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Title: Architectural and Structural Design of a Three Storey Building Office at Burera

District of Rwanda.

Authors: Evode MUNYANEZA BAGENZI and Naon BETABOLE

Corresponding author: Evode MUNYANEZA BAGENZI

Email: munyevode33@gmail.com

ABSTRACT

The main objective of this research was to craft out an Architectural and Structural Design of

a Three Storey Building Office at Burera District of Rwanda because of the inadequate

modern offices that exists in this district. This was a field experimental study design. This is a

creative process of turning abstract ideas into physical representations (products or systems).

The architectural drawings were produced and analyzed by using a pilot study using the

ArchiCAD software, Artlantis; structural design elements were designed basing on British

Standard B.S: 8110 and by using PROKON software. Findings were that a three storey

building of 51.80m *15.56m*12.45m with more than 50 adequate offices, two meeting

rooms, three staircases, one ramp and six wash rooms ready to accommodate all available

services has been architecturally designed while for structural design, the reinforcements in

different structures are as follow: slab short span at bottom Y10@150mm, slab short span at

top Y10@175mm, slab long span at bottom Y10@150mm,slab long span at top

Y10@150mm; internal beam bottom and top 3Y20, External beam bottom 3Y20 and top

3Y16; internal Column 4Y16; external column 4Y12; stair longitudinal Y8@100mm and

Transversal reinforcement Y10@150mm;ramp longitudinal Y14@150 and transversal

Y8@200mm and footing 8Y20@125mm; on the cost of one billion three hundred and fifty

two million eighty nine thousand seven hundred and thirty Rwandan francs

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(1,352,089,730Rwf).It is recommended that before constructing the district office,

geotechnical tests of the soil is required.

Keywords: Slab, Beam, Column, Footing, Stair and Ramp.

1. INTRODUCTION

In modern terms an office usually refers to the location where white-collar workers are

employed. An office is generally a room or other area where administrative work is done, but

may also denote a position within an organization with specific duties attached to it. An

office is an architectural and design phenomenon; whether it is a small office such as

a bench in the corner of a small business of extremely small size, through entire floors of

buildings, up to and including massive buildings dedicated entirely to one company

(Wikipedia, 2018).

The main purpose of an office environment is to support its occupants in performing their

job. Work spaces in an office are typically used for conventional office activities such as

reading, writing and computer work (Wikipedia, 2018).

Due to vision 2020, Rwanda is a developing country in Africa which has speed in growth

development. Rwanda is characterized by low but accelerating urbanization. This has

happened in a rapid and uncoordinated manner, meaning that social services and employment

opportunities are lagging behind. From now until 2010, each town will have regularly

updated urban master plans and specific land management plans. The country will develop

basic infrastructure in urban centers and in other development poles, enabling the

decongestion of agricultural zones (IBPUS, 2003).

BURERA district which is located in Northern Province consist of old buildings with

insufficient number of office required to accommodate all district staffs. In addition to this,

they work in a different buildings some of them are not designed for office (less than 30

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offices). That is why as a master student to be graduated from IST BURKINAFASO in Civil

Engineering, we come up with this proposal of designing ‘A Three Storey Office Building of

Burera District’ by providing enough and comfortable office to accommodate all staff safely

not only in nowadays but also in future with more than 50 adequate offices.

2. METHODS

2.1. Study design

This was as a pilot study design.

2.2 Architectural Drawings

Designing an architectural drawings of this building provided for Burera district office,

ArchiCAD software (version 18) is used to produce neat drawings namely structural plan,

floor plans, elevations, sections and roof plan. In addition to this, Artlantis studio version

(5.1) is used to produce adequate perspectives.

2.3 Structural Design Elements

2.3.1 Slab Design

The basic design procedure of a two-way slab system has five steps.

1. Determine moments at critical sections in each direction, normally the negative

moments at supports and positive moment near mid-span.

2. Distribute moments transverse at critical sections to column and middle-strip and if

beams are used in the column strip, distribute column strip moments between slab and

beam.

3. Determine the area of steel required in the slab at critical sections for column and

middle strips.

4. Select reinforcing bars for the slab and concentrate bars near the column, if necessary

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Slab design inputs are as follows:

h=depth of slab

d= effective depth of slab

α=modification factor

Lx= the length of short span

Ly= the length of long span

A) Classification of slab

Ly/Lx >2: One way slab

Ly/Lx ≤ 2: Two way slab

B) Span-effective depth ratio

𝐿𝑥

𝑑∗α=7 for cantilever slab

𝐿𝑥

𝑑∗α=20 for simply supported slab

𝐿𝑥

𝑑∗α=26 for continuous slab

The value of α are given in table 3.10 from BS 8110

C). Analysis of slab panel

Effective depth of the slab =𝑆𝑝𝑎𝑛(𝐿𝑥)

𝑏𝑎𝑠𝑖𝑐𝑠𝑝𝑎𝑛𝑑𝑒𝑝𝑡ℎ𝑟𝑎𝑡𝑖𝑜∗α

2.3.2 Beam Design

The design of beam for our building began by choosing the most loaded beams in the two

directions of the building. These will be subjected to the maximum moment and maximum

shear. These loadings will be calculated using various methods but for us we are going to use

the computer program.

