RESIDENTIAL ROOF TRUSS CHORD COMPONENTS

B. Mobasher, S.D. Rajan Dept. of Civil & Environmental Engineering Arizona State University Tempe, AZ 85287-5306

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Project Interactions Performance Steel truss field tests ICBO Approvals, code development optimization

Structure Mechanical properties, fracture and FEM modeling on Toughening Mechanisms

Processing CE Composites processing Lab, extrusion, pultrusion, computer assisted manufacturing.

Property materials characterization, SEM facility, XRD, Interfaces and matrix modifications. New fibers & composites

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Typical Section geometry 2.5 g16

Symbol L Em Fy G t a,b,c,e r, r2 u u2

Remarks Length Modulus of elasticity Yield stress Shear modulus Material thickness Cross-section dimensions Cross-section dimensions Length of curve r r2 Length of curve

Value 12.0 in 29,000 ksi 40 ksi 11,154 ksi 0.0566 in {1.5, 1.15, 1.15, 0.3} in {0.1, 0.03} in 0.314159 in 0.0942477 in

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Computed Section Property Symbol Ix Iy

Remarks Second moment of inertia about x axis Second moment of inertia about y axis

Value 4 0.2131 in 4 0.3309 in

J Cwc Cwh m x0 rx ry

St. Venant’s torsion constant Coef. of warping, channel section Coef. of warping, hat section Distance to shear center Distance from centroid to shear center Radius of gyration about x Radius of gyration about y

0.0004207 in4 0.105522 0.129097 1.1459 in 2.2656 in 0.70774 in 0.88196 in

Polar radius of gyration Stress values Please see text Effective area Compressive strength

2.532108 in {379, 3982} ksi {4,0.5103,1,1.5} 0.1847 in2 6.1024 k

r0 tex Kw, w w bw e c Pn

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Computed Section Strengths Length (in.) 12 24 36 48 60 72 84 96 108 120

AISI Maximum Compressive Load (lb) 3.5 CHORD 2.5 CHORD 20 GA. 18 GA. 16 GA. 20 GA. 18 GA. 16 GA. 3,176 4,376 7,035 3,224 4,447 7,176 2,729 3,729 5,788 3,071 4,200 6,706 1,882 2,624 3,776 2,788 3,800 5,918 1,259 1,765 2,576 2,353 3,224 4,835 929 1,318 1,941 1,788 2,494 3,624 729 1,035 1,553 1,388 1,941 2,859 600 859 1,306 1,118 1,588 2,365 506 729 1,118 941 1,341 2,012 435 635 988 800 1,165 1,765 388 565 894 706 1,024 1,565

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Performance Tests • Axial Compression and Four-Point Bending Test • AISI-LRFD Calculations for Axial and Bending • Finite Element Simulations for Axial and Bending • Connection Tests • Splice Test • AISI-LRFD Calculations for Axial and Bending • Finite Element Simulations • Full scale Truss Tests

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Axial Compression Test  



The specimen is fixed-fixed The displacement of the actuator is used as the control parameter Maximum displacement • 0.5" for the 18 and 20 GA. • 0.6" for the 16 GA.

 

2.5 and the 3.5 chord sections Four different gauges - 16 GA., 18 GA., 20 GA., and 22 GA.

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Gage 18- Experimental Compression Results L=12"

Stress, Ksi

20

15

L=24" L=36"

10

5

L=48"

0 0.000

0.002

0.004

0.006

0.008

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0.010

0.012

failure mode of 2.5 16GA 12" specimen under axial compression

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failure mode of 2.5-20GA 48" specimen under axial compression

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Finite Element Method

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Nominal Stress at failure vs. web length to Thickness ratio

Nominal Stress at Failure, Psi

60000

16 gauge, 12" 40000 16 gauge, 48" 18 gauge, 12" 20000

18 gauge, 48"

20 gauge, 12"

20 gauge, 48"

0 40

60 80 100 Web Length / thickness, w/t

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Comparison of the AISI calculations with FEM and Experimental tests Gage 16, 3.5" Chord

Load, Lbs

12000

8000 K=0.5

4000

FEM Experimental AISI-LRFD

K=1

0 0

10

20 30 Effective Length, in

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40

50

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Strain Distribution 3000

2

2000

1 0

Load, lbs

6 5 4

1000

0

7

Ch. 0 Ch. 1 Ch. 2 Ch. 3 Ch. 5 Ch. 6 Ch. 7 -400

-200 0 Member Strain, microstrains

200

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3

Bottom chord deflections versus total load applied on the center truss 4000

Load, lbs

3000

1 2 3 Dial gage locations

2000 Design Load

Dial gage 1

1000

Dial gage 2 Dial gage 3

0 0.00

0.20

0.40 Deflection, in

0.60

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0.80

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