Proposed Condominium Residential Maissonnetts

on Plot 1 Bandali Close Nakawa Division Kampala

Structural Integrity Report and Design Calculations

Client:

Krish Developers and Consultants

P.O.Box 28341, Kampala

Date: March 2014

Report/Calculations by:

Checked /approved by:

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Executive summary

This report presents the structural integrity report, analysis and design of a three-storied

condominium residential development (apartments) on plot 3 Kimera close, Bugolobi in

Nakawa division of Kampala city. The development comprises four blocks A,B,C and D. The

blocks are typical with the same design and dimensions.

The construction started and all the four blocks are halfway done i.e. up to the second floor

level. The original structural design calculations were prepared in India based on Indian

design codes. This report shows a design review based on British standards i.e. BS8110 Part 1

of 1997. The structure was designed to meet both strength and serviceability requirements

when subjected to both gravity and lateral loads.

Since the structure has already been constructed halfway, the KCCA planning committee

demanded for a structural integrity report for the as-is structure before approving further

construction to take place.

For strength design, the Limit state criteria were used where all standard load combinations

were considered and members were designed to resist the ultimate factored loads.

For serviceability design, beam deflections were limited to L/200 and L/360 where relevant

according to the BS8110 1997 structural use of reinforced concrete code. Cracking was also

controlled by the spacing limitations for reinforcement according to the design code.

Findings from integrity report

The quality of workmanship exhibited on the site is quite satisfactory with fair finishes and

straight edges. The structural drawings being used are followed strictly. Number and size of

reinforcing bars are all adhered to. The grade of concrete looks good and to the right grade.

Results from the structural design calculations indicate that the design conforms to the

BS8110 recommendations.

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Table of contents

Executive summary .......................................................................................................................................... 2

Table of contents .............................................................................................................................................. 6

1 Introduction .............................................................................................................................................. 7

2 Visual inspection ...................................................................................................................................... 7

2.1 Design technique and philosophy .................................................................................................. 8

2.2 Loading ............................................................................................................................................. 8

2.3 Geotechnical Conditions .................................................................................................................. 8

2.4 Design Loadings ............................................................................................................................... 8

2.5 Deflection Criteria ........................................................................................................................... 9

2.6 Durability ....................................................................................................................................... 10

3 Framed structural system design .......................................................................................................... 11

3.1 Design of floor slab ........................................................................................................................ 11

3.2 Design of stair case ........................................................................................................................ 13

3.3 Design of beams .............................................................................................................................. 17

3.3.1 Design of ring beam ...................................................................................................................... 17

3.3.2 Design of columns ......................................................................................................................... 20

3.3.3 Design of foundation bases .......................................................................................................... 21

References ....................................................................................................................................................... 22

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1 Introduction

This report shows the design calculations for the most critical elements of the structure. These

elements include the largest slab panel, the staircase, the beams, load-bearing walls, columns,

strip footings and foundation bases. For clarity refer to the architectural and structural

drawings attached.

2 Visual inspection

Scope of Visual Inspection

Prior to the commencement of visual inspection, the structural engineer obtained a set of the

building’s structural layout plans from the building owner. The availability of the structural

layout plan helped the structural engineer to:

(a) Understand the structural system and layout of the building;

(b) Identify critical areas for inspection;

(c) Identify the allowable imposed loads, in order to assess the usage and possibility of

overloading; and

(d) Verify if unauthorised addition or alteration works that affect the structure of the building

have been carried out.

In general, the structural engineer carried out, with reasonable diligence, a visual inspection

of:

a) The condition of the structure of the building

- to identify the types of structural defects

- to identify any signs of structural distress and deformation

- to identify any signs of material deterioration

b) the loading on the structure of the building

- to identify any deviation from intended use, misuse and abuse which can result in

overloading

c) any addition or alteration works affecting the structure of the building

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- to identify any addition or alteration works which can result in overloading or adverse

effects on the structure.

Since there were no signs of any structural deterioration or defects, the visual inspection

should suffice and no further action needs to be taken.

2.1 Design technique and philosophy

It is proposed that the general structural format of the building will include a system of

approximately parallel T-beams on the columns/walls lines. Preliminary design has shown

that the depth of beams will be in the range on 425mm by 230mm wide. The slab will be

designed as a solid slab since that is already done on site.

2.2 Loading

Design codes and floor loadings

The building has been designed in accordance with the re following British standards:

o BS 6399-1 1996 for dead and imposed loads

o BS 6399 Part 2 1997 for wind loads

o BS 8110 1997 – Structural use of concrete

o BS 5950 Part 1, 1985 Structural use of steel

The following design live loads will be used for this building:

2.3 Geotechnical Conditions

The ground conditions are were postulated by visual inspection and experience of the design

engineer. No geotechnical tests were carried out on the site hence a conservative soil bearing

capacity of 200kN/m² has been used in these calculations.

