Monotonic, cyclic and dynamic behaviour of timber-masonry connections

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Monotonic, cyclic and dynamic behaviour of timber-masonry connections

Mirra, Michele; Ravenshorst, Geert

Publication date

2019

Document Version

Final published version

Citation (APA)

Mirra, M., & Ravenshorst, G. (2019). Monotonic, cyclic and dynamic behaviour of timber-masonry

connections. Delft University of Technology.

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Project number CS2B04

File reference CS2B04WP2-3.3

Date 3rd_{December 2019}

Corresponding author Geert J.P. Ravenshorst

(g.j.p.ravenshorst@tudelft.nl)

TU Delft research program 2018/2019 – WP2

MONOTONIC, CYCLIC AND DYNAMIC

BEHAVIOUR OF TIMBER-MASONRY

CONNECTIONS

Authors: Michele Mirra, Geert Ravenshorst

Cite as: Mirra, M., Ravenshorst, G. J. P. Monotonic, cyclic and dynamic behaviour of timber-masonry

connections. Report no. CS2B04WP2-3.3, 3rd_{December 2019. 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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4 Test setup ... 19 Overview on the setup ... 19 4.1 Measurement plan ... 19 4.2 5 Test results ... 25 General ... 25 5.1 Configuration A ... 26 5.2 Specimen A-M-1... 26 5.2.1 Specimen A-QS-1 ... 27 5.2.2 Specimen A-QS-2 ... 29 5.2.3 Specimen A-QS-3 ... 31 5.2.4 Specimen A-HFD-1 ... 33 5.2.5 Specimen A-HFD-2 ... 35 5.2.6 Specimen A-HFD-3 ... 37 5.2.7

General observations on cyclic behaviour of configuration A ... 39 5.2.8

General observations on dynamic behaviour of configuration A ... 39 5.2.9

Configuration B ... 40 5.3

Specimen B-M-1... 40 5.3.1

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_______________________________________________________________________________________ Final version 03/12/2019 Specimen B-QS-1 ... 41 5.3.2 Specimen B-QS-2 ... 43 5.3.3 Specimen B-QS-3 ... 45 5.3.4 Specimen B-HFD-1 ... 47 5.3.5 Specimen B-HFD-2 ... 49 5.3.6 Specimen B-HFD-3 ... 51 5.3.7

General observations on cyclic behaviour of configuration B ... 53 5.3.8

General observations on dynamic behaviour of configuration B ... 53 5.3.9 Configuration C ... 55 5.4 Specimen C-M-1... 55 5.4.1 Specimen C-QS-1 ... 56 5.4.2 Specimen C-QS-2 ... 58 5.4.3 Specimen C-QS-3 ... 60 5.4.4 Specimen C-HFD-1 ... 62 5.4.5 Specimen C-HFD-2 ... 65 5.4.6 Specimen C-HFD-3 ... 68 5.4.7

General observations on cyclic behaviour of configuration C ... 70 5.4.8

General observations on dynamic behaviour of configuration C ... 71 5.4.9 Configuration D ... 72 5.5 Specimen D-M-1 ... 72 5.5.1 Specimen D-QS-1 ... 73 5.5.2 Specimen D-QS-2 ... 76 5.5.3 Specimen D-QS-3 ... 79 5.5.4 Specimen D-HFD-1 ... 81 5.5.5 Specimen D-HFD-2 ... 85 5.5.6 Specimen D-HFD-3 ... 88 5.5.7

General observations on cyclic behaviour of configuration D ... 91 5.5.8

General observations on dynamic behaviour of configuration D ... 92 5.5.9 Configuration E ... 93 5.6 Specimen E-M-1 ... 93 5.6.1 Specimen E-QS-1 ... 94 5.6.2 Specimen E-QS-2 ... 101 5.6.3 Specimen E-QS-3 ... 104 5.6.4 Specimen E-HFD-1 ... 107 5.6.5 Specimen E-HFD-2 ... 116 5.6.6 Specimen E-HFD-3 ... 119 5.6.7

General observations on cyclic behaviour of configuration E ... 122 5.6.8

General observations on dynamic behaviour of configuration E ... 123 5.6.9 Configuration F ... 125 5.7 Specimen F-M-1 ... 125 5.7.1 Specimen F-QS-1 ... 126 5.7.2

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_______________________________________________________________________________________ Final version 03/12/2019 Specimen F-QS-2 ... 129 5.7.3 Specimen F-QS-3 ... 132 5.7.4 Specimen F-HFD-1 ... 139 5.7.5 Specimen F-HFD-2 ... 142 5.7.6 Specimen F-HFD-3 ... 151 5.7.7

General observations on cyclic behaviour of configuration F ... 154 5.7.8

General observations on dynamic behaviour of configuration F ... 155 5.7.9 Configuration G ... 156 5.8 Specimen G-M-1 ... 156 5.8.1 Specimen G-QS-1 ... 157 5.8.2 Specimen G-QS-2 ... 160 5.8.3 Specimen G-QS-3 ... 163 5.8.4 Specimen G-HFD-1 ... 166 5.8.5 Specimen G-HFD-2 ... 169 5.8.6 Specimen G-HFD-3 ... 172 5.8.7

General observations on cyclic behaviour of configuration G ... 175 5.8.8

General observations on dynamic behaviour of configuration G ... 176 5.8.9

6 Companion tests ... 177 7 Conclusions... 178 8 References... 185

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1 Introduction

This document presents the complete overview on the test results obtained in the 2019 experimental campaign on timber-masonry connections, in as-built and strengthened configurations. The tests have been performed in two phases, the first phase in spring 2019 and the second phase in summer 2019. These types of connections were partly analysed in a previous pilot study, in the 2018 testing phase [1].

The aim of this test campaign was to characterize the seismic response of joist-wall connections, therefore monotonic, cyclic and high-frequency dynamic tests were scheduled, as presented in the testing protocol [2], which is included in section 3 of this document.

In the present report, after a general introduction, a detailed overview on the adopted samples and on the testing methods will be presented, followed by discussion of test results and some general conclusions. The outcomes of this campaign are used in the interpretation phase, in which characteristic values of strength and stiffness, and other useful properties (e.g. damping) of the connections were derived.

