AU2018403226B2 - Method and apparatus for performing field elongation measurements - Google Patents

Abstract

An improved method and apparatus for evaluating post-tensioning tendons, where the apparatus uses a positioning head placed directly into the pocket and against the anchor without making contact with the wedges as the apparatus seats on the tendon. From this position the apparatus evaluates the tendon by marking, measuring the tendon, and/or determining its location with increased reliability and precision.

Description

TITLE

Method and Apparatus for Performing Field Elongation Measurements

PRIORITY TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No.

62/709,458, filed January 19, 2018, which is incorporated by reference herein in its

entirety.

TECHNICAL FIELD

The present invention relates in general to post tensioning concrete construction

and in particular to the measurement of the elongation of post tensioning tendons.

.0 BACKGROUND

Post-tensioning construction is a method for reinforcing concrete with steel cables.

Steel reinforced concrete is a composite material with greater strength against sheer

forces than traditional concrete, and can be made even stronger if the steel reinforcement

is stressed in a manner to apply counter forces against anticipated building loads.

.5 In post-tensioning construction relaxed steel tendons are set into a concrete

casting before the concrete is poured. Post-tensioning tendons are enclosed in plastic

sheaths that are filled with grease and tightly wrapped or cast around the tendons to

protect against corrosion and prevent fixation to the concrete. A tendon has freedom of

lateral movement within its sheaths until both ends of the tendon are locked into their

anchors. The sheathed tendons are placed or fixed within a pre-formed concrete casting

area at locations and in geometries designed to exert the desired forces after the concrete

has set and the tendons are tensioned. These tendons are typically arranged to distribute compressive forces in, prevent cracking of, and counteract all loads expected to be placed on the structure.

One end of the tendon may be set into an anchor fixed to the casting form so that

the tendon will not exit the concrete casting area; an end anchored in this way is referred

to as a "dead end." The tendons are set into the anchor by setting a plurality of semi

conical gripping devices, called "wedges," around the tendon and seat in the anchor. The

wedges are locked-in to an anchor when proper gauge pressure is applied.

io Alternatively, an end of the tendon may be initially left with a 'tail' extending through

its anchor and beyond the casting form for later tensioning; such an end is referred to as a

"live end" or "stressing end." Longer tendons will often have both ends as live or stressing

ends.

When the concrete is poured the sheathed tendons within the casting form become

completely surrounded by concrete with only the live end tails exposed. The anchors are

cast into and mostly surrounded by the concrete with a portion of its outer surface exposed

inside a "pocket" of negative space created by a plastic pocket former set into the exterior

face of the concrete structure. The tail of the live end of the tendon extends from the

concrete structure. When the concrete has set, the casting forms and pocket former are

removed and grease is wiped off of the exposed tendon in preparation of the marking

process (to be discussed below). The stressing end is "pre-set" with wedges which sit

around the tendon and partly into the anchor. The pre-set wedges will lock-in to, and fully

seat into, the anchor during tensioning when a sufficient tension is applied. Until the

wedges are locked-in they partially extend out of the anchor and may extend outside of the

anchor after fully seating.

After the concrete has set to acceptable strengths, the desired tension as measured

in kips is loaded onto the tendon. This is typically done by means of a hydraulic jack,

referred to interchangeably as "jack" or "ram." A number of jacks are available on the

market such as the device disclosed in US patent number 4,805,877. The tendon can be

o either "prestressed" with a partial load (generally 30%) within 24 to 72 hours of the pour, or

fully loaded with tension after the concrete has set for 7 to 10 days or otherwise achieved

the specified minimal concrete strength. The ram fits its nosepiece into the pocket and

grips the cable with its teeth. The ram pulls the gripped tendon against the wedges

located within the anchor to load the tendon with the desired force (approx. 33 Kips). The

6s ram presses against the wedges which are pushed forward into the anchor. The jack

applies the desired amount of force as measured out (in kips) on a recently calibrated

meter or gauge. Ideally, this measured amount of force is transferred into the tendon and,

as the tendon attempts to relax, on into the concrete.

However, several reasons prevent the ram's gauge from reliably indicating the force

io transferred into the tendon. These reasons include but not limited to: seating loss; creep;

anchorage strain; improper gauge calibration; damaged tendons; defective tendon

materials; abnormal amounts of friction which may result from fixation to the concrete or

from insufficient seating; and human error. Due to these and other risks, field elongation

measurements have become a standard quality control procedure and are required by

professional and industry organizations such as the Post Tensioning Institute.

