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Tension Members Last Time Structural Elements Subjected to Axial Tensile Forces Cables in Suspension and Cable-Stayed Bridges Trusses Bracing for Buildings and Bridges

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TENSION MEMBERS – TYPES Last Time

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Structural Shapes & Build Up Members rigidity, small lateral loads, load reversal Slenderness L/r > 300 AISC Spec D1 Does not apply to rods in tension

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Limit States Last Time STRENGTH Failure at Main Body Failure at Connection etc

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TENSION MEMBERS - LIMIT STATES AISC Specs Chapter D Last Time Failure at main body if connection is strong enough After yielding deformations become too large and member does not serve its design purpose. Failure at yielding nominal strength P n =F y A g F y = Yielding Strength, A g = Gross Area

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TENSION MEMBERS - LIMIT STATES AISC Specs Chapter D Last Time Failure at Connection if connection is weak it will fracture Failure at ultimate strength nominal strength P n =F u A e F u = Ultimate Strength, A e = Effective Area

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Gross Area – Specs D3.1 p Last Time Gross Area A g : Total Area of Main Body of Member

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Net Area – Specs D3.2 p Last Time Net Area A n : Welded Connections A n = A g Bolded Connections A n = A g - Area of Holes

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Net Area Last Time Size of hole is larger than size of the bolt d h =d b +1/16” Additional 1/16” of material is damaged during drilling or punchning of holes (Commentary D3.2 p )

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Staggered Fasteners Space Limitations Geometry Constraints

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Staggered Fasteners Inclined Fracture Path

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Net Area - Effect of Staggered Holes AISC Specs D3.1 Last Time TT T T Failure paths on net section g s p g = gage s = spacing Reduced diameter

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Example Last Time Different failure lines may be subjected to different loads! 11 holes 8/11 of load

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Net Area - Gage Distance for an Angle Unfold Angle and Visualize as a plate

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Net Area - Gage Distance for an Angle For holes on different legs

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Example

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Effective Net Area – Specs D3.3 p A e =AU A = Area that depends on type of connection A=A g for welded A=A n for bolted U = shear lag coefficient (accounts for eccentricities)

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U Accounts for eccentricities U AISC D3.3 Table D3.1

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Shear Lag Factor 1.General category for any type of tension member except plates and round HSS with 2.Plates 3.Round HSS with 4.Alternative values for single angles 5.Alternative values for W,M,S and HP shapes

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1. General category for any type of tension member except plates and round HSS with Distance from centroid of connected area to the plane of the connection l Length of the connection

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1. General category for any type of tension member except plates and round HSS with

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2. Plates U=1.0 since cross section has one element and it is connected Special Cases a. Longitudinal welds on sides only

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2. Plates U=1.0 since cross section has one element and it is connected Special Cases b. Transverse welds only (uncommon) A n net area of directly connected members

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3. Round HSS with

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4. Alternative values for single angles 2 or 3 fasteners in direction of loading 4 fasteners in direction of loading

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5. Alternative values for W,M,S and HP shapes Connected through flange with 3 or more fasteners in direction of loading

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5. Alternative values for W,M,S and HP shapes Connected through flange with 3 or more fasteners in direction of loading

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5. Alternative values for W,M,S and HP shapes Connected through web with 4 or more fasteners in direction of loading

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Example Determine Effective Net Area

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Example

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Only one element is connected Net area must be reduced

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Example Alternatively 3 bolts in direction of load

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Block Shear

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Block Shear Chapter D User Note -> J4.3 (p ) Failure occurs by rupture on the shear area and rupture on the tension area Both surfaces (shear and tension) contribute to total strength

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Block Shear Chapter D User Note -> J4.3 (p ) A nv : net shear area A nt : net tension area Both surfaces (shear and tension) contribute to total strength

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Block Shear Chapter D User Note -> J4.3 (p ) A nv : net shear area A nt : net tension area For angles and gusset plates

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Block Shear Chapter D User Note -> J4.3 (p ) A nv : net shear area A nt : net tension area AISC U bs =1 for angles, gusset plates and most coped beams See AISC Commentary J4.3 for other less common cases

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Example Compute block shear strength per LRFD and ASD

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Example

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Nominal Strength LRFDASD

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