SLIP CRITICAL JOINTS - Instituto de Metais N??o Ferrosos · SLIP CRITICAL JOINTS Joints subject to...
Transcript of SLIP CRITICAL JOINTS - Instituto de Metais N??o Ferrosos · SLIP CRITICAL JOINTS Joints subject to...
SLIP CRITICAL JOINTS
Joints subject to fatigue load with reversal of loading directions
Joints that utilize oversize holes Joints that utilize slotted holes Joints in which slip at the faying
surfaces would be detrimental Joints where bearing connection is not
practical
Slip Critical JointRelies on friction between faying surfaces for load bearing.
AISC 2010 Specification for Structural Steel Buildings
Class A µ = 0.30 Uncoated clean mill
scale Roughened
galvanized surfaces Class B
μ = 0.50 Unpainted blast
cleaned surfaces Class B coatings on
blast cleaned steel
EARLY TEST RESULTSCurrent provisions for slip performance of galvanized specimens are based on limited data that is not reflective of current galvanizing processes.
Grondin, Gilbert Yves, Ming Jin, and Georg Josi. Slip Critical Bolted Connections: A Reliability Analysis for Design at the Ultimate Limit State. Department of Civil & Environmental Engineering, University of Alberta, 2007.
EARLY TEST – SURFACE ROUGHENING
Early tests done on galvanized plates showed roughening improved the slip performance.
Kulak, G. L., J. W. Fisher, and J. H. Struik. "Guide to design criteria for bolted and riveted joints, 1987.“ American Institute of Steel Construction, Chicago, Il.
CURRENT SLIP FACTOR RCSC has assigned slip factor of 0.35 to
roughened galvanized surfaces AISC has assigned slip factor of 0.30 to roughened
galvanized surfaces Roughening method mentioned by both is wire
brushing No further definition of wire brushing is available All early data was based on a limited number of
samples and no generally accepted test method
AGA STUDY Determine the galvanizer with the lowest “as
received” slip factor – the worst case Determine if wire brushing changes the “as
received” slip factor Use a Class B coating to increase the slip
coefficient of galvanized steel to Class B Paint Preparation needs to be practical and
produce a Class B slip factor Application of paint by galvanizer should be
feasible in galvanizing facility
“AS RECEIVED” TESTS Six Galvanizing kettles were
chosen based on differences in chemistry
Three tests were performed for each bath for repeatability
Bath which produced lowest slip coefficient to be used in further testing – worst case
“AS RECEIVED” SLIP FACTORS
Kettle Average Slip Coefficient A 0.31B 0.33C 0.35D 0.36E 0.58F 0.20
SURFACE ROUGHNESS Surface roughness measurements made in
accordance with ASTM D7127 Rt is the distance between the highest peak and
lowest valley within a given evaluation length Surface roughness produced by wire brushing
SURFACE ROUGHNESS
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
10 15 20 25 30 35
Slip
Coe
ffici
ent
Average Rt (microns)
Surface Roughness and Slip Coefficient
PAINT PREP METHOD
Prep Method Slip CoefficientControl 0.29
Wire Brushing 0.25Sandpaper 0.39
Surface Etchant 0.26Picklex 0.30
CLASS B PAINT OVER HDG Nine paints were chosen for the study Mostly zinc silicates Chosen because PDS claims of achieving Class B
slip coefficient “Sandpaper Roughening” from previous testing was
chosen One test was used for each paint
PAINT TEST RESULTSPaint Slip Coefficient
Control (no paint) 0.34A 0.45B 0.48C 0.48D 0.39E 0.48F 0.53G 0.23H 0.44I 0.55
PAINT QUALIFICATION TESTS
Paint Preparation - Chemical Four paints are chosen
Highest slip coefficient Most practical
Results disappointing None of the paints gave qualifying slip
factors for Category B
FHWA SLIP TEST STUDY Perform Round Robin Test on four labs
performing slip test FHWA Lab CCC&L Lab University of Texas KTA Tator Lab
Test results showed inconsistency in test results
Recommendation that two Linear Variable Differential Transformers (LVDTs) be used in slip tests
AISC SLIP TEST STUDY Project aims to increase the experimental
database of slip performance of modern galvanized pieces. Determine the slip strength of untreated
galvanized pieces Investigate the effect of different galvanizers,
steel chemistry and other variables on the slip behavior of galvanized plates
Evaluate the effectiveness of roughening galvanized surfaces, and, if needed, recommend a more precise procedure for roughening
VARIABLES INVESTIGATED1) Coating Thickness2) Steel Chemistry (2 different steels)3) Pickling Acid4) Variation Among Galvanizers5) Bath Consistency6) Spinning of Galvanized Plates7) Surface Roughening
PREPARATION OF PLATES Holes drilled by Fabricator Plates cut by University
GALVANIZING OF PLATES
COATING TOUCH-UP
TEST SETUP AND PROCDURE Tests conducted in accordance with RCSC - App. A
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Schematic of Test SetupRCSC Figure A-3 (Recreated) for Compression Slip Test Setup
INITIAL RESULTS SLIP TEST Compared with previous slip studies, modern
galvanizing produces coatings with much higher slip coefficients.
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Tabulated slip coefficients represent a five-test average
SLIP VERSUS COATING THICKNESS
In general, coating thickness did not have a significant and consistent impact on the measured slip coefficient.
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SLIP VERSUS CENTRIFUGING Despite the apparent change in coating structure, the
effect of spinning on slip coefficient was minimal.
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SUMMARY OF AISC TESTS Bath chemistry and galvanizing process can vary
between galvanizers, produce significantly different slip coefficients, however all galvanizers produced coefficients higher than historically assumed.
Changes in bath chemistry over time had little effect on the slip coefficient of galvanized pieces.
Spinning of galvanized plates had limited impact on slip performance.
Surface roughening did not improve slip performance. The roughening procedures often reduced the
measured slip resistance and should probably therefore be removed.
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FUTURE TEST PLANS Qualification Tests with candidate paint systems –
Class B qualification Metallized Coatings in contact with Galvanized
Coatings Creep Tests on Galvanized and Metallized
Coatings Creep Tests on qualified paint systems over
galvanized coatings