Experimental Investigation of Vertical Slipform Deformation

Research Article Volume 6 Issue No. 5

Experimental Investigation of Vertical Slipform Deformation A.Sheik Abuthakir Riswan1, DR.G.Jaisankar2 PG Scholar in Structural Engineering1, Professor and Head2 Department of Civil Engineering Dr. Mahalingam College of Engineering and Technology, Pollachi, Tamil Nadu, India

Abstract: The Slipform construction technique is a rapid and economical construction method that can achieve considerable cost savings when compared with the cost of conventional formwork. Slipforming techniques perform better for circular concrete structures of greater height than the non-circular structures. The edges of non-circular slip-formed concrete surface tend to damage and increase the expense of repair work. Thus counteracts the reduced cost of this technique. More issues such as lump formation, lifting cracks may arise while constructing a rectangular shaped vertical structure using slip form. In this paper, the issue such as deformation of formwork during construction and lifting has been attempted. Few studies on workability, setting time and hardening of concrete, friction, bonding between slip form and concrete are found in literature to address the issues. While pouring the concrete between the slipform panels, the concrete exerts pressure on the panel and the panel gets deformed. Deformation in the panel due to the lateral pressure by fresh concrete is examined. After placing and enough hardening of concrete, the slipform gets lifted vertically. Damages happened in the concrete due to the deformation in the formwork is investigated experimentally. This paper deals with the experimental investigation of deformation of slipform panels, by varying the distance of yoke legs from the edges. From the study, the solutions are proposed to reduce the damages and deformation of formwork which enhances high quality slipform construction.

Key Words: Slipform construction, Panel deformation, Formwork deformation, Aspect ratio, Damages in slipform construction, Lifting cracks.

1. INTRODUCTION 4. Lifting Jacks: Lifting jacks facilitate lifting of Slip form Slip-form construction is a continuously formed construction assembly. Jacks are to be suitably located preferably at equal method in which concrete is poured in continuously moving intervals to enable to lift slip form as one integral unit. form. Slipforming technique differs from conventional concrete 5. Jacking/Climbing Rods: Jacking rods are normally located forming because of forming panels that move semi continuously centrally in the wall to be cast or at equal distance in yoke beams in relation to the concrete surface being formed. This technique depending upon the number of jacks. The lifting jack climbs proved to be the valuable tool in cutting cost and man hours and over the jack rod. The entire load of the Slip form assembly is the same time permitting construction to proceed with maximum transferred to jacking rods when jacks are energized. safety.Horizontal slip form has enabled cement concrete road 6. Hydraulic Pump: Hydraulic pumps are provided to circulate pavements, airports, taxiways and various structures with required quantity of hydraulic oil at desired pressure for flawless concrete with superior performance characteristics. energizing jacks to lift the assembly and facilitate its uniform Vertical slipform technique is one of the techniques used for lifting. construction of high rise structures like communication towers, 7. Tapered Sleeve: Tapered sleeve tubes are provided to prevent chimneys, bridge piers, silos. Vertical slip forming allows fresh concrete coming in contact with jack rods, thus, facilitates concrete to be erected monolithic with a highly finished surface extraction of jack rods later. Taper sleeves are attached to yoke in a circular type of structures and thus reduces the duration of beam and move along with slip form and create a hole in construction. concrete around jack rod.

2. VERTICAL SLIPFORMING

2.1 Components of Slipform:

1. Shutters and Walers: The function of shutters and waler assemblies is to maintain correct profile of structure to be slip formed and resists concreting pressure. Horizontal walers prevents panel from deformation and supports the yoke legs. 2. Yoke Legs: Yoke legs are used to lift the slip form structure as one integral unit, transfer lifting reactions to jacks and acts as the main connecting member for walkway platforms, masons’ scaffold, yoke beams, top platforms, etc. 3. Yoke Beam: Yoke beam is mainly a connecting member between inside and outside yoke legs. Two yoke beams are connected at top portion of yoke legs. Jacks are mounted over yoke beams. Yoke beam transfers lifting forces of jacks to yoke Fig -1: Detailed cross section of a Slipform Components legs.

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3. EXPERIMENTAL INVESTIGATION The earth was excavated and the ground surface was leveled. The bed concreting for size 5m x 3m, for the depth of 150mm was laid. Then, the inner slipform wall area was marked. The rectangular wall resembles L-section has the shorter side length 1m and longer side length 2m with one corner. Similarly, two L- sections were marked. Starter wall concreting was laid for the height of 200mm, for both L-sections in order to support the initial shuttering assembly. Then, the assembling of slipform shutters, walers, yoke legs, yoke beams and orientation of jack and jack rods with proper leveling were carried out.

