2C09 Design for seismic and climate change - UPT hazard... · 2C09 Design for seismic and climate change Mario D’Aniello European Erasmus Mundus Master Course Sustainable Constructions

2C09

Design for seismic

and climate change

Mario D’Aniello

European Erasmus Mundus Master Course

Sustainable Constructions

under Natural Hazards and Catastrophic Events 520121-1-2011-1-CZ-ERA MUNDUS-EMMC

European Erasmus Mundus

Master Course


under Natural Hazards

and Catastrophic Events

List of Lectures

1. Earthquake-Resistant Design of Structures I

2. Earthquake-Resistant Design of Structures II

3. Seismic Design of Steel Structures

2


Master Course




Earthquake-Resistant Design of Structures I

1. Seismic Risk

2. Some examples of recent earthquakes

3. Principles and objectives of earthquake resistant design

4. Practical aspects of earthquake resistant design

3


Master Course





1. Seismic Risk




4


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

The term Risk refers to the expected losses from a given hazard to a given element at risk, over a specified future time period. Seismic Risk is the possibility of a seismic disaster (human and economic losses) because of a complex combination of seismic hazard and vulnerability of the elements at risk.

Seismic Risk

5

HAZARD

ELEMENT AT RISK

VULNERABILITY

RISK

the probability of occurrence of a specified natural hazard at a specified severity level in a specified future time period

people or buildings or other elements which would be affected by the hazard if it occurred

how damaged the elements at risk would be if they experienced some level of hazard


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Risk

6

• Assess the HAZARD

SEISMIC RISK MITIGATION

HAZARD Analysis

Seismic zonation

VULNERABILITY Reduction

- Seismic design of new buildings

- Retrofit of existing buildings

• Reduce the VULNERABILITY

of elements at risk


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Probabilistic Seismic Hazard Analysis (PSHA) Probabilistic Seismic Hazard Analysis provides an estimate of the likelihood of hazard from earthquakes based on geological and seismological studies. It is probabilistic in the sense that the analysis takes into consideration the uncertainties in the size and location of earthquakes and the resulting ground motions that could affect a particular site. Probabilistic analysis uses four basic steps in order to characterize the probable seismic hazard: • Identification of the seismic source or faults

• Characterization of annual rates of seismic events

• Development of attenuation relationships

• Combining factors

Seismic Risk

7


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Secondary Earthquake Effects The most drastic effects occur mainly near the causative fault, with appreciable ground displacement and strong ground shaking. At greater distance, noticeable earthquake effects often depend on the topography and nature of the soils, and are more severe in unconsolidated sediment basins. Many earthquake effects are related to the geology and form of the soil: • Ground Shaking Intensity

• Landslides

• Anomalous Water Waves

• Liquefaction

Seismic Risk

8


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Ground Shaking Intensity Seismic intensity on the earth’s surface depends on many factors, including the source moment M0, area of the rupture fault, the fault mechanism, the frequency-spectrum of wave energy released, the geological conditions, and the soils at a given site. The geographical distribution of intensity is summarized by constructing iso-seismal curves, or contour lines, which separate areas of equal intensity. The most probable position of the epicenter and the causative fault rupture is inside the area of highest intensity. Peak Ground Acceleration is used as a measure in the current Seismic Hazard Maps.

Seismic Risk

9


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Risk

10

Global Seismic Hazard Map

- 40% of populated regions concerned

- High humans losses and economic losses every year

- Significant impact on global business (export of know how, services, structures and installations)


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Risk

11

European-Mediterranean seismic hazard map for the peak ground acceleration with 10% probability of exceedance in 50 years for stiff soil condition.

Peak

gro

un

d a

ccel

erat

ion

[g]

1.00

0.40

0.32

0.24

0.16

0.08

0.04

0.02

0.00


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Landslides During an earthquake, a series of seismic waves shakes the ground in all directions, so that under the critical conditions of water saturation, slope, and soil type, even relatively low levels of ground acceleration can cause a landslide. Even if these dynamic accelerations last for only a short time, widespread sliding can occur on marginally stable slopes. In many instances, smaller landslides and avalanches can be detected in advance by suitable instrumentation installed on the slope with the readings monitored at regular intervals. Means of control can then be applied in appropriate circumstances: for example, removing small volumes of material to relieve the load at the head of the slope and adding material to the toe can be accomplished by earth-moving equipment.

Seismic Risk

12


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Landslides

Seismic Risk

13

Landslides in Japan after 16 July 2007 earthquake.


