Anchors limit load

The anchors contribute to the increase in strength resources for the bulkhead. The calculation of the limit load of an anchor must be made considering thee different collapse mechanisms. In fact, the collapse may happen by pull-out off of the bulb, by pull-out off of the steel part of the concrete which contains it or, possibly, by breaking of the anchor (reaching the threshold of the steel strength). The procedure used in the software calculates the limit load with regard to all three collapse mechanisms, and defines as limit load of the anchor the minimum between the three collapse mechanisms.

Limit load for collapse in adherence to the bulb-ground interface

In this case, the limit load is calculated using the following formula (Schneebeli):

In the previous formula, the meaning of the symbols is the following:

where D is the diameter of the bulb and Lb is the length of the bulb

| 20° | 1,3 | | 30° | 5,5 | | 40° | 30,00 |

Table: values provided in the work of Prof. Carlo Cestelli Guidi

"Geotecnica e tecnica delle fondazioni" ("Geotechnics and foundation engineering"), Vol. 2, Ed. Hoepli, year 1980.

Limit load for collapse in adherence to the steel-bulb interface

In this case, the shear stress of ultimate adherence between steel and concrete is involved. The formula which expresses the collapse load of the system is the following:

In the formula, the symbols have the following meaning:

The design adherence shear stress fbd is:

fbd = fbk / gc

where:

fbk = 2,25×h×fctk

where:

In case of very thickened reinforcements or anchorages in zone of stressed concrete, the adherence strength is reduced by diving it at least by 1.5.

Limit load for collapse by reinforcement failure

This is a purely structural check and concerns the circumstance in which the stress in the steel reaches the failure limit stress. In this case, the collapse load is calculated using the following formula:

In the previous formula, the symbols have the following meaning:

Once the collapse loads have been calculated for the three different mechanisms, the limit load of the anchor can be determined using the following formula:

Where the symbols have the following meaning:

For each anchorage, the failure mechanism is returned: ground failure, adherence resistance, steel resistance