WO2020141564A1

WO2020141564A1 - Two way hallow-core slab

Info

Publication number: WO2020141564A1
Application number: PCT/IR2019/050001
Authority: WO
Inventors: Ali BAHAVAR
Original assignee: Bahavar Ali
Priority date: 2019-01-03
Filing date: 2019-01-03
Publication date: 2020-07-09

Abstract

Weight is a highly effective factor in the design of structures with different occupancies, particularly in cases where it increases the gravity and seismic forces acting on the structure. In applications, thickness of the beams and slabs with large spacing must be increased, leading to a corresponding increase in structural weight. Different methods including the hollow-core and the waffle methods have been proposed to reduce ceiling weight in structures. The proposed method in this paper would not only provide a greater ceiling weight reduction than other similar methods, but also eliminate certain limitations associated with the hollow-core method, including the precast production and the one-way action of this design. To this end, permanent forms were designed and placed together inside the concrete to provide end-to-end voids through the midsection of the concrete slab in two mutually perpendicular directions and a greater volume of unworkable concrete would be removed from the slab midsection.

Description

Title of Invention: Two way Hallow-core Slab

Technical Field

[0001 ] Civil Engineering

Background Art

[0002] Numerous efforts have been made in the literature towards reducing the weight of concrete slabs. Examples of the solutions proposed in this respect include flat slabs, ribbed slabs, waffle slabs, hollow-core slabs, and voided slabs. These efforts have so far been focused on increasing slab stiffness for covering wider spans by increasing the overall slab thickness without overly increasing the slab weight.

[0003] Among the slab designs proposed thus far, the hollow-core slab and the voided slab have been the most successful. The main idea in these methods is to reduce the unworkable concrete mass (which adds to the slab weigh) in the midsection of the slab near its neutral axis without significantly decreasing the flexural strength of the slab.

[0004] According to the studies conducted on voided slabs, whereas eliminating the concrete in the midsection of the slab would increase the slab stiffness by only 10%, it would reduce the slab weight by a considerable 30%. Accordingly, the abovementioned two methods have been widely used not only to provide the possibility of covering greater spans, but also to decrease slab weight and materials consumption as well as the seismic forces acting on the structure.

Technical Problem

[0005] Weight is a highly effective factor in the design of structures with different application, particularly in cases where it increases the gravity and seismic forces acting on the structure. In applications where open architectural spaces are required, thickness of the beams and slabs designed for roof structures with large spacing between their columns must be increased, leading to a corresponding increase in the ceiling weight, and consequently, in the gravity and seismic forces applied to the structure.

[0006] Therefore, using different methods to reduce structural weight would, in addition to lowering construction costs as well as materials, improve the seismic behavior of a structure. The purpose of the present invention was to propose a method for reducing the weight of concrete slabs more effectively than other similar methods without introducing any significant change in the slab stiffness.

Solution to Problem [0007] This invention aims to maximally remove the unworkable concrete from the slab midsection, thus achieving greater reductions in slab weight and materials consumption than those acquired through other technologies including the hollow-core and voided-slab technologies. To this end, permanent forms were designed for being placed inside the concrete, as shown in Fig. 1.

[0008] These forms were so designed that by placing them together, continuous (end-to-end) midsection hollows or voids would be provided through the slab along two mutually perpendicular directions, thus reducing a greater volume of the unworkable midsection concrete without affecting the original thickness of the slab (Fig. 2).

[0009] The differences between the proposed method and the hollow-core method are: (1 ) as the voids in the hollow-core method can be arranged along one direction only, hollow-core slabs are one-way slabs, whereas the proposed slab can act along two mutually perpendicular directions and is, therefore, a two-way slab; and (2) in the hollow-core method, the slab is pre-cast (prefabricated), whereas the proposed slab can be cast in-situ.

[0010] According to the research conducted on the proposed system, the weight reduction obtained for the proposed slab was 50% that calculated for a solid slab with identical thickness. Considering that the weight reduction of a voided slab is 30% that of a solid slab, the proposed method provides a greater weight reduction than the voided-slab method (Table 1 ).

Table 1

[001 1 ] Comparison of the flexural and shear strengths obtained for the proposed method via simulation (Fig. 3) and experimentation (Fig. 4) showed that: (1 ) the shear strength reduction of the slab in the proposed method was 0.5 that obtained for a solid slab with identical thickness; and (2) the corresponding flexural strengths varied according to the values given in Table 2.

