COMPUTER AIDED ANALYSIS OF THE STRUCTURAL BEHAVIOUR OF VARYING SLOPED

OPEN LATTICE TOWERS (STATIC LINEAR ANALYSIS)

A thesis presented to the department of civil and environmental engineering, university of lagos, Ako-

ka.

In partial fulfillment of the requirement for the degree of Master of Science

By

Oladunni, Afolabi Olugbenga

099042001

In partial fulfillment of the requirement for the award of the degree of Masters of Science by research

in civil engineering (structural engineering)

July, 2011

Certification

I hereby certify that this m.sc thesis presented by Oladunni, Afolabi Olugbenga was supervised by the

undersigned and have been accepted in partial fulfillment of the award of Master of Science degree

(structural option) in the department of civil and environment engineering, university of lagos, akoka,

Nigeria.

Professor O.M. Sadiq

Project Supervisor

Professor Falade

Head of department

July, 2011

Dedication

This work is dedicated to the Elohim God, the sovereign, eternal and Immortal, the giver of all true

wisdom, discretion, knowledge and understading for His unquantifiable, immeasurable and unending

mercies, favour and grace before, during and after the completion of this project work.

Oladunni Afolabi O.

Acknowledgement

I would like to thank my supervisor, teacher and father for his guidance and support during my studies

and project work in unilag. Working with such respected and inspirational individual has been a privi-

lege and has confirmed my interest in advanced structural analysis and design.

Thanks to my enviable colleagues who provided the basic mast configuration and data used for this

research……..kenya. Engr Idris …

Thanks to Dr. P.O. Agunbiade, Managing Director of Advanced Engineering Consultants, who provid-

ed the timely resource amidst stringent project delivery periods that has helped me make my studies

at UNILAG/

Thanks to the M.Sc class of 2010 for their unparalled and brotherly support during the period of

course work and compilation of this thesis.

Thanks to staff of advanced Engineering Consultants for the brotherly support and prayers that has

brought me this far.

Finally, to my parents, sibling “direct and indirect” and friends for your love and support throughtout

my academic and life experience “hitherto”.

Oladunni Afolabi Olugbenga.

July, 2011

Abstract

List of figures

List of tables

List of symbols and Notation

Table of Content

Title page

Certification

Dedication

Acknowledgement

Abstract

List of figures

List of tables

List of notation and symbols

Introduction

Preamble

Definition: Tower and Mast

Types of tower and mast

Factors affecting choice of tower type

Aim and objective of this research

Scope of research

Literature review

Analysis of tower and mast

Structural response of mast and tower

Failure of mast and towers

Review of Applicable theory, design codes and Computer modeling & analysis tools

structural analysis of towers

structural elements

types of structural elements

Finite element Method: stiffness Matrix

Codal Provisions for the analysis of lattice mast and towers

Computer Modelling and analysis tools:

Mast geometry and loading analysis to BS 8100: 1 & 2

Mast Geometry

Loading analysis to bs 8100:1 & 2

Site and environmental data

Computational analysis for determination of effect of wind loadings

Summary of loadings

Computer Modeling and Analysis with SAP 200 v 14

Result and discussion

Conclusion and recommendation

Conclusion

Recommendation(s)

Appendices

Appendix ---

Appendix ---

References

Introduction

Preamble

In the contemporary era, the communication industry has a unique situation in the history of human

life. In the current century, this field has become significantly important and has been named commu-

nication era. Telecommunication masts and towers have essential role in this industry. They support

radio, television and telephone antennas to transmit telecommunication signals over long distances.

The overall layout of telecommunication masts and towers is governed by the requirements to the

transmission and receiving conditions. Added hereto the access and working conditions for installa-

tion and service are important issues for the design. The first requirement often leads to relatively tall

structures or in mountainous areas smaller structure on the top of hills or mountains. Both solutions

lead to various problems with regard to analysis and construction1.

There are many challenges for the engineers associated with this tall and slender structures many

more especially in trying to balance between safety, economics and aesthetics. The structural sys-

tems of towers and masts are complex and require due diligence in studying the structural behavior

and character under its predominant load, wind load.

