Learning Goal: To design a plate girder for bending, confirm the shear stress limit, and determine the required weld stress limit for the web/flange joints. A half-through bridge is a design that uses two l-section plate girders to support the roadway as shown in the cross section below. Suppose this kind of design is to be used bridge with a span of 80 ft . Each plate girder can be modeled as a simply supported beam with a uniform load of 6 kip/ft. The web thickness tw = 0.5 in. , flange thickne tf = 2 in. , and web depth d = 60 in. have all been determined (Figure 1). The allowable stresses for the plate girder are oallow = 30 ksi and Tallow = 18 ksi Beams support loads perpendicular to their long axes. For beams with long spans, the bending loads typically cause the highest stresses, so the beam section is designed based on the maximum moment. Then the chosen design can be checked for adequate shear stress limit. If the beam has a short span and large loads, chen the shear stress may control the design. To select a beam section based on the maximum moment, the Muax required section modulus can be determined by Sreg =- Oallow For preformed shapes, the section modulus is often tabulated with the section properties. For built-up shapes, the dimensions need I to be chosen so that -> Srea- Part A - Design for bending The girders have fairly long spans, so we assume that bending will control the design. Determine the required flange width bf of the plate girders to prevent yielding in t girders due to bending-induced normal stress. gure 1 of 1 Express your answer with appropriate units to three significant figures. by » View Available Hint(s) HA ? d bf = Value Units H
Learning Goal: To design a plate girder for bending, confirm the shear stress limit, and determine the required weld stress limit for the web/flange joints. A half-through bridge is a design that uses two l-section plate girders to support the roadway as shown in the cross section below. Suppose this kind of design is to be used bridge with a span of 80 ft . Each plate girder can be modeled as a simply supported beam with a uniform load of 6 kip/ft. The web thickness tw = 0.5 in. , flange thickne tf = 2 in. , and web depth d = 60 in. have all been determined (Figure 1). The allowable stresses for the plate girder are oallow = 30 ksi and Tallow = 18 ksi Beams support loads perpendicular to their long axes. For beams with long spans, the bending loads typically cause the highest stresses, so the beam section is designed based on the maximum moment. Then the chosen design can be checked for adequate shear stress limit. If the beam has a short span and large loads, chen the shear stress may control the design. To select a beam section based on the maximum moment, the Muax required section modulus can be determined by Sreg =- Oallow For preformed shapes, the section modulus is often tabulated with the section properties. For built-up shapes, the dimensions need I to be chosen so that -> Srea- Part A - Design for bending The girders have fairly long spans, so we assume that bending will control the design. Determine the required flange width bf of the plate girders to prevent yielding in t girders due to bending-induced normal stress. gure 1 of 1 Express your answer with appropriate units to three significant figures. by » View Available Hint(s) HA ? d bf = Value Units H
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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Transcribed Image Text:Learning Goal:
To design a plate girder for bending, confirm the shear stress limit,
and determine the required weld stress limit for the web/flange
joints.
A half-through bridge is a design that uses two l-section plate girders to support the roadway as shown in the cross section below. Suppose this kind of design is to be used
bridge with a span of 80 ft . Each plate girder can be modeled as a simply supported beam with a uniform load of 6 kip/ft. The web thickness tw = 0.5 in. , flange thickne
tf = 2 in. , and web depth d = 60 in. have all been determined (Figure 1). The allowable stresses for the plate girder are oallow = 30 ksi and Tallow = 18 ksi
Beams support loads perpendicular to their long axes. For beams
with long spans, the bending loads typically cause the highest
stresses, so the beam section is designed based on the maximum
moment. Then the chosen design can be checked for adequate
shear stress limit. If the beam has a short span and large loads,
chen the shear stress may control the design.
To select a beam section based on the maximum moment, the
Muax
required section modulus can be determined by Sreg =-
Oallow
For preformed shapes, the section modulus is often tabulated with
the section properties. For built-up shapes, the dimensions need
I
to be chosen so that -> Srea-
Part A - Design for bending
The girders have fairly long spans, so we assume that bending will control the design. Determine the required flange width bf of the plate girders to prevent yielding in t
girders due to bending-induced normal stress.
gure
1 of 1
Express your answer with appropriate units to three significant figures.
by
» View Available Hint(s)
HA
?
d
bf =
Value
Units
H
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