Calculation of deformation by axial force
The axial force of AC section is - 20KN, not - 10kN. Because - 10kN acts on point C, the AC is disconnected, the left part is taken as the isolator, and only the left end bears the axial force of - 20KN, so the axial force is - 20KN. Similarly, the axial force of CD segment is - 10kN, and that of de segment is + 10kN
For columns with large slenderness ratio, the initial eccentricity caused by various accidental factors cannot be ignored. With the increase of the load, the lateral deflection also increases. The compression deformation and bending deformation of the member occur at the same time. Finally, the member is destroyed under the combined action of axial pressure and additional bending momentfirstly, the concavity compressive concrete is crushed, the longitudinal reinforcement is bent and bulged out, and the concrete cover is peeled off; At the same time, when the convex surface is under tension, the concrete will proce horizontal cracks, the lateral deflection will increase sharply, and the column will be damaged
Extended data:
for short columns with longitudinal bars and stirrups, the strain of the whole section is basically uniform under axial load. When the load is small, the concrete and steel are in the elastic stage. As the load continues to increase, the lateral deformation of the concrete increases, the fiber stress at the edge of the section first reaches the tensile strength of the concrete, and micro cracks begin to appear in the column
Afterbecause the elastic molus of steel bar is greater than that of concrete, the stress of steel bar increases rapidly, the stress of column longitudinal bar first reaches the tensile strength of steel bar and is crushed, and micro cracks begin to appear in the column
I = 63.62cm4
e = 206x10 ^ 3
Fmax = 1500x2000 ^ 3 / (192x636200x206000) = 0.477mm
the actual deflection plus the displacement caused by the self weight of 2000mm long 45 ° shaft
Axial tension (or compression) caused by axial force
The deformation characteristic of axial tension compression deformation is that the bar extends or shortens along the axis under the action of external force
The stress characteristic of axial tension compression deformation is that the two ends of the straight bar act along the axis of the bar with a pair of equal size and opposite direction The geometric characteristics of members are that the length of members is far greater than the width and thickness of the section of members, and beams, arches, trusses and rigid frames are typical forms of member structures According to the deformation characteristics, the basic stress forms of bar structure can be divided into five types: tension, compression, bending, shear and torsion, which are often the combination of several stress forms in practice
extended data
members are widely used in civil engineering, construction, machinery, shipping, water conservancy and other projects. In the structure of bar system, the junction of several bars is the node, and there is no relative linear displacement between the ends of each bar at each node
Thenode is divided into hinge node and rigid node. On the hinge node, the angle between members can be changed freely, and the hinge node can not transfer torque. On the rigid node, the angle between the members remains unchanged, and the rigid node can transfer the moment
for the bar structure, it is mainly to study the internal force distribution, deformation and stability under the influence of various factors (such as load, bearing settlement, temperature change, etc.), so as to provide the basis for seeking safe, effective, economical and reasonable structural form and checking the strength, stiffness and stability of the structure
There are three basic conditions as the basis of structural analysis of bar system:(1) the stress-strain relationship of bar material can be divided into linear relationship (obeying Hooke's law) and nonlinear relationship
(2) the equilibrium condition of force system, the force system of the whole structure, the force system of part of the structure, and the force system of a node should meet the equilibrium condition (3) deformation compatibility condition, that is, all members constrained by a node before deformation are still constrained by the same node after deformationaccording to the above three conditions, the calculation methods of various rod structures can be deced, which can be used to calculate not only the internal force of members and the reaction force of supports, but also the deformation of the structure. If the stress inside the structure is too large, the structure will lose its bearing capacity; The deformation of the structure is too large, or lead to the loss of the bearing capacity of the structure, or affect the normal use of the structure