Experimental Investigation of Construction Joint in RC Beams
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Date
2015
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Addis Ababa University
Abstract
Construction joints are stopping places in the process of placing concrete and they are
required because in many structures it is impractical to place concrete in one continuous
operation. The region which separates the two dissimilar concretes is called interface. The
concept of concrete to concrete interface load transfer plays an important role in assuming the
monolithic behavior of the resulting composite reinforced concrete members.
Many researches have been done over the years to understand the interface shear transfer of
precast elements and joints. However, most of the researches conducted to study interface
shear strength are on pre-cracked or monolithic push off samples and not on construction
joints. But the behavior of construction joints cannot be modeled by samples with or without
cracks. So a study in samples with construction joint could be valuable contribution to an
already existing vast knowledge on interface shear transfer.
The results of the experimental tests indicated that the presence of a construction joint reduces
the interface shear strength. Shear strength reduction up to 35% is noted. The test results also
show that the shear strength of both samples with and without construction joints increased as
the area of steel crossing the shear plane is increased. The shear strength of the monolithic
samples increased from 2.91MPa to 2.97MPa to 3.06MPa and the shear strength of samples
with construction joint generally increase from 2.36MPa to 2.65MPa. We can also see from
the test results that surface treatment could have a major effect in the interface shear strength.
The test result shows that the shear strength for a construction joint with a smooth surface
treatment is reduced from 2.91MPa to 1.91MPa (which is a 35% reduction). This reduction is
mainly due to the reduction in the aggregate interlock forces because of the relatively smooth
interface between the two forces of the shear plane.
The experimental results were compared against shear interface models proposed by different
researchers and building codes. From this comparison, we can see that the results by the
building codes and most researchers are very conservative for both samples with and without
construction joint.
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Keywords
Joint in RC beams, experimental results, Construction