Analytical and experimental examination of reinforced concrete voided slabs

Structures made throughout history have undergone many changes due to need. These needs have sometimes been architecturally and sometimes statically. Architecturally larger openings and flat roofs and statically lighter and ductile structures have always been a need. In this way, the designer has made efforts to reduce weight in slabs and design mushroom slabs. A number of different systems are being solved by recent technological analysis methods. The voided slab formed by leaving gaps in the flooring has been frequently used in large-span in recent years. However, in addition to the acceptance of all calculation made without a gap, it is important to consider how the voided slab is taken into consideration in the analysis and the provisions in the regulations should be investigated. For this reason, in the scope of thesis, six main headings were examined and checked the conformity of the voided slabs to the calculation and theories according to a normal slab without voids. Initially, the first studies of this type of slabs can be considered as mushroom flooring and the studies on the weight of the floor was mentioned. In the second part, plate theories, in-plane shear and bending, out-of-plane shear and bending behaviours were investigated. In order to explain the bending and shear behaviour in the plane, kinematic, constitutive and equilibrium equations were written as differential in the truss and plate element. In order to explain the bending and shear behaviour in the out-of-plane, kinematic, constitutive and equilibrium equations were written as differential in the beam and plate element. Finite element methods to be used in the stiffness matrix, shape functions are obtained by using energy methods are described. For example, shape functions and stiffness matrices were calculated for beam and thin plate elements. Voided slab was considered as an orthotropic cross-section. Only the constitutive equations of three basic equations in general plate theories change between the orthotropic section and the isotropic section. After the recognize that stiffness, area and volume of the voided slab section will change only according to the slab without void, calculation of this exchange expressing correction coefficients are given. With these correction coefficients, it was shown that the voided slab could be modelled as slab without void according to the plate theories. In the third chapter, generally the elastic method used in the section analysis and the currently used capacity design method are mentioned. Then, general cross-sectional analysis principles and comparative solutions were made for the section with and without void. It has been shown that the compression-bearing plate thickness of the voided slab section has the same carrying capacity as the void-free slab as long as the compression-bearing flange thickness in the section analysis is greater than the height of the compression block. In case the compression block height is greater than the compression-bearing flange thickness, the results show differences. Parametric studies were made for convenient voided slab design based on shape of void and section analysis. Parametric studies made on three void shapes as square, hexagonal circular based. In this study, flange thickness F = 8 cm, void height H = 10, 12, 14, 16, 18, 20 cm, body thickness W = 5, 10, 15 cm and void width D = 30, 41, 52, 63, 74 cm alternatives are examined loss of inertia in unit area and changes in volume of concrete in unit area. Square-based shapes for plastic, machine, packaging, formwork, transportation, casualty and profit costs were calculated. As a result, more solutions that are economical can be seen with the increasing width of the selected alternative gap widths. However, due to the width of the body, the shear area drops for the shear force start to become a problem in larger gap widths. The loss of inertia increases with the gap width. However, since the loss of inertia is not too much, this reduction does not affect the cost unless the limit is in the limit state. C20, C30, C40 concrete class alternatives were evaluated in the other parametric study. Upper and lower flange thickness F = 6, 8, 10 cm, void height H = 10, 13, 16, 20, 24, 28 cm, body thickness W = 10, 15, 20 cm and void width 52 cm alternatives section's results were evaluated. In addition to the cross-sectional alternatives, an alternative cross-section analysis was carried out 0.002 reinforcement ratios corresponding to approximately the minimum reinforcement, 0.02 reinforcement ratios corresponding to maximum reinforcement and 0.004 and 0.008 reinforcement ratios as intermediate values. Finally, the body was modelled as confined concrete, which was formed by arranging the tie or stirrup along the voided slab section body, and all alternatives were evaluated according to the confined concrete model. All alternate sections are analyzed to determine the moment, curvature, compression block height, ductility ratio and effective cross section rigidity for linear calculation. In the cross-sectional study, it has been observed in which conditions of the void slab section should not exceed the flange thickness of the compression block height in order to model some coefficients as a used plate element. Based on the ratio of reinforcement, at the minimum reinforcement ratio of 0.12, 0.004 reinforcement ratio of 0.20, 0.008 reinforcement ratio of 0.40 and maximum reinforcement ratio of 0.80 effective section stiffness factor was found. As the section height increased, this factor was found to be above the mean values. It has been observed that the ductility ratio increased from minimum reinforcement to 0.008 reinforcement ratio but decreased at maximum rate of reinforcement. In the fourth chapter, an example of a project that provides the Turkish Seismic Code-2018 conditions of a high-rise building with a voided slab system was made. After the construction of the project sample has been established according to the code requirements, analyzes are completed and reinforced concrete design for slab was made. It has been shown that the special conditions to be checked for TSC-2018 slab convey the earthquake load to the wall, the in-plane stress limits are provided and there is no punching problem in this project sample. In the fifth chapter, in the scope of the thesis and in the acceptance of reinforced concrete calculation, it is investigated whether it is valid for voided slabs. The mathematical model of the voided slab section was tested by using the parameters obtained because of the material test results and using the values of the codes. As a system, the displacement graphs read in the middle of the span and loaded load were compared with the graphs obtained from the mathematical model. As a cross-section, the results of the moments and rotation obtained from the middle of the test were compared with the values defined in the mathematical model. Moment-rotational graphs with displacement meter placed in the middle section and moment-curvature values from mathematical modelling are compared. Reaching the yielding remains at a distance of 2d in the case of a narrow body 2a and d in a large body 2b sample. In the codes, it is observed that the void in unit area changes the value of the plastic hinge length when considering the acceptance of the plastic hinge length d in the middle of the opening in a normal filled section. While it is not expected a non-linear behaviour from the slabs, it is expected to behave ductile like an earthquake. As seen in the voided slab results, the section continues to displace at similar strength after reaching the yield point. It is observed that the effective section stiffness multiplier changes depending on the section size, material strength and elasticity values. In the last chapter, suggestions were made about the results and issues to be considered during the thesis scope.