Transcript Structural Analysis I

LRFD-Steel Design
Dr.
Ali I. Tayeh
second
Semester
Steel Design
Dr. Ali I. Tayeh
Chapter 3
Tension Members
“Part B”
Tension Members
•EFFECTIVE AREA :
–Connections almost always weak the member.
–the measure of joints influence is called the joint efficiency
– Joint efficiency is a function of the ductility of the material.
fastener spacing. stress concentration , and a phenomenon
known as "shear lag ".
– Shear lag occurs when some elements of the cross section are not
connected.
–The consequence of the partial connection is that the connected
element become loaded and the unconnected part is not fully stressed
.
– Shear lag be accounted for by using a reduced, or effective. net area
because shear lag affects both bolted and welded connections. the
Tension Members
•EFFECTIVE AREA :
–For bolted connections, the effective net area.
–For welded connections, the effective net area.
–Where the reduction factor U is given by
– x is the distance from centroid of the connected area to the plane of
connection
–L is the length of the connection.
–For bolted connection : it is measured from the center of the bolt at one end
of the connection to the center of the bolt at the other end
–For welded connection : it is measured from one end of the end
–The longest segment is used if there are segments of different length in the
direction of load .
Tension Members
•EFFECTIVE AREA :
Tension Members
•EFFECTIVE AREA :
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•EFFECTIVE AREA :
–For Bolted connection: These average value of U classified to two groups:
 Values for two fasteners per line in the direction of the applied load .
 Values for three fasteners and more per line in the direction of the applied load .
– Where the reduction factor U is given by
U=0.90
• For W, M , and S shapes that have a width to depth ratio of at least 2/3
(and tee shapes cut from them) and are concreted through the flange
with at least three fastener per line in the direction of applied load.
U=0.85
• For all other shape (including built up shapes) with at least three
fastener per line.
U=0.75
• For all member with only two fastener per line.
Tension Members
•EFFECTIVE AREA :
–For welded connection: These average value of U :
 Where the reduction factor U is given by
U=0.90
• For W, M , and S shapes that have a width to depth ratio of at least 2/3
(and tee shapes cut from them) and are concreted through the flange
with at least three fastener per line in the direction of applied load.
U=0.85
• For all other shape
Tension Members
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• Example 3.4:
Determine the effective net area for the tension member shown bellow
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• Example 3.4 cont.:
•
for L6 ×6×½
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• Example 3.4 cont.:
• Because this shape is not a W, M , S , or tee and has more
than two bolts in the direction of load
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• Example 3.5 :
• if the tension member of this example is welded as shown ,Find the
effective area
Tension Members
Tension members
•Staggered fasteners :
–Reduced diameter
–Where D: Hole diameter
»S : Stagger.
»g: Gage transverse spacing
–The net width in the failure line
–Where
–Wu the net width
–W g the gross width
Tension Members
• Compute the smallest net area for the plate shown in Figure
3.15. The holes are for I-inch-diameter bolts.
Tension Members
Tension members
•Block Shear :
•For tension:
•Ant and A gt : the net and gross areas
along the tension surface bc.
FuAnt : the nominal strength in tension
for fracture.
FyAgt : the nominal strength in tension
for yielding.
•For shear:
•Anv and A gv : the net and gross areas
along the shear surface ba.
0.6 FuA nv : the nominal strength in
shear for fracture.
0.6 FyAgv : the nominal strength in shear
for yielding.
Tension members
•Block Shear :
•There are two failure modes:
•For shear yield and tension fracture the design strength :
•For shear fracture and tension yield the design strength :
•In both cases
Tension members
•Block Shear :
•The block shear strength is given as following:
Tension members
•Block Shear :
•Example 3.10: check the block-shear design strength of the tension
member ,the holes are 7/8 inch-diameter, and A36 steel is used.
Tension members
•Block Shear :
•Example 3.10 Cont.:
Tension members
•Design of tension members :
•The sum of factored loads not exceed the number strength; that is:
•For tension members:
–To prevent yielding:
–To avoid fracture:
•Radius of gyration
Tension members
•Example 3.11
Tension members
H.W (2)
Choose 5 questions ONLY from the following questions:
Question (1)
Question (2)
Question (3)
For each of the cases shown in Figure P3.3-2, compute the effective area two
ways:
1. Use the AI5C Specification equation for U.
2. Use the average value of U as given in the Commentary to the Specification.
Question (4)
Question (5)
Select a single-angle tension member of A36 steel to resist the following
service loads: dead load =:50 kips, live load =: 100 kips, and wind load
=:45 kips. The member will be connected through one leg with l-inchdiameter bolts in two lines. There will be at least three bolts in each line.
The member length is 20 feet.
Question (6)
Use A36 steel and select a double-angle tension member to resist a
service dead load of 20 kips and a service live load of 60 kips.
Assume that the member will be connected with a single line of
three or more 7/R-inch-diameter bolts to a %-inch-thick gusset
plate. The member is 15 feet long.
Question (7)
What size threaded rod is required for member AB in Figure P3.7-2
The given load is a service live load. (Neglect the weight of member
CB.) Use A36 steel.
Tension Members
End
“Part B”