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Problem #1 The statically determinate truss shown in Figure 1 is part of a structure designed to support a large billboard

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Problem #1

The statically determinate truss shown in Figure 1 is part of a structure designed to support a large billboard. The nominal loads are:

1. Wind: F₁ = unknown and F₂ = 0.4F₁

2. Dead: F₃ = 25 kips (self-weight of the structure)

The diagonal member AB (Figure 1) was designed as a tension member against the worst LRFD combination of loads. The final design of AB is shown in Figure 2 (note that the long leg of the angle is bolted to the gusset plate). The material is A572 Gr. 50 steel.

Please find:

1. The design strength of AB in tension per LRFD. Consider limit states LS1 and LS2 only.

2. Given the design strength, find the maximum nominal wind load Fi, which can be carried by

AB per LRFD requirements.

F₃ F₃ 2414

| | mene

F,— . ‘* B

242 | l6X4X 1/2

af jee |

—_ 0 o

F y) bh Gusset Plate

}$—_________ff

10 ft

Figure 1: A truss supporting a Figure 2: Element AB is an L6 X 4 X 4% angle connected with 7/8” billboard. diameter bolts in standard holes.

Problem #2

Compute the LRFD design strength of the C12 X 30 tension member shown in Figure 3. LS1 and

LS2 apply. Use A36 steel (Fy = 36 ksi; Fu = 58 ksi). The bolt diameter is 3/4” and the holes are

standard.

”

2.0", typ.

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_—)

oO oO oO oO oO

”

3.0 CL

Qe a Qe Qa Que eee ee Te.

3.0”

oO Oo oO oO oO

el

Figure 3: C12 X 30 tension member: side view (left) and cross-section view (right). CL = center line.

Problem #3

Compute the LRFD design strength of the WT12x51.5 tension member shown in Figure 4. LS1 and

LS2 apply. Use A992 Gr. 50 steel. The bolt diameter is 7/8” and the holes are standard.

2” 2” 2”

K—}<-— > 1e-— >|

kK—_><— >}

3” 2”

Figure 4: WT 12 X 51.5 tension member: side view (left) and cross section view (right).