Heriot-Watt University Research Gateway Out-of-plane behaviour of masonry specimens strengthened with ECC under impact loading Citation for published version: Pourfalah, S, Cotsovos, DM, Suryanto, B & Moatamedi, M 2018, 'Out-of-plane behaviour of masonry specimens strengthened with ECC under impact loading', Engineering Structures, vol. 173, pp. 1002-1018. https://doi.org/10.1016/j.engstruct.2018.06.078 Digital Object Identifier (DOI): 10.1016/j.engstruct.2018.06.078 Link: Link to publication record in Heriot-Watt Research Portal Document Version: Peer reviewed version Published In: Engineering Structures General rights Copyright for the publications made accessible via Heriot-Watt Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy Heriot-Watt University has made every reasonable effort to ensure that the content in Heriot-Watt Research Portal complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 26. Sep. 2021 1 Out-of-plane behaviour of masonry specimens strengthened with 2 ECC under impact loading 3 4 Saeed Pourfalah (PhD, CEng, MICE, AFHEA)* 5 Senior Engineer for Structural Concrete 6 Ancon Building Products 7 President Way, President Park 8 Sheffield, S47UR 9 Tel.: +44(0)1142381247, Fax: +44(0)1142381240 10 E-mail: [email protected] 11 12 13 Demetrios M. Cotsovos (Dipl Ing, MSc, DIC, PhD, CEng) 14 Associate Professor 15 Institute of Infrastructure and Environment 16 Heriot-Watt University, 17 Edinburgh, EH14 4AS, UK 18 Tel.: +44 (0)131 451 8372 19 E-mail: [email protected] 20 21 Benny Suryanto 22 Assistant Professor, 23 Institute of Infrastructure and Environment 24 Heriot-Watt University, 25 Edinburgh, EH14 4AS, UK 26 E-mail: [email protected] 27 28 29 Professor Mojtaba Moatamedi 30 Faculty of Engineering Science and Technology, 31 UiT The Arctic University of Norway 32 E-mail: [email protected] 33 34 35 36 37 38 * Corresponding Author 39 1 40 Abstract: The work described herein sets out to investigate experimentally (via drop-weight 41 testing) the out-of-plane behaviour of beam-like masonry specimens under impact loading 42 when strengthened with a thin layer of engineered cementitious composite (ECC). The 43 subject prismatic specimens essentially consist of a stack of ten bricks connected with mortar 44 joints which are subjected to four-point bending tests. The impact load is applied via a steel 45 mass allowed to fall from a certain height (drop-test). Specimens are subjected to consecutive 46 impact tests until their collapse. Each specimen is strengthened by applying a thin ECC layer 47 to the lower face of the prism (acting in tension) or to both, upper and lower, faces (acting in 48 compression and tension respectively). These specimens are considered to provide a 49 simplistic representation of a vertical strip of a masonry infill wall subjected to the out-of- 50 plane actions characterised by high loading rates and intensities (associated with impact and 51 blast problems). The drop-weight tests reveal that the proposed strengthening method 52 successfully increases the load-carrying capacity of the subject specimens compared to that 53 observed under equivalent static testing, allowing them to absorb more effectively the energy 54 introduced during impact testing without the production of debris. Nevertheless, it is 55 important to mention that the behaviour of the ECC layer during impact testing is 56 characterised by the formation of more localised and wider cracks compared to those 57 observed under equivalent static testing. 58 59 Keywords: engineered cementitious composite, masonry, out-of-plane behaviour, 60 retrofitting, failure mode, impact loading, dynamic response, drop-weight testing, loading 61 rate, strain rate. 62 63 64 65 2 66 Notation ε Strain 휀̇ Strain rate δ Displacement maxPd Peak value of impact load generated during drop-weight testing maxPs Load carrying capacity of individual specimens established under static loading 푚푎푥푃̅푠 A verage value of maxPs established for different specimens maxd s Peak mid-span deflection exhibited by individual specimen under static testing ̅ 푚푎푥푑푠 Average value of maxd s established for different specimens maxRd Peak reaction force generated when conducting impact tests on individual specimen maxdd Peak value of mid-span deflection measured when conducting impact tests on individual specimen 푃̇ The loading rate measured under drop weight tests Pd I ntensity of contact (impact) load under drop weight testing Ps,cr Load at which cracks start to develop on individual specimen when subjected to static testing 푃̅푠,푐푟 Average value of Ps,cr established