Earthquake Analysis with RSA

Introduction

The following tutorial is focused on the workflow for the earthquake analysis based on the Response Spectrum Analysis (RSA) method, including the subsequent design of beam and area elements for the seismic design situation.

Project Description

Please see the following project information before starting to set up your project files.

Materials

Number

Material

Strength

1

concrete

C 20/25

2

reinforcement steel

S 500

Cross Sections

Element

Dimension

Weight

Column

B/H = 30/30 cm

g = 0,225 t/m

T-Beam

B/H/Bw/Hf = 70/60/30/20 cm

g = 0,300 t/m (w/o slab flange)

T-Beam, edge

B/H/Bw/Hf = 50/60/30/20 cm

g = 0,300 t/m (w/o slab flange)

Slab

D = 20 cm

g = 0,500 t/m²

Geometry

../../_images/example-01.png

Loads

LC Number

Title

Loads

1

Dead Load

g1 = 1,50 kN/m² (100% mass active)

2

Live Load

q2 = 2,00 kN/m² (15% mass active)

3

Live Load Roof

q3 = 3,00 kN/m² (30% mass active)

10

structure self weight

automatic generation “Factor of dead weight” = 1.0

The following picture shows the loads and load cases on the structure.

../../_images/loads.png

For the Response Spectrum Analysis the following values we will be used

Response Spectrum according Eurocode

Type 1 –> EC-1

Type of Spectrum

Design Spectrum

Acceleration

Ag = 0.8 m/s²

Soil Class

A

SSD Earthquake Task

Title: Earthquake analysis with RSA - SSD Earthquake Task| Quality: 1080p HD | Captions: English

Seismic Design Situation

Combinations of the effects of the actions

After calculating the SSD Earthquake Task, by clicking on the “Define Combinations” Task in the SSD project, the necessary Combination Rules, including the ULS seismic combination Rule, will be generated automatically according to the selected design code. By clicking OK the generated Combination Rules will be saved in the database.

../../_images/maxima-comb.png

Selection of available results for each of the previously generated Combination rules is availble in the SSD Task “Superpositioning”. In the tutorial only the results of the ULS fundamental and ULS seismic combination are selected. For example, the resulting forces in beam elements for the ULS seismic combination will be stored in loadcases starting with the First Loadcase No. 2621. By clicking OK the selected superpositioning results will be calculated.

../../_images/maxima-supp.png

In the generated Superpositioning Report the ULS seismic combination rule 109 and the selection of the associated loadcases for the superposition will be listed.

../../_images/maxima-supp2.png

Determining the required reinforcement

To proceed with the design process, please add the following tasks by using the command “Insert Task” from the context menu, with the right mouse click.

  • Design ULS (Area elements)

  • Design SEIS (Area elements)

  • Design ULS (Beams)

  • Design SEIS (Beams)

The tasks are sorted in two groups, “Design Area Elements” and “Design Beam Elements”. Furthermore, the task “Design Parameters of area elements” has been added to the “Design Area Elements” group.

The following tutorial is focused on the Seismic Design Situation, i.e. on the tasks “Design SEIS (Area elements)” and “Design SEIS (Beams)”. For more information about the Design at the Ultimate Limit State please see the SSD Video Tutorial, Chapter 6: Design of Area and Beam Elements.

In the task “Design SEIS (Area elements)” the Designcase number for storing the calculated reinforcement needs to be specified, see point (1) in the picture below. By default it is set to 11. According to Eurocde 1998-1, chapter 5.2.4 (2), the safety partial factors for concrete and steel, adopted for the persistent and transient design situations, should be applied. Therefore, they are set as default values in the Task, see point (2). Furthermore, all resulting forces in area elements for the ULS seismic combination will be automatically selected by the Task, see point (3).

../../_images/desi-acci-quad.png

Similarly, in the task “Design SEIS (Beams)” the Designcase number will be set to 11, see point (1) in the picture below. Design loadcases for beam elements are automatically selected, see point (2), and the default values of the Partial Safety Factors, see point(3), are adopted acc. Eurocode 1998-1, chapter 5.2.4 (2).

../../_images/desi-acci-beam.png

Reinforcement envelope

Required reinforcement from different design cases needs to be combined to establish the reinforcement envelope. This will be done by an additional Text Editor Task, “Combine Design Results BEAM QUAD”

The input for the Text Editor Task is printed below:

+prog bemess urs:37.1
head Combine Design Results QUAD
CTRL LCRI 1,11          $ take results from distribution 1 and 11
CTRL LCR 20             $ accumulate both results and save maximum in distribution 20
end

+prog aqb urs:37.2
head Combine Design Results BEAM
rein rmod accu lcr 1    $ take results from distribution 1
rein rmod accu lcr 11   $ take results from distribution 11
rein rmod sing lcr 20   $ accumulate both results and save maximum in distribution 20
end

The final plot of the necessary beam reinforcement is shown in the picture below.

../../_images/results-reinf01.png