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Construction and Building Materials 21 (2007) 2041–2046

and Building

MATERIALS

Investigation of masonry wall fixings subject to pullout load and torque

Halil Murat Algin *

Civil Engineering Department, Harran University, Osmanbey Campus, 63300 Sanliurfa, Turkey

Received 12 March 2006; accepted 9 August 2006Available online 22 September 2006

Abstract

The experimental investigation into masonry wall fixings is carried out to develop an in-depth knowledge by investigating the factorswhich lead to a reduction in the effectiveness of scaffolding/brickwork anchors. Since the pullout test of fixings is currently not practicalin construction site the research carried out to determine the potential use of torque test as an alternative. The information to assess howvarious parameters in anchor settings could affect the load bearing capacity of an individual anchor used in scaffolding/brickwork sys-tems is presented in this paper. The correlation between the ultimate pullout load bearing capacity, the maximum torque values, theincrements in anchor hole depths and diameters has also been determined. The method, which is described in this paper, can be usedto estimate the in situ pullout strength of scaffolding/brickwork anchors by means of the calibration graph between torque and pulloutload. The torque in practice can be applied by using a simple torque-meter like tool fits into the fixing and is clamped to it. Paper presentsthe results and draws conclusions.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Scaffolding; Brickwork; Masonry wall anchor; Pullout load; Torque

1. Introduction

Scaffolding can provide an efficient and safe means toperform work. However, unsafe scaffolding procedurescan lead to accidents, serious injuries and death. Scaffold-ing fixing is one of the most commonly used methods tomaintain stability between scaffolding and masonry wall.It has a superior capability to prevent motion in each trans-lational plane of motion and rotational axis, with minimalrisk to the scaffolding elements when properly applied. It isimportant to evaluate the performance of fixings becausetheir support is critical to maintain safe working conditionsfor the scaffolding structures. The strength of fixation isprimarily determined by the fixing’s mechanical and mate-rial properties, as well as the mechanical properties of thescaffolding–wall interface. The literature reports manycases of scaffolding failures caused by scaffolding fixings[1–4]. Fixation failure may occur through a number ofmechanisms: Fixings may toggle in wall; they may loosen

0950-0618/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2006.08.004

* Tel.: +90 414 344 0020; fax: +90 414 344 0031.E-mail address: hmalgin@yahoo.co.uk.

gradually over time because of the repeated number ofloads; they may fail acutely in pullout or brick fracture.

The scaffolding–masonry wall interface has been studiedwith respect to loosening and pullout strength. Researchersanalyzed pullout strength and stiffness as well as torque forthe strength of concrete and concluded that the two charac-teristics were correlated [5–8]. However the correlationbetween insertional torque and pullout strength of anchorshas not been investigated in a great detail. Since the pullouttests are not practical in construction site [9–13] it may bepossible to develop a simple handheld torque-meter likeapparatus to measure the maximum torque values of fixingand predict the corresponding pullout load that the fixingscan possibly support. Unlike visual inspections that do notgive a load profile of the fixings, the handheld tool can indi-cate places where support is weak. A scaffolding engineercan also use the tool to analyze the effectiveness of differentfixing types, lengths, and hole sizes in a specific masonrywall type. The in situ torque value is believed to be a goodpredictor of the pullout strength [5] and thus initial stabilityof the fixing. Little is known as to how realistic thisassumption would be when applied to new fixing and

Fig. 1. Drilling the hole and fixing the threaded rod.

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thread designs. The presented investigation carried out todetermine the correlation between the maximum inser-tional torque values and the ultimate pullout resistance ofscaffolding fixings in terms of the increments in anchor holedepths and diameters.

2. Testing of fixings

The M10 · 40 type of anchor and TE92 masonry drillused in the research are produced by HILTI [15]. Theadvantage of this type of anchors is that accurate settingcan be achieved with a flared collar that is fixed flush withthe surface and is independent of hole depth. The internalthread in the anchor is not damaged when hammering thefixing into the hole. It is ideal for the research because ofthe flexibility in using the threaded rods of required length.This allowed the load–displacement measuring system to beset on the threaded rod. The previous research [14] con-cluded that the anchor length must be suitable for the brickthickness as stated by most of the manuals and specifica-tions published by companies that produce masonryanchors such as HILTI [15]. In the presented research[16,17] the pullout tests were followed by 20 tests in whichbolts are fixed into full-depth holes in the bricks. The pro-cess involves setting the anchor is to drill a hole of therequired diameter and length which are of full-depth(40 mm) and full diameter (12 mm) and cleaning the debrisfrom the hole and inserting the wedge anchor, slotted endfirst, pushing or tapping it to the bottom of the hole (Fig. 1).

