Steel Design (Activate Learning with these NEW titles from Engineering!)
Steel Design (Activate Learning with these NEW titles from Engineering!)
6th Edition
ISBN: 9781337094740
Author: Segui, William T.
Publisher: Cengage Learning
Question
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Chapter 7, Problem 7.7.2P
To determine

(a)

The design of a single angle tension member and a bolted connection using Load and Resistance Factor Design (LRFD) method.

Expert Solution
Check Mark

Answer to Problem 7.7.2P

An angle L8×6×58 and 10 bolts of 114inch diameter each of Group A in two lines with a spacing of 4inch and an edge distance of 2.5inch is used.

Explanation of Solution

Given:

Steel used is A36.

Thickness of gusset plate is 38inch.

Dead load is 50kips.

Live load is 100kips.

Wind load is 45kips.

Group A bolts are used.

Calculation:

The properties for A36 steel from the AISC steel table are as follows:

  • The ultimate tensile stress is 58ksi.
  • The yield strength is 36ksi.

From the AISC manual Table J3-1, the minimum tension force per bolt is 71kips.

From the AISC manual Table D3-1, the reduction factor is equal to 0.8.

Write the expression for total factored load by load combination 2.

Pu=1.2D+1.6L     ...... (I)

Here, total factored load is Pu, live load is L, and dead load is D.

Substitute 100kips for L and 50kips for D in Equation (I).

Pu=(1.2×50+1.6×100)kips=220kips

Write the expression for total factored load by load combination 4.

Pu=1.2D+1.0W+0.5L     ...... (II)

Here, the wind load is W.

Substitute 100kips for L, 50kips for D, and 45kips for W in Equation (II).

Pu=(1.2×50+1.0×45+0.5×100)kips=155kips

Thus, the value of total factored load by load combination 2 is greater, so the total factored load is equal to 220kips.

Write the expression for slip critical shear strength per bolt.

ϕRn=ϕ(μDuhfnsTb)     ...... (III)

Here, the ratio of mean actual bolt pre-tensioned to specified bolt pre-tensioned is Du, slip shear strength per bolt is Rn, filler factor is hf, number of slip planes is ns, mean slip coefficient is μ, and minimum tension force per bolt is Tb.

Substitute 1.13 for Du, 0.3 for μ, 1.0 for hf, 1.0 for ϕ, 1 for ns and 71kips for Tb in Equation (III).

ϕRn=1.0(0.3×1.13×1.0×71kips×1)=24.07kips

Write the expression for the design strength.

B=N×ϕRn     ...... (IV)

Here, number of bolts are N and design strength is B.

Substitute 24.07kips for ϕRn and 10 for N in Equation (IV).

B=(10×24.07)kips=240.7kips

Write the expression for required gross area of the member.

Ag=Pu0.9Fy     ...... (V)

Here, the yield strength is Fy and the gross area is Ag.

Substitute 36ksi for Fy and 220kips for Pu in Equation (V).

Ag=220kips0.9×36ksi=6.79inch2

Write the expression for required effective area of the member.

Ae=Pu0.75Fu     ...... (VI)

Here, ultimate strength is Fu and the effective area is Ae.

Substitute 58ksi for Fu and 220kips for Pu in Equation (VI).

Ae=220kips0.75×58ksi=5.06inch2

Write the expression for the minimum value of radius of gyration.

rmin=L300     ...... (VII)

Here, the minimum radius of gyration is rmin and the length of the member is L.

Substitute 240inch for L in Equation (VII).

rmin=240inch300=0.8inch

Thus, try the section L8×6×58, as per the above calculated values.

Write the expression for net area of L8×6×58 section.

An=AgAholes     ...... (VIII)

Here, net area of the section is An and the area of the holes is Aholes.

Substitute tdh for Aholes in Equation (VIII).

An=Ag2(tdh)     ...... (IX)

Here, diameter of the holes is dh.

Substitute 58inch for t and 8.14inch2 for Ag in Equation (IX).

An=8.41inch22(114+18)inch×58inch=6.691inch2

Write the expression for effective net area.

Ae=AnU     ...... (X)

Here, the reduction factor is U and the effective net area is Ae.

Substitute 0.8 for U and 6.691inch2 for An in Equation (X).

Ae=(6.691×0.8)inch2=5.35inch2

Write the expression for minimum spacing.

ms=(223)d     ...... (XI)

Here, the minimum spacing is ms and the bolt diameter is d.

Substitute 114inch for d in Equation (XI).

ms=(2.667×114)inch=3.334inch

Write the expression for design strength of edge bolts for an edge distance of 2.5inch.

From the manual, Table 7-6,

ϕrn=t×70.1kips/inch     ...... (XII)

Here, load resistance factor is ϕ, the strength is rn and the thickness is t.

