Project 2 - MODELLING, ANALYSIS & DESIGN OF COMPOSITE STUCTURES IN COMFLOR & ETABS

Question. A 30 - 40hr project on modelling, analysis & design of a state-of-the-art tall composite building using ETABS software. The composite members to be designed using Comflor software.

Key Highlights:

a. Modelling

• The structural model prepared for the project 1to be used for the project 2.
• Prepare two distinct structural framing plans (location of primary & secondary beams) as discussed in Lecture 11.
• Create member definition for the steel sections by importing through library.
• Select deck slab profile and section using the Comflor Manual.
• Modelling of the composite metal deck section in ETABS
• Modelling of the composite columns in ETABS
• Create steel beam, steel column, bracing & core wall properties to be used further in the project.

b. Loadings & Load combinations

• Comflor: Wet concrete and construction loads for the design of deck slab
• ETABS: Use load patterns and combinations created in project 1
• Definition of Pre-composite dead loads
• Define footfall loadings for the vibration checks.

c. Structural Analysis

• Comflor software to be used for the analysis of composite deck slab
• Obtain the shear force & bending moment diagrams for the floor beams and columns.
• Check the gravity load path in the structure if it follows the designer’s intent.
• Perform quick hand calculations to confirm the base reactions for the gravity load cases.
• Check natural frequency for the floor system and mitigate the floor vibration by keeping fundamental frequency > 3Hz.

d. Design of structural members

• Shear studs & Composite deck design calculations
• Interpretation of the design results for the composite beam from ETABS
• Pre-camber criteria and requirements

Key Deliverables:

• Comflor file with the complete modeling of the slab with appropriate loadings
• Comflor report for the composite slab design (as PDF file)
• Submit a ETABS model with the complete model of the composite structure.
• A comprehensive project report from the ETABS software (as PDF file).

Solution:

a. Modelling

• The structural model prepared for the project 1to be used for the project 2.
• Prepare two distinct structural framing plans (location of primary & secondary beams) as discussed in Lecture 11.
• Create member definition for the steel sections by importing through library.
• Select deck slab profile and section using the Comflor Manual.
• Modelling of the composite metal deck section in ETABS
• Modelling of the composite columns in ETABS
• Create steel beam, steel column, bracing & core wall properties to be used further in the project.

• To analyse and to design the composite high rise building using ETABS. And to design the composite deck profile using Comflor software.

Procedure:

• The structural model prepared for the project 1to be used for the project 2:

Architectural plan study & Column shear wall position marking:

- The yellow hatched columns are positioned for gravity load resistance.

- The green colour RC walls and lift area RC walls are planned for lateral load resistance.

- The column position & RC wall alignment are sketched according to the partition wall layout, so that the structural elements will get hidden.

FRAMING FOR SECONDARY BEAMS:

MEMBER DEFINITION OF STEEL SECTION:

- In order to assign the frame properties,go to the option Define tab just click on that option then there will be a drop-down list and in that list there will be another option called Section Properties click on that option after that there will be another drop-down list and in that list there will be another option called Frame Sections click on that option just as shown in the below given image:

- And after that there will be another dialouge box named as the Frame Properties and in that dialouge box there will be an option Import New Properties just click on that option.

- After that there will be another dialouge box named as the Frame Section Property Import Data and in that dialouge box fill all the details just as shown in the below given image:

• Select deck slab profile and section using the Comflor Manual:

Manual Calculations:

Deck Profile Using Comflor Manual:

Imposed Load - 3kN/sq.m.

Super-Imposed Load - 2.5kN/sq.m.

Total Load - 5.5kN/sq.m.

And from Comflor Table:

Provide double span.

Thickness - 1.00 mm.

Span =2.26=2.95.

Depth of Slab - 160mm.

STRUCTURE:

LOADING:

DESIGN:

ANALYSIS:

- MANUAL CALCULATIONS FOR THE SECONDARY BEAMS:

Self-Weight of Slab - 0.16*2.26*25 = 9.05 kN/m.