In this stage the brick sample was placed into a speciallyfabricated frame to apply a constant compressive load of1 ton throughout the testing process. Fig. 2a shows themethod used for restraining the bricks.

The bricks were restrained with this method to preventtensile failure which would otherwise be caused by the

Fig. 2. (a) Method used to restrain the brick to prevent tensile failu

applied compressive force when the anchor is expandedby the setting tool. After placing and compressing the brickin the metal frame and by using the setting tool the internalwedge is driven into the anchor until the shoulder of thesetting tool touches the face of the anchor. Finally thethreaded rod is fixed into the expanded wedge anchor.The pullout test method is shown in Fig. 2b. In each testthe anchor was extracted and a graph was produced show-ing the relationship between the applied pullout force andcorresponding displacement (see Fig. 3).

The results were assessed and they provided sufficientconsistency which allowed the following phases to proceed.A further 60 tests were undertaken in which anchors werefixed into brick samples and then subjected to a torque.The process involved setting the anchor for the torque testswas repeated for each test (see Fig. 4).

The brick sample was then placed into the same framethat was used earlier of the research. However in this phaseof the project the frame was connected to the support col-umns in the laboratory in order to allow the application atan axial rotation onto the threaded rod (see Fig. 4). Twosteel bars (S1 and S2) acting as a lever arm were weldedon a steel circular plate (SP) as shown in Fig. 4. Whenthe load was applied to the lower end of the steel bars,the applied load generated a torsional action on the circu-lar plate which was fixed on the threaded rod by fillet welds

re when the anchor is expanded. (b) Pullout test configuration.

Fig. 5. Bolt/fixing with and without washer.

Fig. 3. A typical pullout test graph shows the relationship between theapplied pullout loads and corresponding displacements.

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(see Fig. 4). In a typical application of the bolt/fixing sys-tem, the washer’s internal diameter is smaller than theanchor’s external diameter. Because of this reason, whenthe torque is applied onto the bolt, the washer convertsthe torque to an axial compressive force and this force gen-erates a pullout force in the anchor. This assembly failed toprovide direct torque behaviour in anchor (see Fig. 5).

The mechanism shown in Fig. 4 however provided adirect application of axial torque onto the expandedanchors. By this method the torque was directly transferredonto the anchor and the rotation in the anchor caused by

Fig. 4. The rotation in the expanded anchor (

the torsional moment was effectively measured. A lineartransducer was placed on a rectangular metal plate weldedon the circular plate. When the torque was applied onto thecircular plate and subsequently onto the threaded rod andthe expanded anchor, the applied load and correspondinghorizontal displacement were measured by a load cell andthe linear transducer respectively. It was then straightfor-ward to convert the measured horizontal displacement toangular deflection (rotation) of the expanded anchor asshown in Fig. 4.

A parametric study was then undertaken for three cate-gories of anchor hole diameter and four categories ofanchor hole depth. Each category was correlated with thepullout force values. These additional experiments concen-trated on the response of anchors that were fixed in a lessthan perfect manner such that their resistance to pullout

the rotation dimensions are exaggerated).

Table 1Required pullout force in terms of applied proof torque

Pullout force required (kN) Proof torque load (N m)

10 13015 14020 17025 22030 300

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is less than intended. The additional 120 tests were under-taken to determine the performance of anchors subjectedto pullout force. The tests were carried out for variousbrick hole sizes and brick anchor depths. The wedgeanchors were inserted into holes drilled with the diameters;correct size (12 mm), 0.5 mm over size (12.5 mm) and 1 mmover size (13 mm). For each of these conditions the anchorswere inserted into the holes of; full-depth (40 mm), 5 mmshort of full-depth (35 mm), 10 mm short of full-depth(30 mm) and 30 mm short of full-depth (10 mm). The testswere undertaken for 12 different conditions and 10 testswere undertaken for each condition.

3. Implication of results

In each torque test a graph indicating the relationshipbetween the applied moment and rotation was produced.The obtained results allowed developing correlationbetween the torsional moment and various levels of pulloutforces. In this correlation the maximum pullout force val-ues are based on the full-depth (40 mm) and correct size(12 mm) of the anchor holes. Fig. 6 shows the correlationbetween the maximum applied torque and maximum pull-out load values. The results show that the ultimate pulloutload and torque resistance of anchor is directly related withthe anchor hole diameter and depth.

Table 1 can be used for determining the pullout loadcorresponding with a torque value. Table 1 has been devel-oped on the basis of a safety factor of 2, using the regres-sion curve in Fig. 6.