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A) Continuous Beam Design

Continuous beams are a common element in cast-in-situ construction. A reinforced concrete

floor in a multi-storey building is shown in Fig.6 The floor action to support the loads is as

follows:

1. The one-way slab carried on the edge frame, intermediate T-beams and Centre

frame spans transversely across the building;

2. Intermediate T-beams on line AA span between the transverse end and interior

frames to support the floor slab;

3. Transverse end frames DD and interior frames EE span across the building and

carry loads from intermediate T-beams and longitudinal frames;

4. Longitudinal edge frames CC and interior frame BB support the floor slab.

Figure 1: Continuous beam layout, chapter 3.

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B) Loading on continuous beams

Arrangement of loads to give maximum moments

The loading is to be applied to the continuous beam to give the most adverse conditions at

any section along the beam. To achieve this, the following critical loading arrangements are

set out in BS8110: Part 1, clause 3.2.1.2.2 (Gk is the characteristic dead load and Qk is the

characteristic imposed load):

1. All spans are loaded with the maximum design ultimate load 1.4Gk+ 1.6Qk;

2. Alternate spans are loaded with the maximum design ultimate load 1.4Gk+1.6Qk

And all other spans are loaded with the minimum design ultimate load 1.0Gk.

a. Loading from one-way slabs

Continuous beams supporting slabs designed as spanning one way can be considered to be

uniformly loaded. The slab is assumed to consist of a serious of beams as shown in Fig.7.

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Figure 2: (a) floor plan; (b) beam AA, chapter 3.

b. Loading from two-way slabs

If the beam is designed as spanning two ways, the four edge beams assist in carrying the

loading. The load distribution normally assumed for analyses of the edge beams is shown in

Fig.0 where lines at 45° are drawn from the corners of the slab. This distribution gives

triangular and trapezoidal loads on the edge beams as shown in the figure.

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Figure 3: (a) floor plan; (b) load on beam AA; (c) load on beam BB, chapter 3.

2.3.3 Column Design

The columns in a structure carry the loads from the beams and slabs down to the foundations,

and therefore they are primarily compression members, although they may also have to resist

bending forces due to the continuity of the structure Fig.7

In the analysis, it was necessary to classify the column into one of the following types:

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1. A braced column: where the lateral loads are resisted by walls or some other form

of bracing, and

2. An unbraced column: where the lateral loads are resisted by the bending action of

the columns.

Figure 4: Critical load arrangement for column, chapter 3.

A). Design moments and axial loads on columns

Generally, design moments, axial loads and shear forces on columns are that obtained from

structural analysis. Design axial load may be obtained by the simple tributary area method

with beams considered to be simply supported on the column as represented on Fig.8.

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Figure 5: Diagrammatic illustration of determination of column design moments by

simplified sub-frame analysis, chapter 3.

B). Design for axial load and biaxial bending

The general section design of a column is accountant for the axial loads and biaxial bending

moments acting on the section. Nevertheless, the code has reduced biaxial bending into

uniaxial bending in design. The procedure for determination of the design moment, either

Mx’ or My’ bending about the major or minor axes is as follows:

Determine b’ and h’ as defined by the diagram. In case there are more than one rows of bars,

b’ and h’ can be considered of the group of bars Fig.9.

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Figure 6: column design details, chapter 3.

IF '' b

M

h

M YX USE YXX M

b

hMM

'

''

IF '' b

M

h

M YX USE XYY M

b

hMM

'

''

2.3.4 Design of foundation

The foundations are sub-structures located below the ground which transfer and spread the

load from a structure’s columns and walls into the ground.

For the serviceability limit state the total design load is nk=1.0Gk+1.0Qk

The required area of the footing will be Area required=𝒏𝒌

𝒔𝒐𝒊𝒍𝒃𝒆𝒂𝒓𝒊𝒏𝒈𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆

The shear stress Vc at the column face

Vc=𝑵(𝒂𝒙𝒊𝒂𝒍𝒇𝒐𝒓𝒄𝒆𝒂𝒕𝒖𝒍𝒕𝒊𝒎𝒂𝒕𝒆𝒔𝒕𝒂𝒕𝒆)

(𝒄𝒐𝒍𝒖𝒎𝒏𝒑𝒆𝒓𝒊𝒎𝒆𝒕𝒆𝒓∗𝒅)

Critical perimeter=column perimeter+8*1.5d

Area within perimeter=(3d+CS)(3d+CS)

Punching shear force= V=earth pressure x( footing base surface - area within

perimeter)

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Punching shear stress 𝑽 =𝑽

𝒄𝒓𝒊𝒕𝒊𝒄𝒂𝒍𝒑𝒆𝒓𝒊𝒎𝒆𝒕𝒆𝒓∗𝒅

Figure 7: Critical section design for foundation, chapter 3.

