2/23/ WIND PRESSURE FORMULA 2. PERCENT OF ALLOWABLE STRESS 3. FATIGUE DESIGN

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1 Original Title Presented by Northwest Signal copyright 2010 Designing & Building Structural Steel Products since 1976 Primary Users Traffic Signal Strain & Mast Arm Poles Cantilever & Bridge Sign Structures Roadway Lighting Light Rail Power & Overhead Caternary 1975 First Edition Original 1985 Second Edition Minor Changes 1994 Third Edition Minor Changes 2001 Fourth Edition Major Changes 2009 Fifth Edition Minor Changes Covered in this presentation: 1. WIND PRESSURE FORMULA 2. PERCENT OF ALLOWABLE STRESS 3. DESIGN DESIGN OF FIBER-REINFORCED COMPOSITE STRUCTURES DESIGN FOR WOOD POLES THE ADDITION OF THE BROM S METHOD FOR FOUNDATION DESIGN A MORE DETAIL ANALYSIS FOR SPAN WIRE SYSTEMS 1

2 3 RD EDITION WIND PRESSURE FORMULA P= x (C G x V) 2 x C d x C h 4 TH EDITION WIND PRESSURE FORMULA P= x G x V 2 x C d x K z x I r 3 rd Edition 4 th Edition Change P = Wind Pressure P = Wind Pressure None (lb/ft 2 ) (lb/ft 2 ) V = Wind Speed (MPH) V = Wind Speed (MPH) Same V, Different Data C G = Gust Coefficient G = Gust Factor (1.14) C G2 = G (1.3) C d = Drag Coefficient C d = Drag Coefficient None C h = Height Coefficient K z = Height & Exposure C h is equivalent to K z Factor Ir = Importance Factor New Variables that have remained essentially unchanged DRAG COEFFICIENTS (C d ) HEIGHT COEFFICIENT (C h ) IS EQUIVALENT TO HEIGHT AND EXPOSURE FACTOR (K Z ) C h operates over stepped height ranges, whereas K Z is linear and more accurately associates wind velocities over the range of elevations C h or K z Ch Kz Height About Ground Line (ft) C h or K z Ft Pole: C h = 0.80 K z = Ft Pole: C h = 1.10 K z = Ch Kz VALUES USED FOR BASIC WIND SPEED (V) ARE NOT THE SAME FOR BOTH EQUATIONS 3 RD EDITION -- V IS BASED ON INDIVIDUAL WIND SPEED MAPS FOR 10-, 25-, AND 50-YEAR MEAN RECURRENCE INTERVALS. 4 TH EDITION -- V IS BASED ON ONE 3-SECOND PEAK GUST WIND SPEED MAP. IT IS BASED ON PEAK GUST DATA Height About Ground Line (ft) 2

3 IMPORTANCE FACTOR -- ALLOWS THE WIND PRESSURE ASSOCIATED WITH THE 50-YEAR MEAN RECURRENCE INTERVAL (1.0) TO BE ADJUSTED TO REPRESENT WIND PRESSURES ASSOCIATED WITH 10-, 25-, OR 100-YEAR MEAN RECURRENCE INTERVALS (<1.0). 3-SECTION SIGNAL HEAD WEIGHT = 70 LBS WIND AREA = 9.2 SQ FT C d = 1.2 C h = SCHEDULE PIPE WEIGHT = 210 LBS WIND AREA = 6.67 SQ FT C d = 1.1 C h = SECTION SIGNAL HEAD WEIGHT = 70 LBS WIND AREA = 9.2 SQ FT C d = 1.2 K z = 0.90 I r = SCHEDULE PIPE WEIGHT = 210 LBS WIND AREA = 6.67 SQ FT C d = 1.1 K z = 0.87 I r = 1.0 Measurement 3 rd Edition 4 th Edition Pressure on Signal Head lb/ft lb/ft2 Wind Force on lbs lbs Signal Head Pressure on Pipe lb/ft lb/ft2 Wind Force on lbs lbs Pipe 4 TH Edition values are 40% less than values resulting from 3 RD Edition calculations PRESSURE ON SIGNAL HEAD: P = x (C G x V) 2 x C d x C h = x (1.3 x 90) 2 x 1.2 x 1.0 = (LB/FT 2 ) WIND FORCE ON SIGNAL HEAD: = P x WIND AREA = x 9.2 = LBS PRESSURE ON PIPE P = x (C G x V) 2 x C d x C h = x (1.3 x 90) 2 x 1.1 x 0.8 = (LB/FT 2 ) WIND FORCE ON PIPE = P x WIND AREA = x 6.67 = LBS PRESSURE ON SIGNAL HEAD: P = x G x V 2 x K z x I r x C d = x 1.14 x 90 2 x 0.90 x 1.0 x 1.2 = (LB/FT 2 ) WIND FORCE ON SIGNAL HEAD: = P x WIND AREA = x 9.2 = LBS PRESSURE ON PIPE P = x G x V 2 x K z x I r x C d = x 1.14 x 90 2 x 0.87 x 1.0 x 1.1 = (LB/FT 2 ) WIND FORCE ON PIPE = P x WIND AREA = x 6.67 = LBS 3

