Practical Work Report 2011/2012

For work experience undertaken through the University of Auckland Summer Research Scholarship

Student Name:

Fidez Ydella Quintana Oreta (UPI: fore002, ID: 1213796)

Department:

Civil and Environmental Engineering

Name and Address of Employer:

The University of Auckland’s Timber Research Group;

20 Symonds Street, Auckland City

Research Supervisor:

Dr. Pierre Quenneville

Dates of Work Period:

17th

of November 2011 – 21st

February 2012

Date of Report:

1 March 2012

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Abstract This practical work report describes work experience undertaken with the University of Auckland’s Timber

Research Group, through the Summer Research Scholarship Scheme. The period of employment consisted of

400 work hours, from the 17th

of November 2011 until the 21st

of February 2012.

The objective of the summer research project was to develop a new Purlin to Rafter connection using fully

threaded screws which could be used in laminated veneer lumber portal frames. The deliverables for the

project included performing a literature review, developing a design, completing laboratory testing, producing

a final report and making an industry presentation.

The main skills the author learnt during this work period included efficiently using library databases, analysing

the lateral and withdrawal resistance of screws using the Eurocode 5 (BS EN 1995-1-1:2004), using laboratory

machinery to fabricate and test timber joint samples, and making a professional presentation.

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Acknowledgements I would like to thank the following people for assisting me during my summer research project:

Dr. Pierre Quenneville for supervising my project

Felix Scheibmair for his mentoring and advice during various periods throughout my research

The Civil Materials Laboratory Technicians, Mark Byrami and Noel Perinpanayagam, for their support

during the fabrication and testing stages of my research

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Table of Contents Abstract .................................................................................................................................................................. 1

Acknowledgements ................................................................................................................................................ 2

1. Introduction ................................................................................................................................................... 1

1.1 Summer Research Objective ............................................................................................................... 1

1.2 The Timber Research Group ........................................................................................................... 1

1.3 Laboratory Facilities ............................................................................................................................ 2

2. Description of Work Completed .................................................................................................................... 2

2.1 Literature Review ................................................................................................................................ 2

2.2 Design and theoretical analysis ........................................................................................................... 3

2.3. Fabricating Test Samples ................................................................................................................ 3

2.4 Performing Shear and Tension Tests ................................................................................................... 4

2.5 Analysing Experimental Results ........................................................................................................... 5

2.6 Final Report and Timber Day Presentation ......................................................................................... 7

3. Conclusions and Summary of Skills Learnt ..................................................................................................... 8

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Table of Figures

Figure 1: Photo of Rothoblaas fully threaded screw used in research ................................................................... 1

Figure 2: The existing joint detail for Purlin to Rafter connections - Proprietary joist hanger and tension strap .. 1

Figure 3: Existing Purlin/Rafter connection using fully threaded screws and sawn timber lumber ....................... 2

Figure 4: Proposed Purlin/Rafter Joint design developed for shear testing ........................................................... 3

Figure 5: Screen-shot of Microsoft Excel Spread-sheet developed to evaluate the theoretical capacity of a

single screw ............................................................................................................................................................ 3

Figure 6: Photo showing the angle guide and drill press used to predrill the Purlin Test Samples ........................ 4

Figure 7: Photo showing the construction of a test Purlin/Rafter joint sample using a cordless drill and clamps 4

Figure 8: Experimental set-up used for shear testing to determine the lateral resistance of the screws ............. 5

Figure 9: Experimental set-up used for tension testing to determine the lateral resistance of the screws .......... 5

Figure 10: Rothoblaas Spread-sheet used to calculate yield loads and ultimate loads obtained through

experimental testing ............................................................................................................................................... 6

Figure 11: Load slip diagrams obtained during tension testing (left), Load-slip diagrams obtained during shear

testing (right) .......................................................................................................................................................... 6

Figure 12: Extract of the Excel Spread-sheet used to calculate statistical values obtained from experimental

tests ........................................................................................................................................................................ 7

Figure 13: Screen-shot of my Power-point presentation for the University of Auckland Timber Day ................... 7

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1. Introduction This practical work report covers work experience undertaken from the 17

th of November 2011 until the 21

st of

February 2011. In this period a total of 400 hours was completed with the Timber Research Group at the

University of Auckland, through the Summer Research Scholarship Scheme.

The scope of work varied from hands-on laboratory experience in the Civil Materials Timber Laboratory and

theoretical analysis.

1.1 Summer Research Objective

The objective of this summer research project was to develop new Purlin to Rafter connection detail using fully

threaded screws (as shown in Figure 1), which could be used in laminated veneer lumber (LVL) portal frame

structures.

Figure 1: Photo of Rothoblaas fully threaded screw used in research

The proposed detail needed to be able to resist the design vertical shear and horizontal tension loads, in addition to being competitive against the existing proprietary joist hanger and tension strap detail (shown in Figure 2), commonly used for this joint.

