BIG BEAM 2014-2015Dr.GANESH THIAGARAJAN

TIMOTHY HINES

KRISTEN REYNOLDS

PHANINDRA KUMAR KOSARAJU

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.

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.

Loading Of a beam

The beam shall be loaded by applying two point loads, symmetrically, as shown below.

2014 2015

Planning

This contest has been divided into various stages :

Concrete Mix design

Structural Design

Construction

Testing

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)

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.

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.

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.

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.

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

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

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.

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.

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.

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

The test was stopped when buckling of compression steel occurred.

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

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

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.

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

 

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.

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.