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PRECAST CONCRETE AND ITS CONNECTIONS

B Under the guidance of By K.P.NAGARAJA Sachin.R.Biradar Professor

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Introduction Precast construction Advantages and Disadvantages Connections Aspect of design connections Common system of connections Tests carried out Applications References

CONTENTS

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In India there is a large shortage of housing and increase in cost of construction is a big problem to overcome this shortage.

The major cost increase in house built is due to two factors, they are:

i. Increase in basic cost of materials ii. Increase in labour costs.

To reduce material consumption and to reduce labour component many cost reducing system and techniques are essentially required[1]

Introduction

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Precast is the construction product by casting concrete in reusable mould, which is cured in controlled environment and transported to the site.

Traditional in-situ construction is too slow to cope-up with this increasing demand.

By pre-cast, better quality buildings can be constructed at faster rate.

Compared to site-cast concrete, precast concrete erection is faster and less affected by adverse weather conditions.

Precast construction

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As self-supporting ready-made components are used,

shuttering and scaffolding are eliminated to greater extent.

Pre-cast moulds can be used for a large number of times.

It is easier to produce components with structurally efficient

shapes in pre-cast construction.

Production can be done independent of the weather

condition.

Advantages

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Supervision and better quality can be ensured.

Hazards of fire, accidental damage, effects of temporary construction and inaccurate workmanship can be eliminated.

High Efficiency, quality control and greater control on finishes.

Same type of components are produced again and again.

Waste materials can be used.

Cont…

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To ensure monolithically more reinforcement is necessary. Special care should be taken while handling and erection to

avoid damage and breaking. Temporary supports may be necessary in some cases.

Chance of leakage through joints.

Connections should be designed.

Disadvantages

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Precast industry

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Structural integrity of the whole structure.

To transfer forces between the precast elements.

Generally connections are done where BM is zero and SF is max.

The design of connection may be compression joint, tension joint, shear joint etc.

Connections

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These are the basic connection in pre-cast.

i. Bolting.

ii. Grouting reinforcing bars at the site.

iii. Embedding reinforcing bars in epoxy or polyester at the site.

iv. Welding.

Aspect of design connections

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Common systems of connections1. Beam-Beam connection2. Beam-Column connection3. Column-Column connection4. Column-Beam floor connection5. Floor and roof system

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Beam to beam connection

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Beam to column connection

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Cont…

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Column to column connections

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Beam to slab connection

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Tests carried out:-

1.Beam-column connection

2.Column slab connection

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Beam-Column connection [2]

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Sl.no specimen Experimental Yield load(kn)

Experimental ultimate load(kn)

Upward direction

Downward direction

Upward direction

Downward direction

1 ML 8.8 9.40 11.29 11.75

2 PC-TR 6.5 8.62 7.62 10.77

Sl.no Specimen Experimental Ultimate moment(kn-m)

Upward direction Downward direction

1 ML 6.21 6.47

2 PC-TR 4.19 5.92

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Unit description Slab 1 Slab 2 Slab 3Slab thickness(mm)

50 50 63

Reinforcement Ø6@250mm c/c

Ø6@165mm c/c

Ø6@200mm c/c

28-day strength(mpa)

fc' 39.02 37.06 38.38fcu 44.82 43.93 43.33

Column-Slab Connection

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Crack patterns in the beam-column intersection zone and slab

[4]

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ApplicationsParking lotsIndustrial sitesManufacturing sitesStadiumsWall panelsBox culverts

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The two types of connections tested proved to be efficient and reliable systems that simplify and speed up the construction of precast concrete frame structures.

Connections should be carefully designed where the impact or dynamic forces are much higher.

Building can be constructed upto 4 storey height(12m) without extra care at joints.

Used in structure where strength is not major criteria.

Observations

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[1]Mathur, G.C. (1993), Low Cost Housing in Developing Countries, Oxford & IBH Publishing

Co. Pvt. Ltd., New Delhi.

[2]Behaviour of precast beam-column tie-rod Connection ,R. Vidjeapriya1 and K.P. Jaya2

[3]Seismic Safety of Joints in Precast Buildings A State-of-the–art Literature Review Ravikanth

Chittiprolu & Ramancharla Pradeep Kumar Earthquake Engineering Research Centre, IIIT

Hyderabad.

[4]Saddam m, Ahmedi, Umarani Gunasekaran, A Parametric Study of R.C Slab in Beam-

Column Connection Under Cyclic Loading.

[5]Code of practice for precast concrete construction (2003).

References

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