physical test data for the appraisal of the design procedures for bolted - mttram & turvey.pdf

8/10/2019 Physical test data for the appraisal of the design procedures for bolted - MTTRAM & TURVEY.pdf

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Physical test data for the appraisalof design procedures for bolted

joints in pultruded FRP structuralshapes and systemsJ T Mottram1 and G J Turvey2

1 University of Warwick, UK2 University of Lancaster, UK

SummaryA review is presented of the tests undertaken tocharacterize bolted joints (no adhesive bonding)

for pultruded fibre-reinforced plastic (PFRP)

structural shapes and systems. The review is

written with regard to the appraisal of existing

connection design procedures for plate-to-plate

bolted joints. It is shown that 15 uncoordinated

series of tests on single-bolt and multi-bolt double

lap joints provide 800 ultimate strength results.

Each of the series of tests had different objectives

and so different joint variables were studied. This

reflects the current state of guidance on joint

design and installation in pultruders design

manuals and elsewhere, which is shown to be

limited and inconsistent.

By rationalizing the number of variables the

authors have tested a further 900 joints in order

to generate a larger database of strengths and

modes of failure, which may be used to appraise

connection design procedures, such as the Hart-

Smith and EUROCOMP Design Code and

Handbook simplified and rigorous methods.

Observations are made on the findings from 16

series of tests with respect to the current state of

design of PFRP plate-to-plate bolted joints.

Key words: pultruded FRP structurals; bolted joints; test data

Prog. Struct. Engng Mater. 2003; 5:195222 (DOI: 10.1002/pse.154)

Introduction

Pultruded FRP (PFRP) structural shapes and systemsconsist of thin-walled composite profiles havingoverall dimensions up to 1000 mm (typically 300 mm

or less) and wall thicknesses up to 25 mm (typicallyup to 13 mm). They have prismatic section andfirst-generation structural shapes are I, angle, channeland box[13]. Reinforcement is E-glass fibre in twoforms, namely unidirectional rovings and continuousfilament (or strand) mats. The matrix is a thermosetresin such as polyester or vinylester, which oftencontains filler and other additives. PFRP members areused in primary load-bearing structures[4]withmechanical fastening (fabricators often choosestainless steel bolts) being the preferred method ofconnection[5]. Primary joints are expected to provide

strength and stiffness to the PFRP structurethroughout its life[6]. Failure of such joints wouldconstitute major structural damage and be hazardousto life. The safe and reliable design of bolted joints istherefore clearly a priority.

The EUROCOMP Design Code and Handbook[6]isan independent source of guidance for the design ofload-bearing structures of Glass Reinforced Plastic(GRP) materials. The writers intended itsrecommendations to be suitable to PFRP shapes and

systems. Section 5 in the Code and Handbook provideguidance for connection design by bonding andmechanical fastening. Section 5.2 covers mechanicallyfastened joints with the principal methods ofconnection by bolts and rivets. Clause 5.2.2.2 statesthat the performance requirements of bolted andriveted joints in shear can be satisfied either by testingor by calculation. The following serviceability limitstate (SLS) and ultimate limit state (ULS) criteria givenin[6], are performance requirements that shall besatisfied:

a) SLS criteria:

* deflection due to excessive deformation offastener holes;

* onset of nonlinear loaddeflection behaviour ofjoint under constant load;

New Materials in Construction

Copyright & 2003 John Wiley & Sons, Ltd. Prog. Struct. Engng Mater. 2003; 5:195222


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* separation (at edges) of components or spliceplates fastened together;

* weather tightness (and/or water tightness) ofjoint;

* fibre debonding or matrix cracking under loador due to assembly techniques;

* durability of unsealed edges,* fatigue endurance of GRP and fasteners.

b) ULS criteria:

* ultimate load capacity of complete joint;* static failure of joined parts;* progressive failure of hole edge leading to

permanent hole elongation greater than 4% ofthe hole diameter;

* fatigue endurance of laminate and fasteners.

Turvey[4]has provided a brief overview of some ofthe more noteworthy PFRP structures. In his paper he

emphazises the extensive use of bolting as the mainmethod of connection for structural shapes. Hisoverview focuses on moment connections, which arerequired, for example, to join beam and columnmembers. Attention is also given to plate-to-plateconnections where the loading is in the plane ofsymmetry and load transfer can be assumed to be inbearing. Such a connection could be used, forexample, in splice and gusset plate joints in trusses [4].At the time of writing Turvey observed that thequality of the plate-to-plate joint test data was veryvariable and that the series of tests were limited to a

small numbers of joint tests. The lack of coordinationand cross-correlation was felt to have reduced theirvalue somewhat.

Since Turveys overview paper[4]appeared theauthors have completed a project on the structuralintegrity (SI) of bolted joints in PFRP structures. Itconcerns PFRP plate-to-plate joints with single-boltand multi-bolt configurations. Fig. 1 shows a 2 2multi-bolt joint with the various geometric ratiosdefined. Staggering the bolt columns is an option indesign. If a joint has a single bolt, the plates widthW2S. In this paper the completed project will be

known as the SI project. Its objectives were to:

* test virgin/degraded double lap bolted joints withpractical details; loading was concentric and themain forms of material degradation were roomtemperature/wet and hot/wet conditioning;

* start to understand the physical response anddamage mechanisms in joints under normal/adverse conditions;

* relate measured strengths and damage progressionto predictions by advanced finite element analysis;

* transform damage tolerant design procedures[6,7],used with composite materials in the aerospacesector, into joint design guidance for use inconstruction.

In this paper consideration is given to joint test datafor the design of plate-to-plate bolted connections[6].

In-plane loading can be concentric or eccentric innature. The material orientation of the joined PFRPplates is important since their mechanical propertieschange significantly with orientation[13]. In thepultrusion process the direction of pull is thelongitudinal direction, while the direction normal tothis is the transverse direction. The unidirectionalroving reinforcement is aligned with the longitudinaldirection and so mechanical properties are higher inthis direction. The lower strength and stiffnessproperties in the transverse direction are due to the

much lower volume fraction of glass fibres aligned inthis direction. In this paper the 08 orientation refers tothe longitudinal direction, while the transversedirection is the 908 orientation. Off-axis anglestherefore range between these limits.

By co-ordinating the work at the two Universitycentres of Lancaster (LU) and Warwick (WU), andincluding previous results from LU, there are nowsome 1100 double lap-joint test results in the largerdatabase, many with geometric ratios andenvironmental conditioning not previously tested.Not only are ultimate strengths/loads and modes of

failures available from these tests, but also initialfailure strengths/loads. This provides a wide-rangingand consistent body of data for the community toappraise the available design procedures, examinetest variability and analyse for cross-correlation. The

Column

of bolts

E/D

P/DP/D S/DS/D

D

First bolt row

Second bolt row

Concentric tension

Fig. 1 Plate-to-plate joint geometry definitions, D is boltdiameter,E is end distance, S is side distance, and Pis pitchdistance

NEW MATERIALS IN CONSTRUCTION196



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results of the SI project will make an invaluablecontribution to the characterization of PFRP boltedjoints. It is not only relevant to bolted joints for thecurrent range of pultruded profiles, but also providesunderpinning knowledge for similar mechanicallyfastened joints using second-generation profiles,

which are now reaching the market place as thepultrusion industry diversifies.The papers contents are presented in three parts. In

the first part current practice in Europe and Americafor PFRP bolted connections is reviewed inconjunction with practice in structural steelwork. Thesecond part presents basic details of the previous15 series of tests carried out to determine modes offailure, strengths, and occasionally stiffnesses ofbolted plate-to-plate joints. Part three presents therationale behind the 900 joints tests of the SI project.Where relevant, links are made between the test data

and the current rudimentary design specification, andwith the need to appraise and further developconnection design procedures, such as the Hart-Smith[7]and EUROCOMP Design Code andHandbook simplified and rigorous methods[6].

