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Design Proposal of a 5-Storey Steel Building with Cost Analysis
This document presents a design proposal and cost analysis for a 5-storey steel building in Montreal. It describes calculating seismic loads using the National Building Code of Canada and equivalent static force procedure. The project involves redesigning the building using limited ductility braced frames and comparing it to the original design using conventional construction braced frames. The summary designs bracing, beams, and columns. It finds that limited ductility braced frames provide a 15% cost savings over conventional construction braced frames due to lower seismic loads, though other factors like damage to the building must also be considered.
Design Proposal of a 5-Storey Steel Building with Cost Analysis
- 1. Design Proposal ofa 5 Storey Steel Building with Cost Analysis Michael Masi ID: 7737157 Julian Nini ID: 9770887 ADVANCED STEEL STRUCTURES DESIGN (CIVI 691C)
- 2. Project Description: Existing5 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
- 3. Calculation of SeismicLoads: 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
- 4. Calculation of SeismicLoads: Converts dynamic earthquake motion to equivalent static loading if conditions are met Base shear: Equivalent Static Force Procedure (ESFP): NBCC 2010 𝑉 = 𝑆 𝑇𝑎 𝑀𝑣 𝐼 𝐸 𝑊 𝑅 𝑑 𝑅 𝑜 S(Ta) = Design spectral response acceleration Ta = Fundamental lateral period of vibration Mv = Factor accounting for higher mode vibration effects IE = Importance factor W = Seismic weight Rd = Ductility related seismic force modification factor Ro = Overstrength related seismic force modification factor
- 5. Calculation of SeismicLoads: 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):
- 6. Calculation of SeismicLoads: 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
- 7. Calculation of SeismicLoads: 1D + 0.25S + Cladding Weight of the Building (W):
- 8. Calculation of SeismicLoads: 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
- 9. Calculation of SeismicLoads: Seismic Force Modification Factors (Rd, Ro): NBCC 2010
- 10. Calculation of SeismicLoads: 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 𝑀𝑣 𝐼 𝐸 𝑊 𝑅 𝑑 𝑅 𝑜
- 11. Design of StructuralComponents: 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
- 12. Design of StructuralComponents: 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: Existing CC CBF Proposed LD CBF
- 13. Design of StructuralComponents: 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
- 14. Design of StructuralComponents: 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 W310X86W310X129 W310X86W310X129 W250X73W310X158 W250X73W310X158
- 15. Design of StructuralComponents: Design Summary: Existing CC CBF Proposed LD CBF W410X54 W410X54 W410X54 W410X54 W410X54 W360X33 W360X33 W360X33 W360X45 W360X33 W310X86W310X129 W310X86W310X129 W250X73W310X158 W250X73W310X158
- 16. Cost Analysis: $1.65/kgassumed for structural steel Density of 7,850 kg/m3
- 17. Conclusion: 15% savingsis 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
- 18. Conclusion: Clear thatLD 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
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