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!