Monitorizarea constructiilor inalte introducere+capitolul 1.doc

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Modern topographical technologies used

for tall constructions

execution and exploitation

INTRODUCTION

From geometric point of view, the realization of tall buildings is an

interdisciplinary domain that was very little discussed in the specialty

literature.

The extent of this analysis theme covers all the phases that are the

object of a tall construction building up, from design phase to the time

behavior tracing.

The present work analyses this domain starting with the existing data

synthesize and carrying forward with technologies and devices elaboration

that would improve the possibilities of topographical conduction of tall

construction execution, with an ample analysis of the impact of very tall

constructions developing in the last five years over the topographical

technologies used for execution control and those time behavior tracing.

For the quality of the construction, a very important function is hold

by the geodetic measuring and tracing technologies. These must satisfy the

necessary precision on construction’s execution phases starting with the

design-imposed precisions, then tracing, practically the lead of the phase

construction process, carrying forward with the time behavior study both on

execution process and during the exploitation.

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Starting with the accumulated experience during over 25 years, it was

determined that the main difficulties that appear at the realization of those tall

constructions, appealing to land surveyors to solve them, are verticality

assuring during the execution process, the correct arranging of the shutteringtowards executing an adequate structure with regard to its geometry, studying

those constructions behavior through the execution and exploitation process

at the action of various solicitations.

An important problem in the execution process of tall structures is,

therefore, verticality assuring, keeping in mind that this height evolves on

hundreds of meters (the 350 m furnace from Baia Mare, the twin towers

Petronas with their 452m height or the 553m height TV tower from Toronto

are the tallest constructions realized in our country respectively in the word).

The geodesy’s function is exactly to find methods and adjust them to the

execution techniques of the special tall constructions.

In this work, I have presented my research in this domain, the solving

possibilities of these problems, appealing to the established or experimental

top techniques

In the elaboration of this thesis had showed up several difficulties

because of the documentation, the material being insufficient in this domain

and because the lack of this type of investment in our country, in the last

decade.

If until 1990, there were structures (Energoconstrucţia Trust; I.S.P.E;

T.L.S.I.T Bucharest, T.A.G.L.S.IZ.T as part of M.C.Ind.) that looked in the

country after tall constructions design and execution making possible for the

geodetic engineering to participate at the whole process of realization of

those, the lack of investment, in the last years, limited this kind of concerns.

The constructions height is and will be a problem that had always

imposed to the specialists, specific determination limits regarding to the used

material’s endurance, regarding to the continuous development or

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improvement of technologies, to the functional destination, to the requested

precision. Along my studies, initially from my participation to the 205m

furnaces execution at Brăila, 280m at Turceni and Braşov; my activity at

Energoconstrucţia Trust to the execution of works designed by I.S.P.EBucharest and T.L.S.I.T Bucharest I had to offer a precision and technology

surplus. In this activity, I had found a research direction, wanting to establish

the possibilities and devices that would contribute to improving and

increasing the execution’s technologies efficiency.

The made studies in this area, convinced me that an important role in

vertical design through tall structures execution is hold by disturbance

factor’s influence: wind, sun, irregular heating of structure’s walls, which are

usually less deferred both at their design and at execution. The analysis of

these factors influence raises problems at the establishing their correct ratio at

vertical design of construction’s axis.

The research were orientated also to analyze the possibilities of

exposure of climbing shuttering, during the execution, avoiding the

shuttering rotations, to assure those structure’s verticality.

The last achievements in the very tall residential construction’s

domain, the 452m twin towers, Petronas, raised at Kuala Lumpur – Malaysia,

442m building Sears Tower from Chicago, the buildings that are now built in

Taipei-Taiwan, Shanghai and in other cities from China or Japan, generally

on Pacific Coast, are accentuating the actuality degree of the researches made

by surveyor in settling domain new technologies, of perfecting the existing

ones. In this way it is explained that in the activity plan still in progress (2002

– 2006), of F.I.G, commission no 6 are proposing as base themes:

• tall construction’s deviations monitoring, analysis,

interpretations;

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• predictions regarding the deformations and movements of tall

constructions that must sit on base of materialization of

engineering projects from this field.

As base missions are proposed:

• the promotion of surveyors knowledge and researches in

achievement of construction works and in other engineering

professional branch, and

• the development of multi – disciplinary domain’s expertise,

including topographical classic and modern methods, combining

geometric methods with other methods (sensors, accelerometers,

scanners, digital photogrammetry, inertial systems).

From the execution, in 1894, of the first over 100 m height

construction, Manhattan Life Insurance Building, in New York, 106.1m, 18

floors, have past over 100 years, were realized thousands of tall buildings.

The last year’s explosion regarding great number of constructions, of over

400m height, dedicating in the same time a serial of constructors, specializedin those type of works, Turner corporations, from U.S.A. with 139 units,

Takenaca from Japan, with 88 units, Gafisa from Brasil with 82 executed

very tall constructions being the first from the world.

An effect of those anterior presented was reconsideration of calculus

methods, of standards, of concepts regarding mathematical modeling in the

projecting process of tall constructions, but it must be pointed a very

important fact:

• no design method can be validated unless after an analysis

regarding the behavior through execution and in time of the

construction under the action of disturbing factor’s action, wind,

earthquake, unequal sunny, at this chapter the geodesic

measurements being the ones that give possible answers.

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Considering the problems that the designers, from this domain, are

dealing with, regarding the fact that the excessive level of the tall

construction vibrations are affecting the occupants comfort, requiring the

adopt of limitation and prevent methods of this phenomenon with a role of reducing the solicitations structural reaction, only in-situ results can validate

or infirm the adopted solutions efficiency.

This work contains six chapters, the first chapter is an analysis of the

general background where is developing the geometric assist topographical

activity of the execution and time tracing of the tall constructions. After a

general presentation of engineering constructions that make the work’s

analysis object, I mentioned the main tall constructions realized in our

country and in the world, as well as perspectives of the true present made

competition regarding the constant overcoming of the field record, not just

for height chapter, but also for all that represent technology development,

implicit bringing the developing of new topographical methods and the

perfecting of the existing ones, desideratum impossible to realize without a

domain interdisciplinary collaboration. Considering that the optimal methods

picking used for execution tracing and of tall engineering constructions time

behavior, is correlated with a calculus structural model of these, I presented

shortly the base principles in the structure’s calculus, singularizing for very

tall constructions, underlining the importance of topographical

measurements, in verification’s calculus hypothesis concordance concerning

the construction real reaction. I’ve put a special accent on the tall

construction’s behavior analysis under the action of unequal heating of the

construction’s exterior layer, of wind and especially of cumulated

solicitations.

I’ve considered appropriate the presentation in the second chapter of

the topographic work’s organizing way for tall construction’s tracing and

execution, and in the second part of the chapter I’ve analyzed the topographic

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– geodesic technologies, existing at the moment of the research thesis

approach, methods considered to be classical in present.

Considering that, the entire measurement set must be subordinated to

a support system, formed of engineering geodesic spatial networks; I’veconsecrated the third chapter to the analysis of construction’s precision and

mode of these networks.

Chapter four is presenting the modern topographical technologies from

the work’s study domain, presenting my scientific researches that had as

result, the projecting of new technologies, a study regarding the possibility of

using the GPS stations in tall construction’s executing process, as well as of

the devices of type: accelerometers, scanners, sensors, anti-vibrators,

pendulum systems, lasers, the chapter closing with a analysis of manager

systems used lately on execution and tracing the tall construction behavior.

In chapter five of this work is analyzing the problems related to

execution and tracing the 200m furnaces from ferroconcrete situated on Dej –

Cluj chemical platform 100m from ferroconcrete; 100m metallic and 352m

from ferroconcrete from Baia Mare, this being the tallest Romanian

construction and the second furnace from Europe, as height.

The last work chapter is presenting conclusions regarding the

topographical methods that may be used for tall construction’s execution and

tracing, and it makes an analysis regarding the time evolution model of the

structure’s axis under the influence of different factors that was realized

comparing the made measurement results inside the case studies with the data

had at disposal regarding the response of some similar structures under the

environment solicitation factors.