The conducted experimental campaign refers to common typologies of two as-built timber-masonry connections, with five proposed retrofitting solutions. The presence of the as-built tested connections and the field of application of the strengthened versions are quite wide: the percentage of unreinforced masonry buildings in the Groningen gas field area can be quantified as 77% of the building stock [3]. Among these constructions, the tested connections and retrofitting measures pertain to the following building typologies:

• (Semi-)detached houses with flexible timber diaphragms: around 17% of the total

amount of unreinforced masonry buildings. In these constructions, realized before 1970, as-built connections consisting of mortar pocket or hook anchors can be found at floor(s) level and roof level.

• Terraced houses with flexible timber diaphragms: around 24% of the total amount of

unreinforced masonry buildings. In these constructions, realized before 1970, as-built connections consisting of mortar pocket or hook anchors can be found at floor(s) level and roof level.

• Terraced houses with rigid diaphragms: around 23% of the total amount of unreinforced

masonry buildings. In these constructions, realized after 1970, as-built connections consisting of mortar pocket or hook anchors can be found at roof level, where the roof was made with timber elements, while the other floors were made of concrete.

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2 Timber-masonry connection configurations to be tested

Overview of the testing campaign

2.1

In this test program only a limited number of configurations could be tested, therefore some possible options which can be frequently found in practice were chosen. Therefore, a proper selection of connection types was defined with input of consultants of BORG and VIIA [4], [6]: it was agreed to focus more on only one type of wall, combining characteristics of possible configurations that could be found in practice. Therefore, in the test campaign the connection with a single leaf clay brick masonry wall (which could be or could not be a part of a cavity wall) was investigated. The connection at roof level was considered, because this is the governing position in a building, due to the absence of ongoing masonry on top and the frequent presence of low quality or damaged masonry. The load was always applied in the weakest direction, i.e. parallel to the joist (and therefore orthogonal to the wall).

For each configuration 3 replicates were tested in a quasi-static cyclic test and 3 replicates with a high-frequency dynamic test. In addition to that, a monotonic test was performed as well for each option: this was necessary to determine the increasing amplitude of displacement to be progressively assigned during the cyclic tests.

Besides, it was decided to subdivide the testing schedule in two phases, which have different aims:

• In the first phase, as-built connections and some strengthening options already present in the catalogue of strengthening measures used by the consultants were tested [5].

• In the second phase, only strengthening options were tested, taking also into account inputs from consultants [6].

For both phases, samples having the same dimensions and boundary conditions as those tested in the previous pilot experimental campaign were realized [1]. In Figure 1 the principle of the standardised test specimens is shown: they consisted of masonry wall elements of approximately 980 mm by 600 mm. A 65x170 mm timber joist was inserted, having a length of approximately 1600 mm.

On the bottom steel beam a plywood plate was fastened, on which the bottom masonry layer was glued. A diagonal steel bracing (dashed in the figure) was connected to the bottom steel beam to support the timber beam at half of the length during construction. When the specimen was in the test set-up, this bracing was removed. After construction, two plywood plates were glued to the masonry walls over 150 mm length. These plywood plates were connected to a top steel beam. In this way, the masonry outside the connection area was supported horizontally at the top. If this was not done, there would be the possibility of flexural cracking of the masonry near the bottom; then mixed mechanisms could occur. Therefore, to ensure that the behaviour of the joist–masonry connection as such is studied, the horizontal support on the sides with the plywood plates at the top was realized.

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Configurations tested in phase 1

2.2

In the first testing phase both as-built and strengthened timber floors-masonry walls connections were studied. As-built connections are of importance for long-term purposes, because if the earthquake hazard progressively reduces in the future for some of the areas around Groningen, it will be useful to know their capacity in order to properly define the threshold beyond which a strengthening intervention is really needed. This is because the capacity of as-built joints might also be acceptable in lower seismic zones. The two as-built connections analysed in this first phase consisted of a simple masonry pocket (A) and of a joint realized with an hook anchor (B). These connections can be found in detached houses (both configurations) and terraced houses (mainly configuration B). For both connection types, 1 monotonic test (M), 3 quasi-static cyclic tests (QS) and 3 high-frequency dynamic tests (HFD) were performed. Therefore, a total of 14 samples were built.

The strengthening options were tested by properly reusing the samples realized for the as-built connections. The same type and number of tests as for the as-built joints was performed.

The first proposed refurbishment (C) consisted of a steel angle screwed to the joist and anchored to the masonry: this same configuration was studied in [1]. The advantage of this option is that it could be applied on the tested samples representing the as-built masonry pocket connection, because the weakness of this joint prevented the masonry from being damaged.

The second retrofitting method (D) is suitable for masonry which is damaged around the joist or for low quality masonry at the top of the wall, therefore for this option a further 80x80 mm joist was anchored only to sound masonry and then fastened to the existing beam by means of steel brackets. In this case, the samples with the hook anchor could be reused, because its presence caused the masonry to be damaged around the joists, as observed also in the past experimental campaign [1]. Before strengthening these samples, the hook anchor was disconnected from the timber joist.

Table 1 summarizes the aforementioned configurations and the nomenclature used in this document. In the following sections a deeper overview on each type of connection will be given, together with figures showing the various configurations.

Table 1. Tested timber-masonry connection types (first phase)

Configuration Description Test types Specimen names

A

As-built joist-wall connection. Clay bricks single leaf wall with only beam in mortar. See the introduction for the appearance of this connection in URM houses.

1 monotonic test A-M-1

3 quasi-static cyclic tests A-QS-1, A-QS-2, A-QS-3 3 high-frequency dynamic tests A-HFD-1, A-HFD-2, A-HFD-3

B

As-built joist-wall connection. Clay bricks single leaf wall with hook anchor.

See the introduction for the appearance of this connection in URM houses.

1 monotonic test B-M-1

3 quasi-static cyclic tests B-QS-1, B-QS-2, B-QS-3 3 high-frequency dynamic tests B-HFD-1, B-HFD-2, B-HFD-3

C

Strengthening option for joist-wall connections in sound masonry.

Configuration A retrofitted with an angle bracket screwed to the joist and anchored to the wall.