Review of current practice

STRUCTURAL STEELWORKPrior to summarizing the various recommendations

for current practice with PFRP bolted joints, it isappropriate to summarize what is current practicewith joints in structural steelwork. Specifications forbolted connections in steelwork as practised inEuropean countries are available[8]. Black ISO metricbolts are the most commonly used. With regard to thejoint detailing shown in Fig. 1, the geometric ratiosE/D and S/D should not be less than 1.2 and P/Dshould not be less than 2.2. The full bearing value of abolt through a connected plate cannot be developed ifthe end distance is less than 2D. For end distanceslying between the minimum of 1.2D and 2.2Dthe

bearing value is reduced proportionally. In generalsituations a clearance hole is present, often equal tobolt diameter plus 2 mm. For bolt diameters 424mmthe hole size is equal to bolt diameter plus 3 mm. Boltsfor bearing-type connections can be used with orwithout pre-load. There are also high-strength frictiongrip bolts where slip in the connection is notpermitted at the SLS or ULS, and for these joints theload is carried entirely by static frictional force (thereis no bolt bearing). The minimum end distance E forthe full resistance is now 3D. Fitted bolts can be usedwith the corresponding holes in steel members in

agreement with ISO fit b 11/H 11[8]. Only pre-loaded(torqued) bolts can be used when the joint is to besubjected to fatigue loading.

American practice is similar to that found inEurope. For joints that are not slip-critical no pre-load

is required. Installation of high-strength bolts toASTM A325 (types 13) required a high level ofpre-load prior to 1985, regardless of whether or not itwas necessary. Nowadays, when these bolts are usedin bearing-type joints they need only be tightened tothe snug-tight condition. This condition is defined as

the tightness that exists when all parts in a joint are infirm, but not necessarily continuous contact. Togenerate a pre-load of 70% of the specified minimumtensile strength of the bolt, the current specificationrequires half-a-turn of the nut from the snug-tightposition (the actual degree of the turn is dependent onthe bolt length/D ratio and the disposition of outerface of the bolted parts). This specification replacesthe need to apply a specified torque since it gives toomuch variability in bolt tension. The clearance holesize is constant at 1.6 mm (1/16 in). Hardenedwashers to ASTM F436 with an outer diameter twice

the bolt diameter (same as in Europe) are not requiredwhen A325 bolts are installed by the turn-of-nutmethod; they are if these bolts are tightened by thecalibrated wrench method.

STRUCTURAL PFRPFor PFRP shapes and systems several pultruders havewritten and maintained their own design manuals[13],based on in-house testing and a national level ofknowledge and understanding. Each manual

provides specific recommendations for boltedweb-cleat beam-to-column joints and other simpleframe joints[5]. Joint details[13]often mimic equivalentsimple joints in structural steelwork[4]. The resistanceof web-cleat joints is, however, not governed by therecommended joint geometric ratios in Table 1. Thetable presents suggested minimum geometric ratiosfor design of the strongest plate-to-plate boltedjoints; the material orientation is not specified. Thegeometric ratios are defined in Fig. 1. In what followsit is assumed that the P/D ratios are the same for thebolt rows and columns. The geometric ratios in Table

1 are known to be valid for room temperature (RT)conditions; RT is taken to be 20258C.

The design manuals of the US companiesStrongwell[1]and Creative Pultrusions Inc.[3]use theminimum geometric ratios given in the AmericanSociety of Civil Engineers Manual 63[9]. It is believedthat the writers of Manual 63 based these on thosegiven in the 1960 marine design manual for GRPs byGibbs & Cox Inc.[10]. These recommended minimumratios are for hand lay-up GRP materials (isotropic inthe plane) of unknown thicknesses and unknown boltand joint details. Therefore, the actual minimum

ratios might be expected to change when the joints areof PFRP, as many variables will now be different.Ratios from Fiberline Composites A/S[2], given inTable 1, are identical with those given in the DanishStandard DS456. Company and external laboratory

PULTRUDEDFRP STRUCTURAL SHAPES AND SYSTEMS 197



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tests have confirmed these ratios; none of the test datahas been made public.

The objective of specifying the minimum geometricratios given in Table 1, when there is a single-bolt, is tohave the strongest joint failing in the bearing mode(this failure mode is often considered benign, becauseit is characterized by progressive damage growth[5,6]).

Fig. 2 shows the fracture patterns (dashed lines) ofsingle-bolt joints failing in bearing and the otherdistinct modes known as cleavage, shear-out and net-tension. These four modes are for concentric tensionloading and a PFRP orientation of either 08 or 908.Bearing is characterized by the PFRP materialcrushing and delaminating in front of where the boltbears into the plate. Depending on the joints detailsits integrity may remain while this damage regiongrows, and the joint is still able to carry a substantialload. As shown in Fig. 2 the fracture patterns of theother three modes are characterized by significant

material rupturing, which is likely to occur over ashort period of time, and results in a joint that cancarry, post-failure, little or no load. Except for bearing,the modes are deemed unacceptable in connectiondesign because of the brittle nature of failure[6]. Bolt

shear or pull-out failures[6]do not need to beconsidered when steel bolts are used, because the boltdiameter is normally large enough to prevent suchfailures.

It is instructive to summarize and comment onother differences in the limited practical guidancegiven in the pultruders design manuals. Strongwell[1]

include tables of allowable loads for bolt bearing andshear failures. The allowable loads for their own FRPFIBREBOLT1 assume a factor of safety of four. Thetorque applied to these FRP bolts is not proportionalto the unthreaded cross-sectional area, and maximumtorques of 10.9, 21.7 and 32.5 N m are recommendedfor bolt diameters of 12.7 mm (1/2 in), 16.3 mm(5/8 in) and 19.05 mm (3/4 in). The shear loads givenin[1], for structural (unless the first S is for stainless)steel threaded bolts are of unknown origin. Holeclearance is given as 1.6 mm (1/16 in) in the notesaccompanying the engineering drawings of details of

web-cleat frame connections. The type, size or use ofwashers is not given.