2.4 Design Loadings

The following design loadings have been derived from the Courts Standards and Design Guide

2007, in conjunction with relevant British Standards:

Imposed Loads

Offices 2.5 kN/m² (+ 1.0 kN/m² for demountable partitions)

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Court Rooms 4.0 kN/m²

Circulation Areas 4.0 kN/m²

Staircases 4.0 kN/m²

Roof (with only limited access) 0.6 kN/m²

Roof (with access) 0.75 kN/m²

Superimposed Dead Loads

Ceiling and Services 0.5 kN/m²

Raised Access Floor 1.0 kN/m²

Blockwork Partitions 3.0kN/m² generally but will be assessed by calculation

Wind Loading

Wind loading was assessed in accordance with BS 6399-2.

Basic Site Wind Speed Vb = 31m/s

Site Altitude _s = 10 m

Design wind pressures have been derived taking into account the altitude, relevant

topography and building geometry.

2.5 Deflection Criteria

The design code stipulates that the total deflection of the floors and total incremental

deflection of the floors cannot exceed 25 mm and 20 mm respectively. This criterion has been

strictly adhered to in all design considerations.

Design Movements

Settlement

Overall settlement of the building is not expected to exceed 25mm.

Differential settlement between piles is not expected to exceed 5mm.

Vertical Deflection limits

Concrete Slabs/Beams – generally: Span/250

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Concrete Edge Beams – supporting masonry or glazing: Span/500

Concrete Slabs/Beams – supporting brittle finishes: Span/360

Structural Steel Elements – generally: Span/200

Structural Steel Elements – supporting brittle finishes: Span/360

Horizontal Deflection Limits

Structural Elements supporting masonry or glazing: Span/500

Relative Floor to Floor movement generally: Height/300

2.6 Durability

Structural concrete elements of the built form are to have a design durability, which complies

with the requirements of BS8110: 1997. The exposure condition for each element is shown in

the calculations.

Design Life

All structural elements will be designed to achieve a minimum design life of 60 years.

Protective coatings to structural steelwork will be specified to provide a minimum period of

20 years to first maintenance. Any steelwork inaccessible after completion of the structure

will be specified to provide a minimum period of 60 years to first maintenance.

Fire Resistance

The design of structural elements is to be based on fire resistance levels to satisfy code

requirements as advised.

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3 Framed structural system design

The framed structural system is designed to transfer vertical and horizontal loading through

the combined action of beams and columns network. The design of elements is therefore done

string with slabs followed by beams up to the column bases.

3.1 Design of floor slab

The typical slab for all floors below the terrace is similar in geometry hence all panels are

exactly the same. The only difference is the imposed loading on the slabs.

Ref: BS 8110: 1997

Calculations Output

Dimensional considerations: Slab panel S1

Lx = 4.4m , Ly = 5.0m

Ly/Lx = 1.14 ~ 1.2 (2-way slab panel)

Ly/lx = 1.14

Fig. 3.2

Table 3.4

Durability and fire resistance

Minimum floor thickness for 1.5 hour fire resistance = 110mm

Minimum concrete cover for continuous floors for 1.5 hour fire resistance = 20mm

C = 20mm

Loading

Try a slab with thickness 125mm

Dead loads:

