CONTINUOUS BEAMS BASICS AND TUTORIALS

CONTINUOUS BEAMS BASIC INFORMATION
What Are Continuous Beams?


Beam continuity may represent an efficient stactical solution with reference to both load capacity and stiffness. In composite buildings, different kinds of continuity may, in principle, be achieved, as indicated by Puhali et al., between the beams and the columns and, possibly, between adjacent beams.

Furthermore, the degree of continuity can vary significantly in relation to the performance of joints as to both strength and stiffness: joints can be designed to be full or partial strength (strength) and rigid, semi-rigid, or pinned (stiffness).

Despite the growing popularity of semi-rigid partial strength joints, rigid joints may still be considered the solution most used in building frames. Structural solutions for the flooring system were also proposed, which allow an efficient use of beam continuity without the burden of costly joints.

In bridge structures, the use of continuous beams is very advantageous for it enables joints along the beams to be substantially reduced, or even eliminated. This results in a remarkable reduction in design work load, fabrication and construction problems, and structural cost.

From the structural point of view, the main benefits of continuous beams are the following:  at the serviceability limit state: deformability is lower than that of simply supported beams, providing a reduction of deflections and vibrations problems  at the ultimate limit state: moment redistributionmay allow an efficient use of resistance capacity of the sections under positive and negative moment.

However, the continuous beam is subjected to hogging (negative) bending moments at intermediate supports, and its response in these regions is not efficient as under sagging moments, for the slab is in tension and the lower part of the steel section is in compression.

The first practical consequence is the necessity of an adequate reinforcement in the slab. Besides, the following problems arise:  at the serviceability limit state: concrete in tension cracks and the related problems such as control of the cracks width, the need of a minimum reinforcement, etc., have to be accounted for in the design.

Moreover, deformability increases reducing the beneficial effect of the beam continuity  at the ultimate limit state: compression in steel could cause buckling problems either locally (in the bottom flange in compression and/or in the web) or globally (distortional lateral-torsional buckling)

Other problems can arise as well; i.e., in simply supported beams, the shear-moment interaction is usually negligible, while at the intermediate supports of continuous beams both shear and bending can simultaneously attain high values, and shear-moment interaction becomes critical.

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