Creative Pultrusions Inc.[3]gives specific guidancefor web-cleat frame connections joining their standardshape structural members. Like Strongwell, this

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Table 1 Suggested and experimentally determined minimum joint geometric ratios for PFRP bolted joints (at room temperature and noenvironmental conditioning)

Reference Plate

thickness t

(mm)

Bolt

diameter/

plate

thickness

D/t

Edge

distance/

bolt

diameter

E/D

Side

distance/

bolt

diameter

S/D

Width

distance/

bolt

diameter

W/D

Pitch

distance/

bolt

diameter

P/D

Clearance

hole size

(mm)

Washer

diameter/

bolt

diameter

[1] 6.3519.05 1.03.0 2.04.5 (3.0)1 1.53.5 (2.0)1 4.05.0 (5)1 4.05.0 (5)1 1.6[2] 320 0.516.0 2.5, 3.5 2.0 44.0 44.0 1.0 2.0[3] 6.3512.7 Unspecified 2.04.5 (3.0)1 1.53.5 (2.0)1 4.05.0 (5.0)1 43.0 1.6 2.5

[6]2 Unspecified 1.01.5 43.0 4 0.5W/D 4 3.0 43 (4)1 50.05D 42.0

[13]3 6.35 1.6 3.0 Single-bolt 4.0 Close fit

(0.10.3)

[14]3 9.5319.05 0.51.0 5.04 Single-bolt 5.04 1.6

1Recommended minimum design value2General glass-fibre-reinforced plastics (including PFRPs)3From joint tests with tensile load in direction of pultrusion (PFRP material orientation is 08)4D is hole diameter (bolt diameter and hole clearance)

Bearing Shear-out Net-tensionCleavage

Concentric tension

Resultant boltforce

Fig. 2 Failure modes in single-bolt PFRP joints under concentric tension




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pultruder recommends clearance holes equal to thebolt diameter plus 1.6 mm. Based on steel constructionin the USA, the manual recommends high-strength(minimum 700 N/mm2) steel bolts to A325 with gradefive coarse threads. For a 12.7 mm bolt diameter, thespecified low torque is 39 N m (37.5% of bolt proof

load) and the high torque is 77 N m (75%). Thisincreases to 77 and 113 N m, respectively, for a16.3-mm-diameter bolt. This guidance, of unknownorigin, goes against the current USA specificationwhen using A325 bolts to join steel parts. There is areference[3]to single-bolt joint tests performed withsteel grade 8 oversized washers (2.5 times holediameter). Such tests were used to construct a tablewith bearing strengths defined by the 4% holeelongation (in accordance with ASTM D5691). Thesehole deformation strengths are typically 36% of thematerial nominal compressive strength (i.e. 210 MPa)

in the direction of pultrusion.Fiberline Composites A/S in Denmark givesguidance for general practice. For plate-to-plateconnection design the manual[2]covers flat plates(thicknesses 320 mm) fastened by A4 stainless steelbolts (M6 to M48) in a lap-joint configuration. Simpledesign equations, based on bearing, or net-tension orshear-out failure are given to determine joint strength.Two tables give bearing capacities at the ULS in the 08and 908 orientations, with a factor of safety of three.These tables enable many joint configurations to bedesigned from their structural shapes. Hole clearance

is 1 mm for M6 to M48 bolts and the steel washersunder nut and bolt head are twice the bolt diameter.No bolt torque is specified in the manual (on site atorque 4100 N m is applied to M16 bolts).

Although none of the three manuals[13]specifiesthat the shank in contact with the PFRP material mustbe plain, the authors understand that this is standardpractice when steel bolts are used. Such practice is notpossible with Strongwells FRP bolts (FIBREBOLT1)since they have a continuous moulded thread alongtheir whole length.

The EUROCOMP Design Code[6], in Clause 5.2.2.3,

provides general design requirements for glass-reinforced plastics, which have their roots in theaerospace industry. Prior to presenting therecommended GRP minimum geometric ratios (seeTable 1), it needs to be understood that Clause5.2.2.3(2) states that PFRPs do not always have a fibrereinforcement construction which is ideal. By idealthe code-writers are suggesting that single-bolt andmulti-bolt GRP joints, with suitableE/D, S/D and P/Dratios, will fail in bearing with a high bearing strength(i.e. a high joint load). The guidance is seen to be validfor other GRP materials and should therefore be used

with caution when the connected parts are of PFRP.Definition Clause 5.2.2.1, given in[6], introduce thesingle-bolt joint failures depicted in Fig. 2 (however itdoes not include cleavage) and says in 5.2.2.1(7)P thatShear-out failure also occurs in highly orthotropic

laminates, such as pultruded laminates,independently of the end distance. Clearly, if thisEUROCOMP definition is always true it precludesthe use PFRP bolted joints in all situations.

We turn now to the design requirements given inClause 5.2.2.3 and their implications for PFRP joint

details. Referring to Fig. 1 and Table 1 the minimumvalues ofE/D and P/D are 3, and S/D is1.5 (S/D 5 P/D). The joint should be designed,detailed and formed so that the fasteners (steel boltsthat should be self-locking or fitted with lock nuts,type(s) not specified) are tightened to a pre-set torque(not specified) to provide substantial clamping andlateral restraint around the bolt holes. However, thestrength should be assumed to be that correspondingto finger-tight conditions (not specified), in whichthere is little or no lateral restraint; this is to allow forthe effects of creep, cyclic loading, fatigue and

vibration or their combination. The hole diametershould not be less than the thickness of the thinnestpart being joined and be no more than one-and-a-halftimes the thickness (t) (1 4 D/t4 1.5). Any clearanceshould allow the bolt to be inserted easily, even whenall of the other bolts are in place and finger-tight, butshould not be more than 5% of the bolt diameter. Boltsshould be as tight as possible in the holes withoutcausing damage to the GRP parts. Great care isrequired, therefore, in forming the holes. Washersshall be fitted under the head and nut of the bolt andshall have an internal diameter equal to the least

diameter of the hole(s) through which the bolt passes.The least external diameter of the washer shall not beless than twice the larger or largest diameter of theholes. The thickness of the washer shall be sufficientto provide an even surface pressure over the outerGRP surfaces. Preferably, the thickness should be notless than 20% of the thickness of the outermost partthrough which the bolt passes.

There are further requirements given in 5.2.2.3 thatare adopted directly from practice in the aerospaceindustry. It is seen that this guidance iscomprehensive and in a number of respects

corresponds to what is used in structural steelwork.Not many of the detailed requirements are to befound in the pultruders design manuals[13], nor is itknown whether they are appropriate for the design ofPFRP bolted connections.

What is clear from the review of current PFRPpractice is that it is neither coherent nor recognized,and that it is loosely based on practice in steelworkconstruction. By way of very limited, andunpublished, in-house joint testing, two of thepultruders design manuals[1,3]do provide engineerswith tables giving allowable bearing strengths for

PFRP plate-to-plate joint design. Guidance in the threemanuals[13]and EUROCOMP Design Code andHandbook[6] is found to be different and not oftenbased on a sound scientific understanding gainedfrom physical testing and numerical modelling. The




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specific requirement, derived from the aerospaceindustry, to minimize (if not to eliminate) the holeclearance[6]is the most noteworthy difference fromwhat is recommended by pultruders[13]and what isgenerally practised in steelwork construction.The question as to whether or not bolts should be pre-

loaded on installation is another important issuewhich, as the summary shows, needs to be betterunderstood if we are to have reliable designprocedures for PFRP joints.

