T-beam
A T-beam is a supporting element in steel and reinforced concrete construction ( solid construction ). It consists of a plate with belt (s) and bars . The material, height of the bar and the number of straps vary depending on the area of application.
The shape of the cross-section of a girder is used for the more detailed classification of types. ɪ girders for bridge construction are often welded together from individual steel plates, whereby the often high web determines the appearance of the plate. T- beams are used in many construction areas, here the upper strap can be much wider than the web. A beam composed of two T-beams is reminiscent of the Greek letter π and is therefore also called a pi-beam. T-beam constructions were and are used for many ceiling floors and bridges .
history
In Europe in 1892 (according to other sources, 1888) the French civil engineer François Hennebique developed a system for building houses and halls that was used to produce wide-span ceilings. The foundation formed T-shaped elements described as T-beams were called.
Hennebique system
A Hennebique T-beam consists of a plate with an exposed web or webs that are firmly (tensile and shear-proof) connected to one another. Various types with specific reinforcement were successful despite the rejection of a patent application. They were systematically used as ceilings in multi-storey buildings and could be combined according to the modular principle for ceilings of any size.
In general, every girder that is continuously connected to a reinforced concrete ceiling with a force-fit connection can be viewed as a T-beam in combination with the ceiling, as described by Hennebique.
Load-bearing behavior
A T-beam on two columns is essentially subjected to bending loads. This creates a positive bending moment in the field , which creates compressive stresses in the plate at the top and tensile stresses in the beam at the bottom. The compressive stresses are absorbed by the concrete of the large cross-sectional area of the slab, the tensile stresses by the reinforcement in the lower part of the beam (web). Since the reinforcing steel has a very high tensile strength, the webs can be kept narrow, which saves a significant amount of concrete (between the webs) compared to continuous ceiling slabs.
In the case of a T-beam on three or more supports (continuous beams), a negative bending moment arises above the intermediate supports, which creates tensile stresses in the area of the plate and compressive stresses in the webs. Special constructive measures are required here. Reinforced reinforcement can be provided in the upper area of the webs and in the plate . In order to enlarge the pressure zone in the webs, they are often widened and / or increased in the area of the negative moment, for example in the form of coves .
Rating
Depending on the width of the slab, it cannot always be assumed that the full slab width contributes to the load transfer. For the dimensioning of a plate beam, the so-called "effective plate width" is decisive. It depends , among other things, on the span .
In the simplest case (when the pressure zone lies completely in the plate) a T-beam can be treated like a single beam.
If the pressure zone is not only in the plate, but extends into the web, another intermediate calculation is required to calculate the lever arm .