It is accentuated the fact that the research in the thesis study domain

have an interdisciplinary character and, therefore, it cannot be approached

unless in this manner, are made proposals regarding the future research,

starting with domain specialists preoccupations, at global level, from the

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recommendations of the involved domain’s specialty forum (FIG, AIG, ACI,

ASCE), but considering the accumulated experience.

I consider that the possessed bibliography, initially limited, ulterior

getting over a spectacular informational evolution, explainable by anumerous achievements in the last period in the very tall structures domain,

mentioned at the work final, is actual and it covers the research theme.

It must be said that, because the researches, strictly in the this work

research domain, were made throughout over 25 years, just a small part of the

results could be included in the work, the informational explosion in the last

years limiting also the possibility to present the daily stage on world level.

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CHAPTER 1

GENERAL BACKGROUND FOR PROCEEDING THE

TOPOGRAPHICAL ACTIVITY FOR MONITORING THEEXECUTION AND OBSERVATION IN TIME OF TALL

CONSTRUCTIONS

1.1. General notions regarding tall engineered constructions

1.1.1. Reasons concerning the importance of knowledge of structural

solutions and the environmental conditions regarding tall constructions

The explosive development of science and technics nowadays, main

characteristic of the last years, helps the development of economic and social

life.

Constructions branch, witch is the oldest organized technics activity

of mankind, develops itself more and more, following the complex

necessities that are implied by both activities.

The main components that can be found in the constructions activity

are bounded to the activities of design, execution and exploitation. The

design of an endurance structure is referring to choose some construction

parameters which have to correspond to the demands of the final purpose, as

well as to determine the actions which are soliciting the structure and,specially, the possibilities of mixing those actions, to set up the size and the

structure in order to comply with the endurance, stability and design. The

execution and exploitation represents, on the other hand, mixing of adequate

technologies that have to correspond to the selected project level, as well as

finding operative and optimal needs of project transposition, in order to

shorten the construction time, rational use of the raw materials, human factor

and the manufacture tools.

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The objective demand for economic development determines us to

perform the action predicting – saying what the future may bring – analysing

existing data and considering them into a dynamic evolution.

General purpose to set more space for living places, urbanistic buildings, bigger industrial spaces at humankind disposal made, that the

evolution of constructive performance about opening and heights to be

exponential, the more so as the conception process, in conformity with

manufacturing technology, creates the premises for its achievement.

Tall buildings have a spectacular evolution due to the raising number

of population, and on the other hand, due to the raising number of people that

are living in towns but also to architectural and urbanistic ambitions.

Upsizing the chimneys was made in order to enlarge the rank of dispersion

for evacuate carbon dioxide, and upsizing the TV’s antennas heights was

made for increasing the intercept zone of the emitted signals. These

arguments have determined me to concentrate my research efforts on finding

adequate topographical techniques, in order to satisfy precision and

efficiency in high buildings construction. This activity still can not be

conceived without a good knowledge of primary concepts regarding these

particular structures realization, of constructive solutions and executing

technologies, of elements that are affecting execution and the topographical

assisting activity.

Improvement of projection solutions is not possible without validation

of assumed solutions, and this fact can be achieved starting with correct,

continuos and relevant data regarding IN-SITU behaviour of achieved

structures, co-operation between the draftsman, constructor and geodesist

being a obligatory condition in obtaining viable, safe, functional structures,

assuring, in the same time, of the occupant comfort.

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1.1.1. A general classification of constructions

The constructions are divided into two main categories, which are:a) Buildings;

b) Particular engineering constructions.

a) Buildings are those constructions which shelter people, animals,

staples, raw materials, or in which people are doing their daily

activities; this buildings contain, inside them, rooms used in

various purposes.

Taken by their purpose, buildings are divided in:

• Civil constructions – houses, social and cultural buildings

(schools, libraries, hospitals, auditoriums, gyms etc.),

commercial and administrative buildings (headquarters,

railway stations, postal offices, banks, shopping centre

etc.)

• Industrial buildings (factories, works, storage rooms,

warehouses, garages, hangars, industrial labs etc.)

• Agricultural and live-stocks buildings (hangars for

agricultural equipment, silos, greenhouses, stables, bird

houses etc.)

b) particular engineering constructions are including all the other

construction categories, which are:

• pathways works (streets, highways, railways, navigation

paths, landing grounds, subway galleries etc.)

• art works for telecommunication ways (footbridges,

bridges, viaducts, tunnels)

• electrification paths and telecommunication lines;

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• hydrotechnical works (barrages, water pipes, sewers,

sluices, harbour ground planes, wash-out corrections etc.)

• landed improvement works (drains, drainage works,

irrigation works, amelioration land works);

• various works (factory furnaces, cooling towers, extraction

towers for mining exploitations, television towers).

1.1.2. Constructions which can be placed between

engineering tall structures

Representative constructions from this area are presented in the next

lines.

a. Furnaces

Furnaces are vertical columns made for evacuation at great heights of

residues from industrial technological processes. Those furnaces must be

build high because of their draughty condition, as well as their dispersioncondition.

Furnaces are classified, by shape, in: cylindrical and in the shape of a

truncated cone.

By their big heights and reduced plan dimensions, the sliding

shuttering technology at furnaces appears to be as something very

advantageous, permits economization at constructive systems and an

exceptional quality due to the wall strength; it’s to observe Romanian experts

contribution in this technologies improvement.

b. Silos

These are constructions that serve to deposit staples, semi-products or

granular or powdery products at great height. Are characterised through the

great height of the cells in comparison with their plan dimension, as well as

the fact that the walls have to offer resistance at stored materials pushes

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intensity, so those walls are strongly reinforced or are made of compressed

concrete. Counting by the number of the cells, silos can be divided into:

1) Unicellular silos − made from only one cell;

2) Multicellular silos − made from several circular or rectangular

cells.

c. Industrial chimneys

Many industrial installations need towers that are in different shapes

and heights and their execution, using sliding shuttering method, appears as

the most adequate. There for, exist:

1) Granulation towers for chemical industry;2) Cooling towers, constructions that assure water cooling, from the

heat exchanger, in closed circuit and are operating with natural or

forced draughty.

d. Water towers

These constructions are composed of a reservoir that is made of metal

or reinforced-concrete, which is situated up high, sustained by an staging, a

tower or a holder.

Water towers can represent also architectonic reference points due to

their height and their, sometimes, spectacular forms.

e. Telecommunication towers

These are used for transmitting, respectively receiving, amplifying

and re-broadcasting ultra-short waves, which are propagated in straight line,

in television and wireless telephony. In order to solve efficiently those

functions it’s necessary to place the antennas at great heights on holders built

in tower shape using reinforced-concrete or compressed concrete.

The tower shape’s pick results from technical-economical and also

esthetical reasons. Because the wind blowing is, finally, deciding in shape

dimensioning, there is a tendency that the proper tower and specially

constructions that shelter technical storeys sustained by the tower (top of the

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tower) to have a aerodynamic shape. Architectonic reasons determine that

platforms used to sustain parabolic antenna must be grouped together, and

towers diameter, which are placed in towns, to increase slowly, from top to

bottom. Below the terrain level is placed a frustum of a cone for theinsurance of some favourable building foundation. In case of isolated towers,

placed on great heights, is recommended their enlargement down to the basis.

Component elements of the towers are: the proper tower that sustains

the metallic antenna placed on top, the areas that contain technical storeys

and the ones designated for visitors, the platforms that sustain parabolic

antennas.

The construction that shelters technical storeys and also the ones

designated for visitors (here, in this case, the tower) has in horizontal plan a

ring shape, and on height it passes, either gradual or sudden, on changing

cross section.

