Claims:WE CLAIM:

1. A precast raker seating system for stadiums and auditoriums comprising of:-
a) a portal frame with plurality of columns and beams arranged in a seating area of an oval or circular shaped stadiums and auditoriums,

b) a first plurality of support columns C1a, C1b, C1c, C1d positioned in an oval or circular arrangement, the first plurality of support columns having the first end connected to foundation,

c) a second plurality of support columns C2a, C2b, C2c, C2d positioned in an oval or circular arrangement multi concentric with the plurality of first support columns, the second plurality of support columns having the first end connected to foundation,

d) a plurality of radial beams RB1, RB2, RB3, RB4 connected to a second end of corresponding radially positioned first and second support columns,

e) a plurality of circumferential beams CB1a, CB1b, CB1c, CB1d and CB2a, CB2b, CB2c and CB2d connected to a second end of corresponding plurality of first and second support columns, and

f) a plurality of precast 3D rakers R2, R2a, R2b, each raker having plurality of riser beams, a plurality of tread slabs spanning between the said riser beams, and a pair of main beams spaced apart arranged on opposite sides with free ends of tread slabs and riser beams resting on the main beams.

g) the said raker is characterised such that each raker is positioned and connected at its ends to the corresponding circumferential beams positioned on the support columns.

2. The present raker seating system as claimed in claim 1, wherein the seating area is of rectangular or square or any shaped stadiums and auditoriums with straight edges, and such that circumferential beams and radial beams will be substituted with horizontal beams and inclined vertical beams correspondingly. , Description:Field of Invention:

The Present invention belongs to development of unique precast element for seating units used in stadium, Auditorium, Sports centre, etc. An innovative, economical and simple design approach is developed and the three dimensional precast element is evolved. This invention resulted in optimum size of elements, reduction in weight, lesser number of elements, faster construction and hence savings in overall cost.

Background of Invention:

The steps in the lower tier of stadium usually have lesser riser height as per line of sight requirement of spectators. Generally, the steps of the lower tier are made of precast L-Type bleacher elements. It may be either Single L-type, Double L-type and Triple L-type based on design requirement, spanning between the radial beams (refer Figure 1) which are in turn supported by RCC columns. Due to larger span length, the riser of bleacher element would require projection below bottom of bleacher as per design requirement (refer Figure 2). The formwork system required for these type bleachers are complicated, laborious and consumes more time and cost.

In addition to this, when the L shaped bleacher unit spans between the radial beams, the entire cross section of the bleacher will bend about its principal axis (refer Figure 3). In this condition, the thickness of tread slab needs to be increased as per the bending moment requirement which is calculated based on span of bleacher. This will lead to higher thickness of tread slab resulting in more weight and cost.

To overcome the above mentioned difficulties, a unique three-dimensional precast seating unit called “Raker” is developed comprising of Tread slab, Riser beam and inclined Main radial beam on either side (refer Figure 4A, 4B, 4C, 4D, 4E & 4F for Three dimension view, Top plan View, Longitudinal Section, Cross section and Shorter direction elevation view respectively).

Description of drawings:

Figure 1 illustrates Double L - Bleacher arrangement in Typical Bay.
Figure 2 illustrates Bleacher details with projection below tread slab.
Figure 3 illustrates Principal axis and Stress- Strain Diagram.
Figure 4A illustrates Three Dimensional view of Raker Element.
Figure 4B illustrates Top plan view of Raker Element
Figure 4C illustrates Longitudinal Section of Raker Element.
Figure 4D illustrates Cross Section of Raker Element.
Figure 4E illustrates Elevation view of Raker Element.
Figure 4F illustrates Elevation view of Raker Element.
Figure 5A illustrates Raker element arrangement over portal frame in Plan
Figure 5B illustrates Raker element arrangement over portal frame in Section
Figure 5C illustrates Raker element spanning direction over portal frame
Figure 6 illustrates Lower bowl portal frame
Figure 7 illustrates Lower bowl portal frame with Raker element
Figure 8 illustrates Three dimensional view of Raker element.

Description of invention:

Generally radial grids and columns along radial grids are provided with minimum numbers to achieve more space under the stadium which results in more span between the column and radial beam. The number of circumferential beams which spans between the radial beams can be increased to reduce the span. In this invented system, the seating area is divided radially into required segments and seating units are made to span between circumferential beam instead of radial beam which resulted in reduction of span length (refer Figure 5A, 5B & 5C indicating the Raker element arrangement over portal frame in Plan, Section and spanning direction respectively).

The structural behaviour of Raker elements are made simpler and economical. The various important outcome of developing Raker units are explained below.

1. The tread slab is made to span between riser beam. This reduces the span of the tread slab and hence reduction of thickness, weight and cost.
2. The riser beam spans between inclined radial beam provided on both sides of Raker element. As the width of the Raker elements are not more, the depth of riser beam provided as per site line requirement in lower bowl is sufficient without having any projection below.
3. The inclined radial beams can be provided with sufficient depth as per the spacing between circumferential beam in the portal frame. The top level of the circumferential beams can be lowered as per the depth of radial beam which will not affect the space below the lower bowl area.