Single-bolt and multi-bolt joint tests:previous series

As mentioned in the Introduction and the Review ofCurrent Practice, relevant and reliable data (strengthsand modes of failure) from joint tests are required to:

* establish specified minimum joint configurationdetails, such as the geometric ratios given inTable 1;

* underpin the characterization of PFRP joints;* assess and refine connection design procedures, as

given in[6]and [7].

Each joints loaddisplacement response and itsmode(s) of failure will be dependent on its specificdetails and environmental conditioning. Fig. 3 showsthe two most common forms of loaddisplacement(stroke) curves from PFRP single-bolt and multi-bolt

joints, tested under stroke control. Some joints fail atthe ultimate load without any significant warning.This brittle loaddisplacement response is shown inFig. 3(a). Note that the ultimate load is attained whenthe initial failure load is reached and damage occurs.The ultimate failure load might occur at the same orlower load, and at a higher stroke; such a joint doesnot possess any damage tolerance[5, 6]. Other joints,however, do suffer initial damage at a load wellbelow that for ultimate failure. Their more benignloaddisplacement response is shown schematicallyin Fig. 3(b), whereby once damage (e.g. due to

bearing) occurs there is a reduction in joint stiffness

up to a higher ultimate load. Such joints do possessdamage tolerance and their design is more suited tothe structural integrity design procedures, such as thesimplified and rigorous methods described inEUROCOMP Design Code and Handbook[6].

In the context of PFRP bolted joints, damage

tolerance means that there is progressive damagegrowth, often associated with bolt bearing when theload is higher than that which causes initial materialdamage.

What makes the scope of joint testing enormousand possibly impractical to cope with is the largenumber of joint variables that need to be studied tocover those found in practice. Inherent test variabilityis another important factor, not least because PFRPmaterials can have a fibre reinforcement constructionthat is nonuniform. The influence of this factor will beshown later. Ideally, there should be a consensus on

what is a preferred test methodology; to date there isno recognized test standard available to characterizePFRP bolted joints.

Initial variables to be studied ought to include: thetype of loading, the materials (bolts and PFRP); theplate thicknesses and orientations, the jointgeometries (see Fig. 1); the bolt arrangements and theinterface conditions (washer, torque, and clearancehole). To include data that characterizes the long-termdurability and structural integrity of PFRP joints newvariables to be added to any initial set are likely to bethe serviceability (SSL) loading (creep and cyclic) and

the working environment (e.g. hot/wet, etc.).Before we can embark on appraising, and furtherdeveloping design procedures it is necessary to knowthe quality and limitations of the test data, if suchwork is to succeed. In this paper nine tables arepresented that report, in a single source, the variablesstudied in 16 series of tests on double lap-joints usingPFRP flat sheet materials[1127]. Loading is concentricand, except as part of one series[15], always tensile. It isusually applied short-term, by way of a monotonicstroke rate. The number of joints tested are given inthe tables in parentheses and italic type, e.g. (25)

represents 25 tests. In the tables a question mark

Load

Load

Stroke Stroke

initial failure

ultimate failure

initial failure

ultimate failure

(a) (b)

Fig. 3 Typical loadstroke characteristics for single-bolt and multi-bolt PFRP joints under stroke controlled concentric tension:(a)brittle load-displacement characteristic, no damage tolerance; (b) benign loaddisplacement characteristic, damage tolerance




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identifies when that column entry has not beenreported in the source reference. The number ofquestion marks weakens the quality and increases thelimitations of the test results with respect to theobjectives listed above. Joint strengths (andsometimes stiffnesses) derived from the test

loaddisplacement responses are to be foundelsewhere[1125], and were used to constructTables 25. The results from many of the tests inTables 69 have not been reported at the time ofwriting this article.

PRE-SI PROJECT JOINT TESTSTables 2 and 3 present, respectively, a summary of theconcentric single-bolt and multi-bolt tests prior to thestart of the SI project. These 15 series of tests[1125]were unco-ordinated and it is therefore unsurprising

to find that their scope is very wide ranging. All of thejoints were tested, accept for those by Erki[15], in thedouble lap arrangement with either the central orthe outer two plates of PFRP, and, respectively, thetwo outer plates or the central plate of structuralgrade steel. It is noteworthy that the tests by Erki[15]had the only joints with all three plates of PFRP.

Table 2 gives information on the 10 series of single-bolt tests on 640 joints, while Table 3 gives the sameinformation on 5 series of multi-bolt tests on 160joints. Tables 49 present equivalent information onabout 270 single-bolt and about 640 multi-bolt joint

tests from the SI project. To date, therefore, this gives atotal of about 1710 strength (and mode of failure)data points, split 910: 800 between single-bolt andmulti-bolt configurations. Most of the 16 series of testshad a degree of replication of two or three joints perbatch.

Each table summarizing the joint tests isconstructed of 12 (single-bolt) or 13 (multi-bolt)columns. The columns are numbered in the first rowof a table. The reference number for the source ofinformation is given in column 12 or 13 (last), togetherwith the total number of joints tested. Columns 1 and

2 define the PFRP flat sheet material and the nominalor measured thickness(es) used. The PFRP materialswere from three pultruders, with by far the majorityof the tests using Strongwell EXTREN1 500 Series flatsheet with nominal thicknesses of 6.35, 9.53 and12.7 mm[1]. It is to be noted that the FibreforceComposites Ltd. materials labelled Grey 2, Yellowand Grey 1 are custom flat sheets[12, 21]. Columns 36present information on the bolts and their installation.Except for the tests by Erki[15] (fifth series in Table 2)the bolts were of structural steel grade. The range ofclearance hole sizes is large, varying from tight fitting

(say 0.10.3 mm clearance) to 6.35 mm[17]. Column 6gives the bolt torque, or torques when this was avariable to be studied. Irrespective of the boltdiameter the torque was often either zero(pin loaded), or finger-tight (believed to be

53 N m). The washer size is relevant only if the outerplates are of PFRP[14, 15], or if used to separate theinner PFRP plate from the outer plates[12]. Column 7shows that 15 series had the material orientation at 08to the direction of loading. Eight series had thematerial orientation at 908 and of these six also tested

with material at 458

and other material orientations. InTables 2 and 46, columns 8 and 9 give the geometricratios W/D and E/D (see Fig. 1). E/D values inparentheses and underlined are for the single W/Dvalue given in bold type. Column 10 in Tables 3 and79 gives theS/Dratios in the multi-bolt tests (Fig. 1).Column 10 (single-bolt) and 11 (multi-bolt) give, whenavailable, the stroke or load rate, and information onthe environmental conditioning. Prior to the start ofthe SI project, only 30 of the 800 joint tests reported inTables 2 and 3 had been subjected to wet ageing [19]before the loading was applied at RT. None of the

series listed in Tables 2 and 3[1125]include tests onjoints whose temperature is above RT. For multi-boltjoints, column 12 also presents the constant P/Dratioin Table 3 and the variable P/D ratios in Tables 79.Finally, column 11 (single-bolt) and 12 (multi-bolt)give information on the joint configurations and inTables 2 and 3 a breakdown of the number of jointsper group of variables.

