What are the current methods of wall-to-wall connections across the vertical joint (the horizontal direction)?
Wire loop system: Well, I am not a core structural design engineer, but from what I gather, is that this connection is widely used in the residential sector or sometimes even in the commercial projects, but it is well known that these connections cannot be classified as ductile connections. They are often known as ‘soft or notional connections’ to simply align the wall panels together and to avoid a progressive collapse, which also relies more on the shear keys provided in concrete more than the loop itself. Also, the wall panels are designed as individual panels with dedicated vertical reinforcement required for each panel - right from the footing top level to the terrace level. In other words, despite the presence of say, 2-3 walls next to each other, their combined effect cannot be considered (in design) to increase the length of the shear wall, to gain structural benefit. Furthermore, this connection is not recommended in seismic zones by most structural engineers.
Cast in situ Stitch joint / Steel loop system: The design challenge of an “individual panel design”, which is posed by the wire loop system, is somewhat overcome by adopting the steel loop system. By having overlapping loop bars and certain vertical reinforcement inside them, it is assumed to act as a force transferring mechanism from one panel to another. So, if there are multiple panels next to each other, then they can be assumed as a single long panel in the structural analysis and design stage. However, as simple as it may sound on paper, the actual manner in which this is achieved on site is very difficult. There is tremendous congestion in the junction, which is often open for a width of around 300mm. Miniscule quantities of shuttering and concreting (or grouting) is very time-consuming, costly, and the quality assurance of such minor quantity of work is difficult. It is prone to bulging and the joint looks aesthetically different and is difficult to treat. Not only it is difficult on site, but it is also difficult to have protruding loops from the mould shutters as well, at the time of casting, which may include bending/re-bending etc.
What does Precast India Connector (PIC) denote?
PIC is based on a simple and proven precast connection technique – the Dowel and Sleeve connection which is used widely for panel-to-panel connections across the horizontal joint. Usually, the material of the sleeves in such cases is corrugated pipes or sometimes even cast-iron couplers. Use of the dowel-sleeve method in horizontal connection (across the vertical joint) was hitherto considered to be impossible by pre-casters and structural engineers due to the clash between the sideway projecting dowels while lowering the panels during installation. However, we have conceived, innovated, and patented a method of achieving a dowel-sleeve connection even in the horizontal direction, following which, we launched the Precast India Connector (PIC) via our new venture - Precast India Connections.
PIC, a patented product made in India, is providing significant benefits to precasters who are struggling with issues related to cost and time overruns, as well as those seeking an alternative to CIS joints in their precast projects. With its patent already granted in over 20 countries, PIC is gaining global recognition as an effective solution for the challenges faced by the precast industry.
How would you compare PIC with the other connections mentioned above?
PIC cannot be compared to the wire loop as it is a stronger and ductile connection, whereby we get an emulative monolithic connection, and the multiple panels connected via the PIC can be considered as a long wall, which reduces vertical reinforcement and related costs to the precaster by almost 30-40%.
When compared to the CIS Stitch Joint, PIC is an emulative monolithic connection that can replace the CIS Stitch Joint in a very efficient manner by saving time and manpower, enabling ease of operations, and ensuring higher quality. PIC is also a more professional, quantifiable, and qualitative substitute to the messy and laborious CIS Stitch Joint.
How was PIC conceived by your company?
PIC was designed based on the feedback from our own production and installation engineers and under the guidance of product designers and consultants from all over the world. After nurturing the idea and developing the product for almost 7 years, and using it in our own projects, we felt that we were ready to introduce it to other Indian precasters at very economical rates.
The idea of PIC was led by our motto: Strive to eliminate cast in situ joints in precast projects for long term sustenance and profitability. As a precaster for over a decade, we had realised in the first 3-4 years of operations, that if precast as a technology and as an industry has to survive and succeed, it was very important to delink the precast concrete elements (almost 95% of the quantum) and the CIS junctions (only 5%).
The whole advantage of precasting is lost when at site one has to again pour CIS concrete, that too in miniscule quantities at the junctions. This takes time, effort, energy, resources, and coordination issues. This ultimately leads to time and cost overruns, which, more often than not, cannot be quantified, and which cut profits by increasing the overheads.
We felt that there was an urgent need to innovate the connection processes, but in an inexpensive way using some ingenious yet simple ideas that could be implemented easily in the design, detailing, production, and installation stages.
Usually dividing a Precast Project into multiple agencies is a recipe for disaster. Companies need to take their own decisions whether to hire cranes or trailers via agencies or invest in them as capital. But by eliminating CIS junctions, business owners can definitely eliminate one agency and reduce the risk of dependency on multiple agencies. Usually, it is observed that since the quantum of CIS junctions in walls and columns is low, the rates demanded by such agencies are unreasonably high, but (unfortunately), rightly so. Although the quantum (from cost and effort) is low compared to the project cost, believe it or not, the critical path of the entire project then depends on these CIS junctions. We are of the firm view, based on our experience that installation of upper floors should not be halted due to CIS junctions. Installation of columns and walls of upper floor should take place independent of CIS screed or CIS junctions.
The idea of PIC was born by this very thought: if you want to succeed and be profitable to take the advantage of precasting in the factory, then the junctions must be done without CIS concrete, but with the help of a few in-house workers well-trained in grouting.
What support and feedback did PIC get from experts in the field?
We have already used PIC for shear wall to shear wall connection, retaining wall to retaining wall connection, and for rebar continuity in beams to avoid in-situ junction by casting column up to beam top instead of beam bottom. We have got a lot of guidance and support from leading professors worldwide, namely, Prof. Rolf Eligehausen, Germany - Mentor in European Technical Approvals – who gave us overall guidance; Prof. Akira Wada, Japan who gave us guidance and test support; IIT Madras who gave us guidance in testing and approvals; and IIT Bombay who gave us reviews of some projects in which this system has been used.
We received positive feedback from leading Structural Consultants in India, namely, Dr K Shantharaju, SW Mone and Associates, TRC International; Melior, Metey, and Precision Precast Solutions.
Please enumerate the features of PIC.
- Proven Dowel-Sleeve methodology
- Multiple options to slide the bar from Donor to Receptor
- GSI Attachments to indicate grouting completion and non-spillage
- Optional Holdfast cum Supplementary Reinforcement Plates to fix in position
- Indication can be provided to denote that the bar travel is complete
- Tolerance Analysis performed for 12mm to 20mm rebar sizes
- Aligner Plate and end caps to fix to shuttering in an easy manner
- Minimum re-training required to staff for grouting and shuttering
- Least amount of openings seen in elements
- Factory assembled product, very convenient to use and fit in reinforcement cages
- Can be used in horizontal as well as vertical casting
- Same product can be used in left or right orientation
- Universal size of Donor whereas Receptor is in two sizes: Small - for 10 and 12mm dia bars; and Medium - for 16 and 20mm dia bars.