Structural Modelling using Etabs 2018

STRUCTURAL MODELING USING ETABS

AIM -

• To design a structural model based on provisions from IS 1893 and IS 13920 in seismic zone 5.
• To Run a modal response spectrum analysis and check analysis results of the Etabs model for inter-story drift requirements, vertical & planar irregularities, minimum shear wall requirements, maximum axial load ratio for column and shear walls, an effective moment of inertia for beams and columns, etc.

INTRODUCTION-

ETABS is an engineering software product that caters to multi-story building analysis and design. Modeling tools and templates, code-based load prescriptions, analysis methods, and solution techniques, all coordinate with the grid-like geometry unique to this class of structure. We all know that earthquake is a devastating disaster on planet earth. Earthquake codes are revised period by period and updated improvements in the representation of ground motions, soil, and structures. Moreover, these revisions have been made in recent years. The Indian Standard Code (IS 1893:2016(Part-1)) was also revised in 2001 and has been in effect since 2002. Most recent data on earthquakes show that the irregular distribution of mass, stiffness, and strengths may cause serious damage to structural systems.

TASK -

The architectural drawings for a G+7 residential building in zone 5 have been provided. The floor plan is the same for all 7-floor levels. Possible column positions have also been provided. Conceptualize a framing plan layout and then model the building in Etabs. The following architectural drawings have been provided:

• Typical floor plan – The location and thickness of the brick walls and the use of the
  space (for estimating live load) can be obtained from this plan
• A building section through the staircase and lift core is provided
• Parking layout on the ground floor – the column/shear wall arrangement must not
  obstruct entry/exit of vehicles.
  The following loadings are to be taken into account:
• Brickwall made of AAC blocks
• Finishes – floor tiles of 75 mm thickness
• Live loads as per IS 875 part 2
• Water tank of 20 KL above the staircase at Mumty level
• Lift Machine room at mumty level above lift core

The structural model must comply with provisions of IS 1893 and IS 13920.
Run a modal response spectrum analysis and check analysis results of the etabs model for inter-story drift requirements, vertical & planar irregularities, minimum shear wall requirements, maximum axial load ratio for column and shear walls, an effective moment of inertia for beams
and columns, etc.

Please note that the column positions shown in the architectural typical floor plan are only to provide an initial starting point for modeling. Participants will have to change its size, introduce shear walls, and add new vertical elements after running the analysis. You will have to run the analysis multiple times until a structural model is obtained that meets structural code requirements without compromising architectural functions. Also, there is no one ‘correct’ structural system for this challenge. There can be multiple possible solutions for this problem.

PROCEDURE -

Open up the Architectural Plan of the Building

OPEN THE NEW MODEL AND ENTER THE IS CODES

Custom Grid Data

Custom Grid Data

Initial Grid and Story Data Setup

Define Materials

M30 Concrete

HYSD 415 for Shear Reinforcement

HYSD 500 for Longitudinal Reinforcement

Define Frame Properties

Column 450 x 650

BEAM 400 X 500

Slab 150 mm thick

COLUMN ARRANGEMENT

BEAM ARRANGEMENT

SHEAR WALL ARRANGEMENT

COMPLETE STRUCTURAL MODEL WITH FLOORING

Define Load Patterns

Assign Brick Wall Load

Live Loads

Floor Finishes

Live Load Reduction As per the Codebook

Define EQ Load Patterns

Define Mass Source

Add up the Modal Case

Response Spectrum Analysis

Response Spectrum Load Case in X-direction: RSx

Response Spectrum Load Case in Y-direction: RSS

Generate Load Combinations

Define and Assign Pier Labels to the Shear Walls

Assign Diaphragm

Check the Model and Run the Analysis

Base Shear Check

Modal Participation Ratio Check

Check for the Inter-Story Drift

Story Drift in the X-direction

Story Drift in the Y-direction

RESULT:

The structural model of the G+7 model is designed for given architectural planning using Etabs.

A frame model which satisfies both code provisions is analyzed

Columns, shear walls, and beams are provided in a possible symmetrical way without many offsets.

Analyses are done for modal number, base shear story drift aspect ratio, irregularity, etc.,

As per the analysis result, the building is a bit flexible on the y-axis, as shear walls are sufficient to add additional columns as provided in the y-direction to meet the maximum story drift limit.