tall steel buildings

8/9/2019 tall steel buildings

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Prof. Florea Dinu

2014-2015

Steel structures

Part B: High rise buildings


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General Multistory frame buildings Present developments

Structural systems for multistory frame buildings Gravity load-resisting systems Lateral load-resisting systems

Beams and column elements Joints Floor systems Facade systems Fire protection

Response of frames to lateral loads New structural systems for seismic applications

List of contents

-IntroductionL1. Conceptual designof industrial buildings

L2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuilding

L5. Design of a tallbuilding- Concluding remarks


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Multistory frame buildings Multistory buildings

Tall buildings has always fascinated people

The construction techniques, both for infrastructure andsuprastructure, changed during the time

A building can be considered as tall when the effect oflateral loads is reflected in the design

It is important to take into account the effects of dead, live,

wind as well as seismic loads In order to achieve a good performance under these loads,

lateral deflections and accelerations should be limited

Old Walled City of Shibam, YemenMost of the city's houses come mainlyfrom the 16th century. Shibam is often called"the oldest skyscraper-city in the world.

Buildings reach 40 m height.

Old Walled City of Shibam, YemenMost of the city's houses come mainlyfrom the 16th century. Shibam is often called"the oldest skyscraper-city in the world.

Buildings reach 40 m height.

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Evolution of multistory frame buildings The first skyscraper was the ten-story

Home Insurance Building in Chicago,built in 18841885. The architect,Major William Le Baron Jenney,created the first load-bearing structuralframe.

Most early skyscrapers emerged in theareas of Chicago, London, and NewYork toward the end of the 19thcentury.

After an early competition betweenNew York City and Chicago, New Yorktook a firm lead, culminating with thecompletion of the Chrysler Building in1930 and the Empire State Building in1931, the world's tallest building forforty years.

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Evolution of multistory frame buildings

The skyline of New York City

List of contents

-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuilding



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Evolution of multistory frame buildings Multi-storey frame buildings

Skyscrapers also began to appear in other parts of theworld (Mexico City, Tokyo, Shanghai, Hong Kong,Singapore, Kuala Lumpur, Taipei, Jakarta, etc.).

Modern multistory buildings use steel for the main

structural members (or in combination with concrete composite structure) Despite the recent events that threatened the construction

of very tall buildings, their developments have beencontinuously increasing worldwide.

Many tall buildings were recently completed or are goingto be completed in the near future Dubai has 18completed buildings that rise at least 300 metres !!!!!! Thisincludes the tallest man made structure Burj Khalifa

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List of contents



Dubai, 1990

Dubai, 2003

Dubai, 2007


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Burj Dubai: 818mPresent development

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Challenges and uncertainties There are many challenges and

uncertainties related to thedevelopment of high rise buildings Preparedness for natural hazards

and man-made hazards blast and explosions, impact fire strong winds, earthquakes

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Challenges and uncertainties Cost

initial costs operational costs dismantling

Design and erection new design methodologies

(PBD) new systems, materials,

technologies Sustainability (Green or

sustainable buildings) Life Cycle Assessment Energy use Emissions from energy Water use

Waste reduction Productivity and health

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Reduction of wall thickness and weight withincreasing strength of steel

The wind turbines engineeredinto the Bahrain World TradeCenter, Manama


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Structural systems for multistory framebuildingsGravity load-resisting systemsLateral load-resisting systemsBeam and column elementsJointsFloor systemsFacade systemsFire protection

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Gravity load-resist ing system in multistory buildings Tall building floor structures generally do not differ substantially

from those in low-rise buildings; however, there are certain aspectsand properties that need to be considered in design: Floor weight need to be minimized Floor should be able to resist construction loads during the

erection process

Integration of mechanical services (such as ducts and pipes) inthe floor zone

Fire resistance of the floor system Buildability of structures Long spanning capability Necessity to reduce the weight of the floors so as to reduce the

size of columns and foundations and thus permit the use oflarger space. Floors are required to resist vertical loads and theyare usually supported by secondary beams. The spacing of thesupporting beams must be compatible with the resistance of thefloor slabs.

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Floor Structure in Multistory Buildings

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Floor systems in Multistory Buildings Different types of slabs can be used, in either composite or noncomposite form. Most slab types can be designed to act as composite with thesupporting beams if adequate shear connection is provided Faster construction if prefabricated or precasted elements ofsteel and reinforced concrete are used

Openings in the webs of beams are required to permit passageof horizontal services, such as pipes (for water and gas), cables(for electricity and electronic communication), ducts (air-conditioning), etc. Floor spanning systems must provide adequate stiffness to

avoid large deflections due to live load which could lead todamage of plaster and slab finishers. Where the deflection limit is too severe, pre-cambering with anappropriate initial deformation equal and opposite to that due tothe permanent loads can be employed to offset part of the

deflection.

