Project on

“AN EXPERIMENTAL INVESTIGATION OF REINFORCEMENT DETAILING AT THE EAM

COLUMN JOINT”  

BY

ABHINANDAN.N

Reg. No: -1BIO5CSE02

4th Semester M-Tech Structures

 Under The Guidance of:

PROF.R.RUDRA PRASAD

Department of Civil Engineering

SYNOPSIS: scope of the research:

In the past, a large number of RC beam column joints have been damaged by lack of detailing, bond and also by severe earthquakes.

Our investigation is mainly to determine the effectiveness of reinforcement detailing at beam column joint subjected to severe loads.

The investigation is conducted to evaluate the effectiveness of reinforcement detailing called “AN EXPERIMENTAL INVESTIGATION OF REINFORCEMENT DETAILING at the beam-column joint” that is by making the beam column joint 33%, 66% hinge thereby reducing the negative bending moment at the beam column joint and avoiding the column failure at the joint by making the beam to fail first.

The main criterion of our research work is the “model analysis” of reinforced concrete sub assemblage. In particular the assumed prototype frame is converted to a model by considering various “scale factors”. The reduced model is being casted by using regular convention concrete and steel

INTRODUCTION

The beam column joint is a crucial zone in a reinforced concrete moment resisting frame and the integrity of which is essential for the satisfactory performance of the whole structure.

The functional requirement of a joint, which is the zone of intersection of beams and columns, is to enable the adjoining members to develop and sustain their ultimate capacity.

The design of beam column joint is an important part in reinforced concrete moment resisting frames.

HISTORICAL REVIEW: Seismic behavior of beam column joints in reinforced concrete moment resisting frames by Dr.S.R.Uma and prof. Ameher Prasad.

Exact tangent stiffness for imperfect beam column members by Donald W.White and Ronald D.Ziemian.

Shear Strength of Reinforced Concrete Beams having Opening with Eccentricity by Sheikh S.A.

Materials for concrete:

 

The materials used for the concrete are as follows:

 

1)      Cement

2)      Aggregates

i)        Fine aggregates

ii)      Coarse aggregates

3) Water

REVIEW OF THE LITERATURE

In the past, a large number of Reinforced Concrete beam–column joints have been damaged by lack of detailing, bond and also by severe earthquakes. Due to these, the damage is expected to occur in RC joints due to insufficient bonding, shear, bending moment and construction techniques used.

The performance of beam column joint is influenced by many parameters such as column axial load, the amount and detailing pattern of main reinforcement, volumetric ratio of lateral ties and its confinement effect in the joint core, and the characteristics of steel and concrete.

The basic requirements of design is that the joint must be stronger than the adjoining hinging members, usually the beams or columns. It is important to see that the joint size is adequate early in the design phase, since otherwise the column or beam size may need to be changed to satisfy the joint strength or anchorage requirements.

Judicious detailing of reinforcement is of paramount importance to obtain a ductile response of reinforced concrete structures.

The beam column joint design should be able to

1) Prevent brittle shear failure of the joint

2) Maintain integrity of the joint so that the ultimate strength of the connecting beams and columns can be developed.

3)Reduce joint stiffness degradation by minimizing cracking of the joint concrete and by preventing the loss of bond between the concrete and longitudinal beam and column reinforcement

Assumptions in Analysis:

Beam depth and column depth are identical and unified for simplicity and used as the unit of length in this analysis.

Reinforcing bars resist only the transverse force, and the dowel action is neglected.

Diagonal cracks exist, and the inclinations of the cracks are 450.

The concrete cracks transmit compressive normal stress perpendicular to the crack. Distribution of the normal stress is assumed as a rectangular stress block, where the concrete stress is c.

Equilibrium of external forces and internal forces are considered, whereas the compatibility condition is not necessarily satisfied.

Location and magnitude of the external forces acting on the beam-column joint substructure are symmetric in vertical directions.

OBJECTIVE OF THE RESEARCH:

 The main objectives of the research include the study of

Behavior of beam – column joints

Model analysis of RC frames

 Performance of beam – column joints

Total quantity of material required for specimen

In general, for one specimen we need

Water = 9ltr

Cement = 18 kg

Sand = 27.6 kg

Coarse aggregate = 54.3 kg

For six specimens we need

Water = 54ltr

Cement = 108 kg

Sand = 165.6 kg

Coarse aggregate = 325.8 kg

The reinforced frame is placed over a flat surface

This is the wooden frame used as shuttering.

The steel reinforcement is placed inside the wooden frame

Concrete is poured inside the frame in three layers.

The specimens are cured with clean water for 27days.

TESTS CONDUCTED ON MATERIALS STANDARD CONSISTENCY TEST

SIEVE TEST

AGGREGATE IMPACT VALUE

AGGREGATE CRUSHING:

COMPRESSIVE STRENGTH OF CONCRETE

TEST SETUP

The experimental program comprised the design and testing of beam column sub assemblages. The specimens were built in an engineering laboratory and tested under transverse load. The specimen consisting of a two column, two studs and one beam and all the specimens are fixed at the bottom.

The specimen story height is 900mm from base of the stud to the top surface of the column and beam spanning 1200mm. This represents a 1:5 scale model of a prototype of height 4m and beam spanning 6m.

. The test specimen is placed on the loading frame and to maintain fixity, the bottom of the frame is locked to the loading frame through steel locking system. To apply a concentrated load over the specimen, a steel beam section is provided on top of the specimen, which will transfer the point load from the hydraulic jack. So, a hydraulic jack is placed at the middle, on top of the beam to apply the load over the beam section. On top of the hydraulic jack, a proving ring is also placed. Below the beam a dial gauge is placed to measure the deflection when the load is applied and loading machine is used to apply the load, which transfers the load to the hydraulic jack. The test setup is as shown in the fig above.

