risk projects - rc frame - perform

Evaluation of Structures RISK PROJECTS

Evaluation of a RC-Frame using Perform-3D

Name: David Gutierrez Rivera Mtrkl. Nr.: 101082

NHRE - Masters Course Natural Hazards and Risks in Structural Engineering

Risk Projects: Evaluation of Structures

CONTENTS

PAGE

INTRODUCTION --------------------------------------------------------------------------- 2

1) PROJECT DESCRIPTION ------------------------------------------------------------- 3 A) FRAME LAYOUT ------------------------------------------------------------------ 3 B) MATERIAL PROPERTIES -------------------------------------------------------- 4 C) LOADS ------------------------------------------------------------------------------ 5

2) MODELING ----------------------------------------------------------------------------- 6 A) MATERIAL PROPERTIES ------------------------------------------------------- 6 B) CROSS-SECTIONS --------------------------------------------------------------- 8 C) LIMIT-STATES -------------------------------------------------------------------- 8

3) MODAL ANALYSIS -------------------------------------------------------------------- 9 4) TIME-HISTORY ANALYSIS ----------------------------------------------------------- 10

A) RETROFITTING ------------------------------------------------------------------ 10 5) PUSHOVER ANALYSIS --------------------------------------------------------------- 12 6) PERFORMANCE POINT --------------------------------------------------------------- 13 7) PERFORMANCE-BASED DESIGN -------------------------------------------------- 14 8) CONCLUSIONS ------------------------------------------------------------------------ 16 9) ANNEX


INTRODUCTION

In this project we have the task of modeling a 4 storey RC-Frame using the software PERFORM-3D. The purpose of the project is to perform analysis and design for an Earthquake Resistant Design building by using Fiber Elements to model the RC-Frame. We will evaluate the structures performance by using Pushover Analysis and Time-History Analysis. We will also perform a Performance-Based Design to compare cross-section size and overall cost of the structure with the original.


PROJECT DESCRIPTION

The structure of study is a 4-storey RC frame. This frame is representative of the construction 40-50 years old in European, Mediterranean countries such as Italy, Portugal and Greece, this means this structures are non-seismic resisting and where designed to resist a nominal lateral load of about 8% of its self-weight.

Frame Layout

The RC-frame dimension and layout is given in the figure below:


The relevant cross-sections of Columns and Beams are given below:

Material Properties

The following are the materials used for the design of the RC-Frame:


Loads

The following are the loads to which the RC-Frame is subjected to:


MODELING

The Modeling of the Frame elements was performed by using Column-Type Fiber Cross Sections, for both the beams and columns of the Frame.

3 Types of Material Properties were defined to model this elements:

- Steel Reinforcement - Cover Concrete - Core Concrete

Material Properties


We also defined Core Concrete material properties for each type of column; this can be checked in the Perform-3D Model Files.


Cross-Sections

Limit States

The following Limit States were defined:

1) Immediate Occupancy ----------------- IO 2) Damage Limitation ---------------------- DL

i. Concrete Plastic ii. Concrete Spalling

iii. Core Concrete Degradation 3) Life Safety----------------------------------- LS 4) Collapse Prevention --------------------- CP 5) Collapse ------------------------------------- C


MODAL ANALYSIS

A Modal Analysis was performed for the structure to obtain the structures dynamic properties. The first 3 modes are shown with their corresponding natural periods.

Mode1 ; T = 0.9780s Mode2 ; T = 0.3346s

Mode3 ; T = 0.2047s


TIME HISTORY ANALYSIS

We subjected the structure to 3 types of Ground Motion with different Return Periods and performed a Time-History Analysis of the structure to obtain its behavior under the earthquake loads. The Ground Motions we used are shown below:


The highest Ground Motion produces high stresses on column type B1 (indicated in the figure), and gets close (but not there yet) to the Concrete Spalling Damage State.

