Browsing by Author "Yuen, Terry Y. P."

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A fracture energy based damage-plasticity interfacial constitutive law for discrete finite element modelling of masonry structures
(2019-08-01)
Yuen, Terry Y. P.
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Deb, Trissa
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Zhang, Hanhui
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Liu, Yang
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土木工程學系
The robust structural design relies on the accuracy of the response analysis to different loadings. Strut-and-tie models and continuum models are often used for the design of masonry structures but they are generally not able to simulate detailed damage and progressive collapse. To this regard, this paper presents a new and robust interfacial constitutive law, which couples the damage and plastic deformation with fracture energy-based softening rules, for the discrete finite element modelling (DFEM) of masonry structures. The model has 14 required parameters and 2 optional parameters of which calibration methods using the standard test data and physical rules are provided in details. It was demonstrated that the comprehensive mechanical behaviour including the pressure-dependent fracture, wearing-off of the friction, dilatation, stiffness degradation, shear retention, and component disintegration can be well captured. The model validation studies were performed with various material and structural tests including shear-compression and uniaxial tension tests on the joints, and horizontal loading and shake-table tests on large-scale masonry structures. Good agreements between the simulated and experimental results could be observed. Comparing to conventional modelling approaches, the DFEM with the interfacial constitutive law can also simply the meshing work and better control the mesh quality. (C) 2019 Elsevier Ltd. All rights reserved.
Development of low drying shrinkage foamed concrete and hygro-mechanical finite element model for prefabricated building fascade applications
(2018-03-20)
Wan, Kai Tai
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Zhu, Honggang
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Yuen, Terry Y. P.
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Chen, Binmeng
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Hu, Chuanlin
Prefabricated lightweight concrete building fascade can improve the energy efficiency of buildings and reduce the carbon emission of transportation. However, it is essential to maintain the dimensional stability of the full scale element. The drying shrinkage of lightweight foamed concrete was investigated in this study. The hypothesis of using the drying shrinkage of normal weight concrete to approximate that of lightweight foamed concrete of dry density about 1500 kg/m(3) counterpart was verified. Three different strategies of reducing drying shrinkage were studied. The drying shrinkage of common ingredients of ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS) was commonly up to 2000-3000 mu epsilon. The use of magnesium expansive agent with different calcination conditions could not reduce the drying shrinkage. The use of calcium sulfoaluminate (CSA) cement with OPC and GGBS could significantly reduce the drying shrinkage within 1000 me in standard testing environment. The formulation developed in laboratory was scaled up in a concrete production plant for prefabricated concrete elements. A lightweight full scale panel (the wet density was about 1700 kg/m(3)) was fabricated. The drying shrinkage of the developed formulation with CSA cement was only 161 mu epsilon in the field test. A hygro-mechanical model was developed to model the diffusion, shrinkage and plastic strain evolution. The incremental stress-strain constitutive relationship of the hygro-mechanical model was derived for incorporating it into general finite element routine. The model parameters were calibrated by the drying shrinkage measurements in this study. The calibrated model demonstrated the cracking potential of three typical reinforced concrete panels of three different formulations studied in this study. (C) 2018 Elsevier Ltd. All rights reserved.
Impact dynamics and energy dissipation capacity of fibre-reinforced self-compacting concrete plates
(2017-05-01)
Kantar, Erkan
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Yuen, Terry Y. P.
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Kobya, Veysel
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Kuang, J. S.
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土木工程學系
Applications of self-compacting concrete (SCC) in mega constructions have become increasingly popular. However, structures constructed with brittle SCC are extremely vulnerable to impact loading. Fibre reinforced SCC (FR-SCC) could be a viable solution to this problem, since the dynamic cracking in the SCC matrix can be restrained by the dispersed fibres and the overall impact resistance can be enhanced. However, the dynamics and failure mechanisms of FR-SCC subjected to impact loading are seldom explored in the literature. Furthermore, an excessive amount of fibres can deprive SCC of its favourable fluidity and segregation resistance. Hence, the fibre content has to be optimised to strike a balance between impact resistance and fluidity. In this regard, this paper presents a study on the impact dynamics of plates made of one SCC and three fibre-reinforced SCC (FR-SCC) mixes with different fibre content using a drop-weight testing apparatus. The rheological properties of the mixes were also investigated. The kinematic responses, effective impact forces, energy dissipation capacities, momentum transfer, and coefficients of restitution of the plates subjected to impact loading were evaluated and compared to explore the impact mechanisms. On the basis of the experimental results, the relationships between the effective impact forces and coefficients of restitution with the accumulated damage were obtained. The momentum transfer and impact duration remained approximately constant for the FR-SCC plates after being subjected to certain numbers of blows on account of the crack-bridging toughening mechanism. Also, it was found that the impact resistances and the energy dissipation capacities of the FR-SCC plates can be significantly higher than that of pure SCC plates by 6-14 times. (C) 2017 Elsevier Ltd. All rights reserved.
Large Structural Shear Deformation and Failure Monitoring Using Bend Losses in Polymer Optical Fibre
(2020-01-01)
Yuen, Terry Y. P.
