International Journal of Civil Engineering
Volume:16 Issue: 11, Nov 2018

This paper deals with the experimental investigation and the numerical modelling of fibre mortar composite interface. This study focuses on the determination of failure types and the characterisation of mechanical behaviour at a fibre mortar-composite interface. The mechanical properties of fibre mortar are determined through laboratory tests. Experiments are carried out using a series of pull-out and shear tests to study the behaviour of composite/glue/fibre mortar assemblage. Numerical simulations based on the finite element method are used to predict the interface damage parameters as well as mixed mode crack initiation and propagation at the fibre mortar-composite interface. An interfacial decohesion model based on the indirect use of fracture mechanics is used to simulate the damage process. The model assumes a bilinear softening behaviour of the interfacial provided with stress-relative displacement laws. The interface parameters at the interface between fibre mortar and composite are evaluated and the failure mode determined.

This paper presents an experimental study conducted on the seismic behavior of beam-to-column connections based on the components of steel reinforced recycled aggregate concrete beams and recycled aggregate concrete-filled steel tube columns. The main test parameter of the specimens is the replacement ratio of recycled aggregate. The experiment process and failure modes of all specimens were investigated in detail. Several parameters such as hysteretic behavior, bearing capacity, strength and stiffness degradation, ductility coefficients, and energy dissipation were also analyzed. The test results showed that slipping appeared between the steel tube and beam concrete (sandwiched between the circumferential stiffening plates) while the specimen yielded. The shapes of the moment versus rotation hysteresis curve at the end of the beam were plump, which runs through a linear, reverse “S”-shaped and spindle-shaped deformation stages. Analysis of the seismic evaluation index showed that the replacement ratio of the recycled aggregate had no significant effect on the seismic performance. Moreover, a simulation study was also carried out using FEM, and the results showed good agreement with the skeleton curves obtained from the test. Finally, a simplified calculation model was established and the bearing capacity calculation equation of connections was proposed. Compared with the test results, the calculation equation can satisfy engineering application requirements. The results presented in this paper can be used as reference for engineering practice.

The main objective of this investigation is to replace calcined marl (0, 10, 20%) and condensed silica fume (SF, 0, 7, 10%) partially for ordinary Portland cement (OPC). Marl, a calcium-based supplementary cementitious material (SCM) calcines at a considerably lower temperature (750 °C) than OPC (up to 1480 °C). The calcined marl contributes in prolonged pozzolanic reactions and represents characteristics of latent cement chemistry. To approach the major conclusions, 27 mixes were designed based on the three ratios of water to the total binders (W/B) of 0.38, 0.42 and 0.45. The calcined marl and SF proportioned in mixes with “0, 10 and 20%” and “0, 7 and 10%”, respectively. After the ages of 7, 28 and 90 days all mixes improved, mechanically. In particular, the hardened concretes containing 10 and 20% of calcined marl show stronger reaction for substitution of OPC. In the lower limit of W/B ratio (0.38) mixes with 20% calcined marl exhibit a remarkable increase of some 2.4-fold strengths from 7 to 90 days. Also, the results obtained by tensile strength and modulus of rupture for concrete mixes containing 10 and 20% calcined marl highlight the mechanical progress of hardened concrete after 28 days. Collectively, both SCMs replaced OPC in a considerable amount (up to 30%). However, long-term enhancement in mechanical strength and durability indices are typically supported by calcined marl.

