This is our second session of this special inspector training. As I said last time, the following presentation is intended to provide potential special inspectors with an overview of precast concrete fabrication and erection. We are going to look at how precast concrete structures are built and focus on those items which are critical to the successful erection of a precast concrete building. While the program is targeted towards special inspectors, it is important to note that much of the material presented here may be considered outside the normal scope of the inspector's work. This information is presented here in an effort to offer a broad informational overview of precast concrete construction. In our previous session, we covered areas one through six in which we looked at the code requirements, the types of precast concrete structures, types of precast concrete components, a general overview of the precast concrete manufacturing process, the documents required for effective inspections, and how to look at precast concrete components to get an assessment of their condition as they arrive on the job site. Having reviewed the precast concrete fabrication, erection drawings, erection plans, and component condition assessment, we are now going to look at the actual erection process and what considerations are paramount to making sure a precast concrete structure is properly assembled. For the purposes of this program, those considerations are going to be broken down into these four areas. Types of precast framing, the preparation of cast and placed concrete foundations, the bearing conditions, and the connection of precast concrete components to each other and their foundation. We're going to be primarily looking at the primary types of precast framing to begin with. The type of framing utilized for precast structures will play heavily into the types of connections used. The three systems listed here refer to the method used to create the floor systems within a precast concrete building. Wet is typically used to define a floor system that incorporates some amount of cast and placed concrete after precast erection. A field topped wet system will include a cast and placed topping over the entire floor area. A complete dry system, as the name suggests, requires little or no cast and placed topping. A partial wet system includes a narrow band of cast and placed topping, often referred to as pore strips, at various locations in the floor area. Looking first at a field topped wet system, these are examples of beam configuration used in this type of structure. There must be a proper bond surface or mechanical bond on the area to be topped. The double Ts have a roughened surface to develop a bond, and the inverted T beam may have protruding rebar to develop a mechanical bond. There is typically not a need for projecting rebar out of the double Ts, as they have such a large area of roughened surface. It is normally enough to develop the sufficient bond in the precast and the cast and placed concrete. Please note that while the detail on the left calls for these bars drilled in, it's not uncommon for the precaster to embed them during fabrication. Once in place, topping strength by field-based enforcing serves to tie the overall structure together. Note the presence of mechanical connections between the members prior to topping placement. These connections will help provide integrity for the structure until the topping is placed or cured. So, as we look at the drawing, we see an inverted T beam on the left, some double Ts that are setting on bearing pads, and have had weld plates that jump from the top of the double Ts over to the inverted Ts. I don't know what that noise is. On the right, you will see two inverted T beams heading on a column that are connected to the column by a set of coil bolts that go down through the inverted T beam. But the point of this, the field-topped wet system, is to see the gray, the cast-in-place topping on top of the double Ts and the inverted T beam. Here is a picture of an inverted T beam that supported double Ts are shown ready to be topped with concrete. The white and black strips are flashing that cover the open joints between the inverted T beams and the double Ts. Please note that this flashing should not go wide as to compromise the topping's bond, and in turn, the degree for which the topping and precast work compositely. The nuts, bolts, and plate washers you see here are connecting the inverted T beams to the column below, as was shown in the figure before. As you can see here, and as the name implies, the factory-topped complete dry system does not have concrete topping or pore strips. The joints between the precast components are caulked in the final, as well as the temporary. Integrity of the structure is achieved entirely with mechanical, and in this case, welded connections. So again, we see the similar pictures, other than there is no poured-in-place cast topping. Again, this photo shows an example of a factory-topped dry system here. This system is also referred to as being pre-topped. The broom surface was prepared in the precaster's facility, and in the case of parking structures, provides the final traffic-ready surface. It should be pointed out that the term factory-topped is a bit of a misnomer, as the final top surfaces of the components are not applied as a secondary topping, rather the depth of the component itself is established to bring their final top surfaces to the intended floor elevation. In the case of double Ts, a field-topped wet system may utilize a two-inch cast-in-place topping over a two-inch flange of the double T, whereas a dry system would simply use a four-inch thick flange with the desired finish