We are going to talk about designing high performance precast concrete parking structures today. The learning objections are posted on the screen very briefly to describe the attributes of high performance parking structures, to discuss innovations in parking structure design, to explain the differences in various structural systems for parking structures, and to describe proper maintenance procedures. What's a high performance parking structure? Integrates and optimizes on a lifecycle basis for all more major high performance attributes, including sustainability. It integrates and optimizes. This is putting together the system to get the highest performance that we can from precast concrete. Precast concrete's a high performance material. It integrates easily with other systems and inherently provides the versatility, efficiency, and resiliency needed to meet the multi-hazard requirements for long term demands of high performance structures. A lot of long words, what does that mean? And what we're going to talk about today are the details of getting the most out of precast concrete as an assembly that makes the system work with all of the connections and components so that the function for parking is best addressed. The attributes and benefits are many, included on the slide. And I won't read and review all of that in detail. There are simply many benefits to the use of precast concrete in parking structure design. So parking precast is a favored method for parking structure construction, has been for decades. Throughout the years, there have been significant advances in techniques, technology, and details that make these structures more efficient, serviceable, and highly durable. These are more durable garages than we have ever built before. Significant advances in techniques, technology, and details to allow the strength, durability, and resiliency and sustainability of precast concrete to evolve to very high performance levels. The keys to obtaining the best performance in precast concrete comes from a knowledge of the systems, the layouts, the components, the details. This presentation is aimed at providing guidance to achieve these high performance results. The framing basics, precast, prestressed concrete with long span double Ts is modular construction. Double Ts are made in long line steel forms with standard widths with allowance for joints. Typical precast double T widths are 10 feet, 12 feet, 13 feet, 4, 15 feet, 16 feet. These are regional variations and vary from producer to producer. The most common is a 12 foot wide double T that's used today. And 12 foot is a common module used in parking garages. The double T. Flanges, we talk about the slab across the top forming the floor to be the flanges. And two stems that provide the structural ability of the element to span. There are topped and un-topped or pre-topped double Ts. Every producer has a form variation suited to their most efficient operations. The minimum two inch topping as permitted by code may not be sufficient for reinforcement cover. Reinforcing with welded wire fabric has to be done with some care and some caution. The reason that care is required is that there are possibilities of thermal movements that can put a strain demand on the joints that needs to be considered. The high seismic limit to a minimum of 10 inch cross wire spacings is for strain capacity. The thermal movements that concentrate at the joints may challenge the strain capacity. And every joint above a precast joint must be tooled and sealed with topped double Ts. For un-topped double Ts with pore strips, flange connectors are used at the joints for transfer of vertical loads and horizontal shear. Continuous improvements made in commercial and proprietary embedded parts make durable and ductile connections. Cast-in-place concrete pore strips are used in this type of system to shape the final drainage and to provide cover and development over larger core reinforcement at the ends of the members. In other words, collecting and making a diaphragm. There's also a system, which we call a dry system, that uses un-topped double Ts without pore strips. There's no cast-in-place concrete above the foundation except for what might be required at door thresholds in order to make the final leveling. Some prefer putting topping just over the inverted T beams to assist in meeting the tolerance requirements. But mechanical connections carry all of the diaphragm forces in a dry system. It requires a greater attention to care in the fabrication and erection tolerances for the uniform jointing and for floor elevations. But you get plant quality durability, plant cast concrete and control throughout the garage. With the long clear spans, we have open spaces, often head-end parking and two-way traffic. Framing layouts should be designed based on the double T width or the module being used. Changes in framing must occur at the joints between the double Ts. Ramps have to start and stop at joints and end at the end of beams. The most efficient ramps are sloped, full-width bays that also accommodate parking. The slopes of park-on ramps are limited to 1 in 15, or 6.66%, by the International Building Code. But these ramps are commonly framed with 6% slopes or less for higher levels of comfort and improved sight lines. Interior