5
Results and discussion
——————————————————————————————————-
In some extent, we are doing characterization of our loading frame. means we will have to set its limitation also for the further testing of structural models prototype and separate component so there are so many other aspects also about which we will have to understand rather they having strength related significance or not. In that case, we have to follow IS 14877 Part-1 for its geometrical characterization. First of all the test was performed is flatness of top surface.
5.1 Flatness of top surface
As per 14877 Part-1 permissible limit for flatness of top surface can be calculate by formula given bellow
For Grade-1=.015+(.04*L1)/1000
For Grade-2=.03+(.06*L1)/1000
For Grade-3=.06+(.08*L1)/1000
Table 5.1: Readings of flatness of top surfaces
S.no. Distance from left column
(mm) Undulations (mm)
Permissible limits
Grade Limits
1 100 0.06 Grade1 0.085
2 200 0.08
3 250 0.03
4 400 0.07 Grade2 0.135
5 600 0.14
6 750 0.09
7 900 0.13
8 925 0.09
9 1210 0.10 Grade3 0.20
10 1570 0.17
11 1690 0.12
12 1760 0.09
So by the interpretation of results obtain maximum undulations in the top surface exceeds to Grade 1 and Grade2 respectively but they are within Grade3 limit. So its top surface is of grade 3 type of hydraulic press.
5.2 Flatness of bottom surface
For theoretical limits of bottom surface, we will use same formula as earlier for top surface.
Table 5.2: Readings of flatness of bottom surfaces
S.no. Distance from left column(mm) Undulations (mm) Permissible limits
Grade Limits
1 100 0.06
Grade1
0.085
2 250 0.08
3 370 0.03
4 460 0.07
Grade2
0.135
5 600 0.14
6 780 0.09
7 910 0.13
8 925 0.09
9 1280 0.10
Grade3
0.20
10 1520 0.16
11 1630 0.12
12 1730 0.09
5.3 Parallelism
For this there following two criteria’s.
For Grade-1=0.03+(0.08*L2)/1000
But not less than 0.06
For Grade-2=0.06+(0.12*L2)/1000
But not less than 0.12
For Grade-3=0.12+(0.17*L2)/1000
But not less than 0.20
Table 5.3: Readings of Parallelism surfaces
S.no. Distance from left (mm) Undulations (mm) Permissible limits
Grade Limits
1 100 0.13
Grade1
0.17
2 250 0.28
3 370 0.12
4 460 0.31
Grade2
0.27
5 620 0.34
6 810 0.24
7 920 0.26
8 960 0.14
9 1250 0.1
Grade3
0.4175
10 1535 0.38
11 1630 0.35
12 1730 0.29
So we had seen experimental values as well as theoretical values with help of which we can say that our loading frame is characterize as Grade3 type as per IS-14877 part1 defines for straight sided hydraulic press.
5.4 Strain Analysis
For functioning as a hydraulic press or a testing machine, it should possess minimum flexibility as minimum as possible. So our loading frame should be as rigid as possible is desired.
Here first we have to do the theoretical calculation for our box type-loading frame for calculation of distributed moment over the joints. Because it’s a symmetrical frame
with symmetrical loading conditions so carry over moment will be canceled due to symmitricity of box frame so the step included in calculation are as follows.
Its corners ware welded so we can assume it as rigid jointed frame. so its line diagram will be as shown bellow.
Fig.5.1: Line diagram of frame
Fixed end moments Mab= wl/8
Mba=-wl/8
Similarly Mdc=- wl/8
Mcd= wl/8
And because there is no such load or moment on span DA and BC so
Mda=Mad=0
And Mbc=Mcb=0
All corners ware assumed to be rigid so stiffness of each member
Kab=Kba=Kbc=Kcb=Kcd=Kdc=Kda=Kad= 4EI/L
So Distribution factor for AB= 18/43
Distribution factor for AB= 25/43
So ultimately after calculation of moment distribution we got the expression for moment magnitude is.
Mab=Mba=Mbc=Mcb=Mcd=Mdc=Mad=Mda= 25wl/344
Final moment on top of top beam at mid span is
M=61wl/344
And now we can also calculate stress with the help of bending equation i.e. . . .
M/I=o/y=E/R
On which o=MY/I
Moreover, with help of stress we can find strain occur at top of flange of top beam by help of relation given in hook’s law.
ℇ=o/E
for column because there is not any load in whole span only fixed end moment will be distributed over whole span. So at mid where we are finding strain only this moment will acting. And rest of calculation of strain are same as for beam.