1 monotonic test C-M-1

3 quasi-static cyclic tests C-QS-1, C-QS-2, C-QS-3 3 high-frequency dynamic tests C-HFD-1, C-HFD-2, C-HFD-3

D

Strengthening option for joist-wall connections in damaged or low quality masonry. Configuration B retrofitted with a further joist anchored to sound masonry and fixed to the existing joist with steel brackets. The hook anchor is disconnected

1 monotonic test D-M-1

3 quasi-static cyclic tests D-QS-1, D-QS-2, D-QS-3 3 high-frequency dynamic tests D-HFD-1, D-HFD-2, D-HFD-3

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Configuration type A (as-built) 2.2.1

This first configuration consisted of a simple masonry pocket, therefore the resistance to horizontal loads was given only by friction between timber and mortar. The sample that was built representing this situation is depicted in Figure 2.

Figure 2 – Sample representing an as-built connection with simple masonry pocket. Configuration type B (as-built)

2.2.2

This second as-built configuration consisted of an hook anchor connecting the joist to the external side of the wall. The anchor was fastened to the joist by means of 4x55 mm nails and measured 240x240 mm with a diameter of 14 mm. The sample representing this situation is depicted in Figure 3.

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Configuration type C (strengthened) 2.2.3

This strengthening option was already tested during the previous pilot study and consisted of a Rothoblaas steel angle (thickness 3 mm, with 2 stiffeners to extend bending moment capacity) anchored to the masonry (10x95 mm anchors) and screwed to the joist (5x60 mm screws). The specimen representing this retrofitted joint is shown in Figure 4.

Figure 4 – Sample representing a strengthening option consisting of a steel angle screwed to the joist and anchored to the masonry. This retrofitting technique can be applied when the wall is not damaged.

Configuration type D (strengthened) 2.2.4

This strengthening option was intended to be used in presence of masonry which is damaged around the connection or for low quality masonry at the top rows of the wall. 10x165 mm anchors were used to fasten an additional joist to sound masonry and two steel brackets with 5x60 mm screws connected this joist to the existing one. The specimen representing the retrofitted connection is shown in Figure 5.

Figure 5 – Sample representing a strengthening option to be applied when the masonry is damaged around the joist. A further joist is anchored to sound masonry and then to the existing joist.

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_______________________________________________________________________________________ Final version 03/12/2019 For this last configuration, as can be seen from the figure, the hook anchor was also present because the damaged samples of configuration B were used to test this strengthening option, but it was disconnected from the timber joist before retrofitting these samples.

Configurations tested in phase 2

2.3

In the second testing phase only strengthened timber floors-masonry walls connections were studied, with three additional configurations. Therefore, a total of 21 tests were scheduled. The configurations were defined in cooperation with consultants BORG and VIIA [6].

The first proposed refurbishment (E) consisted of an hook anchor nailed to the joist and glued to the wall, after being placed in a previously realised incision on it. This connection type potentially allows to involve a larger portion of masonry in the resisting process, which can take place in both direction, unlike the as-built hook anchor connection system. In this sample, the influence of floor planks in the response was also studied.

The second retrofitting method (F) was realized by connecting the joist to the wall by means of two inclined screws. These were inserted into the joist after drilling in the masonry proper holes, which were filled with injected epoxy: the screws were therefore partly embedded in the glue and partly inserted in the joist. This intervention could be realized from outside: directly, in presence of gables, or just by removing a limited number of bricks from the outer leaf, for a cavity wall.

The third strengthening technique (G) is an additional configuration, and was added because it was part of the strengthening of the diaphragms as well [7]. When testing orthogonal to the joists, lateral blocking of them was realised when strengthening, and this was achieved by using short timber joists placed between each couple of floor beams. These additional joists are also usable as a connection to the masonry walls, as soon as they are anchored to them. Therefore, configuration G consisted of additional timber blocks placed on both sides of the joist. They were anchored to the masonry with mechanical fasteners and screwed to the existing joist. In this sample, the influence of floor planks in the response was also studied.

Table 2 summarizes the aforementioned configurations and the nomenclature used in this document. In the following sections a deeper overview on each type of connection will be given, together with figures showing the various configurations.

Table 2 – Timber-masonry connection types to be tested in the second phase

Configuration Description Test types Specimen names

E

Clay bricks single leaf wall. Strengthening with an hook anchor nailed to the joist and glued to the wall after being placed in a previously realised incision on it.

1 monotonic test E-M-1

3 quasi-static cyclic tests E-QS-1, E-QS-2, E-QS-3 3 high-frequency dynamic tests E-HFD-1, E-HFD-2, E-HFD-3

F

Clay bricks single leaf wall. Strengthening with two inclined screws inserted into the joist after drilling in the masonry proper holes, filled with epoxy.

1 monotonic test F-M-1

3 quasi-static cyclic tests F-QS-1, F-QS-2, F-QS-3 3 high-frequency dynamic tests F-HFD-1, F-HFD-2, F-HFD-3

G

Clay bricks single leaf wall. Strengthening with timber blocks placed on both sides of the existing joist, screwed to it and anchored to the wall.

1 monotonic test G-M-1

3 quasi-static cyclic tests G-QS-1, G-QS-2, G-QS-3 3 high-frequency dynamic tests G-HFD-1, G-HFD-2, G-HFD-3

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Configuration type E (strengthened) 2.3.1

This strengthening option consisted of a standard 240x240x14 mm hook anchor fastened to the joists by means of 4x55 mm nails and glued to the wall. The anchor was therefore embedded in the glue, which filled a 25x40 mm incision realized on the masonry. Beside the strengthening system, also the influence of the floor planks during the seismic motion was studied. This configuration is shown in Figure 6.

Figure 6 – Sample representing a strengthening option consisting of a hook anchor nailed to the joists and glued to the wall.

Configuration type F (strengthened) 2.3.2

In this configuration 7x180 mm screws were used to connect the joist and the wall. The screws were placed at an angle of 45 degrees both in the vertical and horizontal plane, in order to reach a sounder part of the masonry. Before inserting the screws in the timber joist, 10 mm holes were drilled in the wall and then filled with injected epoxy. This intervention presents an important advantage, because it can be performed from outside. This configuration is shown in Figure 7.

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_______________________________________________________________________________________ Final version 03/12/2019 Figure 7 – Sample representing a strengthening option consisting of screws fixed to the timber joist and embedded in epoxy for the whole length of the predrilled hole in the masonry.

