Recess beam (Theory)

Last modified by Fredrik Lagerström on 2020/12/01 09:29

The Recess beam design in PRE-Stress is in accordance with the methodology presented in 'Precast Concrete Structures, K. Elliot'.

The beam itself has to be designed prior to the design of the end-recesses since the design process is dependent on the design values for the concrete material.

To activate the application for designing end-recesses, choose 'Recess beam' under 'Tools' menu, see Figure 1.

Figure 1: Tools menu

Figure 2: Application: Recess beam

In the application for designing end-recesses, see Figure 2, the user can choose between the left or the right side of the beam by choosing the corresponding tab at the top.

The application has four areas/viewports, see Figure 2;

1) A dynamic graphical representation of the recess. This viewport will respond to the inputs in area 3.

Figure 3: Different graphical representations in viewport 1

2) The global prerequisites from the beam i.e. beam dimension, cover values and design concrete material values. Here you can choose each load combination on which the calculation are made. Material values might differ per load combination but the measurements are the same since the calculation is done of the same beam of course.

3) The input data i.e. local prerequisites regarding the recess.

Note: WP and Tp refers to the width and thickness of the plate respectively.

Tip: By hovering over a diameter in this viewport its placement in the beam is presented in viewport 1, see Figure 4.

Figure 4: Dynamic info about reinforcement placement in beam

4) The output/result. This viewport will either tell the user if something is wrong with the input prior to the design or present the result from the design. If there are faulty inputs when the user tries to design the recess the following message will pop-up;


The user is also informed about which control that raised this message via the output in the

output area (viewport 4, see Figure 1). The application also suggests, by color marking in the input area (viewport 3, see Figure 1), which input that most likely is faulty, see Figure 5.

Figure 5: Faulty input

When the user presses the 'Calc' button (or change selection for load combination in viewport 2) the application will calculate all 'ULS' load combinations for the current beam  (viewport 4, see Figure 1). The results in viewport 4 will always be the same regardless which load combination are chosen, the results shows is the 'worst case' of all load combination. However, the color setting (e.g. blue or red) will indicate which results from the current load combination actually ended up as the 'worst case'. Theoretically the worst case can be a mix and match of all load combination, it is not for certain that one load combination will alone be the worst case. A result in black means that this result is taken from another load combination than the one active in the drop-box in the viewport 2.

If the design is successful the result will be available for a printout. To activate the printout of the Recess beam result the user has to tick the check-box in the 'Printout options' dialog, see Figure 7.

Figure 7: Printout options

Figure 8: Printout

Reinforcement placement

Tie bars

The length presented for the tie bars is the combined length of the recess length and 100 mm i.e. Ltie bar = LR + 100

Figure 9: Tie bars

The tie bars are welded to the support plate

Bursting U-bars

The length of the legs presented for the bursting U-bars is (1+2.5) times the recess length i.e. Lleg = 3.5 *LR

Figure 10: Bursting U-bars

Links at recess end

The links at the recess end are placed evenly in the span between c1 (= cover + r0, main + φstir / 2) and c2 (= 0.5 * d).

Figure 11: Links at recess end

Links at beam end

The links at the end of the beam are placed evenly in the span between c1 (= cover + r0, burst + φstir / 2) and c2 (= LR - φstir / 2).

Figure 12: Links at beam end

Top main bars

The length presented for the top bars is the combined length of the recess length and the anchorage length i.e. Ltop bar = LR + lbd

Figure 13: Top main bars

Bottom main bars

The length presented for the bottom bars is the combined length of the recess height minus the cover and the radius plus the anchorage length i.e. Lbtm bar = HR - cover + r0 + lbd

Figure 14: Bottom main bars

Diagonal bars

The lengths presented for the diagonal bars are lbd, top and lbd, btm

Figure 15: Diagonal bars