Field elongation measurements are generally performed as follows: Prior to

tensioning, a reference mark is made on the tendon 'tail' on each 'live end' outside of the

pocket area. This mark is made by placing a guide, normally a 2x4 board, against the

exterior face of the concrete which assurers that the mark is placed lateral to the point at which the ram will grip the tendon. Using the guide as reference, a mark is made on the tendon with spray paint or other methods. Once this reference mark has been made and wedges have been preset in the anchor, the ram loads the tendon with a desired amount of tension. This displaces the mark from its initial position by a distance equal to the tendon's elongation. The ram is then removed and a guide of equivalent length, preferably

'5 the same guide used to make the initial mark, is placed against the face of the concrete

and the distance from the edge of the guide to the reference mark is measured with an L

square type ruler.

The equation for calculating the theoretical elongation of a tendon is well

understood in the field. Third-party elongation measurements are taken and reviewed

io against theoretical values. Deviations from the theoretical value can indicate that the

tendon was loaded with an insufficient amount of tension or that the tendon is damaged or

defective. If there is a discrepancy between the theoretical (usually .078" per foot of

tendon) and observed values, and it is greater than an acceptable threshold (normally 7%

to 10%), then the structural engineer will require a site revisit to confirm that the field

elongation report itself is not user error. If the report is confirmed to be free of transcription

and measurement errors or discrepancy otherwise persists, then the engineer may order a

lift-off test and or re-pull to confirm the elongation of the problem tendon. This test is rarely

performed a third time because the act of tensioning can lead to loss of tension, and

because the tensioning process is not entirely nondestructive on the tendon, as the teeth

of the wedges can harm the tendon on each pull and repeating of its wedges.

Due to the nature of post-tension construction, there are generally a large number

of tendons within the concrete structure that are stressed at any given time. All

elongations measurements tend to be taken at once, with the results hand written onto a datasheet which is later can be transferred manually to digitized form and sent to the

)5 engineer for review. Transcription errors, measurement errors, out of sequence reporting

errors and one-off omissions are common and lead to review of tendon elongation delays

pending a second site visit to attempt to clerically fix the elongation report before it can be

reviewed by the engineer of record.

A problem with current methods is caused by the lack of a standard guide. It is

)o common for the reference guide used during the marking step to be different from the

device used when measuring. This difference can result from using different axes of the

same guide or by incorrectly assuming that two different guides share common lengths; as

variation commonly occurs between nominally sized 2x4 boards.

An additional problem with current methods results from imperfections or angles in

)5 the exterior face or rim of the concrete at the pocket. The rim of the tendon pocket is not

perfectly flush and some edges of the rim can extend nearer or farther from the plane of

the concrete than others. As a result, the mark created by the guide will be different

depending on which edge of the pocket the guide is placed against.

An additional problem with current methods comes from the small interface between

a flat guide and a round tendon. The interface between the paint guide and the tendon is

small and results in a diffuse mark that is crisp only on its top-most part. The tendons are

greased and if not properly cleaned, the grease can deform the mark. The risk of the mark

becoming unreadable continues to increase with the time between when the mark is made

and the final review of the elongation.

The current testing process is time intensive and requires a site re-visit when errors

occur or if restressing is required. The errors are generally not discovered until after the testing team has left the project site and often require a second site visit before work can proceed.

Any discussion of the prior art throughout the specification should in no way be

.0 considered as an admission that such prior art is widely known or forms part of common

general knowledge in the field.

SUMMARY

As a solution to these and other problems with the existing methods, embodiments

of the present invention provide an improved method and apparatus for performing field

.5 elongation measurements. In its current embodiments the apparatus is split into multiple

operative parts referred to as devices such as the 'marking device' and the 'measuring

device.' References to the operative parts as devices should not be read as a limitation of

the invention. Nothing generally requires the operative parts of the apparatus to be

embodied as physically separate devices in situations where context does not otherwise

require it.

Before using the apparatus, the form, pocket void and grease must be wiped off and

cleared of debris. The apparatus includes a standardized positioning head (preferably 4

inches in length) is placed directly into the pocket, around the tendon, and makes multi

point magnetic contact with anchor. The head has a channel running through its center

which fits over and seats onto the tendon. The head has a depression set into its anchor

end, designed to fit around and avoid contact with the wedges which are pre-set in and

partially extending from the anchor.

The contact surface of the head magnetically connects with the anchor at multiple

points which assures that the head runs perpendicular to the anchor and seats flush with the tendon. When the head has made magnetic contact with the anchor and the tendon seats against the top of the channel, the remainder of the apparatus becomes aligned into proper position with respect to the anchor and tendon.

The marking devise comprises the positioning head and a marking tool. The

marking device is used to create a reference mark defining the transverse plane where the

tendon exits the caudal edge of the head. The mark is made a standardized distance

(preferably 4 inches) from the anchor by any non-destructive marking means, such as a

spray paint and shield or by securing an encoded identification tag or tape to the tendon.

The tendon is then loaded with tension by a standard means such as a ram type

device. The ram must grip, or otherwise apply tension to, the tendon at a point medial to

o the reference mark and lateral to the anchor. Once tension is loaded on to the tendon, the

anchor and the wedges seat together to prevent the tendon from relaxing.

