Core Planks

Hollow core planks are supported on bearing surfaces presented by the tops of wall panels at the level below. Planks bear on wall blocks at each end, and are generally detailed to lap over intermediate walls and the edges of parallel end walls (Fig. 48). Hollow core planks are typically notched in the factory at each location where a wall joint occurs to provide a chase for the spliced connection and grouting of the vertical rebar joint pins (Fig. 49). Before shipping from the factory, hollow core cells that are exposed at cut ends and notches are plugged or otherwise sealed where required to prevent inflow during the grouting operation.

At interior conditions, the upper walls bear on the hollow core planks (Fig. 50). But at perimeter walls, the hollow core planks bear in a ledge that is formed by wall panels that bear end to end, as shown in Figures 51 and 52. Similar conditions occur at continuous interior walls, such as at a stairwell or atrium space. Figure 53 shows a hollow core panel bearing at a roof corner. Parapet Wall Construction

Two parapet wall construction types are described here, for walls of significant height and for short extensions of the uppermost wall below. Taller parapet wall construction will be covered first, with short extension details to follow.

Parapet Wall Corner

Where an aligned parapet face is desired above an insulated corner joint, as shown in Figure 54, the parapet corner can be easily constructed using the pilastered parapet wall end joints shown. These maintain a strip of wall on either side of each joint that shares the full 250mm thickness of the insulated wall below to form corner pilasters. The wall shown is thinned to 100mm between ends, except for a bottom of wall horizontal lug. With that lug, the base of the parapet wall matches the 175mm width of insulated wall below where it passes outside of the 75mm wide hollow core ledge. Figure 55 shows the first wall set in place. As before, it is braced by a connection to another wall elsewhere along its length or, if it is the first wall at this level to be erected, it is braced with temporary diagonals. The inside view of the complete parapet corner joint is shown in Figure 56.

Parapet Wall Reentrant Corner

The same rationale drives the configuration of parapet wall blocks at a reentrant corner, as shown in Figure 57. The first block of the joint is set in position in Figure 58, and the completed joint is shown in Figure 59.

Parapet Wall Pilaster - 2 Wall

At an insulated T joint that is formed by two walls, as is shown in a two story stack in Figure 60, the parapet wall above might simply run past this joint and span horizontally to its ends or to other intermediate wall connections. But if additional strength or stiffness is required to resist code specified lateral forces, a pilaster can be provided as shown in Figures 61 and 62. Unlike a typical wall block that frames into other joints, the pilaster, by definition, has no other wall end to anchor it. Engineering analysis is required for a given condition to determine the anchoring requirements of the pilaster. It might be anchored with grout that comes later into a blockout in the hollow core planks as indicated here, or higher load capacities can be generated by anchoring the pilaster into an aligning wall below. Because pilaster walls may rely on grout that has not yet been installed for their anchorage, temporary loads and stability must be analyzed for the condition during construction when the pilaster is unanchored. On the basis of that analysis, temporary bracing or mechanical anchorage to an underlying wall can be detailed for applications that require it.

Parapet Wall Pilaster - 3 Wall

The same joint as that just described, but with two separate parapet walls framing into a pilaster wall, is shown assembled in Figures 63 through 65. Because of the simple nature of parapet walls, a combination of corners, re-entrant corners and T or pilastered joints are all that is typically required to build any parapet of significant height. Parapet Wall Extension - Corner

Simpler still is a parapet that rises only a short distance above the structural deck, as might be used on an inaccessible roof. This can be built with a simple vertical extension of the top of each wall panel. In this case, the parapet is not a separate precast element but a monolithic extension of the insulated wall block below. The components required to build a corner joint of such wall blocks is shown in Figure 66. The two joining walls are shown assembled in Figure 67, and Figure 68 shows how the hollow core plank bears on the ledge created by the walls.

Parapet Wall Extension - Reentrant Corner

The companion joint for a reentrant corner is built with the components shown in Figure 69. Those components are shown assembled in Figure 70, and interfacing with hollow core planks in Figure 71.

