of the special inspector training. As always, the following presentation is intended to provide potential special inspectors with an overview of precast concrete fabrication and erection. We will continue to look at how precast concrete structures are built and focus on those items which are critical to the successful erection of precast concrete buildings. While the program is targeted towards special inspectors, it is important to note that much of the material presented here will 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 and its erection. In previous sessions, we went over the code requirements, the types of precast concrete structures, types of precast concrete components that make up those structures, a general overview of precast concrete manufacturing facilities, the documents required for effective inspections, the condition assessment of precast concrete components as they arrive on a job site. In the previous meeting, we went over the erection of precast concrete structures. We looked at how we should be looking at the cast-in-place concrete foundations and their conditions. Tonight, we are going to go into the specifics of the connections of those precast concrete components. This final portion will focus specifically on those connections. That is not to say that we are almost finished, because the precast concrete construction by nature is a connection of individual pieces connected together to form a structure. It stands to reason that connections will be a big part of the construction in all phases and the inspection process. In broad terms, connections of precast concrete construction are used to transfer loads, restrain movement, and or provide stability. In the three pictures that we see here, we see a plate that connects two panels. It looks like a pre-topped double-T. We see two spandrels that are bolted to a wall or shear wall. Then in the final picture on the right, we see various panel connections there, a column connected to an inverted-T and two double-Ts connected to an inverted-T beam in the middle. Consumers should be aware of the different considerations that are given a connection as it is being designed. The capacity is required by code. The ability to tolerate some deformation without brittle failure. The ability to resist or allow movement due to volume changes. The long-term endurance of the connection materials may demand the use of special materials or coatings. Special materials such as stainless steel or high or low carbon materials and various coatings such as galvanized and the feasibility of all that in the construction process. For this presentation, we are going to be looking at two basic types of connections categorized according to the load that they are intended to transfer. We will be looking at gravity or bearing loads and then lateral loads. The first type of connection load transfer we are going to look at is bearing or gravity load connections. Although precast concrete components are technically connected together at bearing points, a transfer of load from one component to another does take place here and these locations are commonly referred to as connections. The basic intent of these configurations is to transfer the weight of the structure and any loads it is intended to support from the component to an adjacent component until those loads reach the structure's foundation. In this case, in the picture shown here, we see an inverted T setting on a corbel or haunch which also supports a double T. Here you can observe the clear load path from component to component toward the foundation. The yellow arrows show the T stems of the double T and the load transfer to the inverted T which rests on the corbel or haunch that transfers a load to the center of the column on down to the footing or foundation. The transfer loads from component to component is nearly always done with the use of bearing pads, shims, or a combination of shims and grout. Precast-to-precast bearing conditions typically involve a component sitting on a concrete haunch, a secured steel bracket, or a formed pocket in a supporting component. Such bearing conditions typically use a bearing pad or shims between the connected components. Here on the left, we see inverted T beams supporting double Ts. On the right, we see an inverted T setting on a haunch in either a light wall or column. Precast-to-steel or cast-in-place structures bearing conditions most often consist of a formed pocket or projecting steel assemblies in the precast component resting on a bearing bracket that is secured to a steel structure. These types of connections typically include shim stacks that can be adjusted to get the precast component to the proper bearing condition. Note the illustrated bearing configurations on the left is a cantilevering precast stadium bleacher, often referred to as a tub riser, and on the right is an architectural precast cladding unit. In each case, the load centroid of the component is at a distance from the support bracket. We call this loading eccentricity. To maintain component stability and to facilitate component installation, these bearing connections are completed with a corresponding tie-back connection resisting the resultant roll. Bearing conditions for precast components resting on cast-in-place structures are accomplished in a similar connection. We see on the left the setting of a precast tub riser on a steel raker beam. As you can imagine, as that precast is set down and released from the crane, it may want to roll forward or will want to roll forward. In the same way, the picture on the right, the diagram, shows that as we set the precast on a stack of shims, that it's going to want to roll and so there will be a corresponding tie-back. Grouted joints are commonly used to transfer gravity loads from precast foundation or through stacked precast panels. We looked at a lot of these last week. The photo on the left illustrates a column resting on a bed of grout. The wall panel on the right is being lowered onto shims and a bed of grout placed on the top edge of the panel below. You can see that the photo on the right shows dried grout underneath the precast column. You can't tell whether or not there is grout underneath the wall panel that's sitting there