These kinds of works are the next ones:

a) Television and radio relay towers. These have a usual height of

60-120 meters, are composed of a cylindrical or in the shape of a

truncated cone tower;

b) Television and panoramic towers. Are characterised, beside their

great height, by the existence of an emission antenna, sometimes

installed above technical spaces. Their great height makes

necessary to give a special attention on the appearance, the

engineering solution being very closely related to architectonic

necessities.

f. Tall residential buildings

If on industrial tall constructions, the reinforced-concrete applying

method is adopted almost unanimously, on civil constructions it has to be

compared with other methods of executing comb or cellular structures, or

executing metallic structures.

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It can be said that the most dynamic technological development in

constructions domain, for the last ten years, was made exactly in very tall

residential constructions domain; here where yearly are finalised more and

more higher constructions, extremely spectacular (from the architectonic point of view), and, in the same time, being remarkable engineering

achievements, the geodesist engineers part being decisive.

As a primary consequence of this real phenomenon is also

development and improvement of new ensuring and following methods of the

verticality of very tall buildings that it will be described inside this writing.

g. Files for tall suspended bridges

Because of extremely difficult executing conditions and considering

the height that can exceed 300 meters, the files of suspended bridges that

ensure crossings kilometres order are being ones from the most spectacular

engineering work.

It will pass not much time till Europe will be the continent with the

most representative work of this type, through the Messina Bridge, Italy,

which will be finalised in year 2011, with its 376 meters, that the files will

have, will become the category leader.

1.2. Notions about calculus ground rules for tall engineering

constructions

1.2.1. General ground rules of calculus

The making of tall engineering structures is a complex activity, we

may say even a paradoxical activity for the unknowing that are impressed by

the unusual dimensions of these constructions instead of their structural

conception.

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The calculus for the tall constructions supposes getting over the next

complex steps:

a) prolusion of construction’s principal dimensions that derive

from functional requisitions, from technical-economical reasons, as well asfrom the way of making-up of the resistance structure;

b) precision of the actions and their grouping

c) the calculus of maximal effort in the characteristic sections in

the most adverse combinations of actions;

d) the resistance structure dimensioning consists principally of

maximal pressures comparison and of the deformations associated with

maximal limits imputable to the component materials respective to limit

deformations.

In the following sections will be approached b, c and d phases,

initially towards succinct presentation of legal calculus regulations, towards

an analysis of the way they are concerned this aspects both nationally and

internationally; and through this to point out the importance of the

topographical measurements in concordance verification for the calculus

hypothesis and the structure real reaction, fact that is relieved only through

deformation measurements.

1.2.2. The suitability of preliminary approaching of calculus ground

rules towards a good correlation of topographical IN-SITU

measurements results and the prolusions kept in mind at design

level

Starting with existing design solutions, at some point, method

perfection’s steps are:

• follow out the execution design, achieve the projected

construction;

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• topographical measurement of structure behavior in different

combination of stress factors;

• decompose the results towards settling how every stress

factor’s influence acts on the real model

• the geodesist presents the measurements result and the cause

effect explanation to the designer

• the designer starts with supplied data, analyses the adopted

solution, comparing initial assessments and field dates.

The fact that the geodesist knows the ground rules of the design

elaboration may lead to pursuance methods and methods for supplying the

required conclusive dates, avoiding measurements without knowing the

cause-effect rapport.

1.2.3. The current method of calculus

The general ground rules for construction’s safety verification (atglobal level) are based on embracing “semi-probabilistic method for possible

limit situations”; the method has two distinctive characteristics:

• are considered systematically all possible limit situations;

• are considered independently the variation of different factors

that affect the constructions safety, therefore settling

quantitative dates that determine the construction’s assurancelevel.

The meaning of limit situations is a situation that implies:

• reversible or irreversible loss of construction ability to satisfy

exploitation conditions regarding settled destination, or

• the appearance of some risks regarding human life or health,

or risks regarding material or cultural assets whose preservation depends on the construction.

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Among principal phenomenon that may lead to limit situations

appearance are:

- the stability loss for one part of the construction or for the

whole construction; or the position loss through gliding or subsidence. This phenomenon are studied by topographical

means

- excessive static or dynamic deviations;

- excessive fissures.

Analyzing the limit situations that must be considered is necessary to

keep in mind that the phenomena that lead to their occurrence may act

individually or combined.

Beside their frequency, it’s important to point out other important

characteristics of extraordinary actions, as well as the special way in which is

raised the issue of safety regarding this kind of actions.

a) their probable maximal intensities have a degree of

incertitude slightly higher than the one for usual variable load.

b) Unlike the usual load effect (static load), for which the

stress depends virtually only on construction’s static scheme, where the

parameters of structural behavior act only on load redeployment (through

fissure, through elastic deformations), in the case of main extraordinary

actions or seismic actions, that are very important for tall buildings, the

stress depends directly on these structural characteristics (rigidity,

solidity) and on their variation during the stress reiteration process, being the

construction “answer” to the dynamic action. So, the stress has a double

“historical” dependence meaning it depends on action’s development history

(e. g. represented by acceleration chart of a seism) and on structural

properties modification history in critical zones of the construction.

c) Because the infrequency of extraordinary actions and the

high incertitude regarding their intensity it’s natural, unlike the usual stress,

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to admit the ineluctability of non-structural deterioration and for some

construction categories even structural deterioration.

In the main, the construction’s strength assurance indicates the fact

that the inequality:

max minS R≤

(1.1)

for all structure sections is very likely accomplished, or backwards, the

probability that the inequality isn’t true is very low. In the inequality (1.1)

was noted:

maxS = maximal value corresponding to the accepted probability

level (confidence probability) of the load effect for one section (sectional

effort), depending principally on random parameters of the actions.

minR = minimal value corresponding the accepted probability level,

of the section resistibility, regarding the strength of materials random values,

of elements dimensions etc.

The probable maximal values of the load intensity and minimal values

of strength are taditionally called “calculus value” and they are established

such as, virtually, to have a corresponsive assurance level (near 99.5%).

Calculus values of the load and strength are correlated with characteristic

values (in prescriptions are usually called “standardized values”) of the load

and of the strength, often are statistically defined as at least 95% probability

achievable values.

The application of the calculus method for limit-situations for

endurance structures build of metal, reinforced concrete or pre-stressed

concrete means:

- an adequate design;

- a accurate execution;

- construction exploitation according to design establishedconditions;

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- behavior tracing according to the rules established at

design (STAS 10100)

-

1.2.4. Action characteristics and their classification

During the construction assurance verification is considered:

- permanent actions PA, that are applied continuously with a virtually

constant frequency, constant regarding time.

- quasi-permanent actions AQ, that are applied with high intensity for

a long period or frequent.

- temporal variable actions VA, whose frequency is varying time

regarding, or the load is missing for a long period of time.

- exceptional actions EA, that appear rarely having significant

intensities during the construction exploitation.

The calculus for the elements and structures is made considering

unfavorable combinations, practically possible for the load, called load

groups. Will be kept in mind:

a) Fundamental groups (PA+CA+VA+);

b) Special groups (PA+CA+VA+EA)

Permanent load are considered in every case, and quasi-permanent

and variable load are considered when their effects are unfavorable for the

considered section and limit situation.

Exceptional load are considered only in case of special groups, in the

following conditions:

- will be considered one exceptional load (usually a seism)

- for very svelte and wind intolerant constructions (funnels,

antennas, towers) the usual load came from wind action is multiplied with a

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coefficient respective of 0.4 for A and B emplacement zones and of 0,6 for

C,D,E emplacement zones.

- the load from permanent and quasi-permanent actions will

have rated values.For strength calculus, for fundamental groups, in strength limit

situation are considered the permanent quasi-permanent and temporal

variable load with their calculus values (maximal values).

1.3.5. Wind action unto tall engineering constructions

In case of tall buildings wind action interferes having a large balance

for widening the general solicitations. Wind action is usually considered as a

two components sum, static and fluctuant. The static action corresponds to

average speed during a reference time interval of two minutes. Fluctuant

action manifests itself through:

a) dynamic pressure fluctuations, because of the speed

fluctuations around the average value, that leads to construction oscillations

whose predominant direction is almost the air flow direction, the action is

considered variable.

b) the appearance alternate forces, perpendicular unto average

air flow direction, because of alternate twirl emission around cylindrical or

almost cylindrical shaped obstacles, the action is considered as exceptional.

c) generation of self-entertained oscillations, pitching motions

phenomenon, in case of great movement from wind action structures, the

verification is done using special prescriptions and mode trial runs.