SINGLE-BOLT TESTS

Regarding the relevance of the test data in[1120]to ourprogress in appraising and developing designprocedures, a number of points can be made from thebasic details given in Tables 2 and 3. Returning toTable 1 the minimum geometric ratios proposed byRosner & Rizkalla[14]and Cooper & Turvey[13] weresupported by their single-bolt tests, in which the jointvariables E/D and W/D were varied from 1.33 and13.33 (third and fourth row entries in Table 2). Bothseries of tests used EXTREN1 500 Series flat sheetwith a polyester matrix. To explain why the two seriesrecommend different minima (and different from

those given in the Strongwell design manual[1]), weneed look no further than the differences in the testset-up. Rosner & Rizkalla used PFRP of thicknesses9.53 mm (3/8 in), 12.7 mm (1/2 in) and 19.05 mm(3/4 in), with a bolt hole 1.6 mm (1/16 in,[1]) largerthan the 19.05 mm diameter of the high-strength plainshank steel bolt. The double lap tests had two outerPFRP plates and an inner steel plate and standardsteel washers of outer diameter 2D were used. Tocomply with Strongwells design manual[1]specification for their proprietary FIBREBOLT1 studsand nuts, a constant torque equal to 32.5 N m (24 ftlb)

was applied to the 19.05 mm diameter steel bolts. Norecommendation for bolt torque is given byStrongwell[1]for steel bolts. They tested at a strokerate of 2 mm/min, loading at 08, 458 and 908 to thedirection of pultrusion.




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....

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.....

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....

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.....

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.

Tab

le2Summ

aryo

fpreviousconcentrical

lyloadedsingle-

boltdoub

lelap-jointtestswit

hPFRPflatsheetmateria

l

[1]

Plate

[2]

Thickness

(mm)

[3]

Bolt

diameter

D(mm)

[4]

Hole

cleara

nce

(mm)

[5]

Washer

size

(mm)

[6]

Bolt

Torque

(Nm)

[7]

Orienta-

tion(0ois

directionof

pultrusion)

[8]

W/D

[9]

E/D

[10]

Testrate

(tempera-

ture)

[11]

Joint

configura-

tions

(No.oftests)

[12]

Reference

Creative

Pultrusions

Inc.

12.7

A307mild+

high-s

trengt

h

12.7

(shank

incontact)

Interfe

rence

fit

2.7D

2o

ff

13.5

0,40

.8,

81.6,

112.4,

163.4

0 90

4 4

1,2,3,4,6

1,2,3

? stro

ke(RT)

Outer

(?thic

kness)a

nd

innerplatesin

ner

plate

PFRP

[11]

Noreplication

(20)

Total

No.

(20)

Non-stan

dard

Fibreforce

Composites

Ltd.

(not

given)

9.53

?

2.2D

Smal

l

finger-t

ight?

For

bearing

failure

Forbearing

failure

Threegroups(12)

Sizeof

clampingarea

[12]

Grey

2

6

0

7.34

4.19

0.5mm

/min

(RT)

1.Tig

ht-f

itting

was

her

(between

PFRPan

do

uter

plates

)

Yel

low

?

2.Stee

lplates

coveringal

l

potentia

ldamage

area

Grey

1

?

3.Smoot

h

composite

plates

(as2

.)

Y2.10

1.05,1.57

,

2.1,3

.15,

4.2

Outerplates

?

stee

l(?thickness)

innerplatePF

RP

Y3.15

1.05,2.1,

3.15,4.2,

6.3

Yan

dG2

Y4.0

1.05,2.1,

3.15,5.2,

6.3,7

.34

0

G23.15

4.2,5

.2,

6.3,

8.4,10.5

3per

batc

h

(95+3)

G24.72

5.2,6

.3,

7.3,9

.44,

13.6

G27.34

6.3,8

.4,

9.44,10

.5,

12.6,

14.7

Total

No.

(110)

Continued




9/28

Strongwel

l

EXTREN1

500series

polyester

6.35

M10Gra

de

8.8

Tig

htfit

(0.10.3

)

None

0,3,30

(torque

wrenc

h)

0

2,3,4,5,7

4,4,4

,

(1.5,2

,

3,4,5

),4

Outerplates

?

stee

l(?thickn

ess)

innerplatePF

RP

[13]

Shan

kin

contact

2,4,6,8,10

5,5,5

,5,

(2,3,

4,5,6)

10kN/min

2,4,6,8,10

6.5,6

.5,

6.5,6

.5,

(2,3,

4,5,

6.5)

(RT)

3per

batc

h(8

1)

Total

No

.(81)

Strongwel

l

EXTREN1

500series

polyester

9.53

12.7

19.0

5

19.0

5

high-s

trengt

h

shan

kin

contact

1.6

(initial

slipof

1.1mm

)

? Photo

shows

was

her

impression

32.5

as

specified

for

FIBREBOLT1

boltan

d

nutof

3 4inf[1]

0 (22)

0,45

,90

(20

,20,20)

0 (20)

Complexmatrixo

fvalues

1.33

13.33

20specimens,

withsamegeometricratios

forthe

fivetestgroup

s

0.01mm

/s

(RT)

Outerplates

PFRP

andinnerplate

?

stee

l(?thickn

ess)

[14]

Noreplication

(102)

Tota

lNo.

(102)

?Strongwel

l

EXTREN1

500

seriespo

lyester

12.7

19.0

5

FIBREBOLT1

mildstee

l

threadedan

d

shan

k[1]

1.6

None

?

Finger-t

ight

ortig

htened

byhalfturn

ofnut

0,45

,90

Notspecified}

estimated

fromphotos

2.5mm

/min

(RT)

As

Rosner

andRiz

kalla[14

]

Inner

PFRP

plate

25.4

mm

thic

k

[15]

8(Tension

)

3(T)

Tension

(28)

Total

No

.(63)

8(Comp.

)

?(C)high

Compression

(35)

?

3

6stee

l?

Tight

fit

?

?

0,90

2to

7

2

1mm

/min

(RT)

Outerplates

?

stee

l(?thickn

ess)

innerplatePF

RP

2per

batc

h(2

0)

[16]

Total

No

.(20)

No

loadsreporte

d

EXTREN1

500series

polyester

9.53

12.7

shan

kin

contact

06.35

?

Finger-t

ight

0

8

8

?

Effectof

hole

clearance

(25)

[17]

Total

No

.(25)

Strongwel

l

EXTREN1

500series

polyester

6.35

M10

Gra

de8.8

Tig

htfit

(0.10.3

)

None

Finger-t

ight

(about

3)

30

4,6,8,10

6,6,6

,

(3,4.5

,6)

10kN/min

Outerplates

?

stee

l(?thickn

ess)

innerplatePF

RP

[18]

shan

kin

contact

45

4,6,8,10

6,6,6

,

(3,4.5

,6)

(RT)

Threeper

batch

(81)

Total

No

.(81)

90

4,6,8,10

6,6,6

,

(3,4.5

,6)

Continued




10/28

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.....

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....

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....

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.....

.

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.

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.

.

.

.

.

.

.

.

.

.

.