The measuring device includes the positioning head and a measuring tool. The

measuring device's positioning head is designed to be identical to the head of the marking

device. This symmetry guarantees that the measuring device seats over the tendon, into

the pocket, makes flush contact with the anchor and holds the same position as that of the

positioning head on the marking device. The caudal plane of the measuring device is

identical to the caudal plane used to set the reference mark.

The preferred version of the measuring device has its positioning head connected to

a spine which, in turn, is connected to a measuring body. In this embodiment, the spine is

attached to the positioning head of the measuring device and passes through the

measuring body in such a way as to allow the body to slide laterally along the spine. The

bottom of this version of the measuring body has a seating channel which allows the body to seat onto the tendon. While the head of the measuring device maintains contact with the anchor the body has freedom to slide laterally along the tendon and the spine. During i5 operation, the body will slide along the tendon until its cranial edge is directly above the reference mark. Once in position the measuring device determines the elongation by measuring the distance between the reference mark's current and original positions.

Embodiments of the present invention solve many problems associated with prior

methods. The standardized head of the apparatus, by making contact directly with the

'o anchor, bypasses problems associated with marking the tendon from a point defined by

the outer-rim of the pocket. Other post-tensioning tools interact with the pocket but these

tools either secure themselves against the anchor by applying tension to the tendon and/or

push against or otherwise interact with the wedges. The preferred version of the marking

device makes contact with the upper half of the surface of the tendon leaving a crisp mark

'5 over at least 40% of the tendon's circumference, improving on the small, unclear and

diffuse marks made by prior methods.

Some versions of the measuring device include an optional means of determining

its location at the time of each measurement. In these versions, an antenna located at the

cranial edge of the measuring body is used to determine the location of the measuring

8o device when a measurement is made. The location of the measuring device may be

determined by any commercially available measurement method such as GPS or a

triangulation system. This version of the measuring device will confirm the identity of the

tendon being measured by comparing its location at the time of measurement to known

locations of tendons. The elongation data collated with a tendon identification code and

saved to the measuring device. This data file will be transferred to a computer or a

substantially similar device and used to generate an elongation report that ties the more accurate elongation dimensioned to the exact identified tendon reducing a major source of human error.

In other embodiments, the present disclosure provides a method of performing field

elongation measurements of a post-tensioning tendon enclosed by preset wedges and an

anchor set within a pocket of a concrete structure, comprising the following steps:

marking the tendon with a nondestructive marking device positioned into the

pocket of the structure so that the marking device makes magnetic multi-point contact with

the anchor and rests on the tendon without making contact with the preset wedges;

loading the tendon with tension; and

measuring the tendon with a measuring device positioned into the pocket of

the structure so that the measuring device makes magnetic multi-point contact with the

anchor and rests on the tendon without making contact with the preset wedges.

BRIEF DESCRIPTION OF DRAWINGS

)0 For a more complete understanding of the present invention and the advantages

thereof, reference is now made to the following descriptions taken in conjunction with the

accompanying drawings, in which:

FIG 1A is a perspective rear-side view of an embodiment of a marking device illustrating

the general orientation of its parts.

FIG 1B is a perspective front-side view of an embodiment of the marking device showing

placement around a tendon.

FIG 2A is a perspective side view of an alternative embodiment of marking device with a

partial wire-frame view of the interior, illustrating the general orientation of parts and

placement.

.0 FIG 2B is a perspective side view of the alternative embodiment of marking device with a

partial wire-frame view of the interior, illustrating the proper placement of the device and id

tag or tape.

FIG 3 is a sectional view of a marking device showing the placement and operation of the

positioning head within the pocket.

.5 FIG 4A is a perspective side view of a measuring device illustrating the general orientation

of parts within the pocket.

FIG 4B is a sectional view illustrating the proper placement and use of a measuring device.

FIG 5A is a perspective view of an optional base station determining the position of an

alternate embodiment of the marking device.

.0 FIG 5B is an elevation view of an optional base station shown determining the position of

an embodiment of the measuring device.

DETAILED DESCRIPTION

In the Summary above and in the Detailed Description of the invention, as claimed

below, and in the accompanying drawings, reference is made to particular features

(including method steps) of the invention. It is to be understood that the disclosure of the

invention in this specification includes all possible combinations of such particular features.

For example, where a particular feature is disclosed in the context of a particular aspect or

embodiment of the invention, or a particular claim, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects and embodiments of the invention, and in the invention generally.

The term "comprises" and grammatical equivalents thereof are used herein to mean

that other components, ingredients, steps, etc. are optionally present. For example, an

article comprising (or "which comprises") components A, B, and C can consist of (i.e.

contain only) components A, B, and C, or can contain not only components A, B, and C but

also one or more other components.