The last legal regulation regarding rated intensity of static wind action

is STAS 10101/20-90. The exposed surface incident component ( pv

n) is

determined using the expression:

( )n

v ni h v p c c z gβ = ⋅ ⋅ ⋅ (1.2)

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- β = blast coefficient,

- cni = surface aerodynamic coefficient i,

-ch( z ) =the variation of dynamic base pressure coefficient regarding z

height from ground level;

-g v = dynamic base pressure at 10 meter high from ground level.

Constructions that raise special problems due to their wind

intolerance and due their complexity of behavior – that means over 150

meters high funnels, over 100 meters high cooling towers, T.V. towers, over

50 meters wide or high bridge stockades are in the C3 category regarding

wind fluctuant effects, situation in which static and fluctuant windcomponents are apart considered, their resonance is simultaneously checked

up.

The static component, corresponds to the dynamic base pressure that

is determined according to (1.2), minding the blast coefficient β =1. The

wind fluctuant effect is evaluated using forces of inertia determined for each

proper mode of vibration. For constructions which are assimilated to dynamicsystems with a finite degree of freedom number, the rated force of inertia

corresponding to the degree of freedom k and the proper mode of vibration r,

is determined using:

n n

kr k kr P m w= ⋅ (1.3)

where:

mk = the mass corresponding to the degree of freedom k, using tonsn

kr w = the rated acceleration corresponding to the degree of freedom k

and the proper mode of vibration r .

The evaluation is laborious, because it demands determining the

proper period of vibration for the structure and the movements corresponding

to the proper mode r, for the degree of freedom k. For furnaces and cooling

towers is enough to consider the proper fundamental mode.

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(r =I ). For this type of constructions is also executed the resonance

verification in side of which is calculated the wind effects using the calculus

of the resulted vector of resonance effect with sum vector of wind action’s

effect in the plane of wind flowing direction (static and fluctuantcomponents), according to (32), in B Addenda, and STAS 10101/20-90.

2 2( ) ( )r cr N N N= + (1.3)

( ) ( ) ( )cr st flN N N= + (1.5)

Remarkable achievements in “sky-scrapers” domain confirmed, for

this construction type, that the response through vibrations depends on

rigidity, mass and shock absorption of the structure. Excessive values for

relative level movements of for on top total movements, may lead to

unfavorable effects regarding forces of gravity transmission, fissures or

damages at non-structural elements, occupier discomfort etc. This is why

ACI Committee 435 specifies the maximal admissible at top movement for

constructions that use frames or core walls ∆max=0,002 H , H being the total

height of the structure, the admissible relative movement (horizontally and

vertically) ∆max=3,8 mm.

Seismology Committee of Building Engineer Association from

California recommends:

- for structures that have less than 13 levels and a height/width ratio

less than 2.5 the verification for lateral wind produced movements is not

necessary;

- for the other types of structures the maximal admissible movement

of the top, produced by wind action has a limit of 0.0025 H, virtually

comparable to the ones mentioned before.

The general opinion of the specialists is that for constructions for

whom the wind load has an important weight on structure’s elaboration and

dimensioning, the experimental measurements in aerodynamic tunnels are

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necessary, even though these measurements imply difficulties regarding wind

action simulation unto the real construction (reproducing in the tunnel the

Reynolds number corresponding to the real situation, simulation of the real

air turbulence, simulation of the emplacement’s ground roughness etc)The tunnel experiments executed by different research workers

needed comparing with measurements done on real constructions. We

mention that at Hong Kong University was build an experimental

construction having 10 floors, close to 30 m high and the horizontal

dimensions are 20 10× m; the construction is equipped with measuring

instruments to study the turbulences and the wind effects and it is exclusivelyused as a research and recording laboratory, for a closure between simulated

measurements and the real model of the traced structure.

The experimental tests on simulated models as well as measurements

on structures of cylindrical towers showed that the aerodynamic pressure on

transversal section’s contour depends, essentially, on the finishing quality of

exterior surface (even-plastered cylinders, sheet metal, and wood,

respectively harsh-brick work cylinders, raw plaster, corrugated iron)

phenomenon neglected by the actual standard STAS 10101/20-90 (but

considered by German standards DIN 1055 and French NV65).

The assertion regarding wind action on tall engineering constructions

ends with the observation that for their exhaustive evaluation are necessary

information that clearly overcome the standard level (STAS 10101/20-90),

accompanied by verification on models. This requirement becomes strictly

necessary if we keep in mind that the wind is a very important in resistance

structure calculus, is second after seismic actions.

23



1.3.6. The seismic action on tall engineering constructions

According to the domain regulation “Standard for anti-seismic design

of: housing places, social-cultural, agro-zootechnic and industrial places”code P100-92, there will be kept in mind the following manifestation

manners of seismic activity.

a) forces of inertia generated by the vibrations of elevation parts of

the constructions, after their involvement in the seismic movement by

accelerations of ground-construction interface.

b) efforts generated by unequal movements imposed to the

infrastructural parts of the construction.

c) additional pressures came from the forces of inertia created in

liquids, powdery masses.

d) the forces came from the leaning and bonding works of the

installations, of equipments etc.

24



Tabelul 1.3.

25



1.3.7. The response of tall structures on vibrating forces and their effect

on inhabitants

a. Considerations regarding the last domain aspects on world level

Swedish and Swiss standards from this domain specifies the

frequency, speed, acceleration and amplitude of design (projection)

vibrations, maximum admitted of various very high constructions categories

and only topographical in-situ measurements can confirm these values.

Researchers of California University are presently working on

quantification and identification of possible losses due to tall structures

vibrations by using spectral analysis Hilbert – Huang and spectral density

Cross.

A main preoccupation of the researchers is the analysis of possible

loadings combinations, of these effects, of fatale combinations and a

reconsideration of actions provoked from the wind as main solicitant

environment factor.

It is presented in 1.3 table the latest aspect, recommended by ASCE,

regarding the standard procedure of determining charges made by wind.

It’s to mention also the preoccupations about determination of

interaction of type structure – possible wind effects, the new definitions about

solicitant factors, of their combinations scheduled by American standard BS

5950, and especially redefining acceptable limit displacements of the top of

tall structures by the same accepted standard among H/300 for columns and

singular constructions and H/600 for other categories.

26



Standards of American Construction’s Engineering Society ASCE7-

02 are giving also trends about minimum factor combinations in tall

construction’s design.

b. The structure’s reaction on vibrating forces action

The reaction of structures on apparition of a vibrating source is

governed from the next factors:

• the relation between the natural construction’s frequency (or of

some of its elements) and the characteristic frequencies of

vibrations source• amortization of building resonance or of some parts from it

• diffusion of stress in building or of some parts from it

• magnitude – the size of forces that act on structure

• interaction between the building or its elements and the vibrating

source.

Human perception on vibrations – oscillations of tall structures can be

considered in or out normal limits, according to many other factors.

The American standard DIN 4150 (1.5 table) sets up the limits of

human tolerability of the vibrations from the buildings where they live or

work.

In this standard, the value of K’s perception degree is derived from

(1.6) relation, A being the displacement in microns and f the oscillation’sfrequency:

K = 2

2

100

005.0

f

f A

+××

(1.6)

Levels of admissible vibrations for different types of buildings

acceptable intensities (K) by DIN 4150

27



1.3. TableType of

buildingTime

Continuous

vibrations

Repeated

vibrations

Casual

vibrations

SanatoriumDay

Night

0.1

0.1

0.1

0.1

2.5

0.1

HouseDay

Night0.1

0.2 (0.1)

0.1

4

0.1

House and

office

Day

Night

0.3

0.1

0.63 (0.3)

0.1

8

0.1

IndustrialDay

Night

0.63

(0.3)

0.8(0.4)

0.8(0.4)

12

12

The values from the parenthesis are applied to the cases when the

vibration’s frequency is smaller than 15 Hz.

