Mini Project (ETABS, RISA2D, RISA3D)

Mini Personal Project Project Background: During my final year capstone project, our group consisting of 5 talented members, finished Aurora Go Bus Station Renovation and Rehabilitation project, which was awarded A+. Along with 2 other structuralfocused groupmates, I help design the structural members for the 2-storey building station and pedestrian bridge. For this mini-project, I will cover the wind and seismic loading only. In addition, I also added some trusses structural analysis done in RISA2D, RISA 3D, and ETABS, independent of my capstone project.

What I did in the capstone project: • Created the model on SAP2000 v21.0.2 • Wind Load Calculation by hands • Seismic Load Calculation by hands What I did differently in this mini project related to the capstone project: • Recreated the model on ETABS v18.1.1 • Auto-Wind Analysis • Auto-Seismic Analysis What I worked on the additional files other than the capstone project: • RISA2D and ETABS Truss Load Analysis and Comparison • RISA3D Staircase and Simple Truss Analysis What I can achieve in the future from this mini project: • More hands-on practice to use a computer software in the industry • Faster and efficient load analysis compared to repetitive hand calculations Finished on October 14th 2020 Prepared by Kristian Hartono 1|Page

Figure 1 – ETABS 3D Model of Aurora Go Bus Station

Figure 2 – Deflection Behavior of the Structure

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Method: Step 1: Defined Cp and Cg Values

Using NBCC 2015, Clause 4.1.7.5 (2) (a) & (B), we can get Cp for windward and leeward wind forces Cg can be set to 2.0 for more governing load magnitude.

Step 2: In Load Patterns, Set Auto Wind Load According to NBCC 2015 and Change the Properties

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Other Properties: Importance Factor, Iw High Iw

NBCC 2015 ยง Table 4.1.7.3

= 1.15

Reference Velocity Pressure, q

NBCC 2015 ยง 4.1.7.3. (4)

q for Aurora, ON = 0.44 kPa for 1/50 year

Table C-2

Exposure Factor (Ce)

NBCC 2015 ยง 4.1.7.3. (5) (b)

For Rough Terrain and h = 8 meter, Ce = 0.7 (h/12)0.3 = 0.6198 Topographic Factor (Ct)

NBCC 2015 ยง 4.1.7.4

Ct = 1.0 Hand Calculation Analysis to double check the ETABS results later on: P

=

Iw * q * Ce * Ct * Cg * Cp

=

1.15 * 0.44 * 0.62 * 1 * 2 * Cp

=

0.62744 Cp [kPa]

Cp Windward =

0.6

P Windward

=

0.3765 [kPa]

P Leeward

=

-0.1882 [kPa]

Cp Leeward

NBCC 2015 ยง 4.1.7.3. (1)

=

-0.3

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Based on the calculation, Cp values for both cases (Wind going along Y or X-axis) are similar, Cp windward =

0.6

CP leeward

=

-0.3

Cp Parallel

=

-0.7 (not relevant for this load comparison analysis)

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Based on Hand Calculation: For Case 1 (Wider Side - Wind Going along Y-Axis) Roof Tower Structure 1 Wind Force:

Rroof1 = 22.57 kN

Roof Structure 2 Wind Force:

Rroof2= 81.03 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 45.05 kN

For Case 2 (Narrower Side - Wind Going along Y-Axis) Roof Tower Structure 1 Wind Force:

Rroof1 = 56.43 kN

Roof Structure 2 Wind Force:

Rroof2 = 23.51 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 75.24 kN 6|Page

Load Case 1 (Wider Side – Wind Along Y Axis) Wind Story Plot: Gridlines:

Roof Tower Structure 1

(z = 8m)

Roof Structure 2

(z = 5m)

Upper Floor Structure 1

(z = 4m)

ETABS Value: Roof Tower Structure 1 Wind Force:

Rroof1 = 16.93 kN

Roof Structure 2 Wind Force:

Rroof2 = 45.17 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 28.23 kN

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Hand Calculation Portion: Roof Tower Structure 1 Wind Force:

Rroof1 = 22.57 kN

Roof Structure 2 Wind Force:

Rroof2 = 81.03 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 45.05 kN

Comment: Only Roof Structure 2 Wind Force is accurate, both Roof 1 and Upper Floor 1 results are off.

