Rain Barriers and Rain Screens

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In buildings, water has the unfortunate habit of getting where building owners don’t want it to go. And once inside a building it has the potential to do significant damage.

Buildings gain, lose and store moisture along with heat energy through a variety of physical mechanisms. Operating durability, efficiency and serviceability of the structure can be affected by moisture flow. Controlling moisture flow in a building also has significant impacts on occupant health, safety and comfort.

Modes of moisture flow into buildings include:

  • Precipitation – rain and moisture making their way through openings in building surfaces

  • Water vapor evaporation – liquid water changing into gaseous or vapor state and is absorbed into the air

  • Diffusion – water vapor moving under pressure from areas of high concentration to areas of low concentration and also high temperatures to low temperatures

  • Condensation – water changing from a vapor state to a liquid state as air becomes saturated. Where condensation occurs matters.

Architects generally have two approaches:

  1. Keep moisture from penetrating the wall assembly or

  2. Assume it will penetrate the assembly and provide a way to remove it

Rain barriers are often face-sealed curtain walls and have sealed joints between the components. Drainage is generally not required in these assemblies for moisture originating from the exterior. For the wall to remain effective, the joints must be maintained because they typically represent the weakest parts in the system. The most effective rain barriers will have the fewest joints and be made of the most durable building materials.

Precast cladding, including all CarbonCast Enclosure Systems, can be considered a face sealed curtain wall. The concrete, typically over 5,000 psi in strength, absorbs and passes very little liquid water. Panel joints should have either two layers of sealant or sealant and a secondary method of defense against water penetration. Joints around openings should have primary and secondary seals.

Rain screens begin with the premise that water will eventually penetrate the exterior wall system and that a mechanism must be designed to drain it. They are not water-tight and are typically ventilated. The screen relieves most of the driving pressure of water, then drains or evaporates it through a cavity behind the façade. Rain screens generally entail more complicated design and construction practices and material selection to ensure proper water flow and minimize the potential for damage once the water passes the screen. They also have more variability in materials and often more joints and opportunities for water penetration.

Moisture (both liquid and vapor) will accumulate if the rate at which it collects in the space exceeds the rate of removal. Repeated wetting, followed by repeated drying, may be accepted as long as materials do not stay wet long enough to freeze and deteriorate.

CarbonCast High Performance Insulated Wall Panels, like most precast wall panels, are strong enough to withstand high winds and wind-driven projectiles, hurricanes, and wildfires when properly installed to code and maintained. They are also impermeable to air infiltration and wind driven rain. The high tensile strength of reinforced concrete combined with proper compaction imbues the material with the capacity to withstand storms and render it resistant to wind-driven rain and moist outdoor air in hot and humid climates. In many cases this strength is enhanced though prestressing, which further prevents the likelihood of cracking stresses due to shipping and handling.

Architects often ask if precast walls can be designed as a rain screen or drained system. They can. However, because they provide superior resistance to rain penetration and air leakage, they are often used as a rain barrier. In fact, using the drained approach with precast wall panels can introduce risk that water may damage the panel’s structural connections. Why entertain that risk? Design for the sure solution!

-Altus Group

Introducing Tension Encabulation

Due to measurement errors or changing customer requirements, the length of precast hollowcore components can sometimes be wrong.

When elements are too long, the obvious solution is to cut them to length. However, when an element is too short, precasters are forced to completely remake the elements incurring all the costs in doing so.

We’ve been diligently working on a solution to this problem and are pleased to announce through tension encabulation we are able to stretch concrete elements when field conditions dictate we do so.

A plank by any other name

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… is not the same!

Well, ok, it is. Kinda.

When looking at precast hollowcore concrete, you can across quite a few product/brand/trade names. Elematic, Flexicore, Spancrete, Ultra-Span, Dynaspan, etc. It can be hard to derive the difference between them, or to decide it’s worth to parse out these differences, especially when it comes to specifying. Sometimes, a given name is repeated, even while crossing wide gaps in project size, location, and time period.