Substitute 0.375inch for t in Equation (XII).

ϕrn=(0.375inch×70.1kips/inch)=26.3kips

Write the expression for design strength of inner bolts for a spacing of 223d.

From the manual, Table 7-5,

ϕrn=t×105kips/inch     ...... (XIII)

Substitute 0.375inch for t in Equation (XIII).

ϕrn=(0.375inch×105kips/inch)=39.4kips

Thus, the slip critical strength is taken into consideration as it has less value.

Write the expression for gross shear area.

Agv=2(t×ss)     ...... (XIV)

Here, shear length is ss and gross shear area is Agv.

Substitute 0.375inch for t and 18.5inch for ss in Equation (XIV).

Agv=(2×0.375×18.5)inch2=13.88inch2

Write the expression for the net area in shear.

Anv=AgvAholes     ...... (XV)

Here, net area in shear is Anv.

Substitute tdh for Aholes in Equation (XV).

Anv=Agv2(tdh)     ...... (XVI)

Substitute 13.88inch2 for Agv and 0.375inch for t in Equation (XVI).

Anv=(0.375×(18.54.5×1.375)×2)inch2=9.234inch2

Write the expression for net area in tension.

Ant=(t×tL)Aholes     ...... (XVII)

Here, tension length is tL and net area in tension is Ant.

Substitute 3inch for tL and 0.375inch for t Equation (XVII).

Ant=(0.375×(31×1.375))inch2=0.6094inch2

Write the expression for the nominal strength in block shear.

Rnb=0.6FuAnv+UbsFuAnt     ...... (XVIII)

Here, reduction factor is Ubs and nominal strength in block shear is Rnb.

Substitute 9.234inch2 for Anv, 58ksi for Fu, 0.6094inch2 for Ant and 1 for Ubs in Equation (XVIII).

Rnb=[(0.6×58ksi×9.234inch2)+(1×58ksi×0.6094inch2)]=321.35kips+35.35kips=356.7kips

Write the expression for nominal shear strength in gross shear.

Rng=0.6FyAgv+UbsFuAnt     ...... (XIX)

Here, nominal shear strength in gross shear is Rng and yield strength is Fy.

Substitute 13.88inch2 for Agv, 58ksi for Fu, 0.6094inch2 for Ant, 36ksi for Fy and 1 for Ubs in Equation (XIX).

Rng=[(0.6×36ksi×13.88inch2)+(1×58ksi×0.6094inch2)]=299.8kips+35.35kips=335.2kips

Thus, the nominal shear strength is taken as 335.2kips, as it has less value.

Write the expression for design strength per bolt.

Bd=ϕRn     ...... (XX)

Here, design strength of bolt is Bd.

Substitute 335.2kips for Rn and 0.75 for ϕ in Equation (XX).

Bd=0.75×335.2kips=251.4kips

Thus, the design strength is equal to 251.4kips as it is greater than the total factored load.

Conclusion:

Thus, an angle L8×6×58 and 10 bolts of 114inch diameter each of Group A in two lines with a spacing of 4inch and an edge distance of 2.5inch is used.

To determine

(b)

The design of a single angle tension member and a bolted connection using Allowable Stress Design (ASD) method.

Expert Solution
Check Mark

Answer to Problem 7.7.2P

An angle L8×6×58 and 10 bolts of 114inch diameter each of Group A in two lines with a spacing of 4inch and an edge distance of 2.5inch is used.

Explanation of Solution

Calculation:

Write the expression for allowable factored load.

Pa=D+L     ...... (XXI)

Here, allowable factored load is Pa.

Substitute 100kips for L and 50kips for D in Equation (XXI).

Pa=(50+100)kips=150kips

Write the expression for allowable factored load by load combination 6.

Pa=D+0.75L+0.75×0.6W     ...... (XXII)

Substitute 100kips for L, 45kips for W and 50kips for D in Equation (XXII).

Pa=(50+0.75×100+0.75×0.6×45)kips=145.3kips

Thus, the value of allowable factored load by load combination 2 is greater, so the allowable factored load is equal to 150kips.

Write the expression for slip critical shear strength per bolt.

RnΩ=(μDuhfnsTb)Ω     ...... (XXIII)

Here, the load safety factor is Ω.

Substitute 1.13 for Du, 0.3 for μ, 1.0 for hf, 1.5 for Ω, 1 for ns and 71kips for Tb in Equation (XXIII).

RnΩ=(0.3×1.13×1.0×71×1)1.5=16.05kips

Write the expression for the design strength.

B=N×RnΩ     ...... (XXIV)

Here, the design strength is B.

Substitute 16.05kips for RnΩ and 10 for N in Equation (XXIV).

B=(10×16.05)kips=160.5kips

Write the expression for required gross area of the member.

Ag=Pa0.6Fy     ...... (XXV)

Here, the gross area is Ag.