Through the real and protective domain regulations are Swiss

standards regarding vibrations tolerance for buildings (1.3 table).

28



Swiss standard of buildings vibrations

1.5. Table

Structure’s typeFrequency

Band length Hz

Induced

perturbations

PPV

mm/S

Induced traffic vibrations

PPV mm/s²

Structures from ferro-concrete or

steel like those from factories,

support walls, steel towers,

bridges, open channels,

underground tunnels

10-60

60-90

10-30

30-60

30

30-40

12

12-18

Buildings with walls and concrete

floor, concrete or masonry walls, basement rooms and embankment

tunnels

10-60

60-9010-30

30-60

18

18-25

8

8-12

Buildings with masonry walls and

wood floor

10-60

60-90

10-30

30-60

12

12-18

5

5-8

1.2.8. Preoccupation regarding restriction of oscillations of tall

structures under the wind effect and under exploitation

The human perception’s limits regarding the oscillations of the

buildings in which they live or work, are determined traditionally using

movement simulators (Chen & Robertson 1973, Irwin 1981, Gato 1983,

Shioja 1992). Recent studies show that the sinusoidal type oscillations are

perceived slightly different in real situations; there are discrepancies in the

tests results. Anyway, tall structure’s realization needs finding solutions

regarding comfort increasing for the occupants and that is realized by

decrease of construction’s oscillations. Therefore are presented as it follows

some base directions.

a. Structural system

29



Finding a efficient structural system for a tall construction is an

essential condition of designing, and it has as scope a good behavior of the

structure when it comes to lateral action and torsion action of the wind.

Among multiple situations, we mention:

• spatial consolidation used for improving the behavior of the

Melbourne Tower at wind action. The construction has 560 m height that

was provided to be finished in 2005. It was used a kernel and at every 2-3

floors were used strengthening links in the walls.

• similar safety belt systems, starting with a central kernel, with a

consolidation by centering some floors. Are used for building PlazaRakyat, Kuala Lumpur, Malaysia, 77 floors and First Bank Place,

Minneapolis, S.U.A., de 258m.

• The tubular system – conventional for 20th century tall constructions,

starting with the innovating design of Fazlur Khan; significant examples

are Sears Tower – Chicago, World Trade Center – New York, John

Handock Center. The system was successfully continued at ShanghaiWorld Financial Center constructing, work started in 2001 (figure 1.24).

It was estimated that the central core can take over more than 20% of

wind power,

• the aerodynamic modifications – the study of wind effect on tall

constructions consists in finding the ratio between the aerodynamic

features of the structure and the structure’s reaction for wind action.

It was observed that modifications for section height improve the

structure’s behavior to wind action. In 1.25 figure is shown an example of

section’s height variations for Square Building Shape (Hayashida 1990), the

most famous case is the one of twin buildings Petronas, Kuala Lumpur,

Malaysia, where was observed that the structure is spiraled, method which is

used for reducing the tall structure’s reaction at wind action.

30



Table 1.6 presents the main methods for diminution of wind effects on

tall constructions:

Table 1.6

Mean Type Method and scope Gloss

Aerodynamic

modeling

Passive Improving of aerodynamic

properties to reduce the wind

power

Splayed corners,

orifices

Structural

modeling

PassiveMass accession to reduce the

air/construction mass ratio

Expensive

materials

Rigidity accession or natural

frequency accession to reduce

the wind effects

Consolidated walls

Auxiliary

attenuation

systems

Passive

Using materials that have

adequate properties for energy

dissipation, increasing building’s

attenuation degree

SD, SJD, FD,

VED, VD, OD

Annexation auxiliary mass

systems to increase the

attenuation level

TMD, TLD

Active

Generating control forces using

the inertia effect to minimize the

reaction

AMD, HMD, AGS

Generating aerodynamic control

forces to reduce the wind power

or to minimize the reaction

Aerodynamic

accession

Rigidity modification to avoid

resonance

AVS

31



Figure 1.24. Shanghai World Financial Center

32



Figure 1.25. Aerodynamic modifications for square section buildings

1.2.9. Opportunity of amelioration for design solution considering

the disasters in the domain of tall structures

The action of environment factors (wind, quake) and human criminal

actions lead to destruction or demolition of some very tall constructions.

September 11th, 2001 was a subject of great attention for mass media because

of the event, which put a negative mark on all humankind. There arises the

following question:

Is the collapse of tall structures a rarity? Was this event produced onlyat extraordinary actions or by joining of some forces that separately were

situated below the design parameters, too?

Examples that follow will demonstrate the contrary:

23.10.1997 – TV tower of 609.3 meters tall WLBT, Raymond,

Mississippi, U.S.A. is falling apart, killing three Canadian workers;

1982 – another 605m tower is collapsing in U.S.A.; 1978 – is collapsing a 491m tower, WJJY – TV, Illinois, under

the action of a strong wind;

1996 – the disaster hits in Montgomery, U.S.A., when a 2042m

tower – WCOV – TV is completely destroyed by a tornado;

1970 – KCRC – TV tower (near Walker, Indiana, U.S.A.) is

collapsing during some works, causing 5 deaths;

33



KWWL – TV tower (Rowley, Indiana, U.S.A.) is falling apart

under the combined action of ice and wind;

between years of 1980 and 1990, several tall towers are

collapsing in the center of U.S..A under the combined action of ice and

wind;

in the middle of July 1992, in the same area, a 130m commercial

tower is falling apart during a storm, killing one worker;

the great cyclone Tsunami, that had dashed to the ground Pacific

Coasts during 1992 – 1996, made, as well, lots of damages, including

some of very tall constructions.

Therefore, it is imposed an analysis of actual possibilities to predict the

natural or provoked disaster’s effects onto very tall structures.

It is also very useful knowing the producing causes of some degradation

or destructions of some very tall constructions, which were solicited by loads

situated below limit design values, being necessary a analysis of the

combining forces effects.

1.3.10. Use of spectral analysis of Hilbert – Huang type on estimating the

damages provoked by extraordinary actions or by combining of some

soliciting factors, in monitoring structure’s state of moment

a. “Hilbert – Huang” spectral analysis type

During the monitoring action of structure’s health, the technical

analysis demands that the data came from the measurements to be interpreted

and it is to identify the construction’s state after the action of some

extraordinary soliciting factors (strong wind, earthquake). Spectral analysis

of Hilbert – Huang type is applied in order to correlate the system

identification and structure analysis. Therefore, the correlation function,

CROSS, for measurement of the structure’s response acceleration is in the

34



first place decomposed into different modal components, using Empiric

Module of Decomposing (EMD) as method and the filters of passing, of type

Young (2001). Hilbert transformation is applied to every modal component

to obtain time dependency of the angle of phase, the frequency andamplitude.

• All natural frequencies as well as the amortization rate can be identified

as time dependent for: amplitude and angle of phase, using just one

measurement.

• If there are measured the respond to solicitation acceleration of each

level, the modal oscillation configuration, structure’s rigidity andamortization’s matrix can be identified using the approximation

presented below.

• Based on the comparison of degree of rigidity of each level before and

after the oscillations amortization, dimension and amortization’s

parameters can be identified.

• There are simultaneous presented the results of amortization’s analyzedstructure under the effect of solicitation forces actions, using a linear

structural array of type 4 – DOF.

b. The function of correlation and modal contribution

The movement equation of a type n – DOF structure can be

formulated in equation:

)t(F)t(KX)t(XC)t(XM

....

=++

(1.7)

where X(t) = [x1, x2, …, xn]T is the vector of movement, F(t) is

stimulator vector, M, C and K are mass (n x n), respectively amortization

and rigidity matrices.