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List of contents



Structural systems overview


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List of contents



Why is composite system better?


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List of contents



Why is composite system better? Comparison between different construction types


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List of contents



Why is composite system better?

Economic benefit compared to traditional construction: withequivalent loads significant reduction of section possible (up to30 %*, 2 to 3 sections) Decrease of deflection (2 to 4 times) and Increase inbearing resistance (2 to 3 times) compared to pure steel beam Reduction of construction height : The overall height of thebuilding may be reduced significantly (up to 30%* of the steelbeam height / storey ), thus an additional storey may be addedwith the same building height Reduction in surface protection (corrosion or fire) (ca. 15%) Increase in global stiffness of building and optimisedbehaviour in case of fire or earthquake: The connection betweensteel beam and concrete chord is uniform in all directions;Damping behaviour improved as well (vibration)

Comparison between different construction types


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List of contents



Different types of shear connectors

Headed shear studs weldedeither in the shop or on the jobside

Ductile connectors according to EC4


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List of contents



Bearing capacity: C20/25 C50/60


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List of contents



Shear studs in high strength concrete > C50/60

Further increase in bearing capacity

Requirements in construction Increased stress on shear joint Higher demand on shear connector


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List of contents



Shear connectors for special applications

In composite structures using high strength materials, standard

shear connectors show as not suitable as their ductility is nothigh enough

perforated shear connector (perfobond shear connector)


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List of contents

-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Composite construction - Application

In composite structures using high strength materials, standard

shear connectors show as not suitable as their ductility is nothigh enough

Parking Aix en Provence,France

Studs welded before orthrough the trays on site

Composite steel sections with camber

before mounting of the metal decks


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List of contents


Composite construction - Application

Parking Aix en Provence, France


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List of contents


Shanghai Financial Center

IPE 80 - 750 HE 100 - 1000


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List of contents


Welded section beams can be made withparallel flanges or tapered

The economic advantage of welded beamsis that they can be designed to provide therequired moment and shear resistance When tapered, their characteristics can bevaried along the beam span in accordancewith the loading pattern Several forms of tapered beams arepossible


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List of contents


Tapered beam: simply supported beam

A simply supported beam design with a maximum bendingmoment at the mid-span would require that they all effectivelytaper to a minimum at both ends, whereas a rigidly connectedbeam would have a minimum depth towards the mid-span.To make best use of this system, services should be placedtowards the smaller depth of the beam cross-sections.

Tapered composite beams: simply supported beam

Tapered beam is foundto be economical forspans of 13 to 20 m.


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List of contents


Tapered beam: haunched beamThe span length of a composite beam can be increased by

providing haunches or local stiffening of the beam-to-columnconnectionsThe length of haunch is typically 5 to 7% the span length fornon-sway frames or 7 to 15% for sway frames.Service ducts can pass below the beams as in conventional

construction

Haunched composite beam


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List of contents



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Slim-floor system

Integrated steel beams for Slim-floor systems

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List of contents


Request of modern architecture: Transparent structural envelopes with column free

ground floor design Flexibility for sustainable conversion of use Possibility to upgrade services for multifunctionalliving

Slim-floor construction (IFB / SFB):

Combines advantages of prefabricated slabelements with steel framed construction

Economic solutions fulfilling the above specifieddemands

The slim floor system cannot be used as part of theseismic load-resistance system


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List of contents


Slim-Floor beams - Fabrication


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List of contents


Slim-Floor beams - Advantages Floor thickness reduction Constructing floors of variable thicknesses Incorporating under-floor technicalequipment Freeing-up working space Built-in fire resistance Competitive pricing Easy to build Sustainable construction Lighter structures

Less faade surface Heating / cooling cost reduction Lower building height More natural light


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List of contents

-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptual

design of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Slim-Floor beams - Applications


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List of contents



I II III IV

Cellular beams can be made with parallel flanges, tapered orcurved Castellated beams have limited shear capacity and are bestused as long span secondary beams where concentrated loadscan be avoided.


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List of contents



Applications


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List of contents



Trusses are frequently used in multistory buildings for very longspan supports The openings created in the truss braces can be used toaccommodate large services Truss configuration creates difficulty for fire protection. Fireprotection wrapping is labor intensive and sprayed-protection systemscause a substantial mess to the services that pass through the webopening From a structural point of view, the benefit of using a compositetruss is due to the increase in stiffness rather than strength

Composite truss


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List of contents



Applications Composite Trusses WTC application


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List of contents



WTC application views during construction


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List of contents



WTC application fire performance


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Several forms of truss arrangement are possible. The threemost common web framing configurations in floor truss and joist designs are: Warren Truss Modified Warren Truss Pratt Truss

Truss typesList of contents



Truss configuration: (a) Warrentruss, (b) Modified Warren truss,

and (c) Pratt truss.


