Comparative study on Rebar and Post Tensioned Transfer Girder

V. R. Sumathi; S. Vijayan

doi:10.17577/IJERTCONV10IS09046

ICONNECT - 2022 (Volume 10 - Issue 09)

Comparative study on Rebar and Post Tensioned Transfer Girder

DOI : 10.17577/IJERTCONV10IS09046

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Authors : V. R. Sumathi, S. Vijayan
Paper ID : IJERTCONV10IS09046
Volume & Issue : ICONNECT – 2022 (Volume 10 – Issue 09)
Published (First Online): 05-08-2022
ISSN (Online) : 2278-0181
Publisher Name : IJERT
License: This work is licensed under a Creative Commons Attribution 4.0 International License

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Comparative study on Rebar and Post Tensioned Transfer Girder

V. R. Sumathi

P.G Student,

Structural Engg, Department of Civil Engineering, SRMIST,

Chennai, Tamilnadu, India.

Vijayan

Assistant Professor (Sr.G), Department of Civil Engineering, SRMIST,

Chennai, Tamilnadu, India

Abstract:- Transfer girder is one of the primary component in a multi-storeyed building and offers elegant solutions to support vertical members that do not extend below lower levels of high rise buildings, which are mostly used as parking spaces, shopping malls, conference halls etc. without the obstruction of columns. The depth of transfer girders in conventional rebar concrete is very high and increases with increase in the height of the structures. Post tensioned concrete transfer plate system, with post-tensioning tendons is found to be very effective in reducing member thickness and has been widely adopted recently. In this project, a comparative analytical study is made on the structural performance and cost economy of the Rebar and Post tensioned transfer girders in a High rise building. Three- dimensional finite element model of a G+40 Multi-storeyed building is developed and analysed using ETABS 2018 software. Different load combinations and load cases are taken into consideration as per the relevant IS codes. Design of the Rebar and Post tensioned transfer girders is done using ADAPT 2019 software and comparison is done on the structural behavior of the Transfer girders with respect to tensile stress, ultimate moment, crack width, short and long term deflection etc. Cost comparison is done between the two transfer girders, to decide on the economy of the construction. Finally the study aims to highlight the advantages of Post Tensioned Transfer plate over the conventional floor systems.

Keywords Transfer girder, rebar concrete, Post tensioned, Load cases, Load combinations, ETABS, ADAPT

INTRODUCTION

Recent advances in technology have extended the boundaries of the construction industry and innovative designs which were once thought to be unimaginable are now a reality. Rapid urbanization and developments have propelled the construction of many High-rise buildings which have now become the pride of any nation. Moreover, the clients requirements for more building spaces, innovative architectural designs and increase in real estate value have all contributed to surge in the construction of multi-storeyed buildings. Transfer girder is one of the primary component in a multi-storeyed building. Transfer girders offer elegant solutions to support vertical members that do not extend below lower levels of high rise buildings, which are mostly used as parking spaces, shopping malls, conference halls etc. without the obstruction of columns. The problem, however, is that transfer girders are quite massive and expensive, because

heavy loads from the floating columns above them, act on the transfer girders. Hence, it has become essential to implement new and innovative technologies which can provide design economy and structural capacity while performing the same role in architectural terms.

The depth of transfer girders in conventional rebar concrete is very high and increases with increase in height of the structures. Due to this there is a substantial increase in self weight and overall load acting on the foundation. Moreover, in a typical multi storey building, the depth of transfer girder is found to be in the range of 2.5m to 3m ie. an entire storey floor of concrete mass, which is highly uneconomical for a residential multi storeyed building.

In todays world, where the modern engineering is finding new ways to build longer, more efficient and stronger structures, Post tensioned concrete has become one of their chief requirements. Post-tensioning is a method of prestressing, in which the tendons are tensioned after the concrete has hardened and the prestressing force is primarily transferred to the concrete through the end anchorages.

Post tensioned concrete transfer plate system, with post-tensioning tendons is found to be very effective in reducing member thickness and has been widely adopted recently. Post Tensioned concrete is used in different parts of the world for multi-storeyed buildings, bridges, etc., primarily due to its economy and load carrying capacity. Researches have proven Post Tensioned concrete to be more durable, cost effective and higher strength, with reduced depth than conventional concrete.
SCOPE OF THE PROJECT

In this Project it is proposed to compare the rebar and post tensioned transfer girders in a multi-storeyed building, based on its structural behaviour and cost perspective. The analysis of the multi-storeyed structure is done using ETABS 2018 software and design of the transfer girder system in RC structure and Post Tensioned is done using ADAPT 2018 software.
OBJECTIVES

The main objective of the project is tostudy
- Advantages of Transfer Plate when compared with other floor systems.
- To find out the structural behaviour of Conventional transfer plate and Post-tensioning transfer plate.
- Cost comparison of Conventional and Post- tensioning System.

