Test report on cyclic behaviour of replicated timber joist-masonry wall connections

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Test report on cyclic behaviour of replicated timber joist-masonry wall connections

Ravenshorst, Geert; Mirra, Michele

Publication date

2018

Document Version

Final published version

Citation (APA)

Ravenshorst, G., & Mirra, M. (2018). Test report on cyclic behaviour of replicated timber joist-masonry wall

connections. Delft University of Technology.

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Project number C31B67 File reference C31B67WP4-11 Date 16th_{April 2018}

Corresponding author Geert J.P. Ravenshorst (g.j.p.ravenshorst@tudelft.nl)

TU Delft Large-scale testing campaign 2016 – WP4

TEST REPORT ON CYCLIC BEHAVIOUR OF

REPLICATED TIMBER JOIST-MASONRY

WALL CONNECTIONS

Authors: Geert J.P. Ravenshorst, Michele Mirra

Cite as: Ravenshorst, G. J. P., Mirra, M. Test report on cyclic behaviour of replicated timber joist-masonry wall connections. Report no. C31B67WP4-11, 16th_{April 2018. Delft University of Technology.}

This document is made available via the website ‘Structural Response to Earthquakes’ and the TU Delft repository. While citing, please verify if there are recent updates of this research in the form of scientific papers.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of TU Delft.

TU Delft and those who have contributed to this publication did exercise the greatest care in putting together this publication. This report will be available as-is, and TU Delft makes no representations of warranties of any kind concerning this Report. This includes, without limitation, fitness for a particular purpose, non-infringement, absence of latent or other defects, accuracy, or the presence or absence of errors, whether or not discoverable. Except to the extent required by applicable law, in no event will TU Delft be liable for on any legal theory for any special, incidental consequential, punitive or exemplary damages arising out of the use of this report.

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Version 2 – Final 16/04/2018

1 Introduction ... 3

2 Definition of test specimens... 3

2.1 Test specimens for joist-masonry connections ... 3

2.2 Properties of the various types of tested connections ... 7

3 Test set-up for joist-masonry connections ... 10

4 Testing protocol ... 14

5 Test results ... 16

5.1 Companion tests on mortar and masonry ... 16

5.1.1 Introduction ... 16

5.1.2 Mortar flow test ... 16

5.1.3 Bond wrench test for masonry couplets ... 16

5.1.4 Conclusions ... 17

5.2 Cyclic tests on timber-masonry connections ... 18

5.2.1 Specimen A0 ... 18 5.2.2 Specimen A1 ... 22 5.2.3 Specimen A2 ... 27 5.2.4 Specimen B0 ... 32 5.2.5 Specimen B1 ... 36 5.2.6 Specimen B2 ... 40 6 Conclusions... 45 7 References... 48

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1 Introduction

In this report the cyclic behaviour of different timber joist-masonry wall connections is presented. After a short description of how the test setup was designed [1], in the last section the obtained experimental results from the cyclic tests will be reported and commented for the six specimens.

2 Definition of test specimens

2.1 Test specimens for joist-masonry connections

The common way to connect timber floor joists to masonry walls in Dutch houses is by inserting the joists in pockets in the masonry: in figure 1 this is principle is shown. The joist can be inserted at ground level or first floor level, but also at roof level: in the latter case there is no masonry above the joist. In this test program the case of the connection at roof level was studied. The support length in the masonry is normally a stone width, so for a single leaf over the entire width of the wall, and for the double wythe half the width of the wall (see figure 2). Therefore, in this program the joist-masonry connections for a single leaf and a double wythe wall were studied, and then for 3 situations:

1. The joist in the pocket without any anchors (see figure 1);

2. The joist in the pocket with an anchor masoned in the wall and nailed to the joist (see figure 3); 3. The joist in the pocket, without an anchor but strengthened with a folded steel-plate, anchored to

the masonry and connected with screws to the joist (see figure 4). This strengthening option is considered as a serious option in practice.

The single leaf masonry walls were made of calcium silicate bricks and the double wythe walls of clay bricks.

Figure 1 – Timber joist in a masonry pocket in practice.

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Figure 3 – Principle for masoned-in anchors, nailed to the timber joist, for single leaf (left) and double wythe walls (right).

Figure 4 – Principle of strengthening of the joist-masonry connection with a folded steel plate anchored to the masonry and screwed to the joist.

The test specimens were manufactured according to standardised dimensions to be able to be tested in the same test set-up.

In figure 5 the principle of the standardised test specimens is shown: they consist of masonry wall elements of approximately 980 mm by 600 mm. A timber joist of 65 mm x 150 mm or 65 mm x 170 mm is inserted; this timber joist is approximately 1.6 m long.