also, but it probably wasn't wet set as the panel being set on the right. When bearing on ledges or corbels, it's important that these bearing surfaces be surveyed to assure that they are properly located. As we revisit the unreinforced and mislocated ledge from the previous section that we looked at last week, a pre-erection survey revealed a continuous ledge that was constructed too high as denoted by the red dashed line. The condition was corrected by cutting out sections of the ledge and attaching post-installed bearing seats at the correct elevation, the green solid line. By conducting this survey in advance of the scheduled erection, there was sufficient time to develop and implement an appropriate corrective action plan without incurring significant downtime costs for crane and crew. It is also important that bearing surfaces be checked for irregularities that might cause uneven bearing. Here a continuous ledge was seen supporting a precast concrete flat slab. A hump in the ledge has resulted in a point bearing condition, which in turn caused localized spalling in the ledge. In this instance, this did not signify an immediate structural concern, but did require a repair to assure long-term durability and avoid spalling debris from the localized cracking. As you can see, this was found long after erection occurred, which also means that it is going to cost more to correct and have a different repair detail as opposed to it being found prior to erection. An important part of the bearing assembly performance is the material that gets placed between components. Bearing pads are widely used as a buffer between precast components at bearing points. They are intended to create uniform bearing stresses and minimize stress concentrations at irregularities within the bearing surface. They also permit minor movement to occur at the bearing point so as to reduce stress due to restraint. Let's look at those. There are several types of bearing pads commonly used in precast concrete construction and erection. We'll take a look at the most prevalent ones. Unreinforced elastomeric pads are simply homogeneous pieces of elastomeric material such as neoprene. These pads are very economical but have a limited surface life, particularly when exposed to heavy loads, uneven surfaces, and or movement between two interfacing components. Fiber reinforced elastomeric pads contain randomly oriented carbon-cotton fibers throughout the elastomeric material and serve to strengthen the pad and increase its resistance to wear. Carbon-cotton duct fiber pads are commonly used in heavy load applications due to their excellent compressive strength and durability. These are easily distinguished from elastomeric pads by their visible fabric pattern and their tan color. Let's look at some bearing conditions. While bearing pads are intended to compensate for minor surface variations, they cannot fix everything. The photo on the left shows a strongly sloped top surface on a corbel. This results in a very small bearing area, which has already caused some localized falling at the end of the beam. Corbel was repaired by cutting the top surface down to the marked line. Had the concrete cover not been sufficient to tolerate this type of repair, a milled wedge-shaped steel plate might likely have been attached to the top surface of the corbel to recover the intended level surface. Note the gap in the photo on the right. This was created by improper forming of the corbel and resulted in very isolated regions of bearing within the bearing pad area. In order to restore a uniform surface, the high spots on the corbel were ground down to achieve a flat surface without jeopardizing the concrete cover of the corbel reinforcing. Looking further at the corbel from the previous slides, cracks can be seen to have developed as a result of the uneven bearing. The photo on the right shows a similar point bearing condition that has resulted in damage to the corbel. When severe point bearing is observed, particularly in heavily loaded elements such as corbel supporting inverted tees, the structural engineer of record or the structural specialty engineer should be consulted to determine if repairs should be made in an effort to keep loads away from sharp, unreinforced concrete edges. The precaster may elect to place a chamfer along such edges. Shims are also commonly used as precast concrete erection as a mean of bringing the component to its proper elevation or into alignment with adjacent components. The most common materials for these items are steel and high-density plastic. We see on the left stacks of steel shims and on the right plastic high-density shims. A couple of special considerations here. The first item highlights the need to keep shims and bearing pads, for that matter, away from the free edges of the precast components. This will help minimize the risk of localized spalling. The second bullet item refers to the use of extra shim stacks under a component. This can lead to unanticipated negative bending and the potential overstressing of the component. Shims can also be used to alter the bearing surface elevation. This is a shim stack of likely acceptable proportions, although good practice would suggest that these steel shims be tack-welded together to prevent sliding. Note that while this may appear to be a mistake, the need for shims was actually made necessary by the corbel's proximity to the joint between the cast-in-place wall and the precast panel above and was likely detailed as such. The specialty structural engineer should establish the permissible height of such shim stacks. When using plastic shims, perforated models are available that are resistant to sliding. In this situation, please note that the elastomeric pad is always on top of the shim stack. When the shim stack is designed like this, they should either be tack-welded as we suggested or thicker shim plates to be used in that condition. The use of grouted bearing is very prevalent in the precast concrete industry. As discussed earlier, its use is common under columns, shear walls, wall panels, and between stacked wall panels. A grouted joint can be a very effective means of transferring large compressive forces between precast components, but must be installed