applied to the top surface. This approach is effective in eliminating the time and cost of applying a topping in the field, and also provides a high-quality finish surface that is manufactured under controlled environment at the precaster's plant. Note in this photo that the joints of the precast components have been caulked. These diagrams show sections cut that are the same locations that we've seen earlier, while utilizing a factory-topped partial wet system. With this system, concrete toppings, strengthened with field-placed reinforcing, is placed at the ends of double Ts and along the inverted T beams. A wash or slope may be incorporated to divert water away from the double T edge or the double T beam transition. This field poured areas may also be used and contain cord reinforcing, a key component in a building's lateral load-resisting system. Placement of this reinforcement should be in accordance with the approved engineered documents and should adhere to the code-defined cover, spacing, and splicing requirements. As with the field-topped system, temporary integrity is achieved via mechanical connections at these locations. As before, we see the jumper plates or welded plates between the double Ts and the inverted T, or the wall or light wall. In this photo, the inverted T beam with the protruding rebar is seen running down the center of a recessed strip. This strip will receive the poured-in-place topping. Additional reinforcing steel, in the form of welded wire fabric, will also be added. After this photo was taken, to control temperature and shrinkage, cracking within the minimum 2-inch to 3-inch thick floor strip. Such concrete components may be used in conjunction with other building materials, such as cast-in-place concrete, steel, and or masonry to form a complete structural system. Less time will be spent in discussion of these systems during this presentation, but the concepts are similar. Just to offer a couple of examples, we have architectural cladding panels and enclosure panels for industrial applications. Here, in this photo, architectural precast cladding panels can be seen bearing on a main structural element of a steel-framed building. Note the tube steel bearing seat projecting off of the structure. Lateral support is generally developed by several connections that tie the panel back to the building frame. See the bearing, and then the lateral supports to either the floor system or the column system. Architectural precast cladding on a concrete frame is supported and tied back using similar procedures as used for a steel-framed building. Cladding panels, most commonly, have only two bearing points. If more than two bearing points are planned to be used, it is probably prudent to solicit input from the specialty engineer to determine how proper distribution of the panel weight is intended to be ensured. In the case of the panel being erected here, it would not be unusual for the erector to place temporary shims between the adjacent panels so as to control the joint width between the panels. While this is typically an acceptable practice, it is imperative that these temporary shims be removed to ensure the final loads are transferred through the intended path to the structure and not to the adjacent panels. Final shim locations should be in strict accordance with the approved erection drawings. We see the lateral support, which comes from the cast-in-place columns, and the bearing support in which the cladding will rest on the floors or be tied back to the floor. We are now going to take a look at a very important transition that occurs between the precast structural system and cast-in-place foundation. It stands to reason that the first area of concern when erecting precast concrete to a structure is the foundation upon which the structure will sit. Before any precast components are erected, there should be assurance that the cast-in-place foundation system has been properly constructed and suitably coordinated with the precast structure soon to be above it. In the photo, we see cast-in-place walls with a precast column, precast walls, and an inverted T-beam, all of which are integral to the system but rest on the foundation. To understand why this cast-in-place precast interface is so critical and can be so vulnerable, we should first consider how many steps and individuals this system must pass through before it can be complete. Basic structural system is developed by the structural engineer of record. There is some concept of what he has in mind, and then a detailed precast system is developed by a precast engineer. The loads imparted by the precast onto the foundation are quantified by the precast engineer and communicated to the structural engineer of record. That structural engineer of record uses the precast engineer's foundation loads to design or confirm the design of various components of the cast-in-place foundation system. The precast engineer designs the precast components and connections at the cast-in-place concrete and the precast concrete transition. Then the cast-in-place foundation system may or may not be detailed in a separate set of fabrication drawings by a third engineering firm. The cast-in-place foundation system is constructed according to the drawings prepared by the structural engineer of record or the cast-in-place specialty engineer. The precast concrete components are then manufactured according to the precast erection drawings, production drawings, the foundation drawings so that they match up and prepared by the precast engineer. Precast is then erected on the cast-in-place foundation system according to the details presented by the precast erection drawings. To sum up all of that, there were multiple parties