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• A new coupled damage-plasticity interfacial constitutive law for DFEM of masonry. • Detailed calibration methods for each model parameter based on physical rules. • Capturing various mechanical and failure behaviour of masonry structures. • Successful validations with static and dynamic loading tests. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two destructive rockfalls occurred in central Taiwan, wherein falling blocks severely damaged an essential bridge of a mountain expressway. A series of field investigations were conducted to recognize the trajectories of the rockfalls and gather information on the falling blocks and bridge damage. According to the obtained field data, a hybrid model of the discrete element method (DEM) and finite element method (FEM) was developed to assess the rockfall impact on the bridge. A DEM analysis was first performed to simulate the rockfall process, which agreed with the actual condition. A detailed FEM was developed with strain-rate-dependent material models to investigate the process, which caused severe damage to the bridge and protective structures under the rockfall impact based on the calculated velocity and kinetic energy of rock blocks obtained from the DEM analysis. The simulated damage mechanisms agreed well with the field observations. The simulated maximum impact force was 4.5 times higher than the original design load and caused severe damage to the bridge structure. The thorough and objective investigation results of this rockfall event and the rigorous hybrid DEM-FEM analysis framework can be essential guidelines for authorities to formulate future hazard mitigation strategies for similar infrastructures under the threats of rockfall impacts. • A rockfall event severely damaged an essential bridge in central Taiwan. • This study proposes a hybrid model of DEM and FEM to assess the rockfall impact on the bridge. • The simulated damage mechanisms agree well with the field observations. [ABSTRACT FROM AUTHOR]

• Nonlinear behavior of unbonded post-tensioned precast concrete segmental bridges (PT-PCSBs) was investigated by DFEMs. • Proposed DFEMs could well capture global responses and local tendon-stress, duct-slips, and joint-openings responses. • Combined effects of aspect ratios and prestress on the decompression and the ultimate limit states of the bridges were thoroughly investigated. • Third-order two-variable response surfaces could predict the tendon stress change at ULS with high goodness-of-fit R2 values of 0.97. This paper comprehensively studied the combined effects of prestress change and aspect ratios on the nonlinear structural performances of externally prestressed precast concrete segmental bridges (PCSB). An experimentally validated discrete-finite element model was adopted and various analytical cases were generated with variable span lengths. Furthermore, a simulation study is performed considering the change in prestress level to understand its effect on structural response, failure behaviour, and tendon stress at the ultimate limit state (ULS). The result showed that the stress in the unbonded tendon before the failure stage varies from 0.79 to 1.03 f py for the shorter tendon (T6L) and 0.66 to 0.94 f py for the longer tendon (T5L), and on comparing with the prediction of the existing codes, the stresses are highly underestimated. However, for the typical prestress level of around 0.6 - 0.7 f pu , the ACI318-19 code could quite well predict the ultimate tendon stress change. To establish the dependency of stress in the unbonded tendon at ULS to the normalized prestress factor (α) associated with the aspect ratio (L / d), the response surface methodology (RSM) was implemented. The mediocre prediction of one-variable linear regression analysis concludes the dependency of the combined effects of the two variables on the response variables. The 3rd order two-variable response surfaces were able to predict an increase in stress and total stress of tendon at the ULS with high goodness-of-fit values of 0.97 and 0.92 respectively. [ABSTRACT FROM AUTHOR]

Prefabricated lightweight concrete building fasçade 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  μ ε . 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  μ ε 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  μ ε 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. [ABSTRACT FROM AUTHOR]

• First experimental study using prestressed CFRP plates to strengthen or repair RC girders with HOLLOW sections. • Essential experimental results and structural beheaviour obeservations for further analytical development. • Practical solutions for strengthening and repairing aged and over-used hollow RC box girders. The paper presents a well-rounded experimental study on the flexural performance of Reinforced Concrete (RC) box girders strengthened with prestressed carbon fibre reinforced polymer (CFRP) plates. The motivation behind the study was twofold: the rising need for structural reinforcement of existing aged and heavily utilised hollow RC box girders, and the absence of prior attempts to integrate prestressed CFRP plate strengthening for those hollow girders. Previous experimental studies are scarce and fewer studies are focused on the combined prestress and thin-wall effects, such as prestress-related stress condensation and shear lag. However, experimental results are important in directing further analytical studies for hollow sections with more complex behaviours than solid sections since there is a need to predict the behaviour of the prestress-strengthened hollow RC structures for routine design. This pivotal experimental study aims to quantify the structural interactions initiated by prestress in hollow sections and evaluate the impact of age while promoting further analytical initiatives. In this study, two types of CFRP plates, ordinary CFRP and steel-wire-CFRP (SW-CFRP), were used on different specimen beams with varying prestressing levels, sizes of the CFRP plates, and pre-damaged states representing aged and over-used members. Their performance indexes, including cracking load, yield load, ultimate load, structural stiffness, ductility, and crack resistance, were tested and summarised in this paper. The CFRP plates of the eight specimen beams were prestressed to different levels (non-prestressed, and 30% and 40% of the CFRP plate's ultimate strength). The test results suggest that the crack load increased by 86% and 134%, when the specimens were enhanced with the combinations of 30% prestress level for the same CFRP cross-section, and 40% prestress level with a thicker CFRP plate, respectively. The flexural capacity also increased by 42% and 72%, and flexural stiffness increased by 3% and 63%, respectively. The experimental results proved that the proposed prestressed CFRP plate technology effectively strengthens the new or aged RC box girders, but the ductility is sacrificed. These first-hand test results provide an excellent target dataset for further development in the analysis and design of prestressed CFRP plate-strengthened RC box girders. [ABSTRACT FROM AUTHOR]