properly in order to ensure the intended results. With regard to the first bullet item, it should be noted that shims can be used in conjunction with the grout to provide some degree of load carrying capacity until the grout is cured. The specialty structural engineer should be consulted to determine the permissible load that can be applied in such a temporary state. In order to confirm that the placed grout material meets the intended criteria, specimen tubes should be prepared and tested. We spoke about these in our previous meeting. Once tested and approved, good records of samples and their results should be kept in an effort to readily identify the specific areas of the structure that a particular grant sample is referencing and should be available to the inspector. In some circumstances, it is undesirable for adjacent components to be rigidly attached to one another. This is common when two distinct structures abut one another and are anticipated to move, expand, or contract differently from one another. These interfaces typically require the use of expansion joints and in some instances also incorporate slide bearing details to prevent restraint forces at the component's bearing points. These assemblies normally require specialized hardware that in turn require careful inspection. In this figure we see the slide bearing surface, the stainless steel, and then the backing. Look for that. To protect the slide surface from shipping, the hardware may have a protective film. It is important that this film be removed prior to the placement of the component to ensure that dirt does not accumulate on the slick surface. The upper nonstick surface should be larger than the bottom surface. If it's not, the details should be questioned with the engineer to assure that the design intent is being met. When positioning the bearing assembly, it should be placed so as to provide the maximum range of future motion. These photos show the components of a common slide bearing assembly for precast concrete construction. The photo on the left shows the assembly upside down for illustration purposes. The second photo is the correct in-place orientation of the oversized stainless steel plate placed on top of the smaller Teflon-coated bearing pad. We see that. We see the elastomeric on the photo on the left. We see the elastomeric pad, the Teflon slide, and then the stainless steel bearing plate. Then on the right we'll see them upside down the way it should be noted on the connection. When inspecting these slide bearings, consideration should be given to whether the assembly can perform as expected. The left photo here, the undersized recessed area of the beam, has caused the upper plate of the slide bearing pad to bend. In the right photo, the bearing surface of the beam is not level. This has caused the lower elastomeric pad with the Teflon coating to be pinched. Those conditions will restrict the intended movement of the slide bearing and should be adjusted to provide flat, unobstructed surfaces. This should be noted by the inspector and brought to everyone's attention. This photo, the lower portion of the slide bearing assembly has not been centered on the upper portion of the assembly. As a result, only nominal amount of beam movement to the right may cause the lower pad and the Teflon to disengage from the assembly and render it ineffective. All bearings should be checked for adequate bearing length and proper pad positioning. Tolerances, as described in PCI's Manuals 120, 127, and 135, have been established to determine the minimum bearing length. Many variables can play into determining the minimum bearing length. The presence of the bearing plate, chamfers, the size of the member, the applied load, and other things need to be taken into consideration. Where an observed bearing has been called into question, the Precast Specialty Structural Engineer or Structural Engineer of Record should evaluate the observed condition. As we look at the photograph, we can see that the improper placement of the bearing pad has destroyed the bearing pad. It's all because of the short bearing. On the far leg, you can see that the spalling of the T-leg has occurred because of the short bearing, all of which should be red flags to be brought to the attention of the Specialty Engineer or the Structural Engineer of Record. For instances where point bearing has occurred at the face of a corbel, cracks may appear that suggest the entire corbel has been compromised. However, as long as the Precaster has taken proper steps to assure that the corbel reinforcing assembly cannot move within the corbel, the damage is typically found to be inconsequential and can be corrected with a simple cosmetic repair. As we look at something that may appear quite serious, as we look at the photos on the left and in the center, we see that the reinforcing is still substantial in performing its work, so merely a cosmetic repair would be appropriate. Again, it just needs to be brought to the Precast Specialty Engineer's attention. Other things to watch for, double T-bearings are frequently shimmed to assure alignment with adjacent double Ts, especially in parking garages. In doing so, it may be necessary to stack shims, as we talked about earlier. Steel shims are most commonly used in this application and is generally considered good practice to tack weld the shims together to eliminate the potential sliding of the shims as shown in this photo. See how the shims are not in a straight vertical stack? But also note the elastomeric pad at the top. This photo shows a stack of questionable proportions, perhaps too tall. However, a solid effort has been made to stabilize this stack by welding the shims together. This stack was eventually replaced by a permanent repair to the corbel. A good rule of thumb is one to two, the height versus the width. That's when you start getting really nervous, is when you start having shim stacks that are out of those proportions. The next part of our discussion regarding connections will be the lateral load resisting connections. These connections are used to resist wind, seismic, earth pressure, and impact loads or to provide stability to precast concrete components. Lateral load resistance is typically accomplished with