BIG BEAM 2014-2015
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BIG BEAM 2014-2015Dr.GANESH THIAGARAJAN
TIMOTHY HINES
KRISTEN REYNOLDS
PHANINDRA KUMAR KOSARAJU
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Introduction
We take part in the Big Beam contest conducted by PCI Engineering student design competition for every academic year.
We students of UMKC formed a group and designed a beam under the guidance of Dr. Ganesh Thiagarajan and successfully conducted testing of big beam at MS&T.
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Design Requirements
2015 Rules 2014 RulesSimply supported span 17 ft 16 ftMaximum span 19 ft 18 ftFactored Live Load At each point 16 kips 17 kipsLoad Limit 32 kips to 40
kips35.2 kips to 42 kips
Crack load 20 kips 22 kips
The beam design has to be completed using standard code provisions specifically, ACI-318-11 or the 7th edition of the PCI design handbook.
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Loading Of a beam
The beam shall be loaded by applying two point loads, symmetrically, as shown below.
2014 2015
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Planning
This contest has been divided into various stages :
Concrete Mix design
Structural Design
Construction
Testing
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Concrete Mix design
Sr.No Description 2014 2015 Units1. Cement – Portland Cement Type III 175 735 Lbs.
2. Coarse aggregate – AGG 1- Missouri Type E-rock 1757 1752 Lbs.
3. Fine aggregate – AGG 3 (ASTM C33 Material 1160 1116 Lbs.
4. Water 235 270 Lbs.
5. Admix – Type 2 Air-entraining admixture (MB-VR) 70 oz/yd
6. Super Plasticizer Degussa PS-1466 7.5 oz/cwt
7. Unit Weight 144 144 lbs/cu.ft.(pcf)
8. Water/Cement Ratio 0.320 0.370
9. Air Content 7.5 5 %
10. Max Slump 9.5 10 In.
11. 28 day compressive strength (ASTM C39) 8000 8000 Psi.
We had selected standard MODOT mix having compressive strength of 8000 psi. (Light Weight mix was not available)
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Concrete test
Sr.NO Description 2014 2015 Unit1. Measured unit weight 142 142 lbs/cu.ft.(pcf)2. Air Content 5.1 6.6 %3. Measured Slump 9.5 10 In.4. Average compressive strength at 18
days9527 8986 Psi.
Concrete properties were measured at each stage.Fallowing table provides some of the properties.
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Structural Design of beam
Service Load Design
1. Moment Calculation.
2. Permissible stresses Calculation.
3. Prestress Losses Calculation.
4. Section Moduli determination.
5. Selection of a trial section.
6. Prestressing steel and tendon eccentricity selection.
7. Calculation of actual losses.
8. Calculation actual fiber stresses at transfer.
9. Calculation of stress at service load.
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Ultimate Strength Design
1. Ultimate load calculation.
2. Selection of mild reinforcement.
3. Calculation of stresses in Prestressing tendon at nominal strength.
4. Calculation of nominal moment capacity and cracking moment. Shear Reinforcement Design
1. Anchorage Reinforcement Design.
2. Required Shear strength and nominal shear strength calculation.
3. Check and provide Required web steel.
4. Determine plane at which no web steel is required. Deflection
1. Check if section has cracked under service loads.
2. Camber and Deflection at transfer.
3. Immediate service load deflection.
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Final Design of beam
Inverted T-Beam was selected to reduce the area of cross section. The simplicity of the cross section allows for easy construction and
improved accuracy in prediction of the ultimate load. Strain compatibility was used in determining the stress in the Prestressing
strand at failure. ACI conservative method was used for determining the required area of
shear reinforcement in the initial design.
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Dimensions for beam cross section remains same.
Dimensions of a T-Beam.
Total height 17in.
Depth of web 12in.
width of web 4in.
Width of flange 7in.
BEAM CROSS-SECTION
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Two compression bars of #3 were provided. Two 0.6in diameter grade 70 prestressing strands were provided. End eccentricity 2.416in. Mid-span eccentricity 4.916in. #3 U stirrups were provided @ 6.5in c/c as Web reinforcement. The only difference in design is web reinforcement.
BEAM ELEVATION
2014 2015
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Construction Of Beam
Installation of formwork. Wooden boards and steel forms were used for
formwork. Prestressing of steel.
0.6 inch diameter low relaxation strands were used for the pre-stressing steel.
Each of the two strands were tensioned to 46 kips. Placing of non prestressed reinforcement.
#3 Compression steel bars were placed at a clear height of 1.5” from the top.
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Pouring and Finishing of concrete. Concrete was placed into the prepared formwork and
compacted with the help of a needle vibrator without disturbing the reinforcement.