To be fair, all of these trade names do refer to a common construction product: precast, hollowcore, concrete planks (or slabs). The value in hollowcore slabs is their premium span-to-thickness ratio in the spaces underneath them that they provide. By using hollowcore planks, one can eliminate the unsightly and obtrusive combination of columns (obstructing views and lowering space flexibility) and deep beams (lowering ceiling heights/headroom). The value per square foot of this type of product is pretty unbelievable when you compare the resulting living space.

These planks come in a nominal width (depending on manufacturer) and are designed, fabricated, and cut to length based on project needs. Because of their designed-to-order and built-to-order nature, you can be assured that the installation and life span of each of these products is the best you can get. That said, the design and installation requirements of each brand can and will vary; it’s the details that can get ya here. Sometimes a standing name can and does get carried over into multiple projects; it pays to review the project to ensure the correct brand is being referenced. There are many form factors of hollowcore concrete. Heck, even we at Mid-States have changed form factors over the years.

So what does this mean for you? It pays to review either the project or the master precast specifications to make sure they are in line with the current manufacturing market and the resulting construction requirements for this product. While even though you may still question the value of discerning each plank type, there’s still one piece missing from all of this, likely the most important piece of all, the service that comes with the product. Each precast provider has their own way in taking you through the process. We would love the opportunity to show you ours (more on this in a future post so stay tuned).

Confused? It’s OK. It can and does get that way quickly. Really, your best bet is to give us a call to verify. We’d be happy to review your current specs and provide our feedback. If you have master specs that haven’t been updated in a while, we can also help with those. While we’d like to sell you our planks, we’d love to simply be your go-to source for information and pricing. Even if we can’t help you, we’d be happy to refer you to someone who can.

Give us a call anytime at 800.236.1072.

Team Member Takes Second in Archery Tournament

Colin Jones, a member of our preconstruction team, recently tied for second place in the professional class of the Wisconsin State Indoor Archery Tournament.

On Feb. 16 and 17, Jones spent the weekend competing in Wisconsin Rapids, with his wife Jessica spotting for him. On day one, Jones shot a 300 with 59X and on day two, Jones shot a 300 with 58X, for a total of 600 with 117X. A perfect score is 600 with 120X.

Jones started shooting archery in 4H at nine-years-old. Growing up watching the Robinhood movies and reading the books, archery just always fascinated him, plus, he said, he was naturally gifted at it.

He joined the Beloit Field Archers when he was 18-years-old and by 19-years-old, he was shooting competitively. Jones said he first learned how to shoot by watching other people and then just started asking questions of other archers. In 2012, he turned pro after winning the state amateur championship for a second time.

”There’s a little bit of luck involved and a lot of skill,” Jones said.

The skills necessary for archery, according to Jones, are a positive mental attitude, good form and lots of practice. It also helps to have a supportive wife, Jones said, crediting Jessica for taking care of the kids and holding things down at home while he shoots.

Before having kids - Jones is father of Cole, 3, and Lorelei, 3 months - Jones was practicing about four times a week. Now, he only shoots in a league on Thursday nights, sometimes taking Cole with him. Cole already has his own bow and shoots in between dad’s practice when he goes to league night.

”That fact that he’s showing interest, that’s pretty neat,” Jones said.

Jones loves the competitiveness of shooting and chooses to shoot in the professional class because he wants to shoot against the best archers in the world, some of whom are from Wisconsin. He competes up to six times each year across the country. He currently shoots a Dave Barnsdale Bow.

”It’s an older bow, but I feel comfortable with it,” he said.

For anyone interested in trying archery, Jones advises starting with used equipment, joining a club and not being afraid to ask questions.

”Everybody in archery is willing to help everybody, especially someone new,” he said.

Jones will compete in the NFAA Nationals in Cincinnati, Ohio this weekend. Nearly 2,000 archers will compete.

Camber: What is it?