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Anomalous Water Waves The occurrence of an earthquake and a sudden offset along a major fault under the ocean floor, or a large submarine landslide, displaces the water like a giant paddle, thus producing powerful water waves (Tsunamis) at the ocean surface. When they reach a coastline, they may run up on land to many hundreds of meters. The best disaster prevention measures for a tsunami-prone coast involve zoning that controls the types and sizes of buildings that, if any, are permitted. If a site has a high possibility of tsunami incursion, the designer should consider some of the design provisions against flood, such as elevating the building above an estimated waterline. Of course in the case of locally generated tsunami, provisions must also be made for the severe strong shaking.

Seismic Risk

14


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Anomalous Water Waves

Seismic Risk

15


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Liquefaction A notable hazard in case of moderate and large earthquakes is the liquefaction of water-saturated soil and sand produced by the ground shaking. In an earthquake, the fine-grained soil below the ground surface is subjected to alternations of shear and stress. In cases of low-permeability soils and sand, the water does not drain out during the vibration, building up pore pressure that reduces the strength of the soil. In some cases, it is a major cause of damage and therefore is a factor in the assessment of seismic risk.

Seismic Risk

16


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Liquefaction

Seismic Risk

17

Kocaeli earthquake, Turkey, August 17, 1999, Magnitude 7.4

Nigata earthquake, Japan, August 17, 1964, Magnitude 7.6

Effects of liquefaction failure of the foundation soil.


Master Course





1. Seismic Risk




18


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Source: ISIDE

Some examples of recent earthquakes

Recent Italian Earthquakes: • The Emilia Earthquake on 20th May 2012

• The Abruzzo Earthquake on 6th April 2009


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

THE MAINSHOCK THE EPICENTER

On May 20th 2012 an earthquake occurred in Mirandola, near Modena. The maximum acceleration registered is 0.25g (10 km from the epicenter).

Source: ISIDE

The Emilia Earthquake on 20th May 2012


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

NUMBER OF DAILY EARTHQUAKES

On May 20th and 29th 2012 were registered the two mainshocks and several aftershocks in the next days.



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

MAINSHOCKS AND AFTERSHOCKS



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

EPICENTER OF THE MAINSHOCK IN THE NATIONAL HAZARD MAP

The maximum acceleration registered is 0.25g (10 km from the epicenter). The acceleration considered from the national hazard map, corresponding to a return period of 475 years is about 0.125g – 0.15g. The earthquake area can be considered low-medium seismicity in the national classification.



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Comparison between the spectra for the horizontal (sx) and vertical (dx) code spectra for different classed of soil, and the spectra of the waveform registered in Mirandola station.

20th MAY

29th MAY



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

The observed damages MASONRY BUILDINGS

Crisis of a masonry panel for in plane actions Total collapse of a masonry building

Typical X cracking Horizontal crack near the roofing



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

REINFORCED CONCRETE BUILDINGS

R.C. column crisis for soft storey mechanism.

Collapse of a masonry building

Secondary elements damage Shear damage in R.C. column


The observed damages


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

STEEL BUILDINGS

Collapse of a steel industrial building




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

PRESTRESSED CONCRETE BUILDINGS MULTISTOREY BUILDINGS




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

PRESTRESSED CONCRETE BUILDINGS SINGLE STOREY BUILDINGS: TOTAL COLLAPSE




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

PRESTRESSED CONCRETE BUILDINGS COVERINGS COLLAPSE




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

PRESTRESSED CONCRETE BUILDINGS SUPPORT DAMAGING




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

PRESTRESSED CONCRETE BUILDINGS SECONDARY ELEMENTS COLLAPSE




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

THE MAINSHOCKS

Date April 6th, 2009 Local time 03:33 a.m.

Local magnitude Ml=5.8 Moment magnitude Mw= 6.2

ONE AFTERSHOCKS

Date April 7th, 2009 Local time 05:47 p.m.

Local magnitude Ml=5.3

On April 6th 2009 an earthquake occurred near L'Aquila as a result of normal faulting on a NW-SE oriented structure about 15 km long.

The Abruzzo Earthquake on 6th April 2009


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

During the days following the main event the Italian National Seismic Network located several hundreds of aftershocks .

The area interested by seismicity is about 30 km long and strikes in the NW-SE direction, parallel to the Apennine mountain axis and to the main fault structures known in the area.

