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Better Beams and Slabs
Published in Rob Whitehead, Structures by Design, 2019
Two-way slabs don’t have a short-side. They have square proportions with a network of beams fixed together and columns equally spaced around their perimeter. Some two-way slabs take the form of a waffle slab (deeper beams with hollowed out voids between). These are created by pouring the slab and beams together atop pans that are secured to the formwork below. Two-way slabs are efficient, but they offer less integrative possibilities with building elements like conduits, lights, ducts, and sprinklers—unless the pan system is modified to provide voids. (Figure 3.2.22)
Basic layout of concrete structures
Published in Eugene OBrien, Andrew Dixon, Emma Sheils, Reinforced and Prestressed Concrete Design to EC2, 2001
Eugene OBrien, Andrew Dixon, Emma Sheils
Slabs that are supported along all four edges by beams or walls are known as two-way spanning slabs since the applied loads are effectively transferred in two directions to the supported edges (Fig. 2.20). Two-way spanning slabs are normally either solid uniform slabs or, for longer spans, ‘waffle’ slabs (Fig. 2.20(c)) of a shape not unlike edible waffles. In waffle slab construction, the slab is often made solid near the supports to increase the shear and bending moment capacity.
Introduction
Published in R. J. Cope, L. A. Clark, Concrete Slabs, 1984
A waffle slab consists essentially of a thin top slab acting compositely with an orthogonal grid of beam ribs, as shown in Fig. 1.4. The soffit shuttering for the recesses may be left in place. For a waffle slab to respond to loading in the manner of a solid slab, rather than as a scries of intersecting beams, the ribs should be relatively closely spaced. Recommendations on spacing are given in design codes of practice. Suitably reinforced solid areas often have to be provided around supporting columns because of high shear forces. Such solid areas can relatively easily be provided by omitting recesses at the columns. Beams spanning between columns can be incorporated in a similar manner.
Probabilistic Seismic Capacity Analysis of a Novel Mid-rise Large-span Cassette Structure Using Multidirectional Pushover Method
Published in Journal of Earthquake Engineering, 2023
Zhi-Peng Chen, Songye Zhu, Ke-Jian Ma, Gang Wu
To this end, a novel cassette structure, which is composed of an open-web waffle slab (OWWS, also called an open-web sandwich slab) system and an outer grid frame (GF) system that surround a structure, has recently been proposed for mid-rise large-span buildings (Ma, Zhang, and Hang 2000). Different from the traditional beam-slab system, in a cassette structure, the low-efficiency beam web is replaced by regularly spaced large-stiffness shear keys, whereas the upper and bottom parts of the beam that contribute the main parts supplying the bending resistance are still maintained. Such a design can reduce the self-weight of the whole floor system by more than 50% (Ma et al. 1995). Past studies and applications (Ma, Zhang, and Zheng 2006) have already demonstrated that the maximum span of an open-web waffle slab can reach 40 m with a relatively small beam height, i.e., only approximately 1/25 ~ 1/30 of the structural span. In comparison, in a traditional concrete frame structure, even with prestressing technology, the beam height is usually approximately 1/8 ~ 1/12 of the span, which is less efficient in terms of space and material use. Furthermore, to achieve a structure with large usable space, in the cassette structure, the columns that are typically placed inside the structure are completely removed, with columns place around the structure instead. A traditional solution to compensate for the reduction in the column number is to considerably amplify the cross-sections of the columns, which is regarded as technically and economically inefficient. Therefore, the cassette structure adopts a grid frame system, which is composed of dense columns and one or two interstory beams. Compared with traditional frame columns, the grid frame has considerably greater stiffness and strength, the cross-sections of the columns are smaller, and the anti-seismic and energy dissipation capacities are much better. The structural function of the cassette structure, which is composed of a large-span open-web waffle slab and a high-stiffness grid frame, is improved and better anti-seismic performance is achieved in mid-rise large-span buildings (Ma, Zhang, and Xiao 2008).