framing lines supporting ramps are framed more efficiently with walls than with back-to-back beams and columns. These walls can support the different framing levels on each side with less thickness and fewer overall components. It's common to provide modular spaced openings in the walls for ventilation, for light, and for security. The openings allow drivers and pedestrian better sight lines and with reduced shipping costs. So the photo shows a ramp wall with large openings with stems between the openings that provide the support for the double T stems. A typical layout with 12-foot-wide double T's is shown here. Back. Again, what we have is the ramp that breaks at a joint line. A crossover bay with long-span inverted T beams allows head-in parking to the end of the garage, as well as the aisle width that's necessary for two-way traffic to pass through. The spans here can vary 48 feet, 36-foot bays, with some variations may be necessary in order to fit actual site conditions. The inverted T beam spans need to consider the headroom limits. Longer spans require deeper sections. But with higher-strength concrete and with the details that we have the details that we have come to use in the current time, we can make those spans without an intermediate column from the end of the ramp all the way to an outside column and accommodate that space without an interior column. Spandrel beams provide the outside support. The spandrel beam has a span thickness limitation that's imposed by the ACI code. The compression width is not... There's an L over 50 requirement. The L over 50 limit does recognize that the connections intermediate to the spandrel beams below the top level of the section are effectively lateral bracing, and so we can go with thinner sections. We have to fit closed ties into the width of the spandrel beams, and we have to provide support for the double Ts, either through a ledge or a corbel or a pocket in the beam. But recently, alternate plate-bending modeling and design under ACI 318-14, Section 9.5.7, allows us to design the eccentric loading on these beams for plate-bending rather than for torsion rules, and that no longer requires closed ties. Gravity load framing sets the spandrel beam to the outside or to the inside face of a column, depending on the requirements. It could be outside or inside. In this case, it's placed to the inside to provide one continuous line that then avoids having the column projecting into the space. Inside versus outside is considered. It does present some ASC integrity connection challenges when the spandrel beams are on the inside face, and we have to reach to make a connection for integrity in the longitudinal direction to hold the columns. That can be done by grouting one of the ties that are typically used for this type of connection. End columns have spandrel beams with the inverted T beam set. The spandrel beam here provides the barrier railing that's necessary for traffic control to take the impact loads and to provide the pedestrian railing. Pedestrian railings can be mounted on lower-level spandrel beams in that case. Fire resistance and fire rating are important considerations. Pre-stressed concrete is inherently fire-resistant. Section 406.5 covers open parking structures in the IBC. Section 406.6 covers enclosed parking garages. Precast concrete can be done in either case. Open parking structures are generally more economical than enclosed parking structures. Open is defined as 20% of the total perimeter exterior wall area on a tier distributed on not less than 40% of the perimeter. The height and the area limitations are increased for greater openness where the open area percent is measured on the interior wall with the interior wall height taken as 7 feet. It seems to be a conflict within the code of how we measure openness to define the structure versus openness for height and area limitations, but it is developed that way and ultimately provides rules that we can easily use in order to get larger structures that are more economical for meeting those requirements. Structure height and area limitations are associated with the classification for fire ratings. 1A has unlimited area with unlimited tiers, but requires two hour rated floors. 1B is unlimited area with 12 tiers, but it also has two hour fire rated floors. 2A has a limitation of 50,000 square feet per floor and 10 tiers, but requires only one hour fire rating on the floor, which occurs naturally without having a problem with thickness of the floor slabs today. 