5.4.1 Experimental calculation of strain
Because the output which was founded from strain gauge and ultimately from data logger are in form of voltage signals in ppm unit. So we have to convert it in to proper strain format. For that formula should be used is as follows.
strain (micro strain)=(4*(initial reading-final reading))/Gn
Strain in beams
We have done the experiments and results of both with percentage are shown in table given bellow. Based on which we can do comparative study of actual and theoretical results. With help of which we can conclude several things like strain displacement fixity of supports etc.
Table 5.4: Readings of strain in beam
S.no.
Load (KN) Strain in top flange experimental (micro strain) Strain in top flange theoretical (micro strain)
%Error
1 0 0 0 0%
2 51.14 35.23 37.03 -4.88%
3 102.24 74.35 74.049 0.40%
4 149.2 110.33 108.06 2.10%
5 199.88 151.20 144.78 4.44%
6 249.90 187.13 180.99 3.39%
7 299.60 226.84 216.98 4.53%
8 349.20 256.96 252.91 1.59%
9 400.58 298.36 290.01 2.87%
After the results, we had seen that there is some difference between these two strain values of results. So bar chart considering comparative results of both shown bellow.
Fig.5.2: Comparison of strains between experimental and theoretical
There could be two reason behind this difference between these two readings of strain.
Due to error in measurement
Due to fixity of the supports or joints
However, we can check reliability of our sensing and instrumentation system by plotting graph between load and strain, which is ultimately load verses displacement plot. Graph between load and displacement shown bellow.
Fig.5.3: Plot between load and strain
Here we found linear relation between load and displacement, which was desired so we can believe on our setup and reading at some extent.
Strain in columns
Because there is no load in span of column, so not any excess bending moment will act on both of them and there is only fixed end moment and shear force because we
know that there is negligible chances that steel column will fail due to shear force. So total moment in whole column will be-
M=25wl/344
Distributed in span of column.
Table bellow shows comparison between experimental and theoretical values of strain in right column.
S.no
Load (KN) Strain in extreme flange fiber(micro strain) Theoretical values of strain (micro strain)
1 0 0 0
2 51.14 1.51 10.9297
3 102.24 13.58 21.8506
4 149.20 9.35 31.8864
5 199.9 4.95 42.7201
6 249.91 4.27 53.4096
7 299.60 22.01 64.028
8 349.20 28.47 74.6301
9 400.58 32.18 85.612
Table 5.5: Readings of strain in right column
So to find differences between theoretical and experimental values we had plot a bar chart between experimental vales of strain. Shown bellow.
Fig.5.4: Comparison of strains between experimental and theoretical
Table 5.6 Readings of strain in left column
S.no
Load (KN) Strain in extreme flange fiber(micro strain) Theoretical values of strain (micro strain)
1 0 0 0
2 51.14 1.87 10.92
3 102.24 14.02 21.85
4 149.18 10.06 31.89
5 199.89 7.52 42.72
6 249.91 7.89 53.41
7 299.61 20.76 64.02
8 349.19 29.81 74.63
9 400.57 34.89 85.61
We have also done comperative study of results founded theoritically and experimentally for respective values of loads.
Fig.5.5 Comparison of strains between experimental and theoretical
5.5 Deflection analysis
for verifying the frame in structural aspect there is one more study we have done. It was study of deflection at various characteristic loads. For obtaining theoretical values we used moment distribution first to find moment and then for finding the deflection we used energy method.
Deflection of top beam δ=.0064wl*l* l/EI
So we have don e comparative study of result founded from experiments and thory.
Table 5.7: Results of deflections
S.no
Load (KN) Experimental deflection (mm) Theoretical deflection (mm)
1 0 0 0
2 51.14 0.031 0.028
3 102.24 0.057 0.056
4 149.19 0.088 0.081
5 199.89 0.1102 0.11
6 249.90 0.1386 0.13
7 299.6 0.1647 0.16
8 349.19 0.1981 0.19
9 400.56 0.2206 0.22
Bar chart indicating towards comparison of theatrical and experimental data shown bellow.
Fig.5.6: Comparative results of deflection
Fig.5.7: Plot of load verses experimental deflection data
SUMMARIZED RESULTS AND DISCUSSIONS
Characterization of frame had been done satisfactorily and results are as expected were within the limits means acceptable.
As per geometrical specification our frame comes under the Grade-3 as define in Indian standard code IS 14877 part-1.