for different specimens Rd Reaction force generated under drop weight testing resdd Residual value of deflection measured after each drop weight test tR Tim e at which the peak reaction load attended under drop weight testing tP Time at which the peak impact load attended under drop weight testing td Total time duration of impact loads under drop weight testing ΔtP-R Delay which measured between the peak impact load and peak reaction load under drop weight testing 67 68 69 70 71 3 72 1. Introduction 73 The available experimental and numerical information clearly shows that existing masonry 74 infill walls significantly contribute to the redistribution of the internal actions developing 75 within the structural elements of the frame, resulting a considerable influence on the 76 performance of framed structures [1-3]. Infill walls can be subjected to the out-of-plane loads 77 due to various scenarios including wind, hurricanes, earthquakes, impact explosion and blast 78 impact which are characterised by different forms, loading rates and intensities. It is evident 79 that the application of the out-of-plane loads against infill walls caused a critical damage 80 result in a partial or full failure of framed structures [4, 5]. Studying of out-of-plane 81 performance of masonry infill walls under static and dynamic loads ranging from quasi-static 82 to blast impact highlighted that the infill wall’s response is mainly characterized by limited 83 load-carrying capacity and ductility (deformability) [4 - 8]. The field observations recorded 84 after major seismic events (i.e. Italy [9-11], Spain [12] and USA [13]) report that the 85 extensive damages sustained by infill walls due to their out-of-plane response usually result 86 in the production of debris which often cause injuries and fatalities [14]. When infill masonry 87 walls are subjected to more extreme loading conditions, characterised by high loading rates 88 and intensities (associated mainly with impact and blast problems) fragments (of different 89 shapes and sizes) are generated that move at high speeds [15, 16]. The latter is also confirmed 90 by field observation recorded after explosions [17]. 91 92 In order to safeguard structural integrity and public safety, it is often necessary for masonry 93 infill walls to be appropriately strengthened so they can undertake the loads applied in the 94 out-of-plane direction even when characterised by high loading rates and intensities. The 95 limitations (e.g. increase of building mass, time consuming and expensive to apply, unable to 96 safeguard against the generations of debris/fragments [26-28]) characterising existing 4 97 methods employed for strengthening infill masonry walls associated with application of 98 external layers of reinforced concrete/mortar or strips of fibre reinforced polymers (FRP) or 99 metals onto the surface of the masonry wall [18-25] to form a composite member has led to 100 the use of engineered cementitious composites. The application of a thin ECC layer onto the 101 surface of the masonry specimens has been found to enhance their out-of-plane behaviour in 102 terms of load-carrying capacity, stiffness and ductility under static loading [29-32]. This 103 enhancement is associated with the ability of the engineered cementitious composites (ECC) 104 to exhibit a ductile, strain-hardening behaviour under uniaxial tension, typically characterised 105 by a high strain capacity and toughness [33]. This is mainly attributed to the ability of the 106 subject material to form multiple fine cracks, with an average crack width of less than 100 107 microns [34]. The tensile behaviour of ECC is strain-rate dependent [35, 36] because under 108 increasing loading rates it exhibits: (a) an increase in tensile strength, (b) a reduction in strain 109 capacity accompanied by (c) the development of less cracks which are more localised and 110 wider compared to those observed under static loading [35, 36]. Overall the behaviour of 111 ECC specimens subjected to impact tests is characterised by higher integrity and energy 112 absorption, better distribution of the micro-cracks forming in damaged zone, reduction of 113 fragmentation, less spalling and lower damages due to debris compared to that exhibited by 114 the same specimens constructed using regular reinforced concrete [37, 38]. 115 116 Present work investigates experimentally the behaviour of beam-like masonry specimens, 117 essentially consisting of a stack of bricks connected with mortar joints, when subjected to 118 four-point bending tests in which the