On the bottom steel beam a timber plywood plate is bolted, on which the bottom masonry layer is glued. A diagonal steel bracing (not drawn) is connected to the bottom steel beam to support the timber beam at half of the length during construction. When the specimen is in the test set-up this bracing is removed. After the construction phase two plywood plates are glued on top of the masonry walls at the two sides over 100 mm length (see figure 6). These plywood plates are connected to a top steel beam, in order to support the masonry outside the connection area horizontally at the top. If this was not done, there could be the possibility of flexural cracking of the masonry near the bottom; then mixed mechanisms can occur. Therefore, to be sure that the behaviour of the joist–masonry connection as such is studied, the horizontal support on the sides with the plywood plates is chosen.

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Figure 5 – Standardised test specimen to test the masonry-joist connection. Dimensions in mm. In figure 6 the boundary conditions for the standardised test specimen during testing are shown.

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Table 1 – Dimensions of the specimens for joist-masonry connections

Nr. Sample name Anchor system Related situation

1 A0 No anchor As-built

2 A1 With anchor As-built

3 A2 No anchor / steel plate Strengthened

4 B0 No anchor As-built

5 B1 With anchor As-built

6 B2 No anchor / steel plate Strengthened

Explanation:

- A: Double wythe clay brick;

- B: Single leaf calcium silicate bricks;

- Anchor: masoned-in anchor, nailed to the joist;

- Strengthened: No masoned-in anchor, but folded steel plate screwed to the joist and connected to the masonry with mechanical anchors.

Samples A0 and B0 were already shown in figure 5.

Figure 7 shows test specimen A1, while in figure 8 sample B1 is shown.

Figure 7 – Principle of configuration of test specimen A1

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Figure 9 shows test specimen A2, while in figure 10 sample B2 is shown:

Figure 9 – Principle of configuration of test specimen A2

Figure 10 – Principle of configuration of test specimen B2

2.2 Properties of the various types of tested connections

For specimens A0 and B0, no fastener between joist and masonry is present, and only the friction in the mortar pocket can absorb the horizontal loads. The mortar used for these walls was characterized by usual values of the mortar flow test: the two diameters measured were respectively 179 and 181 mm for the clay bricks mortar (Remix droge mortel versie 2), while for the calcium silicate bricks mortar (Remix Brickfix BFM) values of 175 and 177 mm were obtained.

Samples A1 and B1 are characterized by a masoned-in anchor, coming out from the wall as shown in figure 3 (left) for the single leaf wall, or inserted for the whole length between the two brick layers for the double wythe wall (figure 3, right). The steel anchor measured 240x240 mm with a diameter of 14 mm, while the nails used to connect it to the joist had a diameter of 4 mm and a length of 55 mm (figure 11). The execution of this detail is shown in figure 12 for both specimens.

As for the last two specimens, A2 and B2, a Rothoblaas Titan TCN240 steel angle was used (Figure 13). For the connection between the aforementioned plate and the masonry two Fischer FAZ II 10/10 mechanical anchors (10x95 mm) were used (Figure 14), while the connection with the timber joist was realized with four Rothoblaas screws 5x60 mm. The detail of this strengthened connection is shown in figure 15; the

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according to the producer these mechanical anchors are suitable for both concrete and general masonry, the pull-out resistance is reported in the catalogue only with reference to concrete C20/25, and for two fasteners it is about 8 kN. Hence, it was chosen for this configuration to position 4 screws, in order to have a similar value of force transmitted by them. The final aim is then to optimize the failure exploiting the dissipation of energy due to yielding of the screws and wood embedment.

Figure 11 – Anchor to be masoned in specimen A1 and B1 with the nails for the connection to the joist

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Figure 13 – Steel angle used for the strengthened connection in samples A2 and B2 (dimensions in mm)

Figure 14 – Mechanical fastener used to connect the steel plate to the masonry

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Figure 16 shows the set-up for the joist-masonry connections tests.

The specimens are positioned on the right bottom beam of the set-up and the support beam of the test specimen is bolted to this beam. The left support of the timber joist is on a column with Teflon on its top, to ensure frictionless sliding at this support. After the positioning of the test specimen the diagonal bracing for the temporary support of the joist (not drawn) is removed.

To the top beam on both sides of the masonry columns are bolted. These columns are connected with steel plates to the long beams of the set-up to transfer the reaction force.

In the middle of the beam a vertical load of 100 kg is applied to ensure a reasonable vertical load at the support of 50 kg, simulating the self-weight of the portion of floor supported by the joist.

The measurement plan is given in figure 17, while the overview of the applied sensors is given in table 2. The main result is the horizontal displacement between joist and masonry wall, measured by sensor 3, related to the force measured by sensor 1.

In order to obtain reliable results, it was chosen to measure the absolute displacement of the timber joist not only using the sensor in the jack, but adding also one more laser (sensor no. 10) on the opposite side. In this way, it was possible to check the results obtained from sensor 3 by comparing this displacement with the relative one between sensor 4 and sensor 10.

In figure 18 a representative picture of the positioned sensors for specimen B0 is reported: the same configuration was then used for each other sample.

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Figure 17 – Sensors positioned for the conducted tests

Table 2 – Overview of the measuring points and sensor types used in the test.