4 COMPARISON OF WIND PRESSURE CALCULATIONS Measure 3 RD Edition 4 TH Edition Percent Change Base Moment Reaction: Signal l ft-lbs ft-lbs -- 36% Base Moment ft-lbs ft-lbs -- 27% Reaction: Pipe Total Base Moment ft-lbs ft-lbs -- 34% 4 TH EDITION DECREASES THE ALLOWABLE STRESSES IN GROUP II & III LOADING. 3 RD EDITION ALLOWED 140% 4 TH EDITION ALLOWED 133% THE CHANGES WERE IMPLEMENTED TO ENSURE CONSISTENCY WITH MAJOR CODES IN THE U.S. MANUAL FOR STEEL CONSTRUCTION AISC CSR (COMBINED STRESS RATIO) IS THE SAME IN BOTH CODES. CSR = f a /(0.6 * F Y ) + f b /F b + (f v /F v ) 2 (must be < 1) STRESSES (PSI) NEW CODE YIELD STRESS, F Y ALLOWABLE BENDING STRESS, F b ALLOWABLE SHEAR STRESS, F v WHERE: f a = ACTUAL AXIAL STRESS f b = ACTUAL BENDING STRESS f v = ACTUAL SHEAR STRESS F Y = YIELD STRESS (42 KSI FOR PIPE) F b = ALLOWABLE BENDING STRESS F v = ALLOWABLE SHEAR STRESS MULTIPLIED BY ALLOWABLE STRESS NEW CODE INCREASE 140% 133% YIELD STRESS, F Y ALLOWABLE BENDING STRESS, F b ALLOWABLE SHEAR STRESS, F v NEW CODE AXIAL STRESS, f a BENDING STRESS, f b SHEAR STRESS, f v COMBINED STRESS RATIO, CSR WIND CODE CHANGE RESULTS IN LOWER WIND LOADING. EVEN WHEN DECEASING THE ALLOWABLE STRESS, THE NEW CODE STILL RESULTS IN A LOWER CSR. CONSIDERING WIND AND STRESS CHANGES ALONE, POLE CROSS SECTIONS AND WALL THICKNESS COULD BE REDUCED, HOWEVER NEW SECTION TO THE AASHTO CODE THREE CATEGORIES: I, II, & III FOUR LOADING SCENARIOS GALLOPING -- VORTEX SHEDDING -- NATURAL WIND GUST -- TRUCK-INDUCED GUST -- USUALLY DICTATES WELD CONNECTION DETAILS AND CAN RESULT IN LARGER MEMBERS 4

5 DESIGN REQUIRED FOR OVERHEAD CANTILEVERED SIGN STRUCTURES OVERHEAD CANTILEVERED TRAFFIC SIGNAL STRUCTURES HIGH-LEVEL LIGHTING STRUCTURES NOT REQUIRED FOR SIGN BRIDGES TRAFFIC SIGNAL BRIDGES NON-CANTILEVERED SIGN POSTS OR TRAFFIC SIGNAL POSTS. THREE CATEGORIES DICTATE THE IMPORTANCE FACTOR, I F I - CRITICAL CANTILEVERED SUPPORT STRUCTURES INSTALLED ON MAJOR HIGHWAYS II - OTHER CANTILEVERED SUPPORT STRUCTURES INSTALLED ON MAJOR HIGHWAYS AND ALL CANTILEVERED SUPPORT STRUCTURES INSTALLED ON SECONDARY HIGHWAYS III -CANTILEVERED SUPPORT STRUCTURES INSTALLED AT ALL OTHER LOCATIONS TABLE IMPORTANCE FACTOR IMPORTANCE FACTOR, I F CATEGORY NATURAL WIND TRUCK INDUCED GALLOPING VORTEX SHEDDING GUST GUSTS SIGN 1.0 X I TRAFFIC SIGNAL 1.0 X II III LIGHTING X X SIGN 0.65 X TRAFFIC SIGNAL 0.65 X LIGHTING X X SIGN 0.31 X TRAFFIC SIGNAL 0.30 X GALLOPING RESULTS IN LARGE OSCILLATIONS OF THE CANTILEVER ARM NORMAL TO THE WIND DIRECTION OR IN THE VERTICAL PLANE. ONLY REQUIRED FOR SIGN AND TRAFFIC SIGNAL CANTILEVER STRUCTURES. PRESSURE IS APPLIED VERTICALLY TO SURFACE AREA AS VIEWED IN NORMAL ELEVATION OF ALL SIGNS PANELS, TRAFFIC SIGNAL HEADS, AND BACK PLATES. P G = 21 x I F (LB/FT 2 ) LIGHTING X X VORTEX SHEDDING RESULTS IN OSCILLATIONS IN A PLANE NORMAL TO THE DIRECTION OF THE WIND. ONLY REQUIRED ON LIGHTING STRUCTURES. NOT REQUIRED FOR STRUCTURES THAT HAVE TAPERS LESS THEN 0.14 IN/FT PRESSURE IS APPLIED TRANSVERSELY TO POLES AND HORIZONTAL MAST ARMS. P VS = x (V C ) 2 x C d x I F /(2 x β) WHERE: P VS = PRESSURE TO BE APPLIED(LB/FT 2 ) C d = DRAG COEFFICIENT I F = IMPORTANCE FACTOR β = DAMPING RATIO = V C = CRITICAL WIND VELOCITY THAT VORTEX SHEDDING CAN OCCUR 5

