Ultimate Load Capacity of Reinforced Concrete Slab

Table of Contents

CHAPTER 1

1.1 Introduction

1.2 historical background

1.3 Aim

1.4 Objective

1.5 Dissertation outline

CHAPTER 1: INTRODUCTION

1.1 Introduction

Researchers at London South Bank University have spent time investigating the behaviour of slabs and they came up with numerous prospective approaches regarding the analysis and design of reinforced concrete slab. In being able to determine the ultimate load capacity of a reinforced concrete slabs, yield line design or method is the approach used for this dissertation.

Reinforced concrete slab is an imminent of several up-to-date buildings and bridges. When it comes to evaluating or designing a reinforced concrete slab, elastic analysis methods is becoming a powerful tool now days, because of effective computer applications availability (e.g. utilizing robot and finite element analysis techniques). Thus, more often it is useful to use both of them to estimate slab deflection under service load (to establish the ultimate limit state, ULS).

Hence, after yielding of the reinforcement in a slab, a normal elastic analysis does not consider the redistribution of moments that have occurred. In other words, elastic analysis could give totally unexpected estimate of the ULS capacity. In some circumstances where the USL is dangerous, more material is probably needed than the requirements in the design. This could be for example more concrete or steel reinforcement. To show this, different analysis could be conducted such as non-linear finite element analysis. However, such kind of analysis requires experience of operator and computer assets; therefore, this kind of experiment is not advisable. On the other hand, yield line method could be run which is a much easier plastic analysis approach. Now a day, the popularity of using yield line method has reduced due to the absence of effective computer based application.

The first man to use the word ‘yield line’ was Ingerslev, which appeared in the first article: The Structural Engineer in 1923. Soon after, a theory supporting the whole concept of yield line method was established by Johansen, later demonstrated as the upper bound plastic analysis method. Normally a reinforced concrete slab tends to have a low percentage of reinforcement, therefore yielding of the section will occur. Herby the practice of plastic methods is correct. In analysing existing and expensive slab used in design, extra strength can be recognised due to the advantages of yield line method being applied.

In the past, a traditional hand-based technique was used which consisted in assuming a yield line design and then using the work method to calculate the matching load carrying capacity. A different yield line design should be discovered as a result of the upper bound nature. This means that more time is going to be consumed. Still, worrying is the concept where the critical patter may have been done wrongly or misused, as well as risky estimate of load capacity has been done. Having said this, many experts have switched to compute based elastic methods which are considered to be safe (Matthew Gilbert, Linwei He and Thomas Pritchard, 2015).

Therefore, reinforced concrete slab could be resolved by using elastic and plastic method, yet again, to resolve the same size slab using elastic and plastic methods, we might get different results from the actual slab value, this indicate that one is better than the other. A question that can be imposed regarding the above statement could be: which analysis is good enough?

From the application and results of these two methods there are advantages and disadvantages; so in order to be able to answer the question it has to be done more research and compare the advantages and disadvantages for elastics and plastics method. Hence, this project is going to concentrate on analysis method.

1.2 Historical Background

Yield line theory was invented by A. Ingerslev in 1923, shortly after edited by Danish engineer and researcher K.W Johnsen in 1943, his book was translated in English by Cement and Concrete Association, 1962, and other researcher based on Johansen’s they improved and expand his genuine work. Therefore, the acceptability of the theory is well-recognised making yield line theory of considerable universal design. During the 1960s, 1970s and 1980s substantial amount of theoretical work has been done and extensively stated all over the world regarding on yield line analysis for slabs (Toum, 2004).

General testing was take on to prove the acceptability of the theory in order to support the theoretical work. There was reasonable agreement between the theoretical, experimental yield line pattern and the ultimate load. The variances between the experimental and theoretical were minors. Where restraint was adopted during the experiment to reproduce non-stop results, loads forecasted by the theory were much smaller than the ultimate loads which reached at failure because of the member force (Toum, 2004).

1.3 Aim

To find the elastic and plastic method of reinforced concrete slab analysis utilizing yield line and finite element method respectively. From the results the experiment will be compared with the analysis results to evaluate the efficiency of each method. Then the nearest approach for structural analysis to be suggested based on advantages and disadvantage.

1.4 Objective

• Investigate about elastic and plastic methods of analysis to obtain comprehensive knowledge and to find an applicable experimental data of two-way slab continually loaded until failure.
• By using two computer software, which are strand 7 and robot analyse elastic analysis in order to get the slab maximum deflection.
• By utilizing yield line method to find the plastic analysis of the experimental slab to obtain the theoretical collapse load of the slab.
• To compare the results obtained from the experimental result and the values obtained from strand 7 and robot in order to be able to comment which method is more accurate.
• Classify from both methods the advantages and disadvantages in terms of effectiveness, straightforwardness, safety and advice which is the best approach for structural analysis.

1.5 Dissertation Outline

• Chapter 1: – Run through the overview of structures and the progress of structural analysis. Yet, it will go over the Aims and Objectives.
• Chapter 2: – The yield line analysis of slab related to the literature review and the reflection of research accomplishment.
• Chapter 3: – The methodology used to achieve the objectives of the project and means of experimental data collection methods are discussed in this chapter.