2B construction, very common, 50,000 square feet, limited to 8 tiers, has no fire rating, simply that it be non-combustible construction. The heat transmissibility endpoint requiring thicker floor slabs has been the rule for our codes to date, and to get the two hour fire rating, essentially required a four and three quarter or five inch flange thickness. That heat transmissibility endpoint has been waived in the IBC 2015 for open and enclosed parking structures. So going forward as the codes are adopted, it will be significantly easier and more economical to achieve the two hour fire rating when it's needed. Enclosed parking structures have height and area limitations that are governed by S2 construction in Chapter 6 of the IBC. They must, however, have mechanical ventilation, and they must have an automatic sprinkler system, which is generally why the open parking structure tends to be more economical. On the other hand, the height and area limitations for S2 construction with the required sprinkler systems for 2A construction with a sprinkler, they're limited to six stories, but are permitted 117,000 square feet per level. For 2B with a sprinkler, they're limited to four stories with 78,000 square feet per level. Type 1A with a sprinkler, 12 stories, and 237,000 square feet. So we need to talk about how we get high performance details to make the highest level of function that we can get from a precast parking garage. The first concern is drainage. We must get water positively off of the deck for it to function in a high level. We have to consider the joints and the flange connections, developing details that will work for the long term. And we must consider the best way to get performance from the structural system design. Drainage. Drainage requires attention to the global layout as well as the local details. Water needs to be directed by slopes in two directions to the point where the drain is placed. On a continuous ramp structure, the drains and the drain lines are typically on the interior column lines to minimize the architectural impact of the vertical drain line on the exterior. Drainage slopes must be planned to overcome camber. Camber is a natural effect of the pre-stressing of the double Ts. It causes them to bow up some amount. That varies depending on the depth of the double T and the width of the double T that's being used in order to support the loads. For pre-topped double Ts, the design slope parallel to the double T should be 1.5% and the transverse slope should be 1%. Basic guidelines can be found in the new PCI Manual MNL-129, Parking Structures Recommended Practice for Design and Construction, and also, and which has, by the way, just been published by PCI. And in ACI 362.1R-12, The Guide to the Design and Construction of Durable Concrete Parking Structures. Drainage plan is to get the water from a high point to a low point in two directions. It can be done by cross slopes in the length of the double T. Again, 1.5% would mean in a 60-foot bay a drop of 10 to 11 inches. A cross slope in the bay 48 feet for 1% can be six inches. There is a question of whether or not the floors can or should be warped. Warping simply means that the bearings at the ends of the double T are not parallel. If you hold the beams level on the outside and you slope the beams on the inside to drain, then you are twisting or warping the floor. That can be done to a degree without problems. There are limits, however, when you get to the point where the twisting might cause an undesirable crack, and we watch that. First, warping or not. To avoid warping, the slope on the outside supports is the same as the slope on the lower inside. Twisting or warping the precast units is acceptable, providing they are sufficiently flexible and adverse bending stress can be accommodated without cracking the flanges. Again, a general one to 1.5% of warping can be accommodated for pre-top members that span over 50 feet. When the high end of the double Ts are held level, it's more important to provide the sufficient slope over the length. The floor parallel to the end spandrel beam should never be held level with the high end of the double Ts. An architect might look and say, well, I would like my floor to be level all the way around the perimeter. However, that will result in ponding in the high corner because camber will prevent this configuration from draining from that corner. The local details. At the low end of the double Ts, there needs to be a low line to collect water and direct it to the drain. Best not, that water not be directed across seal joints between the double Ts and the inverted T beams so that the drain should be placed on either side of the beam. And a typical configuration shown on the screen now might look like that. In this case, you see that the drains are actually behind a shear wall. There's an inverted T beam on the right hand side of this view that bears on a corbel on a shear wall. The ramp wall is on the left and there are scupper openings or holes in the shear wall for the water to pass through the wall and into the drain. It's also not uncommon to put the drains on the inverted T beam side of the shear wall and the question would be, well, why not do that? That's usually where the drive lane is. There is piping associated with the drains. If you put the drain rim on the drive aisle side and you want to protect the downspout pipe in the corner between the shear wall and the ramp walls, then you're going to have to get piping through the shear walls. This configuration is a more efficient way for the plumbing and the piping work to be done and it can be very, very effective, again, proper detailing and tolerances to be considered. Drains can actually be cast into the double T flange for a pre-topped system. There are low profile drains that are now made that are two, two and a half inches deep that can be set right to the bottom of the flange with some reinforcing around in order to support this from concentrated loads. With a gasket, the drain body is attached to the rim from the underside. This can actually be done