6 NATURAL WIND GUSTS ARE THE MOST BASIC WIND PHENOMENA BECAUSE OF THE INHERENT VARIABILITY IN THE VELOCITY AND DIRECTION OF THE WIND. REQUIRED ON STRUCTURES. PRESSURE IS APPLIED IN THE HORIZONTAL DIRECTION TO THE EXPOSED AREA OF ALL SUPPORT STRUCTURE MEMBERS, SIGNS, AND TRAFFIC SIGNALS. P NW = 5.2 x C d x I F TRUCK-INDUCED GUSTS RESULT FROM THE UPDRAFT OF A TRUCK PASSING UNDER A CANTILEVERED ARM. ASSUMES A TRUCK SPEED OF 65 MPH ONLY REQUIRED FOR CANTILEVER SIGN AND TRAFFIC SIGNAL STRUCTURES. PRESSURE IS APPLIED IN THE VERTICAL DIRECTION OF CANTILEVERS ALONG ANY 12 FT LENGTH THE MAXIMUM STRESS RANGE P TG = 18.8 x C d x I F COMMON WELD CONNECTIONS AFFECTED BY FLANGE PLATE TO TUBE CONNECTION MAST ARM TO COLUMN CONNECTION FLANGE PLATE TO TUBE CONNECTION NEW MORE RESISTANT DESIGN OLD LESS RESISTANT DESIGN MAST ARM COLUMN CONNECTION 3-SECTION SIGNAL HEAD -WEIGHT = 70 LBS -WIND AREA = 9.2 SQ FT -ICE AREA = 22 SQ FT NEW MORE RESISTANT ARM CONNECTION WITH A WRAP AROUND TOP AND BOTTOM GUSSET PLATES OLD LESS RESISTANT ARM CONNECTION DETAIL LUMINAIRE HEAD -WEIGHT = 60 LBS -WIND AREA = 3.3 SQ FT -ICE AREA = 6.6 SQ FT 6

7 VARIABLES FOR 1994 CODE 90 MPH WIND SPEED 140% ALLOWABLE STRESS INCREASE 3 LBS/FT 2 ICE LOAD VARIABLES FOR 2001 CODE 90 MPH WIND SPEED 133% ALLOWABLE STRESS INCREASE 3 LBS/FT 2 ICE LOAD 50 YEAR DESIGN LIFE (I r = 1) CATEGORY II NEW CODE WITH DIFFERENCE FROM OLD TO NEW PERCENT DIFFERENCE BASE CSR % ARM CSR % BASE REACTIONS SHEAR (LBS) % AXIAL (LBS) % MOMENT (FT LBS) % TORSION (FT LBS) % TOTAL STEEL WEIGHT (LBS) % REQUIREMENTS CONTROL THE DESIGN. INCREASE TUBE SIZES TO MEET TOTAL STEEL WEIGHT INCREASES ABOUT 9%. THE DESIGN WILL REQUIRE FULL PENETRATION BASE CONNECTION AND RING STIFFENED ARM TO SHAFT CONNECTION NEW CONNECTIONS ARE MORE TIME CONSUMING. NEW CODE WITHOUT DIFFERENCE FROM OLD TO NEW PERCENT DIFFERENCE BASE CSR % ARM CSR % BASE REACTIONS SHEAR (LBS) % AXIAL (LBS) % MOMENT (FT LBS) % TORSION (FT LBS) % TOTAL STEEL WEIGHT (LBS) % WITHOUT REQUIREMENTS, THE NEW CODE YIELDS A SMALLER STRUCTURE WITH REQUIREMENTS, THE NEW CODE YIELDS A LARGER STRUCTURE Contact: Daniel Emsile, PE Northwest Signal dan.emsile@nwsignal.com 7