Lattice steel towers have been used for many large utilities such as offshore structures, transferring

the radio and television broadcasting, watching safety, fire, lightening and energy transmission lines.

Frame members of these structures do not need to be very big. Thus, lattice towers are produced

lighter than other types of towers. Furthermore, span length of these structures get bigger values from

top to bottom. Loads spread bigger lands in lattoice towers and because of this reason, less sub

structure is needed for thes structures.

Definition: Towers and Masts2

In engineering terms, a tower is a self supporting structure while a mast is supported by stays or guys.

The term „tower‟ and „mast‟ are often used for the same type of structure, which of course can cause

confusion. Tower and mast have different definitions in American and british English. In American

English, both types of structures are often called towers, while in british English, people always use

mast instead.

To avoid confusion, in this write up, engineering terms are adopted as follows:

Tower – self supporting

Mast – supported by stays or guys.

Types of Tower and Mast3

1 Tha analysis of masts and towers, Morgens G. Nielsen: Chief consultants, secretary of IASS Working group no

4 Mast and towers, Rambell Denmark, Bredevej 2, DK – 2830 Virum, Denmark 2Alberto Escudero Pascual, IT +46. ITRAINONLINE communication tower hand-

book.http://www.itrainonline.org/trainoline/mmtk 3 Prof. S.R.Satish Kumar and Prof. A.R.Santha Kumar. Design of Steel Structures, Indian Institute of Technology

The different types of communication towers are based upon their structural action, their cross-

section, the type of sections used and on the placement of tower. A brief description is as given be-

low:

Based on structural action.

Towers are classified into three major groups based on the structural action. They are:

• Self supporting towers

• Guyed towers

• Monopole.

Self supporting towers.

The towers that are supported on ground or on buildings are called as self-supporting towers. Though

the weight of these towers is more they require less base area and are suitable in many situations.

Most of the TV, MW, Power transmission, and flood light towers are self-supporting towers.

Guyed towers.

Guyed towers provide height at a much lower material cost than self supporting towers due to the effi-

cient use of high-strength steel in the guys. Guyed towers are normally guyed in three directions over

an anchor radius of typically 2/3 of the tower height and have a triangular lattice section for the central

mast. Tubular masts are also used, especially where icing is very heavy and lattice sections would ice

up fully. These towers are much lighter than self supporting type but require a large free space to an-

chor guy wires. Whenever large open space is available, guyed towers can be provided. There are

other restrictions to mount dish antennae on these towers and require large anchor blocks to hold the

ropes.

Monopole.

It is single self-supporting pole, and is generally placed over roofs of high raised buildings, when

number of antennae required is less or height of tower required is less than 9m.

Figure 1: Types of towers based on structural action

MonopoleGuyed Self-supporting

Based on cross section of tower.

Towers can be classified, based on their cross section, into square, rectangular, triangular, delta,

hexagonal and polygonal towers. Open steel lattice towers make the most efficient use of material

and enables the construction of extremely light-weight and stiff structures by offering less exposed

area to wind loads. Most of the power transmission, telecommunication and broadcasting towers are

lattice towers. Triangular Lattice Towers have less weight but offer less stiffness in torsion. With the

increase in number of faces, it is observed that weight of tower increases. The increase is 10% and

20% for square and hexagonal cross sections respectively. If the supporting action of adjacent beams

is considered, the expenditure incurred for hexagonal towers is somewhat less.

Based on the type of material sections.

Based on the sections used for fabrication, towers are classified into angular and hybrid towers (with

tubular and angle bracings). Lattice towers are usually made of bolted angles. Tubular legs and brac-

ings can be economic, especially when the stresses are low enough to allow relatively simple connec-

tions. Towers with tubular members may be less than half the weight of angle towers because of the

reduced wind load on circular sections. However the extra cost of the tube and the more complicated

connection details can exceed the saving of steel weight and foundations.

Based on the placement of tower.

Based on this placement, Communication towers are classified as follows:

Green Field Tower Roof Top Tower

Erection

Erected on natural ground with suitable

foundation.