Configuration type G (strengthened) 2.3.3

This strengthening option was realized with 65x170 mm timber blocks placed on both sides of the joist (in practice they would be placed between each couple of joists). The blocks were firstly fixed to the existing joist by means of 5x70 mm screws drilled at an angle of 45 degrees, and then fastened to the masonry with 10x165 mm mechanical anchors. However, since this intervention involves in practice also the diaphragm, it was important to recreate the same conditions: hence, beside the presence of the planks, fixed to the joist with 3x65 mm nails, also an additional plywood panel overlay was placed on them and screwed through the planks inside the blocks, as it would happen in practice and as it was performed for the strengthening (sample DFpar-4 in [7]). This ensured that all the elements of the connections, which were involved in the transfer of the horizontal load, were present.

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_______________________________________________________________________________________ Final version 03/12/2019 Figure 8 – Sample representing a strengthening option consisting of timber blocks anchored to the masonry and screwed to the joist and to the plywood panel overlay used for the diaphragms’ strengthening.

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3 Testing replicated joist-masonry connections

General

3.1

For the testing of connections under seismic behaviour 3 types of tests were performed:

1. Monotonic tests. In this type of test the displacement is gradually increased and the force that is

delivered by a hydraulic jack to achieve this is measured. This test gives an indication of the backbone including the softening part that can be expected from quasi-static cyclic tests. The monotonic test is therefore necessary to determine the displacements steps in the quasi-static cyclic tests.

2. Quasi-static cyclic tests. In this type of tests the specimens are subjected to quasi-static

reversed-cycles. The tests are displacement based and the force is recorded. In addition to the monotonic ones, these tests show the strength reduction within the runs of a cycle (the runs in an cycle have the same maximum displacement) and show the energy dissipation within the cycles: therefore, an indication of the damping can be retrieved.

3. High-frequency dynamic tests. In this type of test the specimens are subjected to a high frequency

signal and a time period comparable with an earthquake in practice. The corresponding displacement is applied to the specimen and the force in the jack is recorded. This test gives specific information on the behaviour of the specimen under the chosen frequency and accelerations, such as its capacity, its energy dissipation and again the damping. In this test also the effect of inertia forces is included.

Monotonic tests

3.2

ISO 16670 [8] indicates to perform a monotonic test to determine the ultimate displacement vu. (see Figure

9). This monotonic test is needed to determine the cyclic scheme of the quasi-static cyclic tests and therefore only one indicative test has to be done, in the most vulnerable direction. Thus, this test was carried out at a constant rate of slip of 0.3 mm/s and it was performed once for each configuration A, B, C, D as a starting point before the other tests.

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Quasi-static cyclic tests

3.3

The specimens were loaded quasi-static reversed-cyclic in accordance with ISO 16670 [8]. This standard was preferred to EN 12512 [9] because the amplitude of the cycles is determined from the ultimate displacement obtained in a monotonic test of the connection. Instead, EN 12512 refers to a conventional yielding displacement, which could be not fully representative of the connections’ behaviour, and at the same time more difficult to be identified, because of the nonlinearities that take place from the very beginning of the load-slip monotonic curves on these kind of joints. This does not have any influence in the test results, because based on the test procedure of ISO 16670 it is also possible to report the test data according to the current version of EN 12512.

The test was carried out at a constant rate of slip of 0.3 mm/s. As previously stated, ISO 16670 suggests to perform a monotonic test to determine the ultimate displacement vu and with this the cycles are defined

according to the loading scheme reported in Table 3. The principle of the cyclic loading scheme is given in figure 10; in every cycle 3 runs are applied and, as can be seen, the final loading scheme depends on the results of the monotonic test. 3 tests of this type were performed for each configuration.

Table 3 – Loading scheme for the tested specimens

Cycle Number of runs Amplitude _{% of}_l Rate Duration

u mm/s s

1

3

1.25

0.3

10

2

3

2.5

0.3

20

3

5

0.3

40

4

3

7.5

0.3

60

5

3

10

0.3

80

6

3

20

0.3

160

7

3

40

0.3

320

8

3

60

0.3

480

9

3

80

0.3

640

10

3

100

0.3

800

11

3

120

0.3

960

12

3

140

0.3 1120

13

3

160

0.3 1280

14

3

180

0.3 1440

15

3

200

0.3 1600

16

3

₂₂₀

_0.3

₁₇₆₀

17

3

₂₄₀

_0.3

₁₉₂₀

18

3

260

0.3 2080

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Figure 10: Graph of the cyclic loading scheme [8]

High-frequency dynamic tests

3.4

Introduction 3.4.1

There are no specific standards for dynamic tests. With these tests the effect of inertial forces can be taken into account. The dynamic tests were performed by excitation of the specimen with a high-frequency displacement generated by the hydraulic jack.

These dynamic tests can be of importance not only because they can take into account inertia forces, but also for the following reasons:

• They can provide a benchmark for numerical models in which normally the properties of the connections determined with the quasi-static tests are inserted; then in the model time-history analyses are run and the obtained results can be compared to the outcomes of these dynamic tests.

• The effect of a sudden signal like the typical Groningen earthquakes can be evaluated: it might happen that a connection which presents good properties after being tested in a quasi-static cyclic way could have a much worse performance because for instance it is not able to produce any dissipation due to the sudden load and therefore immediately damages the masonry.

• They can be of help in the correct interpretation of quasi-static tests, because the strength at the collapse and the displacement capacity of the connections may differ between the two test types. This is of course a way to determine until which point quasi-static tests can be considered reliable. • A correlation between the properties obtained with quasi-static and dynamic tests could be

established.

Dynamic tests require however a careful selection of the parameters which are contained in the signal. These properties were evaluated by taking into account the accelerations and frequencies to which the connections are subjected in reality; the values were derived from shaking table tests on typical Dutch buildings [10] and recorded signals from Groninger earthquakes (which are used as input for time history analyses).

The methodology followed for the dynamic tests was to start with a very weak signal and to progressively repeat it, increasing its amplitude until collapse was reached. More suitable sensors, such as accelerometers, were adopted to have a better characterization of each sample’s behaviour. This will be furtherly addressed in the next chapter, in which the test setup and measurement plan is presented.

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Choice of the reference signal 3.4.2

The chosen dynamic signal consisted of a recorded displacement history of a timber-masonry connection during a shaking table test performed at EUCENTRE [10]. This signal was adopted for the experimental campaign because of its consistency not only with the real expected dynamic behaviour, but also with the preliminary results of the past campaign.

The signal was scaled, because on the one hand it is worth studying the dynamic response of the connection from the very initial stages, on the other also higher forces or displacements might occur in reality, if the building is less dissipative or a weaker connection is present.

