Experimental Investigation on the Effect of Un-Bonded Longitudinal Steel Reinforcement on Flexural Responses of RC Beams
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Date
2021-08
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Addis Ababa University
Abstract
This paper is devoted to the combined effect of unbounded length and steel bar diameter
on the flexural responses of reinforced concrete beams. A test series of eight simply
supported beams having varied un-bounded lengths that bond loss starts at the middle
and extends toward the supports had been performed in this experiment. All beams have
a total span of 1220mm and are loaded at the middle with one concentrated load.
One of the main assumptions in the deigning of the reinforced concrete member is the
efficient concrete-steel bond mechanism. But, loss of bond due to factors, such as errors
during repairing, construction errors, corrosion, rough and dry formwork, formation of
voids, etc. that may reduce the carrying capacity of the reinforced concrete beams and
flexural behavior in general. Therefore, bond-slip has much attention from academic
areas and industries. An experimental program is conducted to examine the effect of
variable un-bonded length of longitudinal reinforcement for bottom reinforcement with
different bar diameters on the flexural capacity of reinforced concrete beams, with shear
reinforcement, subjected to transverse point load. The bond loss was provided with
plastic tubes covering the longitudinal reinforcement by allowing bonded length over
supports which prevent the formation of bond-slip at support.
The effect of un-bonded length with different bar diameters on the response, cracking
load, ultimate load capacity, ultimate mid deflection, and deflection at service load of
beams is discussed in this paper. The cracking load and cracking pattern, ultimate load
capacity, and ultimate deflection are highly affected by increasing bond loss length for
16mm bar diameter. But, the ultimate load-carrying capacity of beams with a bar
diameter of 8mm for the same length of bond loss was 7.31% even for fully unbounded.
This may be attributed to the good bond strength of small bar diameter (8mm) than that
of large bar diameter (16mm), in addition to the bond around the end supports and the
presence of the anchorage
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Keywords
Beams, tensile strength, bond strength, concrete, flexural strength, reinforced concrete, Deflection, ultimate capacity