LRFD - Steel Design

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

2. Steel DesignDr.Ali I. Tayeh Chapter 7

3. 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 membersis 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.

4. SIMPLE CONNECTIONS In 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.

5. SIMPLE CONNECTIONS

6. SIMPLE CONNECTIONS BOLTED SHEAR CONNECTIONS: FAILURE MODES The average shearing stress in this case will be

7. SIMPLE CONNECTIONS BOLTED 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

8. SIMPLE CONNECTIONS The total strength :

9. SIMPLE CONNECTIONS Summary of Bearing Strength, Spacing, and Edge-Distance Requirements (Standard Holes)

10. SIMPLE CONNECTIONS Example 7-1: Solution:

11. SIMPLE CONNECTIONS

12. SIMPLE CONNECTIONS

13. SIMPLE CONNECTIONS

14. SIMPLE CONNECTIONSCommon Bolts

15. SIMPLE CONNECTIONSCommon Bolts Example 7-2: Determine the design strength of the connection in the figure below based on shear and moment.

16. SIMPLE CONNECTIONSCommon Bolts Solution

17. SIMPLE CONNECTIONSCommon Bolts

18. SIMPLE CONNECTIONSCommon Bolts

19. SIMPLE CONNECTIONSCommon Bolts Ans.

20. SIMPLE CONNECTIONSCommon Bolts Example 7-3: Solution:

21. SIMPLE CONNECTIONSCommon Bolts Ans.

22. SHEAR STRENGTH OF HIGH-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

23. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

24. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS Example 7.4 Solution:

25. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

26. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

27. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

28. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

29. SHEAR STRENGTH OF HIGH-STRENGTH BOLTS

30. End Congratulations