FAILURE COST ANALYSIS OF HUMAN ERRORS IN REINFORCED CONCRETE BEAM CONSTRUCTION
FAILURE COST ANALYSIS OF HUMAN ERRORS IN REINFORCED CONCRETE BEAM CONSTRUCTION
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Date
1997-01
Authors
JOSHUA, SUMBELE
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Abstract
This study centres around the evaluation of the expected total
cost of reinforced concrete beams designed to BS 8110 (1985) when
gross errors are accounted for. Beam performance functions are
obtained for bending, shear and torsion. The performance function
for a beam performing in combined bending and torsion is adopted
from CP 110 (1972), where it is explicitly given. Due to the
multiplicity of uncertainties surrounding the performance of beams,
they are only realistically assessed in terms of a probability. In
this study, the reliability index, ft, and hence the probability of
failure Pf, is used as a measure of beam performance.
Consequently, the First Order Second Moment integration technique
is employed to determine the values of ft or Pf implicit in the
design criteria.
Since it is practically impossible to quantify the whole range
of human errors likely to occur in reinforced concrete beam
construction, consideration is therefore limited to workmanship
error involving the transverse and longitudinal positioning of beam
supports. In addition, the effects of perturbations in the design
values of basic variables on the performance and the expected total
cost of beams are examined.
The results show that the BS 8110 (1985) design criteria give
fairly consistent and non-conservative designs. From structural
design considerations only, the code's requirements are found to be
adequate.
The sensitivity analysis also shows that gross errors in the
value of the effective depth, d, lead to the greatest associated
failure cost among other design variables. On the other hand, the
strength of concrete, fcu, is found to show very little sensitivity
to gross errors as far as the design equations are concerned.
Associated failure costs are thus minimal. This assessment shows
that for beams failing in bending, shear, torsion and combined
bending and torsion, expected failure cost surcharges do not go
higher than about 13%, 47%, 36.5% and 24.4% of the initial cost
respectively.
The results of this investigation are only indicative trends
of the BS 8110 (1985) design requirements since the scope of the
work precludes experimental details that may give the actual
distributions of the design parameters. It is therefore indicative
from economic considerations only that the criteria for shear and
torsion be reviewed.
Description
A Thesis Submitted to the Postgraduate School
Ahmadu Bello University, Zaria, In Partial
Fulfillment of the Requirements for the Degree of
Master of Science in Structural Engineering
Department of Civil Engineering
Faculty of Engineering
Ahmadu Bello University
January, 1997.
Keywords
FAILURE COST,, HUMAN ERRORS,, REINFORCED,, CONCRETE BEAM,, CONSTRUCTION