in the precast concrete plant so that the T is shipped to the site with the drain already in place and the only thing the plumber has to do is set the piping. Important to coordinate the drainage layouts and the slopes in the precast system with the drainage at the grade level. Follow the precast layout for efficient piping and to avoid headroom clashes. In other words, the floors are going to slope this one and a half percent in one direction, one percent in the other direction can result in the drain location being as much as 14 inches lower than the high point on an upper floor in the garage. The slab on grade needs to follow that same drainage pattern or you can find that what looks like not a problem for clearance becomes a headroom problem because the floor lines did not follow the same pattern. Joints and flange connections are a key part of making an untopped double T work. As with all precast systems, the jointing and the connections define the behavior and the performance and therefore it's important to pay close attention to the details of joints, particularly in flange to flange connectors. Such things as weather, de-icing salts, traffic loads, seismic strength and volume change loads are more demanding on these types of joints than any other type of structure. The challenge can be met with attention to detail in design and construction and the use of high quality joint material. Joints with topping, where the topping concrete crosses a joint in the underlying precast, there must be a tool joint to provide control joints and a seam for the waterproofing. Joints in precast are natural locations for shrinkage and creep volume change movements to find relief. Tooled joints in a topping slab provide for movement to avoid irregular cracking in the topping as well as to provide more resilient edge that can take the repetitive loading of traffic. High performance double Ts in pre-top parking structures have the top edge of the flanges consolidated and shaped by tooling also. Flange connectors are spaced to provide for alignment of the flange surfaces, the vertical alignment, for continuity under the moving traffic loads and for shear transfer under lateral forces. These are typically spaced four to five feet in the drive lanes with wider spacings in the parking spaces near the ends of the double Ts. Joints in pre-topped decks, the connections must have the capacity to flex without damaging the concrete that holds them. The material for connection should meet the recommendations of ACI 362.1R12 for exposure zone of the project. For most aggressive environment conditions, stainless steel is the recommended connection material. These connections should not be over welded. The strength of the connection is developed with wells that are about one half of the length of the exposed weldable surface in the connections. Limiting the well to the center of the interface gives the flexibility that's needed in the connection to tolerate the traffic and volume change movements without damaging the underlying concrete. The edges of the embedded parts must be isolated from the confining concrete so that the flexing of the parts doesn't cause spalling in the top, sides, or the bottom of the flange of the T. High performance double Ts in pre-topped parking structures have the top edge of the flanges consolidated and shaped by tooling. Joints in the pre-topped T. With this photo, I'm showing a commercially available connector. There are more than one. The importance here is that there is a setting spacer that is provided by the manufacturer of the connectors that provides isolation around the perimeter of this connector so that that flexing or that movement can occur. It's important that the specification includes that the spacers be used in order to achieve this kind of isolation for the high performance of the joint. We can also provide dry cord connectors, that is, plates that have continuous reinforcing across the ends of the members that develop the cord forces for the diaphragm behavior. It's important that those also have isolation around the plates so that under the heat of welding or under temperature changes, the plates have some room to move and breathe without putting pressure on the concrete that's holding the reinforcing bar and causing spalls around the edge. Double Ts are also connected across joints at the ends of the beam, at the spandrel beams, or the walls. When possible, it's best to locate the connections on the underside of the flange for the dry system so that it is isolated from exposure to the top surface as being well below the sealed joint. The guidelines relative to joints include that the completion of the joints requires proper placement of a high quality joint sealant by a qualified installer. One part or multi-part urethane sealant is most commonly used in high performance precast parking structures. These materials must be installed with proper joint preparation, which includes the use of a compatible primer for most installations. Tool joints make installation easier, but any irregularities due to tight joints should be ground to provide a uniform sub-strap strata with soft edges or removing the soft edges or latents. The sealant shape should be maintained using backer rod placed over the proper depth of the floor line. When