And as per structural performance basis its result are also satisfying codal provision of IS-15747 2007 i.e. maximum deflection as a hydraulic press is 17mm for per 1000 mm of span length.
In comparative study there were some discrepancies for them there may be of two conclusions.
It may be due to error in experimental setup
Or may be due to design fault because it is impossible to form a rigid joint or connection in actual practice and our all calculation are done by assuming as all joints are rigid.
4
Experimental studies
——————————————————————————————————-
Like in any characterization, we have to find the upper and lower limitation about that instrument or whatever is characterized. And that will also help in finding that how much it is reliable. So to know about structural performance or can say structural health monitoring is a part of characterization of our loading frame. But in characterization this not only test which we will have to perform there is some more like flatness test of top and bottom surface both and parallelism test etc because currently we would not have any standards specifically for such types of loading frame but we have some codel provision for testing machine in which we can apply static mechanical loads on test specimen. That are provisions for hydraulic press given in IS codes because in our loading frame we used hydraulic jack arrangement for loading purpose and we had applied static load and also we designed it for testing of structural modal and components so we can characterize it as a two column straight sided hydraulic press as per define by bureau of Indian standard in IS codes defined for hydraulic presses.
4.1 Testing of geometrical parameters
First of all we will check is geometrical parameters assuming code IS-14877 Part1 as standard. Tests given bellow.
4.1.1 Flatness of top Surface
In the test we mount, dial gauge on a magnetic base which is again attached with a standardized zero roughness too smooth base plate and slide towards another column to left one and noted the major readings on dial gauge.
4.1.2 Flatness of bottom Surface
We have done or can say repeated same experiment as stated earlier in above paragraph with bottom surface to check the same and noted down major undulations on dial gauge.
4.1.3 Parallelism
It is the test to measure the relative undulation between the surfaces of frame with respect to each other. For this we have to fix dial gauge in a smooth base stand and slide it towards another column from one. We can left 25mm distance from both column as given in Indian code. Means that areas are free to uneven because of joints.
Fig.4.1: Parallelism testing
4.2 Structural performance investigation
Structural performance of any structure consists of several things like it’s rigidity against various loads like in bending shear torsion etc. in our case to find rigidity of structure experimentally we can perform strain analysis using strain gauges and LVDT’s. for this we have to mount strain gauges at further places where stress are supposed to be critical. Since it is a self-straining structure, so it was assumed that no load or moment is supposed to be transfers to ground or foundation. So all strain gauges are placed at mid span and extreme outer fiber.
Locations of strain measurements where we attached strain gauges are shown in figure given bellow
Fig.4.2: Location of strain gauges
We have also done analysis for deflection caused by bending of members at mid span with help of LVDT’s and its digital indicators.
Experimental setup of strain gauges data logger, including LVDT’s shown in figure bellow.
Fig.4.4: Experimental setup
3
Experimental SETUP
————————————————————–
3.1 Instrumentations setup
Because there are so many difficulties in analogue signals about collection and retrieval of result data. So we are performing such the experiment which gives us results in digital form. Which needs an electronic data acquisition system which also enable to store the data which can be retrieved when required that’s why we have to involve some electronics Instruments and circuits which are as follows
(i) Multi-channel Digital Automatic Data Loggers for Strain measurement.
(ii) Strain Gauges
(iii) Wheat stone bridge
(iv) Load Cells & Digital Load Indicators
(v) Displacement Transducers
3.1.1 Multi-channel Data Logger
It’s a major part of data acquisition system as name define its work itself it logs the data in it in its own units or we can also define them. In some cases it also works as an actuator which means it gives excitation or input to the sensors but which haven’t such excitation system in that cases we have to involve external excitation system or external controlled supply like some battery or other one. In our case we are using a
sixteen channel data logger names DT-85 no. of channels define that how many sensors we can attach and read the values. So in our case we can read 16 sensors at one time instant. There is also such type of arrangement is available by which we can expand the no of channels with the help of channel expansion module up to 10 channels. It is also preferred as an actuator for some small range of excitation from 300 mille volt to 3 volt. In this case it receives the signals in certain fix time interval vary from 1 second to 30 seconds. We can also set it in a triggering system by which we can control the frequency of data collection with the help of a small button. Its having some memory in which it can store data up to a certain limit we can retrieve in the system in excel sheet or we can also retrieve it in some other storage device with the help of USB port. Data loggers are available in different frequency range small frequency data loggers are static loading cases.