To achieve an even and smooth top surface for balanced loading the surface was finished with a wooden block.
Releasing of prestressing strand. Formwork was released on the third day of casting the
beam. The prestressed strands were released on the 4th day.
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Testing
The testing of the big beam was performed in the High Bay Laboratory at Missouri S&T in Rolla, Missouri.
The big beam was placed on two metal plates (allowing rotation) at each end to simulate a simply supported condition.
The supports were located at 8ft from the center of the beam on each side
Two MTS actuators were placed between the primary and secondary cross beam to apply the load to the spreader beam.
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LOADING A mark was placed on the spreader beam for loading at 1.5 feet out from the center. There were 6 x 12 x 0.5 inch plates, at each support and loading point along the span of the
beam. The 16bit data acquisition (DAQ) system took readings from the MTS for Load and actuator
displacement, and a 4 inch DC-LVDT was used for reading displacement at the center of beam. The beam was incrementally loaded at a rate of 2 kips every 30 seconds. After each 2 kip increment, the test program was paused and the beam was visually inspected
for cracks.
Crack patterns marked on the beam
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The test was stopped when buckling of compression steel occurred.
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Test results
The load and deflection recorded by the data acquisition system are plotted as a plot of load v/s deflection graph.
Graph shows the initial elastic deformation followed by the “bend over” region.
The cracking load and peak load with peak deflection can be observed in the graph.
2014 Design 2015 DesignCracking load 22.4 kips 22 kips 18.49 kips 20 kips
Peak Load 36.1 kips
35.2kips to 40 kips
32.43 kips
32 kips to 42 kips
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LOAD DEFLECTION CURVE
0.000
6187
0055
1242
236
0.208
3906
2579
1925
0.365
0028
3849
3789
0.416
7934
2127
3292
0.625
7571
4774
8447
0.833
5590
7523
2919
1.041
9459
9177
019
1.250
4622
6335
404
1.355
0827
2872
671
1.563
4836
5916
149
1.771
8348
8975
155
1.823
0067
6677
019
05
101520253035
Mid-span Load Deflection curve
cracking loadpeak loadLoad
Deflection (in)
Load
(kip
s) 18.49 kip
32.43 kip
18.49 kip
32.43 kip
2014 2015
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Observations from testing and graph
The load on the beam steadily increased with deflection up to certain point and then took a much longer time to reach its peak value.
The deflection kept increasing, demonstrating a good ductility with a relatively small drop in the peak load value.
The cracking load was determined from the straight line corresponding to the initial slope of the load deflection curve.
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Conclusions
The beam did well on the fallowing counts. Simplicity of the section resulted in ease of casting, handling and transportation.
Good quality of concreting which resulted in flexural failure by crushing of concrete.
Improvement was needed in the following area: Compression steel buckling is not the preferred mode of failure. A reduced stirrup spacing would
improve this.
Design calculations using the self-developed algorithm were fairly accurate but the algorithm may need to be improved to be on par with commercial software
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Our learnings
Timothy Hines
The Big Beam Competition provided an excellent opportunity to learn and apply prestressed concrete design and practice my skills in planning, construction, testing, and writing. I have never been to a pre-casting facility prior to this competition and it was very educational to see how prestressed concrete components are constructed.
Phanindra Kumar. Kosaraju
Big Beam competition is an excellent opportunity for me to relate my subject directly to the design. Designing of a beam with load limitations, cost effective and also with less weight is a great challenge for us. I had learnt a lot to accomplish this. By this competition I had improved my skills within testing, and writing. Our faculty advisor Dr.Ganesh Thiagarajan had supported us throughout the competition.
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Acknowledgement
Big Beam Team sincerely thanks-
Dr.Ganesh Thiagarajan PhD. P.E. Associate Professor – University of Missouri – Kansas City , faculty advisor for Big Beam Team – UMKC.
Structural engineering association of Kansas & Missouri council for monetary encouragement, ($1500) which was used to test the beam.
Dr. John Myers PhD. P.E. Associate Professor and Mr. Brian Swift, Senior Research Design Engineer – Missouri Science & Technology University- Rolla, providing the facility to test the beam.
Mr. Mark Simpson, Coreslab Structures who has always been a great help throughout the design and construction process and transporting the beam to Rolla.
Coreslab Structures (Kansas) Inc. PCI producer member sponsor for Big Beam, for construction of beam.
Mr. Terry Fleck, Coreslab Structures for co-ordination with construction team and arranging transportation of beam to testing facility.
Civil and Mechanical Engineering Department, University of Missouri Kansas City for administrative support.