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9.13
WEB-BASED INTERACTIVE DESIGN OF PLATE GIRDERS
The applet
presented in this section is for interactive design of homogeneous and
hybrid plate girders according to the ASD and LRFD codes. This applet
consists of three windows: input window, output window and control window
(Fig. 9.29).
The input window consists of Configuration panel, Flange & Web panel, Stiffeners
panel, and Welds Panel. The user
can enter the corresponding input for the design of plate girders in those
panels.
Span length, lateral supports (similar to applet
for design of beams described in Sec. 5.11), and distributed and
concentrated loads are set in the configuration panel (Fig. 9.29). The
loading on the girder may consist of a uniformly distributed load plus a
specified number of concentrated loads. The concentrated loads are named
alphabetically from left. Alphabets “A” and “B” are reserved for the left
and right supports, respectively. The girder may have either full lateral
support or intermediate lateral supports.
Width, thickness, and steel type of flange
plates and thickness and steel type of the web plate are set in the flange
& web panel (9.30a). To begin the design of a plate girder the user
needs to specify the steel types of flange and web plates only. The applet
displays the first design results as shown in Fig. 9.30b. Like other
applets presented in the previous chapters, this applet requires minimum
amount of design entry to perform a design. However, the user can perform
redesigns repeatedly simply by changing only one or several of the input
values.
To design a hybrid girder, the user needs to
select the steel types of flange plates and web plate properly. For
impractical values, for example, if the user selects a steel type for
flange plates with lower strength than that of the web, the applet warns
the user with a pop-up message shown in Fig. 9.31.
Steel type of bearing and intermediate stiffeners,
thickness and width of bearing stiffeners, and thickness, width, the place
of the 1st stiffener, and the number of the intermediate
stiffeners are set in the stiffeners panel (Fig. 9.32). By default, bearing
stiffeners at each concentrated load are designed differently from those at
supports and intermediate stiffeners are designed for each segment (defined
as a portion of the girder between two concentrated loads or a support and
a concentrated load). But the user can change and make them the same throughout
the length of the girder after the first design presented by the applet.
Numbers of bearing stiffeners and segments
depend on the number of concentrated loads given in the input panel. The
applet handles this situation by adding selection lists as the user enters
the concentrated loads. Initially, the applet provides only one segment
selection, i.e. the entire span for girder without any concentrated loads
defined as “From A to B” (Fig. 9.32a). As the user enters additional
concentrated loads the applet creates additional segments. For example, in
Fig. 9.33, the applet has added a second segment and the two segments are
denoted as “From A to C”
and “From C to
B”. Depending on the
selection made by the user, the applet displays the required input items
for the selected segment. This scheme saves screen space by using the same
screen area for all different segments. The same scheme is used for the
bearing stiffeners as well as other panels such as welds panel in the input window, and elevation, sections, and welds
panels in the output window.
Intermediate stiffeners may or may not be
provided and single or double plates may be used as intermediate
stiffeners. If the user chooses to design a plate girder without
intermediate stiffeners, all input components related to intermediate
stiffeners are deactivated (Fig. 9.34).
At the beginning of the design of a plate girder
the user needs to specify the steel types of stiffeners, whether
intermediate stiffeners are provided or not, and whether double or single
intermediate stiffeners are used only (Fig. 9.32a). The applet displays
design results as shown in Fig. 9.32b.
The last panel in the input window is the welds
panel for electrode type, and size, length and spacing of the welds
connecting flange to web, size of the weld connecting bearing stiffeners to
web, and size, length, and spacing of the weld connecting intermediate
stiffeners to web (9.35). The user can choose intermittent or continuous
fillet welds for flange-to-web and intermediate stiffener-to-web
connections. But, continuous fillet welds are used for connecting bearing
stiffeners to web as required by the ASD and LRFD codes. At the beginning
of the design of a plate girder the user needs to specify the electrode
type and whether intermittent or continuous welds are used only (Fig.
9.35a). The applet displays design results as shown in Fig. 9.35b.
The user can select the two primary design
parameters in the control window
placed in the upper right corner of the screen (Figs. 9.29 and 9.36). They
are the method of design, ASD and LRFD, and the web depth-to-span ratio.
Since the web depth-to-span ratio is a key design factor in design of plate
girders, this option is placed separately from the flange & web panel
in the input window so that the
user can design the plate girder with several different values of the web
depth-to-span ratios easily.
The output
window consists of loadings
panel, BMD (bending moment
diagram) panel, SFD (shear force
diagram) panel, Elevation panel, Sections panel, Welds panel, and Girder
Weight Panel (Fig. 9.29). Loadings panel displays the loadings,
supports, and points of lateral support similar to the applet for design of
beams (Fig. 9.37).
BMD
panel displays the bending moment diagram for the given loadings and shows
the magnitude and location of the maximum bending moment (Fig. 9.38).
Similarly, SFD panel shows the shear force diagram along with maximum shear
force and magnitude of shear force at supports and concentrated loads (Fig.
9.39).
Elevation
and sections panels display the elevation and the sections of the plate
girder, respectively as shown in Figs. 9.40 and 9.41. It can display the
section at support or at the location of a concentrated load (Fig. 9.41)
and a section within any segment (Fig. 9.42).
Welds
panel displays the design results of the weld along with minimum and
maximum code requirements (Fig. 9.43). Knowing the minimum and maximum
requirements, the user can easily perform a redesign without trying
improper values.
The girder weight panel is the last panel in the
output window, and displays the various weight components as well as the
total weight of the plate girder (Fig. 9.44).
The
example data used in Figs. 9.29 to 9.36 are the same as those of the
example problem solved in section 9.8. The results shown in Figs. 9.37 to
9.44 are for the same problem also. The hybrid girder presented in section
9.9 also has been solved by the applet. The results are presented in Figs.
9.45 to 9.49.
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