International Concrete Abstracts Portal

Biaxial voided slab is an innovative slab system which results in a self-weight reduction of up to 50% in comparison with solid slabs. In this paper, the effect of voids of various shapes on flexural behavior of reinforced concrete (RC) square slabs was studied through experimental investigations. Five full-scale slab specimens under a 16-point load were tested with two different shapes of voids, such as sphere and cuboid. The results obtained for solid and voided slab specimens were compared and found that the ultimate flexural capacity is almost the same. However, the presence of voids influences flexural stiffness. While such influence accounts for a marginal deviation of the post-cracking flexural stiffness, the initial stiffness of solid slabs is observed to be 37% higher than that of voided slabs. Furthermore, the flexural load-carrying capacity was estimated based on the yield line method with tensile membrane action and compared with experimental results. For this, the experimental results of the present study (five specimens) and test data collected from the literature (seven specimens) were compared with predictions. It was found that the beneficial effect of tensile membrane action is applicable for biaxial voided RC slab in enhancing the flexural load-carrying capacity. Furthermore, through the comparison of experimental and analytical results, it is found that the 16-point load can be adopted to simulate uniformly distributed loading condition.

New types of reinforced concrete voided slabs cast in place with plastic void formers need to be researched. One of the most dangerous zones of biaxial voided slabs is the slab-column connection and zones where concentrated loads are applied. A slab can fail from punching shear. The area of the shear section in the punching zone is significantly smaller because of the cavities formed by the void formers. In this study, three types of punching shear zones of voided slabs were analyzed: without voids, with voids, and with voids and solid cross-shapes. Punching shear tests were performed on all types of voided slabs. Calculations were performed according to ACI 318-14 and Eurocode 2 design codes for comparison. A new calculation method was developed for the punching shear bearing capacity of voided slabs based on the Eurocode 2 design code. The method was verified according to the actual test results and the results of other authors.

Fiber-reinforced concrete (FRC) deck slabs without internal tensile reinforcement are also known as steel-free and corrosion-free deck slabs. The cast-in-place version of these slabs has already been applied to five highway bridges in Canada. This paper describes the significant design details of a 150 mm-thick precast steel-free deck slab supported on girders at a spacing of 3.5 m. The results of tests on full-scale models of the precast slab are also reported. It was found that the precast panels, made composite with the supporting beams, were able to sustain concentrated loads that were several times larger than the factored design loads. The experimental investigation included the study of the panel’s performance to sustain construction loads when it is not connected to the girders. This investigation led to an improved design of the panel, also reported in the paper. When a precast panel without any reinforcement was incorporated in a forestry bridge several years ago, it developed several wide cracks. While these cracks have not impaired the load-carrying capacity of the deck, it is now believed that unsightly wide cracks should be avoided by providing in the panel a crack-control grid of nominal reinforcement, either made of steel or of glass fiber-reinforced polymer (GFRP).

One of the advantages of the use of flat slabs made with high-strength lightweight concrete is the resulting reduction in the weight of a structure, which offers substantial cost savings. However, punching-shear failure of concrete in the column periphery and the crushing of concrete before steel yield are not desirable modes of failure and should be avoided in slab design. To investigate these issues, seven slab-column connections were tested using high-strength lightweight (HSLW) concrete slabs. Two reference slabs were also tested; the first using normal-strength normalweight (NSNW) concrete, and the second using normal-strength lightweight (NSLW) concrete. Ultimate shear strength, deflection, ductility, joint rotation between column and slab, mode of failure, radius of punching, concrete strain, and steel strain were investigated. The variables of the test program were the flexural reinforcement ratio, concrete strength, aggregate type, and moment-load ratio. Deflection and ultimate central load increased as the applied moment decreased. The deflection of HSLW slabs under moment decreased by between 20 and 60%, compared with similar slabs tested under a central load and no moment. The ductility of HSLW slabs decreased as the applied moment increased. A secondary bond-splitting failure with a complete separation between concrete and reinforcement at high moment is unique for lightweight aggregate slabs. The slab stiffness degradation decreased as the moment level increased, while the value of the energy absorption decreased as the tensile steel ratio increased. In general, HSLW concrete slabs were almost equal to normal-strength concrete slabs made with normalweight aggregate in terms of shear strength, flexural strength, and general performance. NSLW concrete slabs were the lowest in shear strength, flexural strength, and general performance, compared with NSNW and HSLW slabs.

The transfer of shearing forces and moments between concrete flat slabs and columns can produce brittle punching failure. Slab-column connections must satisfy adequate strength against punching failure. In seismic zones, the connections are expected to undergo deformations into the inelastic range, and, hence, it is necessary to design connections with adequate strength and ductility. In addition, the connections must be able to undergo a specified limit of interstory drift without punching failure. The interstory drift is defined as the difference of lateral deflections between two successive floors. The ductility and drift requirements that must be adhered to in design are discussed. Tests reported in the literature show that the strength under cyclic moment transfer is less than the strength under monotonic loading. For an earthquake-resistant structure, the design must be based on the strength under cyclic loading. Test results are reviewed and discussed. The results show that under cyclic moment transfer, the nominal shear strength allowed by ACI 318-89 and the Canadian codes can be nonconservative. As an application, a hypothetical structure is designed according to the ACI Building Code (ACI 318-89). The structure is subjected to the 1940 El Centro ground motion, and time-history dynamic analysis is performed. The results show that to obtain adequate strength, drift capacity, and ductile behavior of a slab-column connection without shear reinforcement, it is necessary in most cases to increase substantially the slab thickness in the connection region beyond the minimum thickness required to control deflections by providing shear capitals. The disadvantages of shear capitals can be avoided by using shear reinforcement