Super-Imposed Loads - 2.5*2.26 = 5.65 kN/m.

Live Load - 3*2.26* = 6.78 kN/m.

Ultimate Load - 1.5(DL+LL) = 1.5*(9.05+12.43).

= 32.22 kN/m.

Mu - WL^2/8.

= 32.22*5*5/8 = 100.8 kN/m.

Elastic Modulus - Mu*1.05/fy = 100.8*10^3*10^2/250.

= 423.36 cm^3.

So,Provide ISWB 250,

Section Properties:

Zxx = 475.4 cm^3.

FOR MAIN BEAM:

Dead Load = 0.16*25*5*8.96.

= 179 kN at centre.

Live Load = 3*8.96*5.

= 134 kN at centre.

Super Imposed Load = 2.5*8.96*5.

= 112 kN at centre.

Ultimate load = 1.5(246)+1.5(179).

= 369+268.5.

= 637 kN.

Mu Due to the point load = WL/4 = 637*4.57/4

= 728 kNm.

Elastic Modulus = Zp

= 728*1.05/fy.

= 2215 cub.cm.

Provide ISWB 500.

- And now we will be assigning the Deck Properties.

- And in order to do that first we need to go to the Define tab just click on that option after that there will be another drop-down list and in that list there will be an option called Section tab click on that option and after that there will be another drop-down list and in that list there will be another option called Deck section just click on that option just as shown in the below image:

- And after that there will be another dialouge box named as the Deck properties and in that dialouge box there will be another option called Add New Property... just click on that option just as shown in the below given image:

- After that there will be another dialouge box named as the Deck Property Data and in that dialouge box there will be another options fill the necessary data just as shown in the below given image:

- And now we will be assigning the Frame Section Property and in order to assign the Frame sections go to the Define tab click on that option after that there will be another drop-down list and in that list there will be another option called Section Properties click on that after that there will be another drop-down list and in that list there will be be an option called Frame Section just as shown in the below given image:

- After this there will be another dialouge box named as the Frame Section Property Data and in that dialouge box fill out the all necessary data just as shown in the below given image:

- And now we will be doing the manual calculations for the loadings and the load combinations step-by-step as shown in the below procedure:

Area - Guwahati.

Seismic Zone - 5 (0.36).

Soil Type - Medium.

Importance Factor,R - 1.

Time Period in X-TX - 0.48s.

Time Period in Y-TY - 0.67s.

Basic Wind Speed - 50 m/s.

k1(Risk Factor) - 1.

k2(Terrain Roughness and Height Factor) - 0.91.

k3(Topography Factor) - 1.0.

k4(Importance Factor for Cyclonic Region) - 1.0.

- Now Check the model as shown in the below given image:

- There are no generated errors after checking the model:

Load pattern, Load combinations & earthquake wind assignments:

Modelling of walls, composite columns & Steel beams:

Loading assignment:

Analysis & Composite column design check:

• Since all the composite column Demand Capacity ratios are less than 1, the composite column sections provided in the model are satisfying the requirement.

Vibration check as per code P354:

• The frequency criteria of the composite floor in view of walking resonance, as follow

- It is understood that, the deflection caused by 100% dead load + 10% of imposed load shall be used for determining the frequency of the composite floor.

- And by verifying the frequency of the floor be greater than 3 Hz, we can say the floor vibrations are within the tolerant limit.

- Deflection of steel beam for vibration load combination is noted as 2.9 mm.

- The span to deflection ratio of the steel beam is = 7500 / 2.9 = 2586 which is satisfactory.

Total deflection of the floor = 2.9 + 2.9 = 5.8 mm

So, the frequency of the floor,f = 7.47 Hz

The frequency of the floor is much greater than 3 Hz, which is beyond the walking frequency. Hence satisfied.

ATTACHMENTS:

- Below are the attached ETABS file in e2k form.

- Comflor report for the composite slab design (as PDF file).

- Comflor file with the complete modeling of the slab with appropriate loadings.