involved, at least two contractors, the erector, the foundation preparer, as well as the oversight construction manager or general contractor. You usually have at least two engineers, two separate inspection groups, and a separate erection crew that has had little or no involvement prior to this development. We have significant loads. We have the vertical loads that accumulate throughout the structure and culminate at the transition point or the footings. We have the lateral load systems, usually demand high-capacity connections, many requiring tight tolerances. Key components of this whole system may not be visible to the erector during erection or while planning erection. To assure a thorough understanding among these involved parties, steps should be taken to communicate the design intentions. This communication is crucial. There should be coordination meetings prior to the cast-in-place construction to convey the design assumptions, the required sequencing, how things should be put together, and the responsibilities among these design entities. Meetings are most effective when the structural engineer of record, the general contractor, the specialty inspector, the pre-caster, the pre-cast engineer, and the erector are all present and can express both concerns and desires. Open communications between the design entities early in the design process can help to define responsibilities and avoid these oversights. Before talking about the considerations that should be made when inspecting the pre-cast to cast-in-place transition, let's first consider the systems that are commonly used to create a path for loads to reach the foundation from the building superstructure. First of all, we have columns and beams that support columns, spandrels and beams that are supported by columns. We also have load-bearing walls, shear walls, and we have individual pre-cast components supported by the cast-in-place assemblies. With a spandrel or beam system, horizontal components span from column to column. The load from the horizontal members are translated through the columns to the foundations. This accumulation of load usually becomes large and concentrated in a small area by the time it reaches the foundation. So all of that weight goes through the column to the footprint of the column itself. Gravity loads carried through the load-bearing walls are usually transferred to the foundation through a fully grouted joint. This continuous bearing mechanism typically provides a uniform distribution of gravity loads and results in smaller pressure concentrations on the foundation. So there, the weight is spread across the whole footprint of the wall system instead of just the column. Shear walls are used to resist lateral loads such as wind and seismic loads imparted on the building. These loads are transferred from the structure's floors to the walls via the connections. The walls are also commonly used to carry a portion of the structure's gravity load. Because of the dual functionality, shear walls may be subjected to shear, tension, and or compression. So in the slide, we can see how the loads are moving against the floor and the walls. Here you can see how the lateral loads make it to the shear wall through the floor members. This can result in an overturning behavior which is then resolved by countering tension and compression-resisting forces at the base of the wall. And here is T for tension and C for compression, respectively. In some cases, horizontal members may bear on and connect to the cast-in-place foundation directly. This is usually accomplished through the use of corbels, ledges, pockets, and or embedded steel items. So having considered the various means in which loads are transferred from the precast system to the foundation, let's first look at column bases. Column bases are typically designed to function in one of two manners. In the case of pinned bases, it's primarily transferring gravity loads from the column to the foundation, although there may be a nominal shear force transfer as well. During erection, this type of base may be required to resist nominal tension as well. In the case of moment-resisting frames and cantilevered columns, the bases are designed to transfer gravity loads to the foundation and resist rotation as the column is acting as part of the structure's lateral load-resisting system. The erector should exercise great care in erecting columns, as their bases will be ultimately subjected to large loads over a relatively small area. Lengths and timing are very important to preserving their integrity. Chimbs are sized for anticipated erection loading. This is why an erection plan needs to define points in which the grouting is necessary. So let's take a look at an example of the mechanism here for an erection plan. So during erection, the weight of the column and its first few supporting members are placed on chimbs. This may create heavy, concentrated loads on the chimbs, or point loading. While resting on the chimbs, the column is brought to plumb using the leveling nuts. The nuts are tightened, and the column base is grouted. It is not unusual in certain circumstances for a column to be positioned out of plumb to account for movement caused during subsequent eccentrically placed loads. Anchor bolts are not typically designed to carry significant compression loads. That's why the chimbs are there, not the nuts on the anchor bolts. The grout in the chimbs should carry the vast majority of the load collected by the column. The height to which a structure can be constructed prior to grouting the columns or walls will be determined prior to erection and be included in the erection plan. The erection process for pinned and fixed column bases are essentially