the sealant crosses connections, it's important to provide a bond breaker over the links so that the seal can move with the remaining parts of the joint in order to avoid tearing. In areas of high exposure, such as open roof, silicone sealers are sometimes used for longer effective life. It is a caution once you put silicone in as the sealant on your garage, you're not going to be able to get any other kind of sealant to adhere to that surface. Structural system design is also an important consideration for high performance garages. The designer must assure that the overall structural system layout meets the needs due to the gravity, lateral, and volume change forces. Strength and stiffness of the structure is required to resist wind and earthquake loads, but the structural system performs best with simple and symmetric lateral force resisting elements, such as shear walls, which are favored due to their strength and economy. In many high performance structures, ramp walls provide the dual function of resisting gravity and lateral loads. Site lines when using shear walls can be improved by limiting the wall lengths to only what is necessary and by casting in wall openings as long as the remaining portion of the wall can transfer the required loads. Framing layout used for shear walls instead of columns at the ends of the ramp. Again, more efficient if the shear walls can be the vertical support without the need for columns. If the wall obstructions at a crossover bay is too great, these transfer shear walls can be located further into the structure away from the end of the ramp. They can also be located on the perimeter. These transfer shear walls can also be connected to the ramp walls, forming a cruciform shape and benefiting from the resistance to overturn due to the dead load from the ramp walls. Here is a plan that shows shear walls on the right-hand end near a crossover bay, but an interior transverse or cruciform wall tied to the ramp walls at the other end. The shear wall on the left-hand side is set one column space away from the crossover bay in order to provide better site lines in the garage. The structural system must be configured to accommodate volume change. The location, orientation, and connections to the lateral force resistance should be considered to reduce the restraint and allow the structure to respond to temperature movements. The PCI design handbook provides guidance on the acceptable length of buildings without expansion joints. Well-configured framing with ductile connections can allow these limits to be stretched to eliminate the need for expansion joints, but the designer must take care not to create excessive movement in the joints that are provided. Because expansion joints create additional demands for seismic detailing, for gravity load transfer and for attention to detail, the PCI design handbook provides guidance For gravity load transfer and for attention to the maintenance, when the layout is near its limits, it's usually best to leave the expansion joints out. In conclusion, precast concrete is an outstanding material and system to build high-performance parking structures. Precast concrete is an inherently durable material that provides design and aesthetic versatility, accelerated construction, with a high degree of quality. Careful attention to planning, detailing, and fabrication of the structure, along with proper routine maintenance, will lead to increased service life and reduced lifecycle costs. All of these considerations help designers and owners build and operate high-performance parking structures. So I will thank you, and I'm certainly now available to take questions that may have come up during the course of this presentation. Thank you, Ned. We do have a few questions. One is, in a topped system, what is the correct material to use over the panel joints as the felt generally causes debonding? Could you repeat that, please? Yes. In a topped system, what is the correct material to use over the panel joints as the felt generally causes debonding? Well, in a topped system, first, it's important to tool the joints properly. Some would provide for, you know, a contractor would like to go out and saw cut all of the joints after they place a cast-in-place concrete topping slab. The problem with saw cutting the joints is that they usually have a lot of work to do with saw cutting the joints is that they usually have to wait until they get a significant strength to get onto the top surface, and the shrinkage cracks that become irregular may have already begun to occur before they're on the top surface. The second problem with saw cutting the joints is that the saw blade can't reach the column. Without cutting into the column, it can't cut the entire joint. So, the first step is to properly tool the joints, which creates a proper width that can accept a joint sealant that will adhere to the section, to the concrete. And the process of providing that tooled joint also compacts the edges. It takes the fines and makes a hard edge, a hard surface that's rounded, shaped so that the edge is durable for the transient traffic for the wheels that are crossing the joints. So, once the joint is properly formed, then the best material for most applications is a two-part urethane joint sealant that is specifically