No. Description Sensor Type Stroke _(mm)

1 Horizontal actuator 50 kN – load and displacement Load cell and HBM _LVDT +/-100 2 Horizontal displacement between steel plates connecting _{actuator and joist} Linear potentiometer +/-5 3 Horizontal displacement between joist and masonry Linear potentiometer +/-50 4 Out-of-plane displacement at the top of the masonry wall _(center) Laser +/-50 5 Out-of-plane displacement at half height of the masonry _{wall (center)} Laser +/-50 6 Out-of-plane displacement at the bottom of the masonry _{wall (center)} Linear potentiometer +/-5 7 Out-of-plane displacement at the top of the masonry wall _(side) Linear potentiometer +/-5 8 Out-of-plane displacement at half height of the masonry _{wall (side)} Laser +/-50 9 Out-of-plane displacement at the bottom of the masonry _{wall (side)} Linear potentiometer +/-5 10 Horizontal displacement of the timber joist Laser +/-50

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However, when testing the strengthened connection system, due to the particular configuration adopted, a larger number of sensors were placed around the masonry pocket, in order to obtain more information about the possible different failures: in particular, the behaviour of the screws and of the steel angle was better investigated by means of new sensors, as can be observed in figure 19, in which the instrumentation for the strengthened case is represented. In particular:

• With sensor 3A the relative displacement between the joist and the wall is measured, therefore this sensor is the equivalent of number 3 for the as-built configurations;

• Sensor 3B measures the sliding between the timber joist and the steel angle, useful to investigate the behaviour of the screws;

• By means of sensor 3C is possible to quantify the vertical displacement of the steel angle, and its rotation together with sensor 3D;

• Sensor 3D, in combination with 3A, allows also to calculate the displacement between the steel angle and the wall.

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4 Testing protocol

The specimens is loaded quasi-static reversed-cyclic in accordance with ISO 16670 [2]. The test shall be carried out at a constant rate of slip of between 0,1 mm/s and 10 mm/s.

ISO 16670 suggests to perform a monotonic test to determine the ultimate displacement vu. (see figure 20) However, monotonic tests were not foreseen in this program. From the test results of the plank-joist connections with 2 nails a maximum ultimate displacement around +/-30 mm was found. In this test the maximum displacement was set to +/- 40 mm, since also deformation in the masonry can occur: the tests were anyway stopped before reaching this value. In order to be able to study the elastic behaviour, and to have enough steps small enough in this range, an ultimate displacement of +/- 20 mm was assumed. The principle of the cyclic loading scheme is given in figure 21 . In table 3 the loading scheme is given; in every cycle 3 runs are performed.

Figure 20: Load-displacement curve of a joint with mechanical fasteners [1]

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Table 3 – Loading scheme for the connection joist-wall.

Cycle Number of runs Amplitude Uact Rate Duration

% of vu mm mm/s s 1 3 1,25 0,25 0,3 10 2 3 2,5 0,5 0,3 20 3 3 5 1 0,3 40 4 3 7,5 1,5 0,3 60 5 3 10 2 0,3 80 6 3 20 4 0,3 160 7 3 40 8 0,3 320 8 3 60 12 0,3 480 9 3 80 16 0,3 640 10 3 100 20 0,3 800 11 3 120 24 0,3 960 12 3 140 28 0,3 1120 13 3 160 32 0,3 1280 14 3 180 36 0,3 1440 15 3 200 40 0,3 1600

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5 Test results

5.1 Companion tests on mortar and masonry

5.1.1 Introduction

For the construction of the specimens, the types of mortar and brick masonry were the same used also for the in-plane and out-of-plane tests performed in WP3.

Thus, these companion tests were conducted with the aim to check whether the properties of mortar and masonry are comparable to those measured and calculated in the previous works.

5.1.2 Mortar flow test

The mortar flow test allows to measure the workability of the mortar: the measured values of the diameter of the flow are reported in the following table, and are aligned to those recorded in the previous experimental campaigns.

Table 4 – Mortar flow test results.

Clay bricks Calcium silicate bricks

Type of mortar _amountWater Diam. 1 _(mm) Diam. 2 _(mm) Type of mortar _amountWater Diam. 1 _(mm) Diam. 2 _(mm)

Remix droge

mortel (versie 2) 3,7 l/25 kg 179 181 Remix brickfix BFM 3,1 l/25 kg 175 177

5.1.3 Bond wrench test for masonry couplets

For this series of tests investigating the behaviour of the joist-wall connection, the most significant property of interest for the masonry is related to its flexural behaviour. It was chosen, therefore, to perform together with these tests also a bond wrench companion test, which can provide useful information about this behaviour.

This kind of test was already performed in past experiences and then reported [3], [4], [5]. In this case, 15 couplets of clay bricks and 15 couplets of calcium silicate bricks were prepared during the constructions of the main walls and after at least 28 days of maturation of the mortar they were tested using the setup described in [3]-[5] and calculating then the bond strength according to EN 1052-5:2005 [6].

