Last Updated on July 29, 2023 by Maged kamel
Bearing Type connections-part-2.
The video I used in the illustration.
This is the link for the video in u tube, the content of this post is included starting from 11.0 till the end is the content of this post. the video has a subtitle and a closed caption in English.
The nominal tensile strength for a bolt Rn.
In this post-bearing Type connections-part-2. We have The distance le is the edge distance from the centerline of the bolt to the edge.
We are concerned with the distance behind the bolt, which is (Le-d/2), where d is (the diameter of the bolt+1/16″), which is called lc outer Lco, which is the distance from the edge of the external bolt to the edge of the plate, and this is the section of the two connected plates on the left side.
Please refer to case D for the case of a failure due to bearing.
Due to tearing the shear plane, the bolt is strong in comparison with the surrounding material if the material is weak. What will happen? The nominal force R is split into R/2 and R/2. The shear strength of the material of the plate =lc*t*0.60 Fu, then nominal resistance for edge 2*0.60*Fu*Le*t*2=1.20*Fu*t*Lco, which is =P/n. Since P is acting on three bolts in our case.
What is the nominal strength of the inner bolt? it will =2*0.60*(lci*t*Fu), for S is the spacing from the centerline to the centerline.
Rn =2*0.60*Fu*t *(s-d/2) =1.20*Fu*t*(s-d/2). For the upper limit of Lco or lci, the maximum value does not exceed 2d bolt, setting lco or lci equations as 2d, If tp is the plate thickness. then the upper limit can be written as =2.40*Fu*tp*d.
AISC equations for bearing connections.
For the next slide, a series of equations Rn=1.20*Lc*t*Fu= 1.20*Lc*t*Fu.< or =2.40*d*t*Fu, if deformation around bolt holes is a design consideration if the deformation is less or equal to 0.25 inches.
But if the deformation >0.25 inches, that deformation is not a design consideration then Rn= 1.50*Fu*Lc*t<=3.0*d*t*Fu. There is another condition for long slotted holes.
For the left side of equation 1.2*Lc*t*Fu was developed due to the tearing of the sides of the block behind the bolt when the bearing is done as quoted the formula from Prof. salmon’s handbook item- bearing strength.
The expression for tearing of the plate due to the bearing of the inner bolt is also shown. These are the equations developed based on the deformation around bolt holes whether <=0.25″ or if the deformations are not a design consideration.
In the next slide, refer to definitions as the distance between the centerline of bolts in the direction parallel to the axis of the member is the pitch P. While S is the gage distance, which is the distance between the centerline of bolts in the direction perpendicular to the axis of the member and edge distance.
Minimum edge distance of bolts.
In the next slide, for minimum edge distance varies according to the diameter of the bolts and follows the shown table.
Minimum Spacing S and the inner distance between bolts.
In the post-Bearing Type connections-part-2.The minimum spacing between bolts is S.
The minimum Center to Centerline is not less than (2 2/3 db), where db is the bolt diameter. Preferably to be 3d as 3 diameters. But the clear distance, not less than d.
Minimum Center to Center should be not less than 2 2/3 diameter.
Nominal hole dimension for bearing type connection.
For the hole diameter, add 1/16″ to the bolt diameter, unlike in tension members we were adding (1/16″+1/16″) to the bolt diameter For the calculations. For instance, for a 3/4 ” diameter bolt add 1/16″, then the standard dia will be (3/4+1/16)=13/16″ as shown in table J3.3. The table gives the different hole dimensions as 4 groups of standard oversize short slots and long slots.
The nominal strength of fasteners.
In the next slide, the value of shear strength is shown in table J3.2.
In the second column is the tensile strength, which is written as Fnt which is the nominal tensile strength. For the nominal shear strength symbol, it is called Fnv, in the third column, which is a percentage of Fnt.
For instance. In the first column, there is a description of the type of fasteners, A307, Group A A325-N which are not excluded, the tensile strengthFnt=90 ksi, and the Fnv=0.60*90=54 Ksi, the value shown between brackets is the Mpa value, for A325-X, Fnt=90 ksi. Fnv=68 ksi. For the case of X the shear strength increased, there are categories b) as ASTM-A490 bolts N&X with the corresponding Fnt and Fnv values are shown.
For the case of X the shear strength increased, there are categories b) as ASTM-A490 bolts N&X with the corresponding Fnt and Fnv values are shown.
For part1-bearing type connection-part-1, this is the link.
The next post is the Nominal shear strength and bearing- tear out made simple.
A Beginner’s Guide to the Steel Construction Manual, 15th ed, Chapter 4 – Bolted Connections.