Introduction to Tension members-part 2.
Brief content of the video.
The content of this post is included in the video starting from time 10:0.06 till the end. Consider the case of one angle, having fasteners in one leg, the net area valuation of such an angle will be estimated differently. There are a net and special table to estimate the final value of the effective net area.
The fourth point is the tensile yielding, tensile rupture, and the details of gauge lines. 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. This is a part of the video, from time 10:48 till the end. The video has a subtitle and closed caption in English.
How to estimate the net area of tension members?
While working with a zigzag line distance between the bolts adds S^2/4g, where g is the transverse distance or the distance between gauges, and S is the longitudinal distance center to center spacing.between bolts or pitch.
This is a part of clause 3 of the specification that describes the Gross and net area determination.
Looking back to Prof McCormack’s notes, he mentioned that long-used practice to punch holes with 1/16 inch diameter larger than that of the bolts.
Actually. When this practice was followed, the punching of a hole was assumed to damage or destroy 1/16 inch more of the surrounding metal. Then in practice is to consider 1/16+ 1/16 inch to the diameter of the bolt.
Applicable ASTM specifications for structural shapes table 2-4.
Refer to table page 2-48 in the manual table 2-4, the marked black items are the preferred sections as per different ASTM designations.
We have ASTM A36, ASTM A 53 for carbon, followed by A500 and A501, then the high strength low alloy, for the w section, it is preferred to use ASTM A992. the start yielding is 50 ksi and fult=65 ksi.
The I symbol is the maximum ratio between the Fy/Fult =0.85, which refers to the legend. The g denotes. relates to the wall thickness and the d for 65 d.
For ASTM 572 Gr-50, where fy =50 ksi , for the Fult 65 d is the Fult =65 ksi, but 70 ksi can be specified. For the grey color, for the available Astm for the different shapes, but the dark color is for the preferred ASTM.
The details of the different symbols are shown in the table. from a to L. The table continuation shows the different legend colors, The white color for the material specification does not apply
For HSS rectangle, round and pipe, do not exist in ASTM A 242, and ASTM A 588, but are available in ASTM A 847.
From Prof. Mccormac, you can find values of Fy and fu for various structural steel in table 2-4, the black areas correspond to preferred materials, and the gray areas present other steels that are available.
We see A572 for example, starting from grades 42 to 65, so grades must be specified.
An example of ASTM A 242 for corrosion resistance, the Fy is specified by thickness controlling parameters. For example, if a section of W 33 x221 is to be used,t flange can be estimated from Table- 1 and refer to the three symbols J, K, and symbol L for the conditions of wall thickness specified L for only < or =1 1/2 inch only, while for W 33 x 221 from table 1 has tf=1.28 inch which is t<=1.5 inch.
Check for J,l conditions, for j thickness >2.5 inches, and for, k thickness is >1.5 inch and less or= 2 inches only, then L is to be selected, that matches with t flange thickness. The companion Fy =50 ksi and Fult =70 ksi, while it is gray, not preferred but available.
Applicable ASTM specifications for shapes table 2-5 for plates.
While for plates, from the thickness of 0.75 inch to over 6 to 6 inches, it is preferred to use ASTM A36, This is the continuation of the table.
We continue with table 2-5 for plates refer to table 2-5, for plates and bars, if plates are over 8 inches, it is preferred to use ASTM A32 with Fult =58 to 80 ksi.
Table 2-6 is used for the bolts While table 2-5 was for plates and bars.
While for plates, from a thickness of 0.75 inch to over 6 to 6 inches, it is preferred to use ASTM A36
This is the continuation of the table. Common bolts from 0.25 to 4″ use A307 GR.A.
Workable gauges for angles for tension members-table 1-7A.
A new table Table 1-7A, if we have an unequal angle, for the short leg.
The horizontal distance is shown as g, from the edge to the center to the first fastener line.
For the other, long leg r leg we have gauge distances g1 and g2 their distances are shown for the various leg distance.
Starting from 8 inches descending to 1-inch length, descending to 1-inch length, and g from 5/8 for a 1-inch angle to 4.5 inches, and the values for long leg with two gauge lines for g1 from 3 to 2 inches
For an angle of 4″ leg it can carry only one line of bolts. for an angle of 5 inches leg, it is possible to have two lines of fasteners.
This is the pdf used for the illustration of both post1 and 1A. The next post contains Solved problems for net area estimation.
For a useful external link-Chapter 3 – Tension Members– Bartlett Quimby