Brief content of post-1-Tension members posts.

1- A step-by-step introduction to tension members.

Introduction to Tension members.

Brief content of the video.

We will start a new subject, which is the introduction to tension members, The content of this post is included in the video starting from time 00:0 till the time 10:06. 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 angle will be estimated differently. There are a net and special tables to estimate the final value of the effective net area. The continuation of the video is explained in the next post. This is a part of the video, which has a subtitle and closed caption in English.

You can click on any picture to enlarge then press the small arrow to review all the other images as a slide show.

How to estimate the tensile strength of steel members?

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, tracing the different subjects for the F.E. Exam.

Introduction to 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 angle will be estimated differently.
There are a net and special table 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.

Where to use tension members?


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 LRFDdesign, 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.

AISC provision of tension members-chapter D

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.

AISC provision of tension members-chapter D2-tensile strength formulas.

For the tensile yielding, the Pnominal is estimated as =Fy*Ag, Fy is the yield stress, Ag is the gross area. For the LRFD, φt =0.90, and for the ASD design Ωt=1.67.   

Item b) for tensile rupture at the places of bolts or welds,  Pn = Fu*Ae,  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 as yield strength and fult is the ultimate strength.

 

AISC provision of tension members-chapter D3- effective net area.

D-3 includes the effective net area, and to be estimated from  B 4-3, Aeff=Anet*U factor, U, shear lag factor=1, for 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. U value is obtained from table D3-1.

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. 

What is tension yielding?


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.

What is tension rupture?

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.

What is the net area?

The second failure is shown here as a zigzag line, from which the net area was estimated.



Tensile rupture and tensile yielding cases.

From Prof. Mccormac ‘s handbook, we have values of LRFD parameters for the different cases of Yielding and rupture failures and select the lesser Pn after estimation.


The damage occurs due to the Punching of a hole.

Damage due to punching a hole and added diameter.

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

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