Assuming the existence of normal modules, the movement and the

acceleration of response can be decomposed into n real modes:

35



∑∑==

Φ=Φ=n

1 j

j

..

j

..n

1 j

j j )t(q)t(X ;)t(q)t(X

(1.8)

where Φ j is the number j modal vector and q j(t) is the number j modalcoordinate. Replacing the equation (1.8) into the equation (1.7) and using the

orthogonal properties of modal forms, it can be written:

*

j

T

j j

2

j

.

j j j

..

m/)t(Fqq2q j

Φ=ω+ωζ+ (1.9)

where ω j is the number j modal frequency, ξ is the number j

amortization rate and m j* is the modal mass. When the excitation F(t) is a

stationary disturbing vector, the respond correlation function of the building’s

level response, stated by ( ) st

R τ , may be obtained as:

∑=

τωζ− θ+τωαΦ=

τ+=τ

n

1 j

sjdjsjrjs

..

r

..

rs )sin(e)t(x)t(xE)(R j j

(1.10)

where Φrj is the r element of modal vector Φ j , ωdj=ω j(1 – ξ j2)1/2 is the

number j amortized modal frequency of, θsj is the alteration of phase and αsj is

positive constant. For simplifying, the time difference t will be written as t

and the equation (1.9) will be:

∑∑=

ωζ−

=

ϕ+

π+θ+ωαΦ==

n

1 j

rjsjdj

t

sjrj

n

1 j

j,rsrs2

3tcose)t(R )t(R j j

, (1.10)

where

ϕ+π

+θ+ω⋅= ωζ−rjsjdj

t

j,rs j,rs

2

3tcoseB)t(R j j

(1.11)

( )

<Φπ+±

≥Φπ±=ΦαΦ=

0dacă 1m2

0dacă m2 ;B

rj

rj

rjsjrj j,rs (1.12)

In the equations (1.10-1.12) – R rs,j(t) is the contribution for the

number j mode. The correlation function R rs(t) will be decomposed into

modal contributions R rs,j(t) (j = 1, 2, …, n) using the EMD method. Then

we’ll apply Hilbert transformation to each of the modal contributions R rs,j(t),

36



into (6) equations for the determination of modal frequencies ω j, of

amortization rate ξ j and of the vector Φ j . Assuming that the matrix of mass,

M, into (1) equation is known, the generalized masses, m j* , can be obtained

as ΦT

MΦ = diag (m1

*

, m2

*

, …, mn

*

), where Φ is the modal matrix with modalvector Φ j being the number j column. After the determination of m j

*(j = 1, 2,

…, n), the rigidity k j* and modal amortization c j

* may be obtained as k j* =

m jω j2 şi c j

* = 2 m j ξ jω j. Therefore the matrix of rigidity K an the matrix of

amortization C in (1.6) equation can be identified as:

K = Φ-T diag (k 1*, k 2

*, …, k n*) Φ-1 şi C = Φ-T diag (c1

*, c2*, …, cn

*) Φ-1(1.13)

For a building exposed at the action of environment factors, the

rigidity of every level can be obtained from K coefficient.

c. Hilbert-Huang transformation

Assuming that x(t) is a measured signal, for example the function of

correlation R rs(t) in (1.10) equation. The Hilbert transformation (TH) for x(t)

is:

ττ−π

τ

== ∫

+∞

∞−d)t(

)(x

)]t(x[HT)t(x

~

(1.14)

where )t(x~

can be calculated numerical using Fourier

transformation. The analytic signal Y(t) of x(t) is formulated as:

)t(i~

e)t(A)t(xi)t(x)t(Yθ

−

−=⋅+= (1.15)

where A(t) is the instantaneous amplitude, θ(t) the instantaneous

angle of phase and2/1)1(i −=

−. The instantaneous frequency ω(t) of the

signal is obtained as:

dt

)t(d)t(

θ=ω

(1.16)

In (1.14) – (1.16) equations there is one frequency ω at a moment if to

x(t) signal is applied TH. On the contrary, for a signal x(t) at a moment there

37



is a frequency distribution at that moment. Therefore, to obtain a significant

decomposition of the signal into the domain frequency – time, Huang

proposed in 1998 to decompose at first x(t) signal in m intrinsic functions

IMF using EMF method. Afterwards, it is applied Hilbert transformation for each IMF function to obtain concluding decompositions of the signal in the

domain of frequency. This approach will be used at detecting the defects in

tested buildings.

The Empiric Method of Decomposing (EMD) together with

intermittence criteria of Huang (1998), can be used to extract R rs,j(t)

contributions:

∑∑−

==

++≈nm

1 j

p pj

n

1 j

j,rsrs )t(r )t(c)t(R )t(R (1.17)

where c pj (t) for j = 1, 2, …, m-n are IMF functions of R rs(t) and r p(t) is

the rest, that represents the main tendency of the signal.

Another alternative approach is using the filter of band transformation

and EMD method for the extraction of modal contributions R rs,j(t) in (1.17)

equation as follows: from the Fourier spectrum R rs(t) can be determined the

approximate frequencies for each natural frequency R rs(t) is calculated

through mentioned filter with the band frequency ω jL < ω j < ω jH.. The in

processed through EMD method and the first IMF function is very close to

the number j modal contribution R rs(t). Repeating the above steps for j = 1, 2,

…, n, it is obtained R rs,j(t) in (1.17) equation.

Using Hilbert transformation R rs,j(t), named j(t),R rs~

and forming an

analytical function it is obtained:

[ ])t(iexp)t(A)t(R i)t(R )t(Y j,rs j,rs j,rs

~

j,rs j,rs θ=+=−−

(1.18)

t

j,rs j,rs j jeB)t(Aωζ−=

(1.19)

38



j,rssjdj j,rs2

3t)t( ϕ+

π+θ+ω=θ (1.20)

where were used (5) – (7) equations. From (13) – (14) equations is

obtained:

tBln)t(Aln j j j,rs j,rs ωζ−=

(1.21)

dj j,rs j,rs )t(dt

d)t( ω=θ=ω (1.22)

d. Identifying structural parameters

For the identification of natural frequencies ω j and of amortization’s

rates ξ j for j = 1, 2, …, n only a correlation function is necessary. For ξ j of

small values, there are used (1.20) relations, where natural frequencies ω j can

be obtained from the bent of the phase angle plot ln Ars,j(t) regarding time.

For general case where ξ j doesn’t have small values neither θrs,j(t) and nor ln

Ars,j(t) aren’t linear time functions. In this case, Young propose in 2001

approximation procedures of natural frequencies and of amortization rates as

it follows:

a).The angle of the plot θrs,j(t) time regarding is considered a straight

line using a linearization procedure. This line is the last angular position for

the angle of phase. The straight line bent is ωdj.

b). The amplitude plot ln Ars,j(t) time regarding is considered a straight

line using a linearization procedure. This line is the last angular position for

the amplitude. Then - ξ jω j is estimated from straight line bent andc). Knowing ωdj şi - ξ jω j, can be calculated ω j and ξ j .

As it was shown above, ωdj can be estimated from a) without any

problem. Still, when ξ j has high values, ln Ars,j(t) oscillations near mentioned

line can be significant, so as the ξ jω j bent is dependent of the time interval

used in linearization procedure. In this case it’s proposed calculation of ln

Ars,j(t) through EMD to obtain the rest, named with r Apj(t). As the rest

represents the main tendency of ln Ars,j(t), is approximated by a straight line

39



using the linearization procedure. Then the - ξ jω j bent may be estimated

through mentioned line.

To identify the amortization and rigidity matrices, it has to be

measures all DOF and response times. Using (1.13) and (1.21) relations, theabsolute values of the modal elements φrj and φmj (r, m = 1, 2, …, n) are:

( ) ( )[ ]0 j,ms0 j,rsmjrj t`At`Aexp/ −=ϕϕ (1.23)

where A`rs,j(t0) and A`ms,j(t0) are the amplitude at the t = t0 moment of

approximation lines for the ln Ars,j(t) and ln Ams,j(t) amplitudes, anterior

obtained. Next, the differences between angle of phase φ rs,j of modal element

Φrj are, regarding (1.24) equation:)t(`)t(` 0 j,ms0 j,rs j,ms j,rs j,rm θ−θ=ϕ−ϕ=ϕ∆ (1.24)

where θ`rs,j(t0) and θ`ms,j(t0) are the lines of approximating amplitudes

for the angles of phase θrs,j(t) and θms,j(t) for t=t0 anterior moment. The above

Δφrm,j value is +2mπ or +(2m+1)π. using the equation (1.13)may be

determined the sign φrj that regarding φmj. And so, both absolute values and

the signs for all the elements were determined regarding an element in Φ j

modal vector. Repeating this procedure for all modal contributions j = 1, 2,

…, n it can be identified Φ matrix and in the ending are obtained K and C

matrices.

e. Test results

To obtain reasonable assessments for functions of spectral density are

used altogether 400 seconds of stationary response dates and a frequency of

1000Hz, after removing the starting transition part (approx. 2-3 seconds).