In this section the obtained results for both calcium silicate bricks and clay bricks are reported. All the specimens were characterized by a failure of type A or B, according to the denomination in [6]; only with calcium silicate couplets in two cases a type C failure was observed: in figure 22 these three different failure modes are shown.

In table 4 the experimental results are reported: for clay bricks only 13 specimens were tested because two of them were already irreversibly damaged before starting the tests. For both type of bricks, the resistance appears to be comparable to the values already obtained in the past series of tests [3]-[5].

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Figure 22 – Bond-wrench test failure examples: type A (left), type B (centre) and type C (right). Table 5 – Bond wrench test experimental results

Clay bricks Calcium silicate bricks

Density

(kg/m3₎ _{strength (MPa)}Mean bond St. dev. _(MPa) C. o. V. _(kg/mDensity 3₎ _{strength (MPa)}Mean bond St. dev. _(MPa) C. o. V.

1645 0,06 0,02 32% 1819 0,39 0,10 26%

5.1.4 Conclusions

The companion tests on mortar and masonry which were performed and presented in the first version of this report, show results that are in line with those obtained in WP3:

• From the mortar flow test very similar value for the diameters were obtained;

• For bond wrench test, the value of flexural bond strength were slightly lower for clay bricks couplets and higher for calcium silicate ones. Anyway, the range of values noticeable from both standard deviation and coefficient of variation is moderately wide and therefore, taking into consideration the normal dispersion that affects masonry specimens, the results are comparable to those obtained in the past experiences.

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5.2.1 Specimen A0

Specimen A0 consists of a double wythe wall realized with clay bricks, in which a timber joist is simply placed in its mortar pocket. The length of this pocket is 10 cm, i.e. a half of the total thickness of the wall. Therefore, in this case an as-built non-strengthened situation is analysed.

The sample was tested after a minimum drying period for the mortar of at least 28 days; figure 23 shows the specimen before and after its positioning within the test setup.

Figure 23 – Specimen A0 before (top) and after (bottom) its positioning within the test setup. Specimen A0 showed a non-symmetric behaviour due to the particular configuration of the masonry pocket, because when pushing the joist towards the wall, the second leaf of bricks gives a contribution in the resistance. On the contrary, when the joist is pulled from the wall, the horizontal load can be transferred only by friction between timber and mortar, after the mortar-joist interface has cracked.

The hysteretic cycle of sample A0 is reported in figure 24; positive values of force and displacements are obtained by pulling the joist: in this direction, after a short elastic phase before the cracking of the mortar around the joist, the behaviour is then governed by friction, as already mentioned before. A maximum horizontal force of about 0,7 kN is transmitted to the wall.

For the opposite direction a much stiffer behaviour can be observed, with a maximum transferred horizontal load of about 6,3 kN. After this peak, a softening phase takes place, due to the sliding of part of the second leaf of bricks during the test, as can be noticed also in figures 25 and 26.

An initial stiffness of 3,8 kN/mm was calculated, while at 2 mm displacement this value was reduced to 0,28 kN/mm when pulling and to 2,6 kN/mm when pushing towards the wall.

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Figure 24 – Hysteretic cycle of the joist-masonry connection for specimen A0. Total hysteretic cycle (top) and behaviour of the connection in the initial phases until 2 mm of relative displacement (bottom)

-5 -4 -3 -2 -1 0 1 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ]

Relative displacement between joist and wall [mm]

Initial stiffness Stiffness at 2 mm _displacement

(pulling)

Stiffness at 2 mm displacement (pushing)

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Figure 25 – Comparison between the absolute displacement of the joist and of the wall for specimen A0. Total

cycle (top) and behaviour of the sample in the initial phases until 2 mm of displacement (bottom) -5 -4 -3 -2 -1 0 1 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 26 – Sliding of the bricks around the masonry pocket

Figure 27 – Cracks on sample A0 after testing.

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Specimen A1 consists of a double wythe wall realized with clay bricks, in which a timber joist is placed in its mortar pocket and fastened to the wall by means of a masoned-in anchor, already reported in figure 11 and 12 (left). Therefore, in this case a second type of as-built situation is analysed; figure 28 shows the specimen before and after its positioning within the test setup.

The sample was tested after a minimum drying period for the mortar of at least 28 days.

Figure 28 – Specimen A1 before (top) and after (bottom) its positioning within the test setup. Specimen A1 showed a non-symmetric behaviour, where the resistance of the wall is different depending on the load direction: this can be explained by the fact that when pushing the joist also the second leaf of bricks can play a role against this force, while in the opposite direction the horizontal load is transmitted only by the masoned-in anchor.

The hysteretic cycle of sample A1 is reported in figure 29; positive values of force and displacements are obtained by pulling the joist: being this direction the weakest, relative displacements are larger and a maximum horizontal force of 5,0 kN is transferred to the wall.