Where reference is made herein to a method comprising two or more defined steps,

the defined steps can be carried out in any order or simultaneously (except where the

context excludes that possibility), and the method can include one or more other steps

which are carried out before any of the defined steps, between two of the defined steps, or

after all the defined steps (except where the context excludes that possibility).

The term "at least" followed by a number is used herein to denote the start of a

range beginning with that number (which may be a range having an upper limit or no upper

limit, depending on the variable being defined). For example, "at least 1" means 1 or more

than 1.

Anatomical terms are used to indicate the position of various structures, surfaces,

and elements. The terms "superior" and/or "cranial" refer to parts being close to or

approaching the head of a device with the superior or cranial-most portion of a device

being the anchor-side contact surface. The terms "inferior" and/or "caudal" refer to parts

away from or in the direction away from the head. The term "lateral" refers to portions of

the device or tendon moving away from the center of said device or tendon. The

lateralmost portion of the tendon is the extreme tip of the tail. The term "medial" refers to the portion of the device or tendon tending towards the center of the device or tendon.

The medialmost portion of the tendon is in the center of the concrete structure. The terms

"top,'"upper" and/or "dorsal" refers to portions of the device or tendon that are in the

direction of the antenna, handle, display or base station. The terms "lower," "bottom"

and/or "ventral" refer to portions of the device that are generally away from the direction of

the antenna, handle, display or base station. The term "transverse plane" describes a

plane separating the cranial and caudal surfaces. The term "longitudinal" axis refers to the

axis running through the length of the object. The term "substantially" when used to modify

the similarity or equality of two or more values, features, or elements is meant to include

similar values, features, or elements whose substitution would not fundamentally change

the function of the initial value, feature, or element as understood by a person of ordinary

skill in the relevant art.

The principles of the present invention and their advantages are best understood by

referring to the illustrated embodiments of the apparatus depicted in attached drawings, in

which like numbers designate like parts. In the following description, well-known elements

are presented without detailed description in order not to obscure the present invention in

unnecessary detail. For the most part, details unnecessary to obtain a complete

understanding of the invention have been omitted in as much as such details are within the

skills of persons of ordinary skill in the relevant art.

Positioning Head

A standardized positioning head ("head") 100 is common to the operative parts of

the apparatus referred to as a marking device 200 and a measuring device 400. With

reference to Figures 3 and 4A, the head 100 of the measuring device must be identical to

the head 100 of the marking device. The positioning head of the marking device has the same component elements, geometry, dimensions and connects to the anchor in the same way as the positioning head in the measuring device.

With reference to Figures 1A and 3, the head is of a standardized length

(preferably 4 inches) 104 and comprises a channel 108, a contact surface 101, one or

more magnetic surfaces 102A and a wedge pocket 103. The contact surface 101 is

defined as the flat surface at the cranial most portion of the head. The contact surface 101

either consists of, or is inset with, one or more magnetic surfaces 102A, 102B, 102C

substantially coplanar with the contact surface. The wedge pocket 103 is a depression set

medially into the cranial end of the head-body 107 of a sufficient recessed depth

(preferably 1/2 inch) to allow the contact surface to make magnetic contact with the anchor

without the head making contact with a set of wedges 004 which must be in the anchor.

As stated in the background section, the 'pre-set'wedges will partially extend out of the

anchor and may continue to protrude from the anchor even after they are 'locked in' to the

anchor with gauge pressure; in either case, the wedges will be enclosed by the wedge

pocket without the making physical contact with the head (see FIG 3).

The preferred version of the head comprises a cylindrical head-body 107 and a "U"

shaped channel 108 set into its ventral surface designed to seat around a tendon 001.

The head-body in this embodiment is made of a hard plastic which will not deform with

use, but any substantially similar material may be substituted. When the head is in proper

position, the tendon seats against the top on the channel and the contact surface makes

magnetic multi-point contact with an anchor 003 (see FIG 3). In this position, the contact

surface will be perpendicular to the tendon's longitudinal axis.

Figure 1B further shows the preferred embodiment of the channel 108 of sufficient

size and depth to seat around the tendon 001 coaxially so that the dorsal surface of the channel makes contact with at least 40% of the upper surface of said tendon within the channel the remainder of the channel flaring outwards. While the preferred embodiment has the channel, as shown, continuing through the ventral surface of the cylindrical head body, nothing inherently prohibits the channel from being completely enclosed by the head-body. As discussed in the embodiments below, the head is attached to a tool member such as a marking or measuring tool. During operation the proper placement of the head with respect to the anchor and tendon assures proper alignment of the tool member and its workpiece.