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List of contents



The stub girder system involves the use of short beam stubs that are

welded to the top flange of a continuous, heavier bottom girder member,and connected to the concrete slab through the use of shear studs.Continuous transverse secondary beams and ducts can pass through theopenings formed by the beam stub. The natural openings in the stub girdersystem allow the integration of structural and service zones in two

directions, permitting story-height reduction when compared with someother structural framing systems.


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Parallel Beam System The system consists of two main beams with secondary beams run

over the top of the main beams. The main beams are connected toeither side of the column.

This will help in reducing the construction depth The secondary beams are designed to act compositely with the slab

and may also be made to span continuously over the main beams.The need to cut the secondary beams at every junction is thusavoided.

The parallel beam system is ideallysuited for accommodating large service

ducts in orthogonal directions

Special typesList of contents




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Prestressed Composite Beams Prestressing of the steel girders is carried out such that the

concrete slab remains uncracked under the working loads andthe steel is utilized fully in terms of stress in the tension zone ofthe girder.

It enhances the load-carrying capacity and stiffness of long-

span structures

Special typesList of contents




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A rigid unbraced frame may be capable of resisting lateral loadswithout relying on an additional bracing system in case of a lowto medium-height building

High-rise building systems should use structural systems that areeffective in resisting the larger lateral loads

Types of lateral-load resisting systems (R. Plank, M. McEvoy): Shear frames: beams and columns connected with rigid joints Shear truss: bracing between columns to form vertical shear trusses Shear truss-frames: shear frames + shear trusses Shear truss-frame-outrigger and belt trusses: internal core is connected to

perimeter frames by deep girders outriggers. Framed tubes: close spacing columns on the exterior frames forming a vertical

tube. The tube behaves as a cantilever Truss tubes: the same system as framed tubes, tied by a system of diagonals Bundled or modular tubes: framed or trusses tubes grouped together like cells Super-frame: megaframe in the overall form of a Vierendeel frame Composite systems: mixed RC and steel systems (concrete shear walls or

concrete framed tubes combined with various structural steel framings

Recommended limits for typical multistory frames are given inthe next table

Lateral-load resisting systemsList of contents




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Steel systems

Lever House

building,

New

York, 1952

Chicago Civic Center Building, 1965

First Wisconsin Center Building,1974 WTC Building, 1972

Sears Towers Building, Chicago, 1974 John Hancock Center building, Chicago, 1969

B u

t t r e s s e

d c o r e


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Hongkong and Shanghai BankCompleted 1986180 meters height

Structural systems for multistory buildings

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Structural systems Even for high seismic areas,

for buildings with more then25-30 stories, the wind loadbecomes predominant indesign

However, seismic designphilosophy should taken intoaccount (structural system,local detailing, .)

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Homogenous frames

Unbraced frames (moment resisting frames)

Staggered truss systems

Types of frames

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Homogenous frames Centrically braced frames

One-storyx-bracing

single diagonal

Two-storyx-bracing

Chevron bracing

(V or inverted V)Zipper-column withinverted-V bracing.

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Homogenous frames Eccentrically braced frames

In some bracing arrangements, such as that illustrated infigure (right) with links at each end of the brace, links maynot be fully effective. If the upper link has a significantly

lower design shear strength than that for the link in the storybelow, the upper link will deform inelastically and limit theforce that can be developed in the brace and to the lowerlink. When this condition occurs the upper link is termed anactive link and the lower link is termed an inactive link. Thepresence of potentially inactive links in an EBF increases thedifficulty of analysis.

List of contents


design of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tall

building- Concluding remarks


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Dual frames

Flexible system + Rigid systemPredominantly actingunder gravitationalloads

Predominantly actingunder lateral loads

=

Dual system - Structural system with the following features: (1) anessentially complete space frame that provides support for gravity loads;(2) resistance to lateral load provided by moment frames that are capableof resisting at least 25 percent of the base shear, and concrete or steelshear walls, or steel braced frames (EBF, CBF); and (3) each systemdesigned to resist the total lateral load in proportion to its relative rigidity.

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Examples of dual frames

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Dual frames

Interaction between braced and unbraced spans

Schematic plans showing interacting braced and rigid frames: (a) braced core andperimeter frames; (b) braced core and interior and exterior frames; (c) braced core and

interior frames; (d) full-depth interior bracing and exterior frames

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Interaction between braced and moment frames: a)characteristic deformation shape; b) variation of shear

forces resulting from interaction

Distribution of plastichinges, a g = 0,16g, TCIbuilding, Bucharest

MRFs act predominantly in shear (no web effect) while BFsact in bending

Diaphragm effect of the slab assures the interaction betweenMRF and BF better behavior

Interaction between braced andunbraced spans

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Outrigger and belt truss systemThe outriggers couple the columns

and the coreThe lateral deflections are smallerthan if the core is freestandingBelt trusses around the building

Reduce building deflections and core bending stresses

Reduce the rotational reactionsMinimize the structural cost penalty associated withstability of slender buildingsEffective for improving 3D behavior of irregularbuildings

Advantages:

Bracedcore

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Outrigger and belt truss system - arrangements

(a) outrigger system with a central core: (b) outrigger system with offset core;(c) diagonals acting as outriggers; (d) floor girders acting as outriggers.

