Description:FORM 2
THE PATENT ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
Title of the invention: “Shear Studs in Flat Slab”
Applicant:
NAME NATIONALITY ADDRESS
1. Marwadi University
2. Mr. Shrut Gami
3. Dr. Tarak Vora
4. Dr. Ankur Bhogayata INDIAN Rajkot-Morbi Highway Road, At & Po. Gauridad, Rajkot – 360003, Gujarat
Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is to be performed:

Field of the Invention:
The present invention relates to a civil engineering. More specifically, the present invention is related to the shear studs especially to replace the column head and drop panel in flat slab system by punching shear stud reinforcement system to avail larger clear space. The shear studs are placed in flat slabs around the column support which will reduce the required thickness of the flat slab near to the column.
Background of the Invention:

The composite structural materials have been extensively used in construction of buildings and bridges including flat slabs. The flat slab is defined as a doubly reinforced concrete slab only with or without drops panel or column head and without beams support and mostly used to avoid the beam-column clogging to utilize full height of the floor.
Furthermore, the flat slab systems have gained much more interest from aesthetic and architectural point of view because of their easy framework and reinforcement placements which further reduces the building floor height with the more number of floors having large clear ceiling height and shorter construction time.
The strength of the any structural system (buildings) is mainly dependent on the joint connection of element used during the construction. Generally, in ordinary slab beam floor system, the load is transferred by means of beam to column. Hence, the beam is the primary element to transfer the floor load whereas in the flat slab system, the load is transferred to the columns by slab due to the absence of the beams and flat slab become primary element. In flat slab system, two types of internal stress (bending stress and shear stress) will be generated. The main drawback of flat slab system is lateral stiffness because there is insufficient transverse stiffness to transfer lateral load to columns due to absence of beams.
Moreover, the bending stress in flat slab is generated due to the positive and negative moments at span and the column support which can be controlled by providing sufficient thickness, reinforcement and pre-stress method. On the other hand, shear stress is generated due to the load transfer to the columns by the means of transvers system. In ordinary slab systems, the shear stress is not the major concern as the load is transferred to the beams which is further transfer to the columns so beam is taking the major shear forces. While in the flat slab system, the shear stress is generated near to the column junction as the load is transferred to the column due to absence of beam which give rise to the punching shear effect which is one of the most critical modes of failure in flat slab at column junction. The failure of the structure due to the punching shear stress in the flat slab can be avoided by following options:
Increasing slab thickness
Increase the column dimensions
Providing column drop panel
Providing column head
Providing punching shear reinforcement by shear connectors
Generally, providing punching shear reinforcement by shear connectors in flat slab is most advance and economical solution for both as structural and architecture point of view to control the shear stress. Basically, shear connectors transfer longitudinal shear forces among the beam and linked structural components at an interfacial stratum. It also prevents vertical structural separation from a steel girder. It offers a speedy construction process, reduced vertical spaces, and a lower structural weight may assist in offering inexpensive services to a community. Headed studs are the most common shear connectors used in industry; they feature a steel shank and an anchoring head to resist longitudinal shear forces and the vertical movement of slabs in composite constructions. The punching shear studs (PSS) are widely used as the shear connectors to bear the shear stress in the flat slab systems due to their higher resistance, simple and easy installation and easy framework. The punching shear studs (PSS) are the reinforcement elements consisting of double headed studs welded on an assembly profile which act as a tie and resist the vertical tensile force and slab thickness act as strut and resist the compression force.
US8950151B2 discloses the adjustable floor to wall connectors for use with bottom chord and web bearing joists in which a light steel framed metal joist including an adjustable connector fastened to the joist web that allows one to adjust the length and angle of the joist when attaching to floor and wall systems. The adjustment allows one to install end connectors onto the joists prior to installation while retaining flexibility of orientation during construction. The joist functions in both web bearing and bottom chord bearing configurations. A flat plate distributing member allows one to design a floor system without having to coordinate the positioning of the joist with wall studs. Angle or U shaped members can be fastened to the lower portion of the flat plate distribution member to support joists during construction. The invention further provides a seamless fire stopping system with consideration for acoustic dampening.
EP3366853B1 discloses the prefabricated structural system and assembling method which adopts a tenon-and-mortise-like configuration as a connection for joint and can be used for steel structures, reinforced concrete structures and timber structures.
The above mentioned prior arts discloses the advantage of punching shear studs for structural as well as architecture aspect as they help in avoiding drop panel and column head. The fair amount of work has been done but more experimental investigation will give the better understanding of structural behaviour of the punching shear in the flat slab. Moreover, it is also require to study the effect of the arrangement of the studs on the punching shear capacity and crack propagation in the flat slab.
The present invention relates to the shear studs specially to replace the column head and drop panel in flat slab system by punching shear stud reinforcement system to avail larger clear space with different arrangements of punching shear studs.
Object of the Invention:
The main objective of present invention is to replace the column head and drop panel in flat slab system by punching shear studs reinforcement system to avail larger clear space.