? EXTREN1

625series

viny

lester

6.35

12.7

stee

l

ASTMA325

shan

kin

contact

1.6

Pin-

loaded

,

nowas

her

(spacers

?)

Pin-

loaded

0

5

3,4,5

0.64mm

/min

(RT

,dry

)

Outerplates

76.2

mmstee

l

(6.4

mmthickness

)

innerplatePF

RP(15)

[19]

30,4

5,90

6

5

(RT

,dry

)

(5,

4,5)

0,90

0

5 5

5 5

(22oCwet

)

(RT

,humid

)

Submerge

din

distilledwater

171days

(5,5

)

Moisture

ASTMD5229

,

138days

(0.57%)(5)

Glavanize

d

USS2.5mm

thic

k

35.6

mm

diameterplaced

oneithersi

de

ofPFRPplate

Finger-t

ight

0 30,4

5,60

,90

5 6

3,4,5

5

(RT

,dry

)

(15)

(4,

4,4,

5)

0,90

0

5 5

5 5

(22oCwet

)

(RT

,humid

)

Submerge

din

distilledwater

171days

(5,5

)

Moisture

AST

M

D5229

,138days

(0.5

7%)(5)

(61dry,

30

wet

)

Tota

lNo

.(91)

?

9.53

12.7

stainless

stee

lshan

k

incontact

Close

fit

5

0.8

?

0to

34J

(Nm

)(6

.8,

13.6,

20.3,

27.1,

33.9

J)

?orientation

0,15

,30

,45,

60,7

5,90

?

(RT)

Orientation

tests

(three

per

batc

hfrom

Fig.

4)(21)

[20]

EXTREN1

seealso[17]

?bolttorque

Toensure

bearing

failure

W/D

7an

dE/D

4.5

Bo

lttorquetests

(fourper

batc

h

from

Fig.

5)(2

4)

Tota

lNo

.(45)

.

.

.

.

.

.

.

.

.

.

.

.

....

.

.

.

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.....

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....

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.

.

....

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.....

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.

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.

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.

.

.

.

.

Tab

le2Continued

[1]

Plate

[2]

Thickness

(mm)

[3]

Bolt

diameter

D(mm)

[4]

Hole

cleara

nce

(mm)

[5]

Washer

size

(mm)

[6]

Bolt

Torque

(Nm)

[7]

Orienta-

tion(0ois

directionof

pultrusion)

[8]

W/D

[9]

E/D

[10]

Testrate

(tempera-

ture)

[11]

Joint

configura-

tions

(No.oftests)

[12]

Reference




11/28

Cooper & Turvey[13], in contrast, used a single PFRPthickness of 6.35 mm (1/4 in) with a bolt hole slightlylarger (0.10.3mm) than the plain shank M10 steelbolt (grade 8.8). Their double lap-joints had outer steelplates and the inner plate was PFRP, and no washerswere installed between the PFRP inner plate and steel

outer plates. Testing characterized the three differenttorque levels of 0 N m (pin-bearing), 3 N m (lightlyclamped) and 30 N m (fully clamped). Load wasapplied at a constant rate of 10 kN/min, and thematerial orientation was 08. The positive effect onlateral constraint of increasing the torque from 3 to30 N m increased the mean failure load (strength) by50%. Recommending assembly with fully clampedbolts, Cooper & Turveys parameters[13] in Table 1were based on the resistance data at the lower(finger-tight) torque of 3 N m. This is in accordancewith the EUROCOMP design code requirements from

Clause 5.2.2.3 given earlier. Both series support aminimumW/Dof 4 (higher than the value of 3 in theDesign Code and Handbook[6], and demonstrate thatthe design manuals minimumE/Dof 2 (Table 1) is toolow if failure is to be in bearing (Fig. 2).

All of the series in Tables 2 and 3 provide usefuldata for the future preparation of generalized designguidance (which might be based on severalconnection design procedures). It is observed that the15 series of tests each set out with their own specificobjectives. From the single-bolt series in Table 2 wesee that Abd-El-Naby & Hollaway[12]considered the

effect of friction (by changing the clamping area whenthe bolt torque was finger-tight), and changing theratios W/Dand E/D. Erkis tests[15]provide the onlycompression loaded strength results (520 in number).She compared the mean ultimate failure loads underdifferent torques when the bolts were FRP(FIBREBOLT1) and steel. This showed that the FRPbolt was the weak link and that the strength wasbetween 0.4 and 0.6 of its value when a steel boltwould ensure that the PFRP failed first. Yuan,Liu & Daley[17]investigated how strength changedwith clearance (06.35 mm, in increments of 1.6 mm).

They found that for a clearance above 1.6 mm therewas a decrease in joint strength with increasingclearance. For the American recommended clearanceof 1.6 mm, the tests by Yuan et al. showed no loadreduction compared to the no-clearance situation.Turvey[18]showed that if material orientation is not 08there is little evidence of any benign failure undertension loading. The failures for orientations of 308and 458 were interesting, because they also showedthat cracks propagated along the unidirectionalrovings. Fig. 4 shows schematically the fracturepatterns as observed on the surface of joints with 30

and 45 degrees orientations. Turvey[18] saw that thesecould be viewed either (negatively) as zones ofweakness, or alternatively (positively) as crack guidesand/or arresters. Steffen[19]was the first to show thatthere is a strength reduction on ageing stress-free

PFRP joints in water (even at RT) prior to testing.Finally, Yuan & Liu[20]looked at changing materialorientation and bolt torque for an unspecified jointgeometry that gave bearing failure for 08 orientation.They conducted their tests according to ASTM D953,Procedure A, Standard Test Method for Bearing

Strength of Plastics and found that the bearingstrength at 4% bolt hole deformation, as defined inD953, compared favourably with the incipient failureload (or initial failure load) in their test series. Thisfinding appears to contradict the findings of Yuan, Liu& Daley[17].

Fig. 2 shows the four most common ultimate modesof failure when the single bolts resistance does notcause joint failure. Of these four, those of bearing,shear-out and net-tension are considered as distinctmodes in various connection design procedures[2,57].The tests on 08 material[1120] confirm that all these

modes can occur by changing E/D and W/D. Noseries showed that the mode of failure changed onincreasing bolt torque (probably because the E/Dratios were not less than 4 in these tests).

The degree of clamping between the plates doesraise the load for initial damage and causes the jointspost-yield response to show less damage growth.Doyle[11]comments on the need to define a relativejoint displacement or some other predetermined valueto define the onset of (initial) bearing failure. Whenthe UD reinforcement is at 908 to the load the mostprobable failure mode is net-tension (or cleavage,

which might be due to a tension rupture on one sideof the hole first)[14,15,1820]. Off-axis joint tests[14,18,20]allshow (Fig. 4) that the resultant crack patterns do notcorrespond to one of the distinct modes shown inFig. 2. Several papers mention that failure couldappear to be a combination of the distinct modes inFig. 2[14,16,18,19]. These observations on failure willinfluence joint design.