welded, bolted, or grouted connection details. As an example, the connection detail shown here specifies how to tie a precast concrete wall panel back to a steel structure. A threaded rod is passed through the steel angle that has been welded to the structure. The rod then threaded into its adjustable insert that has been cast into the back of the wall panel. Once the panel has been properly positioned, nuts are tightened on either side of the steel angle to lock the panel into its intended place. A wide variety of connections are used to attach precast concrete components to other precast components. The photo on the left shows a precast concrete spandrel being attached to its supporting column. Bearing is provided by the pocket cast in the face of the column, but the lateral attachment is provided by a threaded rod passed through round sleeves seen within the pocket. The photo on the right shows two precast panels attached by a very typical welded connection. A wide array of welded and bolted connections are used to tie architectural precast concrete cladding panels to a steel structure. In the figure that we see on the left, we see an angle configuration that has a bolt similar to something we've seen in the previous. And on the right, we see a channel that gets welded to a steel column but bolted to a precast fascia panel. Items to look at with lateral load-resisting connections or the proper alignment between the components should be assured before the connection is final. Alignment and clearance between the precast components should be provided, and all attachments should be made in accordance with the approved erection drawings, making sure that they conform to all specified welds and provide adequate thread engagement for any bolted connection. Matter in which a lateral load-resisting connection serves their function can generally be classified into two mechanisms, shear and tension. With the shear mechanism, the implied loads are trying to cause two connecting components to slide with respect to one another. In a tension mechanism, the loads are attempting to separate the two connected components. We'll look at the characteristics of both and identify those things to look for when inspecting both. Looking first at the shear-type connections, here you can see one of the precast industry's most widely used connections, the typical double-T to double-T connection. In most cases, a series of these connections are used at each double-T to double-T joint. These connections are crucial to establishing a continuous floor plate that is in turn used as a diaphragm to carry lateral loads to shear walls or moment-resisting frames. Additionally, these connections serve to prevent uneven deflection of the double-Ts as traffic passes over them. Note the formed recess around the embed. This excess area surrounding the embed provides sufficient space for the embed to expand during welding without cracking the surrounding concrete. The inspector should confirm that the proper amount of weld has been applied and that the welds do not come too close to the end of the embed plate. We can see those connections there. Cracked precast concrete panels are frequently connected using grout-filled sleeves. When sleeves are cast in the top edge of panels, as depicted in this detail, the sleeve is typically filled with grout prior to erection of the upper panel. Proper mixing of the grout and subsequent control of curing conditions are key to achieving the suitable connection. Connections are made to provide a tension-resisting mechanism that will prevent two components from pulling apart from one another. Here you can see a couple of scenarios in which tension connections are used to develop sufficient resistance to prevent the precast concrete component from pulling away from the adjacent component. There are a wide variety of connections that are used to transfer these types of tension loads. On the left, we can see a welded connection with a bolted insert. In the center, we can see those grout-filled sleeves. On the right, we can see through-bolted bolts from the column to the spandrel panel. The vast majority of connections in precast concrete industry are assembled by one of a combination of three different construction types, welded, bolted, or grouted. First we're going to look at welded connections. It's a method that is widely used in the precast concrete erection industry. As with other construction sectors, the precast concrete industry is required to adhere to the welding codes of the American Welding Society. Specified welded details and methods should follow AWS D1.1 for structural welding and AWS D1.4 for the welding of reinforcing bars. For the inspector in the field, the precaster's approved erection drawings, which should abide by these AWS codes, will clearly identify the required welds for each connection. If these requirements are not clear, or if there's a need to deviate from them, the specialty structural engineer or the structural engineer of record should be consulted for direction. We will take a quick look at those welds as denoted in the erection drawings. We can see in these two figures, one is a blow-up of the other. The black flag there on the weld shows that it is a field weld. That means that weld will be done by the erector. This weld on the left shows that it's going to be a quarter-inch fillet weld six inches long on the near side. Because the triangle is on the bottom side of the weld symbol, that means near side. The weld denoted on the right is a quarter-inch fillet weld near side, but it is nine inches long. It's going to have an inch-and-a-half weld on one side, six inches across the other side, and then an inch-and-a-half return. While there are a wide variety of welds that are used in the precast concrete construction industry, the most prominent are the fillet weld, the bevel weld, and the flare bevel weld. The use of AWS-certified welders to construct precast concrete connections is generally considered a good practice and is frequently required by project specifications as well as local jurisdictions' building codes. The three types that we talked about here, the top line shows fillet welds. The first, fillet weld near side, the middle fillet weld farside, and the