• A new concept of bio-based prestress technology. • Experimental proof-of-concept on bamboo-timber composite beams. • Industrial level of trial production of prestressed bamboo-timber composite beams. • Thorough lab investigation on the proposed new bio-based composite beams. This paper presents a pioneering experimental proof-of-concept study to validate a novel concept of prestress technology that used only pure bio-based composite materials while achieved consistent prestressed stress distribution within the structure member, and provided in-situ flexibility, improved structural performance, and maximised the rate of utilisation of each material. Industrial level of facilities were used during this development. The prestress is achieved by pressurised/forced lamination of multiple components with different materials and geometrical properties. The prestressing process is activated during the pressure release stage during which the components are interacting with each other, creating different stress statuses that would favour the weaker and adverse the stronger components to maximise the strength exploitation of different materials. Using laminated bamboo and timber as an example pair, twenty-two glulam, non-prestressed and prestressed laminated bamboo-timber composite beams were manufactured, tested, and analysed to provide an in-depth understanding of the structural behaviours of these novel structural members. Failure modes, yielding, ultimate and serviceability limit loads, and corresponding deflections, as well as the histories of strain development at key positions of the specimens were examined. The experimental study confirmed the feasibility, effectiveness and industrial scalability of the proposed technology. The novel concept provides a new approach for developing the prestress technology for bio-based materials, and this experimental study laid the foundation for its future analytical development and numerical studies. [ABSTRACT FROM AUTHOR]

• Early research attempt on the analytical model of prestressed CFRP plates strengthen RC box girders. • Prestress losss, shear lag effect and different failure modes are considered in the model proposed. • Analytical predictions validated by experimental results. This paper presents a pioneering study that developed the first analytical model to analyse and design reinforced concrete (RC) box girders strengthened by prestressed CFRP plates. The proposed analytical model considered and addressed prestress loss, shear lag effect and failure modes under different design configurations at elastic, elastoplastic and plastic stages. An experimental study was also conducted to validate the proposed analytical model. The study was motivated by the increasing demand for the structural strengthening of aged and over-used hollow RC box girders in transport and other infrastructure systems, as well as the lack of previous attempts to incorporate prestressed CFRP plate strengthening for hollow RC beams. It is very common in many developing countries, the traffic flow increased dramatically due to the economic growth. The original design underestimated the traffic loads. When demolition and re-building may not always be the best option, thus, strengthening and enhanced maintenance have become promising alternatives. But the lack of existing analytical models that can guide the engineers to analyse and design this type of structures effective, has become an urgent need from the industry. In the experimental study, eight box girders with different types, cross-section sizes, and prestress levels were prepared and tested. Two samples were preloaded to create damaged beams before strengthening to simulate the aged or over-used members. The experimental results are in good agreement with the analytical prediction. The proposed analytical framework provides a comprehensive yet practical method for designing the prestressed CFRP strengthened RC box girders in bending and laid the foundation for further studies on shear and torsion behaviours. [ABSTRACT FROM AUTHOR]

This study echoes the rising demand for bio-based material in concrete composite structures in the race to accelerate carbon neutrality in construction. Noticing that most previous studies are focused on straight timber or engineered bamboo-to-concrete composite beams, this study developed straight or curved-and-tapered mechanically laminated bamboo-concrete (LBC) T-beams. Six layers of 26 mm thick laminated bamboo panels were glue laminated together to form the bamboo beams. The curved bamboo beams have three different rises of arch: 50 mm, 100 mm and 150 mm. All specimen beams were tested by four-point bending tests to evaluate their structural performances of the curved and straight LBC T-beams. To monitor the flange-to-web interface shear transfer, a novel interface shear slip calibration method that captures the longitudinal after-slip strain redistribution was developed and validated by strain gauge measurements. This study also highlights the interlayer shear bonding strength of laminated bamboo as the thresholding parameter that determines the composite beams' overall flexural strength, evidenced by detailed failure mode analysis. The proposed interface shear slip calibration method can be extended to the other types of shear connectors such as screws, nails, shear plates and notched connections. • Unique and practical curved laminated bamboo-concrete (LBC) composite beams. • Investigated and compared the structural performances of the curved and straight LBC composite beams experimentally. • Novel and proper method for interface shear slip calibration with stain gauge validation. [ABSTRACT FROM AUTHOR]

This paper reported the very earliest experimental and analytical studies on the bonded Prestressed CFRP tendon enhanced Steel Reinforced Concrete (PSRC) members under eccentric tensile loads. Eight PSRC members were tested under monotonic eccentric tensile loading, and three Steel Reinforced Concrete (SRC) members were simultaneously tested for comparison. The load–deflection relationship, the strain distributions as well as the crack propagation and fracture of concrete were investigated experimentally and analytically. The results demonstrated an improvement in the eccentric tensile capacity of PSRC members upon increasing both the steel and reinforcement ratios, or by reducing the prestress eccentricity. The results also suggested that an enhancement in the level of prestressing increased can decrease the crack propagation and lateral deflection. Moreover, the validity of the plane-section assumption was confirmed. An analytical model was proposed for predicting the elastic bending capacity of the PSRC members based on the experimental results. The study provided an in-depth understanding of the structural behaviour of PSRC members with bonded prestressed CFRP tendon under the eccentric tension underpinned by the elaborate experimental design and practical analytical model. [ABSTRACT FROM AUTHOR]