Erected on existing building with

raised columns and tie beams.

Height 30 – 200 m 9 – 30 m

Usual Location Rural Areas Urban Areas

Economy Less More

Based on the number of segments.

The towers are classified based on the number of segments as Three slope tower; Two slope tower;

Single slope tower; Straight tower.

Factors Affecting choice of tower type

The major factors affecting choice of tower type for deployment are:

i. Antenna load

ii. Tower foot print

iii. Height of tower

iv. Budget

Aim and Objectives of the study

Aim

The aim of the research work is to determine the effect of varying slope configuration on the stability

of self supporting towers.

Objectives of the research

The specific objectives of the research are as follows:

i. Model one , two and three sloped self supporting tower of constant height and base using

SAP software.

ii. Determine magnitude and distribution of forces and moments generated in the towers as a

result of slope variations.

iii. Evaluate and compare analyses result along the length of the towers

iv. Evaluate the effect and significance of slope changes on tower stability

v. Determine the most economic model that can withstand the applied forces.

Scope of Research

This research work will be within the spectra of the following:

i. Model will be

ii. Only one single structure and model of constant height , wind speed and bracing arrangement

will be adopted.

iii. Analyses will only consider wind load as the environmental load and antenna load as the oth-

er load.

iv. Loading computations is based on BS 8100: Part 1 and 2.

v. Static linear analyses will only be considered.

Literature Review

More than a few studies have been conducted over the years into the static and dynamic performance

of mast and towers. In the twentieth century however most of them relate to analysis determining the

fundamental natural frequencies of the mast for application to all dynamic loadings, many are more

applicable to dynamic wind loading including seismic effects on their structural stability. However, the

author has not been able to find a similar study that modeled the effect of varying tower slope on the

structural stability of self supporting towers.

Analysis of towers and Mast

According to Ulrik Støttrup-Andersen4, the analysis of mast and towers requires special knowledge

and experience especially when it concerns guyed masts. The special problems related to these

structures are underlined by the very many collapses during the years. The basis of design for such

antenna supporting structures are sometimes many and often mutual contradictory, and the overall

structural layout may have a dynamic nature of the wind has to be taken into account as masts and

towers are more or less sensitive to dynamic loads. This paper give a brief introduction to the prob-

lems related to the analysis and design, as well as the some practical examples are mentioned. The

aesthetic elements are becoming more and more important for antenna supporting structures and is

also mentioned.

Also, in a related research by Eric James Sullin at the Missouri Department of Transportation radio

communication tower network to develop a systematic evaluation and assessment method that could

provide the necessary information for the repair and maintenance of the tower network. Two towers

were selected for this project to act as model towers. One tower is guyed, the Taum Sauk tower, and

the other is freestanding, Kansas City tower. Both towers are analyzed using the TIA-222-F for wind

and ice loadings. The Taum Sauk tower is then analyzed for seismic loading. Also a parametric study

to determine the effects of deterioration of tower components on the tower as a whole is completed on

the Taum Sauk tower. The controlling components of the Kansas city tower were found to be the di-

agonal bracings. The critical bracings were found to be at 88.9% of their maximum capacity. The max-

imum capacities of the other components of the tower were found not to exceed 51.1% capacity.

Therefore, the tower passes for the current code.

The parametric study was conducted on the Taum Sauk tower under wind, ice and seismic loadings.

For the wind and ice analysis it was determined that the bracing on the tower controls the structural

integrity of the tower. If the braces are damaged by as little as 10%, the capacity exceeds 100% and

the tower fails. When damage is introduced to the guys and the legs, the tower fails at 25% and 42%

damage, respectively.