right fillet weld bowside. Again, the line of welds in the middle, that would be a bevel weld nearside, a bevel weld farside, a bevel weld bowside. And the one on the bottom is a flare bevel groove weld, flare bevel groove weld nearside, flare bevel groove weld farside, flare bevel groove weld bowside. So, the flare bevel groove weld is denoted anytime you have a piece of flat stock up against something with a rounded edge as denoted by the drawing. Loose dirt and debris should be cleaned from the areas to be welded to get a good weld. Additionally, care should be taken to avoid arc strikes outside the weld zone. On this slide, the left photo shows a double T flange to flange connection that has cracked over time. This crack likely started at the time of welding and has progressed with age and repeat traffic loads. In the case of the flange connection, it is important to adhere to the specified weld details. Over welding and welding near the edge of the embeds may cause this type of damage shown in the photo. The right photo shows a stainless steel plate that has been cast into the double T flange with a small groove tooled around its perimeter. This groove effectively accommodates the expansion of the plate during welding and prevented cracking and spalding around the surrounding concrete. Once a weld is complete, slag should be removed to verify the size and quality of the weld. As much as possible, splatters should be kept to a minimum as to prevent staining of the precast component. In this photo, the welder has done a good job of welding three galvanized plates together and then cleaning off the slag of the welds to permit inspection. Welding of galvanized plates is particularly susceptible to splatter if the galvanizing material is not ground off the plate before welding. Welding can be affected by inclement weather conditions, so care should be taken to mitigate the effects of those conditions prior to welding or the welding operation should be suspended until conditions approve. Cold weather and surface moisture can be compensated for with the use of a heating torch as shown in the photo on the left. In the case of the falling rain or high winds, welding should be stopped unless the area to be welded can be safely or adequately shielded. It should be noted that there are emerging research data that suggests that suitable welding in low temperatures and high humidity can be accomplished without the use of preheating. Information on this research can be found in the PCI Journal archives or on PCI's website. The photo on the right shows a welding rod oven to keep the moisture down in the welding rod and to meet AWS specifications for a rod that has been left out. The use of galvanized steel for connection components is prevalent in the precast concrete industry. The level of protection provided by galvanizing can significantly enhance the durability of the connection. However, the zinc coating used in hot dipped galvanizing turns to vapor at temperature 1,000 degrees below the heating point of the steel, melting point of the steel. Not only does this cause the protective coating to be destroyed, but it also induces excess gas into the molten weld material, which could result in porosity. This gas can become trapped in the cooling metal joint and have a deleterious effect on the integrity. In order to prevent this, the galvanized coating is often ground off the connection plate prior to welding. Alternately, there have been some success in establishing custom approved weld procedures using special electrodes and placement techniques. In the photo here, you can see where the galvanized coating was removed from the plate prior to welding. Please note, whenever we do this, we need to make sure that as soon as possible, we go back over that weld area with a zinc rich coating. Approved welding procedures should be used in all connections. Many of these are predefined and pre-qualified by AWS. However, special circumstances, such as welding galvanized materials without first removing that zinc coating, require a custom procedure to be prepared and the specimens tested to confirm to acceptable performance. Procedures should include the type of joint, the base material, the electrode size, the position, heat treatment, pre-heat requirements, polarity, the process we use, the current we're going to use, voltage, and the person authorizing the procedure. The form that you see in the slide shows a typical AWS form that helps you record all of that required data. To ensure long-term durability of the welded connection, it is important to apply the zinc rich paint to all areas from which galvanizing was removed, as we stated in the previous slide, and to areas for which the heat of welding may have compromised the integrity of the galvanizing. For the connections shown in this photo, zinc rich paint has been applied to the weld and to the surrounding area. To illustrate the benefit of the zinc paint, consider the photo on the right. These two steel assemblies were installed by an owner to secure a light fixture on the deck above. For some reason, only one of these assemblies received a coat of zinc rich paint, albeit in somewhat haphazard fashion. Nonetheless, the contrast between the deterioration between the two assemblies is profound, making the benefit of this zinc rich paint very evident. I also want to note that excess welding can be problematic. Many people believe if a little weld is good, a lot of weld is better. But that can be problematic, as we said. Connections that are designed to provide ductile behavior, this excess welding can be problematic. Excess welding can also cause localized damage to the surrounding concrete as plates expand under the heat of welding and the heat sink properties of precast. With a minimum 10% chromium content, the melting point of stainless steel tends to be somewhat higher than regular carbon steel, thus requiring a higher heat for the welding. Additionally, the coefficient of thermal expansion is about 30% higher than that of carbon steel. Both of these factors introduce additional aspects that must be taken into consideration when welding stainless steel plates embedded into concrete. In some cases, like that shown on the right photo, the precaster will