TESTING

The test is conducted on each controlled specimen to know the behavior of the specimen and load taking capacity, strain at the each joint and deflection is compared for each specimen and final results are tabulated in the table.

Initially studs are fixed at the beam column joints to measure the strain. To measure the strain an 8” demountable gauge is used. All controlled specimens are tested and the results are tabulated below.

TESTING

INSTRUMENTATION: Dial gauge, strain gauges or demountable gauge, hydraulic jack, proving ring, loading machine etc were used to monitor the applied loads and displacements, and the resulting strains and deformations.

Readings from these instruments were continuously collected and recorded in the notebook. Using hydraulic jack, the loads are applied and imposed displacement is measured.

Strain is recorded using demountable gauges at each beam column joint. In addition to this the cracks were marked on the specimens after reaching displacement peaks, using different color for each specimens.

Steel beam, which will transfer point load from hydraulic jack

Application of point load at the mid span of the

beam

Strain is recorded using demountable gauge at each

joint

Deflection is recorded below the point load using dial gauge

TEST RESULTS OF BEAM-COLUMN JOINT FOR FIXED CONDITION

FOR CONTROLLED SPECIMEN-1 (TABLE-1)

Continued…

TEST RESULTS OF BEAM-COLUMN JOINT FOR FIXED

CONDITION FOR CONTROLLED SPECIMEN-2 (TABLE-2)

Continued…

CRACK WIDTH FOR FIXED CONDITION SPECIMEN-1

CRACK WIDTH FOR FIXED CONDITION SPECIMEN-2

Crack below the point load for fixed condition specimen

Crack at the joint for fixed condition specimen

TEST RESULTS OF BEAM-COLUMN JOINT FOR 66%FIXED CONDITION FOR CONTROLLED SPECIMEN-1 (TABLE-3)

TEST RESULTS OF BEAM-COLUMN JOINT FOR 66% FIXED

CONDITION FOR CONTROLLED SPECIMEN-2 (TABLE-4)

CRACK WIDTH FOR 66% FIXED CONDITION SPECIMEN-1

CRACK WIDTH FOR 66% FIXED CONDITION SPECIMEN-2

Crack below the point load for 66% fixed condition specimen

Crack at the joint for 66%fixed condition specimen

TEST RESULTS OF BEAM-COLUMN JOINT FOR 33% FIXED

CONDITION FOR CONTROLLED SPECIMEN-1 (TABLE-5)

TEST RESULTS OF BEAM-COLUMN JOINT FOR 33% FIXED

CONDITION FOR CONTROLLED SPECIMEN-2 (TABLE-6)

CRACK WIDTH FOR 33%FIXED CONDITION SPECIMEN-1

CRACK WIDTH FOR 33%FIXED CONDITION SPECIMEN-2

Crack below the point load for 33% fixed condition specimen

Crack at the joint for 33%fixed condition specimen

LOAD V/S DEFORMATION GRAPH FOR FIXED CONDITION SPECIMEN-1

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DISCUSSIONS AND CONCLUSIONS: The test shows that the partial fixity can be used for reinforced concrete beam column joint section. From table (3,4,5&6) it is clear that partial fixity reduces the negative bending moment at the beam column joint and avoids column cracking at the joint. The graph (3 to 6) shows that the 66%fixity beam column joint specimen is less strained compared to the fixed beam column joint specimen. From graph (7 to 12) it is clear that as we increase the percentage of partial fixity at the beam column joint deflection at the mid span of the beam increases. From table (1 to 4) it is observed that, for the same load, the fixed beam column joint specimen fail in shear compared to 66% fixity beam column joint specimen

From test it is clear that, if percentage of partial fixity at the beam column joint decreases beyond 66%, load taking capacity of the beam decreases and deflection at the mid span of the beam increases. Therefore percentage of partial fixity at the beam column joint shall be amount 66% fixity. From table (1 to 4), it is observed that the fixed beam column joint specimen and 66% fixity beam column joint specimen fail in flexure for the same applied load. From table (1 to 4) it is observed that, failure in column occurs in case of fixed beam column joint specimen for 4600Kg whereas no column failure in case of 66% fixed beam column joint even after 5000Kg of load. So from this we can conclude that by giving partial fixity at the beam column joint, we can avoid cracking of column earlier at the joint.

SCOPE FOR FURTHER STUDIES:

The investigation is conducted to evaluate the effectiveness of reinforcement detailing at the beam column joint for portal frame and the test shows that the partial fixity can be used for reinforced beam column joint section. Further investigation on partial fixity at the joint can be carried out for various percentages that are between 33% to 66% to evaluate effectiveness of partial fixity. 

REFERENCES--------------------------------------------------------------

1.      “DESIGN OF REINFORCED CONCRETE STRUCTURES” by S.Ramamrutham – Dhanpat Rai Publishing Company Pvt. Ltd – 15th revised and enlarged edition.

 2.      “THE TEXTBOOK OF FLUID MECHANICS AND HYDRAULIC

MACHINES” by Dr.R.K. Bansal – Laxmi Publications Pvt. Ltd. – 9th edition (Pg :573-575 )

 3.      “EXPERIMENTAL STRESS ANALYSIS” by James.W.Dally and

William.F.Rally – Second edition , International student edition , McGraw Hill, Kogakusha Ltd.

 “STRUCTURAL MODELING AND EXPERIMENTAL TECHNIQUES” by

Harry

1. “LIMIT STATE DESIGN OF REINFORCED CONCRETE” by P.C.Varghese – Copywright 1994 by Prentice Hall of India Pvt. Ltd, New Delhi (5th printing-1999)

 

THANK YOU