Hollow Core Slab Strand

[Phyliss Berard]

KnightcoreHollowcore) plank is a precast, prestressed, concrete plank manufactured by a precision, extrusion process, from zero slump concrete providing outstanding dimensional control and uniformity. Slabs are cut to length to assure dimensional accuracy and smooth end finish.

The underside of hollowcore plank is steel form smooth, and can be either left as is or painted with a textured paint. In many floor applications, hollowcore plank may be used without concrete topping. Joints between slabs are grouted and feathered, suitable under-layment or padding applied, and finishing carpet, wood floor, or tile installed.

Hollowcore plank meets the requirements for the restrained and unrestrained fire ratings of ASTM E119 and is listed by Underwriters Laboratories, Inc. for two hour fire resistant classifications (untopped), restrained and unrestrained conditions. Three and four hour ratings are also available with field-cast toppings.

The use of hollowcore plank structural floor and roof slabs will result in a lower total construction cost for your next project. The time and weather delays of on-site forming and curing of poured concrete are eliminated.

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Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

Abstract: Precast prestressed concrete hollow-core slabs (HCUs) are structural elements with less self-weight, providing improved structural effectiveness in withstanding the straining action and allowing for a long span. This study investigated the additional strand slips and developed machine learning (ML) models for evaluating the final strand slips (Śf) of the precast HCUs. Two groups of HCUs, with nominal widths of 1.2 m and 0.55 m, were subjected to flexural loading conditions. One sample from each group was selected to form composite specimens by casting a concrete topping slab, and the restrain mechanism was attached at the ends of the additional HCU specimens. The experimental datasets used to train the ML models, including the support vector machine (SVM), multi-linear regression (MLR), and improved eliminate particle swamp optimization hybridized artificial neural network (IEPANN) models for the prediction of Śf. The efficacy of the IEPANN model compared to the nonlinear predictive models was evaluated, and the performances of the developed ML models were checked using the evaluation matrices. The results indicated that the prestressing strands with relatively higher initial strand slips may result in larger additional slips during flexural loading. The restraining mechanism and cast-in-place topping slab influenced the additional strand slip rate. The hybridized IEPANN model outperformed other classical models in estimating the additional slips with the R2 values greater than 0.9 in the two modelling stages, indicating the efficacy of the IEPANN compared to the nonlinear predictive modes. Keywords: machine learning; hollow-core slabs; prestressing strand; flexural loading; precast concrete

Haruna, Sadi Ibrahim, Yasser E. Ibrahim, Musa Adamu, and Omar Shabbir Ahmed. 2023. "Determination of Final Strand Slips of Prestressed Precast Hollow-Core Slabs Subjected to Flexural Load Using Machine Learning Algorithms" Buildings 13, no. 8: 2013.

A hollow core slab, also known as a voided slab, hollow core plank or simply a concrete plank is a precast slab of prestressed concrete typically used in the construction of floors in multi-story apartment buildings. The slab has been especially popular in countries where the emphasis of home construction has been on precast concrete, including Northern Europe and former socialist countries of Eastern Europe. Precast concrete popularity is linked with low-seismic zones and more economical constructions because of fast building assembly, lower self weight (less material), etc.

Slabs in prestressed concrete are usually produced in lengths of up to 200 meters. The process involves extruding wet concrete along with the prestressed steel wire rope from a moving mold. The continuous slab is then cut to required lengths by a large diamond circular saw. Factory production provides the obvious advantages of reduced time, labor and training.

Another fabrication system produces hollow-core floor slabs in reinforced concrete (not prestressed). These are made on carousel production lines, directly to exact length, and as a stock product. However, the length is limited to about 7-8 meters. Especially in Belgium, this method is widely used in private housing.

To meet modern standards (both hollow-core and massive slab) of soundproofing the floor needs to be covered with a soft floor covering that is able to dampen the sound of footsteps or a floating floor screed should be installed. An alternative is to put a strip of rubber underneath the floor slabs.

Hollow-core slabs and wall elements without prestressed steel wire can be formed by extruders. The size of these elements will typically range in width from 600 to 2400 mm, in thickness from 150 to 500 mm, and can be delivered in lengths of up to 24 m.[1]

The Elematic Stressing Abutment E9 is designed to hold the stressing strands of hollow core slabs during prestressed precast concrete production. The Stressing Abutment E9 includes a pair of abutments, one active abutment for bundle stressing, and a passive abutment.

The Stressing Abutment E9 is designed for multistrand (bundle stressing) but can also be used for single strand stressing. To equip a casting bed for pre-stressing, a pair of abutments is required; one for each end of the bed, the active end and the passive end.

The abutments at both ends are mounted directly in the concrete foundation of the bed. At the active end, the stressing device and the beam can take a 200-ton maximum stressing force, while the fixed intermediate beam can take a 150-ton stressing force. The total maximum stressing force the abutment can take is 300 tons.

Stressing takes place in one or several stages. The strands in the first pull are stressed with a stressing beam, which is then fixed with wedges if only one pull is needed. If there are a lot of strands and additional pulls are needed, the first strands are fastened to the intermediate beam with anchor grips. After this, the remaining strands are fastened to the stressing beam, the pull is conducted, and the stressing beam is fixed or the process continues with a third pull.

Like all Elematic machinery, safety features are built in. The Stressing Abutment E9 meets the EC Machine Directive requirements. It comes with thorough, clear operator, maintenance and safety manuals in the required language.

Abutment construction differs at the active end and the passive end. The active abutment features a fixed frame, a mobile stressing beam, pins for fixing the hydraulic cylinder shafts and a locking plate for locking the beam after stressing.

Comcast released a press release that announced it is the first ISP in the U.S. that is trialing hollowcore fiber. Hollowcore fiber takes advantage of the phenomenon where light can travel 50% faster through air than it can through fiberglass. As is described by the name, hollowcore fiber is a fiberglass strand with a small hollow tube in the center.

Comcast is interested in the technology because the faster light speed translates into as much as a 33% reduction in latency. Comcast would use the hollowcore fiber for applications that demand low latency.

The press release described a test where Comcast made a 40-kilometer connection between two locations in Philadelpia to be able to test the performance of the fiber in a real-world application. Comcast was able to successfully establish a bidirectional transmission using simultaneous traffic paths ranging from 10 to 400 gigabits per second to 400 Gbps on a single strand of hollowcore fiber.

Hollowcore fiber has been developed by Lumenisity. The concept of hollowcore fiber was born a decade ago in a DARPA lab working with Honeywell to improve fiber performance. Those tests showed that it was possible to create a single straight path of light in tubes that was perfect for military applications. The light could carry more bandwidth for greater distances without having to be regenerated. By not bouncing through glass, the signal maintained intensity for longer distances. DARPA found the fixed orientation of light inside the tubes to be of great value for communication with military-grade gyroscopes.

Lumenisity big breakthrough came when it developed the ability to combine multiple wavelengths of light while avoiding the phenomenon known as interwave mixing, where different light frequencies interfere with each other. By minimizing signal dispersion, Lumenisity eliminated the need for digital signal processors that are used in other fiber to compensate for chromatic dispersion. This means repeater sites that can be placed further apart and require simpler and cheaper electronics.

I am fairly new to Revit and have used it only for architectural modeling so far. I'm trying to model the construction of a project that contains hollow-core slabs. I have managed to model and split the floor (with the precast extension) but the voids and profiles are not showing in the sections (screenshot added).

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