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a) Building plan with cap truss; b) cantilever bending of core; c)tie-down action of cap truss

Outrigger and belt trus system - behaviour

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Schematic structural system for abuilding with two outrigger and belt

trussesConceptual model and loading diagram

for a building with two outriggers andbelt trusses

Optimum location of two outriggersList of contents





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Optimum location of belt and outrigger

trusses: a) one outrigger; b) two outriggers;c) three outriggers; d) for outriggers

Note:

Deflection index =Top displacement with/without outriggers

Top displacement with outriggers

Deflection index vs. level of the outrigger

Outriggers and belt trusses at several locations

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Tube effect Structures with closely spaced columns and deep

spandrels (tube effect)

Columns havemajor axis on

perimeter direction

Isometric view of framed tubeSchematic plan of framed tube

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Important: distribution of axial stresses inthe square tube with/without shear lageffect

Shear lag effect in the tube. Important:distribution of axial stresses is different

comparing to classical bending theory

Shear lag effect

Bending effect and shear lag in caseof a tube with free transversaldisplacement

Bending effect and shear lag in caseof a tube with closely spaced columns

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Tube building with diagonals Structures with closely columns (tube) and perimetral

bracings

a) Tube building with diagonals on multiple stories; b) Buildingwith rotated tubes and super diagonals

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Multiple tubes Structures with multiple tubes

Concept of a structure with multiple tubes: a) perimetral diagonal bracings; b) Xbracings and moment connected spandrels; c) perimeter moment connected frames

List of contents

-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tall



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Beams and column elements Hot rolled profiles, welded sections, with/without

composite action (concrete)

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140 mm

900 high-rise buildings inthe U.S.A.

1500 high-rise buildingsworldwide

Jumbo sections for High-rise buildings


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Beams and column elementsList of contents



Optimized solutions based on rolled profiles


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Beams and column elementsList of contents



Composite action:Partially encased columnsFully encased columns


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Beam-to-column connections

Moment-rotation curves fordifferent types of joints

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Beam to column jointsList of contents



Extended endplate bolted joint

Haunchedextended endplate bolted joint


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Beam to column joints

10.9

.

.

beam

column

.

B-B

BB

3M20 gr6.6

.

.

beam

column

.

C-C

CC

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Welded joint Cover plateswelded joint


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Example of beam-to-column joints failure modesBeam to column joints

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Prequalification of beam-to-column jointsList of contents



Strength and stiffness properties of beam to column jointscan be evaluated with EN 1993-1-8 recommendations

Plastic rotation capacity is a key issue in the seismicperformance of the structure no provisions to evaluate thischaracteristic Provision of qualifying test

Use of a prequalified connection


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Connections for concentrically braced framesList of contents



Brace connections must be designed either to allow brace endrotation if a pinned end condition is assumed or to permit a

plastic hinge to develop at the brace ends if brace fixity isanticipated.

Connection Detail Allowing Brace End rotationdue to Out-of-Plane Buckling


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Connections for concentrically braced framesList of contents



When V- and inverted V-Bracing are used, out-of-plane stability ofthe beams when the bracing members buckle in compression is

critical to achieve a stable response Code provisions require that lateral bracing be provided at both

beam flanges at the point of intersection of the bracing members,as shown in figure

Lateral Bracing of Beams in V- and inverted V-Bracing


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a a a ae

b st tst

a

a

a-a

b

h w

tw

ec=1,5bc c=1,5b c

d d a

a

tst

a-a

b st

b

h w tw

Example of link-to-column

connections.

Connections, detailings for eccentrically braced frames

Long link

Short link

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Splice bolted connections

Columns sections are identical

a) double cleat bolted connectionb) single cleat bolted connectionc) single cleat and cap plate bolted

connection

Columns sections are differentd) double cleat bolted connectione), f) single cleat and cap plate bolted

connection

List of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tall



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Splice welded connectionsColumns sections are identicala) Butt weld connectionb) Butt weld connection (bolted cleat )

Columns sections are differentc) cap plate welded connection




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Floor systems Functions of the floor slabs

Resistance (supporting vertical loads)

Protective functions: Heat (temperature difference, thermal insulation) Noise (airborne noise, impact noise reduction and absorption) Fire Humidity (tightness, vapor barrier) Handling with horizontal force (seismic zones)




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Floor systems - typesList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tall



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List of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks


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Composite slab - ConcretingList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Several floor levels can be prepared prior to the pouring phasePouring on several storeys can be performed without the need

for propsThe intermediate levels below the active level can be freelyaccessed


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Composite slab - AdvantagesList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Steel sheet acts as: lower rebars as sheet is contributing

formwork for the concrete work platform with immediate effect protection of underneath levels stabilization element against lateral torsional buckling ofthe steel beam diaphragm directly after connection to the beam

Furthermore: leads to lighter structure structural savings leads to fast installation

it is placed by hand no lifting equipment it is easy to implement openings in it gives possibility of welding studs avoids visible cracks avoids surface cracks in case of fire is galvanized for durability


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f


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Classification according to structural criteriaFaade systems


Structuralfunction

Load bearing

Non-Load bearing

Design in layersSingle layer

Multi layer

Design in shellsSingle leaf

Additional leaf

VentilationNon ventilated

Ventilated

PrefabricationLoad degree

High degree

Li f


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Faade systemsList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storeysteel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Structuralfunction

Load bearing

Non-Load bearing

Structural function:-Non-bearing faades do not contributeto the bearing resistance,-Loads are: vertical (self-weight, life-loads, snow,plants, racks) horizontal (wind, life-loads as impacts, ) reactive forces (thermal or hybrid)

one fixed and one sliding support,-Standing or hanging (no stabilityproblem, fixed after erection) are optionsin design.

Standing facade

Hanging facade

Li t f t t


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Design in layersSingle layer

Multi layer

Design in shellsSingle leaf

Additional leaf

Layers / Shells:-Non-bearing are defined as layers,-Bearing are defined as shells,-Layers/Shells with varying material,

thickness and structure may becombined to comply with functionalsubtasks.

List of contents


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VentilationNon ventilated

VentilatedVentilation:-Ventilated faades incorporate oneor multiple air layers to evacuate heatand condensate via thermal uplift.

List of contents


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Conception Ventilation Double-skin faadesCorridor Faades

most effective in ventilation butdisadvantages in room-to-roomnoise insulation

Multi-storey Faades

for glass faades withoutopenings or if mechnicalventilation is used anyway forcooling

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Faade systemsList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey

steel buildingsL3. Principals of designand actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks

Conception Ventilation Double-skin faadesBox-type Window

for pier faades and highrequirements onprivacy/confidentiallybetween rooms

Shaft-box Faade

suitable for high noiseinsulation requirements dueto small openings

Internal faadeOuter faadehor. separation

List of contents


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Faade systemsList of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


PrefabricationLoad degree

High degree

Conception Prefabrication and Installation principles

List of contents


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List of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


Principle Single-Beam-Mounting:-Delivery and mounting of single components on-site-Fabrication in conventional way with vertical posts and

transversal beams-Glazing and further additional infills are installed in aseparate working step from the external side Low degree of prefabrication

List of contents


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List of contents-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


Principle Element - Mounting:-Delivery of fully prefabricatedelements to site-Elements are connected andsealed together and to thebuilding

High degree of prefabrication

Element Faade Prefabrication inshop and transport to site

List of contents


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-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


Element Faade Mounting of elements on-site


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List of contents


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Fire resistance-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


List of contents


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List of contents


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Fabrication in the shop

List of contents


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List of contents


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Response of frames to lateral loadsList of contentsI d i


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Response of frames to lateral loads-IntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


Moment frames Lateral loads are resisted primarily

by the rigid frame action Rigid joints SCWB configuration Limiting the lateral drifts

A frame is considered rigid when its beam-to-column connections have sufficient rigidity to holdvirtually unchanged the original angles between intersecting members.

In this system, shown in figure, lateral loads are resisted primarily by the rigid frame action; thatis, by the development of shear forces and bending moments in the frame members and joints.The continuity at both ends of beams also assists in resisting gravity loads more efficiently byreducing positive moments in beam spans. Moment frames have certain advantages in buildingapplications due to their flexibility in architectural planning. They may be placed at the buildingexterior without restrictions on their depths. They may also be located throughout the interior ofthe building with certain limitations on beam depths to allow for passage of mechanical and airconditioning ducts. Because there are no bracing elements, they are considered architecturallymore versatile than other systems such as braced frames or shear walls.

50 0.02

125 0.008adm e e

adm e e

H H

H H

500 0.002adm H H seismic

SLU

SLS

windSLS

Deflection characteristicsList of contentsI t d ti


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Deflection characteristics

Rigid frame deflections: (a) forces and deformations caused by externaloverturning moment; (b) forces and deformations caused by external

shear.



Concentrically braced framesList of contentsIntroduction


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Concentrically braced frames Rigid frame systems are not efficient for buildings taller than

about 20 stories because the shear racking component of

deflection due to the bending of columns and beams causes thestory drift to be too great. Addition of diagonal or V-braces within the frame transforms the

system into a vertical truss, virtually eliminating the bending ofcolumns and beams.