intended for the traffic bearing type of use with a properly prepared surface and the use of the prescribed primer. That system will hold the joint, and it will work for a number of years without any adhesive or cohesive failure. I hope that answers it. Let's see. It just got a follow-up. It said, this question is regarding material that is used, which is added over the joint to prevent the concrete from leaking through the joint, not the top joint material. Oh, I got it. I understand. What I typically recommend, and what happens, historically what has happened with top sections is the contractor will come out and they don't want concrete to leak through the joint while they're pouring the topping. I've seen it handled in different ways. One, which I try to avoid, is that they will take a strip of six or 12-inch wide building felt and lay it down the edge of the joint to make a dam. Unfortunately, what that does is it de-bonds the concrete from the underlying double-T right at the joint, which is the critical section. Two alternatives to that. One is to actually put a backer rod in the joint, the same way that you would have a backer rod for sealant. Pushing a backer rod up in the joint space in order to provide the dam allows the concrete to go all the way to the top surface of the double-T on either side in order to provide a secure bond. The second method I have seen used is to use a thin strip of expanded metal as a catch to hold the concrete along the joint. That can be effective. I have seen it also create some problems in that it can create enough stiffness that it actually will pull a crack at the edge of the expanded metal rather than maintaining the crack or the control joint in the tool joint. Again, when that's done, the best thing is to get on the surface as quickly as possible and to tool that joint properly and deeply enough to ensure that the crack occurs in the proper location. But it's a good question because we have seen problems with debonding along the edges when a more broad strip of material has been placed along the joint in order to keep concrete from going through. Excellent. Thank you. This next question. for live load, do you run a vehicle load or simply use an equivalent uniform load according to IBC and do you also need to consider fire truck load in the design? The load criteria under the IBC is 40 pounds per square foot. It's based on a reference to ASCE-7, which is the load standard. ASCE-7 load standard was changed in 2002. It used to be that the uniform load for parking garage design was 50 pounds per square foot. It's been reduced to 40 pounds per square foot based on a detailed study, surveyed about a dozen parking garages for the actual vehicle content of a passenger vehicle garage that was published in 1999. That study included the dynamic load effects of moving loads and transients and impact on the floors in order to establish that that uniform load was the high end of what was necessary in order to provide for the safe design of garages. At the same time, the recommendation was made that the concentrated load criteria that's used to design local conditions in parking garages be increased from a 2,000 pound concentrated load to a 3,000 pound concentrated load. The 3,000 pound concentrated load was intended to represent the force from a jack lifting up the end of an SUV. It's not really a wheel load. It is a concentrated load that is to be applied on an area not greater than 20 square inches. The combination of the local design for the concentrated load and the global design for the uniform load will result in acceptable and even superior performance in parking garages. The precast concrete can take the concentrated loads very easily. We have an article that is soon to be published in the PCI Journal that deals with experimental work that's been done on full scale double Ts side by side tested under uniform and under concentrated loads that demonstrate that concentrated loads on the flange, the cantilevered or extended flange of the double Ts, actually engage much larger distances along the length of the double Ts than we have thought before now. A concentrated load may distribute over 30 feet of the length of the flange in resistance so that when you push it enough to break, you're breaking a significant part off. We found that the 40 pound per square foot actually is the governing load even for the flange design in bending. It's important to recognize that because except when we get to the ends of the member, at the very ends of the member the concentrated load can break a corner off, but that's also the area of a double T where the cord reinforcing for the diaphragm adds to the local strength of the flange in order to take that local bending condition. We consider the parking or we consider the traffic load in this design criteria, but it's all been incorporated by ASCE 7 and brought into IBC for the purpose of providing sufficient design. These are passenger vehicle garages. They have a minimum headroom of 7 feet. They can get larger, but it's not intended to get commercial vehicles, tow trucks, tractor trailers. They're not what we're designing a parking structure for, and at the same time we're not therefore designing the parking structure unless there is a specific requirement to take the loads from