Marking Device

Figures 1A and 1B show a version of a marking device 200 in isolation and placed

within a pocket 006 set within a pocket 006 of a concrete structure 002. The marking

device comprises the standardized positioning head and a means for nondestructive

creating a reference mark on the tendon. The preferred embodiment of the marking

device is shown with a standardized positioning-head 100 connected to an optional handle

201 and a paint shield 202. The optional handle 201 is shown secured to the dorsal

surface of the head 100 for ease of operator use.

Figures 1A and 1B show the paint shield 202 is attached to the head 100 in such a

way that the caudal surface of the paint shield is coplanar with the caudal surface of the

head 106. The paint shield comprises a surface connected to the caudal surface 106 of

the head designed to direct spray paint (not shown) along the interface 204 of the tendon

001 and the caudal edge of the channel of the head 108. The paint creates a reference

mark 205 in the transverse plane defined by the interface 204, preferably covering at least

40% of the tendon's circumference within this plane creating a large, clear reference mark.

Figures 1A and 1B show optional wings, attached at oblique angles to the shield 203A,

203B which are oriented so as to direct paint onto the tendon and capture diffuse paint.

Measuring Device

The measuring device comprises the positioning head and means for determining

the linear distance of the reference mark and the caudal surface of the head. With

reference next to Figures 4A and 4B which show perspective and sectional views of the

preferred embodiment of the measuring device 400 comprising the positioning-head 100

and a measuring body 411 connected by a rigid rectangular spine 401 running laterally

through a rectangular pathway 406 in the measuring body parallel to the channel 108 of

the head. The spine may be made of steel, aluminum, plastic or any other substantially

similar material that will not lose its shape. In this embodiment, the spine 401 is fixed into

the caudal surface 106 of the positioning-head and passes inside and through the

enclosed rectangular pathway 406 running laterally through the measuring body 411 in

such a way as to permit the measuring body freedom to slide back and forth along the

spine while prohibiting rotation so as to remaining in-line with the tendon.

In this embodiment of the marking device, the caudal surface 106 of the head-body

is attached to the spine 401 and to a measuring target 105. The measuring target is set

into or otherwise coplanar with the caudal surface of the positioning head.

Figures 4A and 4B further show how this version of the measuring device has a "U"

shaped channel ("body-seating channel) 407 set into the ventral surface of the measuring

body. The body-seating channel 407 is in line with; has the same dorsalmost point as; and

has a substantially similar shape as the channel 108 set into the head 100. Figure 4B

shows a version of the measuring body housing an eye unit 403. Figures 4A and 4B show how the measuring body 411 seats onto the tendon 001. The body has the freedom to slide laterally along the tendon and spine without rotating so as to remain in-line with the head. During operation the head remains magnetically connected to the anchor while the measuring body slides along the tendon.

The measuring device's tool for measuring linear displacement, as covered

extensively in the alternative embodiments, may use any known technique that can

measure the distance between the cranial edge of the measuring body and the reference

mark 205. The preferred version of the measuring device comprises the eye unit 403 set

into the cranial surface of the measuring body 411. The eye unit is a device which

determines linier distance by emitting and receiving a signal and interpreting the results.

The eye unit may incorporate any number of standard measuring devices which are

commonly known in the industry, for example a commercially available time-of-flight

modules.

The preferred version of measuring body additionally comprises a signal processing

module 404 electronically connected to the eye unit and housed within the measuring

body. The signal processing module is adapted to process, interpret and manipulate data

from the eye unit or other tools discussed in the alternative embodiments. This version of

the measuring body additionally comprises a memory for signal processing, calculation,

data storage and manipulation, a display 408 for the device to communicate with operator,

a plurality of buttons 410 for operator capture and navigating through data stored in the

device's memory.

An optional version of the measuring device additionally comprises a telescoping

antenna 503A extending from the cranial edge 402 of the body for communication with a base station 501. The telescoping antenna is of sufficient length to reach the level of the base station set discussed below.

Base Station

Figure 5A and 5B show an optional base station 501 which will be used in

conjunction with certain versions of the measuring device for determining the position of

the measuring device at the time a measurement is made. In this embodiment, the base

station is set into a depression 005 cast into the concrete structure 002 and its location

recorded in a digital map. The distance between the fixed position of the base station and

the tendons 001 may be calculated from site specific installation drawings. The base

station emits and/or receives signals which may be used to measure a distance between

the base station and the antenna of the measuring device 502. When the telescoping

antenna 503A of the measuring device is raised to a known height above the measuring

device, preferably the horizontal plane of the base station, the measuring device measures

its position from the fixed base station.

Operation

The above disclosed apparatus is used in the following manner to perform field

elongation measurements with improved accuracy and minimal user error.

