madrazo paper (1)

8/11/2019 Madrazo Paper (1)

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Post-Tensioning and Anchorage Systems

By Geoff Madrazo*

Georgia Institute of Technology

RE at !ehigh ni"ersity

Graduate Mentor# $a"id Ro%e&aculty Ad"isors# $r' Richard Sause* and $r' (ames Ricles*


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Ta)le of ontents

1.0 A)stract

2.0 Introduction

2.1 +hat is Prestressing,

'.'. Science of Post-Tensioning'.' /istory

'.'0 A11lications

2.2 Pur1ose

2.3 2)3ecti"es

'0'. Stress Testing

'0' Beha"iors of Anchorage

'0'0 Range of se

3.0 Methods and Materials

3.1 PT Strand

3.2 Anchors and +edges

3.3 Testing0'0'. Static Tests

0'0' Tensile Tests

4.0 Results

4.1 Static Tests

4'.'. Stress Testing4'.' T5o-1art "s' Three-1art +edge

4.2 Tensile Tests

4''. Stress "s' Strain

4'' Rate of Elongation

5.0 onclusions

5.1 Anchorage System

5.2 Strands

6.0 Ac%no5ledgements

7.0 References


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1.0 Abstract

This 1ro3ect 5as designed to ac6uire data regarding the )eha"iors of a 1ost-

tension strand and anchorage system' &ailure in the strand is caused )y the 5edgesma%ing a notch in one or more of the 5ires7 therefore inducing the strand the )rea% at

high loads' The use of 1ost-tensioning in real-5orld a11lications is limited )y this

failure7 so %no5ing the s1ecific )eha"iors of the system is "alua)le for testing andresearch that in"ol"e 1ost-tensioning'

8umerous stress tests demonstrated the strength of the three-1art 5edge under

hea"y loading7 as 5ell as the strand and anchor system9s a)ility to e:ceed yielding'Referencing this information for future testing 5ill hel1 researchers understand the

1ro1erties of the PT strand and anchors7 and 5ill ho1efully 1romote e:1loiting the

ad"antages of 1ost-tensioning'

2.0 Introduction

2.1 What is Prestressing?

Prestressing is a method of reinforcing different %inds of structural elements' It

5as )ased off of the use of re)ar in concrete as reinforcement7 5ith the maindistinction )eing that an induced stress changes the 1ro1erties of the concrete ;PTI


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to install' It also allo5s for ne5 designs to ta%e ad"antage of a lighter concrete sla)

5ithout com1romising its strength'

The method of 1restressing has )een im1lemented for se"eral decades in all ty1es

of )ridges7 many %inds of ele"ated sla)s ;i'e' residential and high-rise structures7

1ar%ing garages7 etc'


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2.2 Purpose

The 1ur1ose of this 1ro3ect is to o)tain useful data on the strength and )eha"iors

of the 1ost-tension strand and anchor system' A relia)le data set 5ill )e a "alua)lereference for future 1ro3ects 5hich im1lement 1ost-tensioning'

2.3 Obecti!esThe first o)3ecti"e of my 1ro3ect is to 1erform multi1le stress tests on the 1ost-

tension strand and anchor system' I 5ill collect different forms of data7 such as the

)rea%ing strength ;Te:1


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Source# ASTM

3.2 Anchors and Wedges

Anchorages and 5edges are manufactured in different 5ays for different

a11lications' They follo5 the American oncrete Institute ;AI< code 0.7 5hich

fundamentally states that the anchorage system is guaranteed u1 to D of the)rea%ing strength of the strand ;T< ;AI


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The first set of testing 5e 1erformed 5ere static ;monotonic< stress tests on an

analog uni"ersal testing machine at &ritz la)' These initial tests 5ere 1erformed 5ith

strand and anchors lefto"er from 1re"ious testing at the Ad"anced Technology for!arge Structural Systems ;AT!SS< la)' The materials 5ere not outdated7 yet their

condition 5as some5hat in 6uestion 5hich is 5hy 5e tried to ma%e a clear distinction

for these tests in our data' Before 5e could )egin any %ind of testing7 5e made surethat the 1ro1er safety 1recautions 5ere ta%en' +hen ta%ing the strand to its )rea%ing

strength7 there is the ris% of the 5edges 1o11ing out of the anchor' To account for that

5e 1ut a co"er o"er the ends to control any 1ieces that came loose ;&igure 0'@


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&igure 0' ni"ersal Testing Machine setu1 at &ritz

The ne:t 1hase of testing 5as com1leted 5ith ne5 strand7 anchors and 5edges1ro"ided )y $y5idag-Systems International ;$SIsoft zone? 5as im1lemented7 in 5hichthe crossheads dis1laced at a rate of '. inFmin until there 5as .== l)s' tension in the

strand' After the >soft zone7? 5e 1rogrammed the machine to load the strand at a rate

of .'== %i1sFmin for the first three tests7 and D'== %i1sFmin for the ne:t three tests'