the same, although the materials, grout strength, anchor bolt size, base plate thickness, may be more robust in fixed bases. Before erection begins, there should be a clear understanding of the column installation sequence intended by the precast concrete engineer. And although those procedures may vary, again, there should be a system agreed upon. This slide shows an example of a column erection guideline included as part of a project's erection plan. The narrative gives specific instructions to the shim placement, the use of the anchor bolts, and the sequencing of grouting. So if we look at the column erection guidelines, it says that we're going to place four, and in this case, plastic shim packs, one centered on each column face, set one inch back from the face of the column. We're going to shoot those column stacks in to achieve a proper elevation, and then we're going to level across those to make sure that the elevation of those shim stacks are the same. We're going to place the columns on the shims, and we're going to finalize the plumbing using the top nuts in trying to, and in some cases might use a hammer wrench or a cheater bar to get that. And once the plumbing is complete, we hand tighten or draw up the bottom nuts to the base plate. And then it talks about how the grout should be there. And then it goes on to say that we want to use two braces per column, one in each direction to maintain its plumbness until it's loaded. So the notes on this erection drawing shows that we want all columns to have their bases grouted within 24 hours of erection. We are not going to erect more than one elevated level until the columns are grouted. We're going to make sure that we're taking care of properly mixing the grout and watching the temperature as well as the testing of the grout. Taking a closer look at the column erection sequence, we see in the upper left-hand corner four stacks of shims, and in this case those shims are steel shims placed at the face of all four faces of the column. The upper right, we see the setting of the column. On the lower left, we see somebody actually plumbing the column, and then the column in its final position. The upper right also shows the brace being prepared to brace the column in two directions. Prior to beginning erection, a survey should be taken to assure the proper positioning of all anchor bolts or embedded items into the footing. So we can see on the right that we have anchor bolts that should be checked prior to the placement of the column, and on the left we see a placed column that is fully grouted. In instances where the anchor bolts are mislocated, corrective measures should be taken such as enlarging the hole in the base plate or post-installing new anchor bolts with the adhesive materials. These types of modifications should be done at the direction of the precast engineer and the engineer of record. Note that the base plate had a hole that had been enlarged, and on the left we notice plate on top of those anchor bolts. As a column erection is to be carried out and inspected, consideration should be given to the type of foundation in which the column is to be in place, whether or not the column is going to be placed on a spread footing, as we saw in the earlier picture, or on a pedestal or pilaster, as seen in this picture. In the case of spread footings, the risk posed by nearby free edges are reduced, and focus should be placed on the location of the actual anchor bolts and the condition of the bearing surface. Does the bearing surface seem to be of quality concrete, free of voids, and level for good bearing? Where a column is to be placed on a pedestal, the presence of nearby free edges in the foundation may create vulnerabilities if not properly prepared, signs of distress, cracking, and other things along these free edges or around the anchor bolts should be reported immediately to the precast engineer of record. Even before precast erection begins, pedestals should be carefully inspected to ensure appropriate construction. PCI 318 very specifically addresses the need for anchor bolt confinement steel for pedestals in Section 10.7.6.1.6. In this figure, we can see how the bands go around the containment of the anchor bolts and the spacing. If you think they never get let out, it is implausible for the anchor bolt confinement steel to be overlooked during design, detailing, or construction, as evidenced in this photo. Prior to concrete placement in piers, pilasters, and pedestals, the inspector should confirm the presence of these important bars. Again, this may not be your inspection, but the pre-pour inspection of the concrete walls and foundations. Looking at some scenarios, we can see the effect of column placement. Proper concrete footage and proper placement damage to anchor bolts. We see anchor bolts here that are bent over and need to be repaired prior to placement. The inspector should also be on the lookout for signs of subpar concrete quality at the footing or pedestal. We know what those are. Reports of low strength, voids in the concrete, cold joints that are not in the proper places, uneven surfaces, all can be vulnerabilities under high compressive loads that we have been speaking about. One of the most important facets of the load transfer between the precast and the foundation is the placement of high strength grout between the precast component and the cast-in-place surface it is resting on. This material allows even large loads to be evenly distributed over a suitable area. The placement of this material can be done in a couple of different ways, illustrated here. The photo on the left, although depicting a wall panel, is an example of the dry packing operation. The grout bed on the right