After the concrete 002 is cast and before the tendon 001 is stressed, the tendon is

wiped down and the pocket is cleared of debris. The wedges 004 are pre-set around the

tendon and partially into the anchor 003. Next the head of the marking device 200 is

placed into the pocket 006, around the tendon 001, and against the anchor 003, so that it's

contact surface 101 makes flush, magnetic, multi-point contact with the anchor and avoids

contact with the wedges 004 as the dorsal surface of the tendon makes contact with the dorsal surface of the channel of the head 108 (see FIG 3 and 4B). The operator may need to manually lift the relaxed tendon to maximize the interface 204 between the tendon and the channel and assure that the tendon is in the same position as it will be after it has been loaded with tension. In this position the tendon will exit the head at a standardized distance (preferably 4 inches) 104 lateral from and perpendicular to anchor which, itself, is parallel to the caudal surface 106 of the head. The operator will then mark the tendon at the plane defined by the caudal edge 106 of the positioning head. In the preferred embodiment, the operator will apply spray paint to the interface 204 of the tendon as previously discussed.

The tendon 001 is then loaded by traditional methods such as a hydraulic jack (not

shown) as described in the background section.

The head of the measuring device 100 is placed into the pocket, 006 around the

tendon, 001 and against the anchor 003 so that the contact surface 101 makes multi-point

magnetic contact with the anchor. The head makes magnetic contact with the anchor

without making contact with the wedges 004, which are enclosed in the wedge pocket, 103

as the channel of the head 108 and the seating channel of the measuring body 407 seat

over and rest on the tendon (see FIG 4B). With the head in place, the target 105 of the

measuring device is located in the same transverse plane 106 and the same distance from

the anchor 104 as the initial reference mark made prior to elongation 106.

The operator, without breaking the magnetic contact between the head and the

anchor, slides the measuring body 411 along the tendon until the cranial edge of the

measuring body 402 is directly over the reference mark. The measuring body remains in

line with the head as it slides along the spine 401 and the tendon 001 maintaining a

straight-line path 409 between the eye unit 403 and the target 105. When the measuring body is in position the device will initiate a data capture of the elongation measurement.

The data capture may be manually initiated when the operator presses a capture button

410 or may be an automatic process. The captured data may be saved to the memory of

the measuring device. Optionally, the measuring device will determine both the length of

the elongation and the identity of the tendon being measured and collate the results by

storing the values as a single observation.

When performing a measurement, the preferred embodiment of the measuring

device sends a signal in the path 409 from an emitter located within the eye unit 403 on

the measuring body to the target located on the head 105 and is reflected off of the target

and back into a receiver located within the eye unit. The signal processing module 404

within the measuring body determines the distance from the eye and the target by

analyzing the signal using any known technique including time-of-flight calculations, phase

analysis, or triangulation. The distance between the eye and the target 409 is the same

value as the length of the elongation 412 (see Fig 4A). This distance value becomes part

of the data stored as a captured observation to the memory of the device.

In the preferred embodiment, the base station 501 is used to determine the location

of the measuring device at the time of measurement. This location capture is optional, but

if the base station is used, it must first be engaged and placed in a fixed position,

preferably into the depression set into in the concrete structure 002, and calibrated with the

antenna 503A of the measuring device. This calibration sets the reference location from

the base station and starting point of all located tendons. The measuring device will

determine its position with sufficient accuracy to identify the tendon being measured at the

same time as it determines the length of the elongation. This optional location step may

be performed by GPS-type satellite location or by interacting with the base station at its known location. Figures 5A and 5B show the base station 501 which send a signal to the telescoping antenna 503A set into the cranial edge of the measuring device. The antenna should be extended to a known height above the edge of the concrete 002, preferably the same height as the base station 501. The measuring device will determine by the strength of the signal from the base station it's linear distance 502 to the antenna.

In this optional location step, the distance from the antenna to the base station 502

and the distance from the eye unit to the anchor 504 are compared to a digital map of the

locations of the tendons. This digital map can be tabular in nature and populated from site

specific installation drawings and downloaded to the device's memory and analyzed by the

signal processing module. Each tendon that will be tested is identified and given a tendon

identity code. The tendon identity code is associated with a location in physical space. At

the time of capture the measuring device may use its observed distance from the base

station 502 and its observed distance to the target 002 added to the standardized head

length 104 triangulate the distance from the anchor to the base station. This value is

compared to the values in the digital map and used to determine the tendon's identity

code. The identity code is collated with the elongation measurement and stored together

in memory as a captured observation.

After data is captured, the measuring device may visually show the captured

observation on the display 408. The measuring device will continue to store additional

observations to memory which can be exported via a computer or similar device such as a

cellphone application to a cloud-based platform for real-time remote viewing and

commenting.

Although the present invention has been described in considerable detail with

reference to certain preferred versions there are other versions that are possible for

example:

An additional embodiment of the marking device includes a housing for pressurized

spray paint connected to the caudal surface of the paint shield. The ventral end of said

housing having a nozzle for spraying paint onto the tendon. This embodiment includes a

mechanical member for transferring pressure applied at the handle, such as a lever or

tension line, to depress the nozzle of the spray paint housing. This embodiment eases

operator use by allowing him or her to remotely release paint onto the interface between

the paint shield and tendon with one hand and without stooping.