Assumptions to be used in the design of pad footings are set out in clause 3.11.2 of the code:

1. When the base is axially loaded the load may be assumed to be uniformly

distributed. The actual pressure distribution depends on the soil type. Refer to soil

mechanics textbooks;

2. When the base is eccentrically loaded, the reactions may be assumed to vary

linearly across the base.

Refer to the axially loaded pad footing shown in Fig.11(b)where the following symbols are

used:

Gk characteristic dead loadfrom the column (kN)

Qk characteristic imposed load from the column (kN)

W weight of the base (kN)

lx, ly base length and breadth (m)

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pb safe bearing pressure (kN/m2

Figure 8: (a) mass concrete foundation; (b) Reinforced concrete foundation, chapter 3.

The area required is found from the characteristic loads including the weight of the

base: area=(Gk+Qk+W)/pb=lxly in m2

2.4 Cost Estimation

Construction professionals are involved in procuring building work on a daily basis. Effective

procurement aims to provide construction clients with projects which achieve good

value for money. Key objectives include ensuring that accurate budgets are prepared before

work commences and that the correct price is eventually paid for the completed work.

Measurement and valuation are essential processes underpinning these activities and together

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they form the central link between design and cost. On commercial projects these tasks are

usually carried out by quantity surveyors.

The quantity “takeoff” is an important part of the cost estimate. It must be as accurate as

possible and should be based on all available engineering and design data. Use of

appropriate automation tools is highly recommended. Accuracy and completeness are crit ical

factors in all cost estimates. An accurate and complete estimate establishes accountability

and credibility of the cost, therefore, providing greater confidence in the cost estimate.

2.4.1 1Introduction to Quantities Taking off

The quantification process involves recording dimensions and is referred to as taking off

because it involves reading or scaling (taking off) dimensions from a drawing and entering

this information in a standard manner on purpose ruled paper called dimension paper or

take off paper.

A). Quantity take off: Why?

Owner perspective:

Initial (preliminary) estimate of the project costs at the different stages of the project.

Preparing the BOQ as a requirement of the contract documents.

Estimating the work done for issuing the contractor payments.

Contractor perspective:

Pricing different work items;

Identifying the needed resources (Labor, Equipment, etc.);

Project schedule and

Preparing invoices for work done.

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2.4.2 Bill of Quantities

The term Bills of Quantities is defined as a list of items giving brief identifying descriptions

and estimated quantities of the works to be performed. The BOQ forms a part of the contract

documents, and is the basis of payment to the Contractor.

The BOQ also is defined as a list of brief descriptions and estimated quantities. The

quantities are defined as estimated because they are subject to admeasurement and are

not expected to be totally accurate due to the unknown factors which occur in civil

engineering work. The objective of preparing the Bill of Quantities is to assist estimators to

produce an accurate tender efficiently and to assist the post contract administration to

be carried out in an efficient and cost effective manner. It should be noted that the

quality of the drawings plays a major part in achieving these aims by enabling the taker-off

to produce an accurate bill and also by allowing the estimator to make sound

engineering judgments on methods of working. Table 4 shows a sample of a bill of

quantities.

A). Preparation of Bills of Quantities

Step1: The term squaring the dimensions refers to the calculation of the numbers, lengths,

areas or volumes and their entry in the third or squaring column on the dimension paper.

Step2: Abstracting is the process whereby the squared dimensions are transferred to an

abstract sheet or other similar computerized formats, where they are written in are cognized

order, ready for billing, under the appropriate section headings, and are subsequently reduced

to the recognized units of measurement in readiness for transfer to the bills.

Step3:Billing is the final stage in the bill preparation process in which the items and their

associated quantities are transferred from the abstract onto the standard billing sheets or other

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similar computerized formats that are in a format that enables the tenderer to price each item

and arrive at a total tender sum.

3. RESULTS and DISCUSSION

3.1 Structural Design

3.1.1 Slab Design

Using the biggest panel among others of 7.2*5.2m, the area of steel reinforcements provided

for Short span (bottom steel) is 524mm2/m, for Short span (top steel) is 449 mm2/m, for

Long span (bottom steel) is 449 mm2/m, for Long span (top steel) is 524 mm2/m, at support

Lx is 565 mm2/m, and at support Ly is 754 mm2/m. According BS Standard, the steel

reinforcements provided for Short span (bottom steel) is Y10@150mm, for Short span (top

steel) is Y10@175mm, for Long span (bottom steel) is Y10@175mm, Long span (top steel)

is Y10@150mm, at support Lx is Y12@200mm, and at support Ly is Y12@150mm.