The parametric study completed using seismic loading did not provide information about failure. The

results of the parametric study showed the increase or decrease in axial force of the components due

4MASTS AND TOWERS Ulrik Støttrup-Andersen Market Director, Head of Department, RAMBØLL Bredevej 2, DK-2830

Virum, Denmark, usa@ramboll.dk. Chairman of IASS Working Group #4”Masts and Towers”. Lightweight structures in civil

engineering, Proceedings of the international symposium, Warsaw, Poland, 24-28 June, 2002. General lectures

to deterioration in one or all of the tower components. It is seen that there is a 0.5 kip increase in axial

force in the legs when the guy cables are damaged, and a 0.25 kip increase in the legs when the

whole tower is damaged to 50% original cross sections. A 0.15 kip increase in axial force in the guys

is seen when the legs are damaged to 50% their original cross sections. Damage to either the tower

legs or the guys can cause significant increases in axial forces when subjected to seismic loadings. In

this project the towers were analyzed under wind, ice, and seismic loading and the results indicate

that some components of the towers are critical and could control the failure. It is recommended that

detailed inspection of the towers' critical components be performed to perform a detailed risk assess-

ment5.

Mogens G. Nielsen, in his paper at the IASS conference stated that for many years both guyed

masts and self-supporting towers have been used for supporting antennas for mobile and other com-

munications. The choice between masts and towers has often been determined by the tradition. How-

ever masts have its clear advantages in the open country, whereas the towers are more likely to be

chosen in the urban areas. Masts and towers are often used for broadcasting of radio and television

or antennas for cellular phones. The masts and towers consequently are situated on the top of hills

and mountains, where the climate often is extreme with respect to wind load and in some cases due

to atmospheric icing. Since the wind is turbulent and the masts and towers are flexible and sensitive

to dynamic load, the dynamic response becomes important in the analysis of towers and guyed

masts. However there are some differences in the analysis of masts and towers. The wind resistance

for lattice sections is dependent on the type of members, the solidity of the sections and for tubular

members also dependant on the Reynolds number. Furthermore, latest research within the IASS

Working Group for Masts and Towers has shown that the wind resistance of tubular sections is de-

pendent on the turbulence of the wind. The masts act strongly in non-linear fashion since the guy

ropes are varying from slackened to a taut string. Over the years different methods have been used

for analyzing guyed masts making the methods more and more realistic: starting by a gust factor

method, over the IASS patch wind method to the Eurocode patch wind method, which gives results

close to the results from a stochastic analysis and the time domain analysis. The towers do not act as

non-linear as the masts. However, the towers are also sensitive to the dynamics of the wind and a

dynamic factor should be applied depending on the turbulence of the wind, the height of the structure

etc6.

5 Analysis Of Radio Communication Towers Subjected To Wind, Ice And Seismic Loadings

A Thesis Presented to the Faculty of the Graduate School of the University of Missouri – Columbia In Partial Fulfillment of the

Requirements for the Degree Master of Science By ERIC JAMES SULLINS Dr. Hani Salim, Thesis Supervisor. May 2006

6 The Analysis of Masts and Towers. Mogens G. Nielsen, MSc CEng, Chief Consultant, Secretary of IASS Working Group

no. 4 Masts and Towers, Rambøll Denmark, Bredevej 2, DK-2830 Virum, Denmark Received February, 7, 2008; Revised ver-

sion February, 6, 2009; Acceptation March, 25, 2009

Structural response of mast and towers

4e Conférence spécialisée en génie des structures

de la Société canadienne de génie civil

4th Structural Specialty Conference

of the Canadian Society for Civil Engineering

Montréal, Québec, Canada

5-8 juin 2002 / June 5-8, 2002

DYNAMIC RESPONSE OF ANTENNA-SUPPORTING STRUCTURES

G. Ghodrati AmiriA , A. BoostanB

A Department of Civil Engineering, Iran University of Science & Technology, Iran

B Department of Civil Engineering, Islamic Azad University of Tehran, Iran

ABSTRACT: The subject of this paper is the investigation of the dynamic behavior of self- supporting

towers with four legs. In this regard, 10 existing self-supporting telecommunication towers with heights

varying from 18 to 67 m have been studied under Tabas, Naghan and Manjil earthquake spectra,

which are among the important and major earthquakes in Iran. These spectra were scaled to the base

acceleration of 0.35g in order to be compared with the design spectrum of the Iranian 2800 seismic

code of practice. The seismicity level of Iran is one of the high seismicity levels in the world. The re-

sults are studied in parallel to the concepts of the seismic national code for buildings. Also, since in

most cases, the wind force is taken as the controlling force for designing these structures, a compari-

son is made between the results of wind and earthquake loading. These comparisons result the ne-

cessity of considering earthquake loads in tower analysis and design. Their dynamic analyses are

performed by SAP2000 program.