photo was formed and poured. In the case of dry packing, it's very important that the joint be large enough to be effectively pushed grout into all areas under the column, and in such a way that it can be packed tight while doing so. While this is pretty readily achieved when grouting wall panels, which have a shallower depth, it is more difficult with columns due to the larger depth in which the grout has to be pushed. Forming and pouring grout will typically yield a more thorough placement of the grout. However, this requires a more flowable material, which typically results in lower grout strength. Additionally, it's important that the material be well vibrated to assure good consolidation throughout the joint and the absence of air pockets against the precast above. To assure suitable performance of the grout, it's vital that the manufacturer's instructions for mixing and placing the material be followed closely. Adhering to the manufacturer's guidelines for mix proportions, mix paddle requirements, and mixing time, as well as the pot life, how long it sets in the bucket or mixing area, and the temperature thresholds will assure that the grout material achieves the desired strength and workability properties. In addition to regarding the following grout manufacturer's instructions for material, it's important to have the right tools on hand to prepare the grout. Here you see a picture that has been marked with the appropriate water levels for several grouting applications. What you don't want to go out and see is this. Anything that holds water, some pop can, Coke cup, anything like that that somebody is guessing at the mixture, you will have inconsistent strengths of the grout. Cold weather can also be detrimental on grout as it's stored, while it's being mixed, or while it's curing. As such, it's important to store grout material in a sheltered location, preferably within some measure of controlled climate. The use of warm water during mixing and the subsequent use of heated tarps, portable heaters, and temporary enclosures will serve to ensure suitable curing of the material. In the left photo here, grout material has been stockpiled in a small shelter that is being heated with a portable heater. On the right, a temporary enclosure has been created using electric heated blankets to control temperature for a newly grouted joint. To confirm that the grout material is achieving desired compression strength, cube specimens should be collected for testing according to ASTM C109. Specimens are formed using brass molds, and in accordance with the detailed specimen preparation guidelines of C109. It should be noted that molds of material other than brass are sometimes used. But these should be carefully inspected to ensure that they produce specimens with true surfaces and square corners. Even minor variations in the shape of a specimen can have a drastic effect on the compressive test results. So that's column bases. Now let's talk about wall panels. Pretty similar in concept, but there are some unique things to consider. It's worth noting that we're talking about simple wall panels here and not shear walls. So these wall panels that we're talking about provide positive attachments between panels and foundations. The loads collected are predominantly compressive with potential for some moderate shear behavior. And when the base joint is fully grouted, the resulting compression load is distributed over a significant area that uses much smaller in magnitude than those seen in columns. And if you want to consider walls with large openings, they can be an exception, because those loads are transferred to smaller surface areas. When the base joint is fully grouted, compressive forces may become significant at those bearing points. So if we look at the erection procedures, they're similar to the columns. The connections typically incorporate welded plates or grouted dowels. The plumbness of the panel is typically achieved and maintained through the use of pipe braces or some temporary vertical alignment. And then if the base joint is to be grouted, the number of pieces erected prior to grouting must be limited in order to prevent excessive stress on the bearing points. These requirements should be in the erection plan and should limit the height vertically that those columns, I mean that those wall panels can go. Prior to setting a panel, just like we talked about with columns, the locations of any foundation embeds should be surveyed to assure that they're properly spotted to make their connections. In this photo, you can see two steel embed plates cast into the foundation, noted by the yellow arrows. During the placement of the embeds, it's important that the headed studs and other anchors are not bent, cut, or altered in any way without consent of the specialty structural engineer or the structural engineer of record. Also seen in this photo is the placement of some grout for a wet-set panel, which we'll see in the next photos. In these photos, preparations are being made to set precast concrete panel on a bed of plastic grout, plastic meaning ready to receive the grout and not hardened. Because this is being done in cold weather, you also see a rosebud or a heating torch that is used to warm the foundation prior to placing the grout bed. Similarly, the bottom of the panel was also warmed with the rosebud prior to landing the panel on the grout. Such measures help to avoid a rapid drop in the temperature of the grout and minimize the risk of inadequate cure due to grout freezing. One item of note in this series of photos is that the grout is being placed directly on dry cast-in-place footing. Ideally, this substrate should be made wet in order to prevent it from