Presentation on theme: "Tension Member Connections"— Presentation transcript:
1Tension Member Connections Three methods of connecting steel members:RivetsBoltsWelds
2Advantages of WeldingMaterials saving (often no connecting members necessary)Quieter than impact wrenches normally used for boltsMore forgiving when dimensions don’t matchForms rigid jointsSimpler detailing
3Advantages of Bolts Does not require as highly skilled workers Requires less equipmentReduced risk of fireBetter quality control
5Bolts Available Bolts A307 – Non-high strength bolts A325 A490 Strengths given in Table J3.2 (p )- High strength bolts
6Bolt Holes (Sizes in Table J3.3) p. 16.1-62 StandardOversizedShort-slottedLong-slottedConnection typesBearingSlip-critical
7Spacing, Edge, and End Distances MinimumsCenter to center ≥ 2 2/3 x bolt diameter, preferably 3 x bolt diameterEdge distance – Table J3.4For maximum bearing Strength (pitch): (J3.10)Center to center ≥ 3 x bolt diameterEdge (end) distance – p. 7-35, Table 7-13
8Spacing, Edge and End Distances MaximumsCenter to Center (pitch) ≤ 24 x thickness of thinner part ≤ 12”Edge distance ≤ 12 x thickness of part ≤ 6”
9Bolt Shear Strength J3.6→ФFnAb Tabulated on page 7-33, Table 7-10 Ф – Table J3.2Fn – Table J3.2Ab – Area of boltTabulated on page 7-33, Table 7-10
10Bearing Strength at Bolt Holes J3.10 → ФRnФ – 0.75Rn given by equations J3-2Tabulated on page 7-34,35
11Analysis of Tension Connection Example (p. 15 notes) Two A36 steel plate tension members have been connected with a lap splice using ¾” diameter A307 bolts, arranged as shown. Find the allowable service live load. Also find required distances a and b. Assume service live load is two times dead load. Plate edges are likely to be sheared.
12Analysis of Tension Connection Example (p. 15 notes) 3/8 in.PP3/8 in.a3 in.ab10 in.PPb
13Boted Tension Connection Design Procedure p notes
14Bolt Design Example p. 16 notes Design a pair of splice plates to connect the two parts of the channel tension member shown. The forces in the member are 110 kips live load and 69.7 kips dead load. The bolts in the surrounding joints are 1” diameter A325N. All steel is A36. Slip is not critical.
16Block Shear Rupture J4.3 – Equations J4-3a and J4-3b
17Welded Tension Connections Two primary types of welds:
18LRFD Specification for Welds Effective throat thickness = x lWhere l = weld size or leg size
19Limitations on Fillet Welds Minimum weld size – Table J2.4Maximum weld size:along edge of material < ¼” thick = thickness of materialalong edge of material > ¼” thick = material thickness - 1/16”Minimum lengthGreater than 4 x weld size and,If longitudinal filet welds are used alone in end connections of flat bar tension members length ≥ perpendicular distance between them (p )
20Limitations on Fillet Welds Intermittent fillet weld segments must be at least 4 times the weld size and ≥ 1 ½”Lap joints require a lap of at least 5 times the thickness of the thinner part joined, but not less than 1 in. (p )Returns are required when practicable at the ends of fillet welds. The must be at least 2 times the weld size and usually not more than 4 times the weld size.
21Design Strength of Welds Table J2.5 pFillet welds (shear on effective area):Where:Aw = Area of weld = throat thickness x lengthFEXX= Weld metal designation(FE70 = 70 ksi)Welded connection design procedure p. 22 notes
22Weld Design Example p. 22 notes An L 6 x 4x ½ is stressed in tension by a 50 kip live load and a 40 kip dead load. At the truss panel point the angle member is attached to a 5/8” thick gusset plate. The 4” leg of the angle is outstanding. Check the angle for tension strength and design the welded connection of the angle to the plate. Assume all material is A36 steel and that the loading will be static.