Moment Magnitude Mw= 6.2 Max average peak ground acceleration PGA=0.626g



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Onna




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

BEFORE THE EARTHQUAKE




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects



AFTER THE EARTHQUAKE

MASONRY BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Building A Building B


The observed damages REINFORCED CONCRETE BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

BUILDING A




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

BUILDING B




Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

STATISTICS Post-earthquake damage states

A B C D E F

Masonry buildings 48,70% 10,70% 2,60% 1,20% 30,50% 6,30%

Mixed structure 62,90% 11,30% 3,00% 0,60% 17,10% 5,10%

R.C. buildings 61,60% 19,40% 2,30% 1,10% 13,50% 2,10%

Total 52,60% 12,50% 2,60% 1,00% 26,50% 5,40%

A52%

B13%

C3%

D1%

E26%

F5%

A OPERATIONAL

B

C LIMITED OCCUPANCY

D

E UNSAFE

F UNSAFE FOR EXTERNAL RISK

Post-earthquake damage state of buildings

IMMEDIATE OCCUPANCY the building remain safe to

occupy. Any repairs are minor

NO OCCUPANCY UNLESS DETAILED INVESTIGATIONS



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects WHAT ABOUT STEEL CONSTRUCTIONS

?


A52%

B13%

C3%

D1%

E26%

F5%

STATISTICS Post-earthquake damage states


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

INDUSTRIAL DISTRICT, PILE, L’AQUILA


STEEL BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

SHOPPING CENTRE, PILE, L’AQUILA


STEEL BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

SHOPPING CENTRE, PILE, L’AQUILA


STEEL BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

INDUSTRIAL DISTRICT, BAZZANO, L’AQUILA

Most of steel buildings were fully operational. Just few components in industrial plants, i.e. the Bazzano’s steel silos, suffered for post-earthquakes damages.


STEEL BUILDINGS


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Lesson learned from past earthquakes

50

The analysis of post-earthquake scenarios reveals that steel structures most likely will provide high performances even in case of strong ground motions, most likely suffering for negligible earthquake induced damage if compared with traditional masonry and reinforced concrete buildings.

“Buildings of structural steel have performed excellently and better than any other type of substantial construction in protecting life safety, limiting economic loss, and minimizing business interruption due to earthquake-induced damage.”

Yanev, P.I., Gillengerten, J.D., and Hamburger, R.O. (1991). The Performance of Steel Buildings in Past Earthquakes. The American Iron and Steel Institute


Master Course





1. Seismic Risk




51


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

• Dissipative systems

• Tuned mass damper

Passive control systems

Active control systems

Iper-resistant systems

• Base isolation

• Active mass damper

• Stiffness control

• Force control

Earthquake Resistant Design can be applied according to different design strategies, all based on structural control. The differences are about the energy (seismic input) dissipation/absorption technique.

• Non-dissipative systems

STRUCTURAL CONTROL

Earthquake Resistant Design


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Iper-resistant or non-dissipative systems are designed to remain in the elastic range, not only during frequent seismic events, having a return period comparable with the service life of the structure, but also in the case of destructive earthquakes, having a low probability of occurrence. This design strategy is usually adopted for strategical buildings, in which the damage of both structural and non-structural elements (which derives from the development of dissipative mechanisms) is not accepted. The resistance of structural elements in the only parameter to be controlled.


Iper-resistant systems


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Active control systems are designed so that, in case of seismic actions, specific devices are able to modify the structural response. These structural systems typically requires a power source or utilizes the motion of the structure to develop the control forces, the magnitude of which can be adjusted by the external power source. Control forces are developed based on feedback from sensors that measure the excitation and/or the response of the structure. Applications of these systems are developing in the last years.

Taipei Tower 101


Active control systems


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Passive control systems are designed so that the energy dissipation capacity of a structure is increased, by means of energy dissipation devices located either within a seismic isolation system or over the height of the structure. • Dissipative structures are systems in which some structural elements or special devices are able to absorb a significant amount of the seismic input energy, thus reducing the demand on the structural system.

• Seismic isolation is another form of passive control in which an isolation system is introduced between the foundation and the superstructure so as to increase the natural period of the system.


Passive control systems


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Isolation There are basically two types of Base Isolation systems: • Elastomeric bearings, that are composed of rubber sheets, alternated together with levels of steel, and in some types with a solid lead plug, inserted between top and bottom steel plates. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.

• Sliding system, that works by limiting the transfer of shear across the isolation interface. Many sliding systems have been proposed and some have been used. The friction-pendulum system is a sliding system using a special interfacial material sliding on stainless steel and has been used for several projects in the United States.