Joint Treatment

As assembled set of these wall blocks will produce a continuous vertical joint (Fig. 72) between ends of abutting walls. It also presents a continuous horizontal joint at each interface of stacked wall blocks (Fig. 73), and at the foundation ledge below where the ground level wall blocks bear (Fig. 74). These joints are shown with square panel edges, but edges will more commonly be mitered to make them more resistant to chips and spalls. The horizontal and vertical joints are ideally sealed with backer rod and elastomeric joint caulk that accommodates movement with changes in wall temperature, but they might also be mortared or grouted at the discretion of the design professional. Details are offered below regarding the sealing and grouting of joints. Significant value is delivered by the fact that these processes can all occur after the crane is off the site.

Building Blocks Applied

The details described above constitute a joint-based set of building blocks that make the design of a building using this system quick and easy. Consider the intersection of two wall centerlines s on a desired architectural plan as a construction node. It is only necessary to place the appropriate building block at each construction node (Fig. 75), and then join the blocks with wall segments that are penetrated with appropriate door and window openings (Fig. 76), to produce a 3D model for any floor plan that is desired. Then using the details described above, hollow core planks and upper wall levels are added to the model (Fig. 77), the main roof is surrounded with a high parapet, and the penthouse walls are provided with a low parapet extension (Fig. 78). The final step in the refinement of the model shown is to detail the mechanical, electrical, and plumbing features: blockouts, conduits, and junction boxes that will be cast into each building block. The resulting model is then translated into precision precast parts in the factory, and delivered to the jobsite ready to erect. Detail is provided below regarding the steps required to build this structure, but that will come after taking a closer look at the structural connections. It is the innovative connections of this system that enable the speed of construction and tie the building blocks together to yield a building with strength and structural performance that is superior to conventional precast. Structural Connection Details

Joint Pin

As previously described, the LadderBlock wall system interlaces precision precast concrete fingers from two or more panels and then pins them together with a vertical rebar joint pin (Fig. 79), shown here without the centering pipe described above but with a bar coupler at its top end.

Now imagine these walls being twisted and pulled apart. Consider the work required to pull a single interior finger out of a joint (Fig. 80). Two grouted joints would have to fail, and then one large diameter reinforcing steel bar would have to shear on two planes (Fig. 81). Or the concrete finger itself would have to fail, including the failure of reinforcing steel hairpins that wrap around the sleeve in every finger and extend back into the wall panel (Fig. 82). Now multiply that high failure strength by as many as five, but no fewer than two fingers that extend into the joint from each wall. Recognize that those fingers are separated by a large distance that acts a lever arm in resistance to collapse. The resulting high joint strength is provided very cost effectively, and can be won without sacrificing the speed of construction that distinguishes the LadderBlock system. In a completed structure, dozens of these joints work in unison at every level to ensure the strength and stability of the structure.

Finger Shear Keys and Tie Wires

Two features of the typical precast finger play directly into the strength of the joint, but have no impact on fit up, so to manage CADD model file sizes these features are not detailed in the typical 3D models. The unseen features are grout form tie wires and optional finger joint shear keys (Fig. 83). The tie wires occur at the same three levels in every joint, near the top, middle and bottom of the wall as shown. The wires are embedded into the fingers that occur at these three levels in every joint, and they are used to secure the temporary grout forms as described below. The optional shear keys that are precast into each finger (Fig. 84), shown here in the form of truncated cones, are of a more structural nature. These facilitate grout flow up through the joint as the joint is being filled, and then they produce keying action between the fingers - so that the joint cannot be pulled apart without shearing the grout that fills the keys. This feature enhances the strength and interlocking action of the joint. Additionally, the faces of each finger may be roughened or cast with intentional texture to enhance grout bond within the joint and on exposed joint faces.

Ground Slab Connection

As mentioned above, the bottom of every vertical rebar joint pin drops into a hole that is predrilled in the slab (Fig. 85), and the bar is grouted into the hole to develop its strength after the erection is complete as described below. At an X joint, and at perimeter wall joints where the base connection would otherwise be inaccessible, standard wall base connection access blockouts (Fig. 86) are provided.

Pin Coupler

Where two or more stories of this structure are stacked, the wall joints that align from level to level are provided with continuous vertical reinforcement using standard bar couplers (Fig. 87). At discontinuous joints, the tops of joint pins might simply terminate and then be encased in grout, or where analysis indicates the need, the top of these bars can be terminated with an anchor that develops the strength of the bar (Fig. 88). Similarly, a discontinuous wall that is supported on a hollow core plank span and requires base anchorage can have its joint pin fitted with a bottom end anchor that is grouted into the floor to develop limited uplift resistance; Figure 89 is a view from below that demonstrates this concept.

