GGU-STABILITY: Maximum nail forces and verification of punching
The maximum nail forces and punching safety factor are determined using the "Nail wall/Maximum nail forces + punching" menu item .
Whilst calculating slip surfaces the program keeps a protocol of maximum forces per nail position. These forces are compared to the load components which arise from the earth pressure on the concrete shell. The largest value is decisive. The earth pressure on the concrete shell is determined without cohesion, in accordance with current permits. 0,85 times the earth pressure value is distributed rectangularly along the length of the concrete shell. The earth pressure reduction by a factor of 0,85 may not be carried out for surcharge loads. Correspondingly, the calculation of earth pressure on the concrete shell is carried out with the values from permanent and live loads, increased by 1/0.85.
After selecting this menu item a dialog box is shown with the distributed earth pressure value e,d. The value suggested for earth pressure e,d in this dialog box will also be used for punching verification. After confirming or editing of the calculated earth pressure value, the maximum nail forces, determined in accordance with the above description, are shown in a list in another dialog box. The maximum nail value is multiplied with the horizontal separation and suggested as design value for punching verification. This value can, if wished, be edited.
The pressure under the punching area will be subtracted from the nail force, in accordance with EC 2. The pressure is taken as the reduced earth pressure (see above). Besides this information the following must be given, in accordance EC 2, for punching verification:
Effective height of concrete shell in the verification area, as % of concrete shell thickness;
Width of nail slab (= height);
Present bending reinforcement;
Concrete used;
Steel used.
After making the inputs and pressing the "OK" button, verification will be carried out and all decisive values for verification are shown in a dialog box.