Fig -5: Assembling of slipform components

Fig -2: Plan of slipform wall construction showing L-section

Both L-sections have different aspect ratios. Aspect ratio is the ratio between the distances of yoke leg in longer side to that of yoke leg in shorter side from the corner. First L-section has aspect ratio 1 with the distance of yoke leg on both longer and shorter side as 0.5m. Second L-section has aspect ratio 2 with distance of yoke leg on longer side is 1m and shorter side is Fig -6: Fixing of dial gauge 0.5m from the corner.

Fig -3: Plan of L-section showing aspect ratios The dial gauges were fixed along the length and depth of panel at equal intervals in steel stands. Concreting the slipform wall was done layer by layer with M30 grade (1:1.71:2.71).Each Fig -7: Lifting of slipform panels layer of concrete has thickness of 200mm. Initially wall concreting was done up to 800mm (from 200mm to 800mm in panel height) in three layers. After achieving enough concrete strength, lifting the panel was performed.

Fig -8: Slipform wall construction

Fig -4: Plan – Location of dial gauge

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The hydraulic pump was operated under the pressure of 60-70 Table -4: Deformation of longer side outer panel (AR-1) kg/cm2.The lifting of panel was done gradually for the height of 400mm. Again concreting and lifting process were continued till the wall height reached 1.5 m. Hence, the corresponding deformation of panel was evaluated for both aspect ratios.

4. RESULTS The inner and outer panel on both shorter and longer side gets deformed during constructing and lifting. The damages such as lifting cracks and lump formation were observed in the construction of slipform wall. Table -1: Deformation of shorter side inner panel (AR-1)

Table -5: Deformation of shorter side inner panel (AR-2)

Table -2: Deformation of shorter side outer panel (AR-1)

Table -6: Deformation of shorter side outer panel (AR-2)

Table -3: Deformation of longer side inner panel (AR-1)

Table -7: Deformation of longer side inner panel (AR-2)

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Table -8: Deformation of longer side outer panel (AR-2)

Chart -4: Graph showing longer side panel deformation near yoke leg 5. OBSERVATION

Comparative Graph between Aspect Ratio 1 & 2 5.1 Lifting cracks Lifting cracks are occurred at; 1. Outer shorter side wall of Aspect Ratio-1 at height of wall 200 mm – 350 mm @ location B2 – B3. 2. Inner shorter side wall of Aspect Ratio-2 at height of wall 250mm – 350 mm, @ location F2 – F3. 3. Outer longer side of Aspect Ratio-1 at height of wall 300mm @ location D1 – D2.

Chart -1: Graph showing shorter side panel deformation at corner

Fig -9: Lifting cracks

5.2 Panel deformation The panel deformed much in corner, less near yoke legs. From the graph, it is observed that the deformation pattern varies linearly and then increases, showing the lifting of panels. The panel has two horizontal walers, one at the distance of 250 mm from top and another 250mm from bottom. Therefore, the middle portion of the panel gets deflected more. In Aspect Chart -2: Graph showing shorter side panel deformation near Ratio-1, the maximum deflection is 2.58mm occurred at longer yoke leg side inner panel at C5. In Aspect Ratio-2, the maximum deflection is 2.48mm occurred at longer side inner panel at G5. The deformation of the panel in the corner is less in case of Aspect Ratio-1. Aspect Ratio-2 shows more deflection than the Aspect Ratio-1. From this, it is observed that the deformation of panel increases, if the distance of yoke leg increases from the corner.

6. CONCLUSION From the experimental study, in order to reduce damages in vertical slipform construction, it is suggested that:

 The vertical distance between the horizontal walers should be minimum.  The provision of additional horizontal waler at the centre Chart -3: Graph showing longer side panel deformation at of panel will reduce the deformation of panel. corner  The provision of horizontal stiffeners in addition to the vertical stiffeners will minimize the deformation. International Journal of Engineering Science and Computing, May 2016 5966 http://ijesc.org/

 It is recommended to establish Aspect Ratio-1 near the [13] TarekZayed; M. Reza Sharifi; SandelBaciu; and corners, to reduce deflection of panel. Mohamed Amer, “Slip-Form Application to Concrete  Also, the use of additional pair of cross beams will reduce Structures”. considerable deflection in yoke legs.  The panel thickness should be sufficient to resist the concrete pressure. Higher the panel thickness, deformation will be less.

7. REFERENCES

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[8] Kjell Tore Fossa and Dr.Ing thesis(2001) “ Slip forming of Vertical Concrete Structures, Friction between concrete and slip form panel”, Department of StructuralEngineering, The Norwegian University of Science and Technology.

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[10] Sanjay Chandra(1997) “Slip form Technique–A Productivity Study,” P.G.Dissertation, Madhav Institute of Technology and Science, Gwalior( India).

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[12] Smith A.W. (1958), “Development of slip-form construction”, report No.131 of the Division of Building Research Ottawa.

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