INTRODUCTION

This career episode describes my engineering activities to conduct “ultimate strength and parametric study on rectangular slabs with mixed boundary conditions”. In this project I carried out my responsibilities as postgraduate student.

Project Title	Ultimate Strength and Parametric study on rectangular slabs with mixed boundary conditions
Role	Postgraduate Student
Name of the Organization	M. S. Ramaiah Institute of Technology
Location	M. S. Ramaiah Institute of technology, MSR College, MSR Nagar, Bengaluru, Karnataka, 560054
Duration	1 Year ( July’ 13 – June’ 14)

BACKGROUND

M.S. Ramaiah Institute of Technology is a privately owned engineering college located in Bangalore, Karnataka. The college was established in 1962 and is affiliated to the Visvesvaraya Technological University (VTU). Since August 2007, RIT has been offering undergraduate and postgraduate Programs in Engineering and management sciences. It also offers programs in various disciplines leading to award of PhD. In 2013, RIT was ranked 16th best engineering college in India by India Today and Neilson. MSRIT is renowned because of providing practical based learning to its students. There are laboratories containing state of the art equipment that provide opportunities for students to gain hands on experience.

The project was solely based on certain desired objectives. It was mainly aimed to compare ultimate load with existing method (Johansen’s load) and proposed method (Enhanced yield line method), with practical values. Usually the design of slab involves elastic analysis, leading to uneconomical design; however due to the involvement of membrane force within the slab, I predicted a method to calculate ultimate load relatively accurate for two-way slab with three sides fixed and one side simply supported. The material used for this specimens are reinforced high strength self compacting concrete (HSSCC) with a grade of M70, and the thickness of slab is 75mm. A parametric study on membrane action for rectangular slabs was also conducted in order to comprehend the effects of changing parameters in the development of ultimate load. For this purpose, we casted six slabs and compared by changing influential parameters such as aspect ratio, concrete cube strength, grade of steel, coefficient of orthotropy, percentage reinforcement, and effective dept.

The responsibilities which I carried out as a Postgraduate student during the project includes:

• Responsible to prepare concrete mix according to mix design.
• Responsible for taking values when maximum deflections and crack widths were found, and manually calculated the same values with yield line formula.
• Drawn comparison between the values of both methods.
• Predicted the formula for ultimate strength for the slab which is restrained three sides and simply supported in one longer side.
• Attended regular meetings with the supervisor.
• Carried out extensive documentation and prepared project report.

Figure 1 below gives the organizational chart of my project. My position is clearly highlighted in Light Blue:

PERSONAL ENGINEERING ACTTIVITY

Firstly, I designed a line diagram to distribute loads equally as shown in the following figure, where the pressure load was represented by a point load, which approximately distributed to the total load as a uniform pressure on entire area, thereby recorded the deflections and crack widths from the specimens.

Thereafter, I manually calculated different parameters, such as crack width and deflection. I found difficulties while handling this task. Therefore, I made a spreadsheet to make the calculations easier. I was also obligated to calculate deflections by using stiffness matrix method of 6 rows and 6 columns. For that purpose, I made a program in MAT lab and simplified the calculations.

I was also responsible to perform calculations for deflections pertaining to different formulae. At first, I calculated deflections by Park’s equation. The computed ultimate load was obtained from an assumed deflection of ultimate load for all HSSCC slabs with an average value of 0.37 times the thickness of the slab was used. The ultimate loads had been computed and compared with the tested data.

Afterwards, I conducted a parametric study to find out the effects of changed parameters against the load enhancement of the tested slabs. For that purpose, I preferred to use membrane action of slab using park’s formula with three sides fixed and one simply supported by changing all parameters such as reinforcement ratio, concrete grade, steel grade, span/depth, aspect ratio and coefficient of orthography. The Load enhancement was expressed as the load over and above the yield line load. Load Enhancement = (qu-qj/qj)*100 Where, qu = intensity of load at ultimate qj = intensity of Johansen’s load

I carried out analysis to observe the effects of modified parameters individually. I observed that the change in coefficient of orthotropy from 0.3 to 1 with an increment of 0.1, caused a decrease in load enhancement. Moreover, the concrete cube strength was changed from 40 N/mm2 to 100 N/mm2 with an increment of 10 N/mm2 keeping all other variables constant. The results had shown that the load enhancement increases with the increase in the cube strength. Similarly, I observed the corresponding changes in load enhancement by varying all the remaining parameters that are mentioned above. All the results can be summarized as: the increase in load enhancement was experienced only by increasing grade of concrete and span / depth ratio. On the other hand the load enhancement decreased by the increase in coefficient of orthotropy, aspect ratio, steel grade and percentage of reinforcement.

Furthermore, I found that experimental ultimate load for the partially clamped slab with the edges fully fixed and one longer edged simply supported was more than the computed Johansen’s load. The load enhancement of the tested slabs varied from 25% to 52%. I found out that the load enhancement was established due to the development of membranes force at the boundaries.

In order to predict the ultimate load of the tested slabs, the yield line load predictions had been calibrated and I proposed the equation as follows:

Intensity of ultimate load (N/mm2) = 0.514 * intensity of yield line load (N/mm2) + 0.105

The calibrated enhanced yielding load was able to predict the ultimate load satisfactorily.

After carrying out parametric study, I concluded that the load enhancement is more if thinner slabs are used with higher grade of concrete and lesser grade of steel with lesser percentage of reinforcement and aspect ratio.

I always had direct communication with the laboratory manager and laboratory technician about the machine equipment used during my project. They provided me the most valuable knowledge based on their experiences about handling and operating the equipment more efficiently. I always followed the safety measures at work and also guided my team members regarding that.

I arranged weekly meetings with the team members to discuss the progress of the project and to decide the upcoming part. In addition, we used to discuss the problems encountered while performing the assigned tasks and helped each other to resolve them. I had to lead the project team, so I efficiently utilized my interpersonal and managerial skills to ensure the team coordination and come up with the desired deliverables as per the timeline. At the end I gave a presentation on my project.

Summary

The project was a great opportunity for me to gain hands on experience about HSSCC rectangular slabs. I leveraged my previous engineering knowledge to conduct a study on strength and deformation behavior characteristics. The project has bolstered my overall operational and managerial skills. I also carried out a great responsibility to lead my team, which made me confident to handle more challenging projects in future. This project acts as a milestone in my academic career that would help me in future endeavors to become a professional engineer.