Another objective of the present invention is to find appropriate arrangement of punching shear studs which is more effective to resist the punching shear in flat slab.
The yet another objective of the present invention is to identify the parameters that would affect the punching shear capacity of flat slab with punching shear studs.

Summary of the Invention:

The present invention is related to the shear studs specially to replace the column head and drop panel in flat slab system by punching shear stud reinforcement system to avail larger clear space. The shear studs in flat slab system by punching shear stud (PSS) reinforcement system to avail larger clear space.

In one aspect of the present invention, the test sample is examined with and without punching shear studs of different arrangement of studs.

In another aspect of the present invention, the flat slabs are designed with and without shear studs by various design standards.

In yet another aspect of the present invention, to evaluate the punching shear capacity of the flat slabs with and without punching shear studs.

In yet another aspect of the present invention, to perform experimental stress analysis and deformation behaviour of all test samples.

Brief Description of drawings:
Figure 1 shows the schematic arrangement of shear studs around column
Figure 2 shows detail drawing of shear studs
Figure 3 shows the schematic arrangement of shear studs around column along with slab reinforcement
Figure 4 shows slab specimens PSS arrangements for SL, SO, SR and SOX specimens
Specimen SL It is a slab without any punching shear reinforcements which only contains the reinforcements
Specimen SO It is a slab with orthogonal arrangement of punching shear reinforcements with 8 stud rails and 24 punching shear studs
Specimen SR It is a slab with radial arrangement of punching shear reinforcements with 12 stud rails and 36 punching shear studs
Specimen SOX It is a slab with orthogonal and cross arrangement of punching shear reinforcements

Figure 5 shows the plan view of shear studs arranged in radial manner
Figure 6 shows the bird view of shear studs arranged in radial manner
Figure 7 shows the plan view of shear studs placed in the slab around the column
Figure 8 shows the bird view of shear studs placed in the slab around the column
Figure 9 shows the close view of shear studs placed in the slab around the column
Figure 10 shows the finish view of flat slab element with column having shear studs
Figure 11 shows Comparison of crack propagation of SL, SO, SR and SOX specimens
Figure 12 shows Graph of load vs deflection for of SL, SO, SR and SOX specimens
Figure 13 shows Graph of load vs concrete strain of SL, SO, SR and SOX specimens
Figure 14 shows Graph of load vs steel strain of SO, SR and SOX specimens

Detailed Description of the Invention:
Various aspects of the present application will be described in detail in connection with the accompanying drawings, in order to provide a better understanding of the present invention. Generally, flat slab is used to utilize full height of the floor. When span or load increases, shear near to the support (column) increases. To make flat slab safe in shear near to the support, depth of concrete is increased to take excessive shear in the form of column head or column cap. This column head or column caps are reducing effective usable height and also does not give good aesthetic view within the structure.
The shear studs can be used to reduce the thickness requirement of the flat slab near to the support. Shear which was to be carried by column head or column cap will be taken by the shear studs which are placed within the slab only in radial manner. This will avoid the requirement of column head or column cap, increase effective usable height and give good aesthetic view of structures also.
The present invention is Punching Shear Studs (PSS) which consisting of double headed studs welded on an assembly profile to enhance the resistance of reinforced concrete flat slabs against failure by punching. PSS has higher resistances than stirrups, simple and efficient installation and easy formwork.
The aim of the present invention is to find the punching shear capacity of flat slab with and without Punching Shear Studs (PSS). This comparison of experimental results is done with analytical results derived through different design recommendations. The four elements consisting of square flat-slab of 1000 mm x 1000 mm x 130 mm with interior column placed centrally of size 130 mm x 130 mm with overall height 400 mm are tested experimentally. Out of four specimens, one is without PSS and other three are with PSS with different arrangements of studs.
Table 1: Slab specimen PSS arrangements
Sr. No. Specimen PSS Arrangement Ns Nr
1 SL - - -
2 SO Orthogonally 3 8
3 SR Radial 3 12
4 SOX Orthogonal with cross 3 12
Ns – Number of stud perimeters, Nr – Number of studs
Punching Shear Provision for Various Design Code
Punching shear of the studs are carried out as per three design code (1) Indian code (IS-456), (2) American code (ACI - 318) and (3) Euro code (EC-2). Table 2 shows the comparison of different parameter which are consider in different codes. Where the flexural reinforcement contribution in punching shear is only considered in euro code.
Table 2: The comparison between different codes parameters.
Comparison Between Different Codes Parameters
Design code Critical section perimeter Concrete strength Main ?exural reinforcements Punching shear Studs Column aspect ratio Location of critical section
IS – 456 4 x c + 4 x d C N N C d/2
ACI - 318 a) 4 x c + 4 x d
b) 4 x c + p x d C N C C d/2
EC – 2 4 x c + 4 x p x d C C C C 2d
Where C represent parameter considered and N represent parameter not considered.
Table 3: Punching shear capacity of specimen as per code
Punching Shear Capacity of Specimen as Per Code
Specimen fck
(N/mm2) Punching shear capacity (kN)
IS – 456 ACI - 318 EC – 2
SL 35.67 147.37 196.49 214.3
SO 38.94 - 328.69 340.37
SR 37.41 - 413 425.6
SOX 36.06 - 410.25 423.6