Figure 2: The existing joint detail for Purlin to Rafter connections - Proprietary joist hanger and tension strap

The general overview of work included conducting a literature review, developing an design, performing shear

and tension laboratory tests, analysing results and finally producing a recommendation to industry in the form

of a report and presentation.

1.2 The Timber Research Group

The Timber Research Group is based at the University of Auckland’s City Campus. The group is led by Dr. Pierre

Quenneville, and consists of two other academic staff members (Hugh Morris and Gary Raftery), two

laboratory technicians (Mark Byrami and Noel Perinpanayagam), one laboratory assistant (Dennis Nguyen) as

well as several post-doctoral students, including Felix Scheibmair my research mentor, and five summer

research students.

The Timber Research Group regularly meets for a research co-ordination meetings every second Friday. During

these meetings members discuss research developments and each member is required to share their future

research plans for the next two week period.

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1.3 Laboratory Facilities

The main laboratory in which this work experience was performed was the Civil Timber Materials Laboratory

located on Level 2, in the Faculty of Engineering Building at 20 Symonds Street, Auckland.

The laboratory is supervised by Mark Byrami and Noel Perinpanayagam. Full health and safety inductions are

required before being allowed access to laboratory facilities.

The laboratory has three main MTS testing machines ranging from capacities of 100kN to 500kN. General

machinery such as cutting saws, drill presses and power tools are also available to research students.

Test materials such as LVL members or regular sawn lumber are stored in designated areas in the laboratory.

These materials are made available for use to summer research students after obtaining permission from a

laboratory technician.

2. Description of Work Completed

2.1 Literature Review

Before a new joint detail could be designed, a literature review investigating existing research on fully

threaded screws needed to be conducted.

Databases such as SCOPUS, Science Direct and the ASTM Digital Library were accessed through the Engineering

Library website to access journal articles relating to the research.

From the literature review it was discovered that the existing available research available on fully threaded

screws was limited, as the screws are relatively new in the fastener market. Out of the journal articles

reviewed the most relevant research projects were conducted by Blass and Bejtika from The University of

Karlsruhe, (in which they investigated screws with continuous threads in timber connections and effect of

using inclined screws) and research conducted at the University of Auckland, through the development of

Quick- Connect Connections.

From these two research projects I identified key conclusions which would I could use in my research. These

findings were that the higher yield moments associated with the screws meant higher lateral resistances could

be achieved compared to other dowel-type fasteners; and that exploiting the withdrawal capacity of the

screws using inclined configurations could lead to even higher load-carrying capacities.

In addition to reviewing existing technical research, I was also required to investigate similar designs which

were already being used in timber construction. Through this investigation, I noted that all existing details

involved driving screws from the top of the secondary beam into the primary beam, as shown in Figure 3.

Figure 3: Existing Purlin/Rafter connection using fully threaded screws and sawn timber lumber

At the start of the research, I concluded that this configuration would not be suitable as it would cause

potential splitting of the LVL Purlin.

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2.2 Design and theoretical analysis

The proposed design I developed for testing is shown in Figure 4, it consists of four 7mm diameter by 140mm

long fully threaded Rothoblaas screws per Purlin, driven into LVL members at an angle of 30 degrees.

Figure 4: Proposed Purlin/Rafter Joint design developed for shear testing

To investigate the theortical capacity of the proposed detail I was required to use the European Yield Model,

from the Eurocode 5 (BS EN 1995-1-1:2004) to obtain the lateral resistance (under single shear) and

withdrawal resistance of each screw. To do this I developed a Microsoft Excel Spread-sheet to execute the six

equations given in the Eurocode 5 associated with failure modes a-f. A screen shot of this spread sheet is

shown in Figure 5.

Figure 5: Screen-shot of Microsoft Excel Spread-sheet developed to evaluate the theoretical capacity of a single screw

From this Excel Spread-sheet, the theoretical single shear capacity of each screw was calculated to be 6.52kN

(without pre-drilling) and 7.30kN (with pre-drilling). The withdrawal capacity was estimated to be 29.29kN.

These loads were later compared to the experimental values obtained in order to determine if the Eurocode 5

accurately predicted actual values obtained during testing.

2.3. Fabricating Test Samples

In order to assess the structural strength and stiffness of the proposed screw connection, I was required to

manufacture and perform shear tests and tension tests on joint samples. This involved working the Civil

Timber Materials Laboratory under the supervision of Mark Byrami and Noel Perinpanayagam.

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The first component of the laboratory work was to fabricate full scale samples of the proposed connection. I

used 45mm thick and 63mm thick LVL members for the Purlin members, and 90mm thick LVL for the Rafter

members. The joints were constructed using four 7mm diameter by 140mm long Rothoblaas fully threaded

screws driven into the Purlin at 30 degrees.