METHODOLOGY

General Layout

A G+40 story building floor plan, as shown in Fig 1, 2 and 3 was chosen to study the behavior of Post Tensioned and Rebar concrete transfer girders. The building plan was selected such that one half of the Transfer girder floor is designed as Post Tensioned and the other half as Rebar Transfer Girder with similar boundary conditions and the same forces action on the floor. The transfer girder is proposed at the 7thfloor level and depth of the floor is selected as 1000mm based on the size of columns supported by transfer girder. The height of the storeys have been kept as 4 meters equally in all the floors. The general properties of Podium floors, Above Floors and Transfer girder are given in Tables 1, 2 and 3.

Software ETABS v. 18.0.2 has been used for analysis, to calculate the forces acting on the Transfer Girder and software ADAPT 2019 has been used for design of both Post Tensioned and Rebar concrete girders.

Fig 1: Layout plan of Podium floor

Fig 3: Layout plan of above floors

Table 1: General properties of Podium Floors

Description	Podium Floors
Plan Dimension c/c	81 m x 27 m
Bay width	9 m, 10.35m, 6.3m
Slab Thickness	250 mm
Grade of concrete of podium floors	M30 / M40
Size of beams	0.3×0.6 m, 0.3×0.75 m
No. of columns / shear walls	64 columns
Size of columns / shear walls	1200mm x 1200 mm

Table 2: General properties of Above Floors

Description	Above floors
Plan Dimension c/c	81 m x 27 m
Bay width	9 m, 10.35m, 6.3m
Slab Thickness	200 mm
Grade of concrete of podium floors	M30
Size of beams	0.23×0.45 m,0.23×0.4m
No. of columns / shear walls	60 Nos
Size of columns / shear walls	1500 mm x 300mm, 70 mm x 300 mm

Table 3: General properties of Transfer Floor

Plan Dimension	81 m x 27 m
Bay width	9 m, 10.35m, 6.3m
Depth of transfer girder	1000 mm
Grade of concrete for transfer girder	M50
Span of transfer girder	37.35 m (on each side)
No. of columns / shear walls supported on transfer girder	30 Nos. on each side
Size of columns / shear walls supported on transfer girder	1500 mm x 300mm, 750 mm x 300 mm

Load Cases

Different load cases were taken into consideration based on relevant IS Codes as below:

Fig 2: Layout plan of Transfer floor
- (DL) Dead Loads are taken as the self-weight of structural elements, Floor finishes
- Super Imposed Load (SDL)
- Live load (LL)
- Earth Quake in X (EQX) and Y (EQY)Directions- As per IS 1893 : 2002,
- Wind Load in X (WLX) and Y (WLY) Directions
  
  – As per IS 875 : 1987
  
  Overall 49 different load combinations have been taken for analysis.
ETABS Model and Analysis

Based on the above Load cases in structural elements, model was created in ETABS 2018 software as shown in Fig. 5 and 6. Analysis of the Multi-storeyed building was carried out.

Fig 5: ETABS model of the structure

Fig 6: ETABS model at Transfer floor level

Resultant Axial forces and Ultimate Moments acting on the Transfer Girder at the 7th floor level were determined as shown in Figures Fig 7, 8 and 9.

Fig 7: Ultimate Axial forces on Transfer Girder

Fig 8: Ultimate moment (M11) on Transfer girder KNm

Fig 9: Ultimate moment (M22) on Transfer girder (KNm)
Transfer girder model in ADAPT

The forces acting at the transfer girder level was exported and model was developed in ADAPT software, for detailed design of Post-Tension and RC conventional plate as shown in Fig. 10. While exporting the transfer plate from ETABS it was ensured that envelope values for flexural and serviceability load case was included.

Fig 10: ADAPT model of Transfer girder Formation of strips in both X & Y directions is the

basic requirement for analysis and design of any members in ADAPT software as shown in Fig. 11 & 12. Minimum one strip is required for each bay width along the spanning directions.

Fig 12: Design strips in Y directions

DERIVED OUTCOMES OF POST TENSIONED AND REBAR TRANSFER GIRDERS IN ADAPT

Axial forces due to the floating columns determined in ETABS were applied on the Transfer girders and analysis and design carried out in ADAPT. The resulting Tensile stress, shear, bending moment, crack width and long / short deflection on the Post tensioned and Rebar concrete Transfer girders is shown in Fig. 13, 14, 15 and 16.
When both the Transfer Girders are compared for their moment of resistance as shown in Fig.15., it is observed that there is no significant difference in the Bending moment capacity of both Rebar and Post Tensioned slab and is similar considering the results from the calculations.

