In steel structure, there are three types of connection between beam and column, flexible connection (also known as hinge joint), semi-rigid connection and rigid connection.In practice, the angle of rigid connection is not more than 5%, that is to say, the angle of rigid connection should not exceed 5%.

Semi rigid connection is between the two.

The semi-rigid connection of beam and column can be made by welding the upper end plate at the beam end, using high-strength bolts, or using the upper and lower angle steel and high-strength bolts connected to the flange.The design requirements are as follows:

(1) The force transfer of end plate connection in the end plate connection node can simplify the bending moment of beam end into a pair of couple, and the tension is transmitted by tension flange.The tension bolts are symmetrically arranged to the tension flange.The pressure can be transmitted through the end plate or column flange, and a small number of bolts in the pressure area can be set, and the shear force can be transmitted together with the tension bolt.

(2) In the connection of upper and lower angle steel, under the action of bending moment, the connecting angle on the tension side deforms not only the vertical limb but also the horizontal limb.Therefore, the stiffness of angle steel connection is slightly lower than that of end plate.

The division of connection properties should be characterized by the following three indexes: bending stiffness, rotational stiffness and ductility (rotational capacity).

Bending capacity is the main item of connection strength, and shear strength.In theory, the capacity of rigid connection to bear bending moment and shear force should not be lower than that of beam, that is, plastic hinge moment of beam and plastic shear force of web.The frame of seismic area should be more demanding, reflecting the principle of “strong connection weak component”.For flexible connections, only shear capacity is required.The semi-rigid connection is between the rigid and the flexible connection, and must have a certain bending capacity.

The rotational stiffness of the connection is reflected by the slope of the moment angle curve, which is not a constant. The rotational stiffness has an impact on the deformation and bearing capacity of the frame.The influence of deformation needs to be analyzed in combination with normal service limit state.Therefore, the initial stiffness of the connection or the secant stiffness under standard load should be considered.In theory, the rigidity of rigid connection needs to reach infinity, but in fact, as long as it reaches a certain limit value, it can be regarded as a rigid connection. The problem lies in how to define it in terms of quantity.

The rotational capacity belongs to the ductility index, and the plastic hinge is required to have certain rotation capacity in the plastic design frame, so that the subsequent internal force redistribution can occur.

1.The structure of rigid connection assumes that the beam column connection has enough rigidity, there is no relative rotation between beams and columns, and the connection can bear bending moment.The structure of hinged connection assumes that when the structure bears gravity load, only vertical shear force is transferred between the main beam and the column, and no moment is transferred.This connection can rotate freely.

2.In the traditional analysis and design of steel structure frame, in order to simplify the analysis and design process, beam column connection is considered as ideal hinge connection or complete rigid connection, and it is considered that the connection can be regarded as rigid connection if the rotation constraint of the connection reaches more than 90% of the ideal rigid connection; under the action of external force, the connection with the change of the angle between column and beam axis reaches more than 80% of the ideal hinge joint。The assumption of ideal hinge will mean that there is no moment transfer between beams and columns. As far as rotation is concerned, beams and columns connected by hinges will rotate independently

The column base that can resist bending moment is called rigid connection column base, on the contrary, the column base that can not resist bending moment is called hinged column base. The difference between rigid connection and hinge joint is whether it can transfer bending moment. In fact, if the anchor bolt is outside the flange, it is rigid connection, and generally no less than four. If it is inside the flange, it is hinged, generally two or four.

The obvious difference between these two kinds of column bases is the control of lateral displacement. If the structure has strict control on the lateral displacement, the rigid connection column base shall be adopted. For example, in the case of crane load, the crane load is dynamic load, which is sensitive to lateral displacement, and excessive lateral displacement will cause crane rail clamping. Therefore, the column base shall be designed as rigid connection column base.

“If the hinge column base needs to be added with shear key, the anchor bolt can not bear the shear force” is a little lax, it should be said that “if it is an articulated column base, it is generally necessary to add shear key”.Because the axial force of the hinged column base of the steel structure is relatively small, the friction between the bottom plate and the foundation concrete can hardly meet the requirements, so most column bases need to be equipped with shear keys

The difference between rigid joint and hinged joint:

1.Rigid connection can transfer bending moment and shear force, while hinge joint can only transfer shear force

2.There are also differences in structure between the two: if the rigid connection is H-beam, the upper and lower flange and web need to be connected; if the hinge joint is H-beam, only the web plate has connection structure

A little opinion!!

The stress of column base is divided into:

(a) Hinged column base (b) rigid connection column base

The column bases of concrete structure are all rigid joints, that is, axial force N, horizontal shear force V and bending moment M exist at the same time, so the foundation size is large.

There are two common types of column bases in light steel structures: rigid connection and hinged joint,

1.For the hinged column base, there are only axial force N and horizontal force

2.In addition to the axial force N and horizontal force V, there is also a certain bending moment M for the rigidly connected column base,

3.The foundation of rigid connection column base is larger than that of hinged column base.

In addition, please note:

For the joint design of rigid column base:

1.When it is used in industrial plant with overhead crane, the column base should be designed as

rigidity.

2.The following problems should be paid attention to in the rigid column base:

The construction unit should have a certain level of basic technology

Shear members shall be provided

*As for the problem of rigid connection and hinge joint, theoretically speaking, rigid joint refers to whether the node can rotate, and complete rigid connection refers to no rotation at all, and hinge joint can rotate freely.Fully rigid connection means that the joint not only can bear the shear axial force and bending moment, but also has enough stiffness.The deformation of the joint is very small under the action of bending moment.In theory, there is no complete rigid connection, so long as it has effect, there will be deformation. In practical engineering, after reaching a certain stiffness, we will consider it as rigid connection in engineering. If it can bear bending moment, but the deformation is large, we think it is semi-rigid connection and elastic fixation.

Hinge is easy to understand and can rotate freely, that is, it can not bear bending moment, so it can only resist shear force and axial force.For a member, such as I-shaped member, the flange is mainly bent and the web is mainly shear.Since some of the comrades discussed here have not studied mechanics, I will simply say that for bending moment, the farther away from the centroid axis, the greater the contribution of bending moment, so the contribution of bending moment to the farthest distance between flange and centroid is greater.The shear stress is the largest at the centroid, so the web is mainly shear.Generally speaking, for nodes, such as end plate connection, where bolts are arranged outside the flange and the thickness of end plate meets the requirements, it is rigid connection.The hinge joint bolts are arranged near the centroid axis.

Post time: Jul-04-2020