news & information from hamilton form summer .news & information from hamilton form summer 2014
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NEWS & INFORMATION FROM HAMILTON FORM SUMMER 2014
Citrus Bowl Reconstruction
The Florida Citrus Bowl is one of college footballs oldestand most storied venues. The stadium was originally built in 1936 under Franklin D. Roosevelts Works Projects Administration. Originally named Orlando Stadium andlater the Tangerine Bowl, the Florida Department of Citrusbought the naming rights for $250,000 in 1983 and thename was changed to The Citrus Bowl. The first collegefootball bowl game was played there in 1947. In 1952, the game was tagged The Little Bowl with a Big Heart,because all proceeds from the game go to charity.
The stadium was originally built for $115,000. This year, the stadium is undergoing major renovations with a cost of just over $200 million. Eighty percent of the stadium hasbeen demolished; only the upper bowl sections will remainintact. Metromont Corporation is supplying the precast elements for the reconstruction.
Hamilton Form worked with Metromont and CEG (Consulting Engineers Group) to develop forms for the project. Triple risers were provided for the seating sections.Of special interest is the formwork for the raker beams.Three sets of modular forms were provided. Each set consisted of a straight sideform with integral haunches and riser sideform. The sideforms were bolted down to an existing casting table and products were cast on edge. The forms were made modular to accommodate variousproduct configurations. Small sideform sections were supplied to vary the lengths and number of risers. All of the beams were the same height, simplifying the set-up and casting.
The project is currently in process. Most of the renovationsare expected to be completed in November of this year, in time for the next Citrus Bowl game.
Precaster: Metromont Corporation
This 15-foot wide, flat deck double tee is split atcenterline and has an 18-inch center section thatcan be removed to form a 12-foot double tee.
The 30-inch stems can be fitted with stem fillers tochange the depth of the stems. Magnetic side railsare used to change the width of the flange.
Double Tee Form Design
First and foremost, stressing capacityA form designed for 760 kips per stem is significantly differentthan a form designed for 1200 or 1500 kips. More stressing capacity means more steel to resist the prestress forces. More steel means more cost both in materials and labor. While wewould never under design a form, we also dont want to add unnecessary cost by over-designing it either. Thats why stressing capacity is extremely important when designing a self-stressing form.
Strand sizeA few issues ago we talked about changing from to 0.6strand. Even though the overall capacity of the form may be thesame, 0.6 strand has about 50% more capacity than strand.That means the load entering the form is more concentrated with 0.6 strand, making strand size an important element when designing a self-stressing form.
Strand patternA strand pattern tells us where to reinforce the form. Some stressenvelopes are symmetrical. Others have the load concentrated atthe bottom of the stems. Some double tees call for deck strand.Some double tees have depressed strand. Knowing the numberof strand, the size of the strand, and location of the strand are all critical when designing self-stressing forms.
Production detailsOften times we make allowances for production details when designing a double tee form. Many customers use magnetic side rails to eliminate drilling holes in the deck of the form. When bolt-down rails are specified, we drill and make provisionsto fill holes to mount the side rails in whatever positions the customer dictates.
If you plan to run equipment on the edge of the form, such as a tarp cart or utility machine, now or in the future, let us knowand well add reinforcement.
Typically Vibrotrack channels are added to both sides of a double tee. We usually provide hinged jacking plates at the ends of the bed to make it easy to clean the stems of the tee, but other designs can be used if requested by the producer.
Collaborate Needless to say, even a typical form has a number of detailsthat are dictated by the customer. Thats why we dont do genericor ballpark pricing on forms. There are too many variablesinvolved to be accurate.
The next time youre ready to discuss formwork, think about thevariables that can be built into your formwork. The best forms aredesigned with both engineering and productions needs in mind.Give us a call to discuss features and options.