Figure 11 shows the reference displacement signal that was used as input in the dynamic tests, while Table 4 reports the various runs which were performed, together with the correspondent applied scale. A maximum displacement of 20 mm was considered, because in practice this would already mean an overall heavily damaged building. However, since the capacity of the actuator allowed to perform a further step of 24 mm, also this is included in Table 4 and was adopted for the strengthened samples to represent a collapse situation.

Figure 11 – Signal from EUCENTRE test [10] adopted for the high-frequency dynamic tests -1.5 -1 -0.5 0 0.5 1 1.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 D is p la cemen ts ( mm) Time (s)

Displacement vs. Time

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_______________________________________________________________________________________ Final version 03/12/2019 Table 4 – Detail of the runs performed by scaling the reference signal. Run 15 and 16 were performed only for strengthened configurations.

Run # % scaling of reference signal Maximum expected _{displacement (mm)}

1 25 0.25 2 50 0.5 3 75 0.75 4 100 1 5 200 2 6 300 3 7 400 4 8 500 5 9 600 6 10 700 7 11 800 8 12 900 9 13 1000 10 14 1500 15 15 2000 20 16 2400 24

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4 Test setup

Overview on the setup

4.1

Figure 12a shows a 3D view of the test setup which was adopted. The setup was composed of a static part, fastened to the existing laboratory frame, and a moving part in which the specimen was placed. The sliding of the moving part was ensured by rollers, while possible rotations of the sample were prevented by proper plates and wheels close to the rollers and enabling only the horizontal movements transmitted by the jack, which connected the static part of the setup to the bottom beam on which the wall was built.

As in the previous experimental campaign, the wall was surrounded by a steel frame, to guarantee its stability. This frame was also furtherly connected with bracings (not drawn) to the edges of the two sliding horizontal steel beams on rollers, in order to ensure better stability against possible vibrations. A weight of 100 kg was hanged at mid span on the joist, to represent the loads acting on that portion of floor around the connection in practice (0.5 kN).

In order to guarantee an effective action of the hydraulic jack, the column on which it was clamped was furtherly braced to the bottom frame. This bracing, not shown in Figure 12a, is represented in Figure 12b. In this setup the displacements were not imposed directly to the joist, but to the wall. In this way it was possible to use a single setup for all the three types of test. For monotonic or quasi-static cyclic tests there was no difference in moving the wall or the joist, but for dynamic tests it was important to represent how the seismic accelerations are transferred in practice. A signal transmitted from the bottom takes correctly into account inertial forces, because in a real situation a high amount of mass is given by the walls, which are moving due to the earthquake, forcing in turn also the floor’s joists to move.

In order to record the force that the single connection is able to transfer, a load cell was connected to the timber joist and to a stiff frame in the rear part of the setup.

Measurement plan

4.2

Figure 16 shows the adopted measurement plan, while Table 5 contains a more detailed overview on the adopted sensors and measuring points: as a base configuration, only potentiometers were used. For strengthened configurations which needed more investigation, a larger number of sensors was adopted, to detect also local mechanisms: for configurations C and D these additional sensors were:

• For configuration C, beside sensor 3, other two sensors were measuring the deformation of the steel angle and the relative displacement between this and the joist (displacement of the screws); this instrumentation is depicted in Figure 13.

• For configuration D, beside sensor 3, one sensor was measuring the sliding of the joist with respect to the additional one placed for strengthening, and other two sensors were measuring the displacement of the anchors with respect to the wall; this instrumentation is depicted in Figure 14a.

• For configuration E, beside sensor 3, one sensor was measuring the sliding of the hook anchor with respect to the joist, one was measuring the sliding of the floor planks and an additional one the sliding of the joist with respect to the wall; this instrumentation is depicted in Figure 14b. • For configuration F, beside sensor 3, two sensors were measuring the sliding of the joist with

respect to the wall on both sides of the joist itself; this instrumentation is depicted in Figure 15a. • For configuration G, beside sensor 3, one sensor was measuring the sliding of the floor planks on

the joist, and other two the displacement of the additional timber blocks with respect to the wall; this instrumentation is depicted in Figure 15b.

Only for high frequency dynamic tests also accelerometers were used (maximum capacity 2.5g), to have a more accurate detection of the connection’s response due to a sudden solicitation.

A quasi-static test and a dynamic test for both configuration E and F were also analysed by means of DIC (Digital Image Correlation) technique. The specifications of the adopted system are given in Table 6. The results of this additional measurement system will be reported in the pertaining sections.

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(a)

(b)

Figure 12 – (a) Setup for testing of timber joist-masonry wall connections; (b) Plan, lateral and front view of the setup and measurement plan: LVDTs are depicted in red, while accelerometers are represented in blue

1 3 2 4, 5, 6 7, 8, 9 A B C D E 10, 11 12, 13 1 3 2 A B,C4, 7 5, 8 6, 9 C B 4 5 6 7 8 9 D,E D E 10, 12 11, 13 10 11 12 13

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Table 5 - Overview of the measuring points and sensor types used in the test.

No. Description Sensor Type Stroke (mm)

1 Horizontal actuator 100 kN – load and displacement Load cell and HBM LVDT +/-100 2 Horizontal displacement between steel plate connecting load cell _{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 (centre) Linear potentiometer +/-50 5 Out-of-plane displacement at half height of the masonry wall _(centre) Linear potentiometer +/-25 6 Out-of-plane displacement at the bottom of the masonry wall _(centre) Linear potentiometer +/-5 7 Out-of-plane displacement at the top of the masonry wall (side) Linear potentiometer +/-50 8 Out-of-plane displacement at half height of the masonry wall _(side) Linear potentiometer +/-25 9 Out-of-plane displacement at the bottom of the masonry wall _(side) Linear potentiometer +/-5 10 Absolute displacement of the sample (top right) Linear potentiometer +/-100 11 Absolute displacement of the sample (bottom right) Linear potentiometer +/-100 12 Absolute displacement of the sample (top left) Linear potentiometer +/-100 13 Absolute displacement of the sample (bottom left) Linear potentiometer +/-100

A Acceleration induced at joist-wall interface _{(only for dynamic tests)} Accelerometer - B Acceleration induced on the wall, opposite side of the connection _{(only for dynamic tests)} Accelerometer - C Acceleration induced at the side of the wall _{(only for dynamic tests)} Accelerometer - D Acceleration induced at the bottom left side _{(only for dynamic tests)} Accelerometer - E Acceleration induced at the bottom right side _{(only for dynamic tests)} Accelerometer -

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(a)

(b)

Figure 14 – Further sensors applied for configuration D (a) and E (b)

(a)

(b)

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Table 6 - Overview of the main properties of the adopted DIC measuring system.