Fig. 16 : Crack width in X and Y direction

As per IS 1343, Clause 22.7, the allowable crack width in Post Tensioned slab is 0.2 mm and from Fig.6.4, it is observed that the crack width in both X and Y directions, is in the range of 0.05 to 0.1 mm, which is within the codal limit. In the Rebar portion, a crack width of 0.6 mm is observed at the support and 0.22 mm in spans which exceeds the codal limit by 3 times and 1.1 times respectively.
REINFORCEMENT REQUIREMENT Design of Transfer girders were carried out in

ADAPT assuming a depth of 1000 mm for both Post Tensioned and Rebar concrete. It was observed that, in the RC portion, failure due to deflection occurred due to insufficient slab depth and hence the portion was redesigned assuming a depth of 2.3 m. The steel reinforcement requirement for both the Transfer girders are shown in Fig. 18 and 19.

Fig 18 : Steel requirement for Rebar and PT floors

Fig 19 : Additional steel requirement for Rebar floor
RESULTS AND DISCUSSIONS

The analysis and design of the Post Tensioned and Rebar Transfer slabs are done and cost comparisons for concrete and steel are shown in below Graph 1 – Graph 4. Based on the above results, the following is observed
CONCLUSIONS

From the above study the following conclusions are made,

The structural behavior and cost analysis of Post tensioned and Rebar concrete Transfer girder was done in a multi storeyed building.

The results clearly indicate that based on structural performance and cost perspective, the Post tensioned transfer girder is more advantageous than Rebar concrete Transfer girder for multi-storeyed buildings.

ISSN: 2278-0181

ICONNECT 2022 Conference Proceedings

2500

2000

Depth in mm

2300

300

250

200

Cost Rs. in Lakps85.93

213.48

184.87

1500

150 Rebar

PT

1000

500

0

1000

Rebar PT

Rebar

PT

100

50

0

92.81 92.05

72.45

Concrete Steel Total

Graph 1: Depth comparison of RC and PT Transfer slabs

Concrete in cum

Graph 4: Cost Comparison of RC and PT Transfer slabs

REFERENCES

[1] Thayapraba M, Cost Effectiveness of Post – Tensioned and Reinforced Concrete Flat Slab Systems, International Journal of

2500

2000

1500

1000

500

2319

1008

Rebar PT

Innovative Technology and Exploring Engineering (IJITEE) ISSN: 2278-3075, Volum-3, Issue-12, PP107-109, May 2014.

[2] Comparative study on post-tensioned and composite transfer girder for multi story building by Shivani B Patel and Prof. Hitesh K Dhameliya, UTU/CGPIT, International Journal for Engineering Development Research, Volume 7, Issue 4, IJEDR 2019

[3] Dr.Amlan. K.Sengupta & Prof.Devdas Menon, Pre- stressed Concrete, Indian Institute of Technology Madras, NPTEL.

[4] Prestressed Concrete – Sixth Edition by Prof. N. Krishna Raju, B.E., M.Sc (Engg), Ph.D., M.I.E., M.I. Struct., Emeritus Professor of Civil Engineering, M S Ramaiah Institute of Technology, Bangalore.

0

Rebar PT

Graph 2: Concrete comparison of RC and PT

Transfer slabs

Steel in MT



		65

150 140

100

Rebar

CODES

IS 456 (2000): Plain and Reinforced Concrete Code of Practice
IS 1893-1 (2016): Criteria for Earthquake Resistant Design of Structures, part-1: General Provision and buildings
IS 875-1 (1987) : Code of Practice for Design Loads (other than earthquake) for Buildings and Structures : Part 1 Dead Loads Unit weights of building material and stored materials
IS 875-2 (1987) : Code of Practice for Design Loads (other than earthquake) for Buildings and Structures : Part 2 Imposed Loads
IS 875-3 (1987) : Code of Practice for Design Loads (other than earthquake) for Buildings and Structures : Part 3 Wind Loads

50

0

Rebar PT

PT F. IS 875-5 (1987) : Code of Practice for Design Loads (other than earthquake) for Buildings and Structures : Part 5 Special Loads and Loa Combination.

Graph 3: Steel requirement of RC and PT Transfer Slabs

Comparative study on Rebar and Post Tensioned Transfer Girder

Load Cases