Activity 6.1.1 – Structural Calculations
Purpose
The primary function of a building structure is to support and transmit the loads and
forces to the ground. As a structural engineering, it is important to understand how
the stability and strength of a structure help to determine the structures ability to
withstand various loads.
Equipment
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Pencil
Calculator
Computer
Journal
Procedure
In this activity, you will begin to learn about structural calculations. This problem will
be used as an example to teach you how to determine the load of a structure. Your
teacher will take you through the steps of this problem and then provide you with
additional problems to do for homework. This example problem is explained as it
might appear in a structural engineer’s notebook. It is important to read carefully and
to follow the directions.
Bertucci’s Structural Calculations Example
Given a two-bay portion of a building, you will design the structural members for the
second floor. The diagram below depicts the structural steel of the building area.
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*Note: 150 lb/ft3 is the weight of concrete and the Tributary area is used in calculations
to determine the load a beam is caring.
Tributary
area
Information used
in MD Solids
software.
Directions:
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Step 1: Calculating Beam Reaction
This came from
previous
calculation.
This assumption
can be checked
against the actual
beam size.
Step 2: Calculating
Center Girder
Note:
Force X Distance
= Moment
This assumption
can be checked
against the actual
girder size.
This is the reaction
load at the ends of
each girder.
Note: The center girder has 4 beams at two points located at 6’ and 12’.
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Step 3: Using MD Solids
In this part of the activity, you will use MD Solids to help you design a beam
and girder to check the deflection.
When using MD Solids, be sure to check your units and determine if you are
you using pounds/inches/feet or kips/inches/feet. This is important when
entering the Yield Strength of Steel Fy as the units will determine which you
use, such as either Fy=36,000lb/in2 or 36 kips/in2.
You will use Limit the Deflection set to L/360. If you recall from the
PowerPoint® on Beams, you learned that there are three that may be used.
This is the most common one to use. The beam will be designed based on the
most possible worse-case scenario.
BEAM Calculations:
Limit Deflection - L/360
Convert feet to inches because L must be in inches.
16’ is the length of
the beam.
16’ x 12 in/ft
360
= 0.533”
Actual Deflection ∆ = 0.5159” must be less than 0.533”
NOTE: IF deflection is more than 0.533”, you can not use the beam.
You will choose MD Solids that fits within the limit, such as W12X16.
NOTE: W 12 x 16 – the 12 is the size of the depth of the beam while the 16 is
the physical weight of the beam, such as 16 lbs per foot
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There are other beams that fit the deflection criteria, however, the one selected is
the most economical and is a readily available beam size. Typically, the lightest
beam is considered the most economical because the cost of the steel is based on
the weight. Another consideration in choosing this beam size is the depth of the
beam, which is approximately 12 inches. This depth is helpful when mechanical and
electrical building systems are installed. In engineering design practices, the depth
of the floor system may already be set by the architect and the structural engineer.
In those cases, the engineer will need to keep the beam depths to a specified height.
Girder Calculations:
You calculate the Center Girder because it is the worst possible case. The
result will be used for all girders in the area.
Use the Limit Deflection = L/360
18’ is the
length of
the girder.
18’ x 12 in/ft
360
= 0.6”
Actual Deflection ∆ = 0.5441” and must be less than 0.6”
Use W14 X 38 for the Girder.
The following pictures are the MD Solids solution and show the results you may get
with your calculations. When you change the beam size, you should notice the
amount of deflection changes after refreshing the diagram.
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Conclusion
1. How do you determine what loads are applied to a structure?
2. How does design of a structure impact how loads are dispersed on it?
3. In what ways are wind, snow, dead, and live loads similar or different?
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