Aramis 2d/3d 12M system

Camera resolution 2x (4096x3000) pixels

Frame rate 25 up to 100 fps

Measuring area (20x15) up to (5000x4000) mm2

Adopted measuring volume (MV) (750x610x610) mm3

Measuring distance 697 mm

Diameter of the adopted reference point markers 3 mm

Type of pattern Random pattern sprayed with black matt colour

In addition to the measurement plan depicted in Figure 12a, Figures 16 and 17 show the sign convention used throughout the document and the two most signifying parameters that were recorded: the relative displacement between joist and wall (measured by sensor 3) and the maximum out-of-plane displacement of the wall (measured by sensor 4).

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_______________________________________________________________________________________ Final version 03/12/2019 Figure 16 – Sign convention and signifying parameters when pulling the connection: both initial and

deformed state are shown.

Figure 17 – Sign convention and signifying parameters when pushing the connection: both initial and deformed state are shown.

Jack pushing

Pulling in the connection

(+)

Relative displacement

between joist and wall

(Sensor 3)

Wall out-of-plane

displacement

(Sensor 4)

No load applied

Jack pulling

Pushing in the connection

(-)

Relative displacement

between joist and wall

(Sensor 3)

Wall out-of-plane

displacement

(Sensor 4)

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5 Test results

General

5.1

This section contains all the test results obtained in both phases. For each configuration, the discussion is organized as follows:

• Firstly, the preliminary monotonic test results are reported with graphs and pictures of the sample; • Secondly, the three cyclic tests are presented. In each section, a picture of the sample and the

hysteretic cycles, also in comparison to the wall’s out-of-plane displacement, are reported. When this is applicable, pictures of detected damages or failure modes will be present. For strengthened configurations also the hysteretic cycle in the very initial phases is reported;

• The three dynamic tests are then reported, with a picture of the samples, graphs of the initial runs and of the whole set of them until failure. When this is relevant, pictures of detected damages or failure modes will be present.

• After the test results, two further sections contain some general observation on both cyclic and dynamic tests. These are mainly related to how the specific configuration behaved (e.g. displacement of screws, deformation of steel bracket, presence of wood embedment, frictional response, failure modes…)

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Configuration A

5.2

Specimen A-M-1 5.2.1

The sample was loaded monotonically with a 0.3 mm/s rate. Since configuration A was characterized by a simple mortar pocket in the masonry, the behaviour was frictional, with a peak of force of 0.4 kN at the beginning and a sliding with no softening (Figure 18a).

The test was stopped at 50 mm displacement and no signs of failure were observed: the timber joist was simply slided inside its socket (Figure 18b). Given the fact that in practice such a large displacement would imply a total collapse of the global building, it was chosen to adopt an ultimate displacement of 30 mm to calculate the amplitude of the cycles for the quasi-static tests.

(a)

(b)

Figure 18 – Force-displacement graph for sample A-M-1 (a); sliding of the joist in the mortar pocket (b) -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -10 0 10 20 30 40 50 60 Fo rc e o n th e c on nec tio n ( kN )

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Specimen A-QS-1 5.2.2

Based on the ultimate displacement obtained from the test on sample A-M-1, this specimen (Figure 19) was tested cyclically according to the loading protocol in Table 3. The cyclic test confirmed the response obtained through the monotonic one, therefore the sample showed a mainly frictional behaviour characterized by a peak force of 0.5 kN in both loading directions (Figure 20).

No signs of failure were detected on the wall, and this is confirmed by Figure 21, showing that the top part of the specimen close to the masonry pocket experienced no displacement in that area, although the level of displacement reached by the joist was relatively high.

Like in the previous pilot campaign, two values of stiffness were derived from the test results: an initial one, representing the elastic phase of the connection, and one at 2 mm of displacement of the joint, when still the wall did not exhibit severe damage.

In this case, the stiffness at the first cycle’s peak was 3.06 kN/mm, while at 2 mm displacement this value reduced to 0.24 kN/mm.

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Figure 20 – Hysteretic cycle obtained for the connection in sample A-QS-1

Figure 21 – Comparison between the recorded cycles for the connection and for the wall for sample A-QS-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

Displacement between joist and wall (mm)

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Connection Wall

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Specimen A-QS-2 5.2.3

Based on the ultimate displacement obtained from the test on sample A-M-1, this specimen (Figure 22) was tested cyclically according to the loading protocol in Table 3. the sample showed a mainly frictional behaviour characterized by a peak force of approximately 0.5 kN (Figure 23) for both loading directions. No signs of failure were detected on the wall, and this is confirmed by Figure 24, showing that the top part of the specimen close to the masonry pocket experienced no displacement in that area, although the level of displacement reached by the joist was relatively high.

In this case, the stiffness at the first cycle’s peak was 4.40 kN/mm, while at 2 mm displacement this value reduced to 0.22 kN/mm.

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Figure 24 – Comparison between the recorded cycles for the connection and for the wall for sample A-QS-2 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

-0.6 -0.4 -0.2 0 0.2 0.4 0.6 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Connection Wall

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Specimen A-QS-3 5.2.4

Based on the ultimate displacement obtained from the test on sample A-M-1, this specimen (Figure 25) was tested cyclically according to the loading protocol in Table 3. the sample showed a mainly frictional behaviour characterized by a peak force of 1.0 kN (Figure 26) in both loading directions. This peak force was higher compared to the other tests probably because the joist was slightly twisted: this can be noticed also from Figure 25 and it could have given a higher contribution in the resistance, because also the wall itself was slightly moving more than the other two ones (Figure 27).

No signs of failure were detected on the wall, and this is confirmed by Figure 27, showing that the top part of the specimen close to the masonry pocket experienced a very limited displacement in that area, although the level of displacement reached by the joist was relatively high.

In this case, the values of stiffness are higher as well due to the twisted joist: at the first cycle’s peak the stiffness was 9.06 kN/mm, while at 2 mm displacement this value reduced to 0.65 kN/mm.