3.1.2. Beam design

The beam is designed basing on the internal beam and the external beam.

For internal beam, the steel reinforcements provided for Span 1 are 2Y16 (Bottom) and 2Y16

(Top), for Span 2 are 3Y20 (Bottom) and 3Y20 (Top), for Span 3 are 2Y16 (Bottom) and

2Y16 (Top), for Span 4 are 3Y16 (Bottom) and 3Y20 (Top).

The Stirrups provided for Span 1 are R8@150mm, for Span 2 is R8@150mm, for Span 3

R8@150mm and for Span 4 is R8@150mm.

For external beam, the steel reinforcements provided are 3Y16 (Bottom) and 3Y20 (Top).

The Stirrups provided are R8@150mm.

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3.1.3 Column Design

The columns are designed based on the most loaded columns. The designed column cross

section size details are 400×300 mm for the internal column and 300×300 mm for the

external column.

The steel reinforcements provided for internal and external columns from foundation to

ground floor are 4Y16 with stirrups of Y8@150mm, from ground floor to1st floor are 4Y16

with stirrups of Y8@150mm, from 1st floor to 2nd floor are 4Y12 with stirrups of

Y8@150mm, and from 2nd floor to roof are 4Y12 with stirrups of Y8@150mm.

3.1.4 Stair Design

The designed Longitudinal steel reinforcements provided are Y12 with bar spacing of 100

mm and Transversal steel reinforcements provided are Y10 with bar spacing of 150 mm.

3.1.5 Ramp Design

The designed steel reinforcements provided at the top are Y14@200mm and at the bottom are

Y8@200mm.

3.1.6 Footing Design

The designed steel reinforcements provided for Interior and exterior footings are Tension

steel bars of 8T20 with bar spacing of 251.25 mm.

3.2 Cost Estimation

The total cost of building is estimated to be one billion three hundred and fifty-two million

eighty-nine thousands seven hundred and thirty Rwandan francs (1,352,089,730RwF).

3.3 Study limitation

Due to limitation of money, this study limited on the architectural design and structural

design of the district office with architectural drawings such as plans, elevations and sections;

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with additional design of the following elements namely: slab, beam, column, footing,

foundation, stair and ramp. This study did not cover on soil testing because it took the choices

which match with the means of life like a student with insufficient money (financial means).

4. CONCLUSION

The aim of this final year dissertation was to design modern district offices located in

BURERA to increase the good service provided to people and also a comfortable place for

BURERA’s staffs, councils and employees. The objectives were achieved through the

architectural and structural design of this office building. The architectural drawings were

produced and analyzed by using ArchiCAD software, Artlantis, structural design elements

were designed by using PROKON.

From the result, a three storey building of 51.80m *15.56m*12.45m with more than 50

adequate offices, two meeting rooms, three staircases, one ramp and six wash rooms ready to

accommodate all available services has been designed on the cost of one billion three

hundred and fifty two million eighty nine thousands seven hundred and thirty Rwandan

francs (1,352,089,730Rwf)

ACKNOWLEDGEMENT

Firstly, our great thanks go to the almighty God, for his mercy, guidance, and protection that

has been with us during the project. We would like to thank the administration of IST

BURKINAFASO that did every possible, to provide the technical skills needed to complete

this project.

LIST OF ABBREVIATIONS AND SYMBOLS

IST Institut Superieur De Technologies

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ICT Information And Communication Technology

Gk Dead Loads

Gk Imposed Loads

E Modulus Of Elasticity

BS British Standard

CAD Computer Aided Design

Kn Kilonewton

LSD Limit State Design

DL Dead Loads

LL Live Loads

m3 Cubic Meter

m2 Meter Squared

mm2 Millimeter Squared

m Meter

mm Millimeter

WL Wind Loads

W/C Water to Cement Ratio

H Depth of Slab

d Effective Depth of Slab

α Modification Factor

Lx Length of Short Span

Ly The Length of Long Span

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BOQ Bills of Quantities

As Area of Steel Reinforcement

Y Steel Reinforcement

AUTHORS’ CONTRIBUTIONS

EMB conceptualized the idea then EMB and NB drafted and approved the manuscript.

AUTHORS’ AFFILIATION

Institut Supérieur de Technologies, Department of Civil Engineering and Management

Ouagadougou, Burkina Faso.

FUNDING

The author (s) received no financial support for this work.

CONFLICT OF INTERETS

The authors declare no conflict of interest.

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