SEISMIC RESPONSE OF 4-LEGGED SELF-SUPPORTING TELECOMMUNICATION TOWERS

G. Ghodrati Amiri* and S. R. Massah

Center of Excellence for Fundamental Studies in Structural Engineering

Department of Civil Engineering, Iran University of Science and Technology

P.O. Box 16765-163, Narmak, Tehran 16846, Iran

ghodrati@iust.ac.ir - massah@iust.ac.ir

A. Boostan

Department of Civil Engineering, Islamic Azad University Tehran, Iran

*Corresponding Author

(Received: October 12, 2006 – Accepted in Revised Form: May 31, 2007)

Abstract Telecommunication tower is an important component of the basic infrastructure of commu-

nication systems and thus preserving them in events of natural disasters - such as a severe earth-

quake - is of high priority. In past studies, researchers have mostly considered the effects of wind and

earthquake-induced loads on 3-legged (triangular cross-section) self-supporting steel telecommunica-

tion towers. In this study, the seismic sensitivity of 4-legged telecommunication towers is investigated

based on modal superposition analysis. For this purpose, ten of the existing 4-legged self-supporting

telecommunication towers in Iran are studied under the effects of wind and earthquake loadings. To

consider the wind effects on the prototypes, the provisions of the TIA/EIA code are employed and the

wind is treated as a static load throughout the analysis. In addition, to consider the earthquake effects

on the models, the standard design spectrum based on the Iranian seismic code of practice and the

normalized spectra of Manjil, Tabas and Naghan earthquakes have been applied. Since Iran is con-

sidered to be located in a high seismic risk region, a base design acceleration of A = 0.35 g is used

for normalization of the spectra. It was observed that in the case of towers with rectangular cross sec-

tion, the effect of simultaneous earthquake loading in two orthogonal directions is important. At the

end, a number of empirical relations are presented that can help designers to approximate the dy-

namic response of towers under seismic loadings.

Keywords Seismic Response, Earthquake and Wind Loadings, Self-Supporting 4-Legged

Failure of Mast and towers

Finite Element Seismic Analysis of Guyed Masts

A thesis submitted for the degree of Master of Science by Research

Matthew Grey

St Cross College

Hilary Term 2006

Guyed masts are a specialized type of structure commonly used in the broadcasting industry to sup-

port equipment at substantial heights. The dynamic analysis of these structures under seismic loading

is a much understudied field that requires investigation. The complex nature of their analysis arises

as well as P-

mast. These lead to the structure exhibiting significant nonlinear characteristics even under working

load conditions. Full nonlinear analysis of guyed masts is rarely performed as it is complex and time

consuming. Masts are usually designed by equivalent static methods for wind and ice loading only,

with the seismic load case often assumed to be less onerous. The validity of this assumption is inves-

tigated as part of this research.

In this project four existing guyed masts in the UK with heights ranging from 99m to 312m are accu-

rately analysed under various seismic loading conditions using SAP2000 structural analysis software.

The research aims to gain an understanding into the distribution and magnitudes of forces developed

during typical seismic and design wind events, establish indicators and trends that may aid in guyed

mast design, and identify the circumstances in which seismic loading may be the governing load case.

Investigations into the „travelling wave‟ effect, the significance of vertical motion, and the suitability of

a response spectrum analysis are also undertaken. Applicable sections of Eurocode 8 are followed

wherever possible. It is shown that when subjected to substantial seismic events with peak ground

accelerations in the region of 4m/s2, significant forces can develop in masts that are comparable to

those produced during a wind assessment using the Patch Load method. The distribution of forces

can be appreciably different from a wind loading analysis and any regions with irregular or incon-

sistent distribution of wind response forces can be vulnerable to seismic loading, particularly when

mean hourly design wind speeds are less than 22m/s. It is also shown that enough common or pre-

dictable seismic behaviour exists between masts to suggest that the development of a simplified

seismic analysis method for guyed masts is feasible.