create a groove around the stainless steel weld plate to allow the plate to expand without distressing the surrounding plate. The inspector should observe the condition of the concrete regions surrounding stainless steel plates after welding. On occasion, precast design engineers will specify the use of rebar to make welding connections, because some rebar may have a high carbon content. They may need to preheat the rebar prior to welding to avoid embrittlement. To avoid this requirement, some precast concrete fabricators use low carbon content rebar, commonly identified as ASTM A706 steel. As part of the special inspections process, the weld inspector should verify the appropriate weld sizes that are being placed. In this photograph, the inspector is determining, did the erector provide the quarter-inch fillet weld in accordance with the approved erection drawings? Note that the horizontal leg of the weld is somewhat larger than the vertical. It's a result of gravity on the weld while the material was in its molten stage. This is not unusual and not of concern, so long as the vertical leg achieves the detailed dimension, which in this case it has. You see the use of a weld gauge there, which are readily available to inspectors. The next type of connection we'll look at is bolted connections. Bolted connections can offer some distinct advantages to the erection of precast concrete components, as they can be readily constructed without the use of welding machines at the time, although this photograph shows that there's some combination of welded and bolted. It can be adjusted to its final alignment after the crane is released from the piece. Precast concrete industry makes use of various threaded elements for connections. Bolts, threaded rods, coil rods, and high-strength threaded bolts are used in different applications and come in a wide range of materials. The types of thread used on these elements vary with application. The bars shown here on the left are standard National Course threads. The bar on the right is a wider coil thread, which is more tolerant to dirt and debris and is conducive to reuse. These characteristics make coil threads ideal for the use in hoisting hardware, although they are commonly used for connections in the precast industry. PCI is working on a webinar to talk about coil threaded bolts used for lifting, as there is no national standard for coil threads, so mix-matching inserts, nuts, and bolts from different manufacturers can be problematic. When inspecting bolting conditions, you need to consider the threaded connections need to be in accordance with the precast erection drawings. A periodic check should be verifying that bolts are of proper material length and thread and diameter. As I just spoke about, the bolted connections should have proper thread engagement. Note that coil threads can require double nuts or elongated nuts, and we might see one of those in the next slide. Most bolted connections in precast concrete structures did not require some set pretension load or bolt torque. Bolts should be checked to ensure that they are snug. For snug-tight bolts and nuts, provisions should be made to prevent loosening, such as marring the threads using some kind of thread locker or Loctite or tack welding. Tack welding should not be used with high-strength bolts and nuts. Threaded elements typically engage with precast components through the use of embedded inserts. These inserts come in a wide variety of configurations and functions. In most instances, these offer a threaded receptor and a body that serves to secure the anchor to the assembly and the surrounding concrete. The diagram on the left shows a simple ferrule that is attached to a wire loop that provides its required anchorage into the concrete. On the right is a photo of a slotted insert that offers some adjustment to the location of the threaded bar or bolt. The body of the insert with the projecting wings and punched holes allow for concrete to flow around and through the assembly and lock it in firmly into place once the concrete is cured. Again, these inserts and bolt types, when using coil threads, should be from the same manufacturer's supplier. As one might imagine, proper thread engagement is vital to the successful performance of a threaded connection. The inspector should confirm that the required amount of thread is fully engaged and in accordance with the approved erection drawings. In the left photo, it is evident that there will be insufficient rod length to get sufficient engagement. With the photo on the right, the high-strength, double-length nut has been put in place but does not have the sufficient engagement to develop the desired connection capacity. Both connections required fabrication of a new, longer threaded rod for sufficient engagement. The key to look for is can a full nut be established, whether it's a single, double, or high-strength nut should have full engagement of the bolt or threaded rod. Although some grouted connections have already been discussed with regard to securing wall panel bases to foundations, we're going to go ahead and take an additional look at grouted connections between abutting precast components. The things that we want to look at here is the same things that we've talked about before. We need to make sure that the erection drawings indicate the location and strength of grout that is required, that the grout should be mixed in accordance with the material manufacturer's instructions, that the weather, whether hot or cold, should be taken into account during mixing and curing, and that the surrounding area should be wetted prior to grout placement to prevent water from being absorbed out of the grout mix. We should make sure that the sleeves should be clean and dewatered, that the torches not be used to heat the sleeves as this can cause them to expand and fall around the concrete, that the embedment lengths of the dowels should be clearly shown on the drawings and confirmed prior to grouting, and that calcium chloride should never be used as an additive for the grout in colder temperatures. It is important to prevent these grout sleeves from filling with waters we spoke about earlier during cold weather. A water-filled grout sleeve can generate