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Figure 27 – Comparison between the recorded cycles for the connection and for the wall for sample A-QS-3 -1.5 -1 -0.5 0 0.5 1 1.5 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

-1.5 -1 -0.5 0 0.5 1 1.5 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Series1 Wall

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Specimen A-HFD-1 5.2.5

This sample, depicted in Figure 28, was subjected to the reference dynamic signal with the amplitude increased from 0.25 until 15 mm. Figure 29 shows the evolution of the behaviour of the connection until half of the total number of runs (initial phases), while Figure 30 depicts the response until the final amplitude of 15 mm. The behaviour was mainly frictional, but slightly higher forces were reached compared to the quasi-static tests.

The recorded peak force was 0.8 kN in the pulling direction, 1.0 kN in the pushing one. The initial stiffness was quantified in 12.03 kN/mm, while at 2 mm displacement this value reduced to 0.36 kN/mm. The wall appeared to be sound after testing, and no signs of failure were detected.

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Figure 29 – Dynamic response of sample A-HFD-1 until half of the total number of runs (0.25 – 5 mm)

Figure 30 – Dynamic response of sample A-HFD-1 until the final run (0.25 – 15 mm) -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 -6 -4 -2 0 2 4 6 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.5 0.75 1 2 3 4 5 -1.5 -1 -0.5 0 0.5 1 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.5 0.75 1 2 3 4 5 6 7 8 9 10 15

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This sample, depicted in Figure 31, was subjected to the reference dynamic signal with the amplitude increased from 0.25 until 15 mm. Figure 32 shows the evolution of the behaviour of the connection until half of the total number of runs (initial phases), while Figure 33 depicts the response until the final amplitude of 15 mm. The behaviour was mainly frictional, and in this case the obtained values reflected those from quasi-static tests.

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Figure 33 – Dynamic response of sample A-HFD-2 until the final run (0.25 – 15 mm) -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 -6 -4 -2 0 2 4 6 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 15.00

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This sample, depicted in Figure 34, was subjected to the reference dynamic signal with the amplitude increased from 0.25 until 15 mm. Figure 35 shows the evolution of the behaviour of the connection until half of the total number of runs (initial phases), while Figure 36 depicts the response until the final amplitude of 15 mm. The behaviour was mainly frictional, and in this case the obtained values were slightly higher compared to those from quasi-static tests.

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Figure 36 – Dynamic response of sample A-HFD-3 until the final run (0.25 – 15 mm) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 -6 -4 -2 0 2 4 6 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 -20 -15 -10 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 15.00

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General observations on cyclic behaviour of configuration A 5.2.8

From the obtained test results it was clear that the response of configuration A was dominated by friction, as expected. The resisting force could however be slightly increased due to a not perfectly straight shape of the joist, but in any case this joint type was characterized by very low strength and stiffness. No damages in the walls or other failure mechanisms were observed.

General observations on dynamic behaviour of configuration A 5.2.9

The obtained test results for the high-frequency dynamic tests confirmed what was obtained with the quasi-static ones: a behaviour mainly dominated by friction and a very low capacity of the connection. Interestingly, slightly higher values of load were obtained due to the dynamic behaviour of the walls. Again, no damages in the walls or other failure mechanisms were detected.

The values obtained through the quasi-static tests appeared to be reliable in safely predicting also the dynamic response of the connection: as an example, Figure 37 can be considered, in which a comparison of the two tests is given for sample A-QS-1 and A-HFD-1.

Figure 37 – Comparison between quasi-static and dynamic behaviour of configuration A -1.5 -1 -0.5 0 0.5 1 -30 -20 -10 0 10 20 30 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.5 0.75 1 2 3 4 5 6 7 8 9 10 15 QS

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Configuration B

5.3

Specimen B-M-1 5.3.1

The sample was loaded monotonically with a 0.3 mm/s rate. Since configuration B was characterized by the presence of the hook anchor, the wall was expected to be more involved in the resisting process when pulling the connection, with some possible damages to the wall itself. At the same time, since the tested samples representing configuration B had to be strengthened in order to test configuration D, it was not appropriate to reach a too large level of damage in the wall.

The test was therefore stopped at 30 mm displacement of the actuator (corresponding to 17 mm displacement of the connection and 7.4 kN peak force) and some cracks in the wall were observed around the connection but not in the part of the wall in which the subsequent strengthening intervention of configuration D should have been applied (Figure 38a). In this case the direction correspondent to the pulling of the anchor was chosen, because in pushing the response would have been quite similar to the one of sample A-M-1.

The behaviour of the connection (Figure 38b) was characterized by an initial phase in which only friction was present as resisting process, while then the pressure of the anchor towards the masonry led to an increase in force and stiffness until a peak, after which the wall was cracked around the anchor. The following increase in stiffness was given by a further pressure of the anchor in the lower part of the wall. The ultimate displacement adopted for the calculation of the amplitude of the cycles was therefore 15 mm.

(a)

(b)

Figure 38 – Cracks around the connection (a); force-displacement graph for sample B-M-1 (b) -1 0 1 2 3 4 5 6 7 8 -5 0 5 10 15 20 Fo rc e o n th e c on nec tio n ( kN )

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Specimen B-QS-1 5.3.2

Based on the ultimate displacement obtained from the test on sample B-M-1, this specimen (Figure 39) was tested cyclically according to the loading protocol in Table 3. The sample showed a quite asymmetric behaviour, because of the much higher resistance developed by the anchor when the joist was pulled (Figure 40). This caused also the wall to be damaged around the connection in this same direction (Figure 41 and 42), but the rest of the wall did not exhibit further damage.

When pushing the joist the recorded peak force was 1.1 kN, while in the opposite direction 5.1 kN were reached.

The initial stiffness shown by this sample was quantified as 6.51 kN/mm, while at 2 mm displacement this value reduced to 0.44 kN/mm.

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Figure 40 – Hysteretic cycle obtained for the connection in sample B-QS-1

Figure 41 – Comparison between the recorded cycles for the connection and for the wall for sample B-QS-1

Figure 42 – Crack pattern after the test around the hook anchor -2 -1 0 1 2 3 4 5 6 -10 -5 0 5 10 Fo rc e o n th e c on nec tio n ( kN )

-2 -1 0 1 2 3 4 5 6 -15 -10 -5 0 5 10 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Connection Wall

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Specimen B-QS-2 5.3.3

Based on the ultimate displacement obtained from the test on sample B-M-1, this specimen (Figure 43) was tested cyclically according to the loading protocol in Table 3. The sample showed a quite asymmetric behaviour, because of the much higher resistance developed by the anchor when the joist was pulled (Figure 44). This caused also the wall to be damaged around the connection in this same direction (Figure 45 and 46) but the rest of the wall did not exhibit further damage.