On the contrary, for the opposite direction a much stiffer behaviour can be observed, with a maximum transferred horizontal load of about 12,9 kN. After this peak, a softening phase takes place, due to the level of damage which occurred to the specimen, together with the sliding of part of the second leaf during the test, as can be noticed also in figures 30 and 31.

An initial stiffness of 11,1 kN/mm was calculated, while at 2 mm displacement this value was reduced to 1,4 kN/mm when pulling and to 4,0 kN/mm when pushing towards the wall.

Beside the visible damage that occurred to the wall after reaching significant values of displacement, also the nails connecting the masoned-in anchor to the joist were slightly bent, causing also wood embedment and small energy dissipation, as shown in figure 32.

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Figure 29 – Hysteretic cycle of the joist-masonry connection for specimen A1. Total hysteretic cycle (top) and behaviour of the connection in the initial phases until 2 mm of relative displacement (bottom)

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 -20 -15 -10 -5 0 5 10 15 20 25 30 Ho riz on ta l f or ce [ kN ]

-10 -8 -6 -4 -2 0 2 4 -2 -1 0 1 2 3 4 Ho riz on ta l f or ce [ kN ]

Initial stiffness Stiffness at 2 mm displacement (pulling) Stiffness at 2 mm displacement (pushing)

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Figure 30 – Comparison between the absolute displacement of the joist and of the wall for specimen A1.

Total cycle (top) and behaviour of the sample in the initial phases until 2 mm of displacement (bottom) -14 -12 -10 -8 -6 -4 -2 0 2 4 -30 -20 -10 0 10 20 30 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

Joist displacement Wall out-of-plane displacement

-6 -5 -4 -3 -2 -1 0 1 2 3 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 31 – Sliding of the bricks around the masonry pocket (left) and damages and cracks occurred to the wall in the area of the masoned-in anchor (right)

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5.2.3 Specimen A2

Specimen A2 consists of a double wythe wall realized with clay bricks, in which a timber joist is placed in its mortar pocket and screwed to a proper steel angle, already reported in figure 13 and 15 (left), which is bolted to the wall. Therefore, in this case a strengthened configuration is analysed.

Figure 34 – Specimen A2 before (top) and after (bottom) its positioning within the test setup. In order to better understand the behaviour of this connection, it was chosen to perform the test until the ultimate failure, which at the end completely damaged the wall. This strengthening option is therefore able to resist 8,3 kN when pulling the joist and 7,4 kN when pushing it, without causing significant damage to the wall.

Above these values, the wall started to be more and more cracked, with also a significant sliding that occurred to the bricks in the area around the joist. However, before reaching the ultimate failure for both directions, the specimen was still able to resist up to a maximum of 10,3 kN (pulling) and 15,5 kN (pushing), with a profound damage to the wall.

Furthermore, in this case the initial calculated stiffness is 54,9 kN/mm: 5 times higher than the one for specimen A1, and almost 9 times higher than the one for sample A0. This has a reflection also in the obtained graphs. As can be observed in figures 35 and 36, both the relative displacement between joist and wall, and the absolute displacement of them is limited before the complete damaging of the wall. Therefore, the connection is stiff and is able to make the joist and the wall move effectively together: at 2 mm the stiffness is still 4,1 kN/mm.

The critical damage state of the wall during the test is shown in figure 37: beside the out-of-plane cracks, also some cracks around the mechanical anchors were observed, together with their pull-out failure, and also the steel angle was slightly bent.

Furthermore, a fairly high embedment in the timber joist was observed, together with bending of the four screws connecting the steel angle to it (figure 38): therefore, some energy dissipation took place despite the low forces involved, as is possible to notice from figure 39. In fact, the measure of the sliding between timber joist and steel angle is the displacement to which the four screws are subjected, and it was sufficient to start a plastic behaviour.

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Figure 35 – Hysteretic cycle of the joist-masonry connection for specimen A2. Total hysteretic cycle (top) and behaviour of the connection in the initial phases until 2 mm of relative displacement (bottom).

-20 -15 -10 -5 0 5 10 -15 -10 -5 0 5 10 15 Ho riz on ta l f or ce [ kN ]

-10 -8 -6 -4 -2 0 2 4 6 8 10 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5 Ho riz on ta l f or ce [ kN ]

Initial stiffness

Stiffness at 2 mm displacement

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Figure 36 – Comparison between the absolute displacement of the joist and of the wall for specimen A2. Total cycle (top) and behaviour of the sample in the initial phases until 2 mm of wall displacement (bottom).