High stiffness is achieved because the horizontal shear is nowprimarily absorbed by the web members and not by the columns. The webs resist lateral forces by developing internal axial actions

and relatively small flexural actions. In simple terms, bracedframes may be considered cantilevered vertical trusses resisting

lateral loads primarily through the axial stiffness of columns andbraces. The columns act as the chords in resisting theoverturning moment, with tension in the windward column andcompression in the leeward column. The diagonals work as theweb members resisting the horizontal shear in axial compression

or tension, depending on the direction of inclination.



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Axial deformation of columns bending effect a) Axial deformation of braces (web effect) shear effect b)

Braced frame deformation: (a) flexural deformation;(b) shear deformation; (c) combined configuration.

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Ecentrically braced framesList of contents-Introduction


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Ecentrically braced framesIntroductionL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


An eccentric bracing system attemptsto combine the strength and stiffness

of a braced frame with the inelasticbehavior and energy dissipationcharacteristics of a moment frame.

The system is called eccentricbecause deliberate eccentricities areinserted between beam- to-column orbeam-to-brace connections.

The eccentric beam element acts as afuse by limiting large forces fromentering into and causing buckling ofbraces.

The eccentric segment of the beam,called the link, undergoes flexural orshear yielding prior to formation ofplastic hinges in other bendingmembers and well before buckling ofany compression members.

Thus, the system maintainsstability even under large inelasticdeformations. The requiredstiffness during wind or minorearthquakes is maintainedbecause no plastic hinges areformed under these loads and all

behaviour is entirely elastic.

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Strong winds may cause a variety of problems, particularlyin tall buildings Modern tall buildings are even more prone to wind action,due to their lightweight walls and partitions, which reduce themass and the damping Even for high seismic areas, for buildings with more then25-30 stories, the wind load governs the design Attention should be paid to the following criteria: Strength and stability

Fatigue of members and connections Excessive lateral deformations (may cause cracking ofcladdings or permanent deformations to nonstructuralelements) Excessive vibrations that cause discomfort to the occupants

Wind loadWind load vs. seismic load

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Wind loadList of contents

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Wind loadL1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey


Seismic loadList of contents

-Introduction


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Many of European areas are under seismic risk Southern Europe experienced very damaging earthquakes

during the last decades. Many existing structures have inadequate protection againststrong earthquakes. The vulnerability is very much increasing,due to the rapid grow of the construction industry.

Seismic loading requires an understanding of the structural

behavior under inelastic cyclic deformations Behavior under such loading is fundamentally different from

wind loading (and gravity loading). It is necessary to pay moreattention to type of analysis and detailing requirements, in orderto assure acceptable seismic performance beyond the elasticrange.

Some structural damage in members and connections can beexpected under design ground motion, as the majority ofmodern seismic codes allow inelastic energy dissipation in the

structural system


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- Concluding remarks

Local effects on site

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-Introduction


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Soil may act as a filter

It can modify frequency content of theground motion

Amplification of the ground motion (or

reduction) may be recorded on site Duration of the ground motion is increased

Local effects on site L1. Conceptual designof industrial buildingsL2. Conceptualdesign of multi-storey



1985 Mexico City


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1985 Mexico City - Pino Suarez

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-IntroductionL1 C ld i


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1989 Loma Prieta


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Effect of damping

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Effect of damping

Structural response may be reduced by an increase of

the damping properties Damping of the structural elements is limited One option for increasing the damping is the introduction

of external damping devices Viscoelastic passive dampers Passive control (tuned mass dampers) Active control (tuned active dampers)

These systems are effective both against winds andearthquakes




Yokohama Landmark Tower, 295.8 mTuned active dampersTuned mass dampersViscoelastic passive

dampers

World Trade Center, 417 m

Burj al Arab, Dubai, 321 m

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Reduction of the acceleration:29% 39%

10 000 dampers in the structure,about 100 dampers at the ends ofthe floor trusses at each floor fromthe 7th to the 107th

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Buckling-restrained braced frames (BRB)

Steel plate shear walls (SPSW)

Systems with removable dissipative members (RDM)




Schematic and typical types of bucklingrestrained braces

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Application of BRB - Tzu-Chi Culture Building, Taiwan




h l l h ll ( ) l h

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-IntroductionL1. Conceptual design

Steel plate shear walls


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The Steel Plate Shear Walls (SPSWs) application hasincreased in recent years. Design requirements for SPSWsare already implemented in the AISC 2005.

One of the most important application of steel plate shearwalls in a very highly seismic area is the 35-story high-rise inKobe, Japan.

The structure was constructed in 1988 and was subjected tothe 1995 Kobe earthquake.