An additional embodiment of the marking device will incorporate a grip for a marker

such as a grease pencil, stamp, paint brush, or other nondestructive marking member

located on the caudal surface of the paint shield. This embodiment includes a means of

transferring pressure applied to its handle, such as a lever or tension line, to press the

marker against the interface between the paint shield and the tendon.

An additional embodiment of the marking device will additionally comprise a

telescoping antenna 503B of sufficient length to reach the height of the optional base

station (see Fig 5A), a power source (not shown), and an operator control (not shown).

Prior to use, the base station 501 must be engaged and calibrated with the antenna of the

marking device to determine the reference location from the base. This embodiment will

send a signal from its antenna to determine the marking devices using commercial GPS or

any standard measurement techniques known in the relevant art to identify the location of

the marking device with respect to the concrete structure. The operator will send this

signal at the time that the mark is made on the tendon. This embodiment of the base station will determine the tendon identity code and the time of capture. This data will be stored as a record that the reference mark has been made with the correct marking device at the correct tendon.

An alternative embodiment of the marking device 300 can be seen in Figures 2A

and 2B. This version will additionally comprise a tagging body 301 attached to the caudal

surface 106 of the head 100. The tagging body will house a plurality of id tags or tape 302

and will position and secure an id tag to the tendon so that the cranial edge of the tag is

against the caudal surface of the head 106 to serve as the reference mark. This mark will

be made before the tendon is stressed. This embodiment will operate by placing an id tag

303 from the tagging body 301 and secure it to the tendon 001 by means of a tensioning

member, a heating element, or adhesive member so that the fastened tag does not have

any loose material unsecured to the tendon. The id tag is not limited to any material and

may be constructed from tape, sticker or coating. The id tags may additionally encode

location information in the form of optically encoded patterns such as bar codes or

information in the form of induction antenna such as RFID. Many codes of this type are

known in the relevant art and are commercially available. The cranial edge of the id tag

must be placed at the caudal edge of the head. The cranial edge of the tag will act as

reference mark for the measuring device.

An alternative embodiment of the measuring device will further comprise a sensor

405 for reading information encoded onto id tags. An embodiment of this sensor, shown in

Figure 4B, is shown embedded in the ventral side of the measuring body 411, within the

channel 407, and towards the cranial edge of the measuring device 402. The sensor is

electronically connected to the signal processing module. In this embodiment the sensor

is oriented so as to focus on the id tag when the cranial edge of the measuring body is placed over the cranial edge of the tag 303 as shown in Fig 4B. The sensor may be optical for optical-type tags or may include an emitter and receiver for induction antenna type tags. While the sensor 405 in the version of the measuring device shown in Figure

4B locates the sensor on the ventral side of the measuring body, the sensor may be

located anywhere on the apparatus. The information encoded in such tags will be stored

as part of the data observed when the operator initiates a data capture.

An additional embodiment of the sensor 405 may be use the sensor to determine

when the cranial edge 402 of the measuring device is properly placed over the reference

mark. The sensor may be in any other location that enables it to identify that the cranial

edge of the measuring device is in proper position over the mark. The sensor may be

optical adapted to focus on the line directly under the cranial edge of the device. When

such a sensor detects differences in light reflected off the marked 205 and non-marked

portions of the tendon 001, or otherwise determines that the device is in proper position,

the marking device will either automatically capture the elongation and location data or will

visually or audibly prompt the operator initiate the capture.

In an additional embodiment of the measuring device the eye unit 403 will comprise

a laser triangulation-type sensor. In this embodiment a laser within the eye unit will emit a

signal, which will reflect off of the target, and into a collection lens adjacent to the emitter

within the eye unit. The collection lens directs the light at a known angle into a linear

detector. The position of the focused light received by the linear detector is interpreted by

the signal processing module 404 to determine the length from the eye unit to the target.

This type of range finding method is well known in the art.

An additional embodiment of the measuring device the sensor will comprise a cog

or sprocket located within the spine passage 406 within the measuring body 411, the teeth of which interact with depressions in the spine 401 as the measuring body is moved back and forth from the head. As the cog or sprocket is rotated the angular displacement is stored as tension in a spring or charge on a capacitor in proportion to the distance the measuring body has traveled from the head. This is translated into a measurement of distance which can be displayed and captured. These types of measuring devices are well known in the art and are commercially available.

An additional embodiment of the measuring device will further comprise a means of

confirming that it is horizontally level such as a bubble level or an accelerometer.

An additional embodiment of the measuring device uses a graduated ruler as the

rectangular spine. The ruler may be used to confirm measurements made by other

means, or may be visually observed and entered into the measuring body manually by the

operator.

