EFFECT OF VERTICAL RECTANGULAR OPENINGS ON TiHE FLEXURAL STRENGTH OF REINFORCED CONCRETE BEAM

ABSTRACT

Effect of vertical rectangular openings on the flexural strength of reinforced concrete beam is presented. Twelve reinforced concrete beams of dimension 200m x 230mm x 700mm with different sizes of rectangular openings, 25mm x 35mm, 50mm x 60mm and 75mm x 85mm which are placed at 150 mm from the supports, were cast. After curing, these beams were tested under centre-point loading system using universal testing machine and the flexural strength were determined. The results show that the flexural strength of the beams reduces gradually with the increase in the sizes openings. The optimum flexural strength was 13.47 N/mm2 with opening size of 25mm x 35mm, also the maximum deflection was 14.19 mm, which do not exceed 20 mm allowable deflection provided by BS 8110.  Hence, it is hereby recommended that introduction of vertical rectangular openings on reinforced concrete beam should not exceed potions of 150 mm from the supports and openings of 75mm x 85mm sizes.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background to the Study

In modern constructions ducts and pipes are usually placed underneath the soffit of the beams and covered by a suspended ceiling thus creating a dead space. On each floor, the height of these ducts and pipes add dead space to the overall height of the building depending on the number and height of ducts. So concealing the pipe as conduits to pass through walls, columns, beams, and slabs reduce the story heights of buildings and weight of concrete beams as it improves the demand on the supporting frame both under gravity loading and seismic excitation which results in major cost saving (Abdul-Kareem et al.,2017). Utility pipes and ducts are necessary to accommodate essential services in a building. The types of services include air-conditioning, power supply, telecommunication network, computer network, sewerage and water supply (Sharmin, 2014).

In general, the influence of openings on the beam’s strength and deformation depends on the openings’ location and size. If the positions are selected wisely, larger openings on reinforced concrete beam structures can be provided without affecting the ultimate load. However, small openings positioned in an unfavorable place can cause a dramatic decrease in the beam’s strength. For that reason, it is necessary to plan the size and location of the openings accurately. However, if the beam is pre-designed to have an opening of known size and location, this will be sufficient to ensure the safety and serviceability of the structure. These openings can be of different shapes and sizes as circular, square or rectangular, diamond, triangle and irregular shapes (Ali et al.,2017).

It has been noted that the classification of opening depended on the structural response of the beam; when the opening is small enough to maintain the beam-type behavior, then the opening could be termed as small opening. Otherwise, large openings are those that prevent beam-type behavior to develop (Saksena, 2013). A circular opening may be considered as large when its diameter exceeds

40% of the depth of the web, but square opening considered as large when height exceed quarter of the depth of the web.

Little researches are found on the effect of vertical openings in reinforced concrete beams (Oladipo, 2019). However, in ACI 314R-16 (2016) simplified design for reinforced concrete buildings recommends the possibility of creating vertical openings through a beam.

Figure 1.1: Location of conduits and pipes passes vertically through beams, Source: Ahmed

(2020)

1.2   Statement of the Research Problem

The advancement in construction has made the need for vertical openings in beams a necessity. The architects have been working on designing more complex structures, and the ICT world turning homes into smart houses, which has caused the engineering field to work on this opening of different shapes on web (Vivek and Madhavi, 2016) and vertical openings (Oladipo,

2019), the recent researcher recommends further work on the effect of vertical rectangular

openings on beams (Oladipo, 2019) which is the focus of this research as it might fit into the modern structures.

Plate I: A typical structural building under construction with vertical circular pipe passing through a reinforced concrete beam (Abuja – 27/01/2020).

1.3      Aim and Objectives of the Study

1.3.1    Aim

The aim of this research is to the study the effect of vertical rectangular openings on the flexural strength of reinforced concrete beam.

1.3.2    Objectives

The objectives of this study are to:

i.         determine the physical properties of aggregate;

ii.        determine the compressive strength;

iii.       determine the flexural strength and deflection of all cured beam specimens.

1.4     Justification of the Study

With the technical clarity on where to place and the size of rectangular openings in beam and the effect of the rectangular openings at other zones of the beam, would help engineers on field to take right decision in placing the utility pipes, plumping pipes and networking lines on beams, it will also help to ensure the safety in engineering practices and the serviceability of the structures. (Vivek and Madhavi, 2016; Oladipo, 2019)

(a) Mechanical pipe                (b) Electrical pipe                   (c) Mechanical pipe

Plate II: Typical structural buildings under construction with vertical circular pipe passing through a reinforced concrete beam. Source: Sumrec Estate airport road Lugbe, Abuja (27/01/2020)

1.5       Scope of the Study

The scope of this study is to research a reinforced concrete rectangular beam section (200mm x

230mm x 700mm) with vertical rectangular opening through its selected opening size of 25mm x

35mm, 50mm x 60mm, 75mm x 85mm provide at 150mm from the support and obtain the

maximum failure load, deflection with the experimental results of the same rectangular beam section. The summary of the scope is presented in Table 1.1.

Table 1.1: Details of beams specimen

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