tremendous expansion forces. As the water freezes in a precast concrete panel, it usually appears as a solitary crack on the outside of a panel, often away from any free edges as seen in this photo. See the crack? However, the underlying can be extensive as seen in this photo on the right. Although this is not the same panel as the one shown on the left, but the fracture mechanism is the same, and it would have initially manifested itself in the same fashion. For perspective, the damage area had a diameter of roughly 3 feet. You can see the exposed grout sleeve in the center of the spall. While very similar to the attachment of shear walls into foundations discussed earlier, we looked briefly at the steps taken to assure proper construction of precast-to-precast grout in connection. In preparing for a wall panel to be stacked on top of another wall panel, the erector may elect to place a bed of plastic grout on the top of the edge of a supporting panel. Keep in mind, the erector may also choose to dry pack the grout into the joint as well. Available access to the joint can influence the selection between dry packing or pre-placed grout beds. In either case, shims should be used to control the width of the joint and to carry the weight of the panel until the grout is cured. On the left photo, we see the plastic grout, meaning grout that's still flexible, along the grout bed. On the right, we see a stack of shims. Normally, the erectors would set the precast panel on the shims, determine the height, plumbness of the panel, then remove the panel, place the grout, then set the panel back onto the grout bed. Here, a worker is shown pouring flowable grout into the sleeves which were cast in the top edge of the lower supporting panel. The same way, you wouldn't want to fill those sleeves with grout first and then try to test place the panel prior to grouting. That would all come after the panel has been initially checked. Once the upper panel has been delivered to the site, the lower panel is being prepared to support the upper panel. The erector will usually have to install the dowels required for the grouted connection. As you can see in these photos, the dowels would project several feet from the edge of the panel. In order to keep the panel width within the shipping limits, the dowels are typically made from threaded rod, coil rod, or threaded reinforced rods. There are several available systems for threaded rebar. The one shown here on the left utilizes a tapered thread to develop the full strength of the rebar. Care should be taken to assure that these bars are fully engaged in their inserts in conformance with the approved erection drawings and any manufacturer's guidelines. You can see the threaded rod on the left being installed into the form saver and on the right in its position. Here you can see the panel hanging in its upright position. The dowels are threaded into their inserts and are hanging down below in the yellow circles. Note that multiple crane lines had to be used. With the dowels projecting from the bottom of the panel, it could not be rotated on the ground. Instead, both lines of the crane were used to rotate the panel to vertical in the air without damaging the dowels. Now we're going to look at a couple of final topics. We're going to begin with expansion joints. Expansion joints are introduced into precast concrete buildings to prevent the buildup of excessive expansion and contraction forces. Connections at expansion joints maintain alignment between the adjacent precast components without restraining the movement caused by this expansion and contraction. Expansion joints must let the different areas of the building move independently and within design limits. In this photo, opposing angles are installed periodically along the expansion joint to provide the vertical support of the T flange and to prevent pounding of this joint by vehicle traffic. Note that each of the opposing angles are positively attached to only one side of the flange so as to allow the horizontal movement to align the expansion joint. The inspector should confirm that none of the angles are positively attached to both sides of the joint. So we can see on one side it's attached, on the other it's not. Here, connections. The other side, bolted connections, and they alternate throughout the expansion joint. As with any facet of construction, things don't always go according to plan and field adjustments are necessary. Before carrying out these adjustments, it's most important to involve the precast engineer or the structural engineer of record to ensure that the original design intent is still met. Modifications to connections are often required where connection embed plates are out of tolerance in the vertical or horizontal direction. Approval from the precast engineer describing an appropriate corrective measure should be documented when such conditions occur. In this photograph, an extra plate was added to compensate for the embed plate that was recessed too deeply to engage the loose erection plate. See how it had to be built up to be able to reach the adjacent panel? In this photograph, although it looks unusual or undesirable condition, it may be fine in this form and carry out the prescribed function. Inspectors should look for verification that the precast engineer has reviewed the condition such as this and approved its suitability. In all cases, there should be written documentation of this approved use. One widely used connection that has occasional need for field adjustment is the double T flange to flange connection. There are several variations of this connection, but they demand that the embed in one T flange line up with the corresponding embed of the adjacent flange. In some applications, there can be upwards of a dozen or so connections per joint, so the opportunities for minor misalignments are many. In this photo, you can see a spot on assembly where the flange-flange connection is perfect. Note that there are minor separation between the embed plate and the concrete. This is not unusual and is actually a desired behavior for the product. As mentioned earlier in the program, the erector should take care not to over-weld or weld too close to the ends of the embed. In the picture shown, you