LRFD- Steel Design Dr. Ali I. Tayeh First Semester Dr. Ali I. Tayeh First Semester.

LRFD-Steel DesignLRFD-Steel Design

Dr. Ali I. Tayeh

First Semest

er

Dr. Ali I. Tayeh

First Semest

er

Steel DesignDr. Ali I. Tayeh

Chapter 7

SIMPLE CONNECTIONS• Connections of structural steel members are of critical

importance. An inadequate connection, which can be the "weak link" in a structure, has been the cause of numerous failures. Failure of structural members is rare; most structural failures are the result of poorly designed or detailed connections. The problem is compounded by the confusion that sometimes exists regarding responsibility for the design of connections.

• Modern steel structures are connected by welding or bolting or by a combination of both.

• Welding has several advantages over bolting. A welded connection is often simpler in concept and requires few, if any, holes . Connections that are extremely complex with fasteners can become very simple when welds are used.

SIMPLE CONNECTIONSIn considering the behavior of different types of

connections,• The tension member splices shown below subject

the fasteners to forces that tend to shear the shank of the fastener. Similarly, the weld shown below must resist shearing forces.

• The connection of a bracket to a column flange, as in next Figure, whether by fasteners or welds, subjects the connection to shear when loaded as shown.

SIMPLE CONNECTIONS

SIMPLE CONNECTIONSBOLTED SHEAR CONNECTIONS: FAILURE

MODES

The average shearing stress in this case will be

SIMPLE CONNECTIONSBOLTED SHEAR CONNECTIONS: BEARING STRENGTH, SPACING, AND EDGE-

DISTANCE REQUIREMENTS• A possible failure mode resulting from excessive

bearing is shear, tear-out at the end of a connected element, as shown in the next Figure. If the failure surface is idealized as shown in the next Figure, the failure load on one of the two surfaces is equal to the shear fracture stress times the shear area, or

SIMPLE CONNECTIONS• The total strength :

SIMPLE CONNECTIONSSummary of Bearing Strength, Spacing,

and Edge-Distance Requirements (Standard Holes)

SIMPLE CONNECTIONS• Example 7-1:

Solution:

SIMPLE CONNECTIONS

SIMPLE CONNECTIONS Common Bolts


Example 7-2:Determine the design strength of the

connection in the figure below based on shear and moment.


Solution


Ans.Ans.


Example 7-3:

Solution:


Ans.Ans.

SHEAR STRENGTH OFSHEAR STRENGTH OF HIGH-STRENGTH BOLTSHIGH-STRENGTH BOLTS

The design shear strength of both A325 and A490 bolts is øRn, where the resistance factor

Ø is 0.75. As with common bolts, the nominal shear strength of high-strength bolts

is given by the ultimate shearing stress times the nominal bolt area. Unlike A307 bolts,

however, the shear strength of A325 and A490 bolts depends on whether the threads

are in a plane of shear. Rather than use a reduced cross-sectional area when the

threaded portion is subject to shear, the ultimate shearing stress is multiplied by a factor

of 0.75, the approximate ratio of threaded area to unthreaded area. The strengths

are given in AISC Table 13.2 and are summarized in Table 7.1. AISC Table 13.2 refers

to threads in a plane of shear as "not excluded from shear planes" and refers to threads

not in a plane of shear as "excluded from shear planes." The first category, threads included in the shear plane, is sometimes referred to as connection type "N," and an

A325 bolt of this type can be denoted as an A325-N bolt. The designation "X" can be


Example Example 7.47.4

SolutionSolution ::

SHEAR STRENGTH OF HIGH-STRENGTH BOLTSSHEAR STRENGTH OF HIGH-STRENGTH BOLTS

EndCongratulations

LRFD- Steel Design Dr. Ali I. Tayeh First Semester Dr. Ali I. Tayeh First Semester.

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