Retrofitting

Evaluation of the structure predicts that damage will occur on column B1, therefore it seems appropriate to use column jacketing for this column to improve its resistance and the Life-Time of the structure. This can be done after a severe event has occurred that damage the column and it is necessary to improve its strength.


PUSHOVER ANALYSIS

We performed 3 types of Pushover Analysis, with different Load Distributions and in each direction and obtained 3 Capacity Curves for each direction. The 3 types of Loading Distribution we used for the Pushover Analysis are:

- Constant Lateral Loading - Triangular Lateral Load - 1st Mode Shape

PERFORMANCE POINT

00.010.020.030.040.050.060.070.080.09

0 100 200 300 400 500 600 700 800

Sa (g

)

Sd (mm)

Capacity Curves - L-Dir

Modal_L

Triangular_L

Constant_L

00.010.020.030.040.050.060.070.080.09

0 200 400 600 800 1000

Sa (g

)

Sd (mm)

Capacity Curves - R-Dir

Modal_R

Tirangular_R

Constant_R


We observe that the Modal and Triangular Load Distributions produce the most conservative Capacity Curves. We choose the Modal Left Direction as the critical and most representative Capacity Curve for the Structure.

By using this Capacity Curve and the EC8 Response Spectra and converting it to ADRS (Accel. Displ. Response Spectra) we plot both graphs and the intersecting point is the so called Performance Point of the Structure.

Using worst case scenario for the Soil Factor and Seismic Site Coeficientes for my Home Country we plot the ADRS graph with the Capacity curve and obtain the Performance Point:

S = 1.5ag = 0.35 g

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 50 100 150 200 250 300

Sa (g

)

Sd (mm)

Performance Point

CC - Original

ADRS

Dmg States

PP


PERFORMANCE-BASED DESIGN

In order to proceed with the Performance-Based Design we need to establish a Performance Requirement for the Structure. We choose the Performance Requirement for the Structure as the following:

Damage Limitation Requirement (No Concrete Spalling) should be achieved for an event with a Return Period of 475 years

With this we iteratively modify the structure in order to achieve a structure which withstands all other loads and achieves this Performance Requirement.

With the new modified structure we obtain a structure we the following dynamical properties:

Mode # Period (T)1 1.33 s2 0.478 s3 0.3 s

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 50 100 150 200 250 300

Sa (g

)

Sd (mm)

Performance - Based Design

CC - Original

ADRS

Dmg States

PP

CC - PBD

Concrete Spalling


The final structure gets the following cross-sections for Columns and Beams:

500 300

200

4 20 4 12

10

200

250

6 12

10

3 16

1 12

6 16

1 12

3 16 2 16 2 16

2 16 2 16

10 10 10 10 10 10 10 10


CONCLUSIONS

1) Using Triangular or Modal Loading seems to be the best options for Pushover Analysis, preferably the Modal Load Distribution.

2) Column Jacketing (for column B1) seems to be the most appropriate retrofitting technique to apply to this structure to increase its capacity.

3) The T-Beams in the Original structure are a bit overdesigned, they can be reduced considerably.

4) The Column type B1 is critical in this Frame structure and the capacity of the overall frame revolves around it.

5) Performance-Based design has a more influential effect in Higher Seismic Zones with higher loads. PBD has an effect on the design of Column B1, by increasing its size more than if wasnt PBD.


ANNEX


Page No. 2Date:

(+) Bending Design T-Beam Design

Design (+) MomentMed = 35 kN-m

Normalized Bending MomentRev. for Neutral Axis Limit


Page No. 3Date:

(-) Bending Design T-Beam Design

Design (-) MomentMed (-) = 70 kN-m



Page No. 3Date:

Bending Check Column Design

Design MomentMed = 59.153 kN-m



Page No. 3Date:

Bending Check Column Design

Design MomentMed = 16.624 kN-m


risk projects - rc frame - perform

Documents

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frame layout

storey rcframe

storey rc frame

rcframe dimension

structures performance

annex risk projects

pushover analysis