Table 2

[0012] Cone-shaped bases with adjustable heights were designed (Fig. 5) to provide the possibility of placing the proposed frames at the slab midsection and to make way for the cast concrete to freely flow underneath. In addition, fins (acting as spacers) were designed on the permanent frames to prevent the frames from“sticking” to the reinforcing bars of the upper lattice (there are steel reinforcing bars above and beneath the frames), as shown in Fig. 6.

[0013] Since permanent frames must be avoided in the lateral areas as well as near the supports due to the excessive shear stresses developed in these areas, special covers (Fig. 7) were designed for closing off the voids to prevent cast concrete from flowing into these areas.

[0014] The proposed method aimed to solve two major problems, namely, the one-way performance of the hollow-core slabs and the pre-cast production method used for these slabs. The other advantage of the proposed method is that it reduces slab weight as well as concrete consumption by a greater percentage than do the other methods (i.e. , hollow-core and voided-slab methods).

[0015] Though plastic forms were used in this paper, the proposed permanent forms can also be made of other materials including wood, styrene foam, and metal. The proposed forms generally have circular cross sections, but they can also be designed in other cross sectional shapes including square, rectangular, and elliptical shapes. For each new cross sectional shape, the shape of the end-to-end void through the slab must be accordingly modified.

Advantageous Effects of Invention

[0016] The advantages of the proposed design over other similar methods (i.e. , the hollow-core and voided slabs) are: [0017] Reduced concrete consumption and, consequently, reduced structural weight as well as reduced gravity and seismic forces acting on the structure.

[0018] Possibility of in-situ casting of the proposed frames, thus eliminating the limitations associated with precast hollow-core forms.

[0019] Two-way action of the proposed forms and balanced load distribution among adjacent beams (as opposed to the one-way action of hollow-core slabs).

[0020] Providing increased rigidity for the ceiling diaphragm (as compared with waffle slabs).

[0021] Possibility of passing building utility service equipment (cables, etc.) through the end-to-end voids due to these open-ended voids being extended in two different directions.

[0022] Possibility of providing greater concrete coverage for the reinforcing rods due to the special shape of the proposed forms.

[0023] Greater resistance of the proposed forms against construction loads due to the curved cross section of these forms.

[0024] Improved acoustics provided by the two concrete layers placed above and below the slab (as compared with waffle slabs)

[0025] Better thermal insulation due to the upper and lower concrete layers as well as the air trapped within the pipes (as compared with waffle slabs).

Description of Embodiments

[0026] Procedure of Invention (Fig: 8):

[0027] Stage 1 : Formworking

[0028] Stage 2: Putting bottom rebar

[0029] Stage 3: Putting permanent formwork

[0030] Stage 4: Putting top rebar

[0031] Stage 5: Concreting

[0032] Stage 6: Formwork opening

Industrial Applicability

[0033] The proposed slabs can be used in the foundation as well as floor and ceiling of residential, business, administrative, and industrial structures. They also have potential applications in road making and airport runways.

Claims

[Claim 1] A method for producing, via permanent forms, continuous voids through the midsection of a concrete slab to reduce the slab weight as well as concrete consumption, so that by placing these forms together, end-to- end voids can be made through the concrete slab in one or two directions.

[Claim 2] The proposed frames in Item 1 can have circular, elliptical, rectangular, or other cross sectional shapes which would produce corresponding end-to- end void shapes through the concrete slab.

[Claim 3] The proposed frame in Item 1 can be made of plastic, wood, metal, styrene foam, or other similar materials.

[Claim 4] Special covers are used for closing off the ends of the end-to-end void to prevent the cast concrete from flowing into the voids.

[Claim 5] Special bases were designed under the proposed forms for accurately positioning them at the midsection of the slab.

[Claim 6] Spacers were used on the proposed forms for better covering the reinforcing bars with concrete.

[Claim 7] The different parts of the proposed forms can be fabricated either as an integral whole or separately (for later assembly during in-situ casting) to provide the final end-to-end voids.

[Claim 8] By modifying the length and shape of the proposed forms in accordance with the relevant concrete slab design considerations, the spacing of the voids can be changed.