When pushing the joist the recorded peak force was 1.5 kN, while in the opposite direction 6.6 kN were reached.

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Figure 46 – Crack pattern after the test around the hook anchor

-2 -1 0 1 2 3 4 5 6 7 8 -15 -10 -5 0 5 Fo rc e o n th e c on nec tio n ( kN )

-2 -1 0 1 2 3 4 5 6 7 8 -15 -10 -5 0 5 10 15 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Connection Wall

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Specimen B-QS-3 5.3.4

Based on the ultimate displacement obtained from the test on sample B-M-1, this specimen (Figure 47) was tested cyclically according to the loading protocol in Table 3. The sample showed an asymmetric behaviour, because of the much higher resistance developed by the anchor when the joist was pulled (Figure 48). This caused also the wall to be damaged around the connection in this same direction (Figure 49 and 50), while the rest of the wall did not exhibit further damage.

It should be noticed that, contrarily to what was observed for samples B-QS-1 and 2, the pulling direction exhibited a high peak of force instead of a frictional behaviour. This was due to a particle of mortar blocking the sliding of the anchor and forcing the wall to resist in this direction as well.

When pushing the joist the recorded peak force was therefore 5.6 kN, while in the opposite direction 5.1 kN were reached. However, before the particle’s disturbance the peak force was 1.1 kN when pulling the connection, similarly to what was obtained for the previous cases.

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Figure 50 – Crack pattern after the test around the hook anchor

-8 -6 -4 -2 0 2 4 6 8 -15 -10 -5 0 5 10 15 Fo rc e o n th e c on nec tio n ( kN )

-8 -6 -4 -2 0 2 4 6 8 -15 -10 -5 0 5 10 15 Fo rc e o n th e c on nec tio n ( kN ) Displacement (mm) Connection Wall

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Specimen B-HFD-1 5.3.5

This sample, depicted in Figure 51, was subjected to the reference dynamic signal with the amplitude increased from 0.25 until 15 mm. Figure 52 shows the evolution of the behaviour of the connection until half of the total number of runs (initial phases), while Figure 53 depicts the response until the final amplitude of 15 mm. The behaviour was quite asymmetric, and like in the quasi-static tests high values of force could be obtained only when pulling the connection.

The recorded peak force was 3.7 kN in the pulling direction, 1.3 kN in the pushing one. The value in pulling does not correspond to the very maximum capacity of the connection because the wall had not to be too damaged for the subsequent strengthening. However, this peak corresponded to an already high value of displacement for a single connection, which would lead in practice to an heavily damaged building. Therefore, this peak force was anyway suitable for the characterization of the connection. The initial stiffness was quantified in 8.26 kN/mm, while at 2 mm displacement this value reduced to 0.74 kN/mm. The wall exhibited small cracks around the hook anchor but the damage was less compared to the quasi-static tests.

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Figure 52 – Dynamic response of sample B-HFD-1 until half of the total number of runs (0.25 – 5 mm)

Figure 53 – Dynamic response of sample B-HFD-1 until the final run (0.25 – 15 mm) -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 -6 -4 -2 0 2 4 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.5 0.75 1.00 2.00 3.00 4.00 5.00 -2 -1 0 1 2 3 4 5 -20 -15 -10 -5 0 5 10 15 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.5 0.75 1.00 2.00 3.00 4.00 5.00 600 7.00 8.00 9.00 10.00 15.00

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Specimen B-HFD-2 5.3.6

Sample B-HFD-2, depicted in Figure 54, was subjected to the reference dynamic signal with the amplitude increased from 0.25 until 15 mm. Figure 55 shows the evolution of the behaviour of the connection until half of the total number of runs (initial phases), while Figure 56 depicts the response until the final amplitude of 15 mm. The behaviour was quite asymmetric, and like in the quasi-static tests high values of force could be obtained only when pulling the connection.

The recorded peak force was 3.9 kN in the pulling direction, 1.0 kN in the pushing one. The initial stiffness was quantified in 5.95 kN/mm, while at 2 mm displacement this value reduced to 0.35 kN/mm. Also in this case, the wall exhibited small cracks around the hook anchor but the damage was less compared to the quasi-static tests.

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Figure 55 – Dynamic response of sample B-HFD-2 until half of the total number of runs (0.25 – 5 mm)

Figure 56 – Dynamic response of sample B-HFD-2 until the final run (0.25 – 15 mm) -1.5 -1 -0.5 0 0.5 1 1.5 -6 -4 -2 0 2 4 6 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 -2 -1 0 1 2 3 4 5 -20 -15 -10 -5 0 5 10 15 Fo rc e o n th e c on nec tio n ( kN )

0.25 0.50 0.75 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 15.00

Monotonic, cyclic and dynamic behaviour of timber-masonry connections

Monotonic, cyclic and dynamic behaviour of timber-masonry connections

Mirra, Michele; Ravenshorst, Geert

Publication date

2019

Document Version

Final published version

Citation (APA)

Mirra, M., & Ravenshorst, G. (2019). Monotonic, cyclic and dynamic behaviour of timber-masonry

connections. Delft University of Technology.

Important note

To cite this publication, please use the final published version (if applicable).

Please check the document version above.

TU Delft research program 2018/2019 – WP2

MONOTONIC, CYCLIC AND DYNAMIC

BEHAVIOUR OF TIMBER-MASONRY

CONNECTIONS

Authors: Michele Mirra, Geert Ravenshorst

Table of Contents

1 Introduction

2 Timber-masonry connection configurations to be tested

Overview of the testing campaign

2.1

Configurations tested in phase 1

2.2

Configurations tested in phase 2

2.3

3 Testing replicated joist-masonry connections

General

3.1

Monotonic tests

3.2

Quasi-static cyclic tests

3.3

1

1.25

0.3

10

2

2.5

0.3

20

3

5

0.3

40

4

7.5

0.3

60

5

10

0.3

80

6

20

0.3

160

7

40

0.3

320

8

60

0.3

480

9

80

0.3

640

10

100

0.3

800

11

120

0.3

960

12

140

₂₂₀

_0.3

₁₇₆₀

₂₄₀

_0.3

₁₉₂₀