To improve the constructability of the steel and concrete composite coupled wall system while maintaining good seismic performance in terms of strength, stiffness and energy dissipation capacity, the bolted endplate connection between steel reinforced concrete (SRC) wall and SRC beam has been proposed and studied. The endplate is shop welded to the end of steel beam and then fastened to the flange of steel column at boundary element of wall pier through high-strength bolts before the fabrication of reinforcement cage and concrete pouring for the composite beams. Five SRC beam-SRC wall subassembly specimens were designed, constructed and tested subjected to cyclic displacement reversals at SRC beam end. The test parameters included the amount of steel plate embedded in SRC beams and the influence of slab. The responses of the specimens in terms of load–displacement hysteretic responses, cracking patterns, ductility, strength and stiffness degradation characteristics were discussed. The test results show that through rational design the bolted endplate connection can satisfactorily ensure the load transfer mechanism between SRC beam and SRC wall such that the SRC beam can fully develop its strength, ductility, post-yield strength and stiffness retention capacities. The strength, post-yield deformation and energy dissipation capacity of SRC coupling beams can be effectively enhanced by increasing the steel plate ratio. The existence of slab can enhance the overall seismic performance of SRC beam. Nonlinear finite element modeling approach was developed and verified by comparison with the test results, showing good agreement in terms of the skeleton and hysteresis curves.

Recent earthquakes highlighted the vulnerability of some infilled reinforced concrete structures due to the presence and distribution of the infill masonry walls. Buildings such as school buildings and residential buildings are typically not designed considering the contribution of the infill panels to the structure strength and stiffness, when these are subjected to earthquakes. The lack of consideration of the infill panel results in observed poor performance and structural collapses. This manuscript presents a numerical study of a school in Nepal, representative of those existent in the country. Non-linear numerical analyses were carried out to assess the seismic vulnerability in terms of peak inter-storey drifts. In addition, results will be presented and discussed in terms of peak inter-storey drift profiles and peak base shear. Results from a seismic vulnerability assessment of the pre-earthquake structure indicate that the presence of the infill panels in the original structures were responsible for the development a soft-storey mechanism, combined with torsion. Following the seismic vulnerability assessment, four different retrofit solutions were tested and compared with the results of the original structure to gain an understanding on the structural efficiency of each proposed solution. The retrofit solutions proposed revealed to be efficient and reduce the seismic vulnerability. The retrofit solution showing best results correspond to the ones in which reinforced concrete column jacketing was employed.

Migration of heat and water during freeze–thaw cycling has always been one of the significant topics in frozen soil mechanics. This paper first carries out field tests in the heartland of Loess Plateau, i.e., Northern Shaanxi, China, on the water migration and heat transfer in loess slopes during freeze and thaw. Results indicate that the water content within a certain depth shows sudden increase during freezing, while it tends to be more uniform after thawing, strongly depending on the variation of temperature profile over depth. When modeling heat and water migration in seasonal frozen ground, two characteristic curves, i.e., soil freezing curve and water retention curve, were incorporated in an improved Harlan model. The modified Richards’ equation and a nonlinear heat conduction equation considering ice-water phase change were both included. As for the effect of freeze–thaw cycling, laboratory tests were carried out to investigate how the coefficients of heat and water conductivity vary with both the degree of saturation and freeze–thaw cycles, based on which empirical models for loess were derived. A large-scale model test on the loess slope with the gradient of 1:0.75 was carried out to verify the rationality of the proposed model. Comparison of calculated curves and test data shows that the proposed method well describes the migration of both heat and water during cyclic freeze and thaw.

This study investigated the desorption behavior of heavy metals, Zn(II) and Cu(II), in the contaminated soil using citric acid and citric acid-containing wastewater (CACW). Four influence factors, including soil contamination levels, dosage of citric acid, reaction time and soil pH were taken into account. Using the citric acid, the desorption reaction with heavy metals was rapid (i.e., less than 2 h). The removal percentage of Zn(II) and Cu(II) reached more than 90% for one type of Suzhou clay with a pH value of 6.58 and a contaminated level of Zn > 2.7 mg/g and Cu > 3.3 mg/g. The increase of soil pH inhibited the metal desorption. The desorption behavior predicted by Visual MINTEQ was in good agreement with the experimental results. The desorption behavior of Zn(II) and Cu(II) was governed by the affinity of sorption sites for heavy metals and the chelating of organic ligands. Soil contamination levels and contact time were investigated when using CACW as the desorbent. It was concluded that CACW was also effective in extracting Zn(II) and Cu(II) from soil surface. When the contact time between CACW and contaminated soil reached 2 h, the removal percentage of Zn(II) and Cu(II) increased to 33% and 60%, respectively. As a result, CACW that is usually treated as a waste product can be a promising washing solution for soil remediation.

