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Pedagogical application of discrete element simulation to brick masonry in uniaxial and localized compression
Experimental Technology and Management 2024, 41(3): 156-164
Published: 20 March 2024
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[Objective]

Masonry architecture combines science and art, promoting architectural diversity and culture. The requirement of green and low-carbonization of new town construction provides a new opportunity for developing masonry structures. Masonry structure is an essential professional course in civil engineering education, with the compression of unreinforced masonry being an important part of this course. Masonry is a material that combines brick and mortar. Illustrating masonry failure subjected to compression can help students comprehend the concept of the stress contribution of combined materials, which is vital in the design and reinforcement of masonry structures.

[Methods]

Discrete element simulation has become an essential supplement to practical teaching and has been increasingly used because of its economy, reproducibility, whole-process illustration, and ability to obtain micromechanical data. To facilitate students’ comprehension of the contribution of brick and mortar to bearing external forces, we established brick and mortar clusters and then simulated brick masonry using the discrete element method. Uniaxial and localized compression were conducted on the numerical brick masonry, with the stress–strain relationship, masonry failure mode, bond contact breakage, and the contribution of contact forces to stress analyzed.

[Results]

The numerical simulation replicates the failure modes of masonry and the corresponding stress–strain relationships under compression. When the masonry is uniaxially and locally compressed, the axial stress reaches its peak value and decreases rapidly, followed by a slow decrease. When the bond strength of the mortar is 30 MPa, under uniaxial compression, the mortar in horizontal and vertical joints is first damaged, subsequent brick–brick bond breakages lead to the splitting of the bricks, and the cracks continue to expand, causing the blocks to break. Thus, many blocks are extruded, and a diagonal shear band appears. In localized compression, failure occurs primarily within a depth range of twice the compression width. Obvious cracks develop in the weak zones on both sides of the compression zone, and the width of the cracks increases rapidly and extends vertically downward. In uniaxial and localized compression, mortar–mortar and brick–mortar bonds break first before reaching the peak stress. These bonds break quickly at the peak stress, while brick–brick bonds only begin to break quickly after the peak stress. The mortar primarily serves to connect the bricks and does not bear the external forces directly. For brick–brick contacts, brick–mortar contacts, and mortar–mortar contacts, the normal contact forces contribute more than the tangential forces to the axial stress.

[Conclusions]

This study included the introduction of discrete element modeling, uniaxial and localized loading, variations in the number of bonds, and the contribution of contacts to the axial stress. A pedagogical application of these findings was also explored. By combining macro-and microanalysis, students can comprehend that the macromechanical performance of masonry is influenced by the microstructure and micromechanics of the bricks and mortar. They can also recognize the advantages and disadvantages of the discrete element simulation method. Pedagogical application can enhance students’ understanding of the mechanism of force transmission and the strength of masonry. This result can further improve students’ ability to conceptualize masonry structure design and reinforcement.

Issue
Simulation analysis of human-machine closed-loop dynamics of aircraft landing and taxiing attitude under crosswind and wet runway conditions
Journal of Beijing University of Aeronautics and Astronautics 2025, 51(11): 3674-3687
Published: 19 January 2024
Abstract PDF (2.3 MB) Collect
Downloads:9

Aiming at the problem that the aircraft is easy to deviate from the runway when landing and taxiing under slippery crosswind conditions, this paper takes the large civil aircraft A320 as the research object and uses Simulink to establish a dynamic model of aircraft landing and taxiing, including four components: wheels, landing gear, aircraft body, and pilot. Based on this model, a human-machine closed-loop simulation of aircraft taxiing under wet runway and crosswind conditions is conducted. An analysis is carried out on the landing roll attitude and yaw distance of the aircraft under different water film thicknesses, unbalanced friction, and crosswind intensities. The following conclusions are drawn: the water film thickness has a significant impact on the lateral controllability of the aircraft. A larger water thickness leads to increased peak and final values of the yaw angle, thus significantly increasing both the yaw distance and roll distance. A water film thickness of 10 mm or more can cause roll oscillations during the later stages of landing and taxiing, which greatly affects the aircraft’s lateral stability. Pavement friction imbalance has a considerable impact on runway excursion risk, with the maximum yaw distance reaching 24.75 m. The aircraft has already deviated from the runway, severely compromising landing and taxiing safety. The stronger the crosswind, the less effective the pilot’s attitude control becomes. When the crosswind speed increases to 13.9 m/s, the roll angle exceeds the safety threshold of 6° at 7.7 seconds into the taxiing phase. At this point, the aircraft’s engine or wingtip may have touched the ground, and the roll angle peaks at 6.57°. However, under this crosswind intensity, the yaw distance does not exceed half the width of the runway. This indicates that crosswind intensity has a significant effect on roll angle, far exceeding its impact on yaw distance. In wet runway management, strict control should be applied to water film thickness, with takeoff and landing prohibited at or above 13 mm, and crosswind speeds should be kept below 13.9 m/s.

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