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Tsai, Cheng-An
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Deb, Trissa
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Lin, Yu-Hsiang
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Nyienyi, June
Rapid identification of structural damage positions is essential to the post-disaster rehabilitation of structures and infrastructures. Large shear deformation, e.g., shear failure of bridge piers, shear-slip of slopes, and shear cracking of structural walls, is often the cause of structural instability. Distributed optical fibre sensing (DOFS) techniques have an advantage over point-based sensors in terms of spatial continuous structural condition monitoring. This paper presents the development of new measurement theory and algorithm to evaluate the structural shear deflection based on the large beam deflection and optical bend loss theories. The proposed technique adopted a photon-counting Optical Time Domain Reflectometer (nu-OTDR) with polymer optical fibres (POFs) which has a large deformation measurement range and high spatial resolution. In the experiment, shear deformation events can be successfully detected and evaluated from the proposed technique. When the normalised shear deformation is larger than 0.2, both the event locations and the magnitudes can be accurately determined. When normalised shear deformation is lesser than 0.2, the error in the magnitude evaluation increased, but the event location can be found with an absolute error <0.5 m. Multiple shear events can be treated as independent events when they are separated by more than 5 m. Various configurations of POFs attached to concrete beam specimens for rupture failure monitoring were also studied. The configuration that could maximise the POF curvature at the beam failure produced the largest nu-OTDR signals. In other configurations in which the POFs were only stretched at failure, the signals were less strong and were influenced by the POF-structure bonding strength.
Low-seismic damage strategies for infilled RC frames: shake-table tests
(2017-11-01)
Zhang, Hanhui
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Kuang, J. S.
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Yuen, Terry Y. P.
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土木工程學系
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Department of Civil Engineering
Unreinforced masonry (URM) infill panels are widely used as partitions in RC frames and typically considered as non-structural elements in the design process. However, observations from recent major earthquakes have shown that under seismic excitation, the structural interaction between columns and infill walls can significantly alter the structural behaviour, thus causing catastrophic consequences. The purpose of this research was to propose and test an innovative low seismic damage detailing method, which isolates the infill panel from bounding columns with finite width vertical gaps during the infill panel construction phase and deploys steel wire connections in mortar layers anchored to columns. Taking into account the similitude requirements, a total of six one-third scale, single-storey single-bay RC frames with different infill configurations and flexible connection details were carefully designed and tested on a shake-table. Three real earthquake records were selected and scaled to ascending intensity levels and used as input signals. A series of thorough investigations including dynamic characteristics, hysteretic behaviour, failure mechanisms, out-of-plane vulnerabilities and the effect of different gap filling materials and load transfer mechanisms were rigorously studied. The experimental results indicate that the undesirable interaction between infill panels and bounding frame is significantly reduced using the proposed low seismic damage detailing concept. Direct shear failure of columns at an early stage is prevented, and structural redundancy at high levels of excitation can be provided. In general, the structural stability and integrity, and displacement ductility of infilled RC frames can remarkably be improved. Copyright (C) 2017 John Wiley & Sons, Ltd.
Modal-based ground motion selection procedure for nonlinear response time history analysis of high-rise buildings
(1970-01-01)
Liu, Yang
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Kuang, J. S.
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Yuen, Terry Y. P.
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土木工程學系
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Department of Civil Engineering
The selection of representative input ground motions (IGMs) is important for a proper nonlinear response time history analysis (NLRHA) of modern structures. The prevailing IGM selection procedure requires that the response spectra of selected ground motions are matched with the code-specified design spectra, while the effect of the frequency contents combination in the time domain on the multimode interactions is not considered. Ignoring the effect of the frequency contents combination in the time domain of IGMs may cause significant variations in the analysis results for selected IGMs, although they are matched to the same design spectrum. In this paper, a modal-based ground motion selection (MGMS) procedure is proposed as a supplement to spectrum matching-based IGM selection procedures for selecting proper IGMs that can sufficiently induce the multimode interactions. In the proposed procedure, three equivalent single-degree-of-freedom (ESDOF) systems are developed by pushover analysis. NLRHA is then conducted for these ESDOF systems with a set of 20 seed IGMs chosen by the spectrum-matching-based selection procedure. Finally, seven IGMs are selected from the seed IGMs for NLRHA in the full structural model. To verify MGMS, seismic demands of high-rise buildings were computed by NLRHA with seven MGMS-selected IGMs, seven IGMs with closest spectrum matching, and groups of seven randomly selected IGMs derived from three different sets of 20 seed IGMs. The computed seismic demands with MGMS-IGMs show very good agreement with the mean demands determined using the whole set of seed IGMs, while the deviation is much lesser compared with those groups of randomly selected IGMs.
Shake table tests on RC frame infilled by slitted masonry panels
(2018-09-01)
Yuen, Terry Y. P.
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Zhang, Han-hui
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Kuang, J. S.
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Huang, Qunxian
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土木工程學系
Unreinforced masonry infill walls are widely used as non-structural partitions in RC frames. The effects of infills on the structural responses are often ignored in the design process since they are generally considered as expendable elements. However, recent studies have shown that not only shear damage can be inflicted to the columns braced by the infill walls, but also that the structural stability can be jeopardised by the fall-off of the infills. This paper presents the development of new detailing methods for the infill walls, which features slit panels, isolation gaps between the infills and columns, and anchorage of the infills. The proposed detailing methods were tested and verified experimentally using shake-table tests on five 1/3-scale infilled RC frame specimens with different combinations of the features stated above. The design and construction of the shake-table test specimens have taken into account the similitude requirements. The test results indicate that the proposed detailing method effectively reduced the undesirable interaction between column and infill walls. And the use of proper anchorage could prevent the fall off of infills from the bounding frame. Furthermore, the specimens with slit infill walls displayed better seismic performances, which could be attributed to the rocking behaviour of the sub-panels with increased aspect ratios.