trawling the water out of the grout as it's curing for proper cure. So again, we see the panel on the left about to be set on a bed of wet grout. And on the right, we see the bottom of the panel being heated so as not to quick freeze the grout set. Movement of the panel while the grout bed is hardening can cause inconsistent bearing surfaces. So wall panels are to be stabilized to prevent this from happening. In the case of load-bearing wall panels, the precast engineer may allow the erector to place some support components on the wall panels before the grouting takes place. This serves to stabilize the grout joint. But care should be taken not to exceed the engineer's parameters for this practice. Heavily loaded walls resting only on shimpacks can have a catastrophic effect. We see a wall panel on the left being placed with a brace being plumbed prior to grouting so that we're not moving the panel after grouting. And we also see the photos on the right where the panels are braced, again, assuming prior to grouting. But before upper loads are placed, those panels should be grouted in accordance with the erection plan. As with columns, care must be taken to maintain favorable temperatures. It is rare that a grout joint will be negatively impacted by high temperatures as long as some level of moisture is provided, again, wetting down the footing or the other substrate. However, freezing temperatures can have a drastic effect on the ability of the grout to reach its intended compressive strength. The use of heaters, tarps, lumber, and electric blankets can be used to ensure suitable temperatures and a favorable cure. When inspecting embedded plates and cast-in-place foundations, it's important to recognize that most welded connections offer some tolerance. In the left and right photos here, the embed plates are somewhat out of position, level, canted. However, in the center photo, the embed is mislocated to the extent that only half of the intended connection can be made. In such a situation, the precast design engineer should be consulted. He or she may develop a repair detail to correct the nonconformance, or depending on the extent of the redundancy in the original design, may elect to abandon the portion of the connection that cannot be made. Recognizing that some repairs for mislocated embed items may involve the use of adhesive anchors, it is important to follow the adhesive manufacturer's instruction and evaluate any limitations that may prevent welding from being done near the cured adhesive. Can be noted that it's not unusual for connections at mislocated or amended embeds to be disregarded, provided the engineering team on the project concurs. And in any manner, there should be documentation that notes any unused connection. The next type of cast-in-place to precast interface we're going to look at are for shear walls. Some characteristics of shear walls. Shear walls provide lateral stability for the overall building. Design and detailing of the reinforcement and connections for shear walls different from conventional wall panels, because large horizontal loads are applied to the shear wall at each level of a structure. A rotational effect is imposed on the wall, as well as a large base shear. The criticality of the wall's function and the magnitude of the loads involved have led to a requirement for most shear walls to emulate monolithic concrete. With that comes the need for the joints to also mimic solid concrete. The most common way to accomplish this is the use of dowel-type connections, consisting of projecting rebar in the panel or foundation, and then grout filling the sleeves of the other panel. Aside from the connection details, the methods used to set shear walls are essentially the same as conventional wall panels. Noting that the previously mentioned overturning potential, it's common practice for the designing engineer to bear members carrying other components with shear walls in an effect to counteract the overturning tendency. Because these load-supporting members can impose significant loads on the shear walls, it is important not to place too much loads on the wall before a cured grout bed is in place. The project's erection drawings should show that. As the special inspector is monitoring the shear wall placement, the critical consideration is likely going to be the establishment of the connections at the base of the wall. As stated previously, these are most commonly achieved with reinforcing bar dowels embedded into grout-filled sleeves. These sleeves come in two basic varieties. The first is a fully-developed rebar in a corrugated sleeve filled with high-strength grout. The other is a proprietary sleeve that is capable of developing a rebar's capacity in a very short length with the special use of grout, special grout. From a material cost standpoint, this type of connection is ideal. However, shear and tension loads at shear wall bases can be very large and demand the use of high-diameter bars or large-diameter bars. Consequently, the development length and the required depth of the corrugated sleeve become very large and often impractical. In lieu of a long, corrugated sleeve, the use of proprietary grout sleeves allows for reinforcing bars to be fully developed within a fraction of the otherwise prescribed development length. So let's take a look at that. As an example, a typical number 11 grade 60 rebar embedded in 6,000 PSI concrete has a required development length of 55 inches. Using an available grout sleeve, the same degree of development can be achieved with as little as eight and a half inches of embedment into a proprietary sleeve. In this photo, a grout sleeve has been cut away to display the two reinforcing bars embedded in the