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Camber is inherent in all prestressed precast products. It is the upward deflection created by the prestressed forces in the strands located below the center of gravity. This is required to resist design loads and in the hollowcore plank it compresses the bottom more than the top. Span length, plank thickness and design load requirements will determine the amount of prestressing force needed in the plank, from which the engineer can calculate an estimated camber. The benefit of camber in prestressed precast concrete products is that it allows for longer spans, shallower depth sections and higher load carrying capabilities than conventional building materials. Camber should not be specified as a design parameter.

Differential Camber

Differential camber refers to varying amounts of camber between adjacent hollow core planks. Camber differences occur because no two planks have the same exact strength gain, creep and exposure to the elements in storage. Planks in the yard exposed to direct sunlight will experience more camber growth than plank in the shade. Adjacent planks with different span lengths will differ in camber as will those with different prestressing strand patterns. Minimize differential camber by one or more of these methods: jack up low pieces; shim shorter planks at bearing; flash patch; apply self-leveling course.

Theoretical Camber

Theoretical camber is the calculated upward deflection based on relevant design parameters. It is time dependent due to the curing of concrete and can vary significantly from actual camber on site. The optimal storage time for plank in the yard is 2 to 3 weeks. Extensive job schedule delays and increased storage time can lead to camber growth. This is especially true in the early summer where warmer temperatures and low humidity accelerates the curing process.

Important Considerations about Camber

Specify realistic design loads to avoid overly conservative load requirements. Limit plank span to depth ratio to 45 and if necessary, increase plank thickness.

Increase 2-inch topping overlays if maximum plank camber exceeds 3/4 inch. Plan finished floor elevations accordingly.

Minimize differential plank camber prior to grouting keyways by one of more of the following methods: use temporary shoring to jack up low planks; use sandwich plates and bolts at mid span to draw planks vertically together; shim shorter and low planks at bearing points; flash patch (feather) joints between adjacent planks; apply self-leveling coatings (gypcrete) or use structural topping.

Advise subcontractors installing door frames to account for plank camber and topping if any. Contact us today to learn more and be geared up for your next project.

Source: PCI

 

Safety Before All Else

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In this industry, safety isn’t something to take lightly.

At Mid-States Concrete Industries, safety is not a trend or something to sell or be really good at.  It's a journey, our way of life.  We do not compromise safety, ever.

Our vision is to change the world by being the safest and most innovative precast building company.  To ensure this vision is a reality, Mid-States has developed a safety mindset, not just a commitment.  To be truly safe, every employee must learn how to identify hazards and work as a team to eliminate those hazards.  We don't put people in to Mid-States, we put Mid-States in to our people and we train to build the mindset, to create world-class safety habits.

Every day, we are part of creating world-class buildings in which to live, work and play.  And to keep doing that, we must make sure our crews are staying safe, always.  In the plant, in the yard, out in the field, driving from job site to job site – everywhere.  We want our team members to go home to their families every single shift, in the same condition they arrived for their shift.

How do we do this?  Partly with events like Safety Days.  Conducted annually, Safety Days offers all of our team members a refresher course on the company’s safety guidelines and policies.  Safety Days is led by Mike Wolff, Vice President of Safety and Quality.

“Every year, we have customers call to say you guys are the safest guys (they have) ever seen,” Mike shared.

It took plenty of work and dedication for the team to get to this point.  In addition to in-depth internal training of all new employees, and continuing internal education for all employees, all foremen are 30-hour OSHA certified.  The entire field crew is first responder certified.

Safety Days covers safety policies and procedures, like the importance of personal protective equipment, maintaining equipment safely, site safety plans and hazard identification.

Hagen Harker, President of Mid-States Concrete Industries, acknowledged the dedication to safety Mid-States’ employees show.

“What you do to build buildings is incredible,” Hagen told the crew.

He acknowledged that even when employees find themselves at a challenging job site, they still focus on not just getting the job done, but getting the job done safely.

“I don’t take for granted what you do out there every day,” Hagen told the team.

He also commented that every day employees are out on a job site, they have an opportunity to build a world-class building.

“Everything you do out there is a reflection on us,” Hagen said.  “Be world-class.  I know you know how to do it.”