Load Case 2 (Narrower Side – Wind Along X-Axis) Wind Story Plot: Gridlines:

Roof Tower Structure 1

(z = 8m)

Roof Structure 2

(z = 5m)

Upper Floor Structure 1

(z = 4m)

ETABS Value: Roof Tower Structure 1 Wind Force:

Rroof1 = 42.3 kN 8|Page

Roof Structure 2 Wind Force:

Rroof2 = 56.43 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 70.54 kN

Hand Calculation Portion: Roof Tower Structure 1 Wind Force:

Rroof1 = 56.43 kN

Roof Structure 2 Wind Force:

Rroof2 = 23.51 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 75.24 kN

Comment: The L-shaped building analysis is inaccurate. None of the results are accurate.

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Troubleshooting on the ETABS Analysis

Findings: Left diagrams are the hand calculation method on how forces should interact, while the right diagrams are how the ETABS execute the loadings. As can be seen, the existence of the gridline at z = 5m, skewed the results. It affected the effective tributary height. For example, on Load case 1, the tributary height of the Roof Structure 1 should be 2 m [obtained from (8-4)/2], however, ETABS used 1.5 m instead [obtained from (8-5)/2]. A similar pattern repeats on the Upper Floor level and Roof Structure 2. Therefore, the L-shaped analysis should be calculated with precaution.

Solution:

Try running the auto-wind load analysis using only 2 grids (z = 8m, and z = 4m) 10 | P a g e

Load Case 1 (Wider Side – Wind Along Y-Axis) Wind Story Plot: Gridlines:

Roof Tower Structure 1

(z = 8m)

Upper Floor Structure 1

(z = 4m)

ETABS Value: Roof Tower Structure 1 Wind Force:

Rroof1 = 67.71 kN

Roof Structure 2 Wind Force:

Rroof2 = 0 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 45.05 kN

Hand Calculation Portion: Roof Tower Structure 1 Wind Force:

Rroof1 = 22.57 kN

Roof Structure 2 Wind Force:

Rroof2 = 81.03 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 45.05 kN

Comment: Both the Roof 1 and Roof 2 values did not match. Firstly, Roof 2 force was not detected, as the gridline of elevation z = 5m was not registered. Secondly, the Roof 1 value of ETABS is 3 times of our hand calculation value (achieved from 22.57 kN *3. This is because 11 | P a g e

ETABS treated the width of the roof as the whole 60 m instead of 20 m. In my analysis, the force of Roof 2 was transferred to the Roof 1 wind force, and that caused Rroof2 = 0 kN. In addition, the Upper Floor 1 wind force of 45.05 kN matched with the ETABS.

Load Case 2 (Narrower Side – Wind Along X-Axis) Wind Story Plot: Gridlines:

Story 2 - Roof Tower Structure 1

(z = 8m)

Story 1 - Upper Floor Structure 1

(z = 4m)

ETABS Value: Roof Tower Structure 1 Wind Force:

Rroof1 = 56.43 kN

Roof Structure 2 Wind Force:

Rroof2 = 0 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 113 kN

Hand Calculation Portion: Roof Tower Structure 1 Wind Force:

Rroof1 = 56.43 kN

Roof Structure 2 Wind Force:

Rroof2 = 23.51 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 75.24 kN

Comment:

Only the Rroof1 = 56.43 kN matched for both ETABS and hand calculation.

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Troubleshooting on the ETABS Analysis

Findings: The left diagrams are the hand calculation method on how forces should interact, while the right diagrams are how the ETABS perceive the loading. From my analysis, the deletion of gridline at elevation z = 5m, improved the accuracy of the values for both R roof1 and Rfloor1, however, R roof2 was completely ignored. The L-shaped behaviour of the building was oversimplified into square buildings. Therefore, the auto-wind load is a little bit tricky to be applied at L-Shaped/Stepped roof buildings.

