liminfoETABS Reference
Free reference guide: ETABS Reference
About ETABS Reference
The ETABS Reference is a searchable guide to CSI ETABS (Extended Three-Dimensional Analysis of Building Systems), the industry-standard structural analysis and design software for multi-story buildings. It covers six workflow categories: modeling, loading, analysis settings, analysis execution, design, and output, organized to follow the typical ETABS project sequence from grid definition through final report generation.
The modeling section covers grid system definition (X/Y/Z directions with spacing), story data configuration (story heights, similar stories, master stories), material property definitions for concrete (fck, Ec, Poisson ratio), steel (Fy, Fu, Es), and rebar (SD400), section properties for columns, beams, slabs, and walls, and frame/shell element drawing. The loading section includes dead load with self-weight multiplier, live load by occupancy type (office 2.5 kN/m2, corridor 5.0, parking 6.0), auto-generated wind load per KDS 41 17 or ASCE, seismic load with effective ground acceleration and response modification factor, response spectrum functions with CQC combination, and load combination definitions for ultimate and serviceability states.
Analysis features include rigid diaphragm assignment, mass source definition with live load reduction for seismic analysis, P-Delta effect settings, eigenvalue modal analysis with mass participation verification, story drift checks against h/200 allowable limits per KDS, and story force plots. The design section covers concrete frame design per KDS 14 20 (KCI 2012), steel frame design per KDS 14 31 (AISC 360) with D/C ratio checks, and shear wall design with pier/spandrel labeling. Output tools include Excel export, automatic report generation, deformed shape visualization, and section cut force queries.
Key Features
- Modeling workflow: grid definition, story data, material properties (concrete/steel/rebar), and section properties
- Loading reference: dead/live/wind (KDS 41 17)/seismic with response spectrum functions and load combinations
- Analysis settings: rigid diaphragm assignment, mass source with live load reduction, and P-Delta configuration
- Modal analysis guide with eigenvalue setup, mode count recommendation (3x stories), and mass participation check
- Story drift verification against KDS allowable limits (h/200) with directional comparison
- Concrete frame design per KDS 14 20 and steel frame design per KDS 14 31 (AISC 360) with D/C ratio checks
- Shear wall design with pier/spandrel labeling and axial-moment interaction diagrams
- Output tools: Excel table export, deformed shape visualization, section cuts, and report generation
Frequently Asked Questions
How do I set up a grid system in ETABS?
Go to Define > Coord Systems/Grids. Set up X-direction grids (e.g., A, B, C at 8m spacing), Y-direction grids (e.g., 1, 2, 3 at 6m spacing), and Z-direction for story heights (e.g., 3.5m typical). Use Story Data to define floor levels including lobby height (4.5m), typical floors (3.5m), and penthouse (3.0m). Similar Stories can batch-define repeated typical floors.
How do I define seismic loads in ETABS per Korean standards?
Go to Define > Load Patterns and select Seismic type with Auto Lateral Load set to KDS 41 17. Enter the effective ground acceleration (S=0.22g for Seoul area), soil type (S3 for stiff soil), response modification factor (R=5 for special moment frames), and importance factor (I=1.2 for essential facilities). For response spectrum analysis, define the design spectrum function under Define > Functions > Response Spectrum with 5% damping and CQC combination method.
What is the mass participation ratio and how many modes do I need?
The mass participation ratio measures how much of the building mass is captured by the analyzed modes. Per KDS 41 17, the cumulative mass participation must be at least 90% in each horizontal direction. A common rule of thumb is to use at least 3 times the number of stories as the minimum number of modes. Check results in the modal analysis output to verify the 90% threshold is met.
How do I check story drift in ETABS?
After running the analysis, go to Display > Tables > Story Drifts. The allowable inter-story drift ratio per KDS is h/200, where h is the story height. Check drift ratios separately for X and Y directions under each seismic load combination. Identify the story and direction with maximum drift to determine if stiffening is needed. Story Response Plots can visualize drift distribution across all floors.
What is the difference between concrete and steel frame design in ETABS?
Concrete frame design (Design > Concrete Frame > Start Design) uses KDS 14 20 (KCI 2012) code and checks columns for axial-moment interaction and beams for flexural/shear reinforcement requirements, outputting required rebar quantities. Steel frame design (Design > Steel Frame > Start Design) uses KDS 14 31 (AISC 360) and checks tension, compression, flexure, shear, and slenderness (KL/r). Both report Demand/Capacity (D/C) ratios that must be less than 1.0.
How do I assign rigid diaphragms and why are they important?
Go to Assign > Shell > Diaphragms and assign a Rigid Diaphragm to each floor slab. This constrains all nodes on the floor to move together as a rigid body with three degrees of freedom (UX, UY, RZ), automatically generating a master joint at the center of mass. Rigid diaphragms are essential for correct lateral load distribution in seismic and wind analysis of building structures.
How do I enable P-Delta analysis in ETABS?
Go to Analyze > Set Analysis Options and enable P-Delta. Define the P-Delta load combination, typically 1.0D + 0.5L (dead plus reduced live load representing the gravity load during an earthquake). Set a minimum of 2 iterations and a convergence tolerance of 0.01. P-Delta accounts for secondary effects from gravity loads acting on the laterally displaced structure, which can increase member forces by 10-20% in tall buildings.
How do I export ETABS results to Excel?
Go to File > Export > Tables to Excel. You can select specific result tables including Joint Reactions (foundation forces), Frame Forces (member forces), Story Drifts (inter-story displacements), and Design Results (reinforcement or D/C ratios). For formal deliverables, use File > Report Setup to generate automatic reports with graphs, tables, model information, and loading details in Word or PDF format using structural calculation templates.