Most sources for the 10 series of tests citedin Table 2 present a limited number of typicalloaddisplacement plots. Their characteristics can beseen to fit one of the two common joint responses

shown in Fig. 3. The beneficial restraint on initialfailure from a clamping pressure when the bolt ispre-loaded is seen to make the response inFig. 3(b) more likely. Vangrimde[28] has suggestedthat the usefulness of the joint displacement isdependent on what it measures. He states thatdesigners are not interested in hole elongation, butrather in the local bearing deformation. He advocatesthat the design property should be the bearingdisplacement and not the elongation of the hole asprescribed in ASTM D5961. In order to determine abearing displacement the second measurement point

must be at a sufficient distance from the hole such thatthe stress concentrations no longer have aninfluence[28].

Such a measurement methodology is notuniversally recognised and so Vangrimdes




12/28

.

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.....

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....

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....

.

.

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.

.

Tab

le3Summaryofpreviousconcentrical

lyloadedm

ulti-b

oltdoub

lelapjointtestswit

hPFRPflatsheetmateria

l

[1]

Plate

[2]

Thick-

ness(mm)

[3]

Bolt

diameter

(D)(mm)

[4]

Hole

cleara

nce

(mm)

[5]

Washer

size(mm)

[6]

Bolt

torque

(Nm)

[7]

Orientation

(0degrees

isdirection

ofpultru-

sion)

[8]

W/D

[9]

E/D

[10]

S/D

[11]

Test

rate

(temp)

[12]

Joint

configura

-

tionsNo.

oftests(

)

[13]

Reference

Non-s

tandard

Fibreforce

Composites

Ltd.

6

9.5stee

l

Close-

fitting

0.1mm

Fromsing

le-

boltjoint

tests

[12]

was

her

hadouterf

2.2Dinner

Smal

ll

clamping

torque

(finger-tig

ht

condition

)

0

7.36

,15.7

6.32

?

AllP/D1

0

Alltwobo

lts,

one

column

Outerplatesstee

l,

inner

plate

PFRP

Changedsteel

platethickness

(?)to

determine

effectofsti

ffness

(12)?

[21]

Tota

lNo

.

(12)

Grey

2

Blue

1

4 4

f

1D

0 0

12.6

6

6.32

6

Blue

2

Nominal

Creative

Pultrusions

Inc.

Series

1500

12.7

15.9

highstrength

stee

l

0.127mm

0.005inch

tightfit

Stan

dard

was

hers

Finger-t

ight

? 0

4.8

2.4

Type

A

sing

lebolt

[22]

4.8

2.4

?

AllP/D

4.8

Type

B:tw

obolts

,

oneco

lum

n

4.8

2.4

1

(RT)

Type

C:tw

obolts

,

onerow

4.8

2.4

1

Type

D:fo

urbolts,

tworowsan

dtwo

columns

4.8

2.4

1

Type

E:four

bolts

,

tworowsan

d

twoco

lum

ns

(staggered

by2.4D)

Outerplat

es

stee

l(thick

ness

?),

innerplate

PFRP

(15)

Tota

lNo

.

(15) C

ontinued




13/28

Strongwel

l

EXTREN1

500series

polyester

12.7

19.0

5

high

strength

shan

kin

contact

1.6

(initial

slipof

1.1mm

)

Stan

dard

was

herswith

bolts

,see

Rosner

Riz

kalla

sing

le-b

olt

series[14]

32.5

asspecified

for

FIBREBOLT

boltan

dnut

of3 4inf[1]

0,90

45 0,90

45 0,90

0,90

0,90

4.9,7.4,

9.86

,12

.33

9.86

4.9,6.17

,

7.4

4.9

7.4,9.86

,

12.3

3,14

.8

4.11

,4.93

,

5.75

4.9,6.17

,

7.3

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

1.85

,3.08

,

4.93

0.73

,1.04

,

1.35

0.73

,1.04

,

1.35

N/A

0.54

,0.85

,

1.16

0.001mm

/s

RT

AllP/D

4

Type

A:tw

obolts

,

oneco

lumn

Type

B:tw

obolts,

onerow

Type

C:th

ree

bolts,one

column

Type

D:th

ree

bolts,one

row

Type

E:four

bolts

,

tworowsan

d

twoco

lum

ns(105)

[23]

Outerplates

PFRP,inner

platestee

l

(thickness

?)

Proce

dure

sameas

for

sing

le-b

olt

jointtests

byRosner

and

Riz

kalla[14]

Total

No

.

(105)

?

12.7

15.9

stee

l

tightfit

?

Stan

dard

was

hers

Finger-t

ight

27to

81

?0

4.8

4.8

4.8

4.8

N/A

N/A

?

Oneto

four

bolts,

oneco

lumns

(?)

[24]

0.254,

0.381,

0.584

0.813,

?

4.8

4.8

N/A

RT

2bolts

,on

e

column(?)

Outerplates

stee

l

(thickness

?),

innerplate

PFRP

2bolts

,on

e

columnthree

per

batch

Suggests

replication

(12)

Tota

lNo.

(12)

? Fibreforce

Composites

Ltd.

?

?

? (tig

htfit)

?

4 pinne

d

? 0 0

2,3.3,4.2,

5,6

16

? 3

N/A

3

? (RT)

Four

bolts

in

oneco

lumn

(10)

AllP/D

5?(6)

[25]

Nine

bolts

,

threerowsan

d

columns

Eight

bolts

,one

two

boltrow

,

twothree

bolt

rows

Twoper

batc

h

Continued




14/28

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.

Tab

le3Continued

[1]

Plate

[2]

Thick-

ness(mm)

[3]

Bolt

diameter

(D)(mm)

[4]

Hole

cleara

nce

(mm)

[5]

Washer

size(mm)

[6]

Bolt

torque

(Nm)

[7]

Orientation

(0degrees

isdirection

ofpultru-

sion)

[8]

W/D

[9]

E/D

[10]

S/D

[11]

Test

rate

(temp)

[12]

Joint

configura-

tionsNo.

oftests(

)

[13]

Reference

(nooftests)

.

.

.

.

.

.

.

.

.

.

.

.

....

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.....

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....

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.....

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....

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.

.

.

Six

bolts,one

,

twoan

dthree

boltsperr

ow

Eight

bolts

,two

three

boltrows,

andonetw

o

boltrow

Outer

plates

?

inner

plate

PFRP

Six

bolts,three

,

twoan

done

boltsperr

ow

Eight

bolts

,

two

,threean

d

two

bolts

perrow

?No

replication

Tota

lNo.

(16)

1Theor

derofthe

W/Dratiosinco

lumn

8is

direct

lylinkedtotheord

erofS/Dratiosinco

lumn

10[23]




15/28

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.....

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....

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....

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....