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Isolation Elastomeric bearings


Isolated system: Regional Government Building in Nagoya


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Isolation Sliding system


+9.45m

+6.40m

+3.35m

-3.45m

-2.25m

+0.00m


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Seismic Isolation

The isolation system increases the natural period of the system. This results in the deflection of a major portion of the earthquake energy, reducing accelerations in the superstructure while increasing the displacement across the isolation level. Base Isolation also protects non-structural elements and instruments by lessening the entire structure’s speed during an earthquake.

In reality base isolation is not suitable for all buildings. High-rise buildings, buildings rested on soft soil are not suitable for base isolation.



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Dissipative Structures Supplemental energy dissipation devices may take many forms and dissipate energy through a variety of mechanisms (yielding, viscoelastic actions, sliding friction). In ordinary dissipative structures the energy input is dissipated trough the hysteretic plasticization of some structural elements. In the structure are preliminary detected some parts addressed to the plasticization (ductile elements or dissipative zones) and the rest (non-dissipative zones) are considered as brittle elements, addressed to be in elastic range. This strategy results in the controlled damaging of structural elements, avoiding brittle fracture or non global plastic mechanisms.


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

• Define a global plastic mechanism

• Preliminary detection of the ductile elements or dissipative zones, addressed to the plasticization and of the brittle elements, addressed to be in elastic range

Global capacity design

• Non dissipative members have to be overstrength with respect to dissipative zones, to allow the cyclic plasticization of them

Hierarchy criteria

• All intended plastic zones must fully develop: through “detailing rules” it can be given the maximum ductility to the dissipative zones and so to the whole structure

Ductility requirement

• Allows the formation of local plastic mechanisms and ensures the transfer of full plastic forces

• Concerns mainly connections

Local capacity design


Design Principles


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Capacity Design • AT BUILDING LEVEL:

Ductile element: Structure

Brittle elements: Overstrength floor and foundation



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

© Raffaele Landolfo

Capacity Design • AT STRUCTURE LEVEL:

Brittle elements: Overstrength beams and columns

Ductile elements: Plastic hinges at the beam ends



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Capacity Design • AT MEMBER LEVEL:

Shear failure mode = Brittle

Flexural failure mode = Ductile

Facilitate the ductile crisis:



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List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Capacity Design • AT SECTION LEVEL:

Brittle element: Overstrength concrete

Ductile element: Steel bars

Facilitate the ductile crisis (due to steel):



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

Capacity Design • AT CONNECTION LEVEL:

Brittle element: overstrength

Foundation

Colu

mn

Beam

Colu

mn

Ductile elements

Brittle element: overstrength

Connections have to be overstrength with respect to dissipative zones, to allow their cyclic plasticization (local hierarchy).



Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility For capacity design it is important to dissipative zones, considered as ductile elements and non-dissipative zones, considered as brittle elements. Ductility is a fundamental requirement for dissipative structure design. Ductility: capability to perform plastic deformations without failure.

F - ID

-150.00

-100.00

-50.00

0.00

50.00

100.00

150.00

-6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00

ID [%]

F [

kN

]

© R affaele L andolfo

LOAD

DEFORMATION

PLASTICIZATION

PLASTICIZATION

Dissipation of energy is introduced into the structure by plastic cyclic behaviour.


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility The global ductility of a composed system depends on its elements ductility.


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility 1°CASE: the resistance of the ductile element is higher than the brittle element one FRD >> FRF


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility 2°CASE: the resistance of the ductile element is lower than the brittle element one FRD < FRF


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility at different levels


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List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility Ductility is a fundamental requirement for dissipative structure design. In dissipative structures, a reduced value of the seismic action can be considered. The seismic input is reduced proportionally to the available ductility of the structure. The reduction of seismic forces is obtained trough the use of a behaviour factor “q”.


Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects


Ductility and behaviour factor “q” The quantitative measure of global ductility is represented by the behaviour factor “q”,that is used for the reduction of seismic forces . This parameter is influenced by:

Construction system

Structural typology

Ductility classes

• R.C. buildings

• Steel buildings

• Masonry buildings

• Frames

• Walls

• Bracings

• High ductility

• Medium ductility

• Low ductility

BEHAVIOUR

FACTOR “q”


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1. Seismic Risk




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Master Course




List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

Practical aspects

General Design Rules for Buildings

In seismic regions the aspect of seismic hazard shall be taken into account in the early stages of the conceptual design of a building. The guiding principles governing this conceptual design are: • structural simplicity;

• uniformity, symmetry and redundancy;

• bi-directional resistance and stiffness;

• torsional resistance and stiffness;

• diaphragmatic behaviour at storey level;

• adequate foundation.