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Studies of this structure(Fujitani et al 1996)

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(Fujitani et al., 1996)(AIJ, 1995) haveindicated that thedamage was minor andconsisted of localbuckling of stiffened steelplate shear walls on the

26 th story (Fujitani et al.,1996)

Interesting to note theadjacent building was

heavily damaged duringthe same earthquake,suffering a partial collapsedue to a soft story

mechanism

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S t ith bl di i ti b (RDM) llSystems with removable dissipative members

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Systems with removable dissipative members (RDM) allowreplacement of the dissipative elements damaged as a

result of a moderate to strong earthquake, reducing therepair costs. Application of this principle to eccentricallybraced frames, where links act as dissipative zones, ispresented in figure.

e

Removable bolted link concept

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Principals of design and actionsList of contents



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Safe and economical design of buildings is a complex issue Computation of design loads requires a complex analysis involving

considerations such as building use, location and geometry All building codes specify minimum design loads, which includedead load, imposed load, wind load, and, when applicable, snowload, crane load and earthquake load

Excepting earthquake load, all the other loads do not require any

greater understanding of structural behavior beyond elastic point Structural behavior is fundamentally different for seismic loading,and there are a number of detailed requirements and provisionsnecessary to assure acceptable seismic performance

Structures should also be able to resist abnormal loads due to

fire, impact or explosion, so as to limit the effects of local collapseand to prevent or minimize progressive collapse

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Structural designD i i i h ll b l ifi d f ll

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Design situations shall be classified as follows : persistent design situations, which refer to the conditions of

normal use transient design situations, which refer to temporary conditions

applicable to the structure, e.g. during execution or repair accidental design situations, which refer to exceptional

conditions applicable to the structure or to its exposure, e.g. tofire, explosion, impact or the consequences of localised failure

seismic design situations, which refer to conditions applicableto the structure when subjected to seismic events Design for limit states shall be based on the use of

structural and load models for relevant limit states: Ultimate limit states (ULS) Serviceability limit states (SLS)

The verifications shall be carried out for all relevant designsituations and load cases. The requirements should beachieved by the partial factor method



Limit states Ultimate limit state

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Ultimate limit state The limit states that concern:

the safety of people, and/or the safety of the structureshall be classified as ultimate limit states. The following ultimate limit states shall be verified

where they are relevant : loss of equilibrium of the structure or any part of it,considered as a rigid body

failure by excessive deformation, transformation of thestructure or any part of it into

a mechanism, rupture, loss of stability of the structure or anypart of it, including supports and foundations

failure caused by fatigue or other time-dependent effects



Limit states Serviceability limit state

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Serviceability limit state The limit states that concern :

functioning of the structure or structural members undernormal use

the comfort of people the appearance of the construction works

shall be classified as serviceability limit states

The verification of serviceability limit states should bebased on criteria concerning the following: the deformations that affect the appearance, the comfort of

users, or the functioning of the structure (includingequipments), or that cause damage to finishes or non-

structural members vibrations damage that is likely to adversely affects the appearance, the

durability, or the operation of the structure.



Serviceability (SLS) - informative - ridge vertical deflection:

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g

- eaves horizontal deflection

- crane girder horizontal deflection :

- crane beam mid span vertical deflection:

250/Lf max

600/Tf cr max

100/H

700/H cr C

Where:

- L = Main frame span [m];- T = Bay between main frames [m];- H = eave height of main frame [m];- Hcr = level of the crane beam [m];- Q = lifting capacity of crane [t]



Deformations and horizontal displacements Vertical deflections are represented schematically below:

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Vertical deflections are represented schematically below:

where: wc is the precamber in the unloaded structural member w1 is the initial part of the deflection under permanent loads

of the relevant combination of actions w2 is the long-term part of the deflection under permanent

loads w3 is the additional part of the deflection due to the variable

actions of the relevant combination of actions wtot is the total deflection as sum of w1 , w2 , w3 wmax is the remaining total deflection taking into account the

precamber

Definitions of vertical deflections



Deformations and horizontal displacements Horizontal displacements are represented schematically below:

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p p y

where: u is the overall horizontal displacement over the building

height H u i is the horizontal displacement over a storey height H i

Definition of horizontal

displacements



Classification of actions Actions shall be classified by their variation in time as

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yfollows: permanent actions (G), e.g. self-weight of structures, fixed

equipment and road surfacing, and indirect actions causedby shrinkage and uneven settlements;

variable actions (Q), e.g. imposed loads on building floors,beams and roofs, wind actions or snow loads ;

accidental actions (A), e.g. explosions, or impact fromvehicles.

Certain actions, such as seismic actions and snow loads, may beconsidered as either accidental and/or variable actions, depending onthe site location, see EN 1991 and EN 1998.