Stair - Landing Wall Support

Precast stair blocks are built slightly narrower than the stairwell walls that house them to preserve the necessary erection tolerance. They are hoisted into position to first engage the notch in the back wall of the stairwell at the landing level and gain a bearing support there (Fig. 90). At back-to-back stairwells, the stair landing precast tongues engage the full depth slot in the back wall to gain bearing just short of its centerline (Fig. 91). This leaves an erection tolerance that avoids conflict with the abutting landing on the far side of the wall.

Stair - Entry Wall Support

Once the precast stair block is lifted into position and bearing is gained at the landing, it is lowered to gain support at the stair entrance from either the ground slab or a structural wall or beam (Fig. 92). Stair blocks are doweled there to restrain lateral movement in the interim before the hollow core planks and floor screed, if any, is installed.

Hollow Core Support and Confinement

At every level, the hollow core planks transfer their gravity loads directly through bearing on the precast wall panels. Lateral loads are transferred through the grouted interlock and confinement of hollow core diaphragms. When the hollow core planks at a given level are fully erected, they are confined within a perimeter of interconnected precast walls that extend vertically to the mid-depth of the plank (Fig. 93), and by the continuous vertical walls in stair wells and atrium spaces. This is in addition to the shear capacity of the grouted vertical cells which occur at every wall joint and are reinforced with continuous vertical bars (Fig. 94) or post-tensioning strands.

Following conventional practice, the keyways between hollow core planks (Fig. 95) are grouted as described below to establish diaphragm action, and to force load sharing so the planks act as a slab unit. At the discretion of the specifying engineer, the keyway can include reinforcing steel. A reinforced structural screed can also be specified to develop composite action and significantly increase both gravity and lateral load resistance of the floor.

Parapet Wall Connections

The assembly of precast parapet wall blocks is described above. Figure 96 shows a typical parapet wall corner. In this example, the top of the rebar joint pin is fitted with an end anchor. As described above, the joint pin is also tied at its base by a standard bar coupler to the joint pin below. When the joint is grouted solid as described below, the result is an interlocked parapet structure whose walls bear directly on supporting structure and span horizontally to deliver lateral loads to perpendicular walls or pilasters. This independently stable system of parapet walls is tied down at every joint with a continuously reinforced and grouted vertical core.

In building a long, tall parapet wall along a straight face that offers no perpendicular walls for lateral support, the parapet wall joint may require a pilaster as described above. Figure 97 shows the base of a parapet pilaster joint. The figure shows the pilaster block with notches at both edges for base connection access, leaving a center foot that reaches down to bear on the hollow core roof deck. In the foreground is shown the vertical bar in the pilaster with an end anchor penetrating down into what will be the grouted core. At this location, the plugs that prevent the flow of grout into the hollow core cell could be pushed down the cell a short distance. The resulting grout plug within the hollow core cell could be reinforced if needed, and would serve to engage more of the deck in providing uplift resistance to the pilaster.

Wall Shear Key Option

In building assemblies that are tall or are subject to large lateral forces, supplemental features may be required to transfer shear forces downward through the structure. One option available to the design engineer is the addition of keying elements at the top and bottom of selected walls to achieve additional interlock and shear interface across each level, as shown in Figure 98. The ground slab at this location is thickened, and the dowel hole for the joint pin is drilled into the bottom of a slab blockout that is oversized to provide erection tolerance for the precast wall. Extensions of the bottom of the wall then fit into the slab blockout, and top extensions interface with similar oversized blockouts on the hollow core planks that bear on the wall (Fig. 99). Upper walls can be configured similarly (Fig. 100). As with any wall, these could be precast with supplemental sleeves that house additional continuous vertical reinforcement or post-tensioning strands, if required for a given application.

The 3D models are of high value in designing a structure with features such as these shear keys, as the models facilitate the sequencing and study of the erection process to avoid potential conflicts. They demonstrate that the installation of a wall with a keyed base into an existing joint would require an oversized floor blockout to avoid a conflict, as the base key extension would otherwise tend to prevent the alignment and interlacing of the fingers. So in general, a wall which features base shear keys such as those shown should be the first wall erected at the joint, and then receive other standard wall ends to complete the joint. Where multiple keyed ends must frame into a joint, floor blockouts can be oversized as required to enable their assembly.