Regularity in plan Regularity in elevation

Position of seismic resistant systems


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Building attributes for Regular Structural/Architectural Configuration:

• Continuous load path: Uniform loading of structural elements and no stress concentrations.

• Low height-to base ratio: Minimizes tendency to overturn.

• Equal floor heights: Equalizes column or wall stiffness, no stress concentrations.

• Symmetrical plan shape: Minimizes torsion.

• Identical resistance on both axes: Avoid eccentricity between the centers of mass and resistance and provides balanced resistance in all directions, minimizing torsion.

• Identical vertical resistance: No concentrations of strength or weakness.

• Uniform section and elevations: Minimizes stress concentrations.

• Seismic resisting elements at perimeter: Maximum torsional resistance.

• Short spans: Low unit stress in members, multiple columns provide redundancy -loads can be redistributed if some columns are lost.

• No cantilevers: Reduced vulnerability to vertical accelerations.

• No openings in diaphragms(floors and roof): Ensures direct transfer of lateral forces to the resistant elements.


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Use of Regular Configurations A design that has attributes of the ideal configuration should be used when: • The most economical design and construction is needed, including design and analysis for code conformance, simplicity of seismic detailing, and repetition of structural component sizes and placement conditions.

• When best seismic performance for lowest cost is needed.

• When maximum predictability of seismic performance is desired.


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Designs for Irregular Configurations When irregularities cannot be avoided : • The designer should be aware of the implications of design irregularities and should have a feel for the likelihood of stress concentrations and torsional effects (both the cause and remedy of these conditions lie in the architectural/structural design, not in code provisions).

• Extreme irregularities may require extreme engineering solutions, but these may be costly.

• A soft or weak story should never be used: this does not mean that high stories or varied story heights cannot be used, but rather that appropriate structural measures be taken to ensure balanced resistance.


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Earthquake

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Designs for Irregular Configurations Four configuration conditions (two vertical and two in plan) that originate in the structural design and that have the potential to seriously impact seismic performance are: • Soft and weak stories

• Discontinuous shear walls

• Variations in perimeter strength and stiffness

• Reentrant corners


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Designs for Irregular Configurations For the most part, code provisions seek to discourage irregularity in design by imposing penalties, which are of three types: • Requiring increased design forces.

• Requiring a more advanced (and expensive) analysis procedure.

• Disallowing extreme soft stories and extreme torsional imbalance in high seismic zones.


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Seismic Risk

Examples of recent

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To be avoided:


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List of contents:

Seismic Risk

Examples of recent

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Earthquake

Resistant Design

Principles and

objectives

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To be avoided:


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List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

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Regularity in plan:

• With respect to the lateral stiffness and mass distribution, the building structure shall be approximately symmetrical in plan with respect to two orthogonal axes;

• The slenderness l = Lmax/Lmin of the building in plan shall be not higher than 4; • The plan configuration shall be compact. If in plan set-backs (re-entrant corners or edge recesses) exist, their dimensions must not exceed 25 % of the total dimension;

• The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the vertical structural elements, in order to satisfy the rigid diaphragm condition.


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Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

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Regularity in elevation:

• All lateral load resisting systems, such as cores, structural walls, or frames, shall run without interruption from their foundations to the top of the building; • Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually, from the base to the top the building;

• When setbacks are present: - for gradual setbacks, they shall not exceed 20 % of the previous plan dimension; - if the setbacks do not preserve symmetry, in each face the sum of the setbacks at all storeys shall be not greater than 30 % of the plan dimension at the ground floor, and the individual setbacks shall be not greater than 10 % of the previous plan dimension.


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List of contents:

Seismic Risk

Examples of recent

earthquakes

Earthquake

Resistant Design

Principles and

objectives

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Position of seismic resistant elements:

• 3 seismic resistant elements are sufficient to guarantee the equilibrium with respect to the seismic horizontal actions (to be isostatic), but in general practice it is used at least 2 seismic resistant elements for each principal direction (ipertstatic);

• the seismic resistant elements have to be positioned as far as possible from the centre (mass and stiffness) and in a way that the eccentricity between the centre of stiffness and the centre of mass must be minimized.

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List of contents:

Seismic Risk

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Earthquake

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REGULAR

CONFIGURATIONS

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NON REGULAR

CONFIGURATIONS


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In plan bracings

R.C. core

R.C. wall

In plan bracings

Vertical bracings


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Seismic Risk

Examples of recent

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Earthquake

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Position of seismic resistant elements: R.C. CORES

L2

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