Self-weight = 0.125 x 24 = 3 kN/m²

Finishes = 0.05 x 21 = 1.05 kN/m²

Total characteristic dead load gk = 4.05 kN/m²

Imposed/live loads

Qk for residential use) = 1.5 kN/m²

Design loading, n = 1.4gk + 1.6qk

= 1.4 (4.05) + 1.6 (1.5) = 8.07 kN/m²

H = 125mm

Gk = 4.05kN/m²

Qk = 1.5kN/m²

3.5.3.6

Table 3.14

Bending moment and shear

Moments

msx = βsxlx², msy = βsylx²

for a 2-way slab panel with one short edge discontinuous,

support moment in x-direction Msx = 0.052 x 8.07 x 4.4² = 8.12 kNm

Mx = 8.12 kNm

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Table 3.15

span moment in x-direction Msx = 0.039 x 8.07 x 4.4² = 6.09 kNm

support moment in y-direction Msy = 0.037 x 8.07 x 4.4² = 5.78 kNm

span moment in y-direction Msy = 0.028 x 8.07 x 4.4² = 4.37 kNm

Shear forces

Vsx = βvx nlx , Vsy = βvynlx

For a 2-way slab panel with one short edge discontinuous,

Shear force in x-direction Vsx = 0.44 x 8.07 x 4.4 = 15.62 kN

V = 15.62 kN

3.4.4.4

Table 3.25

Reinforcement steel: moment

Support moment steel,

With c = 20mm, assume a 12mm bar diameter,

Therefore effective depth d = 125 – 20 -12/2 = 99mm

Considering a 1m strip of slab,

K = M/fcubd² = 8.12 x 106 /(25 x 1000 x 99²) = 0.033 < 0.042

Z = 0.95d = 94.05mm

As= M/0.95fyZ

= 8.12 x 106/(0.95 x 460 x 94.05)

= 197.56 mm²

100As/bh = 100 x 197.56 /(1000 x 125) = 0.15% >As, min

Provide T10@300 cc, As = 262 mm²

Span moment steel

Md = 6.09 kNm

K = M/fcubd² = 6.09 x 106 /25 x 1000 x 99² = 0.025 < 0.042

Z = 0.95d = 0.95 x 99 = 94.05mm

As = M/0.95fyZ = 6.09 x 106 / (0.95 x 460 x 94.05) = 148.2 mm²

As < As,min calculated above for same section

Provide T10@125mm² As = 800 mm² (to increase resistance to deflection)

Distribution steel

Md = 4.37 kNm

K = M/fcubd² = 4.37 x 106 /25 x 1000 x 99² = 0.013 < 0.042

Z = 0.95d = 0.95 x 99 = 94.05mm

As = M/0.95fyZ = 3.25 x 106 / (0.95 x 460 x 94.05) = 79 mm²

Provide T10@300 cc Top steel

Provide T10@150 cc Bottom steel layer 1

Provide T8@200 cc bottom steel

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As < As,min calculated above for same section

Provide T8@200mm² As = 251 mm²

layer 2

Table 3.8

Table 3.7

Shear

Vd = 15.62 kN

ν = Vd/bvd = 15.62 x 10³ / (1000x99) = 0.16 N/mm² < 5N/mm² < 0.8√fcu = 4N/mm²

νc = 0.79 x (100As/bvd)^1/3 x (400/d)^1/4 x 1/γm

100As/bvd = 100 x 524 /(1000 x 99) = 0.53 < 3 OK

400/d = 400/99 = 4 > 1 OK

νc = 0.79 x 0.53^(1/3) x 4^0.25 x 1/1.25 = 0.72 N/mm²

0.5νc = 0.36 > ν , therefore no shear reinforcement required.

Shear OK

3.4.6.3

Table 3.9

Table 3.10

Deflection

Allowable span/effective depth ratio = 26 x m.f.

Actual span/effective depth ratio = 4015/99 = 40.6

Modification factor for tension steel m.f. is given by

m.f. = 0.55 + (477-fs)/(120x(0.9+M/bd²))

M/bd² = 6.09 x 106 /(1000 x99²) = 0.52 kN/m²

Fs = 2/3 x fy x As,req/As,prov = 2/3 x 460 x 123 /524 = 71.98 N/mm²

M.f. = 0.55 + (477-71)/(120x(0.9+0.52)) = 2.93 but M.f. must be < 2

Hence M.f. = 2

Allowable span/effective depth ratio = 26 x 2 = 52 > 40.6

Deflection OK

3.12.11.2.4

Cracking control

Clear spacing between bars = 200 mm – 12 mm = 188 mm

47000/fs = 47000/71 = 661 mm

Therefore clear spacing < 661 mm and <300mm

Cracking OK

3.2 Design of stair case

The structure has one type of staircase; to be constructed in three positions 2 on block A and 1

on block B.

REF CALCULATIONS OUTPUT Staircase

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REF CALCULATIONS OUTPUT Design parameters

Treads = 0.240 m

Risers = 0.175 m

Waist depth = 0.175 m

Width of stairs = 1.15 m

Effective span = 4.722 m

Concrete unit weight = 24 kN/m²

Finishings unit weight = 21 kN/m²

Imposed loading = 4.0 kN/m²

Thickness of finishing = 0.025 m

Fcu = 25 N/mm²

Fy = 460 N/mm²

Table 3.3

Table 3.5

Durability and fire resistance

Nominal cover for grade 25 concrete with mild exposure = 25 mm

Minimum thickness of floor slab for 1.5 hours fire resistance = 110

mm

Fire resistance OK

Loading and Internal reactions

Tan θ = 172/240 , θ = tan-1 0.73 = 36°

Assume 1 m strip of stair case,

Dead load gk:

Weight of steps = 0.5 x 0.172 x 0.233 x 1 x 24/0.233 = 1.92 kN/m

Weight of waist = 0.15x 1 x 1 x 24/cos 36° = 4.27 kN/m

Weight of finishings = 0.05 x 1 x1 x 21/cos 36° = 1.25 kN/m

Weight of landing = 0.15 x 1 x 1 x 24 = 3.6 kN/m

Total dead load on landing = 3.6 + 1.05 = gk=4.65 kN/m

Total dead load on flight = 1.92+ 4.27 + 1.25 = gk= 7.44 kN/m

Design load on landing = 1.4gk+1.6qk = 1.4(4.65)+1.6(4.0) = 12.91

kN/m

Design load on flight = 1.4gk+1.6qk = 1.4(7.44)+1.6(4.0) = 16.82 kNm

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REF CALCULATIONS OUTPUT Design moment Md = 24.25 kNm

Design Shear Vd = 28.56 kN

Table 3.25

Reinforcements

Assume bar size ф = 16 mm,

Eff. Depth, d = 150 – 25-16/2 = 117 mm

K= M/ fcubd² = 24.25 x 106 /(25 x 1000 x 117²) = 0.071 < 0.156

Z = d(0.5 +√(0.25-k/0.9) = d(0.5+√(0.25-0.071/0.9) = 0.91d

As = M/0.87fyZ = 24.25 x 106 / 0.87 x 460 x 0.91 x 117 = 569.12 mm²

Provide = T12@150 mm = 753 mm²

Distribution steel area should be > 0.13%bh

= > 0.13% x 1000 x 200 = 260 mm

Provide T10@200c/c = 392 mm²

Provide Bottom

T12@150 mm

(As= 753 mm²)

Provide Distribution T10@200 cc (As=392 mm²)

Table 3.8

Shear

Shear force Vd = 28.56 kN

V = V/bvd = 28.56 x 103 / (1000 x 117) = 0.244N/mm²

V= 0.8√fcu = 0.8√25 = 4 N/mm²

Dimensions OK.

100 As/bvd = 100 x 753 / (1000 x 117) = 0.64 N/mm²

Vc = 0.79(100As/bvd)^1/3 x (400/d)^0.25 / γm

= 0.79 x 0.64^1/3 x 2.4^0.25 /1.25 = 0.67 N/mm²

V < 0.5 Vc = 0.30 N/mm²

Shear resistance

OK

Table 3.9

Deflection

Basic span/effective depth ratio = 20

M/bd² = 24.25 x 106 /(1000 x 117²) = 1.77

Fs = 5fyAs,eq/8As,prov = 2 x 460 x 569 /(3 x 753) = 231.7 N/mm²

Modification factor m.f. = 0.55 + (477-fs)/120(0.9+M/bvd²) = 1.56

Limiting span/eff. Dept ratio = 20 x 1.56 = 31.2

Actual Span/eff. Depth ration = 3480/117 = 29.74

Actual < limiting and therefore deflection is ok

Deflection OK

Cracking control

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REF CALCULATIONS OUTPUT

3.12.11.2.4

Clear spacing between bars = 150 mm – 12 mm = 138 mm

47000/fs = 47000/231.7 = 202.8 mm

Therefore clear spacing < 202.8 mm

Cracking OK

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3.3 Design of beams

The beam design was carried out using Prokon design software as shown in the following

attachments.

3.3.1 Design of ring beam

The ring beam is provided to receive the loading from the roof structures and to provide some

robustness to the entire structure especially as far as resistance to notional horizontal forces.

Although much of it is carried directly by the masonry walls, a few sections of it are suspended

at various openings and cantilevered points.

REF: BS 8110-1

CALCULATIONS OUTPUT

Table 3.2, 3.3, 3.4

Fig 3.2

Dimensional considerations

The most critical span where the ring beam is suspended is above the view balcony, length = 4.15 m

For rectangular sections, simply supported the allowable span/eff. Depth = 20

Assuming a modification factor of 1.2, then effective depth , d = 4150 / (20x1.2) = 185.4 mm

Durability and fire resistance

For mild exposure conditions and 1.5 hour fire resistance provide a concrete cover = 25 mm.

Assuming a link size of 8 mm and bar diameter of 16 mm, minimum depth of ring beam, h = 185+25+8+16/2 =226 mm

Minimum beam width for 1.5 hour fire resistance = 200 mm take architectural dimension of 200 mm.