a fire truck. Fire truck loading is its own classification of loading. It doesn't just include the axle or wheel loads of the vehicle, but it also includes the use of outriggers that have to span out in order to run ladders up or to have eccentric bearing on the surface. There are criteria that are written about that as a special vehicle load, and it can be considered and developed in the design, but it's not the ordinary design for a passenger vehicle parking garage. Okay. Excellent. Another question, how often do T-to-T joints need to be replaced? That's a good question, and it depends so much on the environment, the exposure of the garage. It's important to say that the normal warranty for two-part urethane sealants from most manufacturers is five years. That doesn't mean that you have to replace your joint sealants every five years. It's just used the normal extent of a warranty. You can, in some instances, get a 10-year warranty, and what you're buying with a 10-year warranty is some attention to the maintenance that otherwise might not have been taken care of by the owner. Again, a parking garage, as any type of operating and working facility, does take regular maintenance, and the attention to the condition of the joint sealants is one of them. The exposure on the roof level is likely to be more severe because of ultraviolet light and because of greater exposure to temperature changes and weathering. Most of the damage we see in joints, the early damage that we see in joints on the roof is someone who has plowed the roof with a steel-bladed plow, dragged along the top surface, and therefore chipped or hit edges and caused damage that way. Well, that's obviously something you don't want to do. If you do that, you can expect to replace your joints very soon. If you take care of proper snow control, use snow plows with rubber blades, and maintain the distance of the plowing above the surface of the deck, then you won't wear the joints, and they will get the longer performance. I've done a number of renovations and done the restoration of joints. Generally, for well-placed, well-constructed, and well-placed joint sealants, we see that joint sealant replacement can run 12 years to 15 years out, but that's with taking care of small local conditions that might otherwise become a problem because of leaks. Generally speaking, the joint sealants do run anywhere from 10 to 15 years before there is really a necessity to replace it in the joints. Okay, next question. Do you have any recommendation for using fiber-reinforced concrete for the topping concrete? No, I don't. It's not something that we ordinarily will do. Topping concrete does need to be a high-quality concrete. The things that we tend to look at for topping concrete to provide high performance is the same things that we would ask in the precast concrete, low water-cement ratio, the use of durable aggregate, care in the placement, not adding water on the site, and maintaining the proper controls during the placement of the concrete. There are some measures, and often it's recommended that something like a corrosion inhibitor, if your welded wire fabric needs to have proper cover on the roof level of a garage, but if you're trying to maintain 2.5-inch concrete topping and you need to have 2 inches of cover in order to provide that durability, then you might want to either, one, use an epoxy-coated welded wire reinforcement for the topping, or use a corrosion inhibitor such as calcium nitrite as an additive in order to provide a more durable cast-in-place concrete topping surface. I'm not sure you get the extra durability from simply using fiber, but I don't know that it wouldn't be another measure that might actually provide better performance. Next question. Please clarify the difference between un-topped and dry systems. There's a lot of terminology that goes back and forth, and it is somewhat confusing. I think that PCI didn't really do the world a great deal of service when they began to recognize that the world was changing about 30 years ago from having precast concrete double Ts, all of them having a cast-in-place concrete topping to make a parking garage, to where they were going with double Ts that were using the full thickness of a 4-inch flange in order to provide that top surface on the deck. Instead of calling them un-topped, they decided to call them pre-topped to give the idea to the architect that they would come out and the topping was already there. They didn't need to place it in the field. That gave the people the impression that the producer was actually putting topping on to the double Ts in the plant. They're not. They're making them all monolithic, one solid section. When we say pre-topped or un-topped, we're talking about a double T system that has usually a 4-inch flange thickness. Some double Ts are actually made a little bit thinner when high-strength carbon reinforcement, which is non-corrosive, is used instead of steel welded wire reinforcement. But the dry system is a subclass. It's a class of the un-topped double T in a parking garage. Dry system simply means that we're not using pour strips at the ends of the members in order to tie everything together and to shape and form the drainage pattern on the floor. A dry system is an un-topped double T that has the