Solution: Treat them into 2 independent structures. Run auto-wind analysis on 2 separate ETABS files. That way, we can get both more accurate and conservative answers.

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Structure 1 Only Auto-wind Load Analysis: Cp windward: 0.6, Cp leeward = -0.3 for Load Case 1 (wind applied along the y-axis). However, on the other side, there is a slight change in Cp. Cp windward: 0.648, Cp leeward = -0.3456 for Load Case 2 (wind applied along x-axis) Hand Calculation of Structure 1 Only:

Hand Calculation Portion: Case 1

Case 2

Roof Tower Structure 1 Wind Force:

Rroof1 = 62.32 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 124.74 kN

Roof Tower Structure 1 Wind Force:

Rroof1 = 22.57 kN

Upper Floor Structure 1 Wind Force:

Rfloor1 = 45.15 kN

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Load Case 1 (Wind Go Along X-Axis)

ETABS: Rroof1 = 62.32 kN,

Rfloor1 = 124.74 kN

Results: Matched 100%

Load Case 2 (Wind Go Along Y-Axis)

ETABS: Rroof1 = 22.57 kN,

Rfloor1 = 45.15 kN

Results: Matched 100%

Note: The process can be applied to Structure 2 in a similar fashion 15 | P a g e

Seismic Load Analysis

From the Hand Calculation, Upper Floor Structure 1 Seismic Force:

Rfloor1 = 238.3 kN

Roof Tower Structure 1 Seismic Force:

Rroof1 = 195.0 kN

Roof Structure 2 Seismic Force:

Rroof2 = 251 kN

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ETABS Step 1: Defined the Required Variables for the Earthquake Loading Components PGA: 0.085, Sa(0.2): 0.138, Sa(0.5): 0.087, Sa(1.0): 0.05, Sa(2.0): 0.026, Sa(5.0): 0.0064, Sa(10.0): 0.0027 Soil Class C, F(0.2) – F(10.0): 1, Ie(High): 1.3, Mv: 1, Rd: 1.5, Ro:1.3, Type: Braced Frame

Step 2: In Load Patterns, Set Auto Seismic Load According to NBCC 2015 and Change the Properties

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Step 3: Run the Analysis and Go to Display>Story Plot Analysis>Auto Lateral Load due to Seismic

ETABS Value: Roof Tower Structure 1 Seismic Force:

Rroof1 = 197 kN

Roof Structure 2 Seismic Force:

Rroof2 = 246 kN

Upper Floor Structure 1 Seismic Force:

Rfloor1 = 241.5 kN

Compared to Hand Calculation: Roof Tower Structure 1 Seismic Force:

Rroof1 = 195.0 kN

Roof Structure 2 Seismic Force:

Rroof2 = 251 kN

Upper Floor Structure 1 Seismic Force:

Rfloor1 = 238.3 kN

Result: Match 100% Analysis: Unlike Auto-wind Load, the Auto-seismic load can be applied directly to both Structure 1 and Structure 2 (L-Shaped building analysis). There is no need to separate the building into 2 independent structures.

This is the end of the Auto-Wind and Auto-Seismic Mini Project Related to my Capstone Project

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Additional Mini-Project on RISA2D, RISA3D, and ETABS Problem:

Model on RISA 2D:

Analysis Loads Reaction:

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Model done on ETABS: Axial Loads Reaction

Results: Based on the comparison of the result from RISA2D and ETABS, the axial forces match. However, RISA2D did not consider M6 and M6 as Zero Members, Therefore, the magnitude of axial force was read as 1.681 kN. As a result, the nearby member M8 carried a reduced value of the tension force of 48.149 kN instead of 50 kN. The ETABS showed a more accurate answer and matched my hand calculation.

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Model on Staircase RISA 3D:

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Model: RISA3D Simple Truss Analysis

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