# Frame (construction)

Above statically indeterminate frame, below statically determined three-hinged frame
Executed frame of a lift bridge

In structural engineering, a frame is an idealized construction that is made up of bending-stressed bars (actually " beams ") (a set of bars ). At least one of the rods must be clamped in or connected to the neighboring rod via a rigid knot in order to obtain a resilient overall construction.

In the standard case, a frame has a square view and consists of two vertical frame bars ( stems or posts ) and a horizontal transom . The stems can be clamped at the bottom (top picture) or hinged (simply statically indeterminate two- hinged frame ). The frame corners can as according to design rigid , flexurally soft or as articulated be adopted. Several frames can be put together to form a more complex structure , similar to the framework (technical mechanics) . In the case of a story frame, several uniform frames sit one above the other.

In contrast to the frame, a lattice girder manages without rigid rods and nodes, but usually requires additional rods to form stiffening rod triangles.

As a special case, the stems and bars of a frame can also be designed as trusses. When the truss runs around the corners of the frame, it forms rigid corner nodes.

In contrast to joints, rigid nodes can transmit not only normal and transverse forces , but also bending moments and, if necessary, torsional moments .

If a frame also contains disc-shaped components in addition to bars , it can under certain circumstances be viewed as a two- dimensional structure.

The classic method for determining the cutting reactions of a frame is the principle of virtual performance (e.g. principle of virtual forces ), plus the iterative methods of Kani and Cross . More recently, frames have also been calculated using the finite element method . A Vierendeel girder is also described by the static model of the frame.

In the broadest sense, arches can also be viewed as frames. One example is the triple statically indeterminate bearing arch of the Müngsten bridge .