In northern areas, roof loads are determined by the expected maximumsnow loads. However, in southern areas, where snow accumulation isnot a problem, minimum roof live loads should be specified toaccommodate the weight of workers, equipment, and materials duringmaintenance and repair.

gL2. Conceptual designof multi-storey steelbuildingsL3. Principals ofdesign and actionsL4. Design of a low risebuildingL5. Design of a tallbuilding


Combination of actions - ULS Combinations of actions for persistent or transient design

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situations (fundamental combinations):

Combinations of actions for accidental design situations:

Combinations of actions for seismic design situations:

where:-G k, Q k is the characteristic value of the actions- AEd is the design value of seismic action- Ad is the design value of an accidental actionis the partial factor for actions- 0 is the factor for combination value of a variable action- 1 is the factor for frequent value of a variable action

- 2 is the factor for quasi-permanent value of a variable action

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Recommended values of factors for buildings

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Combination of actions - SLS Characteristic combination (normally used for irreversible

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limit states):

Frequent combination (normally used for reversible limit

states):

Quasi-permanent combination (normally used for long-term effects and the appearance of the structure):



Seismic design When applicable, the seismic hazard shall be taken

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into account in the early stages of the conceptual

design of a building, thus enabling the achievementof a structural system which, within acceptable costs,satisfies the fundamental requirements:

structural simplicity uniformity, symmetry and redundancy bi-directional resistance and stiffness torsional resistance and stiffness diaphragmatic behaviour at roof level

adequate foundation



Flow chart and design cri teria for Steel Frames in seismic areas

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Design concepts, ductility classes Earthquake resistant steel buildings shall be designed in

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accordance with one of the following concepts: Concept a) Low-dissipative structural behaviour Concept b) Dissipative structural behaviour

Ductility class Reference value of behaviour factor qRequired cross-sectional class

1,5 < q 2 class 1, 2 or 3DCM

2 < q 4 class 1 or 2

DCH q > 4 class 1

Table 2: Requirements on cross-sectional class of dissipativeelements depending on ductilityclass and reference behaviourfactor

Table 1: Design concepts,

structural ductility classes andupper limit reference values ofthe behaviour factors



Types of structures, behaviour factors Steel buildings shall be assigned to one of the following

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g g gstructural types, according to the behaviour of their primary

resisting structure under seismic actions:a) Moment resisting frames, are those in which the horizontal forces aremainly resisted by members acting in an essentially flexural manner.

b) Frames with concentric bracings, are those in which the horizontalforces are mainly resisted by members subjected to axial forces.

c) Frames with eccentric bracings, are those in which the horizontalforces are mainly

resisted by axially loaded members, but where the eccentricity of thelayout is such that energy can be dissipated in seismic links bymeans of either cyclic bending or cyclic shear.

d) Inverted pendulum structures, are structures in which dissipative

zones are located at the bases of columns.e) Structures with concrete cores or concrete walls, are those in which

horizontal forces are mainly resisted by these cores or walls.f) Moment resisting frames combined with concentric bracings.g) Moment resisting frames combined with infills.



Upper limit of reference values of behaviour factorsfor systems regular in elevation

Ductility Class

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Ductility ClassSTRUCTURAL TYPE

DCM DCHa) Moment resisting frames 4 5 u / 1

b) Frame with concentric bracingsDiagonal bracings 4 4V-bracings 2 2,5

c) Frame with eccentric bracings 4 5 u / 1d) Inverted pendulum 2 2 u / 1e) Structures with concrete cores or concrete walls See section 5f) Moment resisting frame with concentric bracing 4 4 u / 1

2 2See section 7

g) Moment resisting frames with infillsUnconnected concrete or masonry infills, incontact with the frame Connected reinforcedconcrete infills Infills isolated from moment frame(see moment frames)

4 5 u / 1

Moment resisting frames(dissipative zones in beamsand at bottom of columns)



Dissipative vs. non-dissipative structures When dissipative concept isapplied, the design seismic action

When low dissipative concept isapplied, the only requirement is that

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applied, the design seismic actionis considerably smaller than the

one required for an elasticresponse of the structure ( q of theorder of 2 6): Advantageous for high-seismicity regions and/or middle-

rise and high-rise structures special design requirementsshould be fulfilled, in order toassure the necessary ductility ofthe structure (like structural

layout, ductility of members andconnections, steel quality,detailing)

pp , y qseismic action (computed based on a

behaviour factor q = 1) is consideredwhen establishing action effects Values of q factor 1.0 < q < 2.0 canbe adopted only when they can be justified theoretically and/or

experimentally. Economical for low-seismicityareas and/or light structures, likesingle-storey steel frame buildings




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.Co ceptua desgof multi-storey steelbuildingsL3. Principals ofdesign and actionsL4. Design of a low risebuildingL5. Design of a tallbuilding



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p gof multi-storey steelbuildingsL3. Principals ofdesign and actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concluding remarks


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of multi-storey steelbuildingsL3. Principals ofdesign and actionsL4. Design of a low risebuildingL5. Design of a tallbuilding- Concludin

tall steel buildings

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