-20 -15 -10 -5 0 5 10 15 -40 -30 -20 -10 0 10 20 30 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

-6 -4 -2 0 2 4 6 8 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 37 – Damaging of the wall during the test: out-of-plane cracks (left) and cracks around the bolts (right) with pull out failure of the mechanical anchors and slight bending of the steel angle

Figure 38 – Wood embedment (left and centre) and bending of the screws (right) observed after the test

Figure 39 – Hysteretic cycle of the screws -20 -15 -10 -5 0 5 10 15 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 Ho riz on ta l f or ce [ kN ]

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Specimen B0 consists of a single leaf wall realized with calcium silicate bricks, in which a timber joist is simply placed in its mortar pocket. The length of this pocket is 10 cm, i.e. the total thickness of the wall. Therefore, in this case an as-built non-strengthened situation is analysed.

Figure 41 – Specimen B0 before (top) and after (bottom) its positioning within the test setup. Specimen B0 showed the following behaviour: a first elastic phase before that the crack in the mortar-joist connection happened, and then a second phase entirely dominated by friction after the crack. The obtained hysteretic cycle is reported in figure 42 and, as can be observed, the horizontal force that this kind of joist-masonry connection is able to transfer is extremely low (about 0,5 kN only in the very initial phases); an initial stiffness of 3,3 kN/mm was calculated, while at 2 mm displacement this value was reduced to 0,22 kN/mm.

With the applied vertical load, simulating the self-weight of the portion of floor supported by the joist, it is possible to approximately calculate the value of the friction coefficient µ between the timber joist surface and the mortar in the masonry pocket: µ = Fhorizontal/Fvertical ≈ 0,75.

During the test the sample showed practically negligible movements of the wall (0,15 mm) also when the highest displacements were applied, while the joist was simply sliding through the masonry pocket, as can also be noticed in the graph reported in figure 43 and in the picture taken during the test (figure 44). Finally, figure 45 shows the cracks which developed across the wall while the test was performed.

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Figure 42 – Hysteretic cycle of the joist-masonry connection for specimen B0. Total hysteretic cycle (top) and behaviour of the connection in the initial phases until 2 mm of relative displacement (bottom)

-0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 -40 -30 -20 -10 0 10 20 30 40 Ho riz on ta l f or ce [ kN ]

-0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 Ho riz on ta l f or ce [ kN ]

Initial stiffness

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Figure 43 – Comparison between the absolute displacement of the joist and of the wall for specimen B0. Total cycle (top) and behaviour of the sample in the initial phases until 2 mm of displacement (bottom)

-0,7 -0,5 -0,3 -0,1 0,1 0,3 -30 -20 -10 0 10 20 30 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

-0,7 -0,5 -0,3 -0,1 0,1 0,3 0,5 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 44 – Sliding of the joist in the masonry pocket.

Figure 45 – Cracks on sample B0 after testing.

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Specimen B1 consists of a single leaf wall realized with calcium silicate bricks, in which a timber joist is placed in its mortar pocket and fastened to the wall by means of a masoned-in anchor, already reported in figure 11 and 12 (right). Therefore, in this case a second type of as-built situation is analysed.

Figure 46 – Specimen B1 before (top) and after (bottom) its positioning within the test setup.

For specimen B1 the presence of the masoned-in anchor determined a non-symmetric behaviour: when pushing the joist towards the wall there is only resistance due to the friction among timber joist, anchor and mortar, but in the pulling phase the shape of the anchor is able to make the wall move together with the joist, as if a stiffer connection system was present.

The obtained hysteretic cycle is reported in figure 47 and, as can be observed, the horizontal force that this kind of joist-masonry connection is able to transfer depends on the direction of loading, as already remarked: when the force was applied pushing towards the wall, a maximum value of 1,4 kN was registered, while in the opposite direction a peak of 5,3 kN was reached; an initial stiffness of 4,9 kN/mm was calculated, while at 2 mm displacement this value was reduced to 0,58 kN/mm.

However, this value of force is associated to a relative displacement between wall and joist of 17 mm, which is already remarkable for a single connection, causing the wall to be cracked and damaged and not able to bear higher loads anymore: after this peak value, a softening phase takes place.

The comparison between the absolute displacement of the joist and that of the wall is reported in figure 48: it can be noticed that in this case the wall is involved in not negligible values of displacement and then is damaged.

During the test, also a partial expulsion of the mortar from the masonry pocket was observed, which is shown in figure 49.

Furthermore, a slight embedment in the timber joist was observed, together with a small bending of the three nails connecting the anchor to it (figure 50): therefore, a limited energy dissipation was still possible despite the low forces involved.

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Figure 47 – Hysteretic cycle of the joist-masonry connection for specimen B1. Total hysteretic cycle (top) and behaviour of the connection in th e initial phases until 2 mm of relative displacement (bottom).

-2 -1 0 1 2 3 4 5 6 -40 -30 -20 -10 0 10 20 30 Ho riz on ta l f or ce [ kN ]

-1,6 -1,2 -0,8 -0,4 0 0,4 0,8 1,2 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 Ho riz on ta l f or ce [ kN ]

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Figure 48 – Comparison between the absolute displacement of the joist and of the wall for specimen B1. Total cycle (top) and behaviour of the sample in the initial phases until 2 mm of displacement (bottom).

