Black technology! Have you used the anti-pulling and non-shear bolts?
Steel-concrete composite beam is a combination of concrete floor slab and steel beam through shear connectors, giving full play to the tensile performance of steel and compressive performance of concrete, compared with the steel beam working alone, the deflection can be reduced by 1/3~1/2, which is a necessary product for energy conservation and emission reduction.
But this thing is not good when used in super-static structures, because the force state of the super-statically determined structure in the negative bending moment zone is that the concrete is tensile and the steel beam is compressed, and the shear resistance of the bolt connection restricts the longitudinal deformation of the concrete plate, resulting in greater tensile stress on the concrete plate in the negative bending moment area of the combined structure, so the concrete in this area is very easy to crack!
In view of the problem of floor crack resistance in the negative bending moment area, experts have thought of many methods, including encryption steel bar method, longitudinal prestressing technology, group nail technology, and optimization construction process method. For large spans, it is a good choice to apply prestress in the bending moment area, but because there are bolts between the floor and the steel beam, part of the applied prestress is carried by the steel beam, which greatly reduces the efficiency of longitudinal prestress.
The pull-out action prevents the concrete slab from separating and lifting from the steel beam.
The main body of the connection is composed of a screw and a nut, the material is the same as the traditional bolt connection, during construction, the screw is first welded to the steel beam flange, and then the low elastic mold material (such as: foam, EVA foam, rubber, etc.) is sleeved around the screw, and finally the nut is screwed. The specific appearance is shown in the figure below:
The advantages of this connector are clear:
(1) The longitudinal stiffness between the concrete slab and the steel beam is very weak, and it can slide almost freely, which can effectively release the tensile stress in the concrete slab in the negative bending moment zone of the composite beam;
(2) It can effectively reduce the tensile stress in concrete slab caused by live load effect, concrete shrinkage creep and temperature effect, and significantly improve the performance, long-term performance and durability of the composite structure;
(3) The connecting parts are convenient to take materials, simple structure, convenient construction and good economy;
(4) The function of the traditional bolt connection against concrete plate lifting is retained, and the interface between steel and concrete is always closely fitted under the condition of limited slip, ensuring the integrity of the structure and the durability of the interface.
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