With the above mentioned points, the size, weight and cost of the precast Raker element is considerably reduced.

4. It is to be noted that the invented Raker unit is a 3 Dimensional element. The Raker element when modelled as a 3D element and analysed in finite element analysis software, the model will behave as folded plate which results in lesser moment, shear and deflection. With this we can further optimize the section size upto the minimum requirement as per code recommendations.
5. In the event of regular bleacher unit, the top of the radial beams needs to be cast in stepped shape as per the dimension of the bleacher which leads to difficulties in making form wok and pouring of concrete and execution. The invented Raker element avoids these difficulties as the top of the circumferential beam supporting Raker element is made flat and simple (refer figure 5B).
6. Each Raker element has four supporting points (refer Figure 4B) which are less compared to supporting points provided in L shaped bleacher units.
7. Also the length of the joints between each Raker units is considerably reduced than the total length of joints between L shaped bleacher units.

Design Brief

The element in general is considered without any finish and predominantly designed for the live load as per code provision based on occupancy classification. Loads on the Raker element is transferred from the tread slab portion to the riser and in turn to the main beam. The reactions from the main beam are transferred to the supporting portal / frame structure which are designed to resist the loads. The individual elements of the Raker namely tread slab, riser beam and main beams are designed separately for strength and serviceability requirements as per IS 456 – 2000 considering bending moments and shear force and detailed accordingly.

Additionally, the minimum dimensions of the tread slab, riser beam, and main beam are also verified as per fire rating requirement to satisfy the fire safety norms.

The individual elements of the Raker namely tread slab, riser beam, main beam and overall Raker unit are checked for vibration performance as per AISC design guide 11 for rhythmic excitation and found to be within the acceptable limits.

Design of Connections:

The element is analysed as 3D finite element model using plate element for tread slab & riser beam and line element for main beam with four end supports. The boundary condition is considered as one end pinned and other three ends as roller with loads comprising of Dead load, Live load, Wind load and Temperature load. The finite element analysis provides the magnitude of horizontal movement for the roller ends. Based on this, the joint movement width is found out and provisions are made in Raker element to accommodate the movement. The element is provided with preformed sleeves at the ends of the beam (two sleeves at the top and two sleeves at the bottom). The pinned end is provided with vertical shear rod (mild steel bar) which is designed for horizontal shear force at that joint and filled with non shrink grout. The roller ends are provided with mild steel bar and sealed at top to allow for movement due to expansion and contraction.

The advantages of the invention are:-

1. Suitable for lesser riser depth of seating units
2. Structurally behaves in
a. Small span direction,
b. Provides optimum size and weight.
c. Easiness in casting and execution and
d. Reduction in cost and time
3. It avoids complicated formwork required for riser projection in L-Shaped bleacher seating units.
4. It behaves as a folded plate when modelled and analysed using 3D finite element software and provides optimal dimensions.
5. The number of Connections are less compared to the conventional bleacher system.
6. The top of the raker element supporting circumferential beam is flat which makes the construction simpler.
7. As these are made of precast which is done in factory in a controlled environment, it is advantageous in terms of safety and avoids making air pollution during mixing and execution of in-situ concrete works.

The essential features are detailed herein figure 6, 7 and 8. The invention discloses a precast raker seating system (refer Figure 6, 7 & 8) for circular or oval shaped stadiums and auditoriums comprising of a portal frame with plurality of column and beams arranged in seating area of an oval or circular shaped stadium and auditoriums. A first plurality of support columns C1a, C1b, C1c, C1d positioned in an oval or circular arrangement, the first plurality of support columns having the first end connected to foundation, and a second plurality of support columns C2a, C2b, C2c, C2d positioned in an oval or circular arrangement multi concentric with the plurality of first support columns, the second plurality of support columns having the first end connected to foundation. Further it has a plurality of radial beams RB1, RB2, RB3, RB4 connected to a second end of corresponding radially positioned first and second support columns, and a plurality of circumferential beams CB1a, CB1b, CB1c, CB1d and CB2a, CB2b, CB2c and CB2d connected to a second end of corresponding plurality of first and second support columns. The arrangement includes a plurality of precast 3D rakers R2, R2a, R2b, each raker having plurality of riser beams, a plurality of tread slabs spanning between the said riser beams, and a pair of main beams spaced apart arranged on opposite sides with free ends of tread slabs and riser beams resting on the main beams.

The novelty of arrangement lies in that each raker is positioned and connected at its ends to the corresponding circumferential beams positioned on the support columns.

In another aspect, the invention discloses that:-

(i) The Raker seating elements are applicable for stadiums / auditoriums of any shape.
(ii) Incase of rectangular or square shaped stadiums with straight edges, circumferential beam and radial beam of the portal frame shall be read as horizontal beam and inclined vertical beam respectively.

The examples and embodiments are provided only for the purpose of understanding and none of them shall limit the scope of the invention. All variants and modifications as will be envisaged by skilled person are within the spirit and scope of the invention.