New concept of composite steel-reinforced concrete floor slab
Building use
Office building
Country/Region
Poland
Overview
The innovation proposed aims to provide a slim floor system with a total thickness of 282mm with higher mechanical resistance than a comparable conventional slim floor assembly, by strengthening the composite behavior of the steel-concrete bond thanks to rebars that work as shear studs, blocking the differential slip of the concrete to steel connection.
Issue and/or innovation
Test results indicate that the loss of capacity of the so called slim floor (or shallow floor) system is due to the loss of bonds between the composite beam element and the floor slab, usually created with prefabricated prestressed hollow core concrete elements. Special RC studs are used in the proposed innovation to prevent such behavior and increase the strength of the composite floor solution adopted.
Technical details
This research deals with a new concept of composite steel-reinforced concrete floor slab. This type of the floor slab consists of newly constructed steel and concrete composite beam mandatory connected together with cast in situ or prefabricated floor slab. The description of the nonlinear behavior of this newly designed steel and concrete composite beam with horizontal studs is a subject of a separate paper. Existing test results indicate that the loss of capacity of such structures may be linked to the loss of bonds between the composite beam and the floor slab. To prevent such behavior, special connecting elements have been designed in form of RC studs. Two types of structures, each consisting of composite beam and the prefabricated floor slabs, have been the subject of full scale tests performed in cooperation with ITB strength tests laboratory. Prefabricated prestressed hollow-core floor slabs have been supported on lower flanges of the steel part of the composite beam with reversed TT cross-section to provide a flat lower surface of finished floor slab. In order to prevent the separation of composite beam and floor slabs a number of reinforced concrete studs were arranged for ensuring the adequate bond between these components. The studs have been devised as the set of horizontal rebars passing through the perforated webs of the beam and anchored in the circular openings of the hollow-core slabs. Self-compacting concrete have been used to obtain adequate filling of hollow-core slabs openings. The studs have been designed according to the provisions of Eurocode 2. The expression defining the load carrying capacity of this junction, after some rearrangements, enabled the derivation of equations for the determination of the slab width interacting effectively with composite beam. As an interconnection between composite beam and slabs, these studs have sufficient strength and stiffness to enable both components of the structure to be designed as the parts of a single structural member able to attain the ultimate limit states. During the tests no signs of splitting between beam and slabs subjected to design loads were observed. Experimental and computational results showed satisfactory consistence.
The new composite beam is connected with cast in situ or prefab concrete slabs. In the tested case, hollow core prefab slabs are used. They are supported by the lower flange of the reversed TT steel element that provides a flat lower surface for the ceiling. Concrete is poured between the vertical webs of the steel assembly and it is made composite by means of shear studs facing inward. Both the steel webs and the concrete pour have holes that will provide the composite behavior to the whole floor assembly. When the hollow core elements are placed, rebars are passed through the holes, thus acting as shear resistant elements, and self compacting concrete is poured to lock the assembly. The steel element of the composite beam is made with a 602mm plate, 12mm thick while the two vertical webs are 6mm in thickness and 205mm high. The concrete part is reinforced with 12 longitudinal rebars with 25 mm in diameter and a 8mm stirrup.
References / Technical Papers Content
Dershowitz P., Lewinski P. M., Wiech P. P., “New concept of composite steel-reinforced concrete floor slab in the light of computational model and experimental research” Procedia Engineering 193 (2017) 168 – 175
https://doi.org/10.1016/j.proeng.2017.06.200
References / Technical Papers
References / Technical Paper - 1
Categories
Building, Floor (slab)