fck = Average cube strength of concrete after 28 days in N/mm2
Experimental details:
Preparation of Form Work
The water proof shuttering ply of 4’ x 8’ of 12mm thickness were used for formwork and 1.5’’ x 3’’ x 10’ wooden plank was used for strengthening of formwork. The measured ply were cut in to size of 1m x 1m and screwed with the wooden planks for strengthening. After that, the side were screwed with the bottom ply in such a way the internal dimension kept as 130mm. Formwork for column is designed in such a way that the slab and column connection can be casted monolithically.
Slab reinforcement
Thermo Mechanically Treated Bars (TMT) bars with the diameter of 10 mm at spacing of 95mm c/c (0.822%) were provided in both the direction for slab flexural reinforcements which is sufficient for flexural strength, so total 22 number of 10 mm diameter required in one slab specimen the cutting length of reinforcement is 1050 mm for slab.
Column reinforcement
For column, total 4 steel bar of 12 mm diameter were used, bars were cut in to the length of 550 followed by bent into length of 250 mm and then all four bars were tied with 3 binding wires of 8mm diameter ties with the use of binding wires.
Stud Rails
TMT bar with 8 mm diameter were used for punching shear reinforcements. Bars were cut in the size of 90mm and followed by the welding of studs on the steel strips so the arrangement and spacing of reinforcement can be done properly in slab during concreting. For each rail three studs were welded on it first studs are centrally welded 55 mm from the one end of the strip and remaining stud were welded 100 mm c/c from first stud. Figure 5 shows the plan view of shear studs arranged in a radial manner after welding. Figure 6 shows the bird view of the shear studs after welding on the steel strip further arranged in a radial manner.
Reinforcement arrangements of the specimens (SL, SO, SR and SOX)
Specimen SL is a slab without any punching shear reinforcements which only contains the reinforcements. Specimen SO is a slab with orthogonal arrangement of punching shear reinforcements with 8 stud rails and 24 punching shear studs. Specimen SR is a slab with radial arrangement of punching shear reinforcements with 12 stud rails and 36 punching shear studs. Specimen SOX is a slab with orthogonal and cross arrangement of punching shear reinforcements with 12 stud rails and 36 punching shear studs. Figure 7 shows the plan view of shear studs placed in the slab around the column. Figure 8 shows the bird view of shear studs placed in the slab around the column and Figure 9 shows the close view of shear studs placed in the slab around the column.
Casting of specimens
Initially, the oiling was done for the framework and prepared cube followed by the dry mixing of materials containing 100 kg of cement, 91.87 kg of sand, 70.75 kg of 10 mm aggregates, 106 kg of 20 mm aggregates and 45 litres of water to get the good uniformity of the concrete. After mixing, the prepared concrete was added into the framework. After addition of sufficient water in dry mix proper hand mixing of materials that the water is uniformly mixed throughout the concrete and good quality of concrete can be achieved. The compacting was done using tamping rod to get the void free concrete or honeycombing left in concrete. After proper compacting of concrete, top surface of specimen is proper levelled by the use of shovel so that proper dimensions of slab are maintained. After 24 hours of casting when concrete gets hard enough the sides of formwork and the column formwork were removed, the bottom slab formwork were removed after 3 days of casting after that curing of specimen is taken out for 28 days. Figure 10 shows the finish view of flat slab element with column having shear studs. After removal of sides and column framework, 28 Days of curing of specimen will be done by sprinkling the water and by covering the specimen with moisturise jute bags so concrete gain its full strength. After 28 days of curing of cube in curing tank, cube was tested for the compressive strength. For each slab specimen three cube were casted at the time of casting of particular specimens so the compressive strength can be calculated by the mean strength of three cube.
Table 4: Compressive strength result of various slab specimen.
Slab Specimen Compressive Cube strength (N/mm2 ) Average Compressive Cube Strength (N/mm2 )
Cube 1 Cube 2 Cube 3
SL 29.5 41 36.5 35.67
SO 40.8 39.76 36.25 38.94
SR 30.24 41.32 40.68 37.41
SOX 29.3 44.69 31.2 36.06

