Bearing Type connections-part-1.
Detailed content
In this post Bearing Type connections-part-1. a picture of a steelworker, the worker by using a spanner is checking that all bolts are snug tight together. This type, for which the wrench is used, is called the bearing type.
As a definition for the bearing type, the load is transferred between members by bearing on the bolts by using the wrench
The second type is the slip critical for example if a tire is to be replaced, then a tire fixer will fix the car tire and then by using a gun with a compressor, called an impact wrench, or using a Torque Wrench. In the next image at the rightmost, there is a worker fixing bolts using a calibrated wrench.
Types of bearing bolts.
In the bearing type connections-part-1.We proceed to the next slide, the bearing type is classified into two parts.
Type N is the type for which the threads are included, as from the previous lecture we have included the different parts of the bolts, as we can see from the picture at the left, a shear force is developed at the contact plane if the threaded part is included in the shear plane, Then it is called type N bolt.
N means Included threaded. The connection is a bearing type connection and the bolts are installed such that the threads may be included in the shear plane(s) one Plane for the case of single shear, or several planes for double shear. Their definitions for these terms are found in the following sections.
X means excluded, the thread, if we refer to the image at the right is not passing by the shear plane. Excluded using the symbol X, or writing ASTM A 325-X. Group A As a summary, Then group A -N is a bolt made from ASTM A-325, and the threaded is included, while group A-X, means the bolt is made from ASTM-325 and the threaded is excluded.
While the symbol SC includes that the connection is a slip critical connection or pre-tensioning. Due to the pre-tension in the bolt, friction is to occur, or slip a movement will occur.
I quote, for example, that an ASTM-X bolt would be a bolt made from STM A325 steel and would be installed such that the threads are excluded from any shear plane(s).
While the A490-Sc bolt is a bolt made from A490 steel and would be installed in a slip critical connection where the faying surfaces must meet special requirements. Let us have a look at a bearing connection.
In the next slide, the loads are carried by bearing. The loads try to shear the bolt or due to the pressure exerted on the bolt cause pressure on the material of the connection and may cause tearing, as we are going to see later on. the bolt is called a type N bolt.
The next slide includes the previous information for the threads in the shear plane as N or X type.
Single shear connection.
I quote, from the initial discussion, that the reader is referred to part(a) of fig .12.1. it is assumed that the plates shown are connected with a group of snug-tight bolts.
In other words, the bolts are not tightened sufficiently to significantly squeeze the plates together. If there is assumed to be little friction between plates, they will slip a little due to applied loads. The loads will tend to shear the connection between the plates or bear against the sides of the bolts.
The load P acts to the left in a connection, then press the bolt to the left side, causing bearing on the bolt by the value of the load P. he next slide includes the previous information for the threads in the shear plane as N or X type.
Types of failure for the bolted joint.
For the next slide, Bearing Type connections-part-1. The author has talked about the types of failures. One type of failure is by rupture that occurs across the line of bolts, perpendicular to the load direction, Anet*U*Fult is the capacity of the section.
Failure may also occur due to the shear of bolts due to two equal and opposite forces that act on the joint, which causes failure when the load exceeds the shear resistance of the single bolt.
Failure may be due to the bearing of melt behind the bolts, or due to the bearing of the bolts itself. full detailed illustration of these types for the bearing type connections-part-1 is included in the next slide image.
Double shear connection.
In the next slide, the butt joint or the (double shear) is introduced. We have two outer plates and a middle one in that situation, a shear may occur to the bolt due to double shear.
The load P, which acts to the right is transferred to the two plates by a value of P/2 for each plate through the bolt. Referring to picture c), the bearing on the bolt is due to P/2 acting to the left due to the upper left plate.
Balanced by P/2 at the section of the bolt, which again is transferred to load P/2 acts to the right.
Again there is P/2 from the lower portion the total load =P causing bearing on the bolt in the middle section by a value of P to satisfy the equilibrium at the middle portion. For the lower portion, the bearing is P/2. I quote, The members are arranged so that the total shearing forces are split into force into two parts causing the force into the two planes to be only one-half of what it would be on a single plane. Therefore, the carrying capacity is theoretically twice as great as the same number of bolts in a single shear.
The bearing on the material around the bolt, for the bearing-type connections, will be viewed.
We talk about tearing, we have two plates above each other, please refer to Fig.5.4 at the right, as previously discussed having two plates with force acting to the left, at the part of the bolt p acting to the left is acting against the plane with width d and the section with height =t, the failure will occur if the shear stress is exceeded. f we have two plates with two different thicknesses t 1, t 2, then select the thinner thickness of t1 and t2.
The next post is Bearing Type connections 2-2.
A good reference: A Beginner’s Guide to the Steel Construction Manual, 15th ed, Chapter 4 – Bolted Connections