As an added safety 1recaution7 there 5as also a )rea% detection mechanism 5hich5ould sto1 the machine if there 5as a dro1 of at least .= of the load 1ast the ===

l)' stress le"el' The tests 5ere 1hysically set u1 the same 5ay as in &ritz la) ;&igure

0'@


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a granular com1ound ;Millfield


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1 3 5.5 .!7 .!3"7 1.$" 11.7

11 3 5."1 .!7 .!$1$ 1.5! ".77

1 3 5.5 .! .!3 1.315 ".!1

13 3 57." .!7 .!$5! 1."1 "."5

Ta)le 4'. Test data

The data collected from the static tests are documented in Ta)le 4'.' The tests .-05ere 1erformed at &ritz la) 5ith old materials7 tests 4-C at &ritz la) 5ith ne5

materials7 and tests -.0 using ne5 strand on the SATE machine' The "alue

Te:1FTu7mis the recorded )rea%ing strength7 Te:17 normalized 5ith the )rea%ing strength

;Tu7m @='04C %i1s< 1ro"ided )y $SI7 the manufacturer of the strand' These "aluessho5 us that one-third of our tests actually reached the D Tmar% that the anchors

are guaranteed to )y AI codes'

&igure 4'. T5o-1art "ersus three-1art 5edges

The data in &igure 4'. sho5s the difference )et5een the )rea%ing strength of t5o-

1art and three-1art 5edges' The "alue sho5n is a normalized Te:15ith the ASTMstandard minimum )rea%ing strength '@ %i1s' This "alue gi"es a standard of

com1arison for the tests7 and is not re1resentati"e of the actual )rea%ing strength of

the strand' This figure sho5s a strong set of data 5ithin one standard de"iation of thea"erage and higher )rea%ing strength for three-1art 5edges7 )ut the fact that 5e only

1erformed a single t5o-1art 5edge test cannot )e o"erloo%ed'


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The tensile tests didn9t turn out as 5e had ho1ed7 )oth ending u1 in the 5ire

sli11ing out' The +ireloc% tests sli11ed )ecause there 5asn9t enough surface area ofstrand for the resin to )ond to7 so 5hen ta%ing a hea"y load it started to sli1 ;&igure

4'


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.& 7 7' ow elaxation

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&igure 4'0 PT Strand Stress-Strain cur"e

5.0 onc#usions

5.1 Anchorage

Although our o)3ecti"es 5eren9t to find things 5rong 5ith the codes and

standards7 during our testing there 5as one statistic that stood out' In Ta)le 4'.7 it9s

"ery e"ident 5hen you loo% at the Te:1FTu7m"alue that the anchors don9t com1ly 5ithAI code 0.' 2nly three of our tests reached D )rea%ing strength of the strand7

and e"en those hardly made it 1ast' This finding is im1ortant to note )ecause it is 1art

of a )uilding code7 and those codes are su11osed to )e a)le to )e achie"ed'

Aside from all codes7 an im1ortant factor 5e 5anted to loo% as 5as 5hether a

t5o-1art or a three-1art 5edge 1erformed )etter and more relia)ly' In &igure 4'.7 it issho5n that a most of the three-5edge tests fall 5ithin one standard de"iation of the

a"erage7 ma%ing it a strong data set' But the fact that 5e only 1erformed one t5o-1art

5edge test ma%es it hard to )uild u1 any 1oints to5ards one or the other' +e can

loosely say that the three-1art 5edges 1erformed )etter under loading than the t5o-1art 5edges7 )ut more testing should )e com1leted )efore )eing a)le to ma%e a firm

statement'

5.2 &trands

In &igure 4'07 5e can see the "alue range of Te:1as com1ared to the yield strength7

TH' This tells us 5ith confidence that the strands can )e ta%en 1ast their yield 1oint5ith the con"entional anchor system' E"en the lo5est Te:15ell e:ceeded the yield

strength of the strand7 ma%ing it 1ossi)le to design something 1ast the yield strength

of the strand'

ow T+

ig- T+

g. T+

0in. T


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That design %no5ledge is 1articularly useful for the Self-entering $amage-&ree

Seismic-Resistant Steel &rame Systems 1ro3ects currently )eing 5or%ed on )y $r'

Richard Sause and $r' (ames Ricles at !ehigh ni"ersity' This gi"es them an u11erlimit to design to7 5hich could mean higher 1restress "alues7 less strands used7 and a

)etter designed model from %no5ing these 1ro1erties'


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6.0 Ac,no#edge(ents

had us%o

$a"id Ro%e$r' Richard Sause

$r' (ames Ricles

(ohn /offnerGene Matloc%

$r' Eric auffman

!ehigh ni"ersityAT!SS

8EES

8S&

7.0 eerences

American oncrete Institute ;AIAI 0.-='? The Structural oncrete

Standard ;==

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