The roots of column history can be dated back to ancient Greece and Rome where their monumental appearance was to create an effect of pomp and majesty. The recent tendency, on the other hand, has been towards using slender, inconspicuous columns that enable creating flexible open spaces inside.
Let’s have a closer look at a standard, traditional column-beam connection. Concrete corbel is ‘a must’ in a precast column. Otherwise, the connection doesn’t have enough shear capacity. Concrete corbel must secure sufficient bearing area to transfer shear forces from beam to the corbel and to the column. Common bearing length of concrete corbel is about 20 to 25 cm. Shim plates are used as bearing plates between precast beam and concrete corbel. All in all, the eccentricity of shear force with respect to column axis is taken as a half of the column depth and eccentricity of corbel itself. This is the main reason why PCs® Corbel positively contributes to column design in a way that reduces the column’s main reinforcement or even reduces the column cross-section. While eccentricity with traditional concrete corbel is about 15 to 20 cm, by selecting PCs® Corbel a maximum value of less than 6 cm can be obtained! In the end, when using PCs® Corbel, the additional bending moment caused by corbel eccentricity is about 1/3 or even 1/4 compared to traditional solution of concrete corbel. Indeed, it’s worth considering using PCs® Corbel!
Compared to traditional concrete corbel, PCs® Corbel provides more benefits and presents more reasons for selecting it. One of many I often like to point out is that with PCs® Corbel there is no need to damage formwork to create protruding concrete corbel. PCs® column part is aligned in formwork and corbel part is bolted afterwards – on site. Right after being bolted, reduced eccentricity contributes to transferring less bending moment to column, saving column reinforcement and even reducing the need for column-to-foundation joint!
Let’s look at the following, simplified example of precast column design with bolted connection to foundation and main reinforcement design. The example compares two alternatives of corbel connections – traditional concrete corbel and PCs® Corbel.
Simplified column design in a way of shear force and corresponding bending moment transfer only.
The aforementioned savings are achieved only by selecting PCs® Corbel instead of concrete corbel, with equal transfer of loads! The same design logic can be used to optimize dimension and reduce column cross-section. So, could selecting PCs® Corbel be a beneficial contribution to column design? It sure can!