grout-filled sleeve. Note the two semicircles on the top of the edge of the sleeve. These are the grout ports used to pump grout into the sleeve once both bars are in place. Here's a schematic of these proprietary grout sleeves as they can be seen. While this shows two panels connected together with the grout sleeves cast in the lower panel, in the case of cast-in-place precast interfaces, the sleeves are typically cast into the wall panel and the bars are protruding out of the foundation. Looking at a little bit of background on how these grout sleeves work, the key to the grout sleeve's ability to develop a rebar so quickly is the use of the special non-shrink partially ductile grout in the cast, ductile iron sleeve, just slightly larger than the rebar. The volume-stable characteristics of the grout, coupled with the confining nature of the sleeve, allow reinforcing bars to achieve full development with only minimal bar-to-grout contact area. The use of special grout and the need for small sleeve diameter to bar diameter ratios make coordination and inspection critical. So prior to placement, care should be taken to make sure that these bars and sleeves are exactly where they need to be and documented. The special considerations for proprietary grout sleeves begin with the placement of these anchor dowels. As I mentioned, these dowels are typically projected out of the foundation for shear walls. The high capacity of these dowels is driven in large part by the confinement of the volume of stable grout within the sleeve. In order to achieve this confinement, it is imperative that the annular area around the dowel be kept to a minimum. So the placement tolerance for these dowels is usually very restricted. That means that particular attention should be given to the placement of these dowels during construction of the foundation. Just like anchor bolts, care needs to be taken in the placement. But these are not anchor bolts. Because of the tight tolerances required of the dowels, the foundation contractor may choose to provide blockouts around the dowels at the top of the surface of the footing. These blockouts only extend a nominal distance from the top of the footing and serve only to provide a small amount of adjustment to the location of the dowel. Once the dowel is properly positioned, the sleeve is filled with grout. The full required embedment depth of the bar takes place below the blockout. And as you can see in the photo, there is some space to be able to move that dowel around to be able to take on the incoming sleeve. Because of the mentioned need for tight tolerances, dowels projecting out of foundations for shear wall-based connection should be surveyed prior to the start of erection. This will allow sufficient time to make any necessary corrections while minimizing costly downtime for crane and crew. The photo on the left shows two pairs of dowels intended to be placed along a straight line, but clearly not doing so when this picture was taken. On the right, the common method for correcting mislocated dowels is shown. After creating new holes in the correct location, new dowels will be installed using materials and procedures identified by the precast design engineer. Having the dowels in the proper location is important, but if they're not straight or if they're leaning, they will still be problems in getting them to engage properly in the grout sleeves. In this photo, the eight dowels are very well positioned. However, in cutting the bars to length, a shearing machine was used instead of a torch or a saw. The result is that nearly every bar is bent, causing difficulties in lowering the shear wall panel down onto the dowels. As you can see, they're not even bent in the same direction. It's not unusual to see this when working with a group of tightly spaced rebar dowels. In this case, each bar had a 90-degree hook at the base of the cast-in-place wall. In order to accommodate the specified tight spacing, these L bars were nested within each other, and later the projecting portions were all cut to the required length. This is a suitable approach, so long as the engineer has based the bar's length on the proper development of the bar projecting out of the cast-in-place the most. Once final adjustments are made, each group of bars should look straight and evenly spaced at the top and each at the right elevation. Overall, here are some chief considerations in preparing for a good shear wall base. Should make sure that there's sound interface between the foundation and the shear wall. The footing surfaces should be uniform and level so that the grout can be properly placed. The concrete should be of good quality, adequate strength, free of voids and debris. Most frequently encountered problems involve the placement of the embeds in the cast-in-place to receive the precast at cast-in-place connection. And the site should be thoroughly surveyed to verify compliance with the precast embed layout. This should be done well in advance of erection to allow sufficient time for any necessary repairs and to go through the engineering process. Once the foundation and shear wall panels are properly constructed, the next key objective is to make sure that the grout is properly placed in the sleeves. Inspectors should periodically observe this process to assure that the grout is properly mixed and the sleeves are completely filled. Once the foundation and shear wall panels are constructed, we can see the process here. We see on the left the proper mixing of the grout. We see the ports plugged on the picture in the center. And on the right, we can see the grout being pumped into the ports so that they are properly filled. That brings us to the last type of cast-in-place