Substitute 36ksi for Fy and 150kips for Pu in Equation (XXV).

Ag=150kips0.6×36kis=6.94inch2

Write the expression for required effective area of the member.

Ae=Pa0.5Fu     ...... (VI)

Here, the effective area is Ae.

Substitute 58ksi for Fu and 150kips for Pu in Equation (XXVI).

Ae=150kips0.5×58ksi=5.17inch2

Write the expression for minimum value of radius of gyration.

rmin=L300     ...... (XXVII)

Here, minimum radius of gyration is rmin.

Substitute 240inch for L in Equation (XXVII).

rmin=240inch300=0.8inch

Thus, try the section L8×6×58, as per the above calculated value.

Write the expression for net area of L8×6×58 section.

An=AgAholes     ...... (XXVIII)

Here, net area of the section is An.

Substitute tdh for Aholes in Equation (XXVIII).

An=Ag2(tdh)     ...... (XXIX)

Substitute 58inch for t and 8.14inch2 for Ag in Equation (XXIX).

An=8.41inch22(114+18)inch×58inch=6.691inch2

Write the expression for effective net area.

Ae=AnU     ...... (XXX)

Here, the effective net area is Ae.

Substitute 0.8 for U and 6.691inch2 for An in Equation (XXX).

Ae=(6.691×0.8)inch2=5.35inch2

Write the expression for minimum spacing.

ms=(223)d     ...... (XXXI)

Substitute 114inch for d in Equation (XXXI).

ms=(2.667×114)inch=3.334inch

Write the expression for design strength of edge bolts for an edge distance of 2.5inch.

From the manual, Table 7-6,

RnΩ=t×46.8kips/inch     ...... (XXXII)

Substitute 0.375inch for t in Equation (XXXII).

RnΩ=(0.375inch×46.8kips/inch)=17.55kips

Write the expression for design strength of inner bolts for a spacing of 223d.

From the manual, Table 7-5,

RnΩ=t×70.3kips/inch     ...... (XXXIII)

Substitute 0.375inch for t in Equation (XXXIII).

RnΩ=(0.375inch×70.3kips/inch)=26.36kips

Thus, the slip critical strength is taken into consideration as it has less value.

Write the expression for gross shear area.

Agv=2(t×ss)     ...... (XXXIV)

Here, gross shear area is Agv.

Substitute 0.375inch for t and 18.5inch for ss in Equation (XXXIV).

Agv=(2×0.375×18.5)inch2=13.88inch2

Write the expression for the net area in shear.

Anv=AgvAholes     ...... (XXXV)

Here, net area in shear is Anv.

Substitute tdh for Aholes in Equation (XXXV).

Anv=Agv2(tdh)     ...... (XXXVI)

Substitute 13.88inch2 for Agv and 0.375inch for t in Equation (XXXVI).

Anv=(0.375×(18.54.5×1.375)×2)inch2=9.234inch2

Write the expression for net area in tension.

Ant=(t×tL)Aholes     ...... (XXXVII)

Here, net area in tension is Ant.

Substitute 3inch for tL and 0.375inch for t Equation (XXXVII).

Ant=(0.375×(31×1.375))inch2=0.6094inch2

Write the expression for the nominal strength in block shear.

Rnb=0.6FuAnv+UbsFuAnt     ...... (XXXVIII)

Here, nominal strength in block shear is Rnb.

Substitute 9.234inch2 for Anv, 58ksi for Fu, 0.6094inch2 for Ant and 1 for Ubs in Equation (XXXVIII).

Rnb=[(0.6×58ksi×9.234inch2)+(1×58ksi×0.6094inch2)]=321.35kips+35.35kips=356.7kips

Write the expression for nominal shear strength in gross shear.

Rng=0.6FyAgv+UbsFuAnt     ...... (XXXIX)

Here, nominal shear strength in gross shear is Rng.

Substitute 13.88inch2 for Agv, 58ksi for Fu, 0.6094inch2 for Ant, 36ksi for Fy and 1 for Ubs in Equation (XXXIX).

Rng=[(0.6×36ksi×13.88inch2)+(1×58ksi×0.6094inch2)]=299.8kips+35.35kips=335.2kips

Thus, the nominal shear strength is taken as 335.2kips, as it has less value.

Write the expression for allowable strength.

Ba=RnΩ     ...... (XL)

Here, allowable strength of bolt is Ba.

Substitute 335.2kips for Rn and 2.0 for Ω in Equation (XL).

Ba=335.22.0kips=168kips

Thus, the allowable strength is equal to 168kips as it is greater than the total allowable load.

Conclusion:

Thus, an angle L8×6×58 and 10 bolts of 114inch diameter each of Group A in two lines with a spacing of 4inch and an edge distance of 2.5inch is used.

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