Beams placed at ground floor level are called floor beams. Floor beam sizing is designed to accommodate the vertical loads on the beams, the loads transmitted by the floor slabs, and the loads applied by the eccentricities of the column piles. The construction of the floor beam as a unit serves as a rigid floor to control lateral deformations.
Especially in tall buildings, deeper beams are provided to be able to apply higher loads and increase beam spans at lower levels.
Ultimately, the ground floor will be a rigid plane with comparatively greater lateral stiffness, which can minimize lateral deformations of the building.
In addition to floor loads, floor beams are designed to support axial loads from columns when the pile is eccentric.
When individual piles support columns, it is always advisable to take the permissible eccentricity of the pile into account when designing. Generally, pile foundation companies have a design tolerance of 75mm. Therefore, it is always advisable to size floor beams to the allowable pile eccentricity when individual piles support a column.
After mounting the piles, the eccentricity of each pile is checked by comparing the actual coordinates with the design coordinates.
If a pile exceeds the design eccentricity limit (75mm), engineers must be informed and the design of the floor beams must be changed.
Floor beam sizing for pile eccentricities
The effect of pile eccentricity on floor beams can only be considered if the column is supported by a single pile. and when there are two piles and the eccentricity is in the direction of the piles, the effect of pile eccentricity need not be considered as it only increases the pile load.
As the piles have a significant margin of safety, the construction of the piles is not affected by this.
However, the eccentricity is different from the direction of the piles, the eccentricity of the piles must be taken into consideration, and the beam must be designed to a minimum eccentricity.
If there are series of piles that can be designed for eccentricity, the design must take into account all possible load combinations.
Although the position of the pile changes, construction is done by fixed positioning of the pile and varying the positions of the columns by applying the column loads by an eccentricity of 75 mm .
The following diagram shows the possible load cases for three piles.
Essentially, there are four cases that can be considered for analysis. Based on the bending moments due to eccentricity, the piles can be designed.
The following figure shows the bending moment curve that was considered when designing the floor beam reinforcement.
Design should be made for bending moments as discussed and design for shear forces can be avoided as the eccentric load is within the block plate.
The block must be designed for this eccentricity. Taking into account an eccentricity of 75 mm does not significantly change the block plate reinforcement requirements.
Furthermore, the reinforcement determined from this analysis and design must be added to the other reinforcement requirements due to floor loads and beam loads.
Sizing a double-braced beam can be obtained from an article on this web, and additional literature on other beam design categories is also available.
