Evaluation of Anchor Bolt Clearance...
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Evaluation of Anchor Bolt Clearance Discrepancies Ian E. Hosch, Ph.D.1 and Ahmed M. Ahmed2
Department of Civil, Construction and Environmental Engineering
1UAB, Assistant Professor, 2UAB, Doctoral Student
The purpose of the research is to investigate the effect of anchor bolt clear-
ance discrepancies on the stress distribution within the anchor bolt group
due to extreme and fatigue wind loading events.
Anchor bolt clearance is defined as the length between the bottom of
the base plate to the top of the concrete foundation surface.
Clearance discrepancies caused by topographical limitations and level-
ing procedures performed at the construction site.
ABSTRACT
Double nut anchoring system is a type of connections that depends on
resting the sign structure on a leveling nuts, leaving clear distance between
the bottom of the lower nut and the foundation.
The loads are transferred to the foundation through the anchor bolts, result-
ing in shear and bending stress over the exposed length of the anchor
bolts.
Preliminary results showed that, in the case of unleveled clearance dis-
tance, the anchor bolts are experiencing a significant irregularity in the
stress distribution compared to the stress distribution commonly calculated
in design.
The innovation in this research project is to analyze the effects of construc-
tion methods such as leveling and clearance distances on the stress distri-
bution to the anchor bolts.
RESEARCH PROBLEM
Preliminary results were derived from experimental data obtained from a
cantilever sign support structure with ALDOT/UAB Project #930-680,
“Design of Overhead Sign Structures for Fatigue Loads”.
Anchor bolts were instrumented with uni-axial strain gauges attached on
the outer surface of each of the 8 anchor bolts that made up the double
nut moment joint connection.
Results indicated significant irregularity in the stress distribution in the
anchor bolt group believed to be caused by the clearance discrepancy.
Highest stresses found with anchor bolts AB-7 and AB-8 (see figure be-
low) having the largest clearances of approximately 3 in as compared to
0.5 to 1.0 in of other bolts.
Stress ranges for anchor bolts AB-7 and AB-8 exceeded the AASHTO
constant amplitude fatigue limit (see figure below) for the connection type,
as well as from structural analysis design calculations.
PRELIMINARY RESULTS
Orientation of the Anchor Bolt Group and Distribution
of Limit-State Effective Stress Ranges
Front
Face
Back
Face
Direction of Traffic
Anchor Bolt Comparison of Limit State Effective Stress Ranges
The research will involve theoretical and experimental programs.
Specific Objective #1: Study the significance of clearance discrepancies on the stress distribution within the anchor bolt group due to extreme and fatigue wind loading events.
Specific Objective #2: Evaluate the effect of anchor bolt clearance discrepan-cies on the stress distribution in the shaft support above the base plate weld.
Specific Objective #3: Develop structural design methodologies and design aids to account for anchor bolt clearance discrepancies for the calculation of stresses in the anchor bolts and above the base plate weld.
SPECIFIC OBJECTIVES
WORK PLAN
Attaching the Uni-axial Strain Gauge A Close-up View of the Strain Gauge after the
Completion of the Structure
In-situ Experimental Data Analysis (Preliminary Results)
Evaluation of Anchor Bolt Analysis by the Support Specifications
Theoretical Analysis using Finite Element Analysis Modeling (FEA)
Laboratory Experimental Studies
Development of Structural Methodologies and Design Aids
Conclusion that Satisfies the main Purpose of the Research
No. of Anchor
Bolts
Stand-off Dis-
crepancy Distance
Base Plate
Thickness
Anchor Bolts
Geometry
Anchor bolt
Modeling (Beam/
Solid)
Area of Post
above the weld
Loading
Conditions
Parametric
Studies
Conclusion
Structural Methodologies and Aids Experimental Program
Area above Weld /
Study for All Experi-
mental Specimens
Discrepancy Level
[Different θ’s] / De-
termined from FEA
Control Specimen /
Compare to FEA to
Validate
Area under Study Area under Study
p
twDouble Nuts
Anchor Bolts
Steel Post
t
Steel Post
Double Nuts
Anchor Boltstp
tw
.
θ
Test Set-up Parametric Studies
Anchor Bolts
Strap used distribute the
load a round the post
and avoid local failure
Post
Base Plate
Base
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