Fig.3.1: Data logger
For experiment dynamic loading high frequency data loggers are required. Our data logger is of small frequency range so we using it for our case.
3.1.2 Strain Gauges
Again, name suggesting instruments or can say transducer used for strain measurements is called strain Gauges over a free surface of any structure. They follow different principals according to their types. That means there are different types of strain gauge are available according there range least count type of measurement and scope which are as follows.
(i) Mechanical strain gauge
(ii) Acoustical strain gauges
(iii) Optical strain gauges
(iv) Pneumatic strain gauges
(v) Electrical strain gauge
3.1.2.1 Mechanical strain gauges
These are involves with mechanical arrangements in its working principal consist of two jaws clamped with the surface or structural on which strain is desired by means of spring or some clamping arrangements at certain specific distance which is called gauge length. So when specimen or component was loaded it get elongated so the jaw clamped with component is also get displaced from its original position. And this displacement is amplified and by some mechanical arrangement and visualized on the proving ring or some dial meter. Due to its working principal in some extent, it can also be called extensometer. These are also having so many types are as follows.
(i) Berry’s strain gauge
(ii) Huggenbeger extensometer
(iii) Johnsson extensometer
Fig.3.2: Berry’s strain gauge
3.1.2.2 Acoustical Strain Gauge
Its working principal is based on the propagation or traveling of wave. Which mean when bonded wire is stressed or elongated its natural frequency get altered or differs from its original values so we have to amplify this change in terms strain developed. These types of gauges are highly accurate in nature.
3.1.2.3 Optical strain gauges
As the name suggests it is based on the principal of optics. In this type of gauge the pivot jaw containing a mirror and the other jaw o edge is clamped with surface of component on which strain is desired. So when the component is stressed or elongated the pivoted edge which is carrying mirror got tilt and that ‘s why mirror will also got tilt and the reflection of the illuminated scale is visible on this mirror which can be read with the help of telescope. There are two types of optical strain gauge s are known named as follows.
(i) Marten’s optical strain gauge
(ii) Tuckerman optical strain gauge
Fig.3.3: Marten’s optical strain gauge
3.1.2.4 Pneumatic strain gauges
The working principal of these type of gauges are based on relative study of discharge of air between two orifice in which one is fixed and other is variable. Sensitivity of these type gauges are 100000 times of other types. And can be used for both static and dynamic condition.
Fig.3.4: Pneumatic strain gauges
3.1.2.5 Electrical strain gauge
It also having three types but hear we are using resistance so we will explain about resistance type only. Others name are as follows.
(i) Inductance type
(ii) Capacitance type
(iii) Resistance type
These strain gauges works on the principal that they amplify the mechanical deformation or change of structural component in electrical output. It may be of any type in impedance or resistance. It consists of a conductor circuit in its structure attached with component. So when conductor is starched or compressed it results change in resistance of conductor because cross sectional area of conductor got change either increased or decreased. Change in resistance per unit strain is known as gauge factor which indicates about the sensitivity of strain gauge. There different types of strain gauges are available are as follows.
(i) Un-bonded wire strain gauge
(ii) Bonded wire strain gauge
(iii) Weldable strain gauge
(iv) Foil strain gauge
3.1.2.5.1 Un-bonded wire strain gauge
This type of strain gauge gives electrical signal output of relative displacement of one body to another body. It consists of a stationary frame and a movable platform and pins made of insulated material are in those pins loops of wire are wounded
which are in pretension. So when component is elongated or contracted the relative movement between frame and platform will occurs and tension in loops get alters after that this is connected with for arm wheat stone bridge for the accuracy purpose.
These type of strain gauges are also used for the measurement of force pressure acceleration etc.
Fig.3.5: Un-bonded wire strain gauge
3.1.2.5.2 Bonded wire strain gauge
it consists of wire bonded around a core which is sandwiched between two insulating layers. Sometimes core is flattened this then this is called Flat-grid strain gauge type is also sub divided into three another types.
(i) Wrap-around wire strain gauge
(ii) Flat-grid strain gauge
Fig.3.6: Bonded wire strain gauge
3.1.2.5.3 Weldable strain gauge
They are mainly invented due to ease in installation working principal is same as that of other resistance based strain gauges. There installation is easy. And they can work in any environment. It consists of strain sensitive material and stain component is highly insulated by compacted ceramic. Stain gauge is spot weld on structural component and when structure is stressed the stress get transmitted through weld into strain tube. These types of strain gauges also have dynamic application.
