Tie Beam (Straight beam) is a beam which connects the two footings in the substructure. Tie beam is provided when the two footings are in the same line. Strap Beam(inclined beam) is similar to tie beam but it connects two footings at a certain angle.
Strap beam is laid when two footings are at different levels. Tie beam/ Strap beam is specifically located between pile caps and shallow foundations. their primary function is to force all shallow foundations or pile caps to have approximately the same settlements.
Important Points to understand the reinforcement in tie beams
1- Main Bars (Top bar, Bottom bar, Sidebar) are tied to the centre of the one footing to the centre of another footing.
2- Whereas stirrups start from one face of the footing to another face of footing. Refer the below image for a clear view of how reinforcement is tied in Tie beam.
Steps to be followed while finding out the total wt. of steel required for constructing Tie beams / Strap beams
Tie beam reinforcement calculation is divided into two parts Main bars and stirrups.
Part-I:- Main Bars
1- Check the Length of Main bars in the top, bottom, sidebars.
2- Then Check the No. of Main bars in the top, bottom, sidebars
3- Check the Diameter of Main bars in the top, bottom, sidebars.
4- Calculate the total length of Main bars in the top, bottom and side direction.
5- Find the total wt of Main bars.
Part-II:- Stirrups
1- Deduct the concrete cover from all sides of the tie and find out the length of the stirrup.
2- Calculate the length of stirrup including hook.
3- Calculate the total no. of stirrups.
4- Find the total length of stirrups.
5- Then Calculate the total wt. of stirrups.
Length, Dia and No. of Bars are adopted and designed by the structural engineer by executing the load analysis.
Consider the below-shown Figure
Assume for calculation
Dia of Top Bars = 10mm, Dia of Bottom bars = 10mm ,Dia of Side bars = 8mm, Dia of Stirrups = 6mm, Spacing between ties = 0.1m.
No. of Top Main bars = 4, No. of Bottom Main bars = 4, No. of Side Main bars = 2
The calculation for the Number of Tie beams (Main Bars)
All beams in the horizontal axis are all Tie beams except the beam between F5 and F6. Treat all the beams are tie beams, as the direct value of the length of the beam is already given for all. If the length of the Strap beam isn’t given then obtain the Length of Strap beam by using the Pythagorean theorem,
Hyp^2 = Adj^2+ Opp^2
Hypotenuse = length of strap beam.
From the figure,
Part- I. Calculate the Total wt required for Main bars
Apply the above method for all the tie beams in Horizontal and the vertical axis. the result of all tie-beams has been entered in the below table.
The calculation for the number of Tie Beams (Stirrups)
As I have already mentioned that Stirrups are started from one face of the footing to another face footing.
Tie Beam on Axis I between A-B
Below are the five steps for finding the quantities of Tie beam (Stirrups)
1- Deducting the concrete cover from all sides of the tie beam for finding out the length of each tie. From the figure, it implies that reinforcement details of Tie beams in the horizontal axis and vertical axis are different. As per the condition deduct the concrete cover of 0.05 from all sides of stirrups for Horizontal axis tie beams and 0.025 from all sides of stirrups for Vertical axis tie beams Apply the above method for remaining tie beams. The result is mentioned below. Check your result with the below table.
Apply the above method for remaining tie beams. The result is mentioned below. Check your result with the below table.
Abstract For Finding out the total quantity of Steel reinforcement required for Tie Beam/Strap Beam for the above-given plan
Hence, Total wt of Steel 512.81 Kgs required for Tie beam/Strap Beam (for the above plan).