Finite Element Seismic Analysis of Guyed Masts

by

Matthew Grey

A thesis submitted for the degree of

Master of Science by Research

at the University of Oxford

St Cross College

Hilary Term 2006

Journal of Wind Engineering and Industrial Aerodynamics, 23 (1986) 487--499 487

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

A SIMPLIFIED METHOD FOR DYNAMIC ANALYSIS OF A GUYED MAST

PETER GERSTOFT*

Department of Structural Engineering, Technical University of Denmark, L yngby (Denmark)

A.G. DAVENPORT

Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, London, Ontario (Canada)

Summary

The dynamic response of a guyed mast is relatively larger than for other structures. Thus a proper

evaluation of the dynamic response is of major importance. The proposed simplified method sepa-

rates the dynamic response into a low-frequency, background region and a high-frequency, resonant

region. The background response has been estimated using patch loading. The resonant responses

can be taken into account by multiplying the background response by a dynamic magnification factor.

This factor depends, in a systematic way, on the average structural properties of the mast. The ap-

proach is illustrated by examples, and compared to a statistical method.

ISSN 1392–3730 print / ISSN 1822–3605 online

JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT

http:/www.jcem.vgtu.lt

2007, Vol XIII, No 3, 177–182

STATIC BEHAVIOUR ANALYSIS OF MASTS WITH COMBINED GUYS

Donatas Jatulis1, Zenonas Kamaitis2, Algirdas Juozapaitis3

Dept of Bridges and Special Structures, Vilnius Gediminas Technical University,

Saulėtekio al. 11, LT-10223 Vilnius, Lithuania

E-mail:1jatulis@hotmail.com; 2zenonas.kamaitis@ts.vtu.lt, 3alg@st.vtu.lt

Received 26 Jan 2007; accepted 30 March 2007

Abstract. The purpose of this study was to develop a new type of guyed mast that incorporates a

complex guy cable system with a particular focus on the effect of static loading on the response mast

behaviour. The intension of such solution is to increase a number of elastic supports for the mast

shaft that will impact on its stability under loading. The static analysis of a one-level guyed mast has

been undertaken. The effects of geometrical and physical design parameters on the displacements of

the mast were determined. The analysis is illustrated with two-guyed masts: the bending moments

and lateral displacements were determined for a typical guyed mast and guyed mast with combined

guys.

Keywords: guyed mast, combined guys, static loading, geometrical and physical parameters, behav-

iour modelling.

In the present paper the response of steel telecommunication masts under the influence of environ-

mental actions and seismic loading is investigated. As flexible structures, they are highly sensitive to

the effect of wind and ice, while earthquakes can be impor-tant as well, according to the modern

codes for earthquake resistance structures. In the framework of a recent research activity, a large

number of lattice steel masts on the ground of four different typologies were studied taking into ac-

count both the impact of the environmental effects, i.e. wind and ice loading, and seismic actions on

their struc-tural behaviour and all their special geometrical structural features. Emphasis was given to

the evaluation of the wind loading on the steel masts, since the accurate com-putation of the wind

loading is very important due to the fact that wind appears in most cases to be the most critical load-

ing. The analysis has been carried out according to the contemporary relevant codes by means of

innovative software, whereas all parameters of the study are presented and thoroughly described. In

the last part of the paper, use-ful conclusions are presented regarding the performance of the struc-

tural members for each one of the four types of the steel masts under investigation.