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Tab

le4Summ

aryo

fconcentrical

lyloadedsing

le-b

olt

doub

lelap-jointtests

from

SIprojectsub

jectedtoelevatedtemperaturesan

dno

wetageing

[1]

Plate

[2]

Thickness

(mm)

[3]

Bolt

diameter

(D)(mm)

[4]

Hole

cleara

nce

(mm)

[5]

Washer

size(mm)

[6]

Bolt

torque

(Nm)

[7]

O

rientation

(0oisdirec-

tionof

p

ultrusion)

[8]

E/D

[9]

W/D

[10]

Environmental

conditioning

[11]

Joint

configurations

[12]

Reference

(No.oftests)

Strongwel

l

EXTREN1

500series

polyester

6.40

M10

Gra

de8.8

9.8mm

0.2

(tig

htis

hfit)

None,outer

plateso

fstee

l

(8mmthic

k)

innerplate

PFRP

Finger-

tight

(53Nm

)0

5 2 2 7

7 5 103

RT

,40oC

,

60oC

,80oC

Bearing

design

Cleavage

design

Shear-out

design

Net-t

ension

design

[26]

Batchesof

3

45

5

7

RT

,40oC

,

Bearing

design

(to

bereported

2

5

60oC

,80oC

Cleavage

design

byTurveyan

d

2

10

Shear-out

design

Wang)

7

3

Net-t

ension

design

Batchesof

2

90

5

7

RT

,40oC

,

Bearing

design

2

5

60oC

,80oC

Cleavage

design

2

10

Shear-out

design

7

3

Net-t

ension

design

[27]

Batchesof

3

*Fourelevated

temperatures,

noageinginwater

.

(132)




16/28

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Tab

le5Summ

aryo

fconcentrical

lyloadedsing

le-b

olt

doub

le-la

pjointtests

from

SIprojectsu

bjecte

dto

differentenvironmenta

lconditions

[1]

Plate

[2]

Thickness

(mm)

[3]

Bolt

diameter

[4]

Hole

cleara

nce

[5]

Washer

size(mm)

[6]

Bolt

torque

[7]

Orienta-

tion(0ois

[8]

E/D

[9]

W/D

[1

0]

Environmental

co

nditioning

[11]

Joint

configuratio

ns

[12]

Reference

(No.oftests)

D(mm)

(mm)

(Nm)

directionof

pultrusion)

Tempera-

tu

re

Water

immersion

(weeks)

Strongwel

l

6.40

M10

0.2

None

Finger-t

ight

0

5

7

RT

0

Bearing

design

(to

bereported

EXTREN1

500series

polyester

Gra

de8.8

9.8mm

1.2

(53Nm

)

0

5

7

60

oC

6.5

byTurveyan

d

2.2

0

5

7

80

oC

13

Wang)

2.2

45

5

7

60

oC

0

Batcheso

f3

0.2

45

5

7

80

oC

6.5

1.2

45

5

7

RT

13

1.2

90

5

7

80

oC

0

Outerplatesof

2.2

90

5

7

RT

6.5

stee

l(8mmthick

)

0.2

90

5

7

60

oC

13

innerplate

PFRP

0.2

0

2

5

RT

0

Cleavage

design

1.2

0

2

5

60

oC

6.5

2.2

0

2

5

80

oC

13

2.2

45

2

5

60

oC

0

0.2

45

2

5

80

oC

6.5

1.2

45

2

5

RT

13

1.2

90

2

5

80

oC

0

2.2

90

2

5

RT

6.5

0.2

90

2

5

60

oC

13

0.2

0

2

10

RT

0

Shear-out

1.2

0

2

10

60

oC

6.5

design

2.2

0

2

10

80

oC

13

2.2

45

2

10

60

oC

0

0.2

45

2

10

80

oC

6.5

1.2

45

2

10

RT

13

1.2

90

2

10

80

oC

0

2.2

90

2

10

RT

6.5

0.2

90

2

10

60

oC

13

Tota

lNo:(81)

Continued




17/28

observation is a reason why the plots givenelsewhere[1120]cannot readily be compared. When themode of failure is bearing, the loaddisplacementcharacteristics for 08 single-bolt joints, withoutsignificant bolt torque, are seen to be similar to thoseshown in Fig. 3(a)[13,14]. The initial part showsvirtually linear elastic behaviour up to the ultimateload (a change in slope between 80 and 100% of theultimate load would indicate the presence of initialfailure). Following attainment of the ultimate load, theload reduces to between 70 and 80% of its ultimate,

and remains constant (or increases if the failingmaterial in front of the bolt(s) is laterally restrainedand has nowhere to go), as the displacement increasesup to several times the displacement at ultimate load.Under these conditions the loaddisplacementresponse (Fig. 3(a)) provides evidence ofpseudo-ductility[14,15,20].

It can be expected that joint collapse in realstructures will be dynamic in nature. Stresses causingsuch failure will be generated by a load situation thatwill, for a short period of time at least, remain thesame as it was for the joint state just prior to the

ultimate load situation. In stroke control joint tests,the load must follow the instantaneous stiffness of thespecimen. Here, when there is progressive damage,the continuous change in the joints stiffness governsthe load that can be transferred by the joint itself. Inthe real situation, an instantaneous change in loadwith instantaneous change in stiffness cannot occur,and so ultimate failure is more likely to occur withlittle additional joint displacement (unless theultimate load is higher than the initial damage load).We conclude from this observation that bearingfailure and its progressive damage growth (see

Fig. 3a) does not always guarantee a joints ductility.Ductility can be realized only if the jointdisplacement can be several times greater than at theinitial damage load and the higher ultimate load isreached only after this higher displacement has..

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.....

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.

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.

.

.

Strongwel

l

EXTREN1

500series

polyester

6.40

M10

Gra

de8.8

9.8mm

0.2

1.2

2.2

2.2

0.2

1.2

1.2

2.2

0.2

None

Finger-t

ight

(53Nm

)

0 0 0 454545909090

7 7 7 7 7 7 7 7 7

3 3 3 3 3 3 3 3 3

RT

60

oC

80

oC

60

oC

80

oC

RT

80

oC

RT

60

oC

0 6.5

130 6.5

130 6.5

13

Net-t

ension

design

(tobereported

by

Turveyan

d

Wang)

Batcheso

f3

Outerplates

ofstee

l(8mm

thic

k)inner

plate

PFRP

[27]

Tota

lNo:(108)

30

45

(a) (b)

Concentric tension

Fig. 4 Failure modes in single-bolt joints under concentrictension and off-axis PFRP plate orientation (from[18]): (a) 308;(b) 458




18/28

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Tab

le6Summ

aryo

fconcentrical

lysing

le-b

oltloaded

doub

le-la

pjointtests

from

SIprojectsu

bjecte

dto

differentenvironmenta

lconditions

[1]

Plate

[2]

Thickness

(mm)

[3]

Bolt

diameter

[4]Ho

le

clearance

[5]

Washer

size(mm)

[6]

Bolt

torque

[7]

Orientation

(0oisdirec-

[8]

E/D

[9]

W/D

[10]

Environmental

conditioning

[11]

Joint

configur

a-

[12]

Ref.

(No.

oftests)

D(mm)

(mm)

(Nm)

tionof

pultrusion)

Tem-

perature

Waterim-

mersion

(week)

tions

Strongwel

l

EXTREN1

500series

polyester

6.40

M10

Gra

de8.8

9.8mm

0.2

None

Finger-t

ight

(53Nm)

0

5

7

RT

60oC

80oC

RT

6.5

6.5

6.5

13

Bearing

design

(to

bereported

byTurveyan

d

Wang)

Batcheso

f2

60oC

13

80oC

13

Outerplatesof

stee

physical test data for the appraisal of the design procedures for bolted - mttram & turvey.pdf

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