Introduction to Tension members.
Brief content of the video.
We will start a new subject, which is the introduction to tension members. The first item includes, where to use the tension members. the second item, what is the chapter, in the AISC, that governs the design of tension members?
For instance, considering the case of one angle, having fasteners in one leg, the net area valuation of such an angle will be estimated differently. There are net and special tables to estimate the final value of the effective net area. This is a part of the video, which has a subtitle and closed caption in English. This is the U-tube link.
Introduction to tension members- tension yielding.
We are going to start a new subject, which is the introduction to tension members or structural steel tension members. The first item includes, where to use the tension members.
The second item, for the Introduction to Tension members, is the chapter in the AISC, that governs the design of tension members. The third item is the net area and gross area. The net area is the area of the section, from which the fastener’s areas are deducted. Fasteners for example bolts or rivets, in addition to some factors, or allowances, will be discussed later.
For instance, considering the case of one angle, having fasteners in one leg, the net area valuation of such an angle will be estimated differently.
There are net and special tables to estimate the final value of the effective net area.
The fourth item is the tensile yielding, tensile rupture, and the details of gauge lines.
The fifth item is the related design parameters, for tension members for the LRFD and ASD, φt and Ωt.
The sixth items are the tables for various shapes and the relevant yield and f ultimate stresses for tension members.
The tension members are used for bridges and roof trusses, towers, and bracings. Any situation, where they are used as tie rods.
The selection of a section to be used as a tension member is one of the simplest problems encountered in design, for instance as compared with columns and beams, so, the design of the tension members is considered to be simple.
As there is no danger of the member buckling, the designer needs to determine only the load to be supported, like whether the ultimate load is 1.4 D or 1.2 D+ 1.6 L, then choose the biggest values, as for the LRFD design, or D+L as for ASD design.
The related division in the specification for Tension members.
As an introduction to tension members, the next slide includes the chapter used for the design of tension members, then which section in the chapter for tension members is shown. Chapter D is used. D-2 governs the Tensile strength. AISC-360-16 page 16-1-28.
There are two items, Tensile Yielding and Tensile rupture. For the tensile yielding, the P nominal is estimated as =Fy*Ag, Fy is the yield stress, and Ag is the gross area. For the LRFD, φt =0.90, and for the ASD design Ωt=1.67.
Item b) is for tensile rupture at the places of bolts or welds. The nominal load Pn = Fu*Ae, where Ae is the effective area. But the LRFD parameter is different and is φt =0.75, which is less than the value given for tensile yielding. and for the ASD design, based on the relation of φ*Ω=1.5, then Ωt=2.00. Fy is yield strength and Fult is the ultimate strength. D-3 includes the effective net area and is to be estimated from B 4-3, Aeff=Anet*U factor, U, shear lag factor=1.
In the case of plates, and has various values for other shapes and depends on the way you are using for connecting the fasteners.
For instance, if you have bolts in the upper flange and the web has no fasteners, then the whole section is not fully stressed, since a modification will be used, to be discussed later on.
This is the provision from the AISC code for the net area for tension members and the different terms used.
The shear lag factor U value is obtained from table D3-1.
Tension yielding.
Tension yield picture Quoted from The external link. A BEGINNER’S GUIDE TO THE STEEL CONSTRUCTION MANUAL, 14TH ED.
As an introduction to tension members, we are interested to discuss the different modes of failure.
There are many good pictures, for example, a section for W section, if we will deal with the tension yielding, there is a failure mode. On the locations that are away from the bolts. Under the application of tension forces from the ends, the failure will occur on location not passing by the bolts.
This failure mode looks at yielding on the gross cross-sectional area.
Then T=Ag*fy gives the value of the tension force at failure. a is the original shape, and b is the shape after tension yielding of the section occurs.
Tensile Rupture types.
This is The first failure was a vertical line passing by the line of the bolts in the direction that is perpendicular to the force direction.
The second failure is shown here as a zigzag line, from which the net area was estimated.
The damage occurs due to the Punching of a hole.
As can be shown punching for bolts, can cause damage around the bolt and create extra diameter that should be taken into consideration while estimating the net area.
This is the PDF used for the illustration of both posts 1 and 1A from this link.
The next post contains an Easy introduction to Tension members-part-2.
For a useful external link-Chapter 3 – Tension Members– Bartlett Quimby