Even the most common forms require considerable thought and detailing to design and estimate. Although the double tee is one of the most common forms we produce, it is also one of the most diverse. In addition to width, stem spacing, stem configuration and length of bed, there are a number of other criteria we need to know before designing and accurately pricing a double tee form.
Double Tee Does Double Duty
Keeping Kips in CheckHamilton Forms stress skin design utilizes longitudinalstiffeners, as well as the form skin, to resist the prestressforce. The number of stiffeners, their size and location are determined based on stressing information providedby the customer. Below are examples of three differentdouble tees designed for different stressing capacities.
This flat deck, 12-foot double tee has 30-inch stems and is designed for 1100 kips in each stem. The form has a flat deck design with tubes at the edge of the deck to support equipment(such as a tarp cart or utility cart) that will ride on the edge of the form. This double tee will be used with magnetic side rails,therefore no holes are drilled in deck.
This 10 foot-double tee has 26-inch stems and is designed for 720 kips in the stems. Notice only three stiffeners are needed at the stems to resist this load. A continuous foot channel is at the bottom of the form, but no provision was made for Vibrotrack.
This 12-foot wide double tee is designed for adjustabledeck strand. The deck strand can be adjusted both vertically and horizontally. The form has a flat deck foruse with bolt down or magnetic rails and channels areon both sides of the deck for attachment of a top depressing tool.
This 12-foot double tee is designed for 1600 kips in eachstem, more than a typical 12-foot double tee. The stems are 33-inches deep. Notice the number of longitudinal stiffeners at the stems to resist load. The form has a flatdeck, a continuous foot channel and Vibrotrack channels on each side. The side shown is the jacking end of the double tee, fitted for a hinged jacking plate.
Adjustable Deck Strand
ow and then, well get a call from a customer having a problem with product that cracks when its stripped from a self-stressing vessel type form. There may be a number of reasonswhy concrete might crack or spall when its stripped from theform, one of the most common is the detensioning method.
During detensioning, the form elongates due to the release of the prestressed force. At the same time, the prestress force is transferred to the product and the product moves in the opposite direction of the form. Product movement in the form can cause the product to crack especially if your form is not perfectly straight and level. Your goal when detensioning is to minimize the movement of the product in the form so the product stays as close as possible to where it was cast.
To minimize movement in the form, use a balanced detensioningmethod. Start by cutting a few strands (about 20% of the load) at both ends of the bed, simultaneously. Then move in to the first headers from the end of the bed and cut the same strand.Then move to the next set of headers, and the next, until youreach the center. Once you reach the center, work your way out, symmetrically cutting more strands at each header until you reach the end. Cut and repeat until all strand are cut. Try to make the last cuts at the center of the bed.
Never cut all ofthe strands at oneend of the bed,then cut the otherside. Cutting allthe strands at oneend then theother will causethe form to elongate to one side, increasing product movement.You also wouldnt cut strand on a large casting table from left toright or cut all the strand in one leg of a double tee, then theother leg. These processes are not balanced or symmetrical andcan damage the product and the form.
A form that is warped or bowed can also crack product as it is being pulled away from the form. Check that your form is straight.Straighten any noticeable bows or dips in the form. Make surethe form is installed level. Shim and straighten where required.
That said, there is no one size fits all. If youre having problemsstripping, make sure youre using a balanced detensioningprocess. Think through a process that will work for you. As you do,consult with your plant engineer or give us a call at Hamilton Form.
Double Tee Depressor System
raping of prestressing strand in double tee forms can be a time consuming, costly operation. Hamilton Forms depressor systems have proven to be a reliable, labor-efficientmethod of draping strand.
Our solid steel beams clamp to the depressing channel on theedges of the double tee form. Once the beams are placedand attached to the side of the double tee, a fixed length ortelescoping, adjustable pin slides through a hole in the beam.The hydraulic depressor tool fits over the pin. Workers canmove off the form while the depressor tool is remotely activated. The top of the pin is pushed down flush with the top of the beam and is locked in place.
A balanced detensionin