DEEP BEAMS & IT'S DESIGN TYPES

 DEEP BEAMS

In most building codes, the conventional approach of shear design of deep

beams are based on some empirical equations in which the nominal shear strength,

Vn, includes two parts: the concrete contribution, Vc, and the steel contribution, Vs.

Separate equations are introduced for both. Though this approach is easy to apply,

it ignores the interaction between Vc and Vs, whereas the strut-and-tie model, STM,

satisfies this goal.

This article explains the design of deep beams, either simply supported, continuous

or corbels, top or bottom-loaded, directly or indirectly supported. 

Let's start with the modelling of simply supported deep beams and continuous deep

beams. Applications to simply supported deep beams are given to cover different

types of models. Bottom loaded deep beams and deep beams with ledge are covered

as well. Deep beams with indirect supports are discussed too. Applications to continuous

deep beams, top or bottom-loaded, are given. The final part of the chapter

is devoted to brackets and corbels, where the modes of failure and modelling of different

corbel problems are discussed. In addition, the detailing of critical nodes is

examined, a step by step design procedure is illustrated, and the assessment of the

web reinforcement of corbels is explained. An example of strength assessment of

double corbel is given at the end.

SIMPLY SUPPORTED DEEP BEAMS

On the basis of the shear span-to-depth ratio, three STMs are considered: Type I,

Type II, and Type III. Types I and II cover deep and short beams, respectively,

and Type III deals with slender beams. In Type I, a direct STM is utilized,

whereas a fan- or arch-action model is used in Type II. The choice between the two

types I and II in some cases is controlled by the shear span-to-depth ratio, a/d, presence

of vertical web reinforcement, and the concrete strength.

CONTINUOUS DEEP BEAMS

In simple deep beams, the region of high shear coincides with the region of low moment. On the other hand, in continuous deep beams, the regions of high shear and high moment coincide and failure usually occurs in these regions. 

Hence, the failure mechanisms of continuous deep beams are different from those of simply supported deep beams. 

Continuous deep beams are divided into two major groups according to their loading conditions: top and bottom loading. 

Top loaded continuous deep beams are commonly used in reinforced concrete buildings, while indirectly loaded or bottom-loaded deep beams are widely used as cross-girders, for example, in concrete

bridges and water tanks. The two groups behave differently under the same applied loads.