Static structures (e.g. – buildings) – Controlled by condition responsive means
Patent
1985-01-30
1986-12-23
Perham, Alfred C.
Static structures (e.g., buildings)
Controlled by condition responsive means
52 98, 52 99, 52167, 52232, E04B 198, E04H 900
Patent
active
046304126
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a connection device for building structures according to the preamble of claim 1.
BACKGROUND OF THE INVENTION
When erecting building structures of reinforced concrete and especially such containing precast units, not only the characteristic load values in the service and ultimate limit states should be considered, but also special regard should be paid to accidental loading (explosion, impact from vehicles, fire, seismic action, settlements of foundations, etc.), such that progressive collapse will be prevented in case of a local failure in the structure. In this connection, the available ductile capacity of the connections between the various structural units is of great importance. If it is sufficiently large, alternative load bearing paths can develop when the structure is deformed, energy is absorbed from dynamic action and the falling down of structural units is prevented.
Connections between various structural parts can have many forms. Common for most of them is, however, that they contain ties (tie means) anchored in the facing structural parts, and generally made of steel and having the ability to transfer tensile forces. When the structural units are made of reinforced concrete, the ties normally extend a distance into the structural parts where they are anchored.
Current technology normally uses connections which, with regard to the circumstances in case of accidental loading, have a limited ductile capacity before rupture occurs in the ties. Their capacity to absorb energy in case of dynamic action is also limited. The available ductile capacity essentially depends on the yielding capacity, the length and the bond distribution along the tie devices when their ultimate tensile capacity is reached at the joint interface.
Limited arrangements to minimize the risk of progressive collapse are thus often regarded as satisfactory, or the risks are diminished in other ways than by dimensioning the connections utilizing their ductility.
OBJECT OF THE INVENTION
The object of this invention, thus, is to disclose a tie arrangement providing tie connections between precast elements or other structural parts with a large ductile capacity which tie arrangement complementary to conventional ties possibly shall prevent a progressive collapse from occurring in case of accidental loading acting upon a building structure.
SUMMARY OF THE INVENTION
Using the invention, the ductile capacity of a connection may be designed at option choosing a tensile stress in the tie which is equal to or larger than that necessary for the transfer of forces due to design loading, but which is sufficiently lower than the ultimate tensile stress of the tie to prevent the risk for tensile failure by the slippage of end anchors of the tie through a material cast around the tie approximately at a predetermined stress in the tie between said limits, preferably between 60 and 90% of the ultimate tensile stress. According to the invention, the tie means includes one or more bars or wires of preferably high tensile steel having an ultimate tensile stress larger then 1000 MPa. In one or both of the connected structural parts, the tie means is surrounded by a cast material within a zone the length of which is equal to or greater than the predetermined length of possible displacement (distance of slippage). Preferably the length of said zone includes also the necessary anchoring length for anchoring the full tensile capacity of the tie. The tie is, at least at one of its ends provided with an end, anchor, for example a cold formed button head of such a size that the end anchor slips through the cast material at a predetermined tensile force within the tie.
One embodiment of the invention makes use of concrete or grout using cement as binding component for the cast material which surrounds the tie. For such materials it has been shown by tests that the end anchor starts to slip when the compressive stress between the end anchor and the cast material in the direction of the tie, i.e.
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Bernander Karl-Gustav
Engstrom Bjorn M. H.
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