-2 -1 0 1 2 3 4 5 -30 -20 -10 0 10 20 30 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

-1,2 -0,8 -0,4 0 0,4 0,8 1,2 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 49 – Expulsion of part of the mortar in the masonry pocket.

Figure 50 – Slight wood embedment and nail bending observed after the test.

Figure 51 – Cracks on sample B1 after testing.

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Specimen B2 consists of a single leaf wall realized with calcium silicate bricks, in which a timber joist is placed in its mortar pocket and screwed to a proper steel angle, already reported in figure 13 and 15 (right), which is bolted to the wall. Therefore, in this case a strengthened configuration is analysed.

Figure 52 – Specimen B2 before (left) and after (right) its positioning within the test setup.

In order to better understand the behaviour of this connection it was chosen to perform the test until the ultimate failure, which at the end completely damaged the wall. This strengthening option is therefore able to resist 5,6 kN when pulling the joist and 6,0 kN when pushing it, without causing significant damage to the wall.

Above these values, the wall started to be more and more cracked, also in the area around the bolts, which made them unable to bear higher traction forces. On the contrary, when pushing towards the wall it was possible to reach an horizontal force of 10,5 kN, because in this case the bolts are not subjected to traction and therefore not involved in the resisting mechanism.

Furthermore, it is essential to underline that in this case the initial calculated stiffness is 40,7 kN/mm: 8 times higher than the one for specimen B1, and more than 12 times higher than the one for sample B0. This has a reflection also in the obtained graphs. As can be observed in figures 53 and 54, both the relative displacement between joist and wall, and the absolute displacement of them is limited before the complete damaging of the wall. Therefore, the connection is sufficiently stiff and is able to make the joist and the wall move effectively together: at 2 mm the stiffness is still 3,46 kN/mm.

The critical damage state of the wall during the test is shown in figure 55.

Furthermore, a slight embedment in the timber joist was observed, together with a small bending of the four screws connecting the steel angle to it (figure 56): therefore, a limited energy dissipation was still possible despite the low forces involved, as is possible to notice from figure 57. In fact, the measure of the sliding between timber joist and steel angle is the displacement to which the four screws are subjected, and it was sufficient to start a plastic behaviour.

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Figure 53 – Hysteretic cycle of the joist-masonry connection for specimen B2. Total hysteretic cycle (top) and behaviour of the connection in the initial phases until 2 mm of relative displacement (bottom).

-12 -10 -8 -6 -4 -2 0 2 4 6 8 -5 -2,5 0 2,5 5 7,5 10 12,5 15 17,5 20 Ho riz on ta l f or ce [ kN ]

-6 -4 -2 0 2 4 6 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 Ho riz on ta l f or ce [ kN ]

Initial stiffness

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Figure 54 – Comparison between the absolute displacement of the joist and of the wall for specimen B2. Total cycle (top) and behaviour of the sample in the initial phases until 2 mm of wall displacement (bottom).

-12 -10 -8 -6 -4 -2 0 2 4 6 -25 -20 -15 -10 -5 0 5 10 15 20 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

-8 -6 -4 -2 0 2 4 6 8 -4,5 -4 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 Ho riz on ta l f or ce [ kN ] Horizontal displacement [mm]

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Figure 55 – Damaging of the wall during the test: out-of-plane cracks (left) and cracks around the bolts (right)

Figure 56 – Wood embedment (left) and slight bending of the screws (right) observed after the test

Figure 57 – Hysteretic cycle of the screws -12 -10 -8 -6 -4 -2 0 2 4 6 8 -4 -3 -2 -1 0 1 2 3 Ho riz on ta l f or ce [ kN ]

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Figure 58 – Cracks on sample B2 after testing: front (top) and back (bottom)

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6 Conclusions

In this report the cyclic behaviour of replicated timber-joist connections was presented and analysed. Two as-built situations and a possible strengthening option were studied for two different types of wall, according to the following table.

Table 6 – Different analysed specimens and configurations

Specimen Description Type of connection Connection properties A0

Double wythe wall realized with clay bricks.

Timber joist inserted in the wall with no other fasteners. Only friction is able to bear horizontal solicitations.

No fastener is present for this as-built configuration. The mortar used for the construction showed usual values of diameter in the mortar flow test (179 and 181 mm).

A1

Timber joist inserted in the wall and fastened to it by means of an anchor nailed to the joist and masoned in the wall.

As-built configuration with a 240x240 mm steel anchor masoned in the wall and fastened to the joist with three nails 4x55 mm.

A2

Timber joist inserted in the wall and fastened to it by means of a steel angle screwed to the joist and bolted to the wall.

Strengthened configuration obtained by means of a Rothoblaas TCN240 steel angle fastened to the joist with four 5x60 mm screws and bolted to the wall with two 10x95 mm mechanical fasteners.

B0

Single leaf wall realized with calcium silicate bricks.

Timber joist inserted in the wall with no other fasteners. Only friction is able to bear horizontal solicitations.

