Design Proposal of a 5 Storey Steel Building with Cost Analysis

Michael MasiID: 7737157

Julian NiniID: 9770887

ADVANCED STEEL STRUCTURES DESIGN

(CIVI 691C)

Project Description: Existing 5 Storey Steel

Commercial Building Montreal, Site Class C Rectangular Surface Area of 3468 m2

Designed using Conventional Construction

Re-design based on Limited Ductility

Cost Analysis

Calculation of Seismic Loads:

Spectral acceleration ordinates are provided by the NBCC Return period of 1:2500 years Tabulated for T = 0.2, 0.5, 1.0 and 2.0s Depends on earthquake history, proximity to potential

earthquake hypocentres, soil conditions, etc. ‘Life safety’ objective

Spectral Acceleration:

NBCC 2005

Calculation of Seismic Loads:

Converts dynamic earthquake motion to equivalent static loading if conditions are met

Base shear:

Equivalent Static Force Procedure (ESFP):

NBCC 2010

𝑉=𝑆 (𝑇𝑎 )𝑀 𝑣 𝐼𝐸𝑊

𝑅𝑑𝑅𝑜

S(Ta) = Design spectral response accelerationTa = Fundamental lateral period of vibrationMv = Factor accounting for higher mode vibration effects IE = Importance factorW = Seismic weightRd = Ductility related seismic force modification factorRo = Overstrength related seismic force modification factor

Calculation of Seismic Loads:

Depends solely on building height h = 20.73 m → Ta = 0.518s Period can be doubled if proven through dynamic analysis

Fundamental Period of Vibration (Ta):

Calculation of Seismic Loads:

Low Importance: IE = 0.8 Normal Importance: IE = 1.0 High Importance: IE = 1.3 Post-Disaster: IE = 1.5

Requires buildings of higher importance to: resist higher loads be less reliant on inelastic behaviour of structural elements have a greater reserve capacity for ground motions

exceeding design level

Importance of the Building (IE):

NBCC 2010

Calculation of Seismic Loads:

1D + 0.25S + Cladding

Weight of the Building (W):

Calculation of Seismic Loads:

Rd accounts for ductility Ro accounts for overstrength Structure is designed to dissipate ground motion through

inelastic deformations of the SFRS Degree of ductility depends on structural system chosen Overstrength exists since structural elements have factored

resistances, a limited selection and material properties (i.e. Fy) higher than the minimum specified values

Seismic Force Modification Factors (Rd, Ro):

NBCC 2010

Calculation of Seismic Loads:

Seismic Force Modification Factors (Rd, Ro):

NBCC 2010

Calculation of Seismic Loads:

Seismic forces are distributed in proportion with storey height since first mode dominates response of the structure

Ft is added at the top of the building to account for whipping action from higher mode effects

Torsional effects were considered because of type 7 irregularities

Base Shear:

𝑉=𝑆 (𝑇𝑎 )𝑀 𝑣 𝐼𝐸𝑊

𝑅𝑑𝑅𝑜

Design of Structural Components:

Braces should yield in tension and have a controlled buckling or yielding mode in compression, bending or shear

All other members should be sufficiently strong for gravity loads and fuse elements to dissipate energy

Not required for conventional construction since they are designed for much higher loads

Required for limited ductile and probable resistance must be estimated including tensile yielding, buckling and post buckling strength

Capacity Design:

Elements of Earth. Eng. and Strct. Dynamics , by Filiatrault et al. 3rd ed

Design of Structural Components:

Non-seismic design: higher yield strength → safer structures Seismic design: higher yield strength → prevents fuse from

yielding and overloads adjacent components Probable yield stress: RyFy

Ry = 1.1 but RyFy ≥ 460 MPa for HSS sections

≥ 385 MPa for all other sections

Design of Braces:

HSS 152X152X4.8 HSS

152X

152X

4.8

HSS 152X152X4.8HSS 152X152X4.8HSS 203X203X9.5HSS 254X254X9.5

HSS

152X

152X

4.8

HSS

152X

152X

4.8

HSS

203X

203X

9.5

HSS

254X

254X

9.5

Existing CC CBF

HSS 114X114X8.0HSS

114X

114X

8.0

HSS 127X127X9.5HSS 114X114X9.5HSS 203X203X9.5HSS 203X203X16

HSS

127X

127X

9.5

HSS

114X

114X

9.5

HSS

203X

203X

9.5

HSS

203X

203X

16

Proposed LD CBF

Design of Structural Components:

Supports gravity loads while redistributing loads due to brace buckling and yielding

Case 1: Cu in compression braces + Tu in tension braces Case 2: C’u in compression braces + Tu in tension braces

Design of Braced Beams:

Existing CC CBF

Proposed LD CBF

W410X54

W410X54

W410X54

W410X54

W410X54

W360X33

W360X33

W360X33

W360X45

W360X33

Design of Structural Components:

Vertical component of brace forces from higher stories must be considered

Probability of all braces reaching their capacity decreases as number of levels considered increases

Case 1: All braces reach Cu, Tu

Case 2: All braces reach Cf due to 1.0E + 1.0D + 0.5L + 0.25S, where Rd = 1 and RdRo = 1.3

Design of Braced Columns:

Existing CC CBF

Proposed LD CBF

W31

0X

86

W31

0X

129

W31

0X

86

W310

X12

9

W25

0X

73

W310

X15

8

W250

X7

3W

31

0X

158

Design of Structural Components:

Design Summary:HSS 152X152X4.8 HSS

152

X152X

4.8

HSS 152X152X4.8HSS 152X152X4.8HSS 203X203X9.5HSS 254X254X9.5

HSS

152X

152X

4.8

HSS 1

52X15

2X4.

8

HSS 2

03X20

3X9.

5

HSS 2

54X25

4X9.

5

Existing CC CBF

HSS 114X114X8.0HSS

114

X114X

8.0

HSS 127X127X9.5HSS 114X114X9.5HSS 203X203X9.5

HSS 203X203X16HSS

12

7X12

7X9.

5

HSS

114X

114X

9.5

HSS 2

03X20

3X9.

5

HSS 2

03X20

3X16

Proposed LD CBF

W410X54

W410X54

W410X54

W410X54

W410X54

W360X33

W360X33

W360X33

W360X45

W360X33

W3

10

X8

6W

31

0X

12

9

W3

10

X8

6W

31

0X

12

9

W2

50

X7

3W

31

0X

15

8

W2

50

X7

3W

31

0X

15

8

Cost Analysis: $1.65/kg assumed for structural steel Density of 7,850 kg/m3

Conclusion: 15% savings is something to be discussed with owner during

design stage Expected result since much lower loads in LD CBFs than CC

CBFs for a more ductile response Cost savings different per frame since frames themselves are

different Slight overdesign resulting from using only 7 brace, 3 beam and

2 column sections in 9 frames of 5 stories

Conclusion: Clear that LD CBF is more economical however other factors

must be considered when choosing a SFRS Designed to prevent loss of life but accepts probability of

extensive damage to structural and non-structural components Since lateral drift increases with ductility and structure accounts

for only 15% of total building cost, less ductile system might be more desirable

Tirca 2015

Thank You!