On the response of steel lattice telecommunication masts under environmental actions and seismic

loading

E. Efthymiou1, D. N. Kaziolas2 & C.C. Baniotopoulos1

1Institute of Metal Structures, Department of Civil Engineering, Aristotle University of Thessaloniki,

Thessaloniki, Greece

2Technological Educational Institute of Kavala, Drama, Greece

EACWE 5

Florence, Italy

19th – 23rd July 2009

Flying Sphere image © Museo Ideale L. Da Vinci

Keywords: Steel lattice masts, wind loadings, structural codes, combined effects

ABSTRACT

In the last years, a lot of new issues have been arisen regarding the structural behaviour of steel lat-

tice masts which are used either for telecommunication needs or as systems to transfer energy. As

environmental effects are becoming more severe and the earthquake phenomenon is taken into ac-

count in a more detailed way according to the modern codes for earthquake resistance structures, the

thorough investigation of the performance of these structures becomes imperative. In addition, since

these two industries become strategic and growing in today‟s economy, their structural safety and

stability is considered vital. In some cases the financial and social consequences caused by a possi-

ble collapse of this kind of structures are considered as damaging as those caused by the collapse of

traditionally significant infrastructure, such as bridges. The present paper aims at investigating the

structural response of these special structures subjected to the influence of wind loading, as well as

the combination of wind loading and ice. For the purpose of the herein presented research activity, 6

types of steel masts have been analyzed, namely 4 masts located on the ground and 2 masts located

on buildings. The study was carried out by means of innovative software in order to introduce the wind

actions as thoroughly as possible and simulation models have been configured for the masts under

investigation incorporating all special geographical.

Contact person: Evangelos Efthymiou, Dr. Civil Engineer, Institute of Metal Structures, Department of

Civil Engineering, Aristotle University of Thessaloniki, University Campus, GR-54124, Thessaloniki,

Greece.

Tel: +302310994223, Fax: +302310995642. E-mail vefth@civil.auth.gr

On the structural response of steel telecommunication lattice masts

for wind loading and combined effects

Efthymiou E., Gerasimidis S. & Baniotopoulos C.C.

Institute of Metal Structures, Department of Civil Engineering, Faculty of Engineering,

Aristotle University of Thessaloniki GR- 54124, Thessaloniki, Greece

vefth@civil.auth.gr, sgerasim@civil.auth.gr, ccb@civil.auth.gr

EACWE 5

Florence, Italy

19th – 23rd July 2009

Flying Sphere image © Museo Ideale L. Da Vinci

Keywords: Steel lattice masts, wind loadings, structural codes, combined effects

ABSTRACT

In the last years, a lot of new issues have been arisen regarding the structural behaviour of steel lat-

tice masts which are used either for telecommunication needs or as systems to transfer energy. As

environmental effects are becoming more severe and the earthquake phenomenon is taken into ac-

count in a more detailed way according to the modern codes for earthquake resistance structures, the

thorough investigation of the performance of these structures becomes imperative. In addition, since

these two industries become strategic and growing in today‟s economy, their structural safety and

stability is considered vital. In some cases the financial and social consequences caused by a possi-

ble collapse of this kind of structures are considered as damaging as those caused by the collapse of

traditionally significant infrastructure, such as bridges.

The present paper aims at investigating the structural response of these special structures subjected

to the influence of wind loading, as well as the combination of wind loading and ice. For the purpose

of the herein presented research activity, 6 types of steel masts have been analysed, namely 4 masts

located on the ground and 2 masts located on buildings. The study was carried out by means of inno-

vative software in order to introduce the wind actions as thoroughly as possible and simulation models

have been configured for the masts under investigation incorporating all special geographical.

Contact person: Evangelos Efthymiou, Dr. Civil Engineer, Institute of Metal Structures, Department of

Civil

Engineering, Aristotle University of Thessaloniki, University Campus, GR-54124, Thessaloniki,

Greece.

Tel: +302310994223, Fax: +302310995642. E-mail vefth@civil.auth.gr

On the structural response of steel telecommunication lattice masts

for wind loading and combined effects

Efthymiou E., Gerasimidis S. & Baniotopoulos C.C.