can see that the weld stops short of the end of the plate, which makes the connection. This is an alternate detail for the flange connection we looked at, only with a joint width greater than one inch. Notice that the plates of varying width are specified for bridging the plate between the flanges. Having an assortment of plate widths to choose from allows the erector to adapt the detail to a specified condition he observes in the field. This may occur where double Ts on a ramp or a sloped ramp where the joints may vary. So, as we can see, there are a number of materials that can be used to fit that without asking for changes or documentation from the structural engineer of record or the specialty precast engineer. In this condition, one of the embeds was mislocated and does not coincide with the adjacent embed. In order to salvage a connection in this location, the precast engineer has permitted the use of a longer rod to bridge between the two embeds. Note that care was still taken to keep the welds away from the ends of the embed where heat and expansion can cause cracking. Here you can see a steel corbel assembly that was placed too low. To correct the area error, the precast engineer has designed a supplemental steel assembly that rests on top of the original and is secured back to the precast wall. So, we see the original corbel too low, we see the steel stub column, and we see the U-bar that is epoxied back into the column or frame. To assure the precast engineer's intent has been met, a formal repair procedure was provided to the erector and is made part of the project's as-built drawings. So, we see the low corbel, we see the stub column, the U-bar epoxied into the wall, and in this case formed up and poured concrete to make it more aesthetic. The engineer may design repairs to be hidden by an aesthetic finish such as concrete or may do so to satisfy the required fire protection required by the code. Inspectors should coordinate with the precast field representative if they wish to see the structural aspects of the repair before they are hidden and covered by the aesthetic finish. So, again, we see the finished look of the repair. You may recall this connection from earlier in the program. Here we have the opportunity for misalignment in two directions, and as fate would have it, it gives us an example of both. In this photograph, the plate to the wall panel has been cast too low to make contact with the flat plate welded to the plate on the double T flange above. After a check of the anticipated loads in this specific location, the precast engineer verified that an angle would be used to reach the wall panel plate as cast and that a shorter weld could be used to the top leg of the angle. Again, with documentation, that would be an acceptable, but one size doesn't fit all. In this photograph, the plate in the wall panel was too low again. However, the loads in this location are higher, and as such, added eccentricity introduced by a downturned angle could not be tolerated. In order to allow the use of a flat plate, a shim plate would be introduced between the weld plate and the plate embedded in the double T flange. Note this demanded significant welding and that the shortening of the weld length was not acceptable. So, there would be the correction, and again, the need for the structural engineer of record or the specialty engineer to come up with that repair. One size does not fit all. In this case, we see the use of an expansion joint in a similar location because the misalignment plate in the wall was six inches off. So, here we have a completed horizontal misalignment of the embedded plate. At this location, the loads were very nominal, and that connection could be used with the expansion anchor that I spoke of. Again, I must reiterate that any field connections that do not match the erection drawings or the welds specified in the erection drawings, there must be documentation. Temporary connections can be made, but final connections need to be authorized by the specialty engineer or the structural engineer of record. And so, that concludes the final presentation of the Special Inspector Training for Precast Concrete Structures. I thank you all for your attention, and I'm happy to answer any questions. Thank you, Carl. If you have any questions, please type them in the chat box now, and we have a few minutes to answer them. Carl, I do have one. It says, for shims, if the gap is two inches wide, it should only be one inch high for the actual shim. That's the question. Could you repeat the question? Sherri, I'm sorry. For shims, if the gap is two inches wide, it should only be one inch high for the actual shim. The gap is designed, and again, I need to know where you're talking about the gap. There are limitations. The structural engineer of record or the specialty engineer should set limitations on the joint specified. So, there's a range. The range of shims may vary depending on the plumbness of the wall panel being used. So, if there is some out-of-square-ness of the bottom of a panel, you could have an inch and five-eighths stack of shims at one side, and the other bearing point could be an inch and three-quarters. As long as they are still within on the available range of the joint, that would be appropriate. The grout would then make up the bearing difference between. So, the joint should be specified for the amount of shims, but a number of other things may require that joint to be smaller or larger. Okay. I think that is the only question we have thus far. I do have a question about the link to your certificate. You have to go to rcep.net and put in the login information they sent you in an email. If you do not have it, email me, and I will email you the instructions. But again, thank you very much, Carl. I think it went really well, and I'm hoping everybody enjoyed it. So, I will say good night to everyone, and I hope you have a wonderful evening, and see you when the next course we present. I don't know when that'll be, but look out, and we will be presenting it again. Thank you. Goodbye.

training session

special inspectors

precast concrete

fabrication

erection

connections

alignment

welding techniques

bolting techniques

grouting techniques

expansion joints