This research focused on investigating the effects of recycled aggregates on the material properties of concrete and the structural performance of reinforced concrete beams. Two different sources of recycled aggregates, crushed red bricks and demolished concrete, collected from local construction and demolition wastes, were analysed. The pre-wetting method was applied to recycled coarse aggregates aiming to study its effects on concrete specimens. Experimental results assisted by regression analysis revealed that the pre-wetting method could minimize the negative effects caused by recycled aggregate itself on the concrete slump and compressive strength test results. Pre-wetting method was also found improving the dynamic modulus of elasticity for concrete specimens. Adding supplementary cementitious materials was not as effective as the pre-wetting method in enhancing concrete slump, ultrasonic pulse velocity (UPV), strength, or dynamic modulus of elasticity. The reduction of concrete UPV and compressive strength caused by recycled aggregates were more significant in the early curing age. Flexural tests on reinforced concrete beams indicated that although adding recycled concrete aggregates did not significantly change the beam failure load, the ultimate deformation of reinforced concrete beams was reduced by displaying more brittle failure behaviour. It was indicated that the failure mode of beam was changed from flexural to shear, inferring that shear capacity of beam with RCA was reduced. Future research directions were proposed focusing on the durability studies of concrete members containing recycled aggregates especially when the pre-wetting method was applied.

As a part of rock sheds, reinforced concrete (RC) girder is usually covered by traditional soil cushion as a shock-absorbing device. In this paper, expanded polystyrene (EPS) has been numerically modeled using RC girder under impact load analysis. A numerical method was established in comparison with the proposed prototype experiment. Furthermore, expanded polystyrene (EPS) cushions of different thicknesses and densities as an energy dissipation device for rockfall impact were tested using the proposed numerical model. The dynamic analysis and modeling were performed using LS-DYNA. The impact forces and displacements of the RC girder were measured. The simulated results revealed a major increase in terms of energy dissipation after introducing the EPS cushion. The results obtained from this study are: (1) the displacement can be reduced by 25% as compared to sand cushion as absorbing material using an EPS layer, (2) a large decrease in contact force was observed using a layer of EPS cushion at the top of the RC girder having lesser density of 19 kg/m3, and (3) EPS cushions with 0.5 m thicker layer and lower 19 kg/m3 density showed more remarkable energy dissipation effect when all the other conditions were the same.

In this paper, the seismic performance of cold formed steel shear walls sheathed by fiber cement boards (FCB) is investigated. Of particular interest is the seismic response modification factor of FCB shear walls. Nonlinear incremental dynamic analyses of multi-story cold formed steel framed structures were carried out following an approach adopted by FEMA-P695 on the description of building seismic behavior. Different scaled earthquake records in three different earthquake prone regions located on low, medium and high seismic risk zones in Iran were taken into account. One, two and three story CFS archetype buildings were analyzed using models created in OpenSees software to predict structural performance of the buildings. Nonlinear dynamic time history analyses were carried out employing OpenSees software utilizing 2D models of a FCB braced wall tower. A stick model was created whose behavior was fitted to the lateral resistance versus deformation of each story that braced elements in the model. The elements were defined via material Pinching4 to construct a uniaxial material exhibiting pinched load-deformation response and demonstrate degradation under cyclic loading. The results show that most relevant codes which suggest the value of seismic response modification factor equal to 2 for cold formed steel shear walls sheathed by FCB are acceptable only for up to three story buildings in low seismic risk zone, up to two story in medium seismic zone and one story in high seismic risk zone.