Institute of Metal Structures, Department of Civil Engineering, Faculty of Engineering,

Aristotle University of Thessaloniki GR- 54124, Thessaloniki, Greece

vefth@civil.auth.gr, sgerasim@civil.auth.gr, ccb@civil.auth.gr

Effect of changes on joint connections of steel lattice towers due to environmental loads

engine Gucuyen, R. Turgrul Erdem, Umit Gokkus

faculty of Engineering (Civil), Celar Bayar Uniiversity, 45140, Manisa, Turkey

International Journal of Engineering and Industries, volume 2, number 1, March, 2011

Construction of latticed steel towers is growing rapidly through diversification to meet the increasing

demand for communication and energy. In this study, structural behavior of 75 meters offshore lat-

ticed tower, tubular sectioned frame members, under wave and wind loads are investigated. The

structure is handled in two modelsas space truss com[posed of pin – jointeted (model A) and rigid

main legs surround space truss composed of pin jointed (Model B) in this way two different structures

are utilized. Waave forced are obtained from Morrison Equation. Wind force is based on gust factor

and calculated according to EIA-TIA 222-F (structural standard s Abstract for steel antenna towers

and antenna supporting structures) code. The aim of this study is to obtain the effective periods,

masss sources, interstory drift ratios, maximum displacmenet s of peak points and maximum frame

forces of two structyures which have different joint connections to determine the safety of them.

Optimal design of lattice towers made up of solid round steel bars

Donatas Jatulus, Algirdas Juozapatitis, Povillas Vainiunas

Vilnius Gediminas Technical University, Sauletekio ave, 11, LT-10223 Vilnius, Lithuania

May 19 – 21, 2010, Vilnius, Lithuania. The 10th International Conference. Modern Building Materials,

structures and Techniques. http://www.vgtu.lt/en/editions/proceedings.

The article discusses rational design, considering the mass criterion of a lattice steel tower made up

of solid round steel bars affected by the static load. The spacing between the tower truss chords and

the inclination of the bracing members are set as the main variables. A mathematical model of tower

structure was prepared using MATHCAD 14.0 software. The conditions of the marginal safety state of

the tower‟s member were assessed. The numerical experiment was used as a basis to present the

dependence of the tower optimum width and the optima inclination of its struts on the tower height,

wind load intensity and steel strength. Recommendations were provided as well.

Conclusions: the presented mathematical model for rational design of a tower from round solid steel

bars facilitates calculation of optimal values of the tower width and the inclination of its bracing mem-

bers considering the tower height, the steel grade and wind load intensity.

The numerical analysis of the rational design parameters of a steel tower revealed that the tower op-

timal width varies between 1/17 H and 1/55H. an increase of the tower height also causes an increase

of the values of the tower optimal width. Higher wind load intensity demands for increased spacing

between the chords. If the steel strength increases, the tower optimal width decreases.

It has been determined that the optimal inclination of bracing members in a tower of round solid bars

is virtually independent of the tower height and the wind load intensity, its average value is 35o. the

inclination of the struts in designs of such towers should not exceed 39o.

Linear Static Analysis

Most structural analysis problems can be treated as linear

static problems, based on the following assumptions

1. Small deformations (loading pattern is not changed due

to the deformed shape)

2. Elastic materials (no plasticity or failures)

3. Static loads (the load is applied to the structure in a slow

or steady fashion)

Linear analysis can provide most of the information about

the behavior of a structure, and can be a good approximation for

many analyses. It is also the bases of nonlinear analysis in most

of the cases.

MODELLING OF TOWERS

SAP2000 software is used for analyzing the structures. The display environment of SAP2000 is an

appropriate environment for modeling structures like towers that have several members with different

specifications. With regard to the existing connections between members based on the position and

number of used bolts, these connections are classified into 2 types of fixed and joint connections and

accordingly, the members are classified into beam and truss. After determination of the coordinates of

nodes of the towers and their members, the geometric properties of tower sections are given to the

software. The 3D distributed mass of the tower is automatically considered along the members by

specifying the density of the used materials and geometric properties of the sections. In order to con-

sider

the mass of nuts and bolts, ladder and other installed equipment on the tower, since their weights are

known, by modifying the density, this mass is distributed along the height of the structure. It„s im-

portant to

note that this weight is very considerable and ignoring it, has a very substantial effect in the results.

Structure damping is modeled with a value of 2% of critical viscous damping.