Arrangement of Slab on Load Frame
Slab were tested for punching shear failure on a load frame having the maximum load capacity of 500 kN. Slab was arranged on a load frame in such a way that all four edges of slab specimen are simply supported on the steel beam section, so that slab is simply supported on the edges and free at the centre section. One dial gauge was placed at the bottom center of the slab which have least count of 0.01mm to measure slab central deflection, dial gauge reading were captured by the means of video camera, so with the use of video we can plot load deflection curve. TMT Concrete and steel strain gauges were used to measure the strain, the TMR 7200 model number data logger used to take the reading of strain vs time during the test software is used to fetch the data, and the gauge factor coefficient is required to be entered in TMR 7200 which can be calculated by the equation.
Gauge factor coefficient = gauge resistance x gauge factor x 10-6
Furthermore, TML FLA-2-11 (model number) is strain gauge were used to measure the strain in steel, which have gauge factor coefficient 0.0002532, steel strain gauge is applied on first perimeter stud which is located 50mm from column face. FLA-90-11 strain gauge were used to measure the strain in concrete, which have gauge factor coefficient 0.0002532, concrete strain gauge is applied on the bottom surface of the slab specimen at d/2 distance form column face because the perimeter d/2 from column face is the most critical section for punching shear failure. So for 130mm column width and 105mm effective depth strain gauge were applied 117.5 mm from central point of the slab.
Main embodiment of the present invention, a shear stud in flat slab to replace the column head and drop panel in flat slab system by punching shear stud reinforcement system to avail larger clear space comprising of a steel rod with an enlarged head at one end, and a pointed end at the other, wherein the enlarged head has a diameter greater than that of the rod, and the pointed end has a conical shape for easy insertion into concrete.
Another embodiment of the present invention, said shear stud is inserted into a pre-drilled hole in a concrete slab and welded to the headed stud to form a composite member capable of withstanding shear stress.
Another embodiment of the present invention, said shear stud made by cutting a steel rod to a desired length, forming the enlarged head at one end by hot forging, and forming the pointed end at the other end by cold forming.
Another embodiment of the present invention, the cylindrical steel rod has a diameter in the range of 8 mm to 25 mm, the enlarged head has a diameter in the range of 25 mm to 50 mm, and the pointed end has a length in the range of 90 mm to 100 mm.
Another embodiment of the present invention, said shear stud has cracking load of 200 kN, deflection at cracking load of 5.55 mm, ultimate load of 290 kN, maximum deflection of 6.96 mm, maximum strain in concrete of 0.001626, maximum strain in steel of 0.002234 and orthogonally failure perimeter of 80 cm and diagonal failure perimeter of 80 cm.
Results of the analysis:
Punching Shear Failure and Load Capacity of Specimen SL was calculated with the cracking load of 150 kN, deflection at cracking load of 3.34 mm, ultimate load of 225 kN, maximum deflection of 5.94 mm, maximum strain in concrete of 0.00281 and orthogonally failure perimeter of 60 cm and diagonal failure perimeter of 90 cm. Figure 9 shows the the crack propagation of slab specimen SL.
Punching Shear Failure and Load Capacity of Specimen SO was calculated with the cracking load of 200 kN, deflection at cracking load of 4.3 mm, ultimate load of 295 kN, maximum deflection of 6.35 mm, maximum strain in concrete of 0.002863, maximum strain in steel of 0.002337 and orthogonally failure perimeter of 90 cm and diagonal failure perimeter of 100 cm.
Punching Shear Failure and Load Capacity of Specimen SR was calculated with the cracking load of 175 kN, deflection at cracking load of 3.6 mm, ultimate load of 280 kN, maximum deflection of 6.4 mm, maximum strain in concrete of 0.00256, maximum strain in steel of 0.00244 and orthogonally failure perimeter of 80 cm and diagonal failure perimeter of 85 cm.
Punching Shear Failure and Load Capacity of Specimen SOX was calculated with the cracking load of 200 kN, deflection at cracking load of 5.55 mm, ultimate load of 290 kN, maximum deflection of 6.96 mm, maximum strain in concrete of 0.001626, maximum strain in steel of 0.002234 and orthogonally failure perimeter of 80 cm and diagonal failure perimeter of 80 cm.
Comparison of Experimental load and deflection value of specimens:
After testing of specimen, the punching shear failure pattern of all specimen is different than other one as shown in figure 11 the failure perimeter of specimen with stud has more diameter compare with control specimen SL, also the specimen with orthogonal arrangements of stud has larger failure perimeter compare with other specimens.
The comparison of load deflection value for cracking and ultimate load is shown in Table 5. It is observed that the punching shear load capacity of specimen is increases for both cracking and ultimate failure load however the orthogonal arrangement of stud have more punching shear resistance capacity compare with other specimens. The ductility of specimen SOX have more compare to other specimens because it have large cracking deformation compare with other specimens.
Table 5: Comparison of load and deflection value of specimen
Specimen Cracking Load
PCR (kN) Ultimate Failure Load
PU (kN) Deflection at Cracking Load
dCr (mm) Deflection at Ultimate Failure Load
dMax (mm)
SL 150 225 3.34 5.94
SO 200 295 4.3 6.35
SR 175 280 3.6 6.4
SOX 200 290 5.55 6.96
Percentage increase in a load capacity of specimen:
Table 6 shows the percentage increase in load capacity of specimen with studs compare with control specimen SL. So by providing stud, average 30% of increase in ultimate load capacity and 28% increase in cracking load capacity was achieved.
Table 6: Percentage increase in load capacity of specimens.
Specimen % Increases in Cracking Load % Increases in Ultimate Load
SO 33.33 31.31
SR 16.67 24.44
SOX 33.33 28.88

