Column design is performed in this section.
Ultimate forces on columns are calculated according to tributary analysis. Load take down is the transferring process of the loads cumulatively to the vertical members below.
Load Take Down Based On Tributary Analysis
Area Loads On Slabs
Load take down of area loads which are in the same load class is calculated as follows;
→ The loading area within the boundaries of the tributary area of column is determined at each floor ( if exists )
→ This intersection areas are multiplied by the loading value at each floor (in psf)
→ The lumped forces (in kips) are reported cumulatively at each floor depending on their load class in Tributary Forces spreadsheet
Line Loads On Slabs
Load take down of line loads which are in the same load class is calculated as follows;
→ The length of line load within the boundaries of the tributary area of column is determined at each floor (if exists )
→ This length is multiplied by the loading value at each floor (in k/ft)
→ The lumped forces (in kips) are reported cumulatively at each floor depending on their load class in Tributary Forces spreadsheet
Point Loads On Slabs
Before the load take down, distribution factors for the columns near to point load must be calculated.
Distribution factors are determined as follows;
→ Tributary areas of columns near to point load are determined as illustrated in Figure 1
Figure 1
→ A second tributary area calculation is performed by assuming the point load as a column as illustrated in Figure 2
Figure 2
→ The intersection areas of the tributary area of point load and the first tributary areas of the columns are determined as illustrated in Figure 3
Figure 3
→ Intersection ratio is calculated as intersection area divided by tributary area of point load
→ The distribution factor for each column is equal to intersection ratio
Load take down of point loads which are in the same load class is calculated as follows;
→ Distribution factor of the column is multiplied by the value of the point load at each floor ( if exists )
→ The forces (in kips) are reported cumulatively at each floor depending on their load class in Tributary Forces spreadsheet
Live Load Reduction Based On Alternative Method
Live load reduction is performed according to NYCBC - 2014 Chapter 16 Section 1607.9.2.
Figure 4
Click “Run Tributary Analysis” as shown in Figure 4 to start analysis.
Figure 5
Ultimate forces written in blue in column schedule are updated after the analysis as shown in Figure 5.
Figure-6
If there is discontinuity in vertical members, a red point is created on the cell in dahasheet. Move cursor over the red point to see load distribution factors to near vertical members as illustrated in Figure 6.
The distribution factors are calculated as assuming the lumped total force of the column as point load.
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