Temporary Diagonal Brace Connection

Any standard diagonal brace that is common to precast construction could be used with this system, but because the system generally requires only one wall to be braced per floor level, it is convenient to build dedicated braces for each wall height and incorporate simple connections that are consistent with the building system. If the same steel pipe sleeve that lines each precast finger is taped over and cast into the top of the wall at a standard distance from the joint (Fig. 101), then the same centering pipe that is used to erect the structure will slide cleanly into the resulting dowel hole. If that centering pipe is, in this case, welded into a simple bent plate and pipe diagonal brace assembly (Fig. 102), it serves as a quickly established and easily disassembled top connection for a temporary diagonal brace. The top end of the brace is pinned to the wall by dropping the brace into the sleeve, and the bottom end is then field drilled and secured to the slab or hollow core plank with an expansion bolt per standard practice.

Temporary Top Brace Connection

Where analysis shows that the connection of especially large walls, the expectation of especially large lateral forces, or other factors might require it, a temporary top brace can be specified to engage two panels independent of the centering pipe connection. The temporary top brace utilizes the same connection strategy as the temporary diagonal brace: steel pipe sleeves at a standard distance from the joint (Fig. 103) to receive a brace that utilizes centering pipe dowels. But in this case the centering pipe is at both ends of a short steel angle (Fig. 104). To eliminate the tendency for the brace to bind up when being installed or removed, only one of the two centering pipes shown is welded into the top brace assembly. The other is loose, so it may be inserted and pulled independently.

Concrete to Concrete Joints

Where the ground floor wall blocks bear on the ground slab, the wall blocks are set on shims that compensate for what is expected to be an inaccurately cast slab and provide level and consistent bearing points. The gap between shims is closed by floor screed, or may be grouted in cases where the ground floor does not receive a screed. At upper levels of the structure, where precision precast wall and floor building blocks bear on one another, the same approach could be taken to the bearing joints. But in the preferred embodiment, each bearing surface in the superstructure is lined with a thin continuous strip of adhered bearing pad material (Figs. 105 through 107). The bearing pads are installed just before erection, or may be installed before leaving the factory if the travel distance is short.

Wall Thickness Options

Although the standardization of wall thickness offers simplicity that supports consistent quality and real economy in the manufacturing process, there are situations that demand non-standard wall thicknesses. The entire system described here could be built to any scale, but the tooling costs and design complexities of doing so would represent a significant additional expense. The preferred approach to non-standard wall thickness is to pursue an option that maintains the standard finger joint dimensions. Producing variable wall thicknesses can be done most economically if at least one face of the wall remains a standard flat face. With those objectives in mind, three examples are offered to provide thinned walls for differing conditions.

Figure 108 shows a four wall joint where the two walls at the far side of the joint are of standard 150mm thickness, and the two nearer walls have each been thinned to 100mm in the field of the wall by using a 50mm thick coffered form on a flat casting table with standard shuttering. The far side of the thinned walls remains flat, and is the troweled top surface in the manufacturing process. As shown, the thinning of these walls leaves a full thickness band at the perimeter of the wall, protecting the strength of the finger joint and presenting a top of wall that is still wide enough to be the bearing surface for end to end hollow core planks.

Where the full top width is not required because planks do not abut over a given wall, the walls might be thinned as shown in Figure 109. In this example, the walls thin to 100mm after leaving a full thickness pilaster adjacent to the finger joint, shown here as a 150mm wide vertical strip on the face of the wall. As with the previous example, this could be cast using a void form in a standard form set. Or it could alternatively be cast with the far, flat face down by using 100mm shuttering for the top and bottom edge in combination with a standard finger form and a hanging top form at the change in wall thickness.

The third thinning strategy is intended for non structural walls. Here, the full-thickness band adjacent to the finger joint is abandoned, and the whole face of wall is thinned to 100mm. The fingers themselves maintain standard dimensions so they can complete the finger joint, and are offset from the wall centerline so that they project from one face of the thinner wall. The two nearer walls that have been exploded out of the joint in Figure 110 have been thinned in this manner. The walls are assembled into the joint in Figure 111. Note that if the thinning is applied radially about the joint as shown in these figures, the corners of each room remain square after the joint is grouted. Note the 50mm offset between walls at the thinned face and the absence of any projections or corner pilasters, so that the thinning of the wall is transparent to the finished space.