An additional embodiment of the measuring device replaces the rigid spine and

passage with a telescoping spine for ease of use and storage.

An alternative embodiment of the measuring device will use its antenna to

communicate with commercially available satellite location systems such as GPS to

determine the position of the cranial edge of the measuring body. This location method

can supplement or replace other optional location methods. The location data will be

compared to the known locations of the tendon for the purpose of tendon identification.

An alternative embodiment of the apparatus will comprise one or more base

stations set into an additional depression(s) in the concrete structure to triangulate the

location of the antenna of the measuring device. These base stations synchronize with

each other and determine the times at which they receive signals as sent by the measuring device. These times are compared with each other are used to determine the location of the device. The location of the device the distance between the two stations is recorded and sent to the measuring device to determine the time of the final stress and the identity of the tendon being measured.

An additional embodiment of the optional base station device will include a spool

type tape measure dispenser. This tape measure can be drawn from the base and used to

measure the distance from the base station's position to the antenna or cranial edge of the

measuring device. This may be used to confirm or calibrate other measuring methods or

may be visually observed and entered into the measuring body manually by the operator.

Therefore, the spirit and scope of the appended claims should not be limited to the

description of the preferred versions contained herein.

The above disclosed method and apparatus improves over and answers the

problems associated with previous methods and devices. The marking device ensures that

all measurements are made from the same plane by measuring from the anchor and use a

uniform reference mark. The head avoids contact with the wedges, makes flush contact

with the anchor, and ensures the tendon is properly seated in the channel. The marking

device makes a much larger mark which is more resistant to smearing and distortion by

increasing the area of interface between the tendon and the paint guide. The measuring

device and method capture multiple datapoints which ensure accuracy greatly reduces the

problem of time delay in discovering errors and elongation discrepancies by allowing data

to be uploaded in real time. This enables the engineer of record to review trustworthy field

elongation data instantly allowing for real time response. This real time rejection or

approval opens up the possibility for real-time approve of the finalization steps (cutting,

painting, capping and grouting) to occur within hours instead of days. This protects the integrity of the structure by dramatically decreasing the time that the tendons, anchor and wedges are exposed to the elements.

Claims (9)

Claims:

1. A method of performing field elongation measurements of a post-tensioning

tendon enclosed by preset wedges and an anchor within a pocket of a concrete

structure, comprising the following steps:

marking the tendon with a nondestructive marking device positioned into the

pocket of the structure so that the marking device makes magnetic multi-point contact

with the anchor and rests on the tendon without making contact with the preset

wedges;

loading the tendon with tension; and

measuring the tendon with a measuring device positioned into the pocket of

the structure so that the measuring device makes magnetic multi-point contact with

the anchor and rests on the tendon without making contact with the preset wedges.

2. The method of claim 1, wherein the tendon is marked by the nondestructive

marking device with a reference mark, and

wherein measuring the tendon with the measuring device includes sliding the

measuring device along the tendon and away from the anchor until an edge of the

measuring device is directly over the reference mark.

3. The method of claim 2, wherein each of the nondestructive marking device

and the measuring device include a head-body with a contact surface that makes

flush contact with the anchor when the head-body is positioned into the pocket of the

structure, and a caudal surface, and wherein each head-body has an equivalent

length between the contact surface and the caudal surface.

4. The method of claim 1, wherein the nondestructive marking device includes a

first head-body with a first contact surface and a first caudal surface, such that when

the nondestructive marking device is positioned into the pocket of the structure, the

first contact surface makes flush contact with the anchor.

5. The method of claim 4, wherein the nondestructive marking device marks the

tendon with a reference mark at a plane defined by the first caudal surface.

6. The method of claim 5, wherein the measuring device includes a second

head-body with a second contact surface and a second caudal surface, such that

when the measuring device is positioned into the pocket of the structure, the second

contact surface makes flush contact with the anchor.

7. The method of claim 6, wherein measuring the tendon with the measuring

device includes sliding the measuring device along the tendon and away from the

anchor until the second caudal surface of the measuring device is directly over the

reference mark.

8. The method of claim 7, wherein a first length is defined between the first

contact surface and the first caudal surface of the nondestructive marking device,

wherein a second length is defined between the second contact surface and the

second caudal surface of the measuring device, and

wherein the first length is equivalent to the second length.

9. The method of claim 8, wherein the reference mark is defined by an id tag

having a cranial edge, and

wherein marking the tendon at the plane defined by the first caudal surface includes

securing the id tag to the tendon, such that the cranial edge of the id tag is coplanar

with the first caudal surface of the first head-body, and such that when the second

caudal surface of the measuring device is directly over the reference mark, the

second caudal surface of the measuring device is directly over the cranial edge of the

id tag.