drainage washes for creating the drain lines and moving water into the drains already built into the double T in the factory so that the flange at the end of the double T goes from 4 inches thick to 6 inches thick in the end 3 feet of the member at the low end of the double T in order to form the wash line. The connections for the cord reinforcement are made as mechanical connections or welded connections rather than being made by reinforcing in a cast-in-place concrete pour strip. A dry system is an un-topped double T system, but an un-topped double T system with pour strips is not a dry system. I hope that clears it. Thanks. Next question. During the webinar, you said to use caution with WWR in the flange. Can you expand on that? If you do a calculation, it didn't used to be as important as it has become because the joints in double Ts are getting further and further apart. When a structure, particularly an unheated parking structure, goes through temperature changes, it's going to expand and contract based on the coefficient of thermal expansion of concrete. As it does that, it's going to create strains in the floor. The flange of a double T or the flange with the topping in a double T in itself doesn't express those strains in the field of the flange and the topping. It expresses the strains in the joints. When we made parking garages with 8 foot wide, 24 inch double Ts, the spaces of the joints were only 8 feet apart. Now it's typically 12 feet or even wider so that the joint spacing is that wide. If you take the coefficient of thermal expansion of concrete and you take a 50 degree temperature change and apply the coefficient of thermal expansion to it, you will reach the kind of movement that has to be accommodated in the joint as the welded wire fabric runs across the joint. It just turns out that even with a 10 inch spacing of the welded wire fabric wires, to accommodate that strain, that is that's the anchor point for the welded wire fabric in the topping. If you take the amount of movement that is required for the joint to accommodate the temperature change and you spread it over the length of 10 inches in the welded wire fabric, you are very, very close to yielding the welded wire fabric. In some cases where the temperature change can be great, in the higher latitudes, the more northern sections, it might be more appropriate for these wide span spacings between joints to consider using deformed bars or deformed welded wire fabric with longer spacing between the wires or number three bars that depend on the deformations for development because they will tend to spread the strain over a longer distance and avoid the possibility that the temperature changes at the joints, the effect of the strains or the temperature changes of the joints could actually damage the steel. We have a number of questions, however, we will not be able to get to all of them. We do have time for one more. For anyone who submitted a question that we are not able to get to today, we will follow up with you. So, final question for today. What type of traffic coatings do you recommend and how long do they typically last before the coatings need to be replaced? Again, a very good question and I hope I have time to answer it properly here. The first point I would make is that, in general, we do not recommend traffic coatings. There are specific cases where traffic coatings are important, necessary and beneficial. Those cases are when you have habitable space below an active traffic area, then the traffic bearing membrane or traffic coating can be very beneficial in order to maintain the water integrity of that surface. But if we think of traffic coating as being a protective coating to extend the life of the structure, there are, again, we are dealing with high performance concrete, low water cement ratio, high density material whose permeability is already very low. We're probably not providing the most economical solution for protecting that top surface by using a traffic bearing membrane. One of the reasons I tend to avoid traffic bearing membranes is because, at the roof level, again, it's kind of like the same type of material, a two part urethane is often used as the material to create a traffic bearing membrane, is going to have a life based on exposure to UV light and the treatment and the exposure to temperature changes and the environment on the roof level of a garage of somewhere between 10 and 12 years. At that point, you're going to have to spend money not just to put down a new membrane, but to remove it. So a traffic bearing membrane today, and I may be off of this a little because we don't do that work all the time, but it costs about $3 to $3.50 in additional cost to have a traffic bearing membrane. It costs between $1.25 and $1.50 to take one up. So you're looking at $5 a square foot as a maintenance cost when you need to use the traffic bearing membrane on an exposed level. Now, I've had traffic bearing membranes in a garage last 25 years in the lower levels where they're not exposed to the roof and the upper level sections, but that's the information I can give you. You will have to replace them like you have to replace the sealants, and you probably shouldn't use them unless you really need to.

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