Fig.3.7: Weldable strain gauge
3.1.2.5.3 Foil strain gauge
This type of strain gauge consisting of a membrane of larger width as compare to its thickness and it is made up of strain sensitive material and principal is same means when structural component is strained foil also experiences strain and its resistance get changed. A suitable cementing material should also be required for bonding of strain gauge with structural component.
The strain gauge which we are using is of foil type having following specification
Resistance – 120 ohm and 350 ohm lead attached.
We have also used wheat stone bridge system for better accuracy purpose.
Fig.3.8: Foil type strain gauge
3.1.3 Wheat stone bridge
It’s an arrangement of resistances used for achieving greater accuracy in measurement. It consists of two resistances connected in series an again they connected parallel with another two resistance of same resistance value.
Fig.3.9: Wheat stone bridge
3.1.4 Load Cells & Digital Load Indicators
As the name suggests it is an electromechanical device or equipment used to read the value of load is called load cell gives the value of load in digital format. It can be say that it’s a transducer as it converts mechanical forces into the form of electrical energy or signals .Its basic principal of working is based on the strain gauges. The internal structure or sensing system of load cell consists of a Wheatstone full bridge system of strain gauges. So when load is applied then the strain in strain gauges will increases linearly because of another principal hook’s law and because of that resistance will also increasing linearly with the deformation. There are so many different types of load cells are available according to different criteria’s as follows.
3.1.4.1 According to construction material
(i) Aluminum load cell
(ii) Tool steel load cell
(iii) Stainless steel load cell
3.1.4.2 According to external structure and working
(i) Canister type
(ii) Single ended beam type
(iii) Double ended beam type
(iv) Cantilever beam type
(v) S-beam type
(vi) Platform type
Hear we used a canister type of load cell having capacity of 50 ton or 500 KN shown bellow.
Fig.3.10: Load cell
3.1.5 Displacement Transducers (LVDT)
Displacement transducer name LVDT expands and form linear variable differential transducer. Its function is to convert linear displacement caused by any mechanical mean into an electrical signal in output containing magnitude and direction. Its
internal structure consists of transformer means its having two coil named primary and secondary. Primary coil wounded at mid over a hollow cylindrical and non-conductive generally made up of glass polymer. And secondary windings are wounded on top and bottom on hollow tube means on both sides of primary one. A core made up of ferromagnetic material and a its length should be a fraction of length of whole assembly containing insulator tube primary winding and secondary winding. So that when core energized primary one and move towards bottom coil flux changes and voltage, will decreases so voltage difference increases and readings are shows on display. Our LVDT’s maximum range to measure displacement is 40mm that is 20mm in positive side and another 20mm are on negative side. An image of LVDT and its indicator display is shown bellow.
Fig.3.11: LVDT
Fig.3.12: Digital display of LVDT
We also require some more instruments that are not have any electronic phase Name as.
3.2 Loading frame
We have given its brief introduction earlier. And our loading frame having following specifications.
3.2.1 Sectional properties of I-beam
(i) Depth of the section h = 600 mm
(ii) Width of the flange bf = 210 mm
(iii) Thickness of the flange tf = 20.8 mm
(iv) Thickness of the web tw = 12 mm
(v) Radius at root r1 =20 mm
(vi) Depth of web d = h- 2(tf + r1) = 518.4 mm
(vii) Section Modulus Ze= 3060.4 x 103 mm3
(viii) Plastic Modulus Zp = 3510.63 x 103 mm3
(ix) Weight per Meter W = 1202.71 N/m
(x) Capacity of frame=500 KN
3.2.2 Specifications of stiffeners
(i) ISLC 75 section
An image of loading frame is shown bellow
Fig.3.13: Loading frame
3.3 Hydraulic Jack
We can apply large mechanical loads with help of a suitable hydraulic arrangement in a setup. Consists of a pressure gauge with analog dial, piston, cylinder, oil filling and exit arrangement and a lever by which we can apply pumping force and it also have a release valve to remove or to release pressure.
The hydraulic jack we used having maximum capacity to apply load of 50 ton or 500 KN its least count is 2 KN and it also have locking arrangement for lever pump.
Fig.3.14: Hydraulic Jack
3.4 Other accessories
It consists of accessories like adhesive, spacers shielded wires, special cello tape for strain gauges, stands for LVDT, Teflon sheet, soldering iron, machine and wire, flux etc.
..