Although each of these thinning options may be suitable for certain applications and will save material and weight, those savings can be more than consumed by the increased complexity in layout, design, and manufacture of the walls. These factors must be considered in determining the overall economy of pursuing a thinned wall solution strategy.

LadderBlock Wall System - Assembly Method

This is an overview of the LadderBlock wall system erection process. Steps in this process are repetitive and are sequenced with the aid of 3D erection drawings. The LadderBlock erection process is executed by a small professional crew that advances the work with confidence, safety, and speed.

Preparation Phase o LadderBlock engineer coordinates and distributes slab interface plans and details during design. These specify critical dimensions and rebar clearance at drilling locations for integration into foundation engineering and construction by others.

o LadderBlock engineer performs pre -pour observation of slab on grade. Objectives are to spot check critical dimensions and confirm that rebar is clear of drilling locations in accordance with the slab interface plans. o Once the slab is cast and forms are stripped, LadderBlock slab prep crew verifies that as-built

dimensions of the slab conform to slab interface plans, and confirms that ground slab and foundations built by others are ready to receive structure.

o Slab prep crew lays out vertical pin dowel points and face of wall lines on slab (Fig. 112). o Slab prep crew drills, cleans and caps oversized dowel hole in slab for each vertical pin (Fig. 113). o Slab prep crew surveys setting points for ground floor walls and installs standard plastic precast shims as required to provide consistent stetting level for first floor wall blocks - tape shim stacks in position (Fig. 114)

Erection Phase

Steps outlined in this phase are performed by an erection crew consisting of a crane operator, trailer man, pin man, and two floor men. Multiple cranes and crews can be employed to multiply the speed of construction progress. o Ship and offloaded wall blocks in sequence to enable each block to be immediately erected when it is picked (Fig. 115). Hoist first wall block into position and install diagonal braces to slab (Fig. 116)

Pin man gets into position at end of wall, with centering pipe ready. Centering pipe can be pre-loaded into the top finger of the first block erected at each joint before it is hoisted, and vertical rebar joint pins can be preloaded into the fingers of the completing block of each joint.

Hoist second wall block into position, and install centering pipe by aligning holes in adjacent top fingers and lowering pipe through the two finger sleeves (Fig. 117). Second wall is now laterally braced to first wall by the centering pipe pinning the top two fingers together. Confirm alignment of the base of the wall with its slab layout line, and immediately release hoisting lines so the crane can swing into position to pick the next block.

Floor men confirm that grout form tie wires extend from finger joint in the specified directions (Fig. 117).

Hoist third wall block into position, align top finger with centering pipe and lower pipe to engage the third finger and wall block in the joint (Fig. 118).

Erect fourth wall block by the same process. As this wall completes this joint, lower the vertical pin through the centering pipe and finger sleeves (Fig. 119), and into the slab dowel hole below.

Erect fifth and subsequent wall blocks by the same process (Figs. 120 through 124).

Upon completion of ground level walls, set precast stair blocks, and remove diagonal braces in preparation for re -use when first wall at next level above is erected (Fig. 125).

Set first floor hollow core slabs in position (Figs. 126 through 128).

Lay out face of wall chalk lines for first floor walls on first floor hollow core slab (Fig. 129).

Hoist first wall block of level above into position and install diagonal braces to hollow core slab (Fig. 130).

Erect subsequent wall blocks at this level using methods described above (Figs. 131 and 132).

As each joint is completed, connect ends of vertical pins at continuous joints with standard bar couplers (Fig. 133).

Erect remaining wall blocks and precast stair blocks at this level by the same process described above (Fig. 134).

Remove temporary brace and set aside for reuse, and begin setting next level / main roof hollow core slabs in position (Fig. 135 and 136).