The relationship between the pullout force and the cor-responding vertical displacement was determined. Theinfluence of hole size and anchor depth on the maximumload bearing capacity of anchors has been analyzed. Therelationship between the maximum pullout load and thedepth of anchor hole was determined for anchor hole diam-eters of 12, 12.5 and 13 mm. The results are shown in

Fig. 6. Correlation between maximum applied

Fig. 7. The depths of the anchor holes in Fig. 7 are 40,35, 30 and 10 mm. Fig. 8 indicates the influence of anchorhole diameter on maximum pullout load value. Table 2summarizes Figs. 7 and 8 in terms of the percentage reduc-tion in the strength of the anchor.

Fig. 6 confirms that there is a positive correlationbetween the applied torque and pullout loads. Figs. 7 and8 show that the pullout loads are influenced by variationsin anchor hole diameters and depths. The regularity ofthe distribution of data is sufficient to be generalized bythe function of the regression line. The correlation clearlyshows that the maximum pullout load bearing capacityof an anchor can be determined by using the maximum tor-que value that can be transferred by the anchor itself. Themaximum pullout load bearing capacity is substantiallydependent on anchor hole diameter and depth. When theanchor hole diameter is correct there is almost a linear rela-tionship between the maximum pullout load and anchorhole depth. A 25% reduction in anchor depth causes a23% decrease in ultimate pullout load values. There is alsoa dramatic decrease in the load carrying capacity andunpredictability in the behaviour of anchors if the anchorhole diameter is excessively over sized. An 8.3% increasein the anchor hole diameter causes an approximately 90%reduction in the ultimate pullout load values. Figs. 7 and8 show that the probability of failure is clearly dependenton the anchor hole diameter and depth.

pullout load and maximum torque values.

Fig. 8. The relationship between maximum applied pullout load and size of anchor holes.

Table 2Percentage reduction in ultimate pullout load in terms of the variations inanchor hole diameter and depth

Diameter oversizea (mm)

Shortfall in lengthb (mm)

0 (0%)c 5 (12.5%) 10 (25%) 30 (75%)

0 (0%)d 0% 14% 23% 59%0.5 (4.17%) 23% 39% 45% 68%1 (8.33%) 86% 94% 95% 98%

a Increase in another hole diameter.b Reduction in anchor hole depth.c Full-depth (40 mm).d Correct hole diameter (12 mm).

Fig. 7. The relationship between maximum applied pullout load and depth of anchor.

H.M. Algin / Construction and Building Materials 21 (2007) 2041–2046 2045

Fig. 8 shows that the anchor hole diameter is inverselyrelated to the ultimate pullout load values and that thestrength of the anchor increases when the anchor holediameter approaches the correct size. If the anchor holediameter is oversize, the ultimate applied pullout load isreduced. Table 2 indicates that the oversized anchor hole

diameter is much more crucial than the reduction in anchorhole depth. When the anchor hole depth is correct, an 8.3%(1 mm) increase in anchor hole diameter causes an 86%reduction in ultimate pullout load (even a 0.5 mm increasein anchor hole diameter reduces the strength of the anchorby over 23%), whereas, when the anchor hole diameter iscorrect, an 8.3% decrease in anchor hole depth reducesthe ultimate pullout load values by only 10%. The reduc-tion in the strength of the anchor is almost nine times lowerthan that caused by the increments in anchor hole diame-ter. Therefore, it is probable that anchor hole diameteroversizing is the premier reason for the failures in scaffold-ing/brickwork anchors.

4. Conclusion

Parameters other than those investigated in this paper asthe type of brick, the brittleness of brick, environmental

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effects and the changes in the loading configuration mayalso have a crucial effect on the performance of masonryanchors. The sensitivity of parameters is beyond the scopeof this paper. Information developed from the investiga-tions and non-destructive tests were used to assess theextent of certainty involved in the overall performance ofexpanded anchors, and to confirm that there is a sufficientagreement in the correlation of torque and pullout loads.However, since the overall objective of the exercise wasto explore the relationship between torque and pulloutloads, the research could be expanded to cover morediverse factors such as the types of brick used in masonrywalls. In view of the good correlation between pullout forceand torque sustained it is recommended that a simple tor-que mechanism to be developed for use on site. A devicesimilar in concept to a simple torque-meter like tool couldbe used to apply a proof load to a fixing system. The cor-relation given in this paper can be used for determining thepullout load corresponding with a torque value. Such atool would be of great benefit to scaffold engineers and per-sonnel and would enhance safety and installation quality ofscaffolding systems.

Acknowledgments

The author expresses his sincere thanks to Prof. Dr.John Knapton (University of Newcastle upon Tyne, UK)and Hash Matria (Health and Safety Executive, UK) fortheir help to conduct the research presented in this paper.

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