Try beam depth h = 350 mm

Therefore effective depth, d = 350 -25-8-16/2 = 309 mm

Cover = 25 mm

B = 200 mm

H= 350 mm

Loading

Dead load:

- From purlins and tiles = 2.05 kN/m

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REF: BS 8110-1

CALCULATIONS OUTPUT

- From trusses = 0.64 kN/m

- Self-weight of ring beam = 0.2x0.3x24x=1.44 kN/m

- Total dead load, gk = 4.13 kN/m

Live loads:

- From roof ,qk = 3.0 kN/m

Design load w = 1.4gk+1.6qk = 10.58 kN/m

Gk = 4.13 kN/m

Qk = 3.0 kN/m

W = 10.58

Bending moments and shear forces

Design moment Md = wl²/8 = 10.58 x 4.45²/8 = 26.2 kNm

Design shear force Vd = wl/2 = 10.58 x 4.45/2 = 23.5 kN

Md= 26.2 kNm

Vd = 23.5 kN

3.4.3

Table 3.25

Reinforcement

Assume bar size ф = 16 mm,

Eff. Depth, d = 350–25-8-16/2 = 309 mm

K= M/ fcubd² = 26.2 x 106 /(25 x 200 x 309²) = 0.055 < 0.156

Z = d(0.5 +√(0.25-k/0.9) = d(0.5+√(0.25-0.055/0.9) = 0.93d

Hence Z = 0.93d

As = M/0.95fyZ = 26.2 x 106 / 0.95 x 460 x 0.93x 309 = 208.6 mm²

100AS/BH = 0.30 > As Min = 0.13

Provide = 2T16 bars, As = 402 mm²

Provide 2T16 bars Top and 2T16 bars Bottom steel

Shear

Shear force Vd = 23.5 kN

V = V/bvd = 23.5 x 103 / (200 x 309) = 0.38 N/mm²

V= 0.8√fcu = 0.8√25 = 4 N/mm² Dimensions OK.

100 As/bvd = 100 x 402 / (200 x 309) = 0.65 N/mm²

Vc = 0.79(100As/bvd)^1/3 x (400/d)^0.25 / γm

= 0.79 x 0.65^1/3 x 1.29^0.25 /1.25 = 0.58 N/mm²

V < Vc +0.4 = 0.98 N/mm² therefore provide minimum links

Asv = 0.4xbvsv/0.87fy, assume a link spacing of 200 mm with mild steel

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REF: BS 8110-1

CALCULATIONS OUTPUT

Table 3.25 stirrups, Asv = 0.4x200x200/0.87x250 = 73.56 mm² , provide R8@200 mm links

Provide links R8@200 cc

3.4.6

Table 3.9

Table 3.10

Deflection

Basic span/effective depth ratio = 20

M/bd² = 26.2x 106 /(200 x 309²) = 1.37

Fs = 2fyAs,eq/3As,prov = 2 x 460 x 208.6/(3 x 402) = 159.1 N/mm²

Modification factor m.f. = 0.55 + (477-fs)/120(0.9+M/bvd²) = 1.71

Limiting span/eff. Depth ratio = 20 x 1.71 = 36

Actual Span/eff. Depth ration = 4450/309 = 14.4

Actual < limiting and therefore deflection is ok

Deflection OK

3.12.11.2.4

Cracking control

Clear spacing between bars = 200 mm – 16 mm = 184 mm

Therefore clear spacing < 300mm

Cracking OK

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3.3.2 Design of columns

The structure has been designed as a framed structure with the columns carrying the entire

loads from the beams and walls above.

The column design was also carried out using PROKON software and the relevant sheets are

attached below.

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3.3.3 Design of foundation bases

The design of the foundation was carried out in order to safely transfer all the axial loads and

moment in the walls to the bearing ground (soil). The assumed soil bearing capacity based on

the nature of the soil is 200 kN/m².

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References

Reynolds C.E., Steedman C.J. 1992. Examples of the Design of Reinforced Concrete Buildings to

BS 8110. 4th Edition

Ghosh S.K.,Domel Jr. W.A. 1992. Design of Concrete buildings for Earthquake and Wind forces

2nd Edition

Allen A.H. 1988. Reinforced Concrete design to BS 8110: simply explained. E.&F.N. Spon Ltd

Newyork, p. 133-137

Mosley W.H, Bungey J.H. 1990. Reinforced concrete design. Macmillan Press Ltd. Hampshire p

192-230

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Appendix: Images of site works as-is

Figure 1:First floor slab (good and fair finishing)

Figure 2:Well-done blockwork with visibly strong mortar

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Figure 3: Reinforcement doe as per original structural drawings