Complete installation of roof planks, and lay out face of wall chalk lines for non-aligned walls on main roof hollow core slab (Fig. 137). o Hoist first wall of next level into position and install diagonal braces to hollow core roof slab (Fig. 138). o Erect subsequent walls using steps described above (Figs. 139 and 140).

o Remove temporary brace to avoid conflict with penthouse wall, and continue erecting penthouse and parapet walls (Figs. 141 and 142).

o Set penthouse roof hollow core planks in position (Fig. 143) to complete the erection of precast


o Thread ends of vertical pins at parapet wall joints into bar couplers as each parapet wall joint is

completed; tops of pins can be pre-fitted with bar end anchors (Fig. 144) if required by analysis. o Parapet walls resist wind by spanning horizontally to wall ends that are braced by intersecting walls or pilasters (Fig. 145).

...Crane and erection crew are now free to move to next project site.

Grouting Phase

o Fill all slab dowel holes (Fig. 146) with grout (Fig. 147) to anchor vertical joint pins at each wall joint, and grout all stair entry dowel connections at the ground slab and at walls above.

o Hollow core slab joints (Fig. 148) are grouted at each level (Fig. 149). o Seal exterior wall joints with backer rod and caulk (Fig. 150). Note that two lines of backer rod are shown. One is pushed deep into the joint as a dam for the subsequent grouting operation, and the other is pushed a standard depth from the outside face into the joint to back up the caulk or other elastomeric sealant. o Feed tie wires through grout corner and face form slots (Fig. 151), then tighten and secure wires to seal forms tight against the wall blocks (Fig. 152), ensuring that each form is pulled tightly into the joint near the top, mid-height, and bottom of the wall (Fig. 153).

o Fill each finger joint with flowable grout - pump through form pump slot provided in base of corner form (Fig. 154), or gravity tube feed the joint with grout from above. Joint is pumped from the bottom as shown in the preferred embodiment. o Install form slot wedges to seal holes as grout level overtops each tie wire slot (Figs. 155 and 156).

Reusable wedges in the preferred embodiment are precision cut from neoprene or other suitable elastomeric sheet material whose thickness matches the form slot.

o Install form top wedges as grout level overtops form top slot (Fig. 157). Top wedges may be precut from elastomeric sheet, or may optionally be of plate steel or other material that can be hammered into a tight slot. o Disconnect grout pump and immediately install form pump slot wedge (Fig. 158), then move hose and pump head to the next joint. Reusable wedges in the preferred embodiment are precision cut from neoprene or other suitable elastomeric sheet material whose thickness matches the pump slot.

o Strip forms as soon as grout reaches stripping strength (Fig. 159). Grout forms can provide edges that are flush as shown, or they could provide mitered edges or other aesthetic treatment.

o Cut tie wires within grout void formed by slot wedges (Fig. 160), and then fill voids flush with

compatible grout mix.

o Immediately tool, clean and finish joints with compatible grout mix. Grout mix could take a number of forms; one option being a fiber reinforced pumpable mix whose strength is based on engineering requirements. o Where expandable, reconfigurable, or demountable construction is required, "soft grout" joints can be engineered to enable disassembly. This is accomplished by using grout that offers enough strength to resist Code specified forces in the assembled joint, but which is intentionally soft material in comparison with the structural concrete of the walls and fingers. This is to enable pin and grout removal without damage to the walls.

It should be noted that, once a given level of walls is erected and capped with a hollow core deck, it is feasible and safe to begin grouting work at that level even before the remainder of the erection is complete. So grouting of ground level walls can commence in parallel with erection of the next level of walls above. The grouting crew is protected by the hollow core platform above them from the ongoing erection work, and the work space is clear of the braces and shoring that would congest a conventional precast project and make this concurrent work impractical.

Finish-out Phase

Work required by others to complete the villa may begin concurrent with Grouting Phase. Conduit floor runs are connected to vertical runs that are precast into each wall block, as shown for a representative stack of two rooms depicted in Figure 161. Floor runs connect at precast wall blockouts to wall conduit and through hollow core penetrations as shown in the wireframe view of the same rooms (Fig. 162). Screed and flooring is then installed at each level (Fig. 163). The installation of doors, windows, roof insulation and membrane yields a dried-in building ready to finish. Then remaining plumbing, wiring, tile work, surface treatments, fixtures and cabinets are then installed to complete the construction process.


This system redefines the building construction process, and in doing so offers extraordinary speed, safety, strength, and quality. It enables the construction of a complete precast building (Fig. 164) in days, where conventional precast would take weeks and cast in situ construction would takes months. It yields a stronger, better performing structure, and does so with unprecedented precision.