This allows calculating 47 average values for functions of spectral density. A

representative function of spectral density and the function of correlation for

the forth and first floors is represented in figure 1.26.

a)

40



b)

Figure 1.22. Spectral density (a) and function of correlation (b) for an

unaffected construction

EMD method and band pass filters were used to extract every

contribution R rs,j(t). It was applied Hilbert transformation for every R rs,j(t) to

obtain instantaneous amplitude and the angle of phase. Using the above

41

4

12

20

-4

-12

-20

0 1 2 4 5 6 time (sec)

0

f u n c t i o n o f

c o r r e l a

t i o n C R O S S

s p e c t r a l d e n s i t y

C R O S S

( d B )

-100

-60

20

-20

-140

0 10 20 30 40 50 60 70 80 90 100frecvenţa (Hz)

0



procedures, the identified natural frequencies and the amortization rates for

an unaffected structure and respectively for an affected structure (models 1

and 2) are presented in table 1.8 (column a). There are also presented in 1.8

table theoretical values (column b) for comparison. For model 1 all bandswere removed from first floor whereas for model 2 all bands from first and

third floor were removed. It is to observe that the natural frequencies and the

amortization rates that were identified are correct.

Table 1.8.

Man. Unaffected Model 1 Model 2

Frequency

(Hz)

Amortiza-

tion (%) Frequency

(Hz)

Amortiza-

tion (%) Frequency

(Hz)

Amortiza-

tion (%)

Th. Id. Id. Th. Id. Id. Th. Id. Id.

1. 9,41 9,39 1,09 6,24 6,25 1,17 5,82 5,83 1,01

2. 25,54 25,41 1,16 21,53 21,51 1,04 14,89 14,88 1,03

3. 38,66 38,59 1,05 37,37 37,35 0,88 36,06 36,02 1,10

4. 48,01 48,13 1,03 47,83 47,81 1,12 41,35 41,37 1,00

Supposing that the mass matrix is known, the rigidity matrix,

K and the amortization matrix C were estimated. The every level’s

rigidity is calculated un solicited model basis. The obtained results for

rigidity are presented in 1.9 table. Also, in 1.9 table are presented, for

comparison, theoretical values for every presented identified rigidity,

the location of the damages and their ampleness were accurately

detected.

Table 1.9.

rigidity Theoretic values Identified valuesUnaffect. Model Model Unaffect. Model Model

42



(MN/m) 1 2 1 2

k1 67,90 19,68 19,68 67,71 19,02 20,26

k2 67,90 67,90 67,90 68,58 68,38 67,36

k3 67,90 67,90 19,68 68,25 68,38 19,21

k4 67,90 67,90 67,90 67,35 66,91 68,42

f. Conclusions

Build on Hilbert – Huang spectral analysis, it is proposed a disruption

identification and detection method. All natural frequencies and amortization

rates of the structure can be identified using just one measurement of the

response acceleration, which may be affected by the noise.

When the response acceleration is measured for all DOF type

structures, the modal matrix, rigidity matrix and amortization matrix may be

identified supposing that the mass matrix is known. The structure’s defects

may be identified through rigidity comparing for every floor of the

construction before and after the event, which caused the damages. The

simulation results demonstrate that the proposed method detects accurately

the structural damages including their location and ampleness. The method

proved to be efficient for detecting damages at linear structures.

Definitive in method application, for real structures, is the recording

of the construction response for solicitations of whose characteristics were

settled, being not just useful, but even determined the topographical –

geodesic measurements of the cause – effect ratio for this type of

solicitations.

1.3. Contributions regarding the analysis of tall structures behavior

under the action of irregular heat, of the wind, of cumulated

loadings, of execution errors

43



1.3.1. Topographic analysis of tall structures condition under the stress

action needs a good knowledge about those and the way these are

influencing the study methods

The monitoring of very tall construction’s action is a complex process, implying topographical, meteorological measurements, a good

cognition of execution project, in fact of the predictions about structure’s

action in given circumstances.

The adopted topographical methods in this field and not only, must be

adapted to the designer’s field data needs, one geometrical ascertainment,

without saying the conditions when it was recorded, is inconclusive.

The geodesist has to coordinate the entire process of data taking IN-

Situ, geometrical, meteorological and structural, so having the chance of

understanding the entire phenomenon.

1.3.2. The vertical construction’s axis variation – great height column on

irregular solar heat

The constructions – column with closed section (cylindrical or in a

shape of a truncated cone) carries on unilateral heating, by solar exposing, a

parabolic deviation of the vertical central axis. In practice, the deformation

model is amplified, considering that values α ' and d ' are sensible comparable

with the real ones (α and d ) and, anyhow, covering (1.27 figure).

The effects of this evolutional process can be classified into two

groups:

• Influence of softness of vertical axis above construction

functionality;

• Vertical and radial efforts variation in structure (estimated by ACI

505-54/98)

44



In antenna’s case, the deviation from the vertical axis results changing

the emission direction. It’s appreciated that a α = 0,40 deviation is perceived

at a 100 km distance as a linear (D) 700 m deviation (1.28. figure).

Considering that the reception’s stability and quality is in direct ratio

with the position and stability of transmitter antenna, it has to be known

exactly the admissible deviation (α , d ) according to quality imposed to

reception, at external side of transmitting zone.

Softness of vertical chimneys axis can lead to the change of density

and distribution of emanated fume, for certain areas. For the residential

constructions the effects are still studied, having as prevent purpose the

possible discomfort of the inhabitants.

Fig.1.27. Fig.1.28.

1.3.3. The vertical axis variation for the great height column–

constructions on wind action

a. General approaching

45



In the activity of design for great height constructions, column-tower

type is very important to know the behavior of the real structure at wind’s

static action but especially at wind’s dynamic action. It is considered that in

the action modeling as well as in structure reaction’s evaluation it is veryuseful knowing real exploitation’s behavior of some comparable structures.

Studying on models, in aerodynamic tunnels, the structures behavior

in the mentioned category at wind’s action, it’s offering dates to whom can

give a trust limited from simulation possibilities of real conditions. Therefore,

the latest field research made in Universities from Sydney – Australia,

Nottingham - UK, Kansas and Salt Lake City – USA, although these give

dates about real structure modeling, of wind actions and the structure’s

reactions to these actions, are still in confirmation phase. There are big

difficulties and therefore the importance of measurements, which are made

from this point of view on real structures, is growing

Size, shape and oscillations frequency due to wind is important for

constructions stability study, but, it must be said that the difficulties appeared

at tower oscillations measurements under the wind action are special and they

came from several directions. It’s hard to quantize the effects of different

solicitation factors, the continuous haste of the construction (practically there

isn’t a repose state) makes heavy sighting and tracing the structure; wind

characteristics are usually recorded from the ground, and the transposition

through proportional calculus with height does not totally correspond to the

real solicitations.

b. Considerations regarding wind effect measurement onto some

tall constructions

46



The observation of studied structure’s oscillations, under wind effect,

was usually made using the recording method of some buffers movements

placed on structure or with theodolite of precision. When the research were

started there weren’t in the bibliography where we had access only very fewresults, from the second category. The used machines are usually precision

ones, provided with zenithal oculars. Pointing the center of sighting is made

in a calm period and the theodolite sighting axis stays unchanged along the

observation cycle. As sighting centers, may be used fixed elements, visible

from the traced structure’s interior, e.g. optical beacon, and in the control

measurements, the metallic elements of the platforms.