No fastener is present for this as-built configuration. The mortar used for the construction showed usual values of diameter in the mortar flow test (175 and 177 mm).

B1

Timber joist inserted in the wall and fastened to it by means of an anchor nailed to the joist and masoned in the wall.

As-built configuration with a 240x240 mm steel anchor masoned in the wall and fastened to the joist with three nails 4x55 mm.

B2

Timber joist inserted in the wall and fastened to it by means of a steel angle screwed to the joist and bolted to the wall.

Strengthened configuration obtained by means of a Rothoblaas TCN240 steel angle fastened to the joist with four 5x60 mm screws and bolted to the wall with two 10x95 mm mechanical fasteners.

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referred to specimens A0, A1 and A2 are reported, while in figure 59 a comparative graph for the three configurations is shown.

As can be observed, the following main aspects are of relevance:

• If the connection between the joist and the wall is only given by the masonry pocket, its strength and stiffness are depending on the direction of load: when the beam is pulled, the resistance is related only to the friction between timber and mortar, while in the opposite direction the second leaf of bricks acts as a contrast for the joist and therefore a higher level of force can be reached; • The masoned-in anchor is already an improvement of the previously described as-built situation,

however the peak force can be reached only with a large amount of displacement, which causes the wall to be cracked;

• The analysed strengthening option allows to significantly improve the overall behaviour of the connection, because high horizontal loads can be transmitted without causing damage to the wall and with a very limited amount of displacement.

Table 7 – Main experimental results obtained from specimens A0, A1 and A2

Specimen Positive Maximum force (kN) Initial stiffness _(kN/mm) Stiffness at 2 mm displacement _(kN/mm) (pulling) (pushing) Negative

A0 0,69 -6,31 3,78 0,28 if pulling; 2,62 if pushing A1 5,03 -12,93 11,11 1,39 if pulling; 4,05 if pushing

A2 10,35 -15,47 54,95 4,10

Figure 59 – Hysteretic cycle obtained for specimens A0, A1 and A2 before significant damage of the wall -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 -15 -12 -9 -6 -3 0 3 6 9 12 15 Ho riz on ta l f or ce [ kN ]

Relative displacement between joist and wall [mm] Sample A0 Sample A1 Sample A2

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For the calcium silicate bricks samples, a strong improvement of the strength and stiffness of the joist-wall connection was reached. In table 8 the main results referred to specimens B0, B1 and B2 are reported, while in figure 60 a comparative graph for the three configurations is represented.

Basically, as can be noticed:

• The simple insertion of the joist in the masonry pocket leads to a very low stiffness, related only to the friction between timber and mortar;

• The presence of a masoned-in anchor can increase the stiffness of the whole connection, but only if the joist is pulled from the wall, due to the particular shape of this fastener. Moreover, the maximum force that can be transferred to the wall is associated with a large displacement;

• The analysed strengthening option allows to significantly improve the overall behaviour of the connection, which is able to bear a remarkable amount of force with a very limited relative displacement between joist and wall.

Table 8 – Main experimental results obtained from specimens B0, B1 and B2

Specimen Positive Maximum force (kN) Initial stiffness _(kN/mm) Stiffness at 2 mm displacement _(kN/mm) (pulling) (pushing) Negative

B0 0,46 -0,62 3,29 0,22

B1 5,27 -1,43 4,85 0,58

B2 5,66 -10,54 40,69 3,46

Figure 60 – Hysteretic cycle obtained for specimens B0, B1 and B2 before significant damage of the wall -6 -4 -2 0 2 4 6 -4,5 -3 -1,5 0 1,5 3 4,5 Ho riz on ta l f or ce [ kN ]

Relative displacement between joist and wall [mm] Sample B0 Sample B1 Sample B2

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[1] Ravenshorst, G. J. P., Mirra, M. (2018). Test report on cyclic behaviour of replicated timber joist-masonry wall connections. Delft University of Technology. Report number C31B67WP4-10, version 1, 24-01-2018.

[2] ISO 16670:2003. Timber structures – Joints made with mechanical fasteners – Quasi-static reversed-cyclic test method. International Organization for Standardization (ISO).

[3] Jafari, S., Esposito, R. (2017). Material tests for the characterisation of replicated calcium silicate brick masonry. Delft University of Technology. Report number C31B67WP1-9, version 1, 14th November 2016.

[4] Jafari, S., Esposito, R. (2017). Material tests for the characterisation of replicated calcium silicate element masonry. Delft University of Technology. Report number C31B67WP1-11, version 1, 8th August 2017.

[5] Jafari, S., Esposito, R. (2017). Material tests for the characterisation of replicated solid clay brick masonry. Delft University of Technology. Report number C31B67WP1-12, version 1, 16th_August 2017.

[6] EN 1052-5 (2005). Method of test masonry – Part 5: Determination of bond strength by bond wrench method. Nederlands Normalisatie-Instituit (NEN).