to precast interface that we're going to discuss tonight, corbels and ledges. These are poured integrally into the cast-in-place components. We see that this corbel being poured in the wall is supporting a T-stem. Ledger corbel made a part of a cast-in-place wall is typically built by a contractor using drawings developed by an engineer that used loads provided by another engineer that was hired by the precast subcontractor. Obviously, there is ample opportunity here for miscommunication. Proper coordination and a respect for the critical function of this assembly serves as a vital to making sure that this process can be properly constructed. To have an understanding of the key parts of a corbel and ledges, consider the two basic mechanisms that are the basis for their design. First is shear, or the tendency of a corbel to essentially slide off the face of a wall or column. Second is the flexure, or the tendency of a corbel to roll away from the face of the wall or columns, as noted in the two figures to the left. To the left, we see shear, or a panel for a corbel to slide down the face and flexure or rotate or to rotate away or roll away from the face of the wall. As with most every other facet of concrete construction, the key to good corbel and ledge performance is the proper design and placement of the reinforcing steel within them. So again, the top reinforcing bars should be developed behind the corbel and within the corbel. Behind the corbel, the bars are usually developed into hooks. And within the corbel, they can be developed through the use of a plate welded to the bar, transverse bar welded to the bars to make sure that they won't come loose. Again, another inspector should be looking at that and should not be part of the precast special inspection. In terms of proper development of this primary steel, consider the two scenarios. In the first, the primary steel is embedded straight back into the wall or column with no mechanical anchorage or bends to aid in the development of these bars. If the portion of the bar embedded in the wall is too short, the engagement between the bar and the concrete will be insufficient to prevent pullout. Similarly, if the bars are not mechanically anchored within the corbel itself, engagement between the bars and the corbel concrete will be insufficient. Typically, this proper engagement is achieved through the use of hooks in the wall or column, as we said earlier. In the corbel, it is achieved by attaching the primary steel to a transverse bar or an embedded plate. Typically, this proper engagement is achieved through the use of hooks in the wall or column, as we said in the corbel, through the use of a plate or embedded plate. As the foundation is being poured, the inspector should be well aware that all concrete corbels and ledges should have reinforcing steel bridged from the wall or column to the corbel. The engineer of record should be alerted immediately if this condition depicted here in the drawing is observed. And if you think this could never happen, consider these two photographs. The one on the left, the edge of a precast wall is shown, or a cast-in-place wall is shown. The roughened patch with the multiple drill holes is where a corbel had been formed and poured to support a precast load-bearing spandrel. It was only when the corbel was discovered to be at the wrong elevation that it was found completely void of reinforcing steel. Similarly, the ledge on the right photo was determined to be too high. And when pockets were cut out of the ledge to allow for the installation of a gusseted angle, it was discovered that there was virtually no steel cast into the original ledge. If not found at this time, the results could have been catastrophic. I hope that you have been able to find this second session of this special inspector training to be useful. Accordingly, the keys to tonight were the integration and interface between the cast-in-place concrete that is done in the field by a separate contractor, designed by a separate engineer, and the precast, designed by a specialty precast engineer and erected by a separate contractor, all shows that those all need to be integral and need to be checked. So again, I thank you all for being part of tonight's session. The last session will be held one week from today, 6 o'clock central time. Don't forget to watch for the information that will be coming in regard to the test. Good luck with the test. If you have any questions, I would invite you to type those in now, and I will be happy to address them. Thank you. Are there any questions? Hi, Carl. We have one question, but it seems to be for me. It's how much time do we have to complete the test after each session? I believe you have about 24 hours. So once you get the link, take the test as soon as possible. And that link will become invalid, I believe, within 24 hours. So if you cannot take the test through the link you get from GoToTraining, please email me immediately. No, it's just there's no final exam. It's just an exam after each session. That was another question. Well, if you fail the test, you can take it as many times as you need to to pass. You need a 70% to pass. Oh. Well, we are just finishing processing everything from the first test. So I will be sending out links to those people who haven't taken it. And you send me an email, and I will send you the link. OK, snarden at pci.org, OK? Well, we don't have any other questions. Yes, we'll be.

special inspector training

precast concrete fabrication

precast concrete erection

precast concrete structures

code requirements

manufacturing process

concrete foundations

connections for precast components

structural integrity

coordination in construction process