Comparison of failure perimeter and strain of specimens
Table 7 shows the failure perimeter for specimen, specimen SL have small perimeter compare to the other specimen because of the absence of the studs, however the failure perimeter of specimen with stud has higher diameter it shows the better distribution of load.
Table 7: Comparison of failure parameter and strain of specimens.
Specimen Orthogonal Failure Perimeter Bo (cm) Diagonal Failure Perimeter Bd (cm) Concrete Strain
econcrete (x 10-3) Steel Strain
esteel (x 10-3)
SL 60 90 2.81 -
SO 90 100 2.863 2.337
SR 80 85 2.56 2.44
SOX 80 80 1.626 2.234

Figure 12 shows the graph of load Vs deflection for all specimens. It was observed that the its stats that the specimen SOX have more deflection at same load compare with other three specimen, so that the ductility of specimen SOX is better so it would beneficial for lateral seismic loading.
Figure 13 shows the graph of load Vs concrete strain of all specimens and depicted that after the cracking load the value of strain increase drastically its stats that the elastic liner limit was ended and plastic non-liner behaviour is started for concrete and after cracking, load strain in steel increases and which stats that after cracking of concrete steel starts to take load which is shown in Figure 14. , Claims:We claim,
1. A shear stud in flat slab to replace the column head and drop panel in flat slab system by punching shear stud reinforcement system to avail larger clear space comprising of a steel rod with an enlarged head at one end, and a pointed end at the other, wherein the enlarged head has a diameter greater than that of the rod, and the pointed end has a conical shape for easy insertion into concrete.
2. The shear stud in flat slab as claimed in claim 1, wherein said shear stud is inserted into a pre-drilled hole in a concrete slab and welded to the headed stud to form a composite member capable of withstanding shear stress.
3. The shear stud in flat slab as claimed in claim 1, wherein said shear stud made by cutting a steel rod to a desired length, forming the enlarged head at one end by hot forging, and forming the pointed end at the other end by cold forming.
4. The shear stud in flat slab as claimed in claim 1, wherein the cylindrical steel rod has a diameter in the range of 8 mm to 25 mm, the enlarged head has a diameter in the range of 25 mm to 50 mm, and the pointed end has a length in the range of 90 mm to 100 mm.
5. The shear stud in flat slab as claimed in claim 1, wherein said shear stud has cracking load of 200 kN, deflection at cracking load of 5.55 mm, ultimate load of 290 kN, maximum deflection of 6.96 mm, maximum strain in concrete of 0.001626, maximum strain in steel of 0.002234 and orthogonally failure perimeter of 80 cm and diagonal failure perimeter of 80 cm.

Dated 23rd Apr, 2023

Chothani Pritibahen Bipinbhai
Reg. No.: IN/PA-3148
For and on behalf of the applicant