Positive and Negative are just directions. The main concern is whether there exist a bending moment or not. Then according to sign convention we classify bending moment as positive or negative. Elaborating on this point, If clockwise bending moments are taken as negative, then a negative bending moment within an element will cause "sagging", and a positive moment will cause "hogging"
Sagging and hogging moments are important to differentiate. As hogging causes tension in the upper part of the beam x-section whereas sagging causes tension in the lower part of the x-section. This concept is of great importance in designing reinforced concrete members as we have to provide steel rebar in the zone of beam having tensile stress as concrete is weak in tension.
When a cantilever beam is loaded with a Uniformly Distributed Load (UDL), the maximum bending moment occurs at the fixed support or the point of fixation. In other words, the point where the cantilever is attached to the wall or the ground experiences the highest bending moment. A cantilever beam is a structural element that is fixed at one end and free at the other end. When a UDL is applied to the free end of the cantilever, the load is distributed uniformly along the length of the beam. As a result, the bending moment gradually increases from zero at the free end to its maximum value at the fixed support. The bending moment at any section along the cantilever can be calculated using the following formula for a UDL: Bending Moment (M) = (UDL × distance from support) × (length of the cantilever - distance from support) At the fixed support, the distance from the support is zero, which means that the bending moment at that point is: Maximum Bending Moment (Mmax) = UDL × length of the cantilever Therefore, the maximum bending moment in a cantilever beam loaded with a UDL occurs at the fixed support. This information is essential for designing and analyzing cantilever structures to ensure they can withstand the applied loads without failure.
bending moment varies with the distance & the load carried by the beam. And also there is a hogging behavior and a sagging behavior occurs in the beam. According to the sign convention hogging and sagging bears opposite signs.(- & +). So if we are asked to find the maximum bending moment whether it is sagging or hogging we should consider the maximum value without considering the sign. That value is called maximum absolute bending moment.
The term "point of contraflexure" is often used in structural engineering, specifically in the context of analyzing and designing beams subjected to bending loads. In simple terms, the point of contraflexure is the location along the length of a beam where the bending moment is zero. When a beam is subjected to bending loads, it experiences tensile (positive) bending moments and compressive (negative) bending moments along its length. The bending moment varies along the beam, reaching a maximum at the points where the bending is the most significant. These points are usually located near the supports of the beam. However, in some cases, particularly in continuous beams or beams with complex loading conditions, there may be a section along the beam where the bending moment changes direction from positive to negative or vice versa. This section is known as the point of contraflexure. At the point of contraflexure, the bending moment is zero, and the beam's curvature changes direction. This point is essential in the analysis and design of structures as it affects the internal forces and stresses within the beam. Identifying the point of contraflexure is crucial for engineers to ensure the beam's stability and design it appropriately to handle the bending loads effectively. The bending moment diagram is used to visualize the variation of bending moments along the length of the beam and to locate the point of contraflexure if it exists.
Bending moment is the same throughout the beam.
Curtailment is a theoretical point where some of the reinforcement is cut-off along the span of the beam where the bending moment reduces, given that the remaining reinforcement will be able to support the reduced bending moment. (A.P Nangolo)
The internal bending moment formula used to calculate bending stress in a beam is M I / c, where M is the bending moment, is the bending stress, I is the moment of inertia, and c is the distance from the neutral axis to the outermost fiber of the beam.
The bending force is called a moment or bending moment. It is a measure of the internal force at a point in a structure when a bending load is applied.
moment
MAXIMUM SHEAR force bending moment is zero shear force change inside is called bending moment
Bending moment With "bending" you really mean the bending moment. The bending moment in an inner stress within a member (usually beam) that allows it to carry a load. The bending moment doesn't say anything about how much a beam would actually bend (deflect). Deflection Deflection measures the actual change in a material you could call "bending." It measures the physical displacement of a member under a load.
On SFD's and BMD's: The shear force will be 0, the shear force is the derivative of the bending moment at a point on shear force and bending moment diagrams. Otherwise: It depends on the loading.
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If the maximum bending moment occurs at a point, then the corresponding deflection will also be maximum at that point. This is because the deflection of a beam is directly influenced by the bending moment acting on it. So, wherever the bending moment is greatest, the deflection will also be greatest.
when a moment is applied in a structure the element bend
The importance of shear force and bending moment diagram in mechanics lies in structural design and in deflection of beams.
Shear Force: Sum of all Vertical Forces Whose acting on a Beam but Sum of all vertical Forces must be equal to Zero. Bending Moment: The Product of Force And Displacement is known as Bending moment.
Shear is the rate at which bending moment changes or shear is its derivative with respect to span. The integral, bending moment, goes through a maximum when shear goes from positive to negative or vice-versa.