An Experimental Investigation on The Effect and Mechanism of Side Cover for Deep Beams
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Date
2025-06
Authors
Journal Title
Journal ISSN
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Publisher
Addis Ababa University
Abstract
This study investigates the effect and underlying mechanism of side cover spalling in reinforced concrete
deep beams subjected to shear. While prior research, such as that by [2], has focused on slender beams, this
thesis addresses a critical gap by examining deep beams, whose shear behavior is governed by arch action
rather than flexural beam theory. A series of six full-scale deep beams with varying side cover thicknesses
and stirrup cage configurations were experimentally tested under three-point monotonic loading. Two
configurations were explored: SA-series beams, which maintained a constant outer width and reduced the
core with increasing cover, and SB-series beams, which preserved the core width while increasing total width
by adding cover externally.
The primary aim was to determine whether large concrete covers compromise shear performance due to
premature side cover spalling. Observations revealed that spalling initiates near peak load, particularly when
the stirrup cage is confined by a reduced core, as in the SA-series. Despite observable spalling in all
specimens, the presence of adequate core concrete and stirrup confinement significantly influenced the
beams' ability to reach peak load without premature failure. Finite element modeling results from Vector2
were compared with the experimental findings. The Experimental findings highlighted the limitations of
current two-dimensional analyses in capturing out-of-plane spalling.
Importantly, the results demonstrate that increasing the concrete side cover does not enhance the stiffness
(except for the initial stiffness) or peak load capacity of deep beams. This finding sharply contrasts with the
assumptions in most building design codes, such as ACI 318 and Eurocode 2, which treat the entire crosssectional
width—including
the
cover
zones—as
fully
effective
in
resisting
shear
and
flexure.
The
test
results
suggest
that once the core (stirrup-confined zone) is sufficient, additional concrete cover adds little to
structural performance and may even introduce weaknesses due to spalling risk. Additionally, SB-series
beams display stable load-displacement behavior with limited post-peak softening, indicating improved
ductility relative to SA-series specimens.
This research contributes to a more accurate understanding of D-region behavior in deep beams and
underscores the need to re-evaluate code provisions related to effective shear/flexure width, particularly in
the presence of large concrete covers.
Description
Keywords
Deep Beams, Mechanism of Side Cover, SA-series beams, SB-series beams, reinforced concrete deep beams