A drill press and angle guide, shown in Figure 6, was used to pre-drill the Purlin. Only the Purlin was pre-drilled

(not the rafter) as this is how the joint would typically be constructed on site.

Figure 6: Photo showing the angle guide and drill press used to pre-drill the Purlin Test Samples

The screws were then driven into the Purlin using a cordless drill, as shown in Figure 7 . The samples were

clamped in order to ensure there was no gap between the Purlin and Rafter which would influence test results.

Figure 7: Photo showing the construction of a test Purlin/Rafter joint sample using a cordless drill and clamps

2.4 Performing Shear and Tension Tests

As a typical Purlin/Rafter joint is subject to both vertical and horizontal loads, I was required to perform two

sets of tests; Shear tests to assess the lateral resistance of the screws when subject to vertical loading, and

Tension tests to assess the withdrawal capacity of the screws when under horizontal loads. Both tests were

conducted on the 100kN manually controlled MTS machine located in the Civil Materials Laboratory.

For the shear tests, two samples were tested per test-set up as shown in Figure 8. Four LVDTs were used to

measure joint slip and the load applied by the MTS machine was split between the two samples using steel

plates.

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Testing was supervised by Noel Perinpanayagam; During the tests I was responsible for controlling the MTS

machine so that it applied the required loading loop, as given in ISO6891:1983, the international standard used

for determining the strength and stiffness of joints constructed using mechanical fasteners.

Figure 8: Experimental set-up used for shear testing to determine the lateral resistance of the screws

For the tension tests, only one sample was tested per set up, as shown in Figure 9. Similarly, four LVDTs were

used to measure joint slip and the load was applied using the 100kN MTS machine through two M12 bolts.

During the tests, I was responsible for monitoring the load-slip curve obtained to determine when the failure

withdrawal load had been reached so that the test could be stopped.

Figure 9: Experimental set-up used for tension testing to determine the lateral resistance of the screws

2.5 Analysing Experimental Results

In order to compare the experimental results with the theoretical values estimated, I was required to use an

Excel Spread-sheet provided by screw manufacturer (Rothoblaas) to determine the yield loads and ultimate

loads per screw.

I extracted data readings collected by the LVDTs during the test and transferred them into the Rothoblaas

Spread-sheet as shown in Figure 10. Using the Rothoblaas Spread-sheet, I identified the range of forces for

which the screw responded elastically and then determined the corresponding yield limit of the screw.

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Figure 10: Rothoblaas Spread-sheet used to calculate yield loads and ultimate loads obtained through experimental testing

The ultimate loads per screw for both the shear and tension tests were obtained using the experimental load-

slip diagrams obtained during testing, as shown in Figure 11.

Figure 11: Load slip diagrams obtained during tension testing (left), Load-slip diagrams obtained during shear testing (right)

Tension tests were failure controlled such that the ultimate withdrawal capacity of a screw was determined by

indentifying the maximum force on the load-slip curve. This value indictated the point at which the screw

“failed” by pulling out of the LVL.

Shear tests were deformation controlled such that the ultimate shear capacity of a screw was associated with

the force applied at a 15mm displacement.

From the experimental yield loads and ultimate yield loads collected for all tests, data was collated and used to

calaculate important statstical values such as the mean, co-efficient of variation and characteristic loads. This

was summarized in tablular form using an Excel Spread-sheet, as shown in Figure 12.

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Figure 12: Extract of the Excel Spread-sheet used to calculate statistical values obtained from experimental tests

2.6 Final Report and Timber Day Presentation

As part of the Summer Research Scholarship Scheme, all students are required to submit a professional report

summarizing research performed. My report consisted of four main sections a literature review, methodology,

results and recommendations.

In addition to report, at the end of the summer, all members of the Timber Research Group were required to

deliver a fifteen minute presentation to the industry during the University of Auckland Timber Day, held on the

21st

of February 2012.

For the presentation I was required to make an accompanying Power-point presentation (extract shown in

Figure 13). The objective of my presentation was to highlight the competitiveness of the proposed four screw

detail, and the potential cost and labour saving benefits that could be achieved compared to the existing joist

hanger option.

Figure 13: Screen-shot of Power-point presentation for the University of Auckland Timber Day

Throughout this day, I was also responsible for interacting with attendees and answering any questions they

had regarding the proposed screw connection.

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3. Conclusions and Summary of Skills Learnt From the testing and analysis performed during the summer research programme it was concluded that the

proposed four screw detail was able to provide sufficient resistance for the design shear and tension loads.

However, it was recommended that further research be conducted including combined shear and tension tests

in order to fully understand behaviour of the screws when the two forces interact. To further develop the

concept, I also recommended that the use of inclined screws be investigated in order to better exploit the high

withdrawal strength of the screws for vertical loads.

In summary, through this summer research programme I acquired key research skills such using the library

database, writing a literature review and analysing experimental data. In addition to this, I also gained

laboratory experience such as accurately fabricating test samples and operating MTS machines.