Determinations were centralized in the frequency settling directions

(respectively of duration) and the oscillations amplitude as well as of

oscillatory figures. It’s considered that regarding a direction perpendicular

onto axis of sighting, the complete tower oscillation is given by the interval

between two alternate passes of the sighting center through the center of

reticular wires of the machine. (1.29. figure)

The precision wherewith were evaluated the oscillations amplitude

has to be + 10 mm – conditioned by the possibilities of distance pointing for

station –chimney top.

The oscillation recordings from the two stations must be realized in

the same time and were timed by two instruments set in the same system

(origin).

47



Figure 1.29. Wind oscillant figureIt is possible, after the obtained data correlation onto both

perpendicular directions, that it is not to overpass an error of + 1 s for settling

the duration of one complete oscillation. That’s how it is established that the

oscillatory figures are ellipses whose long axis is perpendicular on wind

direction. The characteristics of wind were recorded on ground, in open field

nearby traced structure (figure 1.29).

c. General problems regarding wind action onto

cylindrical (or in the shape of truncated cone) constructions

The wind represents, periodically or quasi-periodical, a soliciting

factor on specific time interval for tall constructions.

In case of objectives that are over 200 m height and a shape of

truncated cone (furnaces, telecommunication towers, antennas), the study of

wind influence is heavier because of some factors, like:

wind speed variation on heights (implicit also of pressure)

different to the other constructions;

increasing buffer zone, fact that decreases the possibilities of

some simplifying hypothesis’s simulation;

absence of some profound studies regarding those structures

behavior in the critical superior domain;

48



chaotic character of model’s behavior into wind tunnels;

existence of some n – liberty degrees leads on appraisal only

approximate the solicitations;

the disaccord between theoretical studies and the real model

behavior, etc.

The practice, on the other hand, presents as sure, the next conclusion:

whatever the dynamic solicitation type (wind, earthquake, sunny) the

construction oscillations into specified section, are produced taking the

shape of an ellipse. (1.30. figure)

At the level of entire structure it can be estimated that oscillatoryfigure would have the shape of a quasi – screw conic – elliptic.

Figure no. 1.30

Real figure’s oscillations for different solicitation type

a) earthquake; b) wind; c) sunny

Strictly coming back at wind’s action analysis on studied assembly

(cylinder or conic), we know that this implies settling the definitivedifferential equations. Because solving them implies a very large amount of

calculus, it’s necessary to adopt some simplifying hypothesis that would

bring some advantages in this purpose. The main condition of the simplified

studied models is that the results must be compatible with those who would

define the real process. Irrotational motion, in which the effect of fluid’s

viscosity is neglected ( µ =0), being one of the simplifying hypothesis, is in the

case of the study of inter-relation fluid-conical assembly, limited by

49



increasing the buffer zone. As in the case of some other structure types,

motion field of the fluid may be split into two regions:

- main current where it may be admitted the hypothesis µ =0;

- the buffer zone and the limit layer where the fluid motion is

rotational, the viscosity must be considered µ≠0;

In these areas, the fluid particles present a rotation that may be defined using

a vortex vector W

Figure no. 1.31. The oscillatory figure provoked by the dynamic solicitations

of the level of entire structure in Cartesian coordinates ( x, y, z ):

k jiWy

u

x

v

x

w

z

u

z

v

y

w

∂∂

−

∂∂

+

∂∂

−

∂∂

+

∂∂

−

∂∂

= (1.25)

where v ui vj wk = + +r

is speed vector. Obvious that the hypothesis µ = 0

implies 0W = .

The measurements made on constructions on hand or on exploitation,

lead to the fact that this secondary wind effect (KARMAN) produces

deformities (oscillations) more powerful than the generating force, in case of

significant charges.

50



d. Transversal oscillations of wind’s direction (KARMAN effect)

Aeolian actions of this kind are studied after it was settled through

one of known methods, the number of oscillations of studied body and wind

action among the predominant direction. Next, it will be presentedsynthetically a few aspects related to KARMAN effect.

Transversal oscillations to wind direction are produced only when

aero dynamical negative amortization is bigger than the positive assembly

amortization.

The conical tubular structure will oscillate always transversal onto

wind direction in an own frequency. The assembly’s amortization is limiting

the amplitudes. There are two domains:

a) Re < Re critic - laminar domain (critic inferior);

b) Re > Re critic - turbulent domain (critic superior).

where R e is Reynolds coefficient (number) and it can be determined

as follows:

cin

e

V D

R ν

⋅

= (1.26)

V – wind speed (m/s);

D – structure’s diameter for h=0,7 H ( m );

cinν

- air kinematical viscoity;

(usually5

cin 1,45 10ν −= ⋅

) (m/s)

ecrit350.000R = (generally ).

In the critic inferior domain the transversal oscillations phenomenon

is caused by the KARMAN vortexes that are regularly changing with a

vortex frequency S = 0.2.

The continuous changing frequency of the vortex will be:

V

f S D= (1.27)

51



S – Strouhal’s number

f becoming liable so as the structure will oscillate in own frequency

and not in vortex’s frequency.

In the critic superior domain these phenomenon still don’t have asatisfying solving. It could be reminded the idea that this phenomenon is a

resonance oscillation of a weak amortizable system by its impulsion with a

continuous frequency spectrum.

Coming back at forming KARMAN’s vortex (1.32. figure) must be

said that this phenomenon takes place behind the cylinder and is moving with

a smaller speed than the main current, having a regular density. The alternate

forming of the vortexes produces transversal motive power. For the calculus

of those above, the current relation is:

aP C q D= ⋅ ⋅ (kP/m ) (1.28)

P - transversal motive power;

C a – lateral pressure coefficient;

212

q v = ⋅ - dynamic pressure.

As regards the Ca term, there are some non-correlations between the

values presented in specialized literature from different countries. Therefore,

it is recommended:

C a = 0,8 in critic inferior domain (R e < 350.000)

C a = 0,2 in critic superior domain (R e > 350.000)

while the correspondently would result C a = 1,1 ÷ 2 respectively

C a = 1,1 ÷ 0,2 regarding the ratio R e/ R e crit.

52



Figure no. 1.32

KARMAN vortex’s distribution

It is considered that a vortex appears on reduced values of Reynolds’s

number or on moderate wind speeds (V ≤ 25 m/s). It was seen, trough

measurements on real models, that produced oscillations after normal wind

directions have higher aplitudes than the longitudinal ones.

As regards the calculus mode for the estimation of transversal motion

powers and of corresponding oscillations, E. Hampe recommends

synthetically the next deployment (1.10 table), in which

yo- the maximal deflection on furnaces top due to the action of

a P = 1,0 M p force

δn – deflection in certain n-position

Gn – mass in n position

D – the diameter of the furnace at h = 0,7 H height

S ≅ 0,2 STROUHAL’s number

5

cin 1,45 10ν −= ⋅

( m2/s ) kinematical air viscosity

ρ = 0,125 ( kp⋅ s2/m4)

53



Table 1.10.

1

ESTABLISHING OF OWN OSCILLATIONS NUMBER ne

ne ≅ 3000

2

n n

y P

Gδ ∫ ( oscillations / sec) (1.29)

↓

2

ESTABLISHING THE RESONANCE SPEED Vrez

reze

n DV

S

⋅= ( m/s ) (1.30)

↓

3

ESTABLISHING OF REYNOLDS COEFFICIENT R e

rez

e

cin

v DR

ν = (1.31)

↓

4

ESTABLISHING THE LATERAL FORCE PL

critic inferior

20,8

20,192L rez

P v D ρ

= (kP/m) (1.32)

critic superior

A possibility of diminution of KARMAN effect especially for

reduced amortization’s constructions is the diminution of transversal

oscillations amplitudes, through spiraled shape envelopment